WLAN Microstrip Patch Array Design[1]

Microstrip Patch Array Design Workflow Using CST MICROWAVE STUDIO®

Introduction Single element

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design optimization

Array factor

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TBP optimization

Antenna array

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full model feeding network

Design Procedure 1. Design a single patch element 

Resonant frequency, (gain)

2. Postprocessing optimization of feeding coefficients and spacing (Array Factor) 

Gain, sidelobe level

3. Design and optimize a feeding network 

S11, bandwidth, gain, sidelobe level

1. Design a Single Patch Element Stackup pW

ABS Cover RO4350 Aluminium

msW

pW Reference plane

Microstrip Width

msW

Create the Waveguide Port Macros -> Solver -> Port -> Calculate port extension coefficient

Symmetry Settings

Magnetic symmetry in YZ plane

Open (add space) boundaries are used to estimate backlobes

Mesh Settings (1/2)

At least 2 - 4 cells per strip width

Mesh Settings (2/2) ABS Cover

RO4350 2 cells per substrate height At least 2 cells per air gap

Aluminium

Patch Width for Resonance at 5.5GHz

pW=19.5mm

Electric Field at 5.5GHz Radiation

Standing wave ABS Radome (not shown)

Travelling wave

Single Patch Farfield Pattern

Discrete face port

Design Procedure 1. Design a single patch element 

Resonant frequency, (gain)

2. Postprocessing optimization of feeding coefficients and spacing (Array Factor) •

Gain, sidelobe level

3. Design and optimize a feeding network 

S11, bandwidth, gain, sidelobe level

Array Factor Array Pattern Multiplication (for 5 patch antennas)

 F array( ,  )  F element  ( ,  ) AF ( ,  ) 

= Assumptions: identical elements with no coupling.

x

Farfield Pattern for Uniform Array phi=0 phi=45 phi=90

Magnitudes for Optimal Array mag2

mag1

mag3

mag2

mag3

mag2

mag2

mag1

Magnitudes will be optimized in order to minimize sidelobe level

Online demonstration

Optimize Feeding Coefficients (Optimal Array)

phi=0 phi=45 phi=90

Optimizer Settings (Optimal Array)

Only TBP results are evaluated Not necessary to optimize mag3 (mag1, mag2 are relative) The spacing parameter was optimized for uniform array

Template Based Postproc. Settings

Arbitrary Array Distribution One TAB there

No ENTER there

File could contain variables from CST MWS Parameter List

Array Factor Approach Validation (Optimal Array)

Array Wizard Macro Construct finite array Update Simultaneous Excitation Combine results (no Sim.Ex.) Setup array factor

Online demonstration

Array Construction with Array Wizard

Design Procedure 1. Design a single patch element 

Resonant frequency, (gain)

2. Postprocessing optimization of feeding coefficients and spacing (Array Factor) 

Gain, sidelobe level

3. Design and optimize a feeding network 

S11, bandwidth, gain, sidelobe level

Farfield – Effects of Housing

Include ABS Cover

Effect of Housing on Farfield Pattern

Effect of Housing on Farfield Pattern

The actual housing effects mainly the back radiation

Feeding Network Design

Compute 16-port S-parameters

Discrete Face port

S-Parameter Symmetry Settings

16-port excitation reduced to 4-port

Design the Feeding Network Using Ideal Transmission Lines

Optimize the Feeding Network in DS (Optimal Array)

16 parameters to be optimized

Farfield + Feeding Network

Feeding Network (3D Model)

This half is mirrored

Curves Trace from Curve…

Symmetry Settings (1/2) Magnetic symmetry (YZ plane)

Open (add Space)

Symmetry Settings (2/2) Is it possible to use a symmetry in ZX plane ?

No symmetry in ZX plane: The microstrip requires magnetic symmetry however the patches require electric symmetry.

Mesh Settings (1/2) 2 cells per strip width

Mesh Settings (2/2) 2 cells per substrate height

Influences simulation speed

Initial Feeding Network Results

3D optimization is necessary to include couplings between the feed network and radiating elements.

Electric Field Coupling between the line and the patch

Phase delay due to couplings.

Full wave 3D optimization

Optimizer Settings (Uniform Array) Very effective for 3D optimization

13 parameters to be optimized

Optimized S-Parameters (Uniform array)

Optimized Farfield Pattern (Uniform array)

Key Features for Antenna Array Design 

Start with simple models and add complexity

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Post processing optimization of farfield pattern

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Array wizard macro for array construction or array factor settings

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3D EM/ Circuit co-simulation (feeding network)

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Trust Region Framework optimizer for 3D optimization

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GPU acceleration

Conclusion Divide complex task into smaller ones. Use best approach at each stage. Optimize your device. Shorten your development cycle.