Re: R: [amsat-bb] Coaxially fed Patch lab results..

["Frederick M. Spinner" <fspinner@xxxxxxxxxxx>]

That drawing looks right.  As I've stated before, though I'm unsure if the 
circularity is good.  I'd also like to measure the thing with a metric 
caliper, as when I posted it, all I had here at work readily available was 
an English ruler!!!

But the design is supposed to be good for a 14.5% bandwidth according to 
Roger Cox's Patch program, and I observed about half of that on the network 
analyzer-- which is probably a result of the "diagonal" patch match as that 
will narrowband things a lot.  The -30 db return loss was about 2390-2410 on 
the LHCP side, and about 2400-2422 on the RHCP so I think I'll be okay.  2:1 
bandwidth was at least 150 MHz.

So it'll work okay as an antenna, but will it be circular?

I'll try to write up a webpage, and do a CAD template for the thing by next 
Monday.  I'll try to listen to the bird on the weekend, wife and schedule 
permitting!

Your feedpoints are correct for the top side (dish side).  Bear in mind 
though, the LHCP feed is the one you want for RHCP after being reflected by 
the dish.  (You knew this, but I said it to make it clearer which feed is 
which!)

Good luck.

Fred W0FMS

>From: "i8cvs" <domenico.i8cvs@tin.it>
>To: "Frederick M. Spinner" <fspinner@hotmail.com>
>Subject: R: [amsat-bb] Coaxially fed Patch lab results..
>Date: Tue, 28 Aug 2001 11:52:05 +0200
>
>Hi  Frederick
>
>Nice results indeed ! !
>
>Reading your text i understend  that this is wath you did:
>
>            <                      2"                     >
>            |--------|-------------------|----------|-
>    /\     |  *        |  3/4"       3/4"|         * No spacers here  |
>            |           |                         |              | on 2" 
>side
>          ..|...........|.*sma    sma *|..............|
>            |   7/16"     L         R        7/16"  |
>            |                                                   |
>  2.25" |                                                   |
>            |                                                   |
>            |                                                   |
>            |                                                   |
>            |   spacer                      spacer   |
>            |  *                                          *   |
>     \/    |---------------------------------------|
>
>Please tell me if this drawing is correct or not.
>and if LHCP and RHCP feedpoints are in  the
>exact position as seen from the dish side.
>
>Tank you very much in advance.
>
>If you aegree you can use this drawing for amsat-BB
>
>73 de i8CVS Domenico
>
>----- Original Message -----
>From: Frederick M. Spinner <fspinner@hotmail.com>
>To: <amsat-bb@AMSAT.Org>
>Sent: Tuesday, August 28, 2001 1:28 AM
>Subject: [amsat-bb] Coaxially fed Patch lab results..
>
>
> > Ok.. I think I have a reasonable coaxially fed, switchable sense, patch
>feed
> > that could work.  I'll have to try it on the bird to see if the
>circularity
> > is okay (as I do not have access to an antenna range), but I have a
> > reasonable match at 2.401 GHz (1.08:1 LHCP on feed, 1.18:1 RHCP on 
>feed--
>I
> > was trimming on a shear, and tried to keep all four sides even when I
> > trimmed, and I was close-- not perfect. (This way the  feedpoint stays 
>on
> > the "near diagonal" scaled from W1GE's GPS Patch) Exact resonance is 
>2409
> > MHz on the LHCP side, 2418 on the RHCP.  2401 is within the design BW 
>spec
> > for this patch at both resonances, so I call it "good enough")  LHCP on
>the
> > feed corresponds to RHCP once the thing is mounted in front of a dish!
> >
> > The patch is exactly 2.25" x 2" and is fed at 7/16" in on the 2" side
> > and 3/4" in on the 2.25" side on both corners.  I selected the feeds to 
>be
> > on the line parallel to the 2" side.  The spacing is 5 millimeters from
>the
> > ground plane.
> >
> > The SMA's on the feed are long shaft stainless steel SMA's sold by Down
>East
> > Microwave.  I left the teflon insulation on, but cut it to 5 mm above 
>the
> > ground plane.  The groundplane is countersunk for #2-56 screws to hold 
>on
> > the SMA's but still provide a flat plane under the patch.
> >
> > Experiments show that the teflon on the SMA and the nylon screws (4-40)  
>&
> > styrene spacers 5mm (cut from 3/8" ID hobby shop styrene tubing) that I
>used
> > do capacitively load (lower frequency) the patch a bit, and since I use
>two
> > SMA's for the feed, it was better to omit the screws and spacers on the
>side
> > close to the feeds.
> >
> > Materials:  Patch "hobby brass", groundplane "aluminum".
> >
> > Anyway this isn't quite enough to build the patch, but if I contiue to
>have
> > good luck with it, I'll webpage it.  The groundplane for a patch needs 
>to
>be
> > at least 50% larger than the patch itself.
> >
> > I'll try to listen to the bird with it, and if that goes well, I'll try 
>to
> > build a second one, and see if its repeatable w/o a network
> > analyzer.
> >
> > But it looks good so far.
> >
> > Fred W0FMS
> >
> > P.S. The straight linear scale of the W1GE 1575 MHz GPS patch to 2401 
>MHz
> > resulted in the resonance being at about 2190 MHz.  So I kept trimming 
>all
> > four sides until we were happy (The dimensions above were measured after
> > tuning). Adding about 1.5mm to each of the four sides resulted in
>resonance
> > about 2304 MHz.
> >
> > _________________________________________________________________
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>
>
>
>
>


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