A novel hybrid reflection method is proposed to realize wideband gain enhancement and radar cross section (RCS) reduction properties for Fabry-Perot (FP) antennas. This method adopts two kinds of Frequency Selective Surface (FSS) units, which are etched on both sides of a single-layer substrate with chessboard arrangement to operate separately as a Hybrid Surface (HS) and a Reflective Surface (RS), to form a Hybrid Partially Reflecting Surface (HPRS). The two FSSs with different positive reflection phase gradient bands and reflection amplitudes collaborate to expand the 3-dB gain bandwidth and improve the gain enhancement on the RS. Meanwhile, the different compensation phases of the two FSSs can redirect reflected waves to reduce the RCS on the HS, and phase cancellation is applied between the retransmitted waves and reflected waves to further reduce the RCS. The simulated and measured results verify the correctness of the proposed method. The prototyped FP antenna has a measured 10-dB impedance bandwidth of 8.64-12.07 GHz (33.1%), a 3-dB gain bandwidth of 8.6-11.1 GHz (25.4%) with a peak gain of 17.08 dBi at 9.5 GHz, and an RCS reduction bandwidth of 8.6-14 GHz with a peak RCS reduction of 19.5 dB.

A method is presented to achieve a slot antenna array with a reconfigurable radar cross section (RCS) by injecting and extracting ethanol. In a complex communication system, this can be used to switch between the detection and stealth modes. The antenna system is formed by combining a liquid absorber with a $2\times $ 2 slot antenna array. The liquid absorber consists of a polymethyl methacrylate (PMMA) container, 45% ethanol layer, and metal ground, which is attached to the surface of the slot antenna array. The incident wave can be absorbed by the absorber rather than reflected in other directions when the PMMA container is filled with ethanol, which reduces the monostatic and bistatic RCS. Thus, the RCS of the antenna can be changed by injecting and extracting ethanol while sustaining the antenna’s radiation performance in terms of bandwidth, radiation patterns, and gain. The mechanism of the absorber is investigated. The simulated results show that the antenna with this absorber has monostatic and bistatic RCS reduction bands from 2.0 to 18.0 GHz and a maximum RCS reduction of 35 dB with an average RCS reduction of 13.28 dB. Without ethanol, the antenna realizes a gain of 12.1 dBi, which drops by 2 dB when the lossy ethanol is injected. The measured and simulated results agree well.

A Fabry–Perot (FP) antenna with high gain-bandwidth product (GBP) and wideband radar cross section (RCS) reduction is proposed using an embedded chessboard polarization conversion metasurface (CPCM). A polarization conversion metasurface (PCM) unit and its mirror unit are etched on both sides of a dielectric substrate with chessboard arrangement to form a CPCM. The in-band and out-of-band low-RCS features of the FP antenna are realized by destructive interference, and the high GBP is attributed to the FP resonant cavity. Moreover, an additional small CPCM designed for another PCM unit is embedded into the original CPCM to construct an embedded CPCM, which helps to improve in-band RCS reduction and has a positive effect on gain enhancement and 10-dB impedance bandwidth. The measured results show that the FP antenna with embedded CPCM has a 10-dB return-loss bandwidth of 8.48-12.21 GHz (36.1%), a GBP of 1338, a 3-dB gain bandwidth of 8.9-11.5 GHz (25.5%) and a maximum realized gain of 17.2 dBi. Meanwhile, the measured RCS reduction band covers 8–26 GHz (105.9%) with a peak RCS reduction of 21.2 dB at 9.4 GHz.

A novel method to enhance the high-frequency gain of a wideband Fabry–Pérot (FP) antenna by using a truncated field correcting structure (TFCS) is proposed. The TFCS is formed by laminated dual-layer dielectric substrates and acts as the high-frequency operating band phase and amplitude correcting structure of the FP antenna for the radiated field. This method not only has a small effect on the operating bandwidth of the antenna, but also has a positive effect on improving the gain over the low-frequency operating band. The simulation and experimental results verify that the TFCS can effectively enhance the gain within the high-frequency operating band, and expand the 3 dB gain bandwidth of the FP antenna. The measured results show that the proposed antenna has a 10 dB return loss bandwidth of 8.49–12.34 GHz (37.0%), a 3 dB gain bandwidth of 8.48–11.82 GHz (32.9%), and a maximum gain of 17.73 dBi. The 3 dB gain bandwidth of the FP antenna is extended from 28.8% to 32.9% after loading with the TFCS, and the maximum gain enhancement within the high-frequency operating band is increased by 3.48 dB at 11.58 GHz.