Hexagonal Waveguide Based Circularly Polarized Horn Antennas for Sub-mm-Wave/Terahertz Band

In this paper, we introduce a class of circularly polarized horns realizable at sub-mm-wave and terahertz frequencies. The proposed designs exploit differential dispersion in hexagonal waveguides (a birefringencelike effect), which allows a linear to circular polarization conversion. These can be fabricated for terahertz applications, as they do not require waveguide partitions or elaborate waveguide assemblies needed in existing designs. In this paper, we discuss the theory of hexagonal waveguides, develop analytical design procedures, and show measurement results for a fabricated prototype. The prototype is developed for WR-8 band (90-140 GHz) operation, showing a midband gain of 18 dBi and 3 dB axial-ratio bandwidth of 37%.