[Ground-station] Weekly report - 10GHz Balloon Launch - antenna options update

[KENT BRITAIN]

10 GHz version would of course be much smaller.




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On Mon, 12/3/18, Michelle Thompson via Ground-Station <ground-station at lists.openresearch.institute> wrote:

 Subject: [Ground-station] Weekly report - 10GHz Balloon Launch - antenna options update
 To: "Michelle Thompson via Ground-Station" <ground-station at lists.openresearch.institute>
 Date: Monday, December 3, 2018, 7:27 PM
 
 Testing 10GHz antenna structures for terrestrial,
 balloon, and satellite applications is part of what we
 do! 
 
 Both existing and new 10GHz antenna designs are in
 progress for  use on a high altitude balloon. 
 The goal is to transmit DVB-S2/X live video from
 a high altitude balloon. This tests transmitter, antenna,
 processing, and sensing. Next steps would be two-way
 communications on 10GHz.  
 High altitude balloon antennas have uncontrolled
 yaw. The current requirements are inexpensive enough to
 lose,  hemispherical coverage, optimal gain at 70 degrees,
 some gain at 0 degrees (directly beneath the balloon).
 Circular polarization would be ideal. Otherwise,
 polarization tracking at the ground is required.
 Four different quadrifilar helix structures were
 simulated that gave a reasonable pattern. The problem so far
 is that these are easily realizable at GPS or 23cm
 frequencies, but the dimensions will be unreasonably small
 at 10.45GHz.
 Another new design is a patch array model. Most
 accessible papers at or near 10GHz for circular polarized
 patch arrays seem to be a record of capturing results of
 trial and error. This gives shapes that can be (in most
 cases) duplicated, but does not give a model that can be
 manipulated and edited to better match the
 requirements. 
 Another aspect of the published work is the heavy
 influence of industrial and commercial requirements on
 antenna design. Very broadband designs that allow 2-3 or
 more bands are the goal. The pattern doesn't have to be
 great and the gain isn't that critical. When the device
 is held near, say, a body, then the pattern is messed up
 from the get go, so optimizing (and adding expense) is not
 generally pursued.
 So, that's where we come in. We don't
 have the same motivations or requirements as a commercial
 antenna deployment. We do need this antenna to be
 inexpensive enough to lose. Balloon payloads (and
 satellites, and even terrestrial gear) are lost in accidents
 and failures.
 Kent Britain's Vivaldi antenna is an existing
 inexpensive design scheduled to be integrated and tested
 with the payload.
 You might be saying "Wait, Vivaldis are only
 linear polarized" and yes you would be right. A single
 Vivaldi as the downlink antenna would give the right pattern
 but linear polarization, meaning polarization losses on the
 ground. Mitigations would be a challenge. 
 However, Vivaldi antennas can be made to be
 circularly polarized in combination.
 To achieve this, two Vivaldi antennas are
 orthogonally placed. They are driven by a specially designed
 feeding network that creates an input signal with two-way
 signals that have equal magnitude and orthogonal phase. This
 can be done with PCB techniques. 
 Next steps? Antenna simulation, building,
 testing, and flying!
 Comment and critique welcome and
 encouraged. 
 Volunteers of any level accepted and
 supported. 
 -Michelle W5NYV
 
 
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