Re: NEC-LIST: How to design a feed network for a microstrip array?

At 03:09 PM 5/17/2006, chen xing wrote:
>Hi all,
> I have designed two microstrip antennas. They have
>different size and cover different frequency bands
>(610MHz-960MHz and 1350MHz-1850MHz respectively), but
>their input impedances are the same, about 90 ohm at
>their working frequency bands. Now I try to integrate
>them on one PCB as an antenna array. I don't know how
>to design the array, especially how to design a feed
>network.

Since the operating frequency band of one is roughly twice the other, I'd
expect a fair amount of interaction between the patches.

But, to start out, what's the impedance of the antenna "out of band". If
it's sufficiently high, you might just be able to hook them in
parallel. This is quite a common technique with narrow band resonant
antennas (like dipoles). Stacked patches are another example, where the
lower frequency patch serves as the ground plane for the higher frequency
patch. there are also stacks of 4: ground:low freq patch:ground:high
frequency patch, where the middle of the low frequency patch is essentially
a stripline between two groundplanes.

if not, then you're looking at some sort of filtering. For instance you
would put a filter in the feedline to the low frequency antenna that blocks
the high frequency (presenting an open circuit at those frequencies to the
combining point). For example, a quarter or half wave stub might be an
effective approach for a narrow band application, but tough to do with your
bandwidth.

One could, for instance, come up with some coupled line type filters that
are sufficiently broad.

However, given the relative frequencies, and the wide band of each element,
this is something you need to design as a single unit. It's also something
I'd hate to design analytically: it just cries out for using a modeling
program and then just basically do cut and try to get the relative sizes of
the patches, etc. correct.

> Thanks,
>

James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875

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