Creating a Large Phased Array Using Subarrays with Phase Centers at Each Element

I'm trying to model and compare the results of a standard URA phased array versus one made of subarrays with element-wise steering. In the code below, I create a full array without subarrays of the final size, a reference subarray, and then a full array using subarrays. I believe that if I use the same steering weights from the single full array for the elements in the array made of subarrays, I should be similar beam patterns. This works fine when the weights are all 1 (boresight beam) but falls apart as soon as the steering angle, so I think I'm incorrectly interpreting the weights for subarrays.

steerang = 45;                  % Steering angle

fc = 9.345e9;                   % Center frequency in Hz
c = 3e8;                        % Speed of light
N = [16 16];                    % Elements per subarray in each dimension
spacing = 0.5;                  % Element spacing in wavelengths
Nsubarray = [3 3];              % Number of subarrays in Az and El

antenna = phased.IsotropicAntennaElement('BackBaffled',true);


% reference array (full size) and reference subarray
refUra = phased.URA(N .* Nsubarray, [spacing*c/fc spacing*c/fc],'Element',antenna);
refSub = phased.URA(N, [spacing*c/fc spacing*c/fc],'Element',antenna);

steeringvec_refUra = phased.SteeringVector('SensorArray',refUra,...
    'PropagationSpeed',c);
wref = steeringvec_refUra(fc,steerang);

steeringvec_refSub = phased.SteeringVector('SensorArray',refSub,...
    'PropagationSpeed',c);
wrefSub = steeringvec_refSub(fc,steerang);


figure
subplot(2,1,1), pattern(refUra,fc,-180:180,0,'Type','powerdb',...
    'CoordinateSystem','rectangular','PropagationSpeed',c); 
title('Full Array Azimuth Cut Boresight'); axis([-90 90 -50 0]);
subplot(2,1,2), pattern(refUra,fc,-180:180,0,'Type','powerdb',...
    'CoordinateSystem','rectangular','PropagationSpeed',c,'Weights',wref); 
title('Fully Array Azimuth Cut Steered'); axis([-90 90 -50 0]);

figure
subplot(2,1,1), pattern(refSub,fc,-180:180,0,'Type','powerdb',...
    'CoordinateSystem','rectangular','PropagationSpeed',c); 
title('Subarray Azimuth Cut Boresight'); axis([-90 90 -50 0]);
subplot(2,1,2), pattern(refSub,fc,-180:180,0,'Type','powerdb',...
    'CoordinateSystem','rectangular','PropagationSpeed',c,'Weights',wrefSub); 
title('Subarray Azimuth Cut Steered'); axis([-90 90 -50 0]);


% Array of subarrays with each element a phase center
replicatedURA = phased.ReplicatedSubarray('Subarray',refSub,...
                               'Layout','Rectangular',...
                               'GridSize',Nsubarray,'GridSpacing','Auto','SubarraySteering', 'Custom' );

figure;
viewArray(replicatedURA,'Title','Tiled Array');

steeringVecReplicatedURA = phased.SteeringVector('SensorArray',replicatedURA,...
    'PropagationSpeed',c, 'IncludeElementResponse', true);

ws = ones(256,9);

wref2 = wrefSub * ones(1,(prod(Nsubarray)));

figure
pattern(replicatedURA,fc,-180:180,0,'Type','powerdb',...
    'CoordinateSystem','rectangular','PropagationSpeed',c,'ElementWeights',wref2); 
title('Steered URA Azimuth Cut'); axis([-90 90 -50 0]);

Answer 1

[ubaid haroon]

Thats because when you set "SubSteering" to "Custom", you have to manually compute the time delay. MATLAB does not allow you to apply taper to each element in a subarray configuration and time delays together.