(2) As systems become more sophisticated through stabilized satellites and ability to use narrow beam antennas the upper frequency limit increases.

(3) The upper frequency limit may extend to above 15 Go/s for sophisticated systems if reception is not required at very low angles.

(4) Theoretical disadvantages at the higher frequencies estimated on the basis of clear channel operation may be offset by the increased likelihood of successful frequency sharing at these frequencies since:

(a) Sharper antema directivity tends to reduce the
vertical angle at which interference or noise from the
earth will dominate the signal from the space vehicle;

(b) Sharper antenna directivity reduces the degrees in
azimuth from which interference is likely;

(c) Wider bandwidths available at the higher frequencies
permit "spread spectrum" modulation techniques which
promise gains in immunity to interference;

(d) Atmospheric absorption tends to reduce low angle interfering signals relative to the higher angle satellite signals.

(BASED ON PARABOLIC ANTENNAS)

20 30 40

Gc/

FREQUENCY

FIGURE 2