Two‐GHz hybrid coaxial bandpass filter fabricated by stereolithography 3‐D printing

This brief presents a fourth‐order hybrid coaxial bandpass filter, which is fabricated using Stereolithography 3‐D printing. The filter is designed to operate at a center frequency of 2 GHz, with a bandwidth of 40 MHz, a Chebyshev response and two symmetrical transmission zeros at 1.96 GHz and 2.04 GHz to achieve a better frequency selectivity. Usually in coaxial cavity filter design, the main‐line couplings and cross couplings are realized using coupling irises or probes. However, in the filter presented here, the main‐line couplings between coaxial resonators and input/output coupling are realized using Printed Circuit Board (PCB) lines instead. This novel idea allows different topologies to be designed easily by altering the PCB layout. It also allows multiple cross couplings to be included in the PCB layout for different filter topologies. In addition, the quality factor of each of the coaxial resonators in the filter is increased by introducing base rounding in the resonator. The filter was tested, and the measurement result of the filter shows very good agreement with simulated result without tuning, which indicates the accuracy of the fabrication process.