Compact Tune-Free Dual-Band Filter Using Metal Insert

This paper presents a compact dual-band (DB) filter based on metal insert technology. It consists of three parts and utilizes a parallel connection of two single-band (SB) filters. The two filter case parts are equipped with waveguide (WG) interfaces and establish two isolated channels for SB filters when connected. The metal insert supports two arrays of U-shaped slot-line resonators - when loaded into their designated channels, these form two SB filters. To improve selectivity of the SB filters, each channel is complemented with a ridge that enables control of cross-coupling. This allows for the implementation and control of one transmission zero (TZ) above the passband in each SB filter.