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Chapter 4
Design Considerations of
Reconfigurable Antenna
4.1 Introduction
This chapter presents design, simulation and optimization of proposed reconfig-
urable antennas carried out using commercially available electromagnetic simu-
lation software Zeland IE3D. The experimental work is also carried out on var-
ious reconfigurable antenna geometries with different configurations and shapes
on Vector Network Analyzer (VNA), Germany make ZVK model Rohde and
Schwarz 1127.865, 10 MHz - 40 GHz in Microwave Electronics Research Labo-
ratory (MERL), Department of Post Graduate Studies and Research in Applied
Electronics, Gulbarga University, Gulbarga sponsored by Department of Science
and Technology (DST), Govt. of India, New Delhi under FIST programme. Few
measurements were also carried out on Network Analyzer at LRDE, Bangalore
and NITK, Surathkal, Mangalore (D.K).
This chapter also presents the detailed concept of reconfigurable antennas
and emerging technologies that make reconfigurable antennas possible for used
in wireless applications. First, a description of the methodologies available for
designing reconfigurable antennas is presented. The antenna characteristics are
described and the mathematical models used in simulating the switches in an
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RF environment are presented. From a systems standpoint, antennas have his-
torically been viewed as static devices with time-constant characteristics. Once
an antenna design is analyzed, its operational characteristics remain unchanged
during system use. However, the recent advent of switching elements likes var-
actor diodes, PIN, microelectromechanical system (MEMS) components into mi-
crowave and millimeter wave applications has opened new and novel avenues of
antenna technology development. High quality, miniature RF switches provide
the antenna designer with a new tool for creating dynamic radiating structures
that can be reconfigured during operation. Varector diode switches are of partic-
ular interest because they offer broadband operation, low insertion loss and high
contrast between active states. In the near future the antenna will evolve as a
component that wills offer intelligence that alters itself to meet operational goals.
While the method of antenna operation is evolving, its role in communication
systems still remains the same. Gain, bandwidth, polarization, antenna feature
size, etc are still the realizable quantities of interest. Only now the introduction
of dynamic radiating structures has given the antenna designer an additional de-
gree of freedom to meet these design goals.
In modern radar and communication systems, various antennas are installed
on a single platform, such as airplane, ship and satellite, for the purpose of com-
munication, navigation and guidance purpose etc. These antennas will increase
the weight and cost of the systems. Furthermore, there are electromagnetic inter-
ferences between various antennas which will severely impact the normal opera-
tion of the antenna system. It is most desirable that all of the required functions
can be achieved through a minimum number of antennas in order to reduce the
weight and cost of systems and to achieve a good electromagnetic compatibil-
ity performance. The concept of reconfigurable antenna is presented due to the
driving of the practical requirements. A common radiation aperture is used for
multiple functions by reconfigurable operating states of the antenna. The recon-
figurable capability can be achieved by using Micro Electromechanical System
(MEMS) switches, PIN diode switches or multi-port feeding. The concept of
reconfigurable antenna was proposed in United States of America (USA) in the
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year 1983.
4.2 Design of conventional microstrip patch an-
tenna
The design of microstrip patch antenna basic parameters required to select the
appropriate geometry are as follows:
• Selection of dielectric substrate of appropriate thickness (h)
• Dielectric constant (εr)
• Operating frequency(fr)
Once these are chosen, the elemental dimensions can be calculated.
For the design point of view, the transmission line model has been selected
due to its simplicity for the design of conventional microstrip patch antennas.
The design procedure of a microstrip patch antenna is proposed by Munson and
Carver. A microstrip antenna generally consists of a dielectric substrate sand-
wiched between a radiating patch on the top and a ground plane on the other
side as shown in Figure 4.1. 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.
For simplicity of analysis, the patch is generally square, rectangular, circular,
triangular, and elliptical or some other common shape. For a rectangular patch,
the length L of the patch is usually in the range of 0.3333 λo < L < 0.5λo 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 of the substrate is usually
0.3333 λo ≤ h ≤ 0.5λo The dielectric constant of the substrate εr is typically in
the range 2.2 ≤ εr ≤ 12.
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Figure 4.1: Structure of microstrip patch antenna.
