Micro Strip Patch Antenna

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Submitted to: Submitted by: Mr. DEEPAK SOOD (Asst. prof. In ece dept.) PRADEEP(1407234)

SHRI KRISHAN DEV BHOOMI INSTITUTE OF ENGINEERING & TECHNOLOGY

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INDEX

Chapter 1 INTRODUCTION BASICS AND HISTORY

1.1 History of Microstrip Patch Antenna 9-10

1.2 Overview 10-22

1.3 How Antenna Radiates 22-31

1.4 Advantage and disadvantage 31-32

Chapter 2 FEEDING

2.1 Feeding Techniques 32-36

Chapter 3 LITERATURE

3.1 Method of Analysis 37-41

3.2 Antenna Literature 42-51

Chapter 4 FABRICATION

4.1 Fabricated Antenna 52-53

Chapter 5 TESTING AND RESULTS

5.1 Antenna Measurement 54-56

5.2 RESULT 57-64

LIST OF REFERENCES 65-66


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LIST OF FIGURES

Figure No. Name of Figures

Fig. 1 Surface waves

Fig. 2 Leaky waves

Fig. 3 Radiation pattern

Fig. 4 Linear polarization

Fig. 5 Circular polarization

Fig. 6 Transmit (Tx) and Receive (Rx) Antennas separated by R.

Fig. 7 A negative charge has an associated Electric Field with it,

everywhere in space.

Fig. 8 The E-fields when the charge is accelerated.F

Fig. 9 (a) Geometry of Microstrip (Patch) Antenna. (b) Side View

Fig. 10 Magnitude of S11 versus Frequency.

Fig. 11 Side view of patch antenna with E-fields shown underneath.

Fig. 12 Radiation pattern of rectangular patch

Fig. 13 Common Shapes of microstrip patch elements

Fig. 14 Microstrip Line Feed

Fig. 15 Probe fed Rectangular Microstrip Patch Antenna

Fig. 16 Aperture Coupled Feed


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Fig. 17 Proximity Coupled Feed

Fig. 18 Transmission Line Model

Fig. 19 Microstrip Patch Antennas

Fig. 20 Top View of Antenna

Fig. 21 Side View of Antenna

Fig. 22 Charge distribution and current density creation on the

microstrip patch

Fig. 23 Various types of circularly polarized microstrip patch antennas:

(a) triangular patch,(b) square patch, (c) circular patch, (d) ring,

(e) pentagonal patch, and (f) elliptical patch.

Fig. 24 Two types of excitations for circularly polarized microstrip

antennas: (a) dual-fed patch and (b) singly fed patch.

Fig. 25 Typical configurations of dual-fed circularly Polarized

microstrip antennas: (a)circular patch and (b) square patch

Fig. 26 Typical configurations of singly fed circularly polarized

microstrip antennas: (a)Circular patch and (b) square patch

Fig. 27 Amplitude and phase of orthogonal modes for singly fed

circularly polarized microstrip antennas.

Fig. 28 Geometry of a ractangular patch antenna on a normally biased

ferrite substrate.

Fig. 29 Geometries of a rectangular patch antenna with (a) a

shortingwall, (b) a shorting

Fig. 30 Surface current distributions for meandered rectangular

microstrip patches with (a) meandering slits and (b) a pair of

triangular notches cut at the patch’s non radiating edges.


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Fig. 31 Microstrip-line-fed Planar Inverted-L Patch Antenna for

Compact Operation.

Fig. 32 Compact broadband microstrip Antenna

Fig. 33 Antenna using chip resistor

Fig. 34 Geometry of a stacked shorted patch antenna for compact

broadband operation.

Fig. 35 Compact circularly polarized rectangular microstrip Antenna

Fig. 36 Compact circularly polarized circular microstrip Antenna

Fig. 37 Back View Of Patch Antenna

Fig. 38 Front View Of Patch Antenna

Fig. 39 Plot of angle vs. voltage

Fig. 40 Block Diagram Of Microwave Setup

Fig. 41 Antenna Setup For Measuring E & H-Plane Characteristics

Fig. 42 Setup For Measurement At X-Band

Fig. 43 VSWR results of simulation

Fig. 44 Impedence plot of antenna

Fig. 45 Magnetic field vector plot of antenna

Fig. 46 Reflection coff. plot of antenna

Fig. 47 Electric field plot of antenna

Fig. 48 3D radiation plot of antenna

Fig. 49 Polarization plot of antenna

Fig. 50 E field plot of antennaSHRI KRISHAN DEV BHOOMI INSTITUTE OF ENGINEERING & TECHNOLOGY

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Fig. 51 Gain plot of antenna

Fig. 52 Impedence plot of antenna

Fig. 53 VSWR plot of antenna

Fig. 54 3D radiation plot of antenna

Fig. 55 Radiation plot of antenna

Fig. 56 H field plot of antenna


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SHRI KRISHAN INSTITUTE OF ENGINEERING & TECHNOLOGY

KURUKSHETRA UNIVERSITY, KURUKSHETRA

(HARYANA)

CERTIFICATE

Certified that this project report “Microstrip Patch Antenna” is the

bonafide work of “Pradeep Attri” who carried out the project work under

my supervision.

SIGNATURE SIGNATURE

PROF. SHARAD SHARMA PROF. DEEPAK SOOD

ASSTT. PROF. & HOD ASSTT. PROF.

( ECE) (ECE)


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C H A P T E R 1

History of Microstrip Patch Antenna

The rapid development of microstrip antenna technology began in the late 1970s. By the early 1980s basic microstrip antenna elements and arrays were fairly well established in terms of design and modeling, and workers were turning their attentions to improving antenna performance features (e.g. bandwidth), and to the increased application of the technology. One of these applications involved the use of microstrip antennas for integrated phased array systems, as the printed technology of microstrip antenna seemed perfectly suited to low-cost and high-density integration with active MIC or MMIC phase shifter and T/R circuitry.

The group at the University of Massachusetts (Dan Schaubert, Bob Jackson, Sigfrid Yngvesson) had received an Air Force contract to study this problem, in terms of design tradeoffs for various integrated phased array architectures, as well as theoretical modeling of large printed phased array antennas. The straightforward approach of building an integrated millimeter wave array (or subarray) using a single GaAs substrate layer had several drawbacks. First, there is generally not enough space on a single layer to hold antenna elements, active phase shifter and amplifier circuitry, bias lines, and RF feed lines. Second, the high permittivity of a semiconductor substrate such as GaAs was a poor choice for antenna bandwidth, since the bandwidth of a microstrip antenna is best for low dielectric constant substrates. And if substrate thickness is increased in an attempt to improve bandwidth, spurious feed radiation increases and surface wave power increases. This latter problem ultimately leads to scan blindness, whereby the antenna is unable to receive or transmit at a particular scan angle. Because of these and other issues, they were looking at the use of a variety of two or more layered substrates. One obvious possibility was to use two back to-back substrates with feed through pins. This would allow plenty of surface area, and had the critical advantage of allowing the use of GaAs (or similar) material for one substrate, with a low dielectric constant for the antenna elements. The main problem with this approach was that the large number of via holes presented fabrication problems in terms of yield and reliability. They had looked at the possibility of using a two sided-substrate with printed slot antennas fed with microstrip lines, but the bidirectionality of the radiating element was unacceptable.

At some point in the summer of 1984 they arrived at the idea of combining these two geometries, using a slot or aperture to couple a microstrip feed line to a resonant microstrip patch antenna.


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After considering the application of small hole coupling theory to the fields of the microstrip line and the microstrip antenna, they designed a prototype element for testing. Their intuitive theory was very simple, but good enough to suggest that maximum coupling would occur when the feed line was centered across the aperture, with the aperture positioned below the center of the patch, and oriented to excite the magnetic field of the patch.

The first aperture coupled microstrip antenna was fabricated and tested by a graduate student, Allen Buck, on August 1, 1984, in the University of Massachusetts Antenna Lab. This antenna used 0.062” Duroid substrates with a circular coupling aperture, and operated at 2 GHz. As is the case with most original antenna developments, the prototype element was designed without any rigorous analysis or CAD - only an intuitive view of how the fields might possibly couple through a small aperture. They were pleasantly surprised to find that this first prototype worked almost perfectly – it was impedance matched, and the radiation patterns were good. Most importantly, the required coupling aperture was small enough so that the back radiation from the coupling aperture was much smaller than the forward radiation level.

The geometry of the basic aperture coupled patch antenna is described. The radiating microstrip patch element is etched on the top of the antenna substrate, and the microstrip feed line is etched on the bottom of the feed substrate. The thickness and dielectric constants of these two substrates may thus be chosen independently to optimize the distinct electrical functions of radiation and circuitry. Although the original prototype antenna used a circular coupling aperture, it was quickly realized that the use of a rectangular slot would improve the coupling, for a given aperture area, due to its increased magnetic polarizability. Most aperture coupled microstrip antennas now use rectangular slots, or variations thereof.

Aim and Objectives

Microstrip patch antenna used to send onboard parameters of article to the ground while under operating conditions. The aim of the thesis is to design and fabricate an probe-fedSquare Microstrip Patch Antenna and study the effect of antenna dimensions Length (L),and substrate parameters relative Dielectric constant (εr), substrate thickness (t) on theRadiation parameters of Bandwidth and Beam-width.

