Reconfigurable Low Profile Patch Antennacegt201.bradley.edu/projects/proj2005/recfgant/... · 2005....

Bradley UniversityDepartment of Electrical and Computer Engineering

ReconfigurableLow Profile

Patch Antenna

Mr. James H. Soon

Advisor: Dr. Prasad Shastry

May 13, 2005

Abstract

The objective of this project was to design, simulate, manufacture and analyze a polarizationdiverse microstrip line fed patch antenna capable of operating selectively with either linear or circularpolarization.

Acknowledgments

I am grateful for Dr. Prasad Shastry’s patient and expert guidance throughout my educationalexperience at Bradley University, and especially during this project.

I would also like to thank my ‘tutors’ - two graduate students - Mr. Balamurugan Sundaram andMr. Krishna Katragadda, who were also very patient and gave of their time and knowledge unselfishly. Thanks guys - I wouldn’t have been able to do this without your help.

of 84

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Patch Radiation Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Circular Patch Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

System Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Project Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Recommendations for Future Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Appendix A: ADS-Momentum Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Appendix B: Antenna Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

of 84

Introduction

Today’s digital communications systems employ a variety of protocols to accurately transfer data. The overall quality of a communications path can be quantified by measuring its bit error rate.

Diversity, in the communications world, refers to transmitting multiple copies of the sameinformation. The probability of receiving errored bits can be reduced by employing different diversitymethods. Polarization is one of those methods.

The primary objective of this project was to test the viability of a polarization diverse device bydesigning, simulating, fabricating and analyzing a polarization diverse low profile patch antenna.

Since ADS-Momentum simulation software was relatively new to the Bradley University RFarea, a secondary objective of this project was to verify the dependability of simulation results from ADS-Momentum compared to measured results of several fabricated antennas.

If simulation results were found to be sufficiently accurate, the ‘trial and error’ element of theantenna design process could be moved from the fabrication and analysis cycle into the simulation cycle. The advantages of not fabricating until a design meets the intended specifications include reducedmaterial costs and development time.

Polarization

Polarization refers to the orientation of the electric field vector. The specific type ofpolarization is defined by the geometric figure traced by the sum of the electric field vector as an observerlooks directly ‘into” the direction of travel (Poynting vector) of the electromagnetic wave.

Figure 1 shows an example of the components of the electric field vector (Ex & Ey), phase difference (N) and relative direction of travel.

Figure 1: Electric Field Components

of 84

The two primary polarization senses are linear - either vertical or horizontal; and circular - eitherright hand or left hand polarization. Figure 2 illustrates the relationship between relative magnitude,phase and polarization sense.

Figure 2: Polarization Relationships

As Figure 2 illustrates, when all the electric field energy resides in the “y” plane, verticalpolarization results. Conversely, when the electric field is in the “x” plane, horizontal polarizationresults. Circular polarization occurs when the electric field magnitude in the x and y planes are equal(their ratio = 1) and the signals are 90° out of phase with each other. Right hand circular polarization(RHCP) occurs when Ex lags Ey by 90°, left hand circular polarization results when Ex leads Ey by 90°.

Figure 3 illustrates RHCP; the magnitudes are equal in x and y plane, and Ex lags Ey by 90°.

Figure 3: Right Hand Circular Polarization

of 84

Patch Radiation Characteristics

Figures 4a and b show the manner in which patch antennas radiate.

Figure 4a: Radiating Patch

Figure 4b: Radiating Patch

Figure 4a shows a microstrip line fed patch - note that the direction of radiation is normal tosurface of the patch. Figure 4b shows a cut-away view of the fields radiating into the substrate material. The fields at the edge of the patch create a ‘fringing’ effect - extending beyond the actual physical edge ofthe patch. This effect is accounted for in initial design calculations and is described later in thisdocument.

Circular Patch Construction

As seen in Figure 2, two conditions for obtaining circular polarization are equal amplitudes and a90° phase difference between the electric field x and y planes. A number of schemes are possible tocause an essentially square patch to radiate circularly. Figures 5a and 5b illustrate four of thosemethods.

