This paper presents an analytical method for designing a high-efficiency frequency selective surface FSS-sandwiched dual-band circularly polarized reflectarray antenna. Results are obtained using the Computer Simulation Technology Microwave Studio (CST MWS). The antenna is designed to operate within the receiving (19.6-21.2 GHz) and transmitting (29.4-31 GHz) bands while sharing the same unit and aperture. A double-layer FSS is loaded between the upper and lower antennas to suppress mutual coupling. An analytic approximation method using conformal mapping to determine the effective permittivity (εr, eff) is observed. The transmission and reflection coefficients of the proposed FSS are synthesized using the transmission line approach. The comprehensive analyzed results obtained are compared with results obtained from the simulations performed in the CST MWS. To validate the performance of the proposed FSS-backed element configuration, a 20/30-GHz dual-band circularly polarized reflectarray with a 90-mm aperture is designed. The simulated gains are 23.3 dBi at 20 GHz and 27.7 dBi at 30 GHz with aperture efficiencies exceeding 45.25% and 57.85% in the receiving and transmitting bands, respectively.
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