Overview of Microstrip Antenna

A microstrip antenna is characterized by its Length, Width, Input impedance, and Gain and radiation patterns. Various parameters of the microstrip antenna and its design considerations were discussed in the subsequent chapters. The A microstrip antenna consists of conducting patch on a ground plane separated by dielectric substrate. This concept was undeveloped until the revolution in electronic circuit miniaturization and large-scale integration in 1970. After that many authors have described the radiation from the ground plane by a dielectric substrate for different configurations. The early work of Munson on micro strip antennas for use as a low profile flush mounted antennas on rockets and missiles showed that this was a practical concept for use in many antenna system problems. Various mathematical models were developed for this antenna and its


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applications were extended to many other fields. The number of papers, articles published in the journals for the last ten years, on these antennas shows the importance gained by them. The micro strip antennas are the present day antenna designer’s choice. Low dielectric constant substrates are generally preferred for maximum radiation. The conducting patch can take any shape but rectangular and circular configurations are the most length of the antenna is nearly half wavelength in the dielectric; it is a very critical parameter, which governs the resonant frequency of the antenna. There are no hard and fast rules to find the width of the patch.

Waves on Microstrip

The mechanisms of transmission and radiation in a microstrip can be understood by considering a point current source (Hertz dipole) located on top of the grounded dielectric substrate (fig. 1.1) This source radiateselectromagnetic waves. Depending on thedirection toward which waves are transmitted, they fall within three distinct categories,each of which exhibits different behaviors.

fig. dipole antenna

Surface Waves

The waves transmitted slightly downward, having elevation angles θ between π/2and π - arcsin (1/√εr), meet the ground plane, which reflects them, and then meet the dielectric-to-air boundary, which also reflects them (total reflection condition). The magnitude of the field amplitudes builds up for some particular incidence angles that leads to the excitation of a discrete set of surface wave modes; which are similar to the modes in metallic waveguide. The fields remain mostly trapped within the dielectric, decaying exponentially above the interface . The vector α, pointing upward, indicates the direction of largest attenuation. The wave propagates horizontally along β, with little absorption in good quality dielectric. With two directions of α and β orthogonal to each other, the wave is anon-uniform plane wave. Surface waves spread out in cylindrical fashion around the excitation point, with field amplitudes decreasing with distance (r), say1/r, more slowly than space waves. The same guiding mechanism provides propagation within optical fibers . Surface waves take up some part of the signal’s energy, which does not reach the intended user. The signal’s amplitude is thus reduced, contributing to an apparent attenuation or a decrease in antenna efficiency. Additionally, surface waves also introduce spurious coupling between different circuit or antenna elements. This effect severely degrades the performance of microstrip filters because the parasitic interaction reduces the isolation in the stop bands .In large periodic phased


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arrays, the effect of surface wave coupling becomes particularly obnoxious, and the array can neither transmit nor receive when it is pointed at some particular directions (blind spots). This is due to a resonance phenomenon, when the surface waves excite in synchronism the Floquet modes of the periodic structure. Surface waves reaching the outer boundaries of an open microstrip structure are reflected and diffracted by the edges. The diffracted waves provide an additional contribution to radiation, degrading the antenna pattern by raising the side lobe and the cross polarization levels. Surface wave effects are mostly negative, for circuits and for antennas, so their excitation should be suppressed if possible.

Fig1. surface waves

Leaky Waves

Waves directed more sharply downward, with θ angles between π – arc sin (1/√εr) and π, are also reflected by the ground plane but only partially by the dielectric-to-air boundary. They progressively leak from the substrate into the air (Fig 1.3), hence their name laky waves, and eventually contribute to radiation. The leaky waves are also non uniform plane waves for which the attenuation direction α points downward, which may appear to be rather odd; the amplitude of the waves increases as one moves away from the dielectric surface. This apparent paradox is easily understood by looking at the figure 1.3; actually, the field amplitude increases as one move away from the substrate because the wave radiates from a point where the signal amplitude is larger. Since the structure is finite, this apparent divergent behaviour can only exist locally, and the wave vanishes abruptly as one crosses the trajectory of the first ray in the figure. In more complex structures made with several layers of different dielectrics, leaky waves can be used to increase the apparent antenna size and thus provide a larger gain .This occurs for favourable stacking arrangements and at a particular frequency. Conversely, leaky waves are not excited in some other multilayer structures.


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Fig2. leaky waves

Guided Waves

When realizing printed circuits, one locally adds a metal layer on top of thesubstrate, which modifies the geometry, introducing an additional reflecting boundary.Waves directed into the dielectric located under the upper conductor bounce back and forth on the metal boundaries, which form a parallel plate waveguide. The waves in the metallic guide can only exist for some Particular values of the angle of incidence, forming a discrete set of waveguide modes. The guided waves provide the normal operation of all transmission lines and circuits,in which the electromagnetic fields are mostly concentrated in the volume below the upper conductor. On the other hand, this build up of electromagnetic energy is not favourable for patch antennas, which behave like resonators with a limited frequency bandwidth.

Parameters for Designing Antenna Bandwidth How can your cell phone and your television work at the same time? Both use antennas to receive information from electromagnetic waves, so why isn't there a problem?

The answer goes back to the fundamental secret of the universe. No matter what information you want to send, that waveform can be represented as the sum of a range of frequencies. By the use of modulation (which in a nutshell shifts the frequency range of the waveform to be sent to a higher frequency band), the waveforms can be relocated to separate frequency bands.

As an example, cell phones that use the PCS (Personal Communications Service) band have their signals shifted to 1850-1900 MHz. Television is broadcast primarily at 54-216 MHz. FM radio operates between 87.5-108 MHz.

The set of all frequencies is referred to as "the spectrum". Cell phone companies have to pay big money to get access to part of the spectrum. For instance, AT&T has to bid on a slice of the spectrum with the FCC, for the "right" to transmit information within that band. The transmission of EM energy is greatly regulated. When AT&T is sold a slice of the spectrum, they can not transmit energy at any other band (technically, the amount transmitted must be below some threshold in adjacent bands)

The Bandwidth of a signal is the difference between the signals high and low frequencies. For instance, a signal transmitting between 40 and 50 MHz has a bandwidth of 10 MHz.

We'll wrap up with a table of frequency bands along with the corresponding wavelengths. From the table, we see that VHF is in the range 30-300 MHz (30 Million-300 Million cycles per second). At the very least then, if someone says they need a "VHF antenna", you should now understand that the antenna should transmit or receive electromagnetic waves that have a frequency of 30-300 MHz.


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Frequency Band Name

Frequency Range Wavelength (Meters)

Application

Extremely Low Frequency (ELF)

3-30 Hz 10,000-100,000 km Underwater Communication

Super Low Frequency (SLF)

30-300 Hz 1,000-10,000 kmAC Power (though not a transmitted wave)

Ultra Low Frequency (ULF)

300-3000 Hz 100-1,000 km

Very Low Frequency (VLF)

3-30 kHz 10-100 km Navigational Beacons

Low Frequency (LF) 30-300 kHz 1-10 km AM Radio

Medium Frequency (MF)

300-3000 kHz 100-1,000 m Aviation and AM Radio

High Frequency (HF) 3-30 MHz 10-100 m Shortwave Radio

Very High Frequency (VHF)

30-300 MHz 1-10 m FM Radio

Ultra High Frequency (UHF)

300-3000 MHz 10-100 cmTelevision, Mobile Phones, GPS

Super High Frequency (SHF)

3-30 GHz 1-10 cmSatellite Links, Wireless Communication

High Frequency (EHF)

30-300 GHz 1-10 mmAstronomy, Remote Sensing

Visible Spectrum400-790 THz (4*10^14-7.9*10^14)

380-750 nm (nanometers)

Human Eye

Table Frequency Bands

Basically the frequency bands each range over from the lowest frequency to 10 times the lowest frequency. Antenna engineers further divide the bands into things like "X-band" and "Ku-band". That is the basics of frequency. To understand at a more advanced level, read on, or move to the next topic.

Bandwidth

Bandwidth is another fundamental antenna parameter. This describes the range of frequencies over which the antenna can properly radiate or receive energy. Often, the desired bandwidth is one of the determining parameters used to decide upon an antenna. For instance, many antenna types have very narrow bandwidths and cannot be used for wideband operation.

Bandwidth is typically quoted in terms of VSWR. For instance, an antenna may be described as operating at 100-400 MHz with a VSWR<1.5. This statement implies that the reflection coefficient is less than 0.2 across the quoted frequency range. Hence, of the power delivered to the antenna, only 4% of the power is reflected back to the transmitter. Alternatively, the


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return loss S11=20*log10(0.2)=-13.98 dB.

Note that the above does not imply that 96% of the power delivered to the antenna is transmitted in the form of EM radiation; losses must still be taken into account. Also, the radiation pattern will vary with frequency. In general, the shape of the radiation pattern does not change radically.

There are also other criteria which may be used to characterize bandwidth. This may be the polarization over a certain range, for instance, an antenna may be described as having circular polarization with an axial ratio <3dB from 1.4-1.6 GHz. This polarization bandwidth sets the range over which the antenna's operation is roughly circular. The bandwidth is often specified in terms of its Fractional Bandwidth (FBW). The antenna Q also relates to bandwidth.

RADIATION PATTERN

A radiation pattern defines the variation of the power radiated by an antenna as a function of the direction away from the antenna. This power variation as a function of the arrival angle is observed in the far field.

As an example, consider the 3-dimensional radiation pattern in Figure 1, plotted in decibels (dB) .


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Fig3. radiation pattern

This is an example of a donut shaped or toroidal pattern. In this case, along the z-axis, which would correspond to the radiation directly overhead the antenna, there is very little power transmitted. In the x-y plane (perpendicular to the z-axis), the radiation is maximum. These plots are useful for visualizing which directions the antenna radiates.