4.3 Patch element design:
For the design of microstrip patch antenna (RMA) the most commonly consid-
ered specifications are dielectric constant of substrate material εr, thickness of
substrate material (h), resonant frequency (fr) and frees pace wavelength (λo)
etc.Some steps are as follows. (a) Elemental width (W):
The width of rectangular micro strip antenna is given by,
W =
[C
2fr
] [εr + 1
2
]−1/2(4.1)
(b) Extension length (∆l):
The extension length (∆l) is given by,
∆l = 0.412h
[εe + 0.3(W
h+ 0.264)
εe − 0.258(Wh
+ 0.8)
](4.2)
Where,εe is the effective dielectric constant. It is calculated using the formula,
εe =
[εr + 1
2
]+
[εr − 1
2
]+
[1 + 12h
W
]−1/2(4.3)
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(c) Elemental length (L): Once the elemental width (w), extension length (∆l)
and effective dielectric constant (εe) are determined using the above equations
then the elemental length is found by using the equation,
L =
[C
2frεe − 12
]− 2∆l (4.4)
(d) Calculation of the ground plane dimensions (Lg and Wg)
The transmission line model is applicable to infinite ground planes only. For
practical considerations, it is essential to have a finite ground plane. The size
of the ground plane is greater than the patch dimensions by approximately six
times the substrate thickness all ground the periphery. Hence for this design, the
ground plane dimensions would be given as:
Lg = 6h+ L,Wg = 6h+W (4.5)
Where h is nothing but the height of substrate.
(e) Determination of feed point location (Xf , Yf ):
The feeding method for various reconfigurable microstrip antennas is co-axial
probe feed as shown in Figure 1.15, the center of the patch is taken as the origin
and the feed point location is given by the co-ordinates (Xf , Yf ) from the origin.
The feed point must locate at that point on the patch where the input impedance
is 50 Ω for the resonant frequency. Hence, a trial and error method is used to
locate the feed point. For different locations of the feed point, the return loss
(R.L) is compared and that feed is selected where the return loss (RL) is most
negative. There exists a point along the length of the patch where return loss
(RL) is minimum. Hence in this design, Yf will be zero and only Xf will be varied
to locate the optimum feed point. Once after selecting the patch dimensions L
and W for a given substrate, the next task is to determine the feed point location
so as to obtain a good impedance match between antenna and load.
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4.4 Design of rectangular spiral slots reconfig-
urable MSA (RSS-RMSA)
A conventional antenna i.e., reconfigurable microstrip patch antenna is shown in
Figure 4.2 (a) and (b),where Figure (a) shows simulated geometry of conventional
antenna and Figure (b) shoes fabricated view of conventional antenna. From the
design equation (4.1) and (4.4) the patch length L = 46.5 mm and width W =
36.5 mm is fed by 50 Ω coaxial dual probe feed is as shown below.
The proposed reconfigurable microstrip antenna with rectangular spiral slot
geometry is illustrated in Figure 4.3 (a) and (b). A reconfigurable microstrip
patch antenna with dimensions L = 36.5 mm and W = 46.5 mm is fabricated on
a single substrate of thickness h = 1.6 mm and relative permittivity εr = 4.2. A
two rectangular spiral slots of vertical length L1 = 46.5 mm and L2 = 37.5 mm,
horizontal spiral slots of length L3 = 33.5 mm and L4 = 31.5 mm, and spiral width
W1 = 3.5 mm and W2 = 2. 5 mm and varactor diode D is placed on second spiral
slot in order to get maximum tuning range and better matching. The dc bias
voltage is supplied from battery and the antenna is electromagnetically coupled
using a 50 Ω design dual co-axial feed line is provided.
4.5 Design of Slotted reconfigurable microstrip
antenna (SRMSA)
The patch is printed on the dielectric substrate, connected to direct co-axial feed.
The dielectric substrate has permittivity (εr) of 4.2 and thickness (h) of 1.6 mm.
The size of square substrate is 60 mm X 60 mm and square patch (P) in the
center configures at 1.98 GHz operation.
A conventional patch antenna with patch size of length L = 36.33 mm and
width W = 36.33 mm fed by 50 Ω coaxial single probe feed is designed for operat-
ing frequency of 1.98 GHz. The proposed conventional patch antenna geometry is
as illustrated in Figure 4.4 (a) and (b), where Figure 4.4 (a) shows cad design of
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Figure 4.2: (a)Geometry of conventional patch antenna (b)Fabricated view ofantenna.
