MMIC compatible bandpass filter design. A survey of applicable techniques

Advances in MMICs now allow engineers to design multifunction, complex circuitry in small amounts of space that were unattainable a few years ago. Broadband, chip level receiver front ends are becoming a realistic alternative to discrete devices in many applications. Despite the fact that MMIC amplifiers, switches and mixers are reducing the size of the active circuitry required, the true size driver of a MMIC receiver are the necessary filters. With discrete circuitry, filters can take up to five times the area of the active circuitry. This statistic is even more lopsided when the active circuit is a MMIC chip 0.01 in2 in size. For engineers to benefit from the size reductions engendered by using MMICs, filter design techniques must be exploited in a manner that is compatible with the reduction in size of active components allowed by MMICs. This paper examines the techniques available to build compact bandpass filters that are size compatible with MMICs. Coupled-line, interdigital and hairpin bandpass filters are described, as well as the various permutations of each. This paper provides engineers with the basic tools needed to design MMIC-compatible bandpass filters, and systems designers with an insight into the true size savings that the introduction of MMICs provide.