Directivity did not match our expectation

As we know, 1X16 linear antenna array arrangement should have larger peak directive gain than 4X4 square array, because the former's beamwidth is narrower which can consentrate beamforming resolution in a given direction.

However, in the phased array system toolbox, this truth cannot be proven... Here is our code,

if true
  % code
figure
ha = phased.ULA('NumElements',16);
phased.ULA('Element',ha,'NumElements',16,'ElementSpacing',0.5 * lambda);
plotResponse(sArray,'RespCut','Az','Format','Polar','Unit','dbi');
hold on;
ha = phased.URA('Size',[4 4]);
phased.URA('Element',ha,'Size',[4 4],'ElementSpacing',0.5 * lambda);
plotResponse(sArray,'RespCut','Az','Format','Polar','Unit','dbi');
hold off;
end

if we find the peak values for 1X16 and 4X4 in the figure, 4X4 always has the higher gain value...

Thanks, Ralph

Answer 1

[Honglei Chen]

Hi Ralph,

In this example you are using an isotropic antenna element. So even though in this cut the beam is more focused, it has strong lobe all around the array axis, so in some sense the energy is not well focused.

If we change the element type to a more realistic pattern, such as cosine antenna pattern, then you can see the directivity of the ULA starts to be better than the URA

figure
ha = phased.ULA('NumElements',16,'Element',phased.CosineAntennaElement);
plotResponse(ha,3e8,3e8,'RespCut','Az','Format','Polar','Unit','dbi');
hold on;
ha = phased.URA('Size',[4 4],'Element',phased.CosineAntennaElement);
plotResponse(ha,3e8,3e8,'RespCut','Az','Format','Polar','Unit','dbi');

If you use a Hertzian dipole, the ULA is also better

figure
ha = phased.ULA('NumElements',16,'Element',phased.ShortDipoleAntennaElement);
plotResponse(ha,3e8,3e8,'RespCut','Az','Format','Polar','Unit','dbi');
hold on;
ha = phased.URA('Size',[4 4],'Element',phased.ShortDipoleAntennaElement);
plotResponse(ha,3e8,3e8,'RespCut','Az','Format','Polar','Unit','dbi');

In short, I'm not saying that you are wrong since I don't really have a theoretical result to back me up. But I'm also not convinced that the toolbox is giving the wrong answer. If you do have a number that I can compare to, please let me know and I'd love to take a look.

Thanks

[Ralph]

Hi Honglei,

How about setting the 'ha' like this? We would like to simulate the 60GHz antenna as well.

if true
  % code
Az = -180:1:180;
El = -90:1:90;
Elresp = cosd(El);
freqVector  = [0 60] * 1e9;
c = 3e8; Fc = 60 * 1e9;
lambda = c/Fc;
ha = phased.CustomAntennaElement('FrequencyVector',freqVector,...
  'AzimuthAngles',Az,...
  'ElevationAngles',El,...
  'RadiationPattern',repmat(Elresp',1,numel(Az)));
end

then put this 'ha' as the input of 'Elements' in phased.ULA and phased.URA.

[Ralph]

Thank you very much for your two examples, they really works well! We know this toolbox mainly focus on radar systems, but if possible, could you give some advices on our setting of 60GHz on antenna elements? Thanks a lot!

[Honglei Chen]

Hi Ralph,

I'm not an expert in antenna design so I am really not at a position to give any recommendation regarding what kind of antenna to use at 60 GHz. The pattern you described above is essentially a dipole. So I'd say it is a valid one. However, a lot of systems also use other types of antennas, such as slot antennas and patch antennas. Their patterns may be different to the cosine.

[Ralph]

Exactly, Honglei. Thank you very much for your help!

As we use the dipole type to generate antenna elements, it works pretty well. BTW, just a quick question, we would like to plot the directivity only from -30 to 30 degrees at azimuth cut rather than omni 361 degrees, is it possible? The idea we came up with was to use the function "phased.CustomAntennaElement" to customize the angles, but we have no idea about how to set it, the available examples are just about Cosine cases. That is, we would like to generate dipole antenna elements and use plotResponse to plot the directivity only from -30 to 30 degree.

Thanks, Ralph

[Honglei Chen]

You should be able to use

plotResponse(ha,3e8,3e8,'RespCut','Az','Format','Polar',...
'Unit','dbi','AzimuthAngles',-30:30)

[Ralph]

Thanks a lot!