A compact five-port waveguide structure and its application as a three-way power divider

A compact five-port waveguide structure consisting of three rectangular ports, one coaxial port, and one circular waveguide port is proposed. The three rectangular waveguides are uniformly distributed in space at angles of 120°, and the coaxial and circular waveguides are located at the top and bottom, respectively, of the rectangular waveguides. The ideal scattering matrix is derived from the symmetry properties of the structure. If the circular and coaxial ports are matched, then the entire five-port waveguide structure is automatically matched. Two connected inserted coaxial probes, a frustum, and a coaxial transition are used to match the five-port waveguide structure with a relatively wide bandwidth. The theoretical and experimental results are generally consistent with each other. With the circular port connected to the load, the five-port waveguide structure becomes a reciprocal TEM mode-to-three-way TE₁₀ mode power divider. Measurements indicate that from 8 to 9.6 GHz, the return losses at the three rectangular ports and the coaxial port are greater than 20 dB and 17 dB, respectively. The isolation among the three rectangular ports is higher than 20 dB. The amplitude and phase imbalances in the division of power are less than 0.1 dB and 2°, respectively. The volume of the five-port waveguide structure is as small as 1.5 λ × 1.5λ × λ.