(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 (b) Sharper antenna directivity reduces the degrees in (c) Wider bandwidths available at the higher frequencies (d) Atmospheric absorption tends to reduce low angle interfering signals relative to the higher angle satellite signals. ANTENNA GAIN AS A FUNCION OF ANTENNA SIZE DB RELATIVE TO .. ISOTROPIC (BASED ON PARABOLIC ANTENNAS) 90 DB 20 30 40 Gc/ FREQUENCY FIGURE 2 |