Typically, because it is simpler, the radiation patterns are plotted in 2-d. In this case, the patterns are given as "slices" through the 3d plane. The same pattern in Figure 1 is plotted in Figure 2. Standard spherical coordinates are used, where ϴ is the angle measured off the z-

axis, and is the angle measured counterclockwise off the x-axis.If you're unfamiliar with radiation patterns or spherical coordinates, it may take a while to see that Figure 2 represents the same pattern as shown in Figure 1. The pattern on the left in Figure 2 is the elevation pattern, which represents the plot of the radiation pattern as a function of the angle measured off the z-axis (for a fixed azimuth angle). Observing Figure 1, we see that the pattern is minimum at 0 and 180 degrees and becomes maximum at broadside to the antenna (90 degrees off the z-axis). This corresponds to the plot on the left in Figure 2.

The plot on the right in Figure 2 is the azimuthal plot. It is a function of the azimuthal angle for a fixed polar angle (90 degrees off the z-axis in this case). Since the pattern in Figure 1 is symmetrical around the z-axis, this plot appears as a constant in Figure 2.

A pattern is "isotropic" if the radiation pattern is the same in all directions. These antennas don't exist in practice, but are sometimes discussed as a means of comparison with real antennas. Some antennas may also be described as "omnidirectional", which for an actual means that it is isotropic in a single plane (as in Figure 1 above for the x-y plane). The third category of antennas are "directional", which do not have a symmetry in the radiation pattern.


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FIELD REGION

The fields surrounding an antenna are divided into 3 principle regions: Reactive Near Field Radiating Near Field or Fresnel Region Far Field or Fraunhofer Region

The far field region is the most important, as this determines the antenna's radiation pattern. Also, antennas are used to communicate wirelessly from long distances, so this is the region of operation for most antennas. We will start with this region.

Far Field (Fraunhofer) Region

The far field is the region far from the antenna, as you might suspect. In this region, the radiation pattern does not change shape with distance (although the fields still die off with 1/R^2). Also, this region is dominated by radiated fields, with the E- and H-fields orthogonal to each other and the direction of propagation as with plane waves.

If the maximum linear dimension of an antenna is D, then the far field region is commonly given as:

This region is sometimes referred to as the Fraunhofer region, a carryover term from optics.

Reactive Near Field Region

In the immediate vicinity of the antenna, we have the reactive near field. In this region, the fields are predominately reactive fields, which means the E- and H- fields are out of phase by 90 degrees to each other (recall that for propagating or radiating fields, the fields are orthogonal (perpendicular) but are in phase).

The boundary of this region is commonly given as:

Radiating Near Field (Fresnel) Region

The radiating near field or Fresnel region is the region between the near and far fields. In this region, the reactive fields are not dominate; the radiating fields begin to emerge. However, unlike the Far Field region, here the shape of the radiation pattern may vary appreciably with distance.


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The region is commonly given by:

Note that depending on the values of R and the wavelength, this field may or may not exist.

Finally, the above can be summarized via the following diagram:

DIRECTIVITY

Directivity is a fundamental antenna parameter. It is a measure of how 'directional' an antenna's radiation pattern is. An antenna that radiates equally in all directions would have effectively zero directionality, and the directivity of this type of antenna would be 1 (or 0 dB).

An antenna's normalized radiation pattern can be written as a function in spherical coordinates

Because the radiation pattern is normalized, the peak value of F over the entire range of angles is 1. Mathematically, the formula for directivity (D) is written as:

This equation might look complicated, but the numerator is the maximum value of F, and the denominator just represents the "average power radiated over all directions". This equation then is just a measure of the peak value of radiated power divided by the average.


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ImpedanceAn antenna's impedance relates the voltage to the current at the input to the antenna. This is extremely important as we will see.

Let's say an antenna has an impedance of 50 ohms. This means that if a sinusoidal voltage is input at the antenna terminals with amplitude 1 Volt, the current will have an amplitude of 1/50 = 0.02 Amps. Since the impedance is a real number, the voltage is in-phase with the current.

Let's say the impedance is given as Z=50 + j*50 ohms (where j is the square root of -1). Then the impedance has a magnitude of

and a phase given by

This means the phase of the current will lag the voltage by 45 degrees. To spell it out, if the voltage (with frequency f) at the antenna terminals is given by

then the current will be given by

So impedance is a simple concept, which relates the voltage and current at the input to the antenna. The real part of an antenna's impedance represents power that is either radiated away or absorbed within the antenna. The imaginary part of the impedance represents power that is stored in the near field of the antenna (non-radiated power). An antenna with a real input impedance (zero imaginary part) is said to be resonant. Note that an antenna's impedance will vary with frequency.

While simple, we will now explain why this is important, considering both the low frequency and high frequency cases. It turns out (after studying transmission line theory for a while), that the input impedance Zin is given by:

This is a little formidable for an equation to understand at a glance. However, the happy thing is:

If the antenna is matched to the transmission line (ZA=ZO), then the input impedance does


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not depend on the length of the transmission line.

Polarization

Linear Polarization

A slot antenna is the counter part and the simplest form of a linearly polarized antenna. On a slot antenna the E field is orientated perpendicular to its length dimension The usual microstrip patches are just different variations of the slot antenna and all radiate due to linear polarization.

fig.4 linear polarization

Circular Polarization

Circular polarization (CP) is usually a result of orthogonally fed signal input. When two signals of equal amplitude but 90o phase shifted the resulting wave is circularly polarized. Circular polarization can result in Left hand circularly polarized (LHCP) where the wave is rotating anticlockwise, or Right hand circularly polarized (RHCP) which denotes a clockwise rotation. The main advantage of using CP is that regardless of receiver orientation, it will always receive a component of the signal. This is due to the resulting wave having an angular variation.


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Fig5. circular polarization

Criteria for Circular Polarization

The E-field must have two orthogonal (perpendicular) components.

The E-field's orthogonal components must have equal magnitude.

The orthogonal components must be 90 degrees out of phase.

Effective Area

A useful parameter calculating the receive power of an antenna is the effective area or effective aperture. Assume that a plane wave with the same polarization as the receive antenna is incident upon the antenna. Further assume that the wave is travelling towards the antenna in the antenna's direction of maximum radiation (the direction from which the most power would be received).

Then the effective aperture parameter describes how much power is captured from a given plane wave. Let W be the power density of the plane wave (in W/m^2). If P represents the power at the antennas terminals available to the antenna's receiver, then:

Hence, the effective area simply represents how much power is captured from the plane wave and delivered by the antenna. This area factors in the losses intrinsic to the antenna (ohmic losses, dielectric losses, etc.). This parameter can be determine by measurement for real antennas.

A general relation for the effective aperture in terms of the peak gain (G) of any antenna is given by:


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Effective aperture will be a useful concept for calculating received power from a plane wave. To see this in action, go to the next section on the Friis transmission formula.

Antenna TemperatureAntenna Temperature ( ) is a parameter that describes how much noise an antenna produces in a given environment. This temperature is not the physical temperature of the antenna. Moreover, an antenna does not have an intrinsic "antenna temperature" associated with it; rather the temperature depends on its gain pattern and the thermal environment that it is placed in.

To define the environment, we'll introduce a temperature distribution - this is the temperature in every direction away from the antenna in spherical coordinates. For instance, the night sky is roughly 4 Kelvin; the value of the temperature pattern in the direction of the Earth's ground is the physical temperature of the Earth's ground. This temperature distribution will

be written as . Hence, an antenna's temperature will vary depending on whether it is directional and pointed into space or staring into the sun.For an antenna with a radiation

pattern given by , the noise temperature is mathematically defined as:

This states that the temperature surrounding the antenna is integrated over the entire sphere, and weighted by the antenna's radiation pattern. Hence, an isotropic antenna would have a noise temperature that is the average of all temperatures around the antenna; for a perfectly directional antenna (with a pencil beam), the antenna temperature will only depend on the temperature in which the antenna is "looking".The noise power received from an antenna at

temperature can be expressed in terms of the bandwidth (B) the antenna (and its receiver) are operating over:

In the above, K is Boltzmann's constant (1.38 * 10^-23 [Joules/Kelvin = J/K]). The receiver

also has a temperature associated with it ( ), and the total system temperature (antenna

plus receiver) has a combined temperature given by . This temperature can be used in the above equation to find the total noise power of the system. These concepts begin to illustrate how antenna engineers must understand receivers and the associated electronics, because the resulting systems very much depend on each other.


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How Antenna Radiates:

FRIIS TRANSMISSION FORMULA

This page is worth reading a couple times and should be fully understood. Consider two antennas in free space (no obstructions nearby) separated by a distance R:

Fig6 Transmit (Tx) and Receive (Rx) Antennas separated by R.

Assume that PTWatts of total power are delivered to the transmit antenna. For the moment, assume that the transmit antenna is omnidirectional, lossless, and that the receive antenna is in the far field of the transmit antenna. Then the power p of the plane wave incident on the receive antenna a distance R from the transmit antenna is given by:

If the transmit antenna has a gain in the direction of the receive antenna given by , then the power equation above becomes:

The gain term factors in the directionality and losses of a real antenna. Assume now that the

receive antenna has an effective aperture given by . Then the power received by this

antenna ( ) is given by:

Since the effective aperture for any antenna can also be expressed as:


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The resulting received power can be written as:

This is known as the Friis Transmission Formula. It relates the free space path loss, antenna gains and wavelength to the received and transmit powers. This is one of the fundamental equations in antenna theory, and should be remembered (as well as the derivation above).

Finally, if the antennas are not polarization matched, the above received power could be multiplied by the Polarization Loss Factor (PLF) to properly account for this mismatch..

