Digital antenna array combiner and divider using FPGAs

Abstract

The first instance of phased array transmission was demonstrated by Nobel laureate, Karl Ferdinand Braun in 1905. Through his work he demonstrated the enhanced transmission of radio waves in a singular direction. Further work using phased arrays was accomplished by Nobel laureate Luis Alvarez, his work made use of the phased array transmission in a readily steerable radar system for a “ground controlled approach”. Presently, phased arrays have found application in fields such as space probe communication, radar, mobile telephony, and broadcasting. With regards to space, the MESSENGER spacecraft was the first deep space probe mission to make use of a phased array antenna for communications. In the ASTREA project, phased arrays are being considered for the ground segment to permit fast scanning of the sky, followed by simultaneous tracking of multiple satellites. A phased array would simplify the mechanical arrangement. For the development of the UoMBSat1, Malta’s first satellite, an accurate multichannel ultra-high-frequency front-end was designed. Such a system employed precision Radio Frequency electronics de/modulators, phase shifters, up and down converters and amplifiers together with significant RF PCB design, all under the supervision of a suitable embedded computer system. Combining the many individual antenna feeds using fixed analogue circuits was deemed to be overly restrictive for the purpose of algorithmically combining the selected antenna feeds to recreate the transmitted signal using the phased array antenna principle. Following the work done on this project, a modular digital antenna array combiner and divider system was developed in order to overcome the inherent limitations of the analogue design. Making use of an array of ADCs and an array of DACs, digitised signals were fed into and out from a central FPGA unit which was used in order to suitably combine and divide the incoming and outgoing signals, respectively, making use of an Ethernet port for external communications. Compatibility with previous project work carried out for the ASTREA project was also ensured.