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Re: Reference/Source for patch antenna



I'm starting to understand how to build a CP "nearly square" patch.
"Nearly square" is an important concept apparently for a coaxially
fed (through the groundplane) CP patch antenna.

The comments of 50 + j XX and 50 - j XX were another good clue...
At one time I built the 1995 QST GPS patch-- its RHCP.  It worked well..

Here's what I'm thinking (and I've verified this somewhat from other 
sources)-- a nearly linear scale of the patch to 2.401 GHz (Small tweak 
after running it through WB0DGF's patch16.exe program)....

Here's my current logic on the CP issue:  If I were to make a perfectly 
square patch and put the feed on the diagonal, how could I be sure of which 
sense the CP is?  Matter of fact, if it were square and on the diagonal, 
wouldn't we still have linear polarization?

This is why on a coax fed patch, the patch needs to be slightly 
rectangular.. to get the +j and -j terms in.  Now we can determine
the vector rotation.  Cool... (This means the feed IS NOT directly on the 
diagonal-- its a little offset in the X and Y axes)

After sleeping on it-- it'd seem if the scaled dimensions for the feed were 
transferred MIRROR imaged the sense of the scaled patch would be LHCP, since 
the original design was RHCP.  Also it would be possible to put on two SMA's 
and have a RHCP port and LHCP port.

What I haven't resolved is whether I should mirror the feedpoint in the 
wider side axis or the narrow side axis?

I know the G3RUH patch is a circular patch, but this should work and
be easily constructed (i.e. cheap!).  With a roughly 120 degree 10 db BW-- 
it should be good for prime focus dishes.

What do the guru's in the group think?

Fred W0FMS


>From: "Howie DeFelice" <hdefelice@petrexintl.com>
>To: <amsat-bb@AMSAT.Org>
>Subject: Re: [amsat-bb] Reference/Source for patch antenna
>Date: Wed, 22 Aug 2001 10:19:25 -0400
>
>OK, I get the part about self phasing.  When talking about feeding a patch
>on the diagonal, I assume it is meant a diagonal line between the two 50 
>ohm
>feedpoints? Looking at the pictures on the web of the G3RUH patch feed and
>after reading the description, I assume the center of his patch is 
>grounded.
>It is hard to tell from the picture, but do you think the patch is circular
>or elliptical? Perhaps someone who owns one can comment.  It also appears
>there is a spring contact of some sort off to one side of the patch, anyone
>have a clue what that is about? I guess the polarity (LHC or RHC) is
>determined by which feed point is fed first by the rotating wavefront. Does
>anyone know what the convention is?
>
>Thanks,
>
>Howie AB2S
>
>----
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