Antenna array design problem

[YCChiou]

Hi everyone:

I met a problem on designing a millimeter-wave multiple-element antenna array with scan of 30 degree. My design methods are described below. At first, I designed a T-junction power divider with phase difference 30 degree (Both circuits and results are attached.) The result show the phase difference between S21 and S31 is 30 degree. However, when I applied it to the angled dipole antenna and simulated by HFSS. The maximum power of E-plane pattern is still located near 0 degree but not 30 degree.

I tried several times and even designed a T-junction power divider with phase difference of 60 degree, the result is alomost the same. Could someone point out what fault I commited?

Thank you

 

[Chinaski]

Hi
Your two antenna ports has a phase difference of 30 degrees. Thats true. But it doesn't mean your array is going to point its maximum towards thetha=30
Assuming that:

the distance between them is d
there is α phase difference between them
your free space wavelength is λ0

your array is going to point its maximum towards
Θ0=Arccos[α λ0 / (2πd)]

Please, get a decent antenna book (eg. Balanis) and study some array theory. Things are going to be easier for you.
Good luck

 

[YCChiou]

Hello Thanks for your reply.

I appreciate it...and read the book relative to antenna array and have the initial result. However, now I met another problem.

The problem is that I used Momentum and HFSS to simulate the T-junction power divider possessing two different phase outputs for antenna scanning application.

Even they have the identical structure parameters; however, their deg (S21-S31) are different obtained by two respective softwares.

For example, I want to generate a divider to have phase different of 171 degree and obtained the results by Momentum; but when I put it on HFSS to simulate again, the phase different become 200 degree.

The magnitudes of S21 and S31 are also changed and generally moved to lower frequency (almost 15% frequency shift).

I know it may be caused by different EM machnisms such that analytical and iterative solver.

Theoretically Momentum should be more accurate on the planar structure; however, I used HFSS for antenna simulation. If HFSS got the wrong phase difference, which may degrade the performance of radiation pattern.

Could someone meet the same problem before? Please give me some comments.