Re: [amsat-bb] Circular patch behaves linear

[K5OE@xxxxxxx]

Fred,

W0FMS writes:

> Impressive.  Those all appear to resonate a little bit high (ideally the 
>  center of the W in the dip should be at 2401 MHz).. but they all look like 
>  they'd work fine and be CP.
>  
>  I never got my K3TZ style to show that dip or CP.   But I do know that 
>  theoretically that design should work.  I've just never gotten one to do 
>  that.
>  
>  Congrats on that.  I probably stand corrected that the G3RUH/W0LMD style 
is 
>  the only one I've ever seen being CP.
>  
>  Also all of the guys who wondered what a CP patch should look like on an 
>  analyzer... there you go.

Earlier in this thread I replied to G3WDG's comments and included my words to 
Charlie below (for others to understand the potential pitfalls with patches), 
but I wanted to show you a couple of other plots on a spectrum analyzer.  
These shots were taken at Ron, AG5RS's shop two weeks--ago getting ready for FD.  
The feed is a dual K3TZ style for our FD dish (identical to the one in the AJ 
journal article and Howard's).  In short, Tony, AA2TX's comments earlier are 
right on the money:  these patches are so sensitive to everything, they are 
really only perfect when individually tuned.  Still, they will work without test 
gear... just not as well as with test gear :-)

Here is an L-band patch at about 28 dB return loss and you can just make out 
the double dip (it is harder to see because the range is not nearly as small 
as Howard's shot):
http://members.aol.com/k5oe/dual_patch_L.jpg
And here is an S-band patch at aobut 22 dB return loss:
http://members.aol.com/k5oe/dual_patch_S.jpg

73,
Jerry, K5OE
-------------------------------------------------
Charlie,
FWIW, I have tested a bunch of K3TZ patches on both 13 and 23 cm using a 
network analyzer.  I find them to be pretty darn finicky, but average about -10 to 
-15 dB return loss, fairly close to the correct frequency (no measurement of 
circularity, but you can see the double-dip pretty easily and I go for the 
middle of it) when built per the specs.  With "tweaking" of the straight corners, 
I can typically get the return loss down to about -25 dB and have achieved 
-32 on several 23 cm patches recently.  

I sure wish somebody would design, build, and make available a circuit board 
patch so the average ham could put one up and know it was close to being good. 
 Without the test gear, most people just have to have faith and then see how 
it operates.
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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