Microstrip patch antenna for wimax applications

DESIGN OF MICROSTRIP PATCH

ANTENNA FOR IEEE 802.16-2004 APPLICATIONS

EHAB ESAM DAWOOD

Department Of Electronic

Faculty of Electronics Engineering

University of Mosul

Contact me:[email protected]

mailto:[email protected]

The IEEE 802 LAN/MAN Standards Committee develops Local Area Network standards and Metropolitan Area Network standards.

The most widely used standards are for the Ethernet family, Token Ring, Wireless LAN, Wireless PAN, Wireless MAN, Bridging and Virtual Bridged LANs. An individual Working Group provides the focus for each area.

The number 802 was simply the next free number IEEE could assign, though “802” is sometimes associated with the date the first meeting was held in February 1980.

IEEE 802

IEEE 802.16 version

IEEE 802.16 version

wireless communication means to transfer information overlong or short distance without using any wires

An antenna is defined a usually metallic device (as a rodor wire) for radiating or receiving radio waves.

the antenna is the transitional structure between free-space and a guiding device

it is used to transport electromagnetic energy from thetransmitting source to the antenna or from the antenna tothe receiver, the antenna can be in a form of microstrip.

INTRODUCTION

Microstrip: is a type of electrical transmission line which can befabricated using printed circuit board used to convey microwavefrequency signals.

Microstrip Patch Antennas (MPA): These antenna comprises ofplanar layers including a radiating element, an intermediate dielectriclaye r, and a ground plane layer.

Microstrip antenna

INTRODUCTION

6

The radiating element may be square, rectangular,triangular, or circular and is separated from theground plane layer

Representative shapes of microstrip patch elements

INTRODUCTION

TERM MEANING??

Surface waves are guided waves captured within the substrate and partially radiated and reflected back at the substrate edges.

The ground plane of a printed antenna is always is finite in size, surface waves propagates until they reach an edge or corner.

The diffracted waves take up apart of energy of the signal thus decreasing the desired signal amplitude and contributing to deterioration in the antenna efficiency as well as increasing both side lobe and cross polarization

Surface Waves

The material of Printed Circuit Board (PCB) used in mydesign is FR4 utilize as substrate.

where "FR" means Flame Retardant, and Type "4" indicateswoven glass reinforced epoxy resin.

Dielectric constant typically in the range (4.3-5.2),depends on glass resin ratio.

popular material and cost effective compared with otherPCB material that make this PCB is preferred.

FR4 Substrate Material

The main drawback of microstrip patch antenna is suffer from narrow BandWidth. Antenna BandWidth (BW) can be improved by increasing the substrate thickness. The thickness of substrate increases surface waves, surface waves pass through the substrate and scattered at bends of the radiating patch which caused degrade the antenna performance.

To overcome this problem, the technique of air-gap that represents substrate layer which has the dielectric constant is 1, by using air substrate, the surface waves is not excited easily.

Problem Statements:

surface waves

0

To increase the efficiency of the microstrip patch antennaby decreasing the loss of the reflection, it is executed byusing air-gap as a substrate in microstrip patch antenna.

To reduce the cost in the fabrication of the antenna byusing the cheap and popular FR4 material. The resonantfrequency can adjusted without requiring new design by justvarying the height of the air-gap also as well as the FR4material this made the fabrications very cost effective.

Project Objectives:

1

To improve the BandWidth (BW) by increasing the thickness of dielectric substrate and dielectric constant with lower value.

To reduce the energy loss due to surface wave, the surface waves consume apart of energy of the signal thus decreasing the desired signal amplitude and contributing to deterioration in the antenna efficiency that weaken the microstrip antenna’s performance.

Project Objectives:

2

Use the resonant frequency 3.5 GHz for WiMax application, theresonant frequency is chosen from IEEE 802.16-2004 span of 2-11GHz.

Choose the air as dielectric substrates that have the value of dielectricconstant 1 in order to reduce the surface wave excisions.

Use the transmission Line model for calculation of patch Dimension. It’s the simplest of all and gives good physical insight.

Simulate and Verify antenna design performance by applying Computer Simulation Technology Software (CST) to design MPA.

Use AutoCAD software to open the DXF file that exported from CST software simulation.

Project Scopes:

FEEDING METHOD

Microstrip Line Feed : A conducting strip directly connected to the patch which is smaller in dimension as compare to patch. It is very easy to fabricate, very simple in modeling and match with characteristic impedance 50Ω or 75Ω. This type of feeding was not successful when using with air-gap substrate.

Coaxial Feed: Feed the inner conductor of coaxial extends through the dielectric and is soldered to the radiating patch, while the outer conductor is connected to ground plane, it is easy to fabricate and match. It has low spurious radiation, and it has narrow bandwidth.

Coaxial FeedMicrostrip Line Feed

Feeding method:

Aperture Coupled Feed: is more complex and more difficult to fabricateas compare to others, High dielectric material is used for bottom substrate andthick and low dielectric constant material for the top substrate .