Figure 4.3: (a)Geometry of reconfigurable antenna with spiral slots (b) Fabricatedview of antenna.
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patch antenna and Figure 4.4 (b) shows photograph of fabricated patch antenna.
Figure 4.4: (a) Geometry of patch antenna (b) photograph of fabricated antenna.
4.5.1 Design of single slot reconfigurable microstrip an-
tenna (SSRMSA)
The square patch antenna is reconfigured and single slot is etched on patch with
dimensions of length L1 = 20.16 mm and L2 = 16 mm as shown in Figure 4.5
(a). The Figure 4.5 (b) shows photograph of fabricated antenna.
A square patch antenna is fabricated on a single sided glass epoxy dielectric
substrate of thickness h = 1.6 mm and relative permittivity εr = 4.2. A vertical
slot of length L1 = 20.16 mm is made on either side of the patch and the slots
are positioned at Ps = 29.25 mm which as shown in Figure 4.6 (a) and (b), where
(a) shows cad design and (b) shows photography of fabricated antenna.
4.5.2 Design of double slot reconfigurable MSA with 2D
(DSRMSA-2D)
The proposed reconfigurable slot antenna with varactor loaded is as shown in
Figure 4.6 (a) and (b).The Figure 4.6 (a) shows cad design of DSRMSA and
the Figure.4.6 (b) shows photograph of fabricated DSRMSA. The dimensions of
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Figure 4.5: (a) Geometry of reconfigurable antenna with one slot (b) photographof fabricated antenna.
proposed slotted antenna and slot length1 (L1) is 20.16 mm, slot length2 (L2) is
16 mm and slot width (SW1) is 3.54 mm and for width of the configured section
for loading the two slots and two varactor diodes are placed at a center of the
slots in order to get maximum tuning range and better matching. The antenna
is electromagnetically coupled using a 50 Ω in single coaxial feed line as shown
below.
4.6 Design of compact reconfigurable multi fre-
quency MSA (CRMFMSA)
The conventional patch antenna is designed for 2.4 GHz frequency as illustrated
in Figure 4.7 (a) simulated and Figure 4.7 (b) shows photograph of fabricated
conventional patch antenna. The proposed rectangular patch antenna is fabri-
cated on glass epoxy substrate εr = 4.4 with thickness (h) of 1.6 mm, width of
the patch is W = 30.69 mm and length L = 38.75 mm. In order to have three
different resonance frequencies without considering the switches in the design,
etching at two horizontal slots are made on patch. Figure 4.8 shows proposed
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Figure 4.6: (a) Geometry of a proposed antenna with double slot loaded withvaractor diodes (b) Fabricated view of antenna.
geometry of ground plane with probe feed.
4.6.1 Design of compact reconfigurable multi-frequency 2
slot MSA (CRM-2SMSA)
By etching two slots (S1) = (S2) = 1 mm on patch position of the antenna is
as shown in Figure 4.9 (a) and (b), where (a) shows simulated and (b) shows
photograph of fabricated antenna. This design makes current path elongates
through radiator which will help for generating multiple resonating frequencies.
4.6.2 Design of compact reconfigurable multi frequency 4
slot MSA (CRM-4SMSA)
Four slots (S1) = (S2) = (S3) = (S4) = 1 mm are made on conventional patch
antenna are designed and fabricated is as shown in Figure 4.10 (a) and (b). The
four slots are etched on patch since the current path elongates more which is also
helpful to generate the different frequencies.
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Figure 4.7: (a) Simulated conventional patch antenna (b) Photograph of fabri-cated antenna (front end).
Figure 4.8: Photograph of antenna ground plane with probe feed (back view).
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Figure 4.9: (a) Simulated geometry of Two slot antenna(b) Photograph of fabri-cated antenna.
Figure 4.10: (a)Simulated geometry of antenna with four slots (b) Photograph ofantenna.
