Design of Millimeter-Wave Resonant Cavity and Filter Using 3-D Substrate-Integrated Circular Waveguide

In this letter, a millimeter-wave filter constructed by 3-D substrate-integrated circular waveguide (SICW) resonant cavity is numerically and experimentally investigated. The 3-D SICW with the sidewall structure of via fences and circular pads is fully integrated in a low-temperature co-fired ceramic (LTCC) substrate. The fundamental mode (quasi-TE
₁₁₁
mode) of 3-D SICW cavity and the TE
₁₃₀
, TE
₁₄₀
modes of overmoded substrate-integrated waveguide cavity are adopted to form the fourth order bandpass filter. Compared with the traditional planar structures, the spatial configuration can enhance the microwave performance of the device and brings more flexibility for the system design. The measurements of the fabricated filter show that the insertion loss is less than 1.9 dB at 174 GHz and the relative bandwidth is about 13.8%, which is in good agreement with electromagnetic simulations.