HOW AN ANTENNA RADIATES

Obtaining an intuitive idea for why antennas radiate is helpful in understanding the fundamentals of antennas. On this page, I'll attempt to give a low-key explanation with no regard to mathematics on how and why antennas radiate electromagnetic fields.

First, lets start with some basic physics. There is electric charge - this is a quantity of nature (like mass or weight or density) that every object possesses. You and I are most likely electrically neutral - we don't have a net charge that is positive or negative. There exists in every atom in the universe particles that contain positive and negative charge (protons and electrons, respectively). Some materials (like metals) that are very electrically conductive have loosely bound electrons. Hence, when a voltage is applied across a metal, the electrons travel around a circuit - this flow of electrons is electric current (measured in Amps).

Lets get back to charge for a moment. Lets say that for some reason, there is a negatively charged particle sitting somewhere in space. The universe has decided, for unknown reasons, that all charged particles will have an associated electric field with them.


http://www.antenna-theory.com/basics/antennapol.php

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Fig7. A negative charge has an associated Electric Field with it, everywhere in space.

So this negatively charged particle produces an electric field around it, everywhere in space. The Electric Field is a vector quantity - it has a magnitude (how strong the field strength is) and a direction (which direction does the field point). The field strength dies off (becomes smaller in magnitude) as you move away from the charge. Further, the magnitude of the E-field depends on how much charge exists. If the charge is positive, the E-field lines point away from the charge. Now, suppose someone came up and punched the charge with their fist, for the fun of it. The charge would accelerate and travel away at a constant velocity. How would the universe react in this situation?

The universe has also decided (again, for no apparent reason) that disturbances due to moving (or accelerating) charges will propagate away from the charge at the speed of light - c0 = 300,000,000 meters/second. This means the electric fields around the charge will be disturbed, and this disturbance propagates away from the charge. This is illustrated in Figure 2.

Fig8.The E-fields when the charge is accelerated.

Once the charge is accelerated, the fields need to re-align themselves. Remember, the fields want to surround the charge exactly as they did in Figure 1. However, the fields can only respond to events at the speed of light. Hence, if a point is very far away from the charge, it will take time for the disturbance (or change in electric fields) to propagate to the point.

we have 3 regions. In the light blue (inner) region, the fields close to the charge have readapted themselves and now line up as they do in Figure 1. In the white region (outermost), the fields are still undisturbed and have the same magnitude and direction as they would if the charge had not moved. In the pink region, the fields are changing - from their old magnitude and direction to their new magnitude and direction.

Hence, we have arrived at the fundamental reason for radiation - the fields change because charges are accelerated. The fields always try to align themselves as in Figure 1 around charges. If we can produce a moving set of charges (this is simply electric current), then we will have radiation.


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Now, you may have some questions. First - if all accelerating electric charges radiate, then the wires that connect my computer to the wall should be antennas, correct? The charges on them are oscillating at 60 Hertz as the current travels so this should yield radiation, correct?

Answer: Yes. Your wires do act as antennas. However, they are very poor antennas. The reason (among other things), is that the wires that carry power to your computer are a transmission line - they carry current to your computer (which travels to one of your battery's terminals and out the other terminal) and then they carry the current away from your computer (all current travels in a circuit or loop). Hence, the radiation from one wire is cancelled by the current flowing in the adjacent wire (that is travelling the opposite direction).

Another question that will arise is - if its so simple, then everything could be an antenna. Why don't I just use a metal paper clip as an antenna, hook it up to my receiver and then forget all about antenna theory?

Answer: A paper clip could definitely act as an antenna if you get current flowing on the antenna. However, it is not so simple to do this. The impedance of the paper clip will control how much power your receiver or transmitter could deliver to the paper clip (i.e. whether or not you could get any current flowing on the paper clip at all). The impedance will depend on what frequency you are operating at. Hence, the paper clip will work at certain frequencies as an antenna. However, you will have to know much more about antennas before you can say when and it may work in a given situation.

In summary, all radiation is caused by accelerating charges which produce changing electric fields. And due to Maxwell's Equations, changing electric fields give rise to changing magnetic fields, and hence we have electromagnetic radiation. The subject of antenna theory is concerned with getting power from your receiver to radiation away from an antenna. This requires the impedance of your antenna to be roughly matched to your receiver, and that the currents that cause radiation add up in-phase (that is, they don't cancel each other out as they would in a transmission line). A multitude of antenna types produce ways of achieving this, and you can find descriptions about them on the antenna list page.

Microstrip or patch antennas are becoming increasingly useful because they can be printed directly onto a circuit board. They are becoming very widespread within the mobile phone market. They are low cost, have a low profile and are easily fabricated.

Consider the microstrip antenna shown in Figure 1, fed by a microstrip transmission line. The patch, microstrip and ground plane are made of high conductivity metal. The patch is of length L, width W, and sitting on top of a substrate (some dielectric circuit board) of

thickness h with permittivity . The thickness of the ground plane or of the microstrip is not critically important. Typically the height h is much smaller than the wavelength of operation.


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(a) Top View

fig. 9Geometry of Microstrip (Patch) Antenna. (b) Side View

The frequency of operation of the patch antenna of Figure 1 is determined by the length L. The center frequency will be approximately given by:

The above equation says that the patch antenna should have a length equal to one half of a wavelength within the dielectric (substrate) medium.

The width W of the antenna controls the input impedance. For a square patch fed in the manner above, the input impedance will be on the order of 300 Ohms. By increasing the width, the impedance can be reduced. However, to decrease the input impedance to 50 Ohms often requires a very wide patch. The width further controls the radiation pattern. The normalized pattern is approximately given by:


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In the above, k is the free-space wave number, given by 2π/λ. The magnitude of the fields, given by:

The directivity of patch antennas is approximately 5-7 dB. The fields are linearly polarized. Next we'll consider more aspects involved in Patch (Microstrip) antennas.

Consider a square patch antenna fed at the end as before. Assume the substrate is air (or styrofoam, with a permittivity equal to 1), and that L=W=1.5 meters, so that the patch is to resonate at 100 MHz. The height h is taken to be 3 cm. Note that microstrips are usually made for higher frequencies, so that they are much smaller in practice. When matched to a 200 Ohm load, the magnitude of S11 is shown in Figure 1.

Fig10. Magnitude of S11 versus Frequency.


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Some noteworthy observations are apparent from Figure 1. First, the bandwidth of the patch antenna is very small. Rectangular patch antennas are notoriously narrowband; the bandwidth of rectangular patches are typically 3%. Secondly, the antenna was designed to operate at 100 MHz, but it is resonant at approximately 96 MHz. This shift is due to fringing fields around the antenna, which makes the patch seem longer. Hence, when designing a patch it is typically trimmed by 2-4% to achieve resonance at the desired frequency.

The fringing fields around the antenna can help explain why the microstrip antenna radiates. Consider the side view of a patch antenna, shown in Figure 2. Note that since the current at the end of the patch is zero (open circuit end), the current is maximum at the center of the half-wave patch and (theoretically) zero at the beginning of the patch. This low current value at the feed explains in part why the impedance is high when fed at the end.

Since the patch antenna can be viewed as an open circuited transmission line, the voltage reflection coefficient will be -1. When this occurs, the voltage and current are out of phase. Hence, at the end of the patch the voltage is at a maximum (say +V volts). At the start of the patch (a half-wavelength away), the voltage must be at minimum (-V Volts). Hence, the fields underneath the patch will resemble that of Figure 2, which roughly displays the fringing of the fields around the edges.

Fig11. Side view of patch antenna with E-fields shown underneath.

It is the fringing fields that are responsible for the radiation. Note that the fringing fields near the surface of the patch are both in the +y direction. Hence, these E-fields add up in phase and produce the radiation of the microstrip antenna. As a side note, the smaller ε r is, the more "bowed" the fringing fields become; they extend farther away from the patch. Therefore, using a smaller permittivity for the substrate yields better radiation. In contrast, when making a microstrip transmission line (where no power is to be radiated), a high value of ε r is desired, so that the fields are more tightly contained (less fringing), resulting in less radiation. This is one of the trade-offs in patch antenna design. There have been research papers written were distinct dielectrics (different permittivities) are used under the patch and transmission line sections, to circumvent this issue.


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RADIATION PATTERN OF A RECTANGULAR PATCH

Fig12. RADIATION PATTERN OF A RECTANGULAR PATCH

MICROSTRIP PATCH ANTENNA

Microstrip antennas are attractive due to their light weight, conformability and lowcost. These antennas can be integrated with printed strip-line feed networks and active devices.


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This is a relatively new area of antenna engineering. The radiation properties of micro strip structures have been known since the mid 1950’s. The application of this type of antennas started in early 1970’s when conformal antennas were required for missiles. Rectangular and circular micro strip resonant patches have been used extensively in a variety of array configurations. A major contributing factor for recent advances of microstrip antennas is the current revolution in electronic circuit miniaturization brought about by developments in large scale integration. As conventional antennas are often bulky and costly part of an electronic system, micro strip antennas based on photolithographic technology are seen as an engineering breakthrough.

Introduction

In its most fundamental form, a Microstrip Patch antenna consists of a radiatingpatch on one side of a dielectric substrate which has a ground plane on the other side asshown in Figure below The patch is generally made of conducting material such as copper or gold and can take any possible shape. The radiating patch and the feed lines are usually photo etched on the dielectric substrate.

In order to simplify analysis and performance prediction, the patch is generally square, rectangular, circular, triangular, and elliptical or some other common shape as shown in Figure 2.2. For a rectangular patch, the length L of the patch is usually 0.3333λo< L < 0.5 λo, where λo is the free-space wavelength. The patch is selected to be very thin such that t << λo (where t is the patch thickness).The height h of the dielectric substrate is usually .003 λo≤h≤0.05 λo. The dielectric constant of the substrate (ε r) is typically in the range 2.2 ≤ εr≤ 12.


