Theory of Polarization-Selective Coupling and Its Application to Design of Planar Orthomode Transducers

With the rapid and continuous development of new generations of wireless technologies and networks, exploring the underutilized millimeter-wave (mm-wave) band becomes inescapable. Polarization diversity has been an essential factor in the performance and capacity enhancement of various wireless systems including cellular networks. Accordingly, the design and development of dual-polarized antenna feeding structures in the mm-wave band is a must. In this paper, a compact wideband orthomode transducer design in the Ka-band is proposed and explored. The proposed architecture and design are based on a forward mode polarization-selective coupling strategy between two unconventional waveguides. These special waveguides are a combination between two types of guiding structure, namely, nonradiative dielectric waveguide and substrate-integrated waveguide. Polarization-selective coupling can be achieved in these structures due to different mechanisms by which orthogonally oriented modes are guided. Theoretical coupling levels of 0 dB are possible in the designed structure. Analytical analysis and design steps are given in detail. This analysis facilitates a complete control on the single-mode operation for each polarization. This control, besides the structure being planar, represents the main advantages of the proposed structure. Finally, a prototype is implemented and measured where an excellent agreement is achieved with the simulation results.