Planar Insert Loaded Triple Band Waveguide Bandpass Filter for X-Band Applications

This paper presents a novel design of second-order triple band waveguide bandpass filter using planar insert technology. A conventional WR-90 rectangular waveguide has two identical inserts inserted into its transverse plane at an optimal spacing of 8.41[Formula: see text]mm. The insert consists of a combination of a double-split square resonator and a single split square resonator with stub. These resonators are used to achieve triple-band bandpass characteristics. The structure allows independent control of three center frequencies, insertion loss, return loss and 3-dB bandwidth. The simulation analysis of the proposed filter is carried out using the CST microwave studio, and its frequency response is compared with its equivalent circuit response. To validate the numerical analysis, the WR-90 waveguide and planar insert are fabricated independently and inserted manually. The dual-pole triple band bandpass characteristic of the manufactured filter, with center frequencies of 8.19, 9.39 and 11.09[Formula: see text]GHz, is shown by the measured data. The complete design process has also been provided, along with a corresponding circuit diagram. The suggested waveguide filter’s performance is evaluated against those found in the literature already.