Efficient full-wave analysis of large radial-line slot-array antennas loaded with parasitic strips

Radial-line slot-array antennas (RLSA) show some appealing features like low cost, low profile, and good efficiency levels at microwave/millimeter-wave frequencies. The basic RLSA configuration consists of a set of slot antennas arranged on the upper face of a radial line. The line is usually fed by a probe located at its center. The type of polarization obtained from a RLSA depends on the slot arrangement along the radial line. We focus on the linearly polarized RLSA (LPRLSA). This antenna has the slots arranged in concentric rings whose radii are an integer multiple of λ_g/2, λ_g being the wavelength in the radial line. This arrangement and the proper tilting of each slot in the ring produce linear polarization and a directive beam in the broadside direction. Such an initial design presents a poor reflection coefficient due to its critical ring spacing. A matching technique for an LPRLSA was proposed by the authors (Herranz-Herruzo, J.I. et al., 2003 IEEE AP-S Int. Symp. Digest, 2003). It adds parasitic strips supported by a dielectric layer above the radiating slots to improve their matching to the radial guide and consequently minimizing reflections from them. The authors provide a more accurate modelling of this LPRLSA than in the earlier paper, taking into account the presence of the dielectric layer.