External mutual coupling between inclined slots cut in the narrow wall of a rectangular waveguide

In this paper, a modeling technique to calculate the external mutual coupling between inclined slots cut in the narrow wall of a rectangular waveguide is presented. A voltage source is inserted across the center of the first slot opening to excite one of them and a monitor on the second one captures the voltage. To eliminate the internal coupling between slots, an absorbing slab is inserted between two slots in the waveguide. The coupling between two slots cut in the narrow wall of a WR-284 waveguide is simulated at 3 GHz and the effect of waveguide wall thickness, slot width, slot angle, and spacing between slots is investigated. Based on our numerical results, a mathematical expression to approximate the external coupling is obtained. In order to verify the results experimentally, a real thin absorber is fabricated and placed between two slots, which are realized in a WR-284 waveguide. Finally, the coupling between the two slots is measured in terms of S-parameters and then converted into a coupling factor. The measured results are shown to have an acceptable agreement compared to the simulation results. The coupling from the simulation is 0.45 at 3 GHz, while this value occurs at 3.1 GHz in the measurement.