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This work proposes a new methodology for widening the bandwidth of a reflectarray (RA) antenna. The narrow impedance of the conventional dielectric RA can be effectively widened on the basis of the gradual impedance matching principle. A multilayer element can realize impedance matching to free space by suitably choosing the different diameters in different layers of the drilled air-vias. Besides, a series of air-vias with varying diameters changes the resonance frequencies and partially overlapped bandwidth between one another, which results in widening the bandwidth. To validate the wideband RA antenna design, a circular RA prototype with diameter of 96 mm is simulated, fabricated, and measured. The measured RA exhibits an improved 1-dB gain bandwidth of 18.4%. A peak gain of 25.18 dBi with maximum aperture efficiency of 52.18% is obtained. The significant experimental performance improvement confirms that bandwidth can be efficiently broadened by introducing the tapered scheme.

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 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 analytical approximation method using conformal mapping to determine the effective permittivity (ε r,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 simulations performed in 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 47.25% and 57.85% in the receiving and transmitting bands, respectively.