antenna-theory.com

[drick]

I'm a rank beginner at antenna design, but I've been reading the literature on array design with a growing sense of deja vu. Much of the math is familiar to me from studying acoustics, and I've realized that synthesis of line arrays is equivalent to the FIR filter designs I've been doing for years.

Let's suppose I'm designing a narrowband microstrip phased array for a K-band radar application. I know how to specify the complex weights of for the line array elements to obtain my desired far-field polar response, but I'm puzzled at how to actually implement this weighting in practice. The design of the individual patch elements is well taught on this web site. But each needs a different feed magnitude and phase and I haven't a clue how to accomplish that. (Note: this is for fixed aim, not adaptive steering.) Well, the phase is easy: I just need a different line length to get the right delay. But how is the magnitude adjustment done? I haven't yet found surface-mount attenuators for 24 GHz. Is there some microstrip design trick for that? What am I missing?

David

[Schubert]

The FIR filter design is exactly like array weight selection. I believe the antenna guys did it first, or possibly independently, but I am not sure on that. The math is about the same. I'm sure the 2D array weight selection preceded 2D-FIR filters, as I think that mainly deals with images.

Your question at 24 Gig is tough. I'm not sure. Some quick thoughts:

1) If you have a receive only array, then often the Amplifier Gain will be voltage dependent, and you can toggle the magnitude of the received signals in that manner
2) At 24 Gig you can probably use small waveguides, and when attenuation is needed you can make them smaller than cutoff to attenuate signals where you want
3) You could also use impedance mismatch - if the antenna is designed for 50 Ohms or whatever you could adjust the transmission lines to be 100 or 200 Ohms or whatever in order for there to be more reflected power
4) Use lossy dielectrics somewhere?

I'd be interested if you let me me know if you come up with something or what works.

Cool

-Schubert