Design of Optimized Selective Quasi-Elliptic Filters

Abstract

A new technique is presented for the derivation of the quasi-elliptic function. Based on maximizing the band-edge selectivity (BES) of elliptic filters without increasing filter order, the equal ripple parameter of quasi-elliptic function can be obtained when the BES of the elliptic function and quasi-elliptic function are the same. The exact quasi-elliptic function not only keeps the bandwidth invariable, but effectively improves the selectivity. Finally, a novel quasi-elliptic microstrip filter composed of four spiral stepped-impedance resonators (SIR) is designed. The simulated and measured results show that the filter has not only smaller size, but also a wider upper stopband.