A dynamic efficient bias scheme improves SSPA performance in aeronautical satellite communication systems

The advent of satellite services and airborne equipment are revolutionising voice and data communications on civil aircraft. Airborne Satcom offers advantages in terms of aircraft accessibility anywhere in the world for both air travel services and operational control as well as a more reliable service available to passengers. The Satcom equipment installed on aircraft, (Air Earth Station, AES) is divided into three sub-systems; avionics, antenna subsystem and interfacing cabin telecommunication equipment. The avionics hardware comprises three units which are the Satellite Date Unit (SDU), the Radio Frequency Unit (RFU) and the High Power Amplifier (HPA). The need for high quality communications places a demand on the reliability and performance of the airborne hardware. All airborne equipment must comply with the Inmarsat requirements to permit access to satellite and also conform to the stringent performance and interoperability standards defined by the Airlines Electronic Engineering Committee, ARINC 741. In particular the AES EIRP and intermodulation distortion are some of parameters from the satellite system aspect, whilst the power dissipation and weight are paramount to the ARINC 741 specification. This paper describes the specification of the HPA, the design considerations and how a Dynamic Efficient Bias System (DEBS) of transistor bias enables an HPA to meet these requirements