The case for an all Digital military satellite communications Earth terminal

Abstract

This paper considers the case for using a ¿digital IF¿ (intermediate format) as an alternative to conventional analog IF (intermediate frequency) for distributing satellite uplink and downlink signals within modern high-capacity military satellite communications Earth terminals. ¿Digital IF¿ is defined as a purely digital format enabled by digital I & Q (in-phase and quadrature) sampling for the conversion of signals to and from their native RF media. Digital IF is suitable for the deconstruction, transport and reconstruction of RF waveforms in general and of RF modulation waveforms in particular. This paper first considers conventional Earth terminal architectures, analyzing their strengths and weaknesses by evaluating them against a set of common merit criteria. This paper continues by introducing fundamental digital IF concepts necessary for understanding the configuration, features and value of the most advantageous digital IF terminal architecture. A high level digital IF terminal architecture is then presented, with a description of its relevant features and an analysis against the same common merit criteria. Digital IF, if done properly, is shown capable of cost-effectively meeting today's Earth terminal design challenges such as EIRP noise, scalability, terminal control and terminal testing. Digital IF lends itself to performance improvements over conventional analog IF systems throughout the transmit and receive signal chains. Digital IF also lends itself to COTS implementation with existing technology. All this is presently possible while also reducing cost and complexity in all phases of terminal life cycle, from design and development to setup, operations and maintenance.