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Fig13. Common Shapes of microstrip patch elementsMicrostrip patch antennas radiate primarily because of the fringing fields between the patch edge and the ground plane. For good antenna performance, a thick dielectric substrate having a low dielectric constant is desirable since this provides better efficiency ,larger bandwidth and better radiation. However, such a configuration leads to a larger antenna size. In order to design a compact Microstrip patch antenna, substrates with higher dielectric constants must be used which are less efficient and result in narrower bandwidth. Hence a trade-off must be realized between the antenna dimensions and antenna performance.

ADVANTAGES

Microstrip patch antennas are increasing in popularity for use in wirelessapplications due to their low-profile structure. Therefore they are extremely compatible for embedded antennas in handheld wireless devices such as cellular phones, pagers etc... The telemetry and communication antennas on missiles need to be thin and conformal and are often in the form of Microstrip patch antennas. Another area where they have been used successfully is in Satellite communication. Some of their principal advantages are given below:• Light weight and low volume.• Low profile planar configuration which can be easily made conformal tohost surface.• Low fabrication cost, hence can be manufactured in large quantities.• Supports both, linear as well as circular polarization.• Can be easily integrated with microwave integrated circuits (MICs).• Capable of dual and triple frequency operations.• Mechanically robust when mounted on rigid surfaces.

DISADVANTAGES

Microstrip patch antennas suffer from more drawbacks as compared to conventional antennas. Some of their major disadvantages aregiven below:• Narrow bandwidth.• Low efficiency.• Low Gain.• Extraneous radiation from feeds and junctions.• Poor end fire radiator except tapered slot antennas.


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• Low power handling capacity.• Surface wave excitation.

Microstrip patch antennas have a very high antenna quality factor (Q). It represents the losses associated with the antenna where a large Q leads to narrow bandwidth and low efficiency. Q can be reduced by increasing the thickness of the dielectric substrate. But as the thickness increases, an increasing fraction of the total power delivered by the source goes into a surface wave. This surface wave contribution can be counted as an unwanted power loss since it is ultimately scattered at the dielectric bends and causes degradation of the antenna characteristics. Other problems such as lower gain and lower power handling capacity can be overcome by using an arrayconfiguration for the elements

C H A P T E R 2

Feed Techniques

Microstrip patch antennas can be fed by a variety of methods. These methods can be classified into two categories- contacting and non-contacting. In the contacting method, the RF power is fed directly to the radiating patch using a connecting element such as a microstrip line. In the non-contacting scheme, electromagnetic field coupling is done to transfer power between the microstrip line and the radiating patch. The four most popular feed techniques used are the microstrip line, coaxial probe (both contacting schemes), aperture coupling and proximity coupling (both non-contacting schemes).

Microstrip Line Feed

In this type of feed technique, a conducting strip is connected directly to the edge of the Microstrip patch as shown in Figure 2.3. The conducting strip is smaller in width as compared to the patch and this kind of feed arrangement has the advantage that the feed can be etched on the same substrate to provide a planar structure.


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Fig14. Microstrip Line FeedThe purpose of the inset cut in the patch is to match the impedance of the feed line to the patch without the need for any additional matching element. This is achieved by properly controlling the inset position. Hence this is an easy feeding scheme, since it provides ease of fabrication and simplicity in modeling as well as impedance matching. However as the thickness of the dielectric substrate being used, increases, surface waves and spurious feed radiation also increases, which hampers the bandwidth of the antenna.The feed radiation also

leads to undesired cross polarized radiation. Coaxial Feed

The Coaxial feed or probe feed is a very common technique used for feeding Microstrip patch antennas. As seen from Figure 2.4, the inner conductor of the coaxial connector extends through the dielectric and is soldered to the radiating patch, while the outer conductor is connected to the ground plane.Figure


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Fig15. Probe fed Rectangular Microstrip Patch Antenna

The main advantage of this type of feeding scheme is that the feed can be placed at any desired location inside the patch in order to match with its input impedance. This feed method is easy to fabricate and has low spurious radiation. However, a major disadvantage is that it provides narrow bandwidth and is difficult to model since a hole has to be drilled in the substrate and the connector protrudes outside the ground plane, thus not making it completely planar for thick substrates (h > 0.02λo). Also, for thicker substrates, the increased probe length makes the input impedance more inductive, leading to matching problems. It is seen above that for a thick dielectric substrate, which provides broad bandwidth, the microstrip line feed and the coaxial feed suffer from numerous disadvantages. The non-contacting feed techniques which have been discussed below,solve these issues.

Aperture Coupled Feed

In this type of feed technique, the radiating patch and the microstrip feed line are separated by the ground plane as shown in Figure below. Coupling between the patch and the feed line is made through a slot or an aperture in the ground plane.


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Fig16.Aperture Coupled Feed

The coupling aperture is usually centered under the patch, leading to lower crosspolarization due to symmetry of the configuration. The amount of coupling from the feed line to the patch is determined by the shape, size and location of the aperture. Since the ground plane separates the patch and the feed line, spurious radiation is minimized. Generally, a high dielectric material is used for bottom substrate and a thick, low dielectric constant material is used for the top substrate to optimize radiation from the patch. The major disadvantage of this feed technique is that it is difficult to fabricate due to multiple layers, which also increases the antenna thickness. This feeding scheme also provides narrow bandwidth.

Proximity Coupled Feed

This type of feed technique is also called as the electromagnetic coupling scheme. As shown in Figure 2.6, two dielectric substrates are used such that the feed line is between the two

substrates and the radiating patch is on top of the upper substrate. The main advantage of this feed technique is that it eliminates spurious feed radiation and provides very high bandwidth

(as high as 13%), due to overall increase in the thickness of the microstrip patch antenna. This scheme also provides choices between two different dielectric media, one for the patch

Fig.17 Proximity Coupled Feed

and one for the feed line to optimize the individual performances. Matching can be achieved by controlling the length of the feed line and the width to-line ratio of the patch. The major disadvantage of this feed scheme is that it is difficultto fabricate because of the two dielectric


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layers which need proper alignment. Also, thereis an increase in the overall thickness of the antenna.

C H A P T E R 3

Methods of AnalysisThe preferred models for the analysis of Microstrip patch antennas are the transmission line model, cavity model, and full wave model (which include primarily integral equations/Moment Method). The transmission line model is the simplest of all and it gives good physical insight but it is less accurate. The cavity model is more accurate and gives good physical insight but is complex in nature. The full wave models are extremely accurate, versatile and can treat single elements, finite and infinite arrays, stacked elements, arbitrary shaped elements and coupling. These give less insight as compared to the two models mentioned above and are far more complex in nature.

Transmission Line Model


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This model represents the microstrip antenna by two slots of width W and height h, separated by a transmission line of length L. The microstrip is essentially a nonhomogeneous line of two dielectrics, typically the substrate and air.

Fig18. Transmission Line Model

Hence, as seen from Figure 2.8, most of the electric field lines reside in the substrate and parts of some lines in air. As a result, this transmission line cannot support pure transverse-electric-magnetic (TEM) mode of transmission, since the phase velocities would be different in the air and the substrate. Instead, the dominant mode of propagation would be the quasi-TEM mode. Hence, an effective dielectric constant (εreff) must be obtained in order to account for the fringing and the wave propagation in the line. The value of εreff is slightly less then εr because the fringing fields around the periphery of the patch are not confined in the dielectric substrate but are also spread in the air as shown in Figure 3.8 above. The expression for εreff is given by Balanis as:

Where εreff = Effective dielectric constant

εr = Dielectric constant of substrate

h = Height of dielectric substrate

W = Width of the patch

Consider Figure 2.9 below, which shows a rectangular microstrip patch antenna of length L, width W resting on a substrate of height h. The co-ordinate axis is selected such that the length is along the x direction, width is along the y direction and the height is along the z direction.


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Fig19. Microstrip Patch Antennas

In order to operate in the fundamental TM10 mode, the length of the patch must be slightly less than λ/2 where λ is the wavelength in the dielectric medium and is equal to λo/√εreff where λo is the free space wavelength. The TM10 mode implies that the field varies one λ/2 cycle along the length, and there is no variation along the width of the patch. In the Figure 2.10 shown below, the microstrip patch antenna is represented by two slots, separated by a transmission line of length L and open circuited at both the ends. Along the width of the patch, the voltage is maximum and current is minimum due to the open ends. The fields at the edges can be resolved into normal and tangential components with respect to the ground plane.

Fig20. Top View of Antenna fig21. Side View of Antenna

It is seen from Figure 1.11 that the normal components of the electric field at the two edges along the width are in opposite directions and thus out of phase since the patch is λ/2 long and hence they cancel each other in the broadside direction. The tangential components (seen SHRI KRISHAN DEV BHOOMI INSTITUTE OF ENGINEERING & TECHNOLOGY

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in Figure 1.11), which are in phase, means that the resulting fields combine to give maximum radiated field normal to the surface of the structure. Hence the edges along the width can be represented as two radiating slots, which are 2 / λ apart and excited in phase and radiating in the half space above the ground plane. The fringing fields along the width can be modeled as radiating slots and electrically the patch of the microstrip antenna looks greater than its physical dimensions. The dimensions of the patch along its length have now been extended on each end by a distance L ∆, which is given empirically by Hammerstad [11] as:

The effective length of the patch Leff now becomes:

For a given resonance frequency o f, the effective length is given by [9] as:

For a rectangular Microstrip patch antenna, the resonance frequency for any TMnm mode is given by James and Hall [14] as:

Where m and n are modes along L and W respectively. For efficient radiation, the width W is given by Bahl and Bhartia [15] as:

Cavity Model

Although the transmission line model discussed in the previous section is easy to use, it has some inherent disadvantages. Specifically, it is useful for patches of rectangular design and it ignores field variations along the radiating edges. These disadvantages can be overcome by using the cavity model. A brief overview of this model is given below.

