Satellite Uplink Frequency ~145 MHz, wavelength = 2 meters
Satellite Downlink Frequency ~435 MHz, wavelength = 70cm
Note: This document is only a consideration of downlink antenna, since higher gain will
be desired for the downlink.
Fairly certain that we will use a 3CS antenna (conformal coated ‘rubber duck’ antenna)
for uplink, since ground station can output high amounts of RF power (up to 50 watts).
Gain of conformal coated rubber duck antenna = -2 dB (according to Jen Michels).
Downlink Antenna Options:
1) Axial Mode Helix (see attached photocopy from ARRLSatellite Handbook.)
Advantages of this design:
--Circular polarization  no 3 dB polarization loss to ground station.
--This antenna can be matched by changing the feedpoint of the antenna.
--64 degree half-power beamwidth covers most, if not all of horizon.
--10.0 dBi is high gain.
Disadvantages of this design:
--Antenna will be approximately 2.0 feet long after it is deployed.
--Minimum 3 helix turns needed to keep desirable gain pattern.
--Need to make antenna out of wire that is very stiff, so that the wire will
keep its shape when it is deployed.
2) Split Dipole Antenna with Circular Polarization CP (see attached photocopy
from ARRL Satellite Handbook)
Advantages of this design:
--Circular Polarization can be achieved (again, no 3 dB polarization loss)
--Will fit underneath the spacecraft
Disadvantages of this design:
--Coax Length for phasing will add extra weight:
One side: (1/4-wavelength+1/2-wavelength) = 3/4 wavelength coax
Other side: (1/2-wavelength+1/4 wavelength+1/2 wavelength) = 1.25 wavelength coax
Total coax to antennas (not including initial feedline from radio)
1 wavelength = 70cm.
3) 3CS antenna (conformal coated “rubber duck” antenna)
Advantages of this design:
--No antenna design needed
--very easy to deploy
Disadvantages of this design
--low gain
--non-directional