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Re: Re: Smaller size patch



All good points. 
Fred, one thing about the patch array for a feed (it's been done a lot in mil/comm circles) is the loss in the (inevitably) microstripline feed network.  It's quite significant for our purposes.


> 
> From: "Frederick M. Spinner" <fspinner@hotmail.com>
> Date: 2003/02/05 Wed PM 12:18:37 EST
> To: pe1rah@hotmail.com,  amsat-bb@AMSAT.Org
> Subject: Re: [amsat-bb] 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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Scott Townley NX7U
Gilbert, AZ  DM43di

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