Analysis and design of a W-band circular polarized feed horn with built-in polarizer for low f/D offset-reflector antenna

A novel low-axial-ratio W-band left-hand-circularly-polarized (LHCP) cylindrical waveguide feed horn antenna is described using a built-in polarizer. The built-in polarizer section of the horn consisted of nine pairs of circular cavities to generate circular polarization, eliminating the need for an external orthomode transducer or a complex septum. The polarizer was analyzed using the differential dispersion effect from the cavities along the length of the waveguide. The antenna had impedance matching (|S11| < −15 dB) and an axial ratio below 1.2 dB from 79.5 GHz to 88 GHz. The horn antenna was then used as a feed source to illuminate an offset parabolic reflector of 10 cm diameter and a low f/D = 0.25. The feed-reflector assembly was also integrated inside a 1U volume of a 6U-CubeSat chassis. The radiation performance was analyzed using the Multilevel Fast Multipole Method (MLFMM) along with the Method of Moments (MoM) in TICRA GRASP. The measurement of the prototyped feed horn and the offset parabolic reflector antenna validated the analysis and simulation results.