93
4.6.3 Design of compact reconfigurable multi-frequency 7
slot MSA (CRM-7SMSA)
Figure 4.11 (a) and (b) shows simulated and proposed reconfigurable seven slot
microstrip antenna. The width of all the slots is 1 mm. The use of multi slots
offers size reduction which is due to the excitation of both horizontal and vertical
currents paths. Such slot does not have any effects on the far-field radiation
characteristics. It is also studied that, the different orientation slots offers lower
mutual coupling between the slots.
Figure 4.11: (a) simulated geometry of proposed antenna with multi slots (b)Photograph of fabricated antenna.
4.6.4 Design of compact reconfigurable multi-frequency 7
slot MSA with 1D (CRM-7SMSA1D)
Figure 4.12 (a) shows simulated geometry of proposed antenna with one diode
and Figure 4.12 (b) shows photograph of fabricated antenna. The exact positions
for diodes are found during the design by various simulation iterations on different
positions. It is also noted that as the diodes are loaded far away from the co-axial
feed which results in broadsided radiation patterns.
94
Figure 4.12: (a) Simulated geometry of proposed antenna with multi slots loadedwith one varactor diode (b) Photograph of fabricated antenna.
4.6.5 Design of compact reconfigurable multi-frequency 7
slot MSA with 2D (CRM-7SMSA2D)
Also shown in Figure 4.13 (a) and (b) shows seven slot antenna with two varactor
diodes are placed 0.2 mm from either sides of each slot. The proposed reconfig-
urable antennas are simulated using Zeland IE3D software. Resonance does not
change when the diodes turn off or on, which leads to the same pattern for the
same resonance in different states.
4.7 Design of bridge reconfigurable microstrip
antenna (B-RMSA)
The Rhombus shaped microstrip antenna is as shown in Figure 4.14 (a) and
(b).The simulated geometry is as shown in Figure 4.14 (a) and Figure 4.14 (b)
shows photograph of fabricated antenna. The size of the patch is (L x W) 28
mm x 28 mm is printed on a dielectric substrate of thickness h = 1.6 mm. The
material used is glass epoxy with dielectric permittivity of εr = 4.4 is designed
to operate at 2.4 GHz. This designed antenna is fed by microstrip feed line of
dimension (Lf ) = 15 mm,(Wf ) = 4.84 mm through quarter wave transformer
95
Figure 4.13: (a) Simulated geometry of proposed antenna with multi slots loadedwith two varactor diode (b) Photograph of fabricated antenna.
having (Lt) = 24.05 mm, Wt = 0.72 mm. They are mounted on substrate of
dimension 106 mm x 67.6 mm connected through 50 Ω SMA connector.
4.7.1 Design of bridge reconfigurable MSA with BW 1mm
(BRMSA-BW1mm)
This rombus shaped patch is divided into two parts, inner patch (p1) and outer
patch (p2). Double squares are made with dimensions, the outer patch having 28
mm and inner patch having 13 mm. Bridges are made for the connection between
two patches. Bridge widths (BW) are varies from 1mm to 4mm as shown below.
(Figure 4.15 and Figure 4.16).
Figure 4.15 (a) and (b) shows geometry of simulated and photography of fab-
ricated antenna respectively with Bridge width (BW) = 1mm. This designed
antenna is fed by microstrip feed line and the dimensions of quarter wave trans-
former is explained above. These antennas are analyzed using Zeland IE3D soft-
ware simulator and also practically tested on Vector Network Analyzer (VNA).
96
Figure 4.14: (a) simulated geometry of rombus shape patch antenna (b) Photog-raphy of fabricated antenna.
97
Figure 4.15: (a) Simulated geometry of proposed antenna with BW=1mm (b)Photograph of fabricated antenna.
98
4.7.2 Design of bridge reconfigurable MSA with BW 2mm
(BRMSA-BW2mm)
Figure 4.16 (a) and (b) shows geometry of simulated and photograph of fabri-
cated antenna with BW = 2 mm. Four-bridges make a connection between inner
patch (P1) and outer patch (P2). Operating frequency of antenna is achieved by
changing bridge width (BW) from 1 mm to 4 mm.
Figure 4.16: (a) Simulated geometry of proposed antenna with BW=2mm (b)Photography of fabricated antenna.
