Cross-Aperture Waveguide Coupler

Model

The coupling between waveguides has an important role in many applications such as power dividers, combiners, directional couplers, filters, etc. The coupling can be achieved through various shapes, namely, rectangular-, circular- and cross-apertures. In this example, a narrow-wall cross-aperture waveguide coupler is investigated. These types of couplers are frequently used in high-power applications. The first figure shows the geometry of a Ku-band narrow-wall coupler (using WR62 waveguide). The waveguide ports of the structure are modeled by using Rectangular Waveguide tool with TE₁₀ mode excitations.

Simulation

A template broadband simulation is prepared with a maximum grid step of 0.50mm and a minimum grid step of 0.01m in the frequency region of interest in order to model the very thin metallic wall with the coupling aperture accurately. The UPML absorbing and PEC boundary conditions are used to truncate the domain.

Results

he S-parameter Evaluation tool is used to extract the four-port S-parameters of the structure after simulations finished. The simulated performance of the coupler is presented in the middle figure. A flat coupling of -5 dB is achieved between ports 1 and 3 over a wide band and the isolation is bettern than -33 dB. The E-field distribution at 13.50 GHz is shown in bottom figure.

Ref. Z. Jiang, et. al, Full-Wave Analysis of Cross-Aperture Waveguide Couplers, IEEE Microwave Wireless Compon. Lett., vol. 12, no. 7, July 2002.