MATLAB: Remove back lobe in ArraySynthesisExample.m

antenna arrayback lobe suppressionMATLABPhased Array System Toolboxula

In the ArraySynthesisExample.m example code, I'm trying to remove the back lobe, but so far I can't.

First I set the "BackBaffled" property of the ULA to false.

Then, I make sure my plot covers the full -180:180 range of Azimuth values.

When I set the interference direction to -180 degrees, unfortunately it makes the entire beam go away.

thetaan = -180;           % interference direction

So, is there a way I can suppress the back lobe digitally? I want to make all of the power go forward, not backwards. Is this method even possible?

Thanks in advance!!

Best Answer

Hi Chris,

I'm not sure what you mean here but it seems that you are using an isotropic element. Therefore, the lobe is generated because of the array geometry and because of the symmetry of a ULA, the -180 degree lobe is the same as the 0 degree lobe. Hence, if you remove -180 degree lobe, it removes 0 degree lobe too. In reality, the antennas are unlikely to be isotropic so it back lobe is in general much smaller compared to the main lobe.

HTH

Related Solutions

MATLAB: Array Pattern Synthesis: is first plot not correct

Hi Chris,

This is because in setting up the antennas, the example used a very crude way to remove the response at the back by setting the BackBaffled to true. Therefore, there is really no response beyond -90 to 90 degrees. MATLAB plot is smart enough to know that there is really nothing to plot beyond that region. The polar plot probably shows is more clearly

plotResponse(myULA,fc,c,'Format','polar','Weights',w,'AzimuthAngles',-120:120);

HTH

MATLAB: How to separate signals from different directions

The result you see is due to the symmetry of the array. You can think the array as a spatial filter. For a ULA, it can distinguish two directions if these two directions make different angles with the array axis. Therefore, in a 3D space, you can think of that the iso-angle surfaces for a ULA make up cones around the array axis. In your example, like you have observed, because 30 degrees and 150 degrees both are 60 degrees from the array axis, from the array perspective, they are the same. Just like a frequency domain filter that cannot separate two signals in the same frequency, the spatial filter fails to separate two signals that appear to be at the identical angle from the array.

There are ways to get around it. One possible way is to use a element pattern that is not isotropic. For example, if you use an array with cosine element, like

ula = phased.ULA('NumElements',10,'ElementSpacing',wavelength/2,...
           'Element',phased.CosineAntennaElement);

Then the array only looks toward the forward direction and only the signal from 30 degrees will be received. Another way is to explore the time/frequency domain characteristics of the signals. If the two signals are orthogonal in time domain, then even though they cannot be separated in space, they can be separated via some time domain processing.

HTH

Best Answer

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MATLAB: Array Pattern Synthesis: is first plot not correct

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