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.

This work presents the design of an additively manufactured W-band bandpass filter and a subtractively manufactured W-band diplexer to demonstrate the use of admittance inverter sequences for the ease of manufacture at millimeter-wave frequencies. Contrary to typical impedance inverters (E-plane and H-plane irises), the use of admittance inverters (E-plane and H-plane stubs) allows for larger dimensions to be specified and ultimately does not impede the general waveguide path. The proposed bandpass filter is designed with all E-plane stubs, while the diplexer is designed with one branch using both E-plane and H-plane stubs as an arbitrary sequence, and the second branch using all H-plane irises. The additively manufactured bandpass filter is fabricated using the most elementary-level stereolithography (SLA)-based methods, demonstrating that a hobbyist-type SLA printer and metallization method can procure exceptional results for millimeter-wave filter designs. The subtractively manufactured diplexer is fabricated using high-precision computer numerical control (CNC) milling to highlight the use of arbitrary inverter sequences in a more complex and robust design profile, while the dispersive transmission zeros that are caused by over-moding of the inverter stubs are used to demonstrate unique isolation characteristics in the upper W-band region. The design concepts, fabrication profiles, simulations, and measurements which are presented in this work highlight a viable option for overcoming miniaturized dimensions in millimeter and submillimeter-wave applications.

This article presents a design technique of quasi-elliptic filters by applying two novel planar triplets, which eliminates the need for negative couplings. A composite right-/left-handed (CRLH) resonator, together with a meander-line resonator, is investigated first in this article. These two resonators demonstrate a significant difference with respect to their phase shift characteristics that are completely opposite below and above their resonant frequencies. With such a feature, two meander-line and CRLH-loaded substrate integrated waveguide (SIW) triplets are proposed, which can produce a transmission zero (TZ) above and below the passbands if an inductive cross coupling is applied. Therefore, all couplings would be positive regardless of the location of TZs. The applications of the two triplets to quasi-elliptic filters, which are realized by parallel and cascaded triplet topologies, are then illustrated. Two filter prototypes operating at the $X$ -band are designed and fabricated for validation. They show outstanding electrical performance in terms of high selectivity, low loss, and compactness. It indicates that a joint application of conventional shunt LC resonant nodes and a CRLH node is a viable option in filter design.

A printed‐circuit differential‐fed Yagi–Uda antenna is presented that features enhanced bandwidth by employing a parasitic quarter‐wavelength coplanar stripline (CPS) resonator which adds one more resonant mode within the operating bandwidth. The proposed antenna is designed, fabricated and measured. Experimental results are in good agreement with simulations. In the band of 2.27–2.58 GHz, the return loss is better than 10 dB and the gain better than 6 dBi. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:156–159, 2017

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.