An Air-Filled Cavity Bandpass Filter Processed by Microstructure Electrochemical Fabrication With Self-Supported GSG Feeding Probe

In this letter, a bandpass filter (BPF) operating at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> band is presented by utilizing microstructure electrochemical fabrication (MEFAB) technology. The BPF is made up of two coupled air-filled rectangular cavities which are purposely developed for a second-order Chebyshev response. Inside each cavity, half-wavelength short-circuited stubs are attached to support the vertical ground-signal–ground (GSG) feeding probes. Naturally, by means of adjusting the relative position of two feeding probes, extra transmission zeros (TZs) can be introduced to improve the out-of-band rejection. Finally, a practical air-cavity filter is fabricated for validation. The measured results show good agreement with the simulated ones, exhibiting a low in-band insertion loss of about 0.66 dB and the 3-dB fractional bandwidth (FBW) of 3.6% with the central frequency at 94 GHz.