ABSTRACT
Mechanical filters have been manufactured since the early 1950s primarily for use in high-performance HF radios and frequency-division multiplex (FDM) telephone equipment. The popularity of FDM mechanical filters was because of their high performance, small size, and reliability. The monolithic crystal filter could match the mechanical filter for size, cost, and reliability, but in the case of realizing filters that meet international specifications, only the mechanical filter and lumped element crystal filters could meet those specifications. Mechanical filters are designed with various transducers, resonators, means of mechanical coupling, and spatial configurations. This chapter discusses the principles of operation of the elements that compose a mechanical filter. It describes the filtering function of each of the components of the mechanical filter. The chapter focuses on the unique features of mechanical filters regarding their use in electronic equipment. It looks at the mechanical filter and its relationship with surrounding electrical circuits.
