Dualband horn with inherent isolation between its transmit and receive ports

A dualband antenna operating in the 4 GHz and 6 GHz frequency bands is developed using a coaxial waveguide configuration. The 6 GHz part of the antenna is contained within the inside conductor of the coaxial guide, which is homogeneously filled with a dielectric rod that is extended beyond the circular aperture. The 4 GHz part of the antenna, on the other hand, is the coaxial waveguide itself, the dimensions of which are optimised for a symmetric radiation pattern. This dimensional optimisation was initially achieved numerically to select proper radii of the inner and outer conductors. The final optimisation was carried out experimentally using a quarter-wavelength choke flange to further equalise its E- H-plane patterns. To optimise the radiation patterns at 6 GHz, the exposed length of the dielectric rod was adjusted experimentally. An additional improvement in the pattern symmetry is also obtained using a small iris at the coaxial waveguide aperture. The performance of the unit as a dualband feed for a paraboloid reflector antenna is computed, and the isolation between the two frequency bands is discussed.