John:
So why not a full-wave loop at 100mm high?
Indeed it might not be like your station antenna, but we are not asking
a huge amount from that antenna. I am quite concerned for the
potential s/c envelop. There are other possibilities such as the side-mounted
antennas such as for P3E (AO-13-type), although sweeping shadow patterns will
cross the solar panels, such momentary interruptions of cell strings has not yet
been evaluated. Could it be acceptable? I don't know the answer to this, but I
do know that I feel we must be perhaps a little less conventional on the
solution for Eagle.
Dick Jansson
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The U antenna can be anything that gives a 120-degree beamwidth and can be
centered on the spin axis. There's no way to correct spin modulation on that
band and the 30-50 bps uplinks will be more sensitive to phase pertubations than
any other uplink. I'm assumng that there will be no class 1 uplinks on
the L receiver. The advantage that I see in the crossed dipoles is that they
leave more space for the S2 phased array.
The V antenna is the most problematic. I modelled the 3 dipole array (ends
bent down to make each 600 mm long) six weeks ago and the main problem will
be getting the antenna high enough off the satellite body to broaden the beam. I
modelled a full-wavength loop today and it is almost the same. The
0.2h/0.5h/0.75h in the file names is the antenna height in meters.
73,
John
KD6OZH
----- Original Message -----
Sent: Monday, September 25, 2006 13:35
UTC
Subject: [eagle] Antenna Plans
It is well that the antenna plans are
starting to congeal. I do have some comments upon the diagram that John
presented, herewith attached.
1) There is an option, whether employed or
not, that the U band could be the stacked CP patch design previously
shown, with the L band array mounted thereon, also as previously
shown.
2) The U band antenna currently shown in
John's design could use a modification of the dipole design used for all
of the AMSAT-DL P3 satellites. We call that "design adaptation" (not
stealing!).
3) The V band antennas are of a great
concern as shown in John's design. The P3D V antennas were more than 880mm
end-to-end span, and a nominal 144mm spaced off of the spaceframe. Three
of these on top of the Eagle seems to me to be of a gargantuan,
unwieldy concept. These antennas would greatly impact the
spacecraft envelop as mounting in a launcher. John has talked of a
bent-end antenna design, is that really practical from an RF
sense?
I am wondering if some form of dual-feed
full-wave V band loop might not serve better in this application. Stan
Wood had shown such a full-wave loop design for the Small Eagle that was
only about 50mm high. Properly designed, it would not
necessarily have to be 144mm high, so I am led to believe. Can some
astute antenna designer look at this for us? I feel that we need to look at
the options.
Dick Jansson
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