Coupled resonator distributed-element circuits for monolithic crystal filters

The distributed-element equivalent circuit of the monolithic crystal filter is useful for analyzing the characteristics of the filter, but it is not suitable for physical interpretation of the filter behavior. A more refined coupled resonator circuit is derived by application of a sequence of transformations of the original distributed-element circuit. The frequency dependences of the circuit elements are discussed and some approximations of the equivalent circuits are introduced based on the discussion. Moderately wideband filters are designed using an approximate circuit.<>