The beginning of new millenium sees an important milestone in military aviation communication with the introduction of the first Super-High-Frequency(SHF) airborne satellite communication (Satcom) terminals, which are due to enter service on Nimrod maritime reconnaissance aircraft (MRA4). Satcom terminals using the Ultra-High-Frequency (UHF) band have been fitted to larger aircrafts for a number of years. Although relatively simple to install and comparatively inexpensive, UHF satcoms(240-270 & 290-320 MHz bands) suffers from very limited capacity (a few 25 KHz channels per satellite) and are prone to multipath & unintensional interference due to their poor antenna selectivity. SHF satcoms (7.25 – 7.75 & 7.9-8.4 GHz) offer significantly increased bandwidths (hundreds of MHz) for high data rates or increased use of spread-spectrum techniques, together with localised coverage and adaptive antenna techniques for nulling unwanted signals or interference.
For airborne platforms, the advantages of SHF satcoms come at the expense of a significant additional burden in terms of antenna siting and pointing, particularly for smaller, highly agile aircrafts. Antenna should be large enough to support the desired data rate and to provide enough directivity to minimise interference with adjascent satellites and avoid detection by hostile forces. Another feature of satcoms, unique to aircraft, is the effect of unwanted modulation from moving parts such as helicopter rotor blades, propellers and jet engines.
This paper gives an overview of development of airborne SHF and also Extremely-High-Frequency (EHF) satcom techniques, and terminal demonstrators by DERA (Defence Evaluation and Research Agency). This research is aimed at providing affordable, secure and robust satcoms to a range of military aircraft, supporting ground attack and reconnaissance roles to surveillance, transport and tanker aircraft.
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