Proximity coupled Feed: Its fabrication is not easy as compare to otherfeed techniques, the advantage is eliminates spurious radiation and provides highbandwidth (as high as 13%), due to overall increase in the thickness of themicrostrip patch antenna.

Proximity coupled FeedAperture Coupled Feed

Feeding method:

MICROSTRIP PATCH ANTENNA

DESIGN

Resonant frequency: The Resonant frequency was used in MPA for IEEE802.16-2004 is 3.5 GHz, and take the span (3 - 4) GHz used in reflection loss and BW calculations.

Dielectric Substrate: FR4 PCB material is used as a substrate. Reflection loss and BW are calculated when using singleFR4 PCB. Subsequently, air is used as the substrate between two PCB FR4 substrates that improves the BW as well as reduce the loss of the reflection. These are compared with the data when using singleFR4 PCB.

Thickness of Substrate: The thickness of Air substrate was designed and fabricated by using 2mm spacer, the thickness of the FR4 substrate is 1.6mm.

Many factors were determined before begin the design

FR4 Substrate Dimension:

λ » λ = 85.71 mm,

The width and the length of substrate is λ/2,

FR4 substrate dimensions:

SIDE VIEW

TOP VIEW

The effective dielectric constant is a function of a frequency.

Effective Patch Width (W)

Frings factor (ΔL)

Transmission line model formula:

Effective length (Leff):

Length:

The patch is actually a bit larger electrically than its physicaldimensions due to the fringing fields and the difference betweenelectrical and physical size is mainly dependent on the PC boardthickness and dielectric constant of the substrate.

Transmission line model formula(continued) :

The design and fabrication process

included two case

SECOND CASEAir-gap TECHNIQUE

First CaseSINGLE FR4 Board

1 2

First CaseSINGLE FR4 Board Using As Substrate

Material

Effective Dielectric Constant (εreff) is

W=26.33 mm

= 3.90

First Case (Single PCB-FR4 Only) as Substrate Material:

Calculations for Patch Antenna Dimension:

Width of the Patch (W) is

resonant frequency f° =3.5 GHz, dielectric constant for FR4 substrate isεr= 4.3, height of substrate for Fr4 PCB is h=1.6 is the principleparameters must be decided.

ΔL = 0.74 mm

L = 20.22 mm

Length of the patch is:

Fringing Field Length Extension (ΔL) is:

Length of the patch is:

(13.16, 3.41) mmLocation of the feed

Design location of the coax line feed

x

SECOND CASEAir-gap

TECHNIQUE

By using the same formula for case 1, and substitute f° =3.5 GHz, εr = 1, Air h= 2mm Will get

W=42 mm

ΔL = 1.41mm L =40 mm

Second Case (Air-gap with two PCB-FR4) as Substrate Material

W=42 mm

ΔL = 1.41mm

Edge Impedance = 120.11Position of the feed (21, 8.93)

Second Case (Air-gap with two PCB-FR4) as Substrate Material

Design structure&

Simulation Resultwith

Single patch antennaUsing

CST Software

The ground plane is made of copper have thickness 0.07 for the patch

Structure of Design single patch antenna

Design, Simulation, Fabrication and Measurement Result

61

Structure design simulation of single FR4 board

Structure design of Single patch antenna using CST software

(Operating frequency and S11) Simulation of single patch antenna

S11 for single Patch Antenna Without air-gap

1D Results:

At resonant frequency 3.5 GHz is exhibit S11 equal (-10.38 dB) simulated by CST, the BandWidth (BW), the simulated BW is exhibit 36 MHz that become clear when using FR4 only without Air-gap have narrow BW.

Bandwidth Simulation of single patch antenna

Bandwidth Simulation of Single Patch Antenna without air-gap

The plot displays some important properties of the coaxial mode such as TEM mode type, line impedance.

Input impedance simulation with single patch antenna

2D Results:


Design structure&

Simulation Resultwith

Air-gap TechniqueUsing

CST Software

The ground plane is made of copper have thickness 0.07 for the patch

Structure Design with Air-gap technique


2

Structure design simulation with air-gap technique

Structure design of Single patch antenna using CST software

(Operating frequency and S11) Simulation with air-gap technique

2D Results:

Simulation Result for Patch Antenna with Air-gap

At resonant frequency 3.499 GHz is display S11 equal (-42.87 dB) simulated by CST, The BW that getting by using Air-gap that have value is 96 MHz

Bandwidth Simulation with air-gap technique

Bandwidth Simulation with air-gap technique

Input Impedance simulation with air-gap technique

2D Results:

Design, Fabrication, Measurement and Result

Fabrication Measurement

MPA with air-gap technique

MPA With air-gap Technique

81

S11 Measurement

Reflection Loss of Fabrication 7

Resonant frequency 3.5 GHz is exhibit reflection loss (-27.650 dB) measured by VNA. The BW for MPA with Air-gap fabrication is (158 MHz), calculation is achieved by subtract the value 3.589 GHz of M3 from M2 that have value 3.431GHz.

measured microstrip patch antenna with air-gap results

Measurement

Parameter Measured MPA Results

Resonant Frequency (fo GHz) 3.5 GHz

Reflection loss (S11 dB) -27.650 dB

Input Impedance, (Zin ohm) 54.270 ohm

BandWidth (BW MHz) 158 MHz

Smith Chart

Smith chart

Smith Chart display the resonant frequency 3.5 GHz and it exhibit impedance matching is 54.270 ohm which is actually closer to the 50ohm.