4.7.3 Design of bridge reconfigurable MSA with BW 2mm
and 1D (BRMSA-BW2mm1D)
Figure 4.17 (a) and (b) shows geometry of simulated and photography of fab-
ricated antenna with BW = 2 mm with one varactor diode. Varactor diode is
integrated with the bridge slot, and is used to tune the operating frequencies
without affecting the radiation characteristics. Desired operating frequencies val-
99
ues can be obtained by incorporate the active devices, i. e, varactor diode. This
active device will provides a long path for current to flow in the radiating patch.
This result in shifting of frequency hence reduction in antenna size is observed.
Figure 4.17: (a) Simulated geometry of proposed antenna with BW=2mm andvaractor diode (b) Photography of fabricated antenna.
4.7.4 Design of bridge reconfigurable MSA with BW 2mm
and 2D (BRMSA-BW2mm2D)
Figure 4.18 (a) and (b) shows geometry of simulated and photography of fab-
ricated antenna with BW = 2 mm with two diodes. Two varactor diodes are
integrated with the bridge slot, and is used to tune the operating frequencies and
these two diodes will provides a long path for current to flow in the radiating
patch.
100
Figure 4.18: (a) Simulated geometry of proposed antenna with BW=2mm andtwo varactor diode(b) Photography of fabricated antenna.
101
4.7.5 Design of bridge reconfigurable MSA with BW 2mm
and 3D (BRMSA-BW2mm3D)
Figure 4.19 (a) and (b) shows geometry of simulated and photograph of fabricated
antenna with BW = 2 mm with three diodes. In this design three varactor diodes
are mounted between inner patch and three bridges and it helps to generate
multi operating frequencies. The bridges are very important to make a current
through the diodes. The current path more elongate, hence multiple frequencies
are generate and frequencies are tuning from higher to lower this makes antenna
size reduction.
Figure 4.19: (a) Simulated geometry of proposed antenna with BW=2mm andthree varactor diode(b) Photography of fabricated antenna.
102
4.8 Design E-slot Reconfigurable microstrip an-
tenna (ES-RMSA)
The various parameters for the antenna were calculated for 2.4 GHz. The di-
electric substrate chosen here was glass epoxy (εr = 4.4) and the height of the
substrate h = 1.6 mm. To feed the patch antenna a microstrip feed line can
be attached to the center of one of the radiating edges. The E-slot is made on
rectangular patch with main slot dimension is slot width Sw is 2 mm, slot length
SL is 1.5 mm.
This design employs techniques namely, the coaxial probe feeding, E-slot tech-
niques to meet the design requirement. The E- shaped slots are made on the
radiating element and patch is fed by a coaxial probe at a distance fp from the
edge of the patch as shown in Figure 4.20 A dielectric substrate with dielectric
permittivity, εr of 4.4 and thickness, h of 1.6 mm has been used in this research.
Figure 4.20: (a)Geometry of E-slot antenna (b)Fabricated view.
103
4.8.1 Design of E-slot reconfigurable MSA with 1C (ES-
RMSA-1C)
The capacitor loaded E-slot RMSA is as shown in Figure 4.21 (a) and (b) sim-
ulated and fabricated view respectively. The dimensions of E-slot and Patch is
same as that of the Figure 4.21 and one capacitor value of 10 pF is mounted on
one of the E-slot arm. This is tuning the frequency from higher to lower side.
Figure 4.21: (a)Geometry of E-slot antenna with one chip capacitor (b) Fabri-cated view.
4.8.2 Design of E-slot reconfigurable MSA with 2C (ES-
RMSA-2C)
Figure.4.22 (a) shows geometry of E-slot antenna with two chip capacitors. The
two capacitors are mounted on E-slot arms to make the shifting of resonating
frequency from higher to lower level and hence the antenna size reduction.
104
Figure 4.22: (a) Geometry of E-slot antenna with two chip capacitor (b) Fabri-cated view.
4.9 Design of multi-slot reconfigurable MSA with
capacitive loading (MS-RMSA-CL)
In this section, the structure of the proposed antenna is described. This design
consists of multi-slots to generate multiple resonant frequencies for wireless ap-
plications. The first design consisting of three slots with slot width (sw) of 2 mm,
permittivity of 4.4, and tangential loss of 0.0025. The Zeland IE3D Computer
software is used to simulate the designed antenna.
