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Re: question regarding patch antennas




I've built linear polarized 1691 MHz WEFAX (WEFAX is linear polarized) and 
terrestrial linear 1296 MHz patches.  Coupled with a prime focus 4' dish 
they seems to work fairly well.  I'm going to post info to my website 
(w0fms.org) when I have time to work on it.  I was going to work on it this 
weekend, but had several mechanical breakdowns of home appliances at the 
same time this weekend!...grrr.. so hopefully I'll have plans online in the 
next couple of weeks.

Scaling, BTW, is a bit touchy on patches as they are really narrowbanded 
devices.  I found that I had to trim on a network analyzer after I built a 
"scaled patch", for what it's worth...

Fred W0FMS

>From: Bruce Bostwick <lihan161051@earthlink.net>
>To: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] question regarding patch antennas
>Date: Sun, 3 Mar 2002 13:43:29 -0600
>
>>There have been many very favourable comments recently regarding patch
>>antenna as feeds for parabolic dishes. All the construction articles I
>>have
>>seen are for 2.4 GHz. Has anyone successfully scaled these antennas to
>>other
>>commonly used frequencies? I was thinking of (say) 1691 MHz for the
>>NOAA and
>>GMS satellites and 1296/1269 MHz for use in our 23cm band. Any
>>references
>>would be appreciated. Scaling seems to work well for antennas like the
>>helix
>>and loop yagi but perhaps patches are more 'perfinicky' and I don't have
>>access to any modelling or analysis apparatus.
>
>Scaling almost always works as long as you scale *all* dimensions.  Many
>people scale antenna designs and neglect to scale minor dimensions such
>as element thickness/diameter -- some antenna designs require elements
>to be a certain thickness to control skin current and frequency
>stability -- or use components that have unanticipated side effects on
>element behavior, such as insulated or coated conductors, which is why
>scaled antenna designs most often do unexpected things.
>
>I don't *think* the thickness of a patch antenna element is critical,
>but you may want to experiment with different metal thicknesses just to
>be sure.  You *do* want to avoid using things like copper clad PC board
>because it will put a distributed capacitive loading on the element
>(just like insulation on a wire dipole! ;-) and I'd suggest low-loss
>standoffs like ceramics if you can get them.  With those caveats, you
>should be able to scale a patch pretty nicely.  Having an antenna
>analyzer like an MFJ-259 will help a *lot*.
>
>The discussion of the AO-40 UHF patches posted a while ago (thanks
>KD4APP!) does have dimensions for 436, I believe, and you can scale
>those for most UHF/microwave frequencies if my instincts are right.  Try
>it and see, and let us know what you find out.
>
>"Go ahead and do it, you can apologize later." -- RADM Grace Hopper,
>1906-1992
>"The sunset is an illusion, but the beauty is real." -- Richard Bach
>
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