A Dual-Band Waveguide Bandpass Filter with Adjustable Transmission Zeros

Abstract

This paper presents a planar insert-loaded compact, dual-pole, dual-band, waveguide bandpass filter with adjustable multiple transmission zeros. Two identical inserts are placed on the transverse plane of a standard WR-90 waveguide at 8.41[Formula: see text]mm distance to achieve the filter characteristics. The insert consists of a stub-loaded C-shaped resonator and two asymmetric slot resonators. Two stub-loaded C-shaped resonators have been used to achieve dual-pole, dual-band response whereas the asymmetric slot pairs have been used to introduce transmission zeros. The structure allows independent control of the center frequencies of the passbands and transmission zeros, which is useful to control the rejection level of out-of-band signals without disturbing the center frequency. Measured result shows a dual-pole, dual-band, bandpass response with center frequencies at 8.81[Formula: see text]GHz and 10.9[Formula: see text]GHz, the respective 3[Formula: see text]dB bandwidths of 0.276[Formula: see text]GHz and 0.398[Formula: see text]GHz and transmission zeros at 8.02, 8.5, 9.46, 10.13, 11.53 and 12 GHz.