A microstrip-fed W-band waveguide filter using H-shaped coupling slots

A novel microstrip-fed waveguide filter is proposed in this letter. The H-shaped slots on the back side of the substrate are utilized to connect waveguide cavities and the microstrip circuit. Simultaneously, they are used to realize external coupling of the filter. This design can effectively reduce the size of the circuit and avoid extra transition loss, which is good for system integration. A fifth-order filter at W-band based on H-shaped coupling slots have been fabricated and measured. Good agreements between the simulated and measured results are observed.