sdars: front end antenna design - bradley...

SDARS: Front End Antenna

Design

Keven Lockwood

Advisor: Dr. Prasad Shastry

1

Outline

• Project Overview

• Antenna Characteristics

• Feeding Techniques

• Performance Specifications

• Design Process

• Expected results

• Design Dependencies

• Equipment

• Schedule

2

Project Overview

• Patch Antenna for receiving SDARS

– Compact size

• Idea from “A Circularly Polarized

Microstrip Antenna using Singly-Fed

Proximity Coupled Feed” by Iwasaki,

Sawada, Kawabata

– Not previously designed at BU

• Past Projects

– Greg Zomchek and Erik Zeliasz• Probe feed antenna

• Aperture coupled feed antenna

– Sasidhar Vajha• Proximity coupled, linearly polarized, 1.9

GHz patch antenna

Source: H. Iwasaki, H. Sawada, K. Kawabata. “A Circularly Polarized

Microstrip Antenna Using Singly-Fed Proximity Coupled Feed.” Institute

of Electronics, Information and Communication Engineers. September

1992. pp. 797-800.3

Circular Polarization

Above: Illustration of a right-hand circularly

polarized wave. Right: Circularly polarized waves

travelling in the +Z direction (out of page). Source

(both figures): Ulaby, Fawwaz T. Fundamentals of

Applied Electromagnetics. Pearson Education, Inc.

2007. p. 298

4

System Block Diagram

AntennaLow-Noise

Amplifier

Sirius Radio

Receiver

Mixer Band pass filter IF amplifier

Local Oscillator

Active Antenna

Down Converter

Intermediate

frequency ready for

decoding

5

Antenna Characteristics

• Gain

• VSWR, input

impedance

• Polarization

• 3-dB

beamwidth

• Axial Ratio

Representative plots of the normalized radiation pattern of a microwave antenna in (a) polar

form and (b) rectangular form. Source: Ulaby, Fawwaz T. Fundamentals of Applied

Electromagnetics. Pearson Education, Inc. 2007. p. 382

6

Feeding Mechanism

Source: Balanis, Constantine A. Antenna Theory: Analysis and Design. 2nd ed. John Wiley & Sons, Inc. 1997. p. 725.

7

Feeding Mechanism: Microstrip

• Simple to fabricate / model

• Simple to match with inset position

• Prone to spurious feed radiation, limiting

bandwidth

Source: Balanis, Constantine A. Antenna Theory:

Analysis and Design. 2nd ed. John Wiley & Sons, Inc.

1997. p. 725.

8

Feeding Mechanism: Coaxial

• Easy to fabricate, difficult to model

• Narrow bandwidth

• Low spurious radiation

Source: Balanis, Constantine A.

Antenna Theory: Analysis and Design.

2nd ed. John Wiley & Sons, Inc. 1997.

p. 725.

9

Feed: Aperture Coupled

• Independent

optimization of

patch and feed

• Difficult to

fabricate

• Narrow bandwidth

• Easier to model

Source: Balanis, Constantine A. Antenna Theory: Analysis and Design. 2nd ed. John Wiley & Sons, Inc. 1997. p.

725.

10

Feed: Proximity Coupled

• Wide bandwidth

• Easy to model

• Low spurious radiation

Source: Balanis, Constantine A. Antenna Theory: Analysis and Design. 2nd ed. John Wiley & Sons, Inc. 1997. p.

725.

11

Performance Specifications

• 2320 MHz to 2332.5 MHz (BW = 12.5

MHz)

– 100 channels, 125 kHz per channel

• VSWRmax = 2:1

• Left-hand circular polarization

• Total active gain 28.5 dB - 32.5 dB

12

Antenna Design Process

Paper Design Simulation Optimization

FabricationPhysical Testing

13

Paper Design

• Substrate selection– Thick, with low dielectric constant for better radiation efficiency,

larger bandwidth (top layer)

– Same dielectric constant, thin bottom layer

• Patch Dimensions– Influenced by

• Operating frequency

• Collective height and dielectric constants of the substrates

• Transmission line model equations

• Feed line dimensions– Calculated using “MSTRIP” with Zo = 50 Ohms, dielectric

constant, height of bottom substrate

14

Design Dependencies

15

• ɛr eff depends on h, t, and ɛr of each

• Wp and Leff are inversely proportional to fr and the ɛr eff

• Leff = L + 2*(∆L)

• ∆L is proportional to h+t

• Ws depends on h and ɛr of bottom layer

Source: Balanis, Constantine A. Antenna Theory: Analysis and Design. 2nd

ed. John Wiley & Sons, Inc. 1997. p. 729.

Simulations

• Momentum

– Uses Maxwell’s

equations

– Measures and graphs

• S11 (reflection

coefficient)

• VSWR,

• input impedance

• Radiation pattern

– Optimization through

variable sweeps

16

Fabrication

• Create a template using final

simulation dimensions (out-source)

• Use template and substrate boards

to fabricate individual layers

• Carefully glue layers together

• Solder on the packaged LNA and

add SMA port (include picture of

where LNA sits / what final product

looks like

17

Physical Testing

• Network analyzer

– Graphs S11,VSWR, return loss

– Gain of LNA, Noise Figure

• Anechoic chamber

– Beam pattern

– Gain

18

Expected Results: VSWR

Image taken from: Erik Zeliasz, Greg Zomcheck. “SDARS Front-End Receiver: Senior Capstone Project

Report.” Bradley University Department of Electrical Engineering, May 13, 2001. p.

Simulated

VSWR of a

linearly

polarized patch

antenna.

VSWR

measures the

degree of input

impedance

match to 50

Ohms

19

Expected Results: S11

• Measures return loss at a

center frequency of 1.9 GHz

20

Graph taken from source: Vajha, Sashidar. “A Proximity

Coupled Active Integrated Antenna.” Bradley University, 2000.

p.26

Expected Results: Input

Impedance

21Graph taken from source: Vajha, Sashidar. “A Proximity Coupled

Active Integrated Antenna.” Bradley University, 2000. p.26

• No matching circuitry

Equipment

• Anechoic Chamber

• HP 8722C Network Analyzer

• RF fabrication machines

• CAD with Momentum

• Spectrum Analyzer

22

Schedule

1/23 –

1/26

1/27 –

2/2

2/3 –

2/9

2/10 –

2/16

2/17 –

2/23

2/24 –

3/1

3/2 –

3/8

3/9 –

3/15

3/16 –

3/22

3/23 –

3/29

3/30 –

4/5

4/6 –

4/12

4/13 –

4/19

4/20 –

4/26

4/27 –

5/3

Design

Simulation/optimization

(linearly polarized

antenna)Simulation/optimization

(circularly polarized

antenna)Fabricate Antenna and

testing

Fabricate LNA board

and testing

Incorporate both the

antenna and LNA and

test

integrate with

commercial receiver

and test

Presentation and Final

Project Report

23

Questions

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