Hybrid waveguide/coaxial feeder for dual-pol Fabry-Perot cavity antennas radiating omnidirectional TM/TE waves

A hybrid waveguide/coaxial transverse magnetic (TM)/transverse electric (TE) launcher is proposed as a feeder for planar Fabry-Perot (FP) cavity antennas radiating omnidirectional beams. The structure is based on a pair of nested coaxial cables. The inner coax (TM launcher) operates on the standard TEM mode and feeds a vertical probe protruding into the antenna cavity through the ground plane. The outer coax (TE launcher) operates on the TE01 mode excited by an aperture-coupled rectangular-waveguide feeding network. Geometrical symmetry ensures high isolation between the TM and TE input ports, which can be alternatively excited to achieve dualpol operation with either horizontal or vertical linearly-polarised far field. Good impedance matching and omnidirectional dual-pol radiative features are demonstrated for an FP cavity antenna operating at 16 GHz and based on a thin periodic metal partially-reflecting surface.