Figure 5a: Truncated and Nearly Square Patches

of 84

Figure 5b: Hybrid Fed and Reactive Splitter Fed Patches

The truncated and nearly square patches alter the radiation pattern on the patches causingcircular polarization, while the hybrid fed and reactive splitter patches feed the signal into the patch witha 90° offset, causing circular polarization. This project used a truncated patch - the simulation patchantenna is shown in Figure A-59.

System Description

The objective of this project was to use a microstrip line fed patch antenna capable ofpolarization diverse operation.

An illustration of a dual polarization antenna is illustrated in Figure 6.

Figure 6: Polarization Diverse Antenna

of 84

As Figure 6 illustrates, energy fed into the left port will result in horizontal polarization andenergy fed into the bottom port will result in vertical polarization. While this antenna would beinteresting to design, simulate, fabricate and analyze, this project’s objective was to experiment withcircular polarization as well.

Figure 7 illustrates a circular and linear polarization diverse antenna.

Figure 7: Switchable Polarization Antenna

The two ‘channels’ in Figure 7 are exaggerated to be able to show the diode operation. When thediodes are forward biased, the triangles are connected to the patch, which radiates linearly. When thediodes are reverse biased, the patch is truncated, resulting in circular (left circular) polarization. That’sthe objective of this project. The idea for this type of antenna came from “A Reconfigurable AntennaFor Switchable Polarization” an IEEE paper by Mr. Y.J. Sung, T.U. Jang, and Y.S. Kim. 1

Design

Specifications

Gain > 5dBiFrequency Range: 1.5 – 1.6 GHz rangeReturn Loss < -15 dBRadiation patternPolarization: Linear, LHCPBandwidth: approx. 2%VSWR 2.0:1

Process

The project process consisted of an iterative approach - design, simulate, optimize design,simulate, optimize design, simulate - until satisfactory results are reached; then fabricate the final design,and lastly analyze the resulting fabrication. Then repeat the design - simulate - fabricate - analyze cyclefor each antenna.

of 84

The plan called for a total of six antennas to be fabricated; one baseline linear polarization, onebaseline circular polarization, and the final, switchable polarization antenna. Two antennae of each typewere necessary for gain evaluation in the anechoic chamber.

Design began with some fundamental patch antenna equations from “Antenna Theory” byConstantine Balanis 2. (See below) A short C++ program was written to obtain numerical convergence.

PCAAD (Personal Computer Aided Antenna Design) was then used to further optimize thephysical dimensions of the patch, and obtain an initial input impedance value.

Those dimensions were then used to construct the first patch simulation in ADS-Momentum(Advanced Design System), and the resonant frequency, return loss, VSWR and input impedance wereverified. After optimizing those values by adjusting the physical size in several simulations, final physicalpatch dimensions were obtained.

Values for a quarter wave impedance matching network were obtained using the input impedancevalues from PCAAD and Momentum and the software programs “Match” and “Mstrip”.

The quarter wave matching network was then constructed on the patch and the completeantenna, with a short 50 S length for a connector was simulated using Momentum.

After a final design was obtained, a post script file containing a mask was created, the file wasdelivered to Technicraft Display & Graphics, who manufactured a black linotype film. This film wasthen used during the fabrication process in the Microwave Integrated Circuit Fabrication Laboratory.

Antenna analysis was performed by using a Network Analyzer and Anechoic Chamber tomeasure return loss, bandwidth, resonant frequency, VSWR, gain, the radiation pattern and axial ratio.

Equations

The following fundamental design equations from the Balanis text were used:

(Equation 9.1)

V0 is the speed of light in a vacuum, fr is the resonant frequency desired, and ,r is the dielectricconstant of the laminate material. The width was obtained and plugged into the next equation. For thisproject, fr = 2.4 GHz, ,r = 3.0, h = 120 mil (0.3048 cm).

