Ultra-Wideband, True-Time-Delay Reflectarray Antennas Using Ground-Plane-Backed, Miniaturized-Element Frequency Selective Surfaces

We introduce a new method for designing low-profile reflectarray antennas with broadband, true-time-delay (TTD) responses. Such structures are composed of numerous reflective spatial time-delay units distributed over a planar surface. Each spatial time-delay unit is a unit cell of a ground-plane-backed miniaturized-element frequency selective surface (MEFSS) composed of nonresonant elements. Each element is a lowpass type MEFSS composed of a stack of nonresonant patches separated from one another by thin dielectric substrates, and the whole structure is backed with a ground plane. A prototype of the proposed MEFSS-based TTD reflectarray with the focal length to aperture diameter ratio (f/D) of 0.87 operating at the center frequency of 10 GHz is designed, fabricated, and experimentally characterized both in time and frequency domains. It is demonstrated that the fabricated TTD reflectarray operates over a bandwidth of 40% without any significant chromatic aberrations. The proposed antenna provides a realized gain of 23 dB when fed with an X-band horn antenna and shows a gain variation of about 4 dB in the 8-12 GHz range. The antenna also shows consistent radiation characteristics and relatively low side-lobe levels across its entire band of operation.