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RE: Patch plans anyone?




Ok, I think I knew the answer to that before I asked it, but I wanted 
other's opinion on that.

So, this should mean that a small amount of loading could be a decent 
tradeoff for a PCB feed.  The smaller bandwidth is a problem, and it doubles 
since the smaller spacing of PCB would also reduce the bandwidth of the 
patch, probably down to <15 MHz or so.  But on good microwave substrate with 
good tolerences it could be done.

Adding thermal noise isn't good, but reduction in gain isn't so important as 
pattern when using as a dish feed.

Fred W0FMS

>From: "Tom Clark \(W3IWI\)" <w3iwi@toad.net>
>To: "'Frederick M. Spinner'" <fspinner@hotmail.com>, <Mike73@aol.com>,   
><howard@howardlong.com>, <amsat-bb@AMSAT.Org>
>Subject: RE: [amsat-bb] Patch plans anyone?
>Date: Sat, 1 Jun 2002 13:48:32 -0400
>
>Fred
>
> > Does going to teflon (Er=2.1), shrinking the patch 2x, make that much
> > difference in the pattern?  Or just the gain?  Has anyone
> > been able to model this?
>
>The physical size scales as sqrt(epsilon). For example at GPS, the
>free-space wavelength is 19cm so an unload patch will be ~ 1/2 wavelength =
>9.5 cm = 3.8 inches on a side. The smallest of the patches are about 1.2
>inches on a side and use Er ~ 10 ceramic.
>
>As you load the antenna with dielectric to make it smaller, it becomes a
>higher Q device. I have seen small GPS patches with an intrinsic bandwidth
><10 MHz, i.e. a Q >60. As the Q of the antenna increases, it becomes much
>more sensitive to ohmic losses. In the transmit case, the patch gets hot 
>and
>your signal is attenuated. In the receive case (like 2,4 GHz), you take a
>double "hit" -- the losses soak up the signal and the losses add thermal
>noise. Every dB of internal loss in an antenna (and the associated cables)
>adds 1 dB to the noise figure.
>
>The pattern of a patch is essentially a dipole (or its circularly polarized
>equivalent). even the pattern of an infinitesimal dipole is nearly the same
>as a real half-wave dipole. So the pattern is unaffected.
>
>73, Tom
>
>----
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