Chip capacitance is placed at the top of the first slot of the antenna to change
the effective length of the slot, thus producing controllable narrow band fre-
quencies. A compact and small frequency-reconfigurable microstrip antenna is
achieved by feed line and the slot of the antenna. Thereby, 76% size reduction is
achieved compared to the normal reconfigurable microstrip antenna.
4.9.1 Design of three-slot reconfigurable MSA (3S-RMSA)
Figure 4.23 (a) and (b) shows geometry simulated and fabricated view of 3S-
RMSA The dimensions of the antenna are in mm. The length of the slot S1 is 26
mm, S2 is 24 mm and S3 is 22 mm.The slot width (SW) is also in mm and slot
105
width is uniform for all three slots i.e 2 mm.The coaxial probe feed is connected
at -6 and -8 of xy plane with respect to the center of the antenna. The slot is
perpendicular to the feed line where the feed line excites the slot.
Figure 4.23: (a) Geometry of proposed antenna with three slots (b) Fabricatedview.
Three slots are etched on rectangular patch with uniform dimensions to achieve
frequency reconfiguration. This design is able to generate the resonant frequency
of 2.3 GHZ, 2.5 GHz and 2.8 GHz. The vertical slot arms splits the fundamen-
tal resonant frequency of the rectangular microstrip patch with slots, into two
separate resonant modes TM10 and TM01 with orthogonal polarization planes.
Thus three vertical slot considerably increases the effective lengths of the two
excited resonant modes, TM10 and TM01, and the excited patch surface current
densities are perturbed in such a way that these two modes can be excited for
different frequency operation with a single feed.
4.9.2 Design of four-slot reconfigurable MSA (4S-RMSA)
In order to vary the resonant frequency, four vertical slots are etched on rectan-
gular patch is as shown in the Figure 4.24 (a) and (b). The lengths of all vertical
slots are varied by 1 mm and determine the resonant frequencies. Thus by varying
the length of all the four slots simultaneously, reconfigurable frequency operation
with narrow band tuning range is achieved.
106
Figure 4.24: (a) Geometry of proposed antenna with four slots (b) Fabricatedview.
4.9.3 Design of five-slot reconfigurable MSA (5S-RMSA)
Figure 4.25 (a) and (b) shows simulated geometry of 5S-RMSA and fabricated
view of proposed antenna respectively. In this design five vertical slots are etching
on rectangular patch with respect to above said dimensions. This also increases
the current path length, generating the multi-frequencies and more size reduction.
Figure 4.25: (a) Geometry of proposed antenna with five slots (b) Fabricatedview.
107
4.9.4 Design of five-slot reconfigurable MSA with one ca-
pacitor loaded (5S-RMSA-1C)
The capacitor loaded across the protruding slot provides various capacitive load-
ings to the slot is as shown in Figure 4.26 (a) and (b). The junction capacitance of
the capacitor varies against the RF voltage and these different capacitive loadings
correspond to different electrical lengths and thus different resonant frequencies
are obtained.
Figure 4.26: (a)Geometry of proposed antenna with five slots,1C (b) Fabricatedview.
4.9.5 Design of five-slot reconfigurable MSA with two ca-
pacitor loaded (5S-RMSA-2C)
The capacitor loaded across the protruding slot provides various capacitive load-
ings to the slot is as shown in Figure 4.27. The two chip capacitors are connected
at the top of the first slot and this will elongates the current path and hence the
multiple frequencies.Due to the high capacitance added by the capacitors with
the radiator resonating frequencies obtained and moving towards the lower side.
108
Figure 4.27: Geometry of proposed antenna with five slots,2C.
4.10 Design of U and E-shape slots Reconfig-
urable MSA (UES -RMSA)
This section deals with capacitive loaded reconfigurable microstrip antenna with
two geometric shapes (U and E type) loaded with capacitive device are designed
and studied. The proposed antennas are simulated using Zeland IE3D software
and the results compared with the conventional rectangular microstrip antenna.
The results show that, bandwidth of conventional rectangular microstrip antenna
is enhanced from 16.01% (100 MHz) to 24.01% (257 MHz), 24.01% (257 MHz) and
4.92% (94 MHz) respectively using novel U and E shape patch over the substrate.
