Highly Polarized, Directive Radiation From a Fabry-Perot Cavity Leaky-Wave Antenna Based on a Metal Strip Grating

A metal strip grating (MSG) above a ground plane is studied as a Fabry-Perot-cavity antenna excited by a horizontal electric dipole through a rigorous moment-method approach. Azimuthally omnidirectional radiation is shown to be produced, in the form of very directive pencil beams pointing at broadside or of conical scanned beams, with excellent polarization purity. An approximate homogenized model of the antenna based on a transverse-equivalent-network representation shows that the particular temporally and spatially dispersive equivalent susceptance of the MSG accounts for the observed peculiar radiation properties. Furthermore, it shows that the wavenumbers of the modes supported by the structure are independent of their direction of propagation, thus providing an explanation of the above-mentioned properties in terms of cylindrical leaky waves propagating omnidirectionally along the structure. We also show that this antenna, despite its high directivity, essentially has the same polarization properties of a dipole in free space.