Time-modulated Arrays Research Articles

Sidelobes and sideband minimization in time-modulated array antenna based on chaotic exchange nonlinear dandelion optimization algorithm

Time-modulated array antenna (TMAA) is a new type of array antenna based on time modulation technology. By introducing "time" as the fourth dimensional design freedom into the design of conventional array antennas in three-dimensional space, the array antenna has time modulation characteristics, which better controls the radiation characteristics of the array antenna and achieves the best far-field radiation pattern synthesis. This paper designs a Time-modulated linear array (TMLA) with low sidelobe level (SLL) and low sideband level (SBL) based on the chaotic exchange nonlinear dandelion optimization (CENDO) algorithm. Three optimization methods are studied: firstly, determining the optimal on-time (τnn) for each array element; The second is to determine the optimal on-time (τnn) and optimal uniform array element spacing (d) for each array element; The third is to determine the optimal opening time (ton), closing time (toff), and optimal uniform array element spacing (d) for each array element. To achieve simultaneous reduction of sidelobe level and suppression of harmonic interference. The same array model contains different harmonic frequency radiation. In this article, we only considered two harmonic frequencies, namely the first sideband frequency and the second sideband frequency. Because the harmonic of other sideband frequencies has a very small impact on the radiation of the fundamental wave, it can be ignored. To demonstrate the stronger ability of the CENDO algorithm in optimizing Time-modulated array antennas, and in line with the principle of fairness and impartiality, this paper also simulates different Time-modulated array models and compares the results of the CENDO algorithm with other published literature. It is concluded that this study shows lower SLL and lower SBL in different models. This provides a more scientific and accurate explanation of the superiority of the CENDO algorithm compared to other algorithms in the field of antenna optimization in electromagnetics. At the same time, this also provides great research value and fundamental support for designing high-performance Time-modulated array antennas in subsequent engineering applications.

Directional Modulation With Artificial-Noise Injection Into Time-Modulated Arrays

Directional Modulation With Artificial-Noise Injection Into Time-Modulated Arrays

Noniterative DOA Estimation in Time-Modulated Array Under Unidirectional Phase Center Motion

Noniterative DOA Estimation in Time-Modulated Array Under Unidirectional Phase Center Motion

Controlling surface acoustic waves (SAWs) via temporally graded metasurfaces

In this manuscript, the temporal rainbow effect for surface acoustic waves (SAWs) is illustrated through a temporal analog of space metagradings. We show that a time-modulated array of mechanical resonators induces a wavenumber-preserving frequency transformation which, in turn, dictates Rayleigh-to-Shear wave conversion. The process is unfolded through the adiabatic theorem, which allows us to delineate the transition between a solely frequency-converted wave packet and a temporally-driven mode conversion. In other words, our paper explores the role of time modulation in the context of elastic metasurfaces, and we envision our implementation to be suitable for designing a new family of SAW devices with frequency conversion, mode conversion, and unusual transport capabilities.

Single-Channel DoA Estimation Based on Nonuniform Time-Modulated Array With Asynchronous Sampling

Single-Channel DoA Estimation Based on Nonuniform Time-Modulated Array With Asynchronous Sampling

A Planar Time-Modulated Array With Integrated 2-bit Phase Modulators

A Planar Time-Modulated Array With Integrated 2-bit Phase Modulators

Direct Antenna Frequency-Hopped M-FSK Modulation With Time-Modulated Arrays

Direct Antenna Frequency-Hopped M-FSK Modulation With Time-Modulated Arrays

Broadband Direction Finding Based on a Three-Element Time-Modulated Array

Broadband Direction Finding Based on a Three-Element Time-Modulated Array

Deception Jamming Method for Wideband Linear Frequency Modulation Radar Based on Time-modulated Array

Deception Jamming Method for Wideband Linear Frequency Modulation Radar Based on Time-modulated Array

Improving Age of Information for Covert Communication With Time-Modulated Arrays

Improving Age of Information for Covert Communication With Time-Modulated Arrays

Security-Enhanced Directional Modulation Symbol Synthesis Using High Efficiency Time-Modulated Arrays

Security-Enhanced Directional Modulation Symbol Synthesis Using High Efficiency Time-Modulated Arrays

Failure diagnosis for time-modulated arrays based on compressed sensing

Time-modulated arrays (TMAs) have a high design degrees of freedom (DoFs) to improve radiation performance, while they are prone to failure due to their hardware characteristics. In this article, we propose a novel technique to diagnose impaired TMAs based on compressed sensing (CS). The TMA diagnosis problem is reformulated as a sparse signal recovery problem at the center frequency and sidebands. Then, a method based on the difference of convex sets theory and sequential convex programming (DCS-SCP) is developed to implement diagnosis for impaired TMAs. Using a small number of far-field measurements at the same position but different frequencies, the joint recovery of the equivalent excitations at the center frequency and sidebands is realized by a mixed l 0 / l 2 -norm minimization method. The numerical simulation and the successful comparison with the state-of-the-art algorithms demonstrate the superiority of the proposed methods in terms of noise robustness and diagnosis accuracy.