The size reduction of 80.17% is achieved with proposed antenna in comparison
with conventional microstrip antenna. The E-shaped patch antenna has achieved
highest bandwidth followed by U-shaped patch antenna. The proposed antenna
finds applications in Wireless Local Area Network (WLAN), Personnel Commu-
nication System (PCS) and Global System for Mobile Communication (GSM).
109
4.10.1 Design of U shape slot reconfigurable MSA (US-
RMSA)
Figure 4.28 shows the IE3D schematic geometry of proposed antenna which con-
sists of U-slot patch with dual probe feed. The length and width of the patch are
L = 38.75 mm and W = 30.69 mm. The dimensions of slot length and width are
L1 = L2 = L3 = 14 mm and W1 = W2 = W3 = 2 mm respectively. The proposed
antennas are designed and simulated using Zeland IE3D simulation software with
thickness (h) of 1.6 mm and a relative permittivity (εr) of 4.4. The dimensions
of the patch antenna are optimized to operate in the 2.4 GHz WLAN band.
Figure 4.28: Geometry of proposed antenna with U slot.
4.10.2 Design of U and horizontal slot reconfigurable MSA
(UHS-RMSA)
Figure 4.29 shows the IE3D geometry of proposed antenna which consists of U-
slot patch having horizontal slot having dimensions of slot length and width are
Sl = 38.7 5mm and Sw = 2 mm respectively. By etching one U-slot on patch and
one horizontal slot which will separate the part of patch. By this configuration,
change in the current path leads to shift in lower resonating frequency with better
return loss (RL) of -23.73 dB compared to conventional rectangular microstrip
antenna is given.
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Figure 4.29: Geometry of proposed antenna with U and horizontal slot.
4.10.3 Design of E and horizontal slot reconfigurable MSA
(EHS- RMSA)
Figure 4.30 shows the geometry of proposed antenna which consists of E-slot with
one horizontal slot loaded with two chip capacitor at each end having a value of 10
pF each. The dimensions of slot length and width are same as that of Figure 4.29
By etching E slot and one horizontal slot on patch, loaded with capacitor makes
the current path more elongate which helps to shift the resonating frequency
lower side with dual band nature and hence size reduction.
Figure 4.30: Geometry of proposed antenna with E and horizontal slot.
111
4.11 Design of T-slot reconfigurable microstrip
antenna (TS-RMSA)
In this section, the structure of T-slot reconfigurable microstrip antenna is de-
scribed. This design consists of T-slots to generate dual resonant frequencies for
wireless applications. The first design consisting of T-slots, next is without T-
slot,T-slot with one chipa capacitor and last design is T-slot with two chip capac-
itors. This structure consists of permittivity of 4.4, dielectric constant thickness
1.6 mm and tangential loss of 0.0025. The Zeland IE3D Computer software is
used to simulate the designed antenna. The proposed antenna is also fabricated
and test by using Vector network analyzer and corresponding explanation is given
below.
4.11.1 Design of T-slot microstrip antenna (TS-MSA)
Figure 4.31 (a) and (b) shows geometry of simulated and fabricated view of T-
slot antenna. This geometry consists of T-slot with Horizontal slot length (Hsl)
is 30.8 mm, horizontal slot width (Hsw) is 4.5 mm, vertical slot length (Vsl) is
12.26 mm and vertical slot width (Vsw) is 4.5 mm. The gap between T-slot and
patch is 1 mm is maintained is shown below. This T-slot structure is acting like
parasitic element. Dut to this parasitic element, the small amount of current is
entered into this and radiates small power.
4.11.2 Design of antenna without T-slot
The Figure 4.32 (a) and (b) shows Geometry of simulated and fabricated view of
antenna without T-slot. The slot length (Sl) is 32.8 mm and slot width (Sw) is
6.5 mm with single coaxial probe feed is as shown below. The entire current is
flow through the patch so this structure gives a lower resonating frequency with
good return loss compared to standard rectangular patch.
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Figure 4.31: (a)Geometry of T-slot antenna(b) Fabricated view.
Figure 4.32: (a)Geometry of antenna without T-slot (b)Fabricated view.
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4.11.3 Design of T-slot reconfigurable MSA with one chip
capacitor (TS-RMSA-1C)
The geometry of simulated and fabricated view of T-slot reconfigurable antenna
with one chip capacitor is shown in Figure 4.33 (a) and (b) respectively. The
dimensions of this design are as shown in Figure 4.31 (a). In this design chip
capacitor is mounted between T-slot and patch. The capacitance is added by
this chip capacitor the resonating frequency is shifted to lower from higher with
good band width and return loss compared to rectangular patch.
