Maximize Impedance Bandwidth of Triangular Patch Antenna

This example uses:

This example shows how to optimize a triangular microstrip patch antenna to maximize its bandwidth such that its gain remains constant.

Define Antenna Geometry

Define the initial geometry of the antenna.

% Define Antenna
ant = patchMicrostripTriangular;

% Center frequency and frequency range 
fc = 10e9;
% For BW ~20%
minFreq = fc * 0.8;
maxFreq = fc * 1.2;
freqRange = linspace(minFreq,maxFreq,35);

% Initial point
ant = design(ant,fc)

ant = 
  patchMicrostripTriangular with properties:

                 Side: 0.0210
               Height: 0.0012
            Substrate: [1×1 dielectric]
    GroundPlaneLength: 0.0300
     GroundPlaneWidth: 0.0300
    PatchCenterOffset: [0 0]
           FeedOffset: [0 0.0029]
         FeedDiameter: 3.7474e-04
            Conductor: [1×1 metal]
                 Tilt: 0
             TiltAxis: [1 0 0]
                 Load: [1×1 lumpedElement]

Use show function to view the antenna.

show(ant)

Figure contains an axes object. The axes object with title patchMicrostripTriangular antenna element, xlabel x (mm), ylabel y (mm) contains 5 objects of type patch, surface. These objects represent PEC, feed.

Initial Analysis

Analyze the gain of the antenna. Record the maximum gain of the antenna before optimization.

pattern(ant,fc);

Figure contains 2 axes objects and other objects of type uicontrol. Axes object 1 contains 5 objects of type patch, surface. Hidden axes object 2 contains 17 objects of type surface, line, text, patch.

Analyze the impedance bandwidth of the antenna using S-parameters.

rfplot(sparameters(ant,freqRange));

$Figure contains an axes object. The axes object with xlabel Frequency (GHz), ylabel Magnitude (dB) contains an object of type line. This object represents dB(S_{11}).$

Set Up Optimization Problem

You will need the following inputs for the optimization problem:

1. Objective Function: Choose 'maximizeBandwidth' as the objective function. The main goal of this example is maximizing the bandwidth of the antenna.

2. Design variables: Select side length, height of the triangular patch antenna, and feed offset as control variables for the objective function. The side length of the triangular patch will affect the front lobe gain. The height and the feed location will enhance the impedance bandwidth of the antenna and help improve its matching.

3. Constraints: The constraint function is gain more than 8.5 dBi.

% Design Variables
% Property Names
propNames = {'Side', 'Height', 'FeedOffset'};

% Bounds for the properties {lower bounds; upper bounds}          
bounds = {0.017 0.001 [0 0.0017]; ... % Specify the FeedOffset vector to move the feed along [x, y]
    0.023 0.004 [0.0002 0.0034]};

Optimization Process

Use canUseParallelPool function to check whether Parallel Computing Toolbox™ is installed and licensed for use. This lets you decide whether to choose parallel processing or not during the optimization process. Use the optimize function to optimize the antenna.

figure; % Figure to display the convergence trend
% Optimize
tf = canUseParallelPool();
optAnt = optimize(ant, fc, "maximizeBandwidth",...
    propNames, bounds,...
    Constraints={"Gain > 8.5"},...
    FrequencyRange=freqRange,...
    UseParallel=tf);

Starting parallel pool (parpool) using the 'Processes' profile ...
06-Nov-2024 15:45:32: Job Queued. Waiting for parallel pool job with ID 1 to start ...
Connected to parallel pool with 8 workers.

Warning: MATLAB has disabled some advanced graphics rendering features by switching to software OpenGL. For more information, click <a href="matlab:opengl('problems')">here</a>.

Figure contains 2 axes objects. Axes object 1 with title Population Diversity contains an object of type line. Axes object 2 with title Convergence Trend contains an object of type line.

Set 'EnableLog' as true, in order to print the iteration number and best value of convergence on the command line.

Optimization Result

Compare the analysis parameters of the antenna from before and after the optimization.

optAnt

optAnt = 
  patchMicrostripTriangular with properties:

                 Side: 0.0185
               Height: 0.0029
            Substrate: [1×1 dielectric]
    GroundPlaneLength: 0.0300
     GroundPlaneWidth: 0.0300
    PatchCenterOffset: [0 0]
           FeedOffset: [1.2788e-05 0.0034]
         FeedDiameter: 3.7474e-04
            Conductor: [1×1 metal]
                 Tilt: 0
             TiltAxis: [1 0 0]
                 Load: [1×1 lumpedElement]

show(optAnt)

pattern(optAnt, fc)

rfplot(sparameters(optAnt, freqRange))