A 128-kHz mechanical channel filter with finite-frequency attenuation poles

The paper describes the design and manufacture of a miniaturized 128-kHz pole-type mechanical channel filter for FDM communication systems. By introducing a new phase inversion structure to realize the finite attenuation poles, and by minimizing sensitivity in the circuit design, we have designed and manufactured a miniaturized high-performance mechanical channel filter. The filter volume is 10.7 cm³, which is about ⅙ that of conventional LC channel filters. The passband response satisfies the 1/20 CCITT Recommendation. With this filter, we have developed a channel modem compact enough to mount 900 channel units per standard bay. Manufacturing steps and material characteristics are described in some detail. We also briefly discuss some future considerations in further miniaturizing the channel filter.