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Scanning Antenna Array

 
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pascualhr
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Joined: 03 Dec 2015
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PostPosted: Thu Nov 17, 2016 5:11 pm    Post subject: Scanning Antenna Array Reply with quote

Hi,

I am performing some simulations in CST in which I need the radiation patterns of a 2x1 array of CP patches pointing at certain angles.
The formula that defines the progressive phase difference (beta) that must be applied to each antenna (if I have 4 antennas, I would apply, 0,beta,2*beta,3*beta to the phases of the ports that excites each antenna).

The expression of beta (in radians) is:

beta = -k*d*cos(theta_0)

being,
k = 2pi/lambda
d = distance between the elements
theta_0 = the angle at which I want to point my beam

My problem is that I am not getting what I want. Am I missing something?

Many thanks in advance,
Pascual
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Parna
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Joined: 14 Apr 2015
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Location: Canada

PostPosted: Mon Nov 21, 2016 5:50 pm    Post subject: Reply with quote

The formula looks alright, but please note that in the formula theta is the angle between the beam peak and the line where your elements are placed on. If your theta is relative to braodside (normal to your array), then changing the cos to sin may solve your problem.

If that's not the problem, then it could be a unit (degree vs radian) problem. If you calculate beta in radian, make sure you don't put the phase shift in CST in degrees

Hope this helps
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pascualhr
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Joined: 03 Dec 2015
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PostPosted: Tue Nov 22, 2016 11:56 am    Post subject: Reply with quote

Parna wrote:
The formula looks alright, but please note that in the formula theta is the angle between the beam peak and the line where your elements are placed on. If your theta is relative to braodside (normal to your array), then changing the cos to sin may solve your problem.

If that's not the problem, then it could be a unit (degree vs radian) problem. If you calculate beta in radian, make sure you don't put the phase shift in CST in degrees

Hope this helps


Hi Parna,
Many thanks for your useful suggestions. From my side I have to say that I have already checked both and I am still having the same issues. To be more precise, my 2x1 is scanning nicely from -20 to +20 degrees (referenced from broadside).
This behaviour makes me pose this question: have the arrays any scanning limitation regarding maybe the number of elements or the distance between each other? At the moment this is the only thing I can think of. What do you think?

Thank you very much ,
Pascual Smile
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Parna
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Location: Canada

PostPosted: Wed Nov 23, 2016 10:23 pm    Post subject: Reply with quote

Is it outside the -20 to +20 deg range that you see issues?

Yes there are limitations for scanning the beam. There are two issues, the grating lobe that can happen if your element spacing is large and which causes two main beams instead of one and drops the directivity of the array. There is also something called scan blindness that happens due to mutual coupling between the elements that results in surface waves instead of waves that radiate. If this happens, if I'm not mistaken, you should be able to see it in the active s11 (or return loss) of the elements and it should be 0 dB. I don't know much more about scan blindness, perhaps somebody with a stronger background can help you more
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