Design of Triple-Band Bandpass Filter Using Inverted Microstrip Ridge Gap Waveguide for Ka-Band Applications

In this paper, a triple-band inverted microstrip Ridge Gap Waveguide (RGW) filter is designed using a double octagonal ring resonator (RR) with corner cuts. The design parameters are optimized using the Finite Difference Time Domain (FDTD) method (CST studio simulator). The filter is implemented on Rogers RT5880 (ε
r
=2.2, thickness of 0.787 mm and loss tangent tanδ = 0.0009). It is selected because of its low losses at high frequencies. The proposed design operates within the Ka frequency band (27–40 GHz), with resonance frequencies of 32.32 GHz, 35.75 GHz, and 38.12 GHz. The return losses reach levels of about −35 dB, −25 dB, and −32 dB for the three bands, respectively. The filter exhibits a low insertion losses of about 0.6 dB, 1.1 dB, and 0.9 dB at the three resonant frequencies, respectively.