A low-profile, all-metal, dual-band, dual-polarized shared-aperture phased array (SAPA) is proposed for UAV radar systems. The phased array element consists of a semi-open stepped radiating slot loaded with a pair of metal ridges to achieve the desired small aperture, wide beam, and low cross-polarization properties. Compared with traditional all-metal phased array element, the antenna profile can be reduced while not compromising radiation characteristics. Based on this element, a single-polarized phased array and two dual-polarized SAPAs with different frequency ratio have been developed. By adjusting the spacing between the dual ridges of the elements, the frequency ratio of the dual-band dual-polarized SAPA can be flexibly controlled ranging from 1:1 to 3:1. To validate this concept, a prototype of the SAPA operating in the S-band and C-band was fabricated and measured. The measured results demonstrate a beam scanning range of ± 60° in the dual-band range with a gain drop of within 5.5 dB. The proposed SAPA represents a promise candidate for UAV radar systems that facilitate communication within the Internet of Vehicles.

Contactless physiological signal sensing is an emerging technology for routine health monitoring, ambient-assisted living, automotive, search and rescue, and public security. In this work, we propose MetaPhys, a reconfigurable intelligent surface (RIS)-based contactless physiological signal monitoring system that can simultaneously sense multiple persons and their respiratory and cardiac signals. The proposed system localizes the human targets by utilizing RIS to dynamically manipulate the electromagnetic waves in the environment for beamforming and 3-D radar imaging in the spatial dimension. Then, it extracts the respiration and cardiac signals from the sequential echoes in the temporal dimension. The high-resolution information in the four dimensions as “3-D space + 1-D time” makes it comprehensively perceive the targets and environment. The beamforming allows the radiated energy to focus on the thoraxes, which helps reduce interference and distortion caused by stationary reflectors (i.e., clutters, static body parts, and multipath), thereby improving the signal-to-noise ratio and enabling long-range measurements. We also verify the measured data in a real indoor environment, and the experimental results show that the proposed system can accurately monitor the physiological signals of multiple subjects. The root mean square errors of respiratory rate and heart rate at a distance of 3 m are 0.2 breaths per minute and 1.1 beats per minute, respectively.

The integration of aerial platforms to provide ubiquitous coverage and connectivity for densely deployed terrestrial networks is expected to be a reality in the emerging sixth-generation networks. Energy-effificient and secure transmission designs are two important components for integrated terrestrial-aerial networks (ITAN). Inlight of the potential of reconfigurable intelligent surface (RIS) for significantly reducing the system power consumption and boosting information security, this paper proposes a multi-layer RIS-assisted secure ITAN architecture to defend against simultaneous jamming and eavesdropping attacks, and investigates energy-efficient hybrid beamforming for it. Specifically, with the availability of imperfect angular channel state information (CSI), we propose a block coordinate descent (BCD) framework for the joint optimization of the user’s received decoder, the terrestrial and aerial digital precoder, and the multi-layer RIS analog precoder to maximize the system energy efficiency (EE) performance. For the design of the received decoder, a heuristic beamforming scheme is proposed to convert the worst-case design problem into a min-max one and facilitate the developing a closed-form solution. For the design of the digital precoder, we propose an iterative sequential convex approximation approach via capitalizing the auxiliary variables and first-order Taylor series expansion. Finally, a monotonic vertex-update algorithm with a penalty convex-concave procedure (P-CCP) is proposed to obtain the analog precoder with satisfactory performance. Numerical results show the superiority and effectiveness of the proposed optimization framework and architecture over various benchmark schemes.

With the small sampling length, a novel Direction-of-Arrival (DOA) estimation method based on a single programmable metasurface sensor is proposed in this article. Serving as a physical random sampling receiver, a dynamic metasurface generates series of random radiation patterns to sense the incident signals, which is subsequently processed by the compressive sensing (CS) orthogonal matching pursuit (OMP) algorithm to recover the DOA information. A mathematical model of DOA estimation is first built for theoretical analyses. Furthermore, numerical simulations are investigated with extensive performance analyses. In comparison with the metasuface-based beam-scanning method, metasurface-based CS for DOA estimation has superior performance with a smaller sampling length. Finally, a proof-of-concept experiment is made to verify the feasibility of the programmable metasurface for DOA estimation. Compared to other traditional estimation techniques that require multiple channels, the programmable metasurface can achieve estimation with only a single channel and small sampling length.

In this paper, a novel mode composite waveguide based on hybrid substrate integrated waveguide and spoof surface plasmon polariton (SIW-SSPP) is proposed. Through different feeding methods, the odd mode and even mode of SSPP are excited simultaneously and operate at the same frequency band. Thus, co-frequency mode multiplexing is achieved for the proposed odd-even mode composite waveguide (OEMCW). The design principle and characteristics of the OEMCW are analyzed in this work. A prototype is fabricated and measured to demonstrate its transmission performance. The measured results indicate that the proposed waveguide can operate from 10.3 GHz to 18 GHz in two modes with the isolation larger than 18 dB.