In this model, the interior region of the dielectric substrate is modeled as a cavity bounded by electric walls on the top and bottom. The basis for this assumption is the following observations for thin substrates (h << λ).


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• Since the substrate is thin, the fields in the interior region do not vary much in the z direction, i.e. normal to the patch.

• The electric field is z directed only, and the magnetic field has only the transverse components Hx and Hy in the region bounded by the patch metallization and the ground plane. This observation provides for the electric walls at the top and the bottom.

Fig22. Charge distribution and current density creation on the microstrip patch

Consider Figure 2.12 shown above. When the microstrip patch is provided power, a charge distribution is seen on the upper and lower surfaces of the patch and at the bottom of the ground plane. This charge distribution is controlled by two mechanisms-an attractive mechanism and a repulsive mechanism as discussed by Richards. The attractive mechanism is between the opposite charges on the bottom side of the patch and the ground plane, which helps in keeping the charge concentration intact at the bottom of the patch. The repulsive mechanism is between the like charges on the bottom surface of the patch, which causes pushing of some charges from the bottom, to the top of the patch. As a result of this charge movement, currents flow at the top and bottom surface of the patch. The cavity model assumes that the height to width ratio (i.e. height of substrate and width of the patch) is very small and as a result of this the attractive mechanism dominates and causes most of the charge concentration and the current to be below the patch surface. Much less current would flow on the top surface of the patch and as the height to width ratio further decreases, the current on the top surface of the patch would be almost equal to zero, which would not allow the creation of any tangential magnetic field components to the patch edges. Hence, the four sidewalls could be modeled as perfectly magnetic conducting surfaces. This implies that the magnetic fields and the electric field distribution beneath the patch would not be disturbed. However, in practice, a finite width to height ratio would be there and this would not make the tangential magnetic fields to be completely zero, but they being very small, the side walls could be approximated to be perfectly magnetic conducting. Since the walls of the cavity, as well as the material within it are lossless, the cavity would not radiate and its input impedance would be purely reactive. Hence, in order to account for radiation and a loss mechanism, one must introduce a radiation resistance RR and a loss resistance RL. A lossy cavity would now represent an antenna and the loss is taken into account by the effective loss tangent δeff which is given as:


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Qt is the total antenna quality factor and has been expressed by [4] in the form:

•Ad represents the quality factor of the dielectric and is given as:

Where ωr is the angular resonant frequency.

W T is the total energy stored in the patch at resonance.

P d is the dielectric loss.

tanδ is the loss tangent of the dielectric.

•Qc represents the quality factor of the conductor and is given as:

Where Pc is the conductor loss.

∆ is the skin depth of the conductor.

H is the height of the substrate.

• Q r represents the quality factor for radiation and is given as:

Where Pr is the power radiated from the patch.

Thus, equation (1.12) describes the total effective loss tangent for the microstrip patch antenna.


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Circularly Polarized Microstrip Antennas

In this content, the design consideration for circularly polarized microstrip antennas is presented. Various techniques for circularly polarized radiation generation and bandwidth enhancement are also discussed.

Different Types of Circularly Polarized Antennas.

Generally antenna radiates an elliptical polarization, which is defined by three parameters: axial ratio, tilt angle and sense of rotation. When the axial ratio is infinite or zero, the polarization becomes linear with the tilt angle defining the orientation. The quality of linear polarization is usually indicated by the level of the cross polarization. For the unity axial ratio, a perfect circular polarization results and the tilt angle is not applicable. In general the axial ratio is used to specify the quality of circularly polarized waves. Antennas produce circularly polarized waves when two orthogonal field components with equal amplitude but in phase quadrature are radiated. Various antennas are capable of satisfying these requirements. They can be classified as a resonator and traveling-wave types. A resonator-type antenna consists of a single patch antenna that is capable of simultaneously supporting two orthogonal modes in phase quadrature or an array of linearly polarized resonating patches with proper orientation and phasing. A traveling-wave type of antenna is usually constructed from a microstrip transmission line. It generates circular polarization by radiating orthogonal components with appropriate phasing along discontinuities is the travelling-wave line.

Microstrip Patch Antennas

A microstrip antenna is a resonator type antenna. It is usually designed for single mode operation that radiates mainly linear polarization. For a circular polarization radiation, a patch must support orthogonal fields of equal magnitude but in-phase quadrature. This requirement can be accomplished by single patch with proper excitations or by an array of patches with an appropriate arrangement and phasing.

Circularly Polarized Patch

A microstrip patch is one of the most widely used radiators for circular polarization. Figure 3.1shows some patches, including square, circular, pentagonal, equilateral triangular, ring, and elliptical shapes which are capable of circular polarization operation. However square and circular patches are widely utilized in practice. A single patch antenna can be made to radiate circular polarization if two orthogonal patch modes are simultaneously excited with equal amplitude and out of phase with sign determining the sense of rotation. Two types of SHRI KRISHAN DEV BHOOMI INSTITUTE OF ENGINEERING & TECHNOLOGY

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feeding schemes can accomplish the task as given in figure 3.2. The first type is a dual-orthogonal feed, which employs an external power divider network. The other is a single point for which an external power divider is not required.

Dual-Orthogonal Fed circularly Polarized Patch

The fundamental configurations of a dual-orthogonal fed circularly polarized patch using an external power divider is shown in figure 3.3. The patch is usually square or circular. The dual-orthogonal feeds excite two orthogonal modes with equal amplitude but inphase quadrature. Several power divider circuits that have been successfully employed for CP generation include the quadrature hybrid, the ring hybrid, the Wilkinson power divider, and the T-junction power splitter. The quadrature hybrid splits the input into two outputs with equal magnitude but 900 out of phase. Other types of dividers, however, need a quarter-wavelength line in one of the output arms to produce a 900 phase shift at the two feeds. Consequently, the quadrature hybrid provides a broader axial ratio bandwidth. These splitters can be easily constructed from various planar transmission lines.

Figure23 Various types of circularly polarized microstrip patch antennas: (a) triangular patch,(b) square patch, (c) circular patch, (d) ring, (e) pentagonal patch, and (f) elliptical patch.


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Dual-Orthogonal Fed circularly Polarized Patch

Fig24.Two types of excitations for circularly polarized microstrip antennas: (a) dual-fed patch and (b) singly fed patch.

Fig25. Typical configurations of dual-fed circularly Polarized microstrip antennas: (a)circular patch and (b) square patch

Singly Fed Circularly Polarized Patch


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Typical configurations for a singly fed CP microstrip antennas are shown in figure 3.4 A single point feed patch capable of producing CP radiation is very desirable is situations where it is difficult to accommodate dual-orthogonal feeds with a power divider network.

Fig26. Typical configurations of singly fed circularly polarized microstrip antennas: (a)Circular patch and (b) square patch

Because a patch with single-point feed generally radiates linear polarization, in order to radiate CP, it is necessary for two orthogonal patch modes with equal amplitude an in phase quadrature to be induced. This can be accomplished by slightly perturbing a patch at appropriate locations with respect to the feed. Purturbation configurations for generating CP operate on the principle of detuning degenrate modes of a symmetrical patch by perturabation segments as shown in figure 3.5. The fields of a singly fed patch can be resolved into two orthogonal degenerates modes 1 and 2. Proper purturbation segments will detune the frequency response of mode 2 such that, at the operating frequency f0, the axial ratio rapidly degrades while the input match remains acceptable. The actual detunig occurs either for one or both modes depending on the placement of perturbation segments.


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Fig27.Amplitude and phase of orthogonal modes for singly fed circularly polarizedmocrostrip antennas.

A circular polarization can also be obtained from a single-point-fed square or circular patch on a normally biased ferrite substrate, as shown in fig 3.6. Pozar demostrated that a singly fed patch radiates both left hand circularly polarized (LHCP) and right hand circularly polarized(RHCP) at the same level and polarity of bias magnetic field; however LHCP and RHCP have different resonan frequencies. At the same operating frequency, the sence of polarization can be reversed by reversing the polarity of bias field. The axial ratio bandwidth is found to be larger than the impedance bandwidth. The radiation efficiency is on the order of 70%. Dual circular polarization have also been achieved using a singly fed triangular or pentagonal microstrip antenna. A schematic diagram of an isoceles triangular patch and its feed loci is shown in figure 3.7. A triangular patch radiates CP at dual frequencies, f1 and f2, with the separation ratio depending on the aspect ratio b/a. As shown in figure 3.7

RHCP can be changed to LHCP at each frequency by moving the feed location Ѓ1to Ѓ2 or from Ѓ4 to Ѓ3. The aspect ratio b/a is generally very close to unity; hence, a triangularpatch is almost equilateral. A pentagonal patch in figure 3.8, with the aspect ratio c/a as a design parameter, also behaves in a similar manner. It radiates RHCP when the feed pointis on Ѓ2 or Ѓ3 and LHCP for the feed on Ѓ1 to Ѓ4.

Fig28. Geometry of a ractangular patch antenna on a normally biased ferrite substrate.

