A Dual-Band Transmitarray Antenna Employing Ultra-Thin, Polarization-Rotating Spatial Phase Shifters

Abstract

We present a dual-band transmitarray (TA) comprising ultrathin polarization-rotating (PR) spatial phase shifters. The PR elements provide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$+ 90^\circ $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 90^\circ $ </tex-math></inline-formula> polarization rotation independently in two different frequency bands, used as dual-band 1-bit spatial phase shifters. Independent polarization rotation in the two operating frequency bands is realized by interleaving high-band and low-band features that include dipoles, strips, and slots printed on three metallic layers with ultrathin interlayer spacings. The concept is generally applicable to any frequency band where TAs are practical. To illustrate the concept, we simulated and tuned a PR unit cell to achieve 1-bit phase shifts in two operating frequency bands at X- and Ku-bands, with center frequencies at 9.5 and 14.5 GHz, respectively. Subsequently, a dual-band TA was designed using the proposed unit cell to provide beam collimation at broadside directions at both operating frequency bands. The proposed ultrathin spatial phase shifter results in a TA with an overall thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.07\lambda _{LB}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{LB}$ </tex-math></inline-formula> is the wavelength at the center frequency of the lower band. Measurement results of a fabricated prototype of the TA show maximum gains of 25.2 and 26.2 dBi as well as 3 dB gain bandwidths of 26% and 6.2% for the lower and higher bands, respectively.