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MO7-OROLA Technical Developments
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SMALL APERTURE TRACKING TERMINAL
by Rich Torkington and Rich Heidinger
This publication describes the collective physi- cal packaging design of a low cost tracking antenna suitable for ground use to communicate with a non- geostationary satellite system. With a proliferation of non-geostationary satellite communications sys- tems currently being proposed and funded in today's global telecommunications market, there is ample evidence that a low cost tracking terminal could rep- resent a very lucrative product line for its maker.
A number of tracking terminals exist on the market, categorized as:
Maritime applications - Designed for tracking GEOs while in motion. These products correct for boat pitch and yaw (using digital gyms) as well as heading, but cost typically >$SK, Land vehicle auulications - Designed for tracking GEOs, usually while the vehicle is not in motion. Useful for mobile homes employing satellite television systems, etc. Typical cost >$5K,
Militarv auulications - Generally cost prohibitive
Similarly, there are 'optical' tracking terminals that have relevance, namely:
Trackinz surveillance camera mounts - E.g. rooftop and ceiling mounts, typically >$3K, Tracking telescope mounts - typically $lOK and up.
What is desired is a low cost (less than $500) small aperture (equivalent to a 18"D parabola or less) tracking terminal for high volume production. The product should be mountable onto rooftops, have full hemispherical (2 DOF) pointing capability, better than 0.5' pointing accuracy, capable of trans- mit/receive at Ka-band +I-, and be designed for at least 5 years of continuous use.
To answer these needs, a small aperture tracking terminal illustrated in Figure 1 was designed com- prising a combination of well known elements into a previously unavailable product. This design con- sists of:
a) Parabolic reflective collector. An aperture size ranging between 10 and 30 inches in diameter is proposed, based on system gain requirements.
b) RF feed. May be positioned on-axis or off- axis (off-axis shown).
c) Azimuth control motor. Current designs use, microstepping motors, although other designs could employ gearmotors, gearhead motors, servo control, pneumatics, track drives, worm drives, or other electromechanical combinations.
d) Elevation control motor, similar to azimuth control motor.
e) Counterbalance subassembly, creating a balanced reflector design to minimize motor loading.
f) Housing for control electronics. This housing might...