(Equation 9.2)

of 84

h, the height of the laminate material is known, and ,r effective is then found and used inequation for )L, to account for the fringing effect of the patch, see “Patch Radiation Characteristics” onpage 6.

(Equation 10.1)

Once the fringing effect is known, the length of the patch can be found.

(Equation 10.2)

Since this is a square patch, the length = the width, and the length becomes the new width. Thecalculations are repeated until the length and width converge. This becomes the value used in PCAAD.

One other set of equations was used - from Robert Sainati’s book, “CAD of Microstrip Antennasfor Wireless Applications3, to calculate ‘c’ - the length of the truncated segment (see Figure 5a).

Where:)s = area of the perturbation segmentS = are of the patchc = length of a side of the cut out triangleL = length of the patchQ = patch quality factor

(Equation 10.3)

(Equation 10.4)

(Equation 10.5)

of 84

Simulation Results

A total of 20 Momentum simulations were performed, ranging in processing time of 30 minutesto around 2 hours. Simulation results of Reconfig 01, Reconfig 14, 16 and 20 designs can be found inAppendix A.

The initial Momentum simulation showed a patch input impedance of around 1600 S,compared to PCAAD’s projected input impedance of 284 S. At this point, simulation results fromMomentum did not appear to be reliable.

A quarter wave matching network based on the input impedance results from PCAAD wasconstructed and simulated in Momentum. The resulting 3D simulation (Figure 8, also Figure A-23)revealed a distorted radiation pattern, that was initially not expected. Further analysis of the situationsuggested that although the quarter wave matching network was indeed correct, it was physically large andwas creating another radiating surface which caused the pattern distortion.

Figure 8: Reconfig 14 3D Top View

It was decided to proceed with the fabrication of this antenna (Fab14), take the opportunity toanalyze it, and verify the accuracy of the simulated results. A second linearly polarized baseline antenna(Reconfig 16) would also be designed, simulated, fabricated and analyzed using the second set of quarterwave matching network dimensions.

of 84

Figure 9 shows Reconfig 14 - linear baseline antenna #1 and Figure 10 shows Reconfig 16,linear baseline antenna #2.

Figure 9: Reconfig 14


of 84

Simulation of Reconfig 16 did show an improvement in the projected radiation pattern (Figure11).

Figure 11: Reconfig 16 3D Top View

One other Momentum simulation, Reconfig 20, is of interest. Figure 12 shows the antenna,using the first quarter wave matching design (3 additional designs remain un-simulated), Figure 13shows the radiation pattern results - distortion is clearly apparent.


of 84

Figure 12: Reconfig20 Top View

Simulated results of the axial ratio of Reconfig 20 (Figure 13), show non-linear but non-circular polarization sense. In other words, this design is moving toward circular polarization, but it’s notthere yet.

Figure 13: Reconfig 20 Polarization

of 84

Fabrication

Figure 14 shows the mask for Fab14. Fabrication of both antennas (Fab14_1 & 2) wasattempted at the same time - using an entire 6 inch laminate board. Since much photo resist seemed tobe wasted using such a large board, it was determined to cut the board in half and fabricate one antenna ata time for the next set of antennas. Figure 15 shows Fab14_1.

Two changes were recommended for the next fabrication round due to the complications arisingfrom attempting to fabricate a large board.

• change the developer solution to 100 ml developer /400 ml of water• allow the antenna to remain in the oven for the full 15 minutes during the drying cycles.

This information is recorded in Lab notebook #2, pages 24 - 29.

Figure 14: Fab14 Mask

Figure 15: Fab14_1

of 84

Note the silver marks (solder) on both the main patch and quarter wave matching network. Duston the mask during the fabrication process left holes etched into both surfaces. This antenna was firstmeasured in its original condition, then the holes were filled in with solder and measured again. Nonoticeable improvement was observed.

Figures 16 & 17 show the Reconfig 16 mask and antennas. Note the lack of holes in theantennas - implying an increasing measure of fabrication skill.

