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RE: Experience with K3TZ patch -> updated webpage [LONG]



Tim, I've been in the same boat as you have been on time.

A few comments:

I've built this type of feed (original credit goes to 7N1JVW in Japan, who's 
Japanese pages are dated July 2001-- no offense to Tim, but we should 
probably be calling this feed the 7N1JVW feed) and I've even built a 
grounded center feed version with a scalar ring that seems to work well.  I 
have not brought it to work to hook to a Network analyzer yet, and I should 
as I could "tweak" the dimensions with the ground in place.

I've analyzed the spacer situation, and here is the problem:

If they are close to the center of the patch, then they have little effect.  
Dead center in the patch, the impedance is 0 + j0 ohms (if in the symmetric 
center of the patch).  Thus either an insulated of conductive post can be 
used at this low-current, low-radiation point.  If the post is conductive, 
it should be as small as possible or the dimensions of the patch should be 
adjusted somewhat to compensate for the shorting effect.  This is analogous 
to the Yagi on a conductive boom case where the elements need to be 
lengthened a little to compensate for the fact the boom has some diameter to 
it.

In the case of my original patch antenna design (a "Nearly Square CP" 
patch), I DID get a design to work with spacers on the outside 
(high-current) area of the patch.  Unfortunately the capacitive loading of 
the spacers decreased the patch's size by about 12% and therefore 
theoretically the gain is less, BW is more, etc. And it is highly dependant 
on the materials used.  The patch is really senitive to any dielectrics 
between the plates. But, if I did not have the Network Analyzer available, I 
could have never gotten the patch to be resonant at 2401 MHz.  I also 
suspect the spacers throw off the phase enough that the circularity suffers 
a bit.  On the other hand, as long as the materials are duplicated exactly, 
it seems to work good.

I'm glad to hear that that type of patch is CP.  All the theory shows that 
it should be, and I'd be interested to see details of the axial ratio, etc.

As far as the "scalar rings" go, I think hams tend to oversimplify this a 
bit.  The actual optimal height of the ring should be taylored to the f/D 
ratio of the dish that is being used. The higher f/D, the taller the ring 
should be.  Slip a cardbord tube around a flashlight if you need a mental 
helper on this. Since many TVRO type prime focus dishes are similiar to the 
G3RUH dish, copying the height of the ring on his patch is a good starting 
point.

I plan on writing a few web pages about what I've learned (right or wrong!) 
on patches, dishes, helixes, feeds, etc. as soon as my new
"high-speed" cable modem provider decides to give me permanent web space 
again.  This is why I've held off on updating my pages..  Which are only 
available now on a "backup system"... sigh...

Fred W0FMS

>From: "Tim Zibrat" <tzibrat@adelphia.net>
>To: <K5OE@aol.com>, <avollhar@physik.unizh.ch>, <fspinner@hotmail.com>
>CC: <amsat-bb@AMSAT.Org>
>Subject: RE: [amsat-bb] Experience with K3TZ patch -> updated webpage 
>[LONG]
>Date: Tue, 19 Feb 2002 07:54:10 -0500
>
>Hello all,
>
>It's been nice to see the interest in the "K3TZ Patch".  I really 
>appreciate
>all of the emails I have received, and the help and encouragement from all
>of you.
>
>I would like to apologize to everyone for not getting my web page updated
>with the latest information.  I have really been working massive overtime
>for the last month, my computer motherboard smoked, and the list goes 
>on....
>
>Back to the subject at hand.  The "K3TZ Patch" is indeed circular.  Charlie
>G3WDG, did some independent testing on his own and shared his results with
>me.  After some discussion with him, I figured my test procedure was in 
>fact
>flawed.
>
>So I repeated the testing, with a few minor, but important changes, and
>found the patch to be circular as well.
>
>Charlie also found that the use of any spacer between the patch element and
>reflector degrades performance significantly.  If you use a stiff enough
>material for the patch element, you probably don't need the spacers anyway.
>
>I also found that the use of a 1" high "cup" reflector (or scalar ring)
>increased the performance of the antenna as well.  This was confirmed by
>Jerry, K5OE.
>
>The antenna can definitely use some improvement on its design.  However, as
>it is, it works quite well, and much better than a helix feed (or so I've
>been told).
>
>In my very limited spare time, I am currently working on a new version that
>has the center of the patch grounded.  This will improve the mechanical
>stability, hopefully make construction a little easier, and help to bleed
>off any static build-up on the patch to protect sensitive LNAs.
>
>Again, I apologize for the very late update.  I know several of you have
>suggested to me to at least update the BB while the web page is being
>updated.  I should of taken your advise!!
>
>Thanks again for your all of your emails!!!
>
>Best 73,
>Tim
>K3TZ
>
><snip>
>
>----
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