MODELING OF RING-SLOT-ELEMENT FLOQUET CELL FOR REFLECTARRAY ANTENNAS

Abstract

The ring-slot-element cell for reflectarray antennas is investigated. The mathematical model of the unit cell is based on the integral equation that is solved by the moment method with the use of the spectral domain Green’s function. Coaxial-line higher modes expressed in terms of cylindrical functions are used as the basis for magnet-current representation. It is shown that “stricken” frequencies at which resonance modes occur are an inherent part of slot elements. These frequencies are determined by the Green’s function poles. Moreover, the lowest resonance mode may occur in the operating band under certain conditions. Reflection-phase dependencies on the ring-slot size are provided, demonstrating that at “stricken” frequencies the unit cell does not operate properly. Field plots are presented, which show that the resonance-mode field distribution on the ring slot is significantly different from the normal-mode field distribution. It is found that the “stricken” frequencies might be shifted beyond the operating band by means of thorough selection of unit-cell geometric parameters.