Practical Considerations in the Design of Lossy Cavity Filters
Lossy filter synthesis is known to minimize the effects of finite resonator Q in filters. In this synthesis approach, the transfer functions are proportional to those attainable with a lossless filter so that, despite having finite resonator Q, the scaled-down transfer functions maintain the properties of insertion loss flatness and selectivity of a lossless filter at the expense of some frequency-independent insertion loss. This paper describes the detailed design, fabrication and measurement of a lossy C band cavity filter having a reflective behavior in the stop-band, including synthesis procedure, homogeneization of the requirements in Q among the filter resonator, simulation procedures and measured performance. The filter compares favorably with designs using classical (lossless) techniques having the same resonator Qs.