Figure 16: Fab16 Mask

Figure 17: Fab16_1 & _2

of 84

Analysis

Appendix B contains the measured results for Fab14 & 16 antennas. Images of the NetworkAnalyzer and Anechoic chamber used to analyze these antennas can be found in Lab Notebook #2 pages83 - 85 and 145. Additional images can be found on the Bradley University ECE Department WebSite under Research, Projects, 2005, Reconfigurable Antenna.

A summary of antenna performance vs design specifications is in Table 17-1

Figure of Merit Design Spec Fab14 Fab16

Gain > 5 dBi 5.57 dBi Not measured

Resonant Freq 2.40 GHz 2.42 GHz 2.42 GHz

Return Loss < -15 dB -25 dB -14.3 dB

Polarization Linear/Circular Linear Linear

Bandwidth 2.0 % 2.7 % 1.2 %

VSWR 2.0:1 1.11:1 1.48:1

Table 17-1

A summary of antenna performance vs simulated results is in Table 17-2

Antenna Resonant Freq Return Loss VSWR Zin

Fab 14 Simulation 2.40 GHz -13.2 dB 1.55 38.5 S

Fab 14 Measured 2.42 GHz -25 dB 1.11 44.9 S

Fab 16 Simulation 2.41 GHz -14.3 dB 1.48 42.8 S

Fab 16 Measured 2.42 GHz -14.3 dB 1.48 33.8 S

Table 17-2

of 84

Conclusions

Project Summary

This was, for me, a fascinating project - I wish I could have completed it.

The fabricated antennas met the design specifications fairly well - sensitivity analysis of bothantennas should be performed to determine more precisely how well. Simulated results were also fairlyclose to measured results. Again, sensitivity analysis would reveal how well they match.

It appears that the simulations can be trusted - this could significantly decrease total antennadesign time. Antenna design will still be iterative however, and require much patience.

Recommendations for Future Projects

• Complete the analysis of Fab 16 and continue design and implementation of the circularlypolarized antennas; simulate an ideal short and open on the switchable polarizationantenna, then finish the project!

• Implement the use of a self-leveling 360° laser level for accurate vertical positioning of theantennas in the anechoic chamber

• Obtain 3D anechoic chamber measurements

• Convert ADS-Momentum 3D simulation results to compare with the 2D results from theanechoic chamber

• Investigate quarter wave matching network for both circular and linear polarization

of 84

References

1. SUNG, Y.J., JANG, T.U., KIM, Y.S., ‘A Reconfigurable Antenna for Switchable Polarization’, IEEEMicrowave and Wireless Letters, Volume 14, Number 11, November 2004, pp. 534 - 536.

2. BALANIS, C.A., Antenna Theory - Analysis & Design, second Ed., John Wiley, 1997, Chapter 14- Microstrip Antennas, pp. 722- 736.

