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Re: Smaller size patch



Actually, the gain of the patch element (and therefore beamwidth) is a 
function of the physical area of the patch.
The Q (bandwidth) is also a function of the spacing-- the wider the spacing 
the more beamwidth.
On top of that, the dielectric adds thermal noise to the patch antenna and 
"loads" it increasing Q further.

I'm not saying that it is impossible to use teflon for a patch.  I think it 
is and if you get a good design let us know.
But the theory anyway say the following with the above conditions:

1. The f/d ratio of the dish will have to be less than for an air patch for 
optimal efficiency due to the smaller gain of the smaller patch.  (How much? 
  Probably just a little)

2. The dimensions of the patch are much more critical, being physically 
smaller, one but also because of the higher Q of the "loaded" structure (the 
dielectric is a load like a capacitor or inductor would be in a trap in a HF 
antenna) and the tighter spacing makes the patch higher Q as well.

3.  Increased thermal noise in the patch will mean that it will be 
effectively less efficient than the air patch.

There are some designs, such as the "apature coupled" patches that will fix 
#2 above, but the design is complex.

Not to say it won't work.  But be aware of the tradeoffs.

Another possibility is to try to make a non-conductive "radome" for the air 
patch to give it mechanical ruggedness.  You'd still likely have
to compensate for this "radome" when designing the air patch, but the 
effects above would be greatly less.  (Although still present a little).

Good Luck.

I've thought for awhile that an array of four patches on a substrate could 
be a good alternative to a helix feed on a offset-fed dish, but I've not had 
the time to pursue this.

Fred W0FMS








>From: "William Leijenaar" <pe1rah@hotmail.com>
>To: amsat-bb@amsat.org
>Subject: [amsat-bb] Smaller size patch
>Date: Tue, 04 Feb 2003 23:06:11 +0100
>
>Hi AMSATs,
>
>I am upgrading my portable station to be smaller and less heavier than now.
>The 13cm patch antenna I have for AO40 is very fragile to carry in a 
>backpack and besides that I want to have something smaller in size.
>
>As a solution I tought maybe teflon PCB will be a solution.
>With teflon instead of air, the epsilon R will be more and the antenna 
>length smaller. I have no idea if the gain will be infected, and to order 
>some expensive teflon material for just testing out is a little to 
>expensive for me.
>
>Maybe someone has experience with this kind of antenna size reducion ?
>
>73 de PE1RAH, William
>---
>
>
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