Filter designers are a special breed and deserve much credit for what they attempt and what they accomplish. Yes, interesting things have been done with digital signal processing (DSP) and advanced digital filter algorithms, but today's column is devoted to old-fashioned analog microwave filters with real resonators, and folks like Dick Snyder, Founder and President of RS Microwave, who bring a real passion to the design of these filters.

Filter designers do not graduate from accredited universities. Rather, they typically learn at the workplace. Watching the frustration of young engineers trying to tune multipole filters during visits to such companies as K & L Microwave and Lorch Microwave made it clear that these were skills not learned from books but from people like Dick Bernstein of K & L and Dick Snyder of RS Microwave. And the progress is slow, cutting passband insertion loss maybe 0.1 dB from design to design. But the quality of newer high-performance microwave filters is testimony to the fine efforts made by many filter designerswith or without help from design softwareeven when they know they are in pursuit of design goals that will only come in small increments.