<div dir="ltr">Let's make some!<br><br clear="all"><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr">-Michelle W5NYV<br><br><div dir="ltr"><br></div></div></div></div></div></div></div></div></div><br></div><br><div class="gmail_quote"><div dir="ltr">On Mon, Dec 3, 2018 at 5:43 PM KENT BRITAIN <<a href="mailto:wa5vjb@flash.net">wa5vjb@flash.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
10 GHz version would of course be much smaller.<br>
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On Mon, 12/3/18, Michelle Thompson via Ground-Station <ground-station@lists.openresearch.institute> wrote:<br>
<br>
Subject: [Ground-station] Weekly report - 10GHz Balloon Launch - antenna options update<br>
To: "Michelle Thompson via Ground-Station" <ground-station@lists.openresearch.institute><br>
Date: Monday, December 3, 2018, 7:27 PM<br>
<br>
Testing 10GHz antenna structures for terrestrial,<br>
balloon, and satellite applications is part of what we<br>
do! <br>
<br>
Both existing and new 10GHz antenna designs are in<br>
progress for use on a high altitude balloon. <br>
The goal is to transmit DVB-S2/X live video from<br>
a high altitude balloon. This tests transmitter, antenna,<br>
processing, and sensing. Next steps would be two-way<br>
communications on 10GHz. <br>
High altitude balloon antennas have uncontrolled<br>
yaw. The current requirements are inexpensive enough to<br>
lose, hemispherical coverage, optimal gain at 70 degrees,<br>
some gain at 0 degrees (directly beneath the balloon).<br>
Circular polarization would be ideal. Otherwise,<br>
polarization tracking at the ground is required.<br>
Four different quadrifilar helix structures were<br>
simulated that gave a reasonable pattern. The problem so far<br>
is that these are easily realizable at GPS or 23cm<br>
frequencies, but the dimensions will be unreasonably small<br>
at 10.45GHz.<br>
Another new design is a patch array model. Most<br>
accessible papers at or near 10GHz for circular polarized<br>
patch arrays seem to be a record of capturing results of<br>
trial and error. This gives shapes that can be (in most<br>
cases) duplicated, but does not give a model that can be<br>
manipulated and edited to better match the<br>
requirements. <br>
Another aspect of the published work is the heavy<br>
influence of industrial and commercial requirements on<br>
antenna design. Very broadband designs that allow 2-3 or<br>
more bands are the goal. The pattern doesn't have to be<br>
great and the gain isn't that critical. When the device<br>
is held near, say, a body, then the pattern is messed up<br>
from the get go, so optimizing (and adding expense) is not<br>
generally pursued.<br>
So, that's where we come in. We don't<br>
have the same motivations or requirements as a commercial<br>
antenna deployment. We do need this antenna to be<br>
inexpensive enough to lose. Balloon payloads (and<br>
satellites, and even terrestrial gear) are lost in accidents<br>
and failures.<br>
Kent Britain's Vivaldi antenna is an existing<br>
inexpensive design scheduled to be integrated and tested<br>
with the payload.<br>
You might be saying "Wait, Vivaldis are only<br>
linear polarized" and yes you would be right. A single<br>
Vivaldi as the downlink antenna would give the right pattern<br>
but linear polarization, meaning polarization losses on the<br>
ground. Mitigations would be a challenge. <br>
However, Vivaldi antennas can be made to be<br>
circularly polarized in combination.<br>
To achieve this, two Vivaldi antennas are<br>
orthogonally placed. They are driven by a specially designed<br>
feeding network that creates an input signal with two-way<br>
signals that have equal magnitude and orthogonal phase. This<br>
can be done with PCB techniques. <br>
Next steps? Antenna simulation, building,<br>
testing, and flying!<br>
Comment and critique welcome and<br>
encouraged. <br>
Volunteers of any level accepted and<br>
supported. <br>
-Michelle W5NYV<br>
<br>
<br>
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