Reduction in Size of Antenna

The use of an edge-shorted patch for size reduction is also well known [see the geometry in Figure below, and makes a microstrip antenna act as a quarter wavelength structure and thus can reduce the antenna’s physical length by half at a fixed operating frequency. When a shorting plate (also called a partial shorting wall) [see Figure 1.2(b)] or a shorting pin [Figure 1.2(c)] is used instead of a shorting wall, the antennas fundamental resonant frequency can be further lowered and further size reduction can be obtained. In this case, the diameter of a shorting-pin-loaded circular microstrip patch or the linear dimension of a shorting-pin-loaded rectangular microstrip patch can be as small as one-third of that of the corresponding


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microstrip patch without a shorting pin at the same operating frequency. This suggests that an antenna size reduction of about 89% can be obtained. Moreover, by applying the

Fig29. Geometries of a rectangular patch antenna with (a) a shortingwall, (b) a shorting

plate or partial shorting wall, and (c) a shorting pin. The feeds are not shown. shorting-pin loading technique to an equilateral-triangular microstrip antenna, the size reduction can be made even greater, reaching as large as 94%.This is largely because an equilateral-triangular microstrip antenna operates at its fundamental resonant mode, whose null-voltage point is at two-thirds of the distance from the triangle tip to the bottom side of the triangle; when a shorting pin is loaded at the triangle tip, a larger shifting of the null-voltage point compared to the cases of shorted rectangular and circular microstrip antennas occurs, leading to a greatly lowered antenna fundamental resonant frequency.

Lowering Resonant Frequency

Meandering the excited patch surface current paths in the antenna’s radiating patch is also an effective method for achieving a lowered fundamental resonant frequency for the microstrip antenna. For the case of a rectangular radiating patch, the meandering can be achieved by inserting several narrow slits at the patch’s nonradiating edges. It can be seen in Figure given below that the excited patch’s surface currents are effectively meandered, leading to a greatly lengthened current path for a fixed patch linear dimension. This behavior results in a greatly lowered antenna fundamental resonant frequency, and thus a large antenna size reduction at a fixed operating frequency can be obtained. Figure 1.3(b) shows similar design, cutting a pair of triangular


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Fig30. Surface current distributions for meandered rectangular microstrip patches with(a) meandering slits and (b) a pair of triangular notches cut at the patch’s nonradiating

edges.

Compactness

By embedding suitable slots in the radiating patch, compact operation of microstrip antennas can be obtained. Figure below shows some slotted patches suitable for the design of compact microstrip antennas. In Figure , the embedded slot is a cross slot, whose two orthogonal arms can be of unequal or equal lengths. This kind of slotted patch causes meandering of the patch surface current path in two orthogonal directions and is suitable for achieving compact circularly polarized radiation or compact dual- Compact microstrip antennas with (a) an inverted U-shaped patch, (b) a folded patch, and (c) a double-folded patch for achieving lengthening of the excited patch surface current path at a fixed patch projection area. The feeds are not shown.


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Fig31. Microstrip-line-fed Planar Inverted-L Patch Antenna for Compact Operation.

The microstrip-line-fed planar inverted-L (PIL) patch antenna is a good candidate for compact operation. The antenna geometry is shown in Figure 1.6. When the antenna height is less than 0.1λ0 (λ0 is the free-space wavelength of the center operating frequency), a PIL patch antenna can be used for broadside radiation with a resonant length of about 0.25λ0 [24]; that is, the PIL patch antenna is a quarter-wavelength structure, and has the same broadside radiation characteristics as conventional half wavelength microstrip antennas. This suggests that at a fixed operating frequency, the PIL patch antenna can have much reduced physical dimensions (by about 50%) compared to the conventional microstrip antenna.

COMPACT BROADBAND MICROSTRIP ANTENNAS

With a size reduction at a fixed operating frequency, the impedance bandwidth of a microstrip antenna is usually decreased. To obtain an enhanced impedance bandwidth, one can simply increase the antenna’s substrate thickness to compensate for the decreased electrical thickness of the substrate due to the lowered operating frequency, or one can use a meandering ground plane (Figure 1.7) or a slotted ground plane (Figure 1.8). These design methods lower the quality factor of compact microstrip antennas and result in an enhanced impedance bandwidth.

By embedding suitable slots in a radiating patch, compact operation with an enhanced impedance bandwidth can be obtained.Atypical design is shown in Figure.

However, the obtained impedance bandwidth for such a design is usually about equal to or less than 2.0 times that of the corresponding conventional microstrip antenna.


50

Fig32 .COMPACT BROADBAND MICROSTRIP ANTENNAS

Antenna using chip resistor

To achieve a much greater impedance bandwidth with a reduction in antenna size, one can use compact designs with chip-resistor loading or stacked shorted patches. The former design is achieved by replacing the shorting pin in a shorted patch antenna with a chip resistor of low resistance (generally 1 ohm)

Fig33 .Antenna using chip resistor

In this case, with the same antenna parameters, the obtained antenna size reduction can be greater than for the design using chip-resistor loading. Moreover, the obtained impedance bandwidth can be increased by a factor of six compared to a design using shorting-pin loading. For an FR4 substrate of thickness 1.6 mm and relative permittivity 4.4, the impedance bandwidth can reach 10% in L-band operation [26]. However, due to the introduced ohmic loss of the chip-resistor loading, the antenna gain is decreased, and is estimated to be about 2 dBi, compared to a shorted patch antenna with a shorting pin. For the latter design with stacked shorted patches, an impedance bandwidth of greater than 10% can be obtained. For this design, of course, the total antenna volume or height is increased.SHRI KRISHAN DEV BHOOMI INSTITUTE OF ENGINEERING & TECHNOLOGY

51

COMPACT DUAL-FREQUENCY MICROSTRIP ANTENNAS

Compact microstrip antennas with dual-frequency operation have attracted much attention. The two operating frequencies can have the same polarization planes or orthogonal polarization planes. One of the reported compact dual-frequency designs with the same polarization planes uses the first two operating frequencies of shorted microstrip antennas with a shorting pin, and the obtained frequency ratios between the two operating frequencies have been reported to be about

Fig34. Geometry of a stacked shorted patch antenna for compact broadband operation.

COMPACT CIRCULARLY POLARIZED MICROSTRIP ANTENNAS

Various novel designs have been reported recently to achieve compact circularly polarizedradiation with microstrip antennas. In addition to the well-known technique of

Fig35. COMPACT CIRCULARLY POLARIZED MICROSTRIP ANTENNAS

using a high-permittivity substrate as described in, compact CP designs can be achieved by embedding suitable slots or slits in the radiating patch or the antenna’s ground plane. These designs mainly use a single probe feed or an edge-fed microstrip-line feed. By using a single


52

inset microstrip-line feed, it is possible for microstrip antennas with a slotted patch to achieve compact CP radiation.For a compact CP design using a tuning stub [12, 47] the required length of the tuning stub increases as the CP center operating frequency is lowered. The increase in allowable tuning-stub length accompanying the reduction in antenna size for such compact CP designs allows a greatly relaxed manufacturing tolerance compared to the corresponding conventional circularly polarized microstrip antenna at the same operating frequency. This is a great advantage for practical applications,

Fig36. COMPACT CIRCULARLY POLARIZED MICROSTRIP ANTENNAS

Geometries of (a) a microstrip-line-fed compact circularly polarized microstrip antenna with a tuning stub and (b) an aperture-coupled compact circularly polarized microstrip antenna with a bent tuning stub.


53

C H A P T E R 4

FULLY FABRICATED MICROSTRIP PATCH ANTENNA

The following figures 5.1 (a),(b) and show the resultant fabricated microstrip patch antenna. The figures shown are front, side and back view of antenna. This patch radiates at a frequency of 8.5 GHz.

Fig 37 Back View Of Patch Antenna


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Fig38 Front View Of Patch Antenna

CHARACTERISTICS OF MICROSTRIP X-BAND PATCH ANTENNA

RECIEVING Antenna: Microstrip Patch Antenna

Transmitting Antenna: Horn Antenna

Beam Voltage: 329 Volts

Repeller Voltage 132Volts

S.No. Rotation Angle(degree) Voltage(mv)1 0 1.32 Left hand 20 1.13 Left hand 40 0.84 Left hand 60 0.35 Right hand 20 1.16 Right hand 40 1.97 Right hand 60 28 Right hand 80 2.1

RECEPTION PLOT:


55

Fig.39 Angle vs Voltage plot

C H A P T E R 5

TESTING AND MEASUREMENT

Fig40.Block Diagram Of Microwave Setup


56

Antenna Setup For Measurement

Fig41. Antenna Setup For Measuring E & H-Plane Characteristics

Antenna Measurement

If a transmission line propagating energy is left open at the end, there will be radiating from this end. In case of a rectangular waveguide this antenna presents a mismatch of about 2:1 and it radiates in many directions. The match will improve if the open waveguide is horn shape.

The radiation pattern of an antenna is a diagram of field strength or more often the power intensity as a function of the aspect angle at a constant distance from the radiating antenna. An antenna pattern is presented as a two dimensional pattern in one or several planes. An antenna pattern is consists of several labels, the main lobe, side lobe, back bone lobe . The major power is concentrated in the main lobe as low as possible. The power intensity at the main lobe compared to the power intensity achieved from an imaginary omni-directional antenna (radiating equally in all directions) with the same power fed to the antenna is defined as gin of the antenna.

3dB Beam Width:

The angle between two points on a main lob e where yhe power intensity is half the maximum power intensity where measuring an antenna pattern , it is normally most interesting to plot the pattern far from the antenna.

Far field pattern is achieved at a minimum distance of

2D2/λ (for rectangular Horn antenna)


57

where D is size of the broad wall of horn aperture is free wavelength

It is also very imported to avoid disturbing reflection. Antenna measurement is normally made at outdoor rangers or in so called anechoic chambers made of absorbing materials.

