Suppression of Cavity Resonant Coupling by L-Shaped Metal Plate on Microwave Module Lid

This article proposes and implements a novel technique for high spatial isolation that includes the placement of L-shaped metal-plate resonator shunt open-circuited stubs as a band-rejection filter on the lid of a microwave/radio frequency (RF) module. The low-cost, lightweight resonators are realized using a thin metal plate, which is patterned, with high design flexibility, and bent. This article demonstrates that the resonator is equivalent to a quarter-wavelength shunt open-circuited stub in a parallel-plate waveguide, which effectively suppresses the cavity resonant mode in the housed microwave/RF module. In addition, the robust design of the bent section and the determination of the resonator size, from the common ground to the open-circuited end, are presented. The suppression of the coupling level via cavity resonance is demonstrated by the X-band measurements, where the suppressed fractional bandwidth is 46.8% of -63 dB, which is the highest reduction level achieved with an absorber model in this frequency band. These measurement results are in good agreement with the theoretical and electromagnetic simulation results.