The Smith Chart Parameter

Smith chart parameter

The parameter

measurement

Resonant Frequency

(M 1)

Frequency measured 3.5 GHz

Input Impedance measured 54.27 ohm

Analysis Result

Compare between Measurement and Simulations with Air-gap and without air-gap

Analysis Result1 3

Exel

Comparison between the Simulated Result of the MPA without Air-gap and simulated as well as measured results of MPA with Air-gap

Comparison Table of Simulated and Measured Results:

Parameter

Microstrip Patch

Antenna without

Air-gap

Microstrip Patch Antenna with

Air-gap

Simulated Simulated Measured

Resonant Frequency (fo GHz) 3.5 3.5 3.5

Reflection loss (S11 dB) -10.38 -42.87 -27.650

Input Impedance (Zin ohm) 46.16 45.63 54.270

BandWidth (BW MHz)36

(1.02 %)

96

(2.74 %)

158

(4.51 %)

3

Fabrication process

Fabrications process

Flow chart for fabrication process

Fabrications process

Dry film printed

Fixing dry film on PCB

1

2

UV exposure process

3

4

The FR4 PCB after exposed

to UV light

5

UV exposure machine

Removing the

transparent layer

Developing process

7

6Developing machine

FR4 after developing

process

Etching process

8

9 10

Etching machine

Etching process

11

Ground

Front Face

Stripping process

12

13

Stripping machine

The FR4 board after

stripping process

Dry Process

14

15

The FR4 board after

stripping and Dry process

Dry machine

PCB Cutter Machine

16

17

PCB Cutter machine

18

The FR4 board after

stripping and dry process

Drilling Machine

19

20

PCB Cutter machine

21

Make hole for location of probe

The spacer between two FR4 boards is cylinder wood material; the diameter for the standing is 6mm.

Spacer between the Substrate Layers

Spacer

FR4 Substrate Material: The joining between the Fr4 substrate layers with spacing is doing by

SUPA GLUE implement at 10 seconds.

Supa Glue

Stick

Technique design with air-gap, use two FR4 PCB substrate each layer have thickness is 1.6mm, the first board is consist of FR4 substrate have radiating patch but it strip from ground plane, the second board is consist of radiating patch and ground plane separated by FR4 substrate, the separation between two layers is air-gap.

FR4 Substrate with Air gap Separation

MPA with Air-gap technique

CST Simulations

CST Microwave Studio: Computer Simulation Technology (CST) develops and markets

software tools for the numerical simulation of electromagnetic fields. CST was founded in 1992 in Darmstadt, Germany.

Select Template Create a new CST microwave studio project after open CST design

environment.

CST Microwave Studio

http://en.wikipedia.org/wiki/Electromagnetic_field

CST Microwave Studio:

Antenna Template



Draw the Substrate Brick

Creation Brick


CST Microwave Studio: continue with the same thing by drawing the air-gap and second layer for

substrate-2, but only change the material in air-gap substrate to air from material library list

The Air-gap with Two Layers Substrate


CST Microwave Studio: Draw the ground plane, this perform by choose the pick face and clicking

to the surface of substrate FR4-2 and pick to the surface of substrate


CST Microwave Studio: By using extrude tool to create the ground plane for the second layer of

FR4 substrate.

Ground PlaneExtrude

Face


Ground PlaneExtrude

Face


CST Microwave Studio: Construct the dual patch first is stacked patch antenna and the second

is the probe fed patch,

stacked patch antenna probe fed patch antenna



Model the Coaxial Feed

Outer InnerFeed Feed

,



Common Solver Setting: Define Waveguide Port

Wave guide port consist of add the excitation port

Solve →Waveguide Ports

Waveguide Port Excite Port



Define the Frequency Range and Boundary Conditions

+

Frequency Range Boundary Conditions



Define Farfield Monitor

Farfield Monitor


Network Analyzer

Network analyzer 4

The VNA device is divided into two parts, the first isscreen and the second is control button. The screenis used for display the graph, this graph representthe S11and BW that will be measured and analysed.The control button consists of seven sectionsarranged from top to bottom and from left to right is(TRACE, NAVIGATION, CHANNEL, SUPPORT,DISPLAY, DATA ENTRY, SYSTEM). The start ofthe frequency range and the stop span on VNAdevice, its accomplished by selecting CHANNELsection from control button. Then, checking theresonant frequency and it was 3.5 GHz, and thespan 1 GHz.

Network analyzer

4

Calibration of VNA

Calibration of VNA

MPA connect with VNA 41

MPA with Air-gap Measurement 7

Related Slide

Air gap technique

0

VNA 4

Improvement of bandwidth 2

Single patch antenna simulation Air–gap technique simulation

Coax line feed

Coax line feed location

x