Microwave Planar Varactor Tuned Bandpass Filters: Historical Overview

Abstract

This paper overviews the history of a class of varactor tuned bandpass filters. Since the miniaturization as well as the high performance of the tunable bandpass filters is required for the next generation mobile communication systems, the discussion is focused on the various planar type tunable filters including active configurations. Brief design concepts of various tunable filter configurations as well as their characteristics are discussed.