Wieired pattern in scan beam array.

Hi,

I am now working on a 60 GHz scan beam linear patch array, consisting of 4 patch antennas and fed by a Butler Matrix.

Dielectric constant is 5.9, substrate thickness is 0.3 mm. It works pretty good at 57 GHz and 60 GHz, but when it comes to 64 GHz things are wieired:

When exciting in one port in Butler Matrix, the pattern direciton (15 degree) and sidelobe level is the same with other frequencies, which is fine. When exciting the other port, the pattern direction switched from 50 degree to 32 degree. But at other frequencies the pattern directions are all 50 degree.

Can anyone explain this to me? Or suggest ways to solve this?

Is it because of surface wave? Mutual coupling between patches? Edge effects? Or some other factors.

Thanks in advance.

Reasons for this:
(1) When multiply the array factor of four-element linear array, the answer is clear for the weired patterns at 57 GHz and 64 GHz.
(2) Since the wavelength is very small, diffraction on the edge of the substrate can badly influence the patterns.
(3) Thick substrate gives rise to high level of surface waves which can affect the patterns.
(4) Microstrip Butler Matrix is a 'narrow band' structure for 60 GHz application. So the phase of out put signals maybe totally messed at 57 GHz or 64 GHz when the Butler Matrix is designed at 60 GHz

Hi,
Now I have a project to make a 4 elements phased array weather radar in X-band or C-Band. But I almost have no idea about this?
Would you pls suggest a configuration about this? Any papers?
Thanks in advance.

Hi Tony,
For 4 element phased array. You can build a 2 by 2 planar array or 4 element linear array. For the feeding network or so called 'phase distributor', lens and matrix are what we usually use. Because they can be easily fabricated in microstrip structure.

I think maybe you can choose patch as the radiator and Butler Matrix as the feeding network the 10 % impedance BW can be easily achieved. That's the most common way to build a phased array.

Or you can keep the antenna unchanged but use Rotman Lens as the feeding network.

Sorry that I do not have any papers available that may help. Maybe you can search for 'Butler Matrix' or 'Rotman Lens' or just 'Matrix' & 'Lens'.

Here is some related fundamentals on Butler Matrix:
Butler Matrix - Microwave Encyclopedia - Microwaves101.com

And Rotman Lens:
Rotman Lens - Microwave Encyclopedia - Microwaves101.com

Hi, shmily0447,

thank you very much.