Electromagnetic coupling mechanism to a conducting strip through a narrow slit in a parallel-plate waveguide

The problem of electromagnetic coupling to a conducting strip through a narrow slit in a parallel-plate waveguide (PPW) is reconsidered with an emphasis on the radiative coupling mechanism. Two different types of coupling are discussed: cavity and parasitic. The maximum coupled power in both cases is observed to be almost the maximum available power from the slit (half of the incident power in the PPW), even though the two types of coupling are quite different from each other in their equivalent circuit representation or coupling mechanism. The similarity between the problem of cavity-type coupling and the previously reported transmission resonance problem through a narrow slit in thick screens is also described in connection with the aperture-body resonance phenomenon.