Matching of E-plane waveguide 5-port with polygonal junction cavity

An ideal network for making 6-port measurements can be built of a perfect directional coupler and a matched reciprocal five port. In the millimeter region, waveguides are the natural medium for measurement equipment. In this connection it has been observed that E-plane coupled 5-port possesses certain advantages as against the H-plane one, and that the return loss of the junction can be reduced by choosing the diameter of the circular connecting region. In this work, we consider a star junction of E-plane coupled waveguides whose coupling region is bounded by the waveguides apertures and walls of truncated reentering angles. The structure is studied at the electrodynamics level using the domain-product technique. Numerical analysis of the unit is performed for the operating range of the guide. Scattering characteristics (subject to the geometry and frequency parameter) are examined. It has been determined that the matching of the 5-port considered can be appreciably improved in a broad frequency range by fitting the altitude of the truncated parts of the reentering angles. The optimal geometry ensuring the best return loss has been found. The data obtained are useful for developing both the actual 5-ports of rectangular waveguides and also the junctions of other transmission lines whose analysis is based on the waveguide models.