A new approach for the gain enhancement and wideband radar cross section (RCS) reduction of an antenna based on the chessboard polarization conversion metasurfaces (CPCMs) is proposed. Compared with the previous low-RCS antennas, high gain and wideband low RCS of a circularly polarized (CP) antenna are achieved simultaneously. The proposed CPCM is the chessboard configuration of the polarization conversion metasurfaces (PCMs), which is made up of adjoining two-layer substrates with three metallic patterns. Low RCS is realized by 180° (±30°) reflection phase variations between two neighboring PCMs. Gain enhancement is achieved by employing a Fabry-Perot cavity, which is constructed by the PCM and the ground of the antenna. The antenna with CPCM operating at the $X$ -band, excited by a sequentially rotated feeding network, is fabricated and measured. Simulated and measured results show that the left-hand CP gain of the antenna with CPCM is at least 3 dB higher than that of the reference antenna from 8.5 to 9.5 GHz and the monostatic RCS is effectively reduced from 6 to 14 GHz.

An ultra-wideband polarization rotation reflective surface (PRRS) with a high polarization conversion ratio (PCR) is proposed, which can reflect a linearly polarized incident wave with 90° polarization rotation. The unit cell of the proposed PRRS consists of a square and L-shaped patches printed on a substrate, which is covered by a superstrate and backed by a metallic ground. The two patches are connected to the ground using two metallic vias, respectively. Compared with the previously reported PRRS, the polarization rotation bandwidth of the proposed PRRS is enhanced from 49% to 97% with a high PCR of 96%. The frequency responses within the operation frequency band are consistent under oblique incident waves. Furthermore, the designed PRRS is applied to the ultra-wideband radar cross-section (RCS) reduction by forming a checkerboard surface. A 10-dB RCS reduction is achieved over an ultra-wideband of 98%. To validate the simulation results, a prototype of the checkerboard surface is fabricated and measured. A good agreement between the experimental and simulation results is obtained.

This communication presents a low-profile, compact, high gain dual-band and dual-circularly polarized (CP) folded transmitarray antenna (FTA) with independent beam control at Ku-band. The element with independent phase control capability in two bands is designed to achieve the functionality of linear polarization to different circular polarization conversion. To reduce the profile of the whole FTA, a dual-band and dual-linearly polarized patch antenna is adopted as the feed source. By controlling the phase distribution and circular polarization of the transmitarray (TA) according to the phase compensation principle, the proposed antenna can radiate left-hand CP (LCP) waves and right-hand CP (RCP) waves at 12 and 15 GHz, respectively. On the basis, three typical FTA prototypes with different beam directions are simulated to validate the capability of independent beam control. Two of the prototypes are fabricated and measured, and the results are shown in reasonable agreement with the simulation. The proposed antenna not only reduces the profile by 2/3 compared to the traditional TA antenna, but also has the advantages of compact planar structure, low cost, high gain, and easy integration, which presents great application potential in two-way satellite communication systems with limited volume and space.

A slot array antenna integrated with a hybrid metasurface (HM) for wideband monostatic and bistatic RCS reduction is proposed in this paper. The HM consists of an anisotropic frequency selective absorber (AFSA) and a polarization rotation reflective surface (PRRS). The proposed AFSA absorbs the electromagnetic wave for one polarization while letting the cross-polarized wave pass through. When putting the PRRS under AFSA, the cross-polarized wave will be reflected by the PRRS with 90° polarization rotation and then the reflected wave will be absorbed by AFSA. Thus, both the co-polarized and cross-polarized incident waves are absorbed by HM. Because the incident energy is absorbed rather than reflected to the other directions, both the monostatic RCS and bistatic RCS are reduced in a wide frequency band. In addition, since the radiation wave emitted by the slot array antenna will not be reflected by the PRRS, the proposed antenna has a reasonable gain. The simulated results show that both the monostatic and bistatic RCS of the proposed slot array antenna are significantly reduced in the frequency range from 6 GHz to 18 GHz and the gain decreases about only 0.8 dB when compared with the reference antenna. The measured results are in good agreement with the simulated ones.

In this communication, a microfluidically frequency and polarization reconfigurable slot antenna using liquid metal (LM) is proposed. The polydimethylsiloxane (PDMS) structure with narrow banded microchannels is loaded on the printed circuit board (PCB) of a square slot antenna, providing condition for reconfiguration. The left-hand circular polarization (LHCP), right-hand circular polarization (RHCP), and linear polarization (LP) are achieved by injecting LM into +45° and -45° channels with respect to the x-axis or keeping the channels empty. Three operating frequency bands of LHCP and RHCP states can be realized by filling the microchannels with different lengths. Both states have an overall tuning 3 dB axial ratio bandwidth (ARBW) of 26.42% (2.3-3 GHz). In LP state, the proposed antenna realizes a -10 dB impedance bandwidth of 11.6% (2.03-2.28 GHz). A prototype of the proposed antenna has been fabricated and measured. Good agreement between the simulated and measured results validates the feasibility of this technique.

A circularly polarized (CP) metasurface-inspired antenna array with low radar cross section (RCS) over a wideband based on polarization conversion metasurface (PCM) is proposed. Without increasing the structural complexity, the PCM units serve directly as antenna radiators, which not only maintains good radiation characteristics but also reduces both the in-band and out-of-band RCS of the antenna. Simulations show that the proposed PCM-inspired antenna array has an impedance bandwidth of 37.6% (8.2 to 12 GHz), a 3 dB axial ratio (AR) bandwidth of 32.5% (8.5 to 11.8 GHz), and a 3 dB gain bandwidth of 23.3% (9.5 to 12 GHz). The RCS of the proposed antenna array is greatly reduced for both polarizations in the frequency range of 7.6 to 16.2 GHz (72.3%) compared to conventional microstrip patch antenna array, with a maximum reduction of 20.6 dB. Moreover, the proposed PCM-inspired antenna array has a smaller element size compared to conventional low-RCS metasurface antennas, making it more conducive to the composition of a phased array. Finally, the proposed array is fabricated and measured, and the results confirm the simulations.