Link margin for UHF airborne satellite communications (SATCOM) operation

SATCOM link performance for aircraft operation tends to be marginal, especially at high latitude operation or during maneuvers. The weak components of the link (antenna gain and multipath fading) have been examined. The weapons to combat negative link margin are increased antenna gain, lower system noise figure, FEC and, diversity. Input noise figure is about as low as it can go, due to the inherent loss of the SATCOM duplexer. To maintain hemispherical coverage, additional antennas must be combined with quadrature diversity. Finally FEC is employed to maintain link margin, but the user must be willing to operate at a data rate less than the SATCOM channel capacity for unencoded data.