Rectangular to Cylindrical Waveguide Transducer

Model

The geometry of a rectangular to cylindrical waveguide transducer couples the dominant modes of rectangular waveguide (TE₁₀) and cylindrical waveguide (TE₁₁). The structure consists of a series of E- and H-plane truncated cylindrical waveguides, three H-plane steps with rectangular cross section and a cylindrical waveguide. In other words, overall structure has three types of cross sections inlcuding octagonal cross sections with rounded corners. A waveguide source with T E₁₀ mode excitation is used to feed the transducer.

Simulation

Broadband simulation is run to compute the reflection coefficient of the transducer. The maximum grid step is 7.5mm and the minimum grid step is 0.3mm in the frequency region of interest. The UPML absorbing boundary conditions are used to truncate the domain.

Results

The second figure shows simulated reflection coeficient of the structure in the frequency range of interets. Broadband transition from rectangular to circular waveguide is achieved. E- and H-fields at different cross sections are recorded and presented in the bottom figures. As expected, rectangular waveguide TE₁₀ mode and cylindrical waveguide TE₁₁ modes are obtained.

Ref. Fritz Arndt, et. al., Automated Design of Waveguide Components using Hybrid Mode-Matching/Numerical EM-Building Blocks in Optimization-Oriented CAD Frame-works - State-of-the-Art and Recent Advances. IEEE Tran. Microwave Theory and Tech., vol. 45, no. 5, May 1997.