[eagle] Re: Eagle Microwave Antenna Arrays -- mechanical concepts

Louis McFadin w5did at amsat.org
Fri Mar 23 08:15:54 PST 2007


Tom,
As far as how to assemble the array IE whether it's made of  
individual cups, milled out of a solid block or as some have  
suggested milled from a casting, that should be left to the  
implementor. What we need now is a solid foundation to build upon. If  
you can show how you will be able to  drive this array, we can figure  
a way to build it.
Stan and I have had some experience building patches on S band and we  
believe we can build C band patches. It's obvious that putting the  
patches in a hex array gets more for the same amount of real estate  
and therefore gets you more gain. Do you think you can come up with a  
way to drive a hex array or not is the question. It would seem be be  
more symmetrical around the Z axis and therefore have less spin  
modulation.

Fred Parker has been experimenting with castings for an S band array.  
His casting is still rough but has promise. It has 1/2 inch under the  
array to put the amplifiers and phasing harness. The array looks like  
this. We made a test casting. It weighs .8 Kg.
We will put some patches in and see how they work.

On Mar 23, 2007, at 1:22 AM, Tom Clark, K3IO wrote:

> Back in Feb, Bob Davis wrote:
>> Jim,
>> I would like to add to the agenda: top-level antenna  
>> configuration. I've begun to seriously consider what to build for  
>> the Eagle mockup at Dayton. Several people exchanged antenna  
>> configuration sketches late last year (September 2006), and don't  
>> know if there was resolution on A sketch. Something must be  
>> baselined soon (maybe by mid-March)), if we're to have the mockup  
>> ready for mid-May.
>> bob
>> Robert Davis
>> KF4KSS
> Bob -- I finally "got a round tuit" on this topic :-[
>
> This applies to both the C-band and S2 phased arrays. Instead of  
> drawing the possibilities, I figured it was easiest to build (spare  
> no expense!) simple models and three possibilities are attached.  
> When we computed the needed array gain, we came up wanting about  
> 35-40 individual patch antennas (15-16 dB of array gain added to  
> ~5-6 dB of element gain for a single patch). The individual patches  
> will need to be about 0.7 wavelengths in diameter; my guess is that  
> the patch itself will be about ½ wavelength in size and it will sit  
> inside a "cup" cavity that is about ¼ wavelength deep. This cavity  
> (a.k.a.  choke ring) will help minimize the mutual coupling between  
> the antennas. For the two frequencies, we have
> S2 = 3400 MHz = 8.8 cm wavelength. Therefore the "cup" will be ~6.2  
> cm diameter and ~2.2 cm tall.
> C  = 5800 MHz = 5.2 cm wavelength. Therefore the "cup" will be ~3.6  
> cm diameter and ~1.3 cm tall.
> We will want good symmetry in the array to make the phasing as  
> painless as possible. This led me to the 3 models I've attached:
> "Square" is a 6x6 array (36 elements). I think I have "invented" a  
> nice way to do the phasing for a square array based on the Butler  
> combiner matrix (the antenna analog of the Cooley-Tukey FFT) which  
> looks like it will work well (meaning easy to phase to  
> electronically de-spin the antenna) on an 8x8 array and I think it  
> can be trimmed down to 6x6. Since the rows/columns are spaces 0.7  
> wavelengths, the diagonal element spacing will be just one  
> wavelength, so we won't have much power wasted in sidelobes.
> "Hex" is 37 element array that is the tightest possible packing. It  
> approximates a 4.2 wavelength dish in its properties. So far, I  
> have not yet "invented" a Butler-like matrix for a hexagonal array,  
> so I don't know how well it can be implemented.
> "Ehex" extends the Hex geometry by adding 6 elements (total=43) for  
> a bit more gain, with a pattern more like a 4.6 wavelength dish.
> Stan and Lew have suggested that the honeycomb structures might be  
> done on an NC mill, which could give us a good thermal radiating  
> surface. For the transmit phased array we have thought in terms of  
> a ~1 watt (RF) power amplifier at each patch. Depending on what  
> kind of DC => RF efficiency we can achieve, this will mean that we  
> will have 20-30 watts of heat to dump from the array.
>
> My idea, instead of milling a big block, was to use extruded  
> aluminum cups (something like http://www.zerocases.com/catalog/deep- 
> drawn-enclosures/round-precision-miniatures.html).
>
> Maybe we can chat about this Saturday at the DC AMSAT meeting ---  
> 73, Tom
> <hex.jpg>
> <Ehex.jpg>
> <square.jpg>
> _______________________________________________
> Via the Eagle mailing list courtesy of AMSAT-NA
> Eagle at amsat.org
> http://amsat.org/mailman/listinfo/eagle

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