Wideband Dielectric Substrate-Loaded Cavity Filter

This article presents the design and implementation of a novel structure for wideband dielectric substrate (DS)-based filters. The cavity of the filter is separated into two thin DSs, a metal frame for holding the DSs, and two metal covers. The filter is compact in size and ideal for integration with antennas because of its relatively thin profile. Since it uses separated DSs attached to the two sides of the metal frame, the input-output probe can be placed in the middle of the cavity, leading to a significant increase in the input-output coupling compared to conventional dielectric resonator filters. In addition, the filter structure lends itself to realizing relatively large values of inter-resonator coupling. A five-pole Chebyshev filter with a fractional bandwidth of 9.6%, a four-pole filter having two transmission zeros with a fractional bandwidth of 9%, and a three-pole filter with a fractional bandwidth of 13% have been designed, fabricated, and tested. The filter structure promises to be useful in sub-6-GHz 5G applications that require the use of low-cost, miniature, high-$Q$ wideband filters with a thin profile.