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.

Beam scanning antenna brings new opportunities to reduce the data collision of multinode communication in the Internet of Things (IoT). This article proposes a new type antenna design scheme that can be used for IoT relay communication. A programmable beam scanning antenna without phase shifters operating in the X-band is designed to evaluate the feasibility of this scheme. The integrated design of excitation source and phase-modulated structure greatly reduces the profile of the antenna and improves the integrated degrees of freedom with other equipment. By switching the state of the PIN diode loaded on each element, different radiators can be selected and the direction of current polarization on elements can be adjusted to change the radiation phase. Furthermore, the diode states are encoded by the holographic antenna theory and controlled by the FPGA controller to realize programmable beam scanning. One-element, two-element, and 1-D array containing 32 elements are fabricated and measured. The experimental results are in good agreement with the simulation data. The operating bandwidth is 7.5% at 10 GHz while the beam scanning range of the array is $- 60{^\circ }$ –60°, with a good scanning accuracy and stability. The proposed low-profile beam scanning antenna can provide stable communication services to multiple users and smart devices as a new type of beam scanning array antenna solution for the IoT application, which is beneficial to this field.

Radiating twisted beams, orbital angular momentum (OAM) based radar provides a new perspective for present radar techniques. However, estimation methods now used has a demerit of resolution. Thus, we raised multiple signal classification (MUSIC) algorithm to improve resolution ability based on this innovative concept. The echo model based on uniform circular array for MUSIC was first built. In contrast to uncorrelated signals in classical MUSIC algorithm, echo signals from targets are fully coherent with each other. Spatial smoothing technique was subsequently utilised in OAM regime to tackle it. Simulation results showed the super‐resolution capacity of MUSIC to detect objectives compared with the traditional fast Fourier transform method.

Uniform circular array (UCA) is a pioneering approach to generate radio twisted beams carrying orbital angular momentum (OAM). However, faulty antenna elements in a UCA could render the array into an imperfect UCA (IUCA), consequently creating distortion for OAM-based communication or radar systems. To analyze the effects of an IUCA on generating OAM, elementary wave function and wave transformation are derived to obtain field equations of a general circular array. Further derivation of IUCA shows that the field of an IUCA is a superposition of OAM modes, which is caused by polluted orthogonalities of OAM modes. To achieve pure OAM modes, the orthogonal matching pursuit algorithm, the convex optimization tool, and the analytical solution are employed to design a feeding network to retrieve the orthogonal property at the cost of strong gain loss. Then, the reduced constraints method is proposed for the IUCA to achieve high-purity and low-loss OAM mode. Finally, four circular arrays with different shapes are explored for limited installation space to generate twisted beams.

A novel design method for ultra-broadband energy selective surface (ESS) is presented in this paper based on the equivalent theory from filter circuits to metamaterial units. This method provides a new way of designing ESS in ultra-broadband with low insertion loss and high shielding efficiency from the perspective of filter circuit topology. It is illustrated and verified with a three layer ultra-broadband ESS. Firstly, a third-order filter with a switching bandpass to bandstop in C to Ku band is designed and optimized. Then, the filter is mapped to a physical model of a three-layer ESS which has a nonlinear transmission response for low-intensity radiation field (LIRF) and high-intensity radiation field (HIRF) in C/X/Ku-band. The three ESS prototypes are fabricated and measured in three different band waveguides to prove the design method of the ESS proposed in ultra-broadband. Simulated and measured results demonstrate that low insertion loss and high shielding efficiency at the same time can be obtained under low and high incident power levels, respectively, where the 1 dB loss and 23 dB shielding bandwidth cover from 5.4 GHz to 14.45 GHz. Furthermore, the insertion loss is less than 0.5 dB in the frequency band of 5.45 GHz to 13.8 GHz and maximum shielding effectiveness reaches 25 dB at 10 GHz.

This paper presents a high selectivity frequency selective rasorber (FSR) with an adjustable out-band absorptivity property. This rasorber is composed of a dynamic absorptive-frequency-selective-surface (AFSS) on the top, with PIN diodes employed to achieve tunable absorptivity, and a high-quality (Q)-factor bandpass frequency-selective-surface (FSS) in the bottom, with aperture-coupled resonators (ACRs) structure to obtain a high-selectivity transparent window. To begin with, theoretical analyses and extensive simulations are performed to evaluate the performance. Subsequently, a prototype is fabricated and measured, showing a 1 dB transmission window with high selectivity at 8.43-8.51 GHz and electrical tuning on the absorption rate response with a wide tunable span of 0.9 at out bands of 4.43-7.76 GHz and 9.21-13.45 GHz, respectively. The proposed rasorber with dynamic tunability of absorptivity can provide radar cross section (RCS) consistent with the environment, which is potential for radar stealth, deception, and anti-identification.