Design of a polarization-diverse planar leaky-wave antenna for broadside radiation

The design of a K-band radial leaky-wave antenna is presented for polarization diversity applications. The antenna structure is constituted by an annular, radially periodic, and metallic strip grating printed on top of a single-layer grounded dielectric slab. The integrated feeding system is defined by a 2 × 2 array of planar slot sources for cylindrical surface-wave excitation. By the addition of the grating, the surface wave is perturbed and enables cylindrical leaky-wave radiation by means of a fast $n =-1$ space harmonic, whose behavior is characterized through a full-wave dispersive analysis. By proper phasing and spacing of the four independent TM feeds, positioned close to the center of the annular grating and on the ground plane, we demonstrate the possibility of radiating directive broadside beams offering linear, left-or right-handed circularly polarized radiation, and sum and delta patterns. Thus, we propose an original solution to flexibly control the polarization of a high-gain beam by means of a simple and low-cost feeding system, made by the minimum number of integrated array sources. To accurately assess the antenna features and performance, the role of a zeroth- A nd first-order cylindrical leaky waves propagating along the antenna aperture is also discussed. The proposed antenna design may be of interest for direction-of-arrival estimation by means of monopulse radars, as well as for a wide class of applications where flexible control of the polarization is desired, such as satellite and terrestrial point-to-point communication systems and earth observation.