High Q-factor compact filters with wide-band spurious rejection

Abstract

A stepped-impedance configuration for coaxial resonators is employed to realize filters in the L-, S-, and C-bands exhibiting a wide spurious-free range. The geometry of a single rod resonator is optimized, by enlarging its top head, in order to maximize the ratio between the frequency of the first higher-order mode and that of the fundamental mode. This leads to the design of a very compact filter with high Q-factors and wide spurious-free bands, up to nearly 5 times the center frequency. To prove the effectiveness of the approach, a sixth-order filter has been designed and manufactured; the comparison between the full-wave simulations and the measurement show excellent agreement.