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

[Michelle Thompson]

Let's make some!

-Michelle W5NYV




On Mon, Dec 3, 2018 at 5:43 PM KENT BRITAIN <wa5vjb at flash.net> wrote:

>
> 10 GHz version would of course be much smaller.
>
>
>
>
> --------------------------------------------
> 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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