Dual-Polarized Filtering Transmitarray Antennas With Low-Scattering Characteristic

A filtering transmitarray antenna (TAA) with high-gain in-band radiations at the
$X$
-band and an out-of-band low-scattering characteristic is presented in this communication. The proposed composite TAA element consists of a dual-polarized resistive sheet, a fixed bandstop frequency-selective surface (FSS) element, and an adjustable bandpass FSS element also serving as a phase shifter. The resistive element is constructed by inserting a parallel inductor–capacitor (PLC) resonant structure into the center of a lumped-resistor-loaded metallic dipole. A transparent frequency-domain window at the center operating frequency (
$f_{c}$
) is created by the PLC resonance and is further shared by both FSS elements, hence allowing for high in-band transmission herein. At frequencies below or above
$f_{c}$
, the whole composite TAA element acts as an absorber with the bandpass or bandstop FSS elements as the ground planes for the resistive sheet, respectively. The measured results show that the composite TAA can achieve gain-filtering responses with out-of-band suppression levels ≥25 dB, ~8 dB scattering cross section (SCS) reductions in 4–7 and 14–20 GHz, and the radiation gain of 25.3 dBi simultaneously. Because of these merits, the proposed design can relieve the stress on filtering circuit designs, also offering an attractive solution in stealth technology.