Broadband True-Time-Delay Circularly Polarized Reflectarray With Linearly Polarized Feed

We introduce a new technique for designing low-profile circularly polarized reflectarray antennas with ultrawideband, true-time-delay responses. The proposed reflectarray uses the unit cells of ground-plane-backed, anisotropic miniaturized-element frequency selective surfaces as its spatial time-delay units (TDUs). Each TDU is composed of a stack of nonresonant rectangular-shaped capacitive patches featuring asymmetric gap spacings and separated from one another by thin dielectric substrates. The TDUs are designed to provide a reflection phase difference of 90° between the horizontal and vertical components of the incident wave over a wide bandwidth. This way, a linearly polarized incident field is converted to a circularly polarized radiated wave. A device prototype that operates at X-band is designed, fabricated, and measured. Measurement results demonstrated that the reflectarray antenna provides a gain of 23.7 dB with variations less than 3 dB within the 8-12 GHz operating frequency range or equivalently 40% bandwidth. Time-domain measurement results demonstrate the suitability of this device for operation with wideband pulses. The reflectarray is also used in a multibeam antenna and it is shown that the structure provides a wide-angle scanning performance with a field of view of ±45°.