Antenna measurements are mostly made with unknown antennas as receiver. Therefor several methods to measure the gain of antenna. One method is to compare the unknown antenna with known gain. A method is to use two identical antennas, as transmitters and other as receiver from following formula the gain can be calculated.

PR = Pt G1 G2/(4S)2

where Pt is transmitted and receiving antenna S is to radial distance between antenna.

Is free space wavelength.

If both transmitting & receiving antenna are identical having gain G the

G=4SPr/Pt

In the above equation Pt, S,Pr and can be measured and gain can be computed. As from the above equation it is not necessary to know the absolute of Pt & Pr. Only is required, which can be measured by VSWR meters.

Procedure

Antenna Diagram Plotting

1.Setup the equipments as shown in fig 4.3 .keeping the axis of both antenna in the same axis line.


58

Fig42.Setup For Measurement At X-Band

2. Energise the gunn oscillator for maximum output at desired frequency with square wave modulation by tunning square wave amplitude and frequency of modulating signal of gunn power supply and by tunning of detector.

3. Also tune the S.S. Tuner in the line for maximum output(if S.S Tuner in the setup.

4. Obtain full scale deflection (0dB) on normal dB scale(0-10dB) at any convenient range switch position of the V.S.W.R meter by gain control knob of V.S.W.R meter or by variable attenuator.

5. Turn the receiving horn to the left in 10degree steps up to -130 to 130 degree and note the corresponding V.S.W.R dB reading in normal dB range. When necessary change the range switch to next higher range and add 10 dB to the observed value.

6. Repeat the above steps but this time turn the receiving horn to the right and note down the readings.

7. Draw the relative power pattern i.e. output v/s angle.

8. from the diagram determine 3dB width of the horn antenna can be measured.

Gain measurement

1. Set up the equipments as shown in fig. both horns should be in line.

2. Keep the range db switch of VSWR meter at 50 db position with gain control full.

3. Energize the gunn oscillator for maximum output at desired frequency of gunn power

supply and by tuning of detector.

4. Obtain full scale deflection in VSWR meter with variable attenuator.

5. Replace the transmitting horn by detector mount and change the appropriate range db

position to get the deflection. On scale . note and record the range db position and

deflection of VSWR meter.

6. Calculate the difference in db between the power measured in step 4 and 5.

Antenna1 results:


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5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Freq [GHz]

0.00

10.00

20.00

30.00

40.00

50.00

60.00

dB

(VS

WR

(Wa

veP

ort

1))

Ansoft Corporation HFSSDesign1XY Plot 5

Curve Info

dB(VSWR(WavePort1))Setup1 : Sw eep1

Fig43. vswr results of simulation

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Freq [GHz]

-400.00

-300.00

-200.00

-100.00

0.00

100.00

200.00

300.00

400.00

Y1


Curve Info

re(Z(WavePort1,WavePort1))Setup1 : Sw eep1

im(Z(WavePort1,WavePort1))Setup1 : Sw eep1

Fig44. impedence plot of antenna


60

Fig45. magnetic field vector plot of antenna

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Freq [GHz]

-20.00

-15.00

-10.00

-5.00

0.00

5.00

10.00

dB

(S(W

ave

Po

rt1

,Wa

veP

ort

1))


Curve Info

dB(S(WavePort1,WavePort1))Setup1 : Sw eep1

Fig46. reflection coff.plot of antenna


61

fig.47electric field plot of antenna

fig.48 3d radiation plot of antenna


62

fig.49. polarization plot of antenna


63

Antenna 2:

After changing the dimensions of substrate and ground plate new improved results are formed as:

fig.50 E field plot of antenna


64

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Freq [GHz]

-40.00

-30.00

-20.00

-10.00

0.00

10.00

20.00

dB

(S(W

ave

Po

rt1

,Wa

veP

ort

1))


Curve Info

dB(S(WavePort1,WavePort1))Setup1 : Sw eep1

fig.51 Gain plot of antenna

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Freq [GHz]

-300.00

-200.00

-100.00

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

Y1


Curve Info

re(Z(WavePort1,WavePort1))Setup1 : Sw eep1

im(Z(WavePort1,WavePort1))Setup1 : Sw eep1

fig.52 impedence plot of antenna


65

5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Freq [GHz]

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

dB

(VS

WR

(Wa

veP

ort

1))


Curve Info

dB(VSWR(WavePort1))Setup1 : Sw eep1

fig.53 VSWRplot of antenna

fig.54 3D radiation plot of antenna


66

fig.55 radiation plot of antenna

fig.56 H field plot of antenna


67

Conclusion and Future Scope

The design of slotted square patch antenna for circular polarization and dual bandwidth operated has been completed using HFSS software. The simulation gave results good enough to satisfy our requirements to fabricate it on hardware which can be used wherever needed. The investigation has been limited mostly to theoretical studies and simulations due to lack of fabrication facilities. Detailed experimental studies can be taken up at a later stage to fabricate the antenna. Before going for fabrication we can optimize the parameters of antenna using one of the soft computing techniques known as Particle Swarm Optimization(PSO).


68

REFRENCES[1] Jordan E C & Balmain K G, “Electromagnetic Waves and RadiatingSystems”, 2nd ed., PHI, 1968.

[2] Weeks W.L, “Antenna Engineering”, McGraw-Hill, 1968.

[3] Balanis C.A, “Antenna Theory: Analysis and Design”, 2nd ed., Wiley, 1996.

[4] Elliot R.S, “Antenna Theory and Design”, Prentice-Hall, 1981.

[5] Stutzman W.L &. Thiele G.A , “Antenna Theory and Design,Wiley”, 1998.

[6] Johnson R.C, “Antenna Engineering Handbook”, 3rd ed., McGraw-Hill, 1993.

[7] Collin R.E & Zucker F.J, “Antenna Theory”, eds., Part I, McGraw-Hill, 1969.

[8] Kiang Jean-Fu, “Antennas”, Chapter 3, National Taiwan University,Taipei,Taiwan.

[9] Biswas M & Guha D, “Broadband Microstrip Patches for M.C System", University of Kolkatta, Kolkatta, India.

[10] Etd.lib.fsu.edu, “Microstrip Patch Antenna Design & Results”, Chapter 3.

[11] Greig D.D, & Enlemann, H.F.,”Microstrip-A New Transmission Technique for the

Kilomegacycle Range,”Proceedings of The IRE, 1952, Vol .40,No.10,pp.1644-1650.

[12] Deschamps G.A., “Microstrip Microwave Antennas”, The Third Symposium on The

USAF Antenna Research & Development Program, University of Illinois, Monticello , Illinois, October 18-22,1953.

[13] Wu T.T, “Theory of the Microstrip”, Journal of Applied Physics, March, 1957, Vol. 28, No. 3, pp. 299-302.

[14] Wheeler H.A., “Transmission Line Properties of Parallel Strips Separated by a Dielectric Sheet”, IEEE Transactions on Microwave Theory of Techniques, Vol. MTT-13, pp 172-185, March 1965.

[15] Purcel R.A., Masse D.J. & Hartwig C.P., “Losses in Microstrip” IEEE Transactions on Microwave Theory & Techniques, June, 1968, 342-350.

[16] Purcel R.A., Masse D.J. ,Hartwig C.P. & Errata: “Losses in Microstrip” IEEE Transactions on Microwave Theory & Techniques, December, 1968, 1064.

[17] Denlinger E.J., “Radiation from Microstrip Radiators”, IEEE Transactions on Microwave Theory & Techniques, pp 235-236, April 1969.

[18] Watkins J., “Circular Resonant Structures in Microstrip”, Electronics Letters, Vol 5,

No.21, October 16, 1969, pp. 524-525.

[19] Bancroft, Randy ,Etd.lib.fsu.edu, “Microstrip Patch Antenna Design & Results”,


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Chapter 1.

[20] Haider S & Young L, “Microstrip Patch Antenna for Broadband Indoor Wireless Systems”, University of Auckland, 2003, pp. 3-5.

[21] Etd.lib.fsu.edu, “Microstrip Patch Antenna Design & Results”, Chapter 4.

[22] Guha D, “Microstrip & Printed Antennas: Recent trends & Developments”, December 2003, pp. 10-12.

[23] Wong K.L, “Design of Nonplanar Microstrip Antennas and Transmission Lines”, Wiley, New York, October 4,2001.

[24] Biswas M, Siddiqui J.Y. & Guha D, “CAD of Triangular Microstrip Patch Antenna in Multilayered Media”, Institute of Radio Physics & Electronics, University of Calcutta, Calcutta, India.

[25] Verma, A.K. & Nasimuddin, “Fast & Accurate Model for Analysis of Equilateral Triangular Patch Antenna”.Department of Electronics Science,University of Delhi,New Delhi, India.

[26] Wojciech J.K.,"Triangular Microstrip Antenna Loaded by Slots for GPS Applications." Wroclaw University of Technology, Faculty of Electronics, Institute of Telecommunications, Teleinformatics & Acoustics, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.

[27] Solanki M.R., Kiran U.K & Vinoy K.J, “Broadband Design of a Triangular Microstrip Antenna with Capacitive Feed”, Microwave Laboratory, ECE Department, IIS, Bangalore, India.

[28] Siddiqui J.Y. & Guha D, “Applications of TMP: Circuit Elements for Modern Wireless Antenna.”

[29] Fassetta A.S, “Low-profile circular array of equilateral triangular patches for angular diversity” IEE Proc. Microwaves,Antennas and Propagation, vol. 150, pp. 34-36, Feb. 2003.


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Micro Strip Patch Antenna