Intermodulation products in military satcom systems

The UK military satellite communications system (UKMSCS) is likely to make increased use of personnel portable satcom systems. In addition to wanted accesses the transponders will also contain unwanted and spurious signals, most significantly due to intermodulation products (IMPs) of existing large satcom accesses. Because of the size and low radiated power of the deployed personnel portable satcom terminals their accesses will be comparable in size to unwanted and spurious signals and therefore susceptible to interference. Consequently, the successful operation of any such portable satcom system will depend on detailed and accurate frequency and power planning of the transponder accesses and resulting unwanted signals. A study has concentrated on the generation of active IMPs. By a combination of experimental measurement and modelling, using proprietary software tools for the prediction of frequency and levels of IMPs generated by any element with a nonlinear transfer characteristic, the optimum operating points for the satellite and ground terminal transmitting equipment have been identified. The conclusion of the study is that the operation of a personnel portable satcom system is viable in a satellite transponder which supports a wide variety of access powers provided that appropriate planning processes are implemented to identify and avoid the frequencies of, at least, 3rd and 5th order IMPs