The Development of a Surface Mount Hybrid if Section Using Low Loss SAW Filters

Abstract

A thick film hybrid circuit incorporating two low loss group-type unidirectional transducer (GUDT) SAW filters was developed for use in a receiver IF section centered at 310.7 MHz. The two filters were cascaded with a preamp and a buffer amplifier on one hybrid to achieve IF gain and filtering. The low loss GUDT SAW filter was designed using a Hamming apodization. Performance, assembly and reliability were enhanced by taking a surface mount hybrid approach. A leadless chip carrier package for the SAW device was designed and optimized for low loss and high out of band rejection. Surface mount chip inductors were evaluated and optimized for match and insertion loss. A high temperature hermetic seal process was developed for the custom SAW package and extensive environmental tests were performed on both the packaged SAW and the fully assembled hybrid to insure a high degree of reliability. Packaged filter losses were less than 6.5 dB per filter. Rejection at the image frequency for the hybrid IF section exceeded 90 dBc. Typical peak-to-peak passband ripple was .2 dB.