A Novel Circularly Polarized Filtering Reflectarray by Manipulating the Multimode Reflective Phase of Orthogonal Polarizations

This article presents a novel design methodology for circularly polarized (CP) filtering reflectarray (RA). Unlike conventional filtering techniques based on magnitude response, the proposed filtering RA solely manipulates the phase responses of the reflected wave under the total reflection condition. An isosceles triangle patch radiator loaded with slots is employed as the unit cell. Two sets of orthogonal resonant modes of the triangular patch are exploited to produce a phase difference between the u- and v-polarized components. By adopting slot loading, the first- and third-order resonant states are induced in the two orthogonal directions. Next, the phase difference is fully controlled by adjusting the slope of the reflection phase. In the passband, the phase difference is maintained at 180°, while outside the band, it rapidly rolls down (up) to 0° (360°), enabling steep band edges. Finally, a CP filtering RA using the optimized element is constructed for the first time, which verifies the validity of the proposed method. The fabricated RA exhibits satisfactory performance, including a 3-dB gain bandwidth of 25.7%, 3-dB axial ratio (AR) bandwidth of 29.8%, and the out-of-band suppression levels of 33.5 dB (22.8 dB) in the low- (high) frequency band.