3. SAINATI, ROBERT A., CAD of Microstrip Antennas for Wireless Applications, Artech House,1996, p 114.

4. LEE, K.F. & CHEN, W., Advances in Microstrip and Printed Antennas, John Wiley, 1997.

5. NAVARU, J.A., & CHANG, K, Integrated Active Antennas and Spatial Power Combining, JohnWiley, 1996.

of 84

Appendix A: ADS-Momentum Simulations

of 84

Reconfig 01

Figure A-1

Figure A-2

of 84

Figure A-3

Figure A-4

of 84

Reconfig 14

Figure A-5

Figure A-6

of 84

Figure A-7

Figure A-8

of 84

Figure A-9

Figure A-10

of 84

Figure A-11

Figure A-12

of 84

Figure A-13

Figure A-14

of 84

Figure A-15

Figure A-16

of 84

Figure A-17: 3D Current Distribution

Figure A-18: 3D Back Angle View

of 84

Figure A-19: 3D Front Angle View

Figure A-20: 3D Front View

of 84

Figure A-21: 3D Bottom View

Figure A-22: 3D Side View

of 84

Figure A-23: 3D Top View

Figure A-24

of 84

Figure A-25

Figure A-26

of 84

Figure A -27

Figure A-28

of 84

Figure A-29

Figure A-30

of 84

Figure A-31

Figure A-32

of 84

Figure A-33

Figure A-34

of 84

Reconfig 16

Figure A-35

Figure A-36

of 84

Figure A-37

Figure A-38

of 84

Figure A-39

Figure A-40

of 84

Figure A-41

Figure A-42

of 84

Figure A-43

Figure A-44

of 84

Figure A-45

Figure A-46

of 84

Figure A-47

Figure A-48

of 84

Figure A-49

Figure A-50

of 84

Figure A-51

Figure A-52: 3D Back Angle View

of 84

Figure A-53: 3D Bottom View

Figure A-54: 3D Current Distribution

of 84

Figure A-55: 3D Front Angle View

Figure A-56: 3D Front View

of 84

Figure A-57: 3D Side View

Figure A-58: 3D Top View

of 84

Reconfig 20

Figure A-59

of 84

Figure A-60

of 84

Figure A-61

Figure A-62

of 84

Figure A-63

Figure A-64: Reconfig20 Top View

of 84

Figure A-65: Reconfig20 Side View

Figure A-66: Reconfig20 Front View

of 84

Figure A-67: Reconfig20 Front Angle View

Figure A-68: Reconfig20 Back Angle View

of 84

Figure A-69: Reconfig20 Bottom View

Figure A-70: Reconfig20 Circular Axial Top View

of 84

Figure A-71: Reconfig20 Circular Axial Side View

Figure A-72: Reconfig20 Circular Axial Front View

of 84

Figure A-73: Reconfig20 Circular Axial Back Angle View

Figure A-74: Reconfig20 Circular Axial Bottom View

of 84

Figure A-75: Reconfig20 Linear Axial Top View

Figure A-76: Reconfig20 Linear Axial Side View

of 84

Figure A-77: Reconfig20 Linear Axial Front View

Figure A-78: Reconfig20 Linear Axial Front Angle View

of 84

Figure A-79: Reconfig20 Linear Axial Back Angle View

Figure A-80

of 84

Figure A-81

Figure A-82

of 84

Figure A-83

Figure A-84

of 84

Figure A-85

Figure A-86

of 84

Figure A-87

Figure A-88

of 84

Figure A-89

Figure A-90

of 84

Figure A-91

Figure A-92

of 84

Appendix B: Antenna Measurements

of 84

Fab 14_1

Figure B-1

Figure B-2

of 84

Figure B-3

Figure B-4

of 84

Figure B-5

Figure B-6

of 84

Figure B-7

Figure B-8

of 84

Figure B-9

Figure B-10With laser level

of 84

Figure B-11: With laser level

Figure B-12: With laser level

of 84

Fab 14_2

Figure B-13

Figure B-14

of 84

Figure B-15

Bandwidth = 2.44500 GHz - 2.40000 GHz = 0.045 GHz = 45 MHz

Figure B-16

Bandwidth = 2.45080 GHz - 2.38420 GHz = 0.0666 GHz = 66.6 MHz

of 84

Figure B-17

Figure B-18

of 84

Figure B-19

Figure B-20

of 84

Figure B-21

Figure B-22: Commercial Antenna to Fab14_1

of 84

Figure B-23: Fab14_2 (Tx) to Fab14_1 (Rx)

of 84

Fab 16

Figure B-24

Figure B-25

of 84

Figure B-26

Figure B-27

of 84

Figure B-28

Figure B-29

of 84

Figure B-30

Reconfigurable Low Profile Patch Antennacegt201.bradley.edu/projects/proj2005/recfgant/... · 2005....

Documents

Transcript of Reconfigurable Low Profile Patch Antennacegt201.bradley.edu/projects/proj2005/recfgant/... · 2005....