A Q-band low-profile waveguide BRF with built-in open-ended λ/2 microstrip resonators

A new and low profile waveguide band-rejection filter (BRF) is proposed. In the waveguide BRF, two dielectric substrates with open-ended λ/2 mictostrip resonators are employed without via holes, and they are inserted in a hollow waveguide. For this simple configuration, this waveguide BRF is low-profile and easy to be fabricated compared with a conventional waveguide BRF, which employs resonant waveguide cavities outside the waveguide and needs costly machining processes. Q-band prototype waveguide BRFs were fabricated using alumina substrates, and the measured results showed high attenuation more than 50 dB at 47 GHz in 2% fractional bandwidth with less variability.