Modal Analysis and Propagation Characteristics of Leaky Waves on a 2-D Periodic Leaky-Wave Antenna

A 2-D periodic leaky-wave antenna is studied to examine the mechanism of beam formation from leaky-wave modes and the properties of the leaky-wave modes. The structure consists of a grounded dielectric slab with a periodic arrangement of narrow rectangular patches of metal on the upper surface of the dielectric, excited by a slot in the ground plane. The dimensions of the unit cell and the size of the patches determine the phase constant and the attenuation (leakage) constant of the leaky modes supported by the structure. The narrow beam that is formed is found to be due to an aperture distribution mainly consisting of the radiating space harmonics (Floquet waves) of two different leaky modes, one determining the E-plane behavior and one determining the H-plane behavior. The beamwidth is larger in the H-plane than in the E-plane due to the larger leakage constant of the H-plane mode. It is found that the two leaky modes also have different field distributions, in addition to having very different leakage constants.