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Re: Patch Back Element -- when is the geometry incidental?



>W0LMD states that the resonance point of the patch
>moves down a bit (I swear  I saw 4% somewhere but
>I've not been able to find it again) when the feed is

>placed on a dish.  Since I brought my feed into work
>to be tested, I couldn't practically bring the dish
>with me.  But I did notice when the feed 
>is resonant at 2520 MHZ it was MUCH more sensitive
>to "large metal objects" than it was when brought
>into resonance at 2401 MHz.  So far the "lab tuned" 
>2401 MHz patch seems to work wonders on the 1.37M DH
>satellite dish it's attached to.

Thanks for posting this great info, Fred.

Are you able to measure complex impedances at work, or
just SWR?  If the former, did you measure the patch
without the tuning screw installed?  If so, was it
50-j50 ohms?

Another way of 'tuning' a grounded patch might be to
change the diameter of the grounding post.  Increasing
it's diameter sould increase the resonant frequency of
one of the modes of the patch, while decreasing it's
diameter should make the patch effectively larger, and
lower in frequency.  

Unfortunately, I can only measure return loss, and
only at one frequency at the moment.  I'm hoping to
use my Q7A and some sort of multiplier to have an
adjustable frequency source on 2.4 GHz.

vy 73 de va3rr

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