Multi-conductor coaxial cavity resonators for miniaturization of UHF bandpass filters

Abstract

In this paper, we present the compact bandpass cavity filters for UHF range. We investigate the properties of coaxial resonators with various numbers of tubular posts from one to four. We show that the resonant frequency can be four times smaller for the four-post resonator in comparison with the single post resonator with the same cavity dimensions. We synthesized and manufactured fifth-order bandpass cavity filter on four-post coaxial resonators for the 690–806 MHz frequency range with 20-dB return loss. The filter dimensions were 30 mm × 44 mm × 127 mm. We also synthesized and manufactured the fifth-order bandpass cavity filter on four-post coaxial resonators with inductive and capacitive cross-coupling between first and fifth resonators to provide transmission zeros in amplitude–frequency characteristic in lower- and upper-frequency band, respectively. Comparison with the standard double-post coaxial cavity filters demonstrates more than 30% volume reduction with similar transmission characteristics.