In this paper, spoof surface plasmon polariton (SPP) is integrated in the closed substrate integrated waveguide (SIW) structure and a novel hybrid SIW-SPP guided-wave transmission line (TL) is proposed. In this design, the surface wave mode of SPP can be excited and transmitted inside the closed structure of SIW. The dispersion property of the proposed SIW-SPP hybrid structure indicates that it has both slow wave feature of SPP and fast-wave feature of SIW. With the low-pass feature of SSP and the high-pass feature of SIW, the proposed hybrid SIW-SPP TL becomes a bandpass filter (BPF) naturally. The concept of integrating SPP and SIW opens a new way to develop novel wideband BPFs. A broadband filter is fabricated to verify the theory and the measured passband is from 16.1 to 25.4 GHz with a relative bandwidth of 43.8%. The filter bandwidth can be easily controlled by tuning parameters, thus the proposed structure is attractive and useful for the design of various BPFs.

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 communication, we propose a high scanning rate leaky-wave antenna (LWA) based on a slow-wave substrate integrated waveguide (SIW) structure. The slow-wave effect is introduced by etching periodical slots on the top surface of SIW. The LWA radiation is subsequently realized by introducing sinusoidal modulation to the slots profile. Such a structure significantly improves the scanning rate of LWA due to the small group velocity at the slow-wave region. Simulation and measured results indicate that the proposed LWA scans a wide angle in a narrow bandwidth near the cutoff frequency of surface plasmon polariton. Within the frequency band 13.5-13.9 GHz (3% relative bandwidth), the measured scanning angle is from 2° to 37° with the measured gain all above 9.2 dBi.

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.

In this letter, a wide-angle narrow-band leaky-wave antenna (LWA) based on substrate integrated waveguide-spoof surface plasmon polariton (SIW-SSPP) structure is proposed. Periodic slots are etched on both the top and bottom surfaces of substrate integrated waveguide (SIW) to introduce spoof surface plasmon polariton (SSPP) mode. The periodic slots on the top surface are sinusoidally modulated to realize bi-directional LWA radiation. The problem of open stopband is solved by the asymmetrical design of the top and bottom slots. Thus, a wide bi-directional scanning range from -60° to +63° is achieved. Besides, the relative bandwidth of the fabricated antenna is reduced to only 9% by introducing the slow-wave effect of SSPP. It means the proposed antenna has a large scanning rate, or equivalently beam scanning range/bandwidth ratio.

In this paper, we propose a novel slow-wave half-mode substrate integrated waveguide (HMSIW) combined with spoof surface plasmon polariton (SPP) structure. In this design, subwavelength corrugated grooves are etched on the up metal layer of HMSIW to support an SPP mode. The dispersion and transmission characteristics of the proposed hybrid HMSIW-SPP structure are analyzed and compared with the classic HMSIW. To experimentally validate this design, a prototype is fabricated and measured. A slow-wave effect is clearly observed in the proposed hybrid transmission line, and its wavelength is reduced by over 50% without sacrificing its transmission performance. This structure features a simple architecture and excellent slow-wave effect.