Wide bandwidth SAW filters for satellite-borne signal processing

Quartz SAW filters have been used in satellite communication systems for some years because they offer a well defined filter function combined with low mass, low cost, stable operation over temperature and high reliability. Recently the trend has been towards systems that can carry much larger amounts of data. These often require bandwidths not achievable with quartz. This paper therefore discusses the design and performance of lithium niobate SAW filters for space applications. Highly refined design software and electron-beam lithography techniques produce SAW filters which show excellent agreement with predictions. This allows low amplitude and phase ripple to be achieved in practice, together with excellent reproducibility between devices. The design method and manufacturing process are briefly summarized and the packaging and matching methods described. Work on SAW filters up to the S-band range is discussed. At these frequencies packaging and tuning become even more critical in terms of their effect upon device reproducibility and general filter performance, particularly the achievable stopband levels.