Effective Artificial Neural Network Framework for Time-Modulated Arrays Synthesis

Effective Artificial Neural Network Framework for Time-Modulated Arrays Synthesis

Directional Modulation With Dynamic Distributed Time-Modulated Arrays

Directional Modulation With Dynamic Distributed Time-Modulated Arrays

Harmonic-Based MIMO Transceiver With Time-Modulated Arrays

A simple harmonic-based multiple-input multiple-output (MIMO) transceiver based on the time-modulated array (TMA) is proposed and verified, including detailed performance analysis, comparisons with state-of-the-art works and experiment verification. The essential concept is utilizing the time modulation technique to linearly map the actual multipath channels between multiple users and the antenna elements of the TMA to the equivalent virtual channels between users and harmonics with different frequencies. Models of the received and transmitted signals in both uplink and downlink transmissions based on the multi-user single-input multiple-output (SIMO) and multiple-input single-output (MISO) scenario are analyzed and derived, followed by the proposed harmonic channel estimation, detection and beamforming methods. Simulations on the performance of the proposed harmonic-based MIMO transceiver are provided and compared to the also TMA-based space division multiple access (SDMA) scheme, showing that the latter is more like a special case of the proposed scheme. An experimental 2-user wireless communication prototype based on a 4-element TMA is fabricated and tested to verify the feasibility and effectiveness of uplink signal transmission.

DOA estimation based on smoothed sparse reconstruction with time-modulated linear arrays

A novel direction of arrival (DOA) estimation method based on smoothed sparse reconstruction with time-modulated linear arrays (TMLA) is proposed in this paper. With the analysis of the noise variation after time modulation, a closed-form expression for the noise covariance under the optimized unidirectional phase center motion time sequence scheme is derived. Then a reweighted continuous function is designed for the smooth approximation to ℓ0-norm based on the orthogonality between the signal subspace and the noise subspace. Simulation results demonstrate that, compared with conventional DOA estimation method with time-modulated arrays, the proposed method possesses higher estimation accuracy and lower computational complexity, especially for the scenario with small snapshot and low signal-to-noise ratio.

Effect of Pulse-Shifting on Calculating Sideband Power Losses in Non-uniform Time-Modulated Array

ABSTRACT In nonuniform time-modulated array (NTMA), despite modulating the antenna elements with nonidentical modulation frequencies, some harmonics may overlap in space at a particular frequency. In this paper, considering the overlapping and nonoverlapping nature of the radiated harmonics, the mathematical formulations for calculating the total sideband power (P SR) loss of nondegenerate NTMA (ND-NTMA) and degenerate NTMA (D-NTMA) using pulse shifting strategy are presented. Employing the derived closed-form expressions, the effect of shifting the pulse position on P SR is studied. It is investigated that, though the P SR of ND-NTMA does not depend on the shifted pulse position, for D-NTMA, it depends on the intersected switching time duration of the pulses. Through representative numerical results, it is shown that the derived expression is useful to accurately calculate the total sideband power of NTMA with pulse-shifting strategy.

Measurement of Phase Difference and Direction of Arrival Using Time-Modulated Array With General Modulation Parameters

An extraction method and formulas are proposed for phase difference and direction of arrival (DOA) using a two-element time modulated array with the general modulation parameters. The relevant spectral components are described with the help of a phasor diagram and equations for phase difference and the DOA are derived from the measured magnitude and complex quantities of these spectral components. Issues involving measurement with frequency down-conversion are addressed. Simulations and experiments are performed to evaluate the proposed method and the related theory.

Transmissive Reconfigurable Intelligent Surface Transmitter Empowered Cognitive RSMA Networks

In this paper, we investigated the downlink transmission problem of a cognitive radio network (CRN) equipped with a novel transmissive reconfigurable intelligent surface (TRIS) transmitter. In order to achieve low power consumption and high-rate multi-streams communication, time-modulated arrays (TMA) is implemented and users access the network using rate splitting multiple access (RSMA). With such a network framework, a multi-objective optimization problem with joint design of the precoding matrix and the common stream rate is constructed to achieve higher energy efficiency (EE) and spectral efficiency (SE). Since the objective function is a non-convex fractional function, we proposed a joint optimization algorithm based on difference-of-convex (DC) programming and successive convex approximation (SCA). Numerical results show that under this framework the proposed algorithm can considerably improve and balance the EE and SE.

An Interpolation-Based Time-Modulated Antenna Array for Beam Scanning at Carrier Frequency

The formula of the Fourier series for a periodic function indicates that traditional periodic time modulation only provides amplitude weighting at the carrier frequency of a time-modulated array (TMA). Therefore, beam scanning through time modulation technique could only be realized at harmonic frequencies. In order to achieve low sideband levels (SBLs) in harmonic beam scanning, a large number of modulation statuses are required in TMAs, which significantly increases the cost and complexity of the entire system. The intent of this work is to develop a novel TMA with array-interpolation aperture and ON–OFF time modulation to achieve beam scanning at the carrier frequency. By performing interpolation computation at the antenna array level, high-precision beam scanning with low SBLs can be realized with pseudorandom ON–OFF time modulation and a static 1-bit phase control. As compared with the state-of-the-art designs, the proposed TMA requires much fewer modulation statuses, and it significantly facilitates beam-scanning control. A forward design strategy is presented to analytically determine the time modulation sequences and the static 1-bit phase statuses for specified beam scanning angles and sidelobe levels (SLLs). Numerical and experimental results well demonstrate the effectiveness of the proposed TMA.