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Re: More Mobile 9600 Baud Station



Paul's suggestion of an array of patch antennas is very promising.
There have been articles on patch antenna design in various VHF
and microwave publications. An array of 6 patch antennas for 435
will form the gain antenna for P3D. I worked on the bird a little
bit this spring and was surprized how thin the antennas were (thinner
than the aluminum used for the skin of the spacecraft, if memory
serves) and each was about the size of a small dinner plate. There are
six in the array in a pattern about 4 feet across -- definitely will
fit on an RV.

For 144, three folded dipoles form the P3D gain antenna. These are also
low profile (about 3 inches) and are made of mechanically substantial
tubing.

Here is the question, however: Both of these arrays are fixed in their
gain direction (normal to the surface onto which they are mounted).
What are the requirements for the radiation pattern of the individual
elements that make up a phased array?

Another aspect that should be kept in mind: For LEO spacecraft, 
something well above 60% of the total time above the horizon is
spent within 15 degrees of the horizon. (This comes from a brute-force
analysis of rs-10 orbits for an entire month that I did for my 
antenna case with my city.) If you could 'tune' a yagi-like gain
antenna for a take-off angle of about 10 degrees above the
horizon for each band, mount them firmly on a turn-table platform
that rotates, it would take care of much of the accessible air-time
perhaps. A patch antenna for overhead would take care of the rest?

Best of luck.

--Paul Beckmann, wa0rse@amsat.org
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