Figure 4.33: (a)Geometry of T-slot with chip capacitor(b)Fabricated view.
4.11.4 Design of T-slot reconfigurable MSA with two chip
capacitors (TS-RMSA-2C)
The proposed simulated and fabricated view of T-slot reconfigurable microstrip
antenna with two chip capacitors is shown in Figure 4.34 (a) and (b) respectively.
The dimensions of this geometry are same as given in Figure 4.31 (a). T-slot is
made in patch as parasitic element and two chip capacitors are mounted on either
side of the T-slot, which gives a higher capacitance and makes a current path
elongates, hence the resonating frequency is very much lower than rectangular
patch.
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Figure 4.34: (a)Geometry of proposed antenna(b)Fabricated view.
4.12 Fabrication Process
A considerable care is required in the fabrication process of microstrip antennas.
A slight error in the dimension causes drastic reduction in the antenna band-
width. Hence high dimensional tolerances are maintained during the fabrication
process of microstrip antennas. The steps typically involved in the fabrication of
microstrip antennas are shown in Figure 4.35.
The first step in the fabrication process is to generate the artwork from the
drawing. Here the artwork of the test antenna is developed using computer soft-
ware Auto CAD 2005. In the development of artwork of microstrip antennas the
accuracy is maintained upto four decimal points. Accuracy is vital at this stage
and depending on the complexity and dimensions of the microstrip antennas ei-
ther full or enlarged scale artwork should be prepared on stabline or Rubylith
film or prepared on buffer paper. Using the precision cutting blade of a manually
operated co-ordinograph the opaque layer of the stabline or rubylith film is cut to
the proper geometry and can be removed to produce either a positive or negative
representation of the microstrip antennas. The design dimensions and tolerances
are verified on a cordax measuring instrument using optical scanning. Enlarged
artwork should be photo reduced using a high precession camera to produce high
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resolution negative, which is later used for exposing the photo resists.
The laminate should be cleared using the substrate manufacturer recommend-
ed procedure to insure proper adhesion of the photo resist and the necessary reso-
lution in the photo development process. The photo resist is now applied to both
sides of the laminate using laminator. The laminate is then allowed to obtain nor-
mal at room temperature prior to exposure and development. The photographic
negative must be now held in very close contact with the polyethylene cover sheet
of the applied photo resist using a vacuum frame copy board or other technique
to assure the fine line resolution required. With exposure to proper wavelength of
light, polymerization of the exposed photo resist occurs making it insoluble in the
developer solution. The both side of microstrip antenna is exposed completely
without a mask, since the copper file is retained to act as a ground plane. The
protective in a developer, which removes the soluble photo-resist material. Visual
inspection is needed to assure proper development of microstrip antenna.
When these steps are completed, the antenna is ready for etching. This is
the critical steps and requires considerable care so that proper etch rates are
achieved. After etching, photo-resist is removed using a strip line solution. Vi-
sual and optical inspection should be carried out to ensure a good product and
to ensure performance with dimensional tolerances, with a final acceptance or
rejection being based on resonant frequency, radiation patterns and impedance
measurement. For acceptable units, the edges are smoothened and the antenna
is rinsed in water and dried. If desired, a thermal cover bonding may be applied
by placing a bonding film between the laminates to be bounded out placing these
between tooling plates. Dowel pins can be used for alignment and the assembly
is then heated under pressure until the bonding temperature is reached. Then
assembly allowed to cool under pressure below the melting point of bonding film
and the laminate is then removed for inspection.
The above procedure comprises the general steps necessary in producing a mi-
crostrip antenna. The substances used for the various processes e. g., cleaning,
etching or the tools used for machining etc depends on the substrate chosen.
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Figure 4.35: Fabrication steps of Reconfigurable Microstrip Antenna.
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By using the design and fabrication procedure explained above the study of
reconfigurable microstrip antennas for wireless communication have been devel-
oped.
All the proposed antennas are simulated using IE3D and then fabricated and
measured by using Vector Network Analyzer. The results obtained are discussed
in next chapter.
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