Time-modulated Antenna Research Articles

Efficient Synthesis of Large-Scale Time-Modulated Antenna Arrays Using Artificial Neural Networks and Inverse FFT

Efficient Synthesis of Large-Scale Time-Modulated Antenna Arrays Using Artificial Neural Networks and Inverse FFT

Sideband power control in Time-Modulated antenna arrays for bidirectional harmonic beamforming and beam scanning

Beamforming and beam scanning in a specific angular region for establishing a secure communication channel has become the dire need of modern wireless communication system. This paper aims to propose an unconventional yet cost effective solution for beamforming and scanning by controlling the inherent sideband patterns of time-modulated antenna arrays. First of all, beam scanning with different scan angles is targeted by proposing asymmetric sequential time schemes. To achieve that, the phase center of the array is unidirectionally shifted by controlling a cluster of array elements. The idea is to model suitable pulse-shifted time schemes so that a good scanning coverage can be achieved without affecting the shapes of the radiation beam patterns. In this way, simultaneous bidirectional sideband patterns can be controlled for beam scanning. Furthermore, beamforming with enhanced efficiency for single channel secure communication is also addressed in this work by reducing the sideband levels (SBLs) of the array. The same concept of shifting the phase center unidirectionally is used for reducing the SBL, but with a higher number of clusters of array elements. The mathematical validation behind the proposed idea is thoroughly discussed and the closed-form sideband power expression is derived after investigating all possible combinations of pulse-shifted time schemes. 16-element linear timed arrays have been chosen to investigate the proposed idea and the supportive outcomes are presented in detail with comparisons.

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.

A Time-Modulated Antenna Array With Continuous Sideband Spectrum Distribution

Traditional time-modulated antenna arrays (TMAs) usually introduce sideband radiations at a multiple of discrete harmonic frequencies. To improve radiation efficiency of TMAs, various evolutionary algorithms become very popular in sideband suppressions. Apparently, the sideband radiation levels highly depend on the performance of these evolutionary algorithms. To achieve robust sideband suppression through physical designs, a novel pseudorandom hybrid phase–amplitude modulation technique is proposed to distribute the sideband radiation power over a continuous spectrum, rather than only at discrete harmonic frequencies. Following the law of energy conservation, sideband levels (SBLs) in this case naturally become extremely low, which eliminates the difficulty arising in TMAs’ sideband suppressions. Moreover, the novel modulation technique allows the synthesis of scanning beams with ultralow sidelobe levels, and the corresponding time modulation sequences could be directly calculated from analytical formulations. Therefore, evolutionary optimization algorithms are not necessary in the proposed TMA design procedure, which facilitates the real-time on-board calculation with an field-programmable gate array (FPGA) board. As compared with traditional TMAs, the proposed TMA achieves ultralow SBLs ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; -35.0$ </tex-math></inline-formula> dB) with much fewer time modulation statuses. Numerical and experimental results are presented to demonstrate the effectiveness of the proposed TMA.

Receive Mode Time-Modulated Antenna Array Incorporating Subsampling—Theoretical Concept and Laboratory Investigation

Receive Mode Time-Modulated Antenna Array Incorporating Subsampling—Theoretical Concept and Laboratory Investigation

Time-Modulated Antenna Arrays for Ultra-Wideband 5G Applications.

This research presents the design of time-modulated antenna arrays with UWB performance. The antenna arrays consider a linear topology with eight UWB disk-notch patch antennas. The technological problem is to find out the optimum antenna positions and/or time sequences to reduce the side lobes and the sidebands in all of the UWB frequency ranges. The design process is formulated as a bacterial foraging optimization. The results show that the uniform array generates a better SLL performance whereas the non-uniform array obtains a wider bandwidth. The uniform array obtains an SLL &lt; -20 dB from 3.37 GHz to 4.8 GHz and the non-uniform array generates an SLL &lt; -7 dB from 2.97 GHz to 5.26 GHz. The sideband levels are very similar for both cases with a value of around -17 dB.

Biquaternion-based DOA estimation of noncircular signals with time-modulated antenna arrays

A novel direction of arrival (DOA) estimation method of noncircular signals based on biquaternion with time-modulated antenna arrays is proposed in this paper. Time-modulated antenna arrays (TMAA) is introduced into the DOA estimation of noncircular signals for the first time, which makes the receiver only need a single RF processing channel, which effectively saves hardware resources. The noncircular features of the signal are fully exploited for virtual array expansion with the biquaternion framework. Aiming at the problem of nonuniform noise in the array output after time modulation, the nonuniform noise correction is realized by using the theoretical analysis of the time sequence scheme. The simulation illustrates that the proposed method has superior performance than conventional DOA estimation method with TMAA, in terms of resolution and numbers of localizable sources.

Time-Modulated Patch Antennas With Tunable and Nonreciprocal Polarization Response

Time-Modulated Patch Antennas With Tunable and Nonreciprocal Polarization Response

Nonreciprocal-Beam Phased-Array Antennas Based on Transistor-Loaded Phase Shifters

This study presents a nonreciprocal-beam phased-array antenna constituted of phase-gradient patch radiators integrated with transistor-based nonreciprocal phase shifters. Such an antenna exhibits different beams for transmission and reception states. The proposed phased-array antenna provides power amplification for both transmission and reception states, which is of paramount importance in most practical applications. In addition, in contrast to the recently proposed time-modulated antennas, the proposed nonreciprocal-beam phased-array antenna introduces no undesired time harmonics and unwanted frequency conversion, which requires no radio frequency bias signal. Furthermore, the nonreciprocal phased-array antenna is lightweight and is amenable to integrated circuit fabrication. The transmission and reception beam angles, the beam shapes, and the power amplification level may be easily tuned by changing the direct current (dc) bias of the transistors and phase of the passive phase shifters. Such a nonreciprocal-beam phased-array antenna is expected to find military and commercial applications.

Design and analysis of an amplitude-phase weighting module for harmonic beamforming in time-modulated antenna arrays

Amplitude-phase weighting modelling and analysis are indispensable for the performance evaluation of a practical, nonideal time-modulated antenna array (TMA). This paper investigates the effective performance evaluation of a crucial component in TMAs, named the time-modulated amplitude-phase weighting (TMAPW) module, while its performance is analysed through a single radio frequency (RF) channel and radiation patterns. A mathematical model is developed for amplitude-phase evaluation with nonideal time modulation sequence (TMS). A comparative measurement methodology is proposed to directly measure the attenuated amplitude and shifted phase at harmonic frequencies. Experimental validation for the developed mathematical model is carried out through an X-band prototype of the TMAPW module. Harmonic beamforming is then analysed in a 32-element nonideal TMA. Based on the developed model, the nonideal TMS can accurately evaluate the attenuated amplitude, shifted phase, and power spectrum leakage effect of the fabricated TMAPW module. Moreover, the sidelobe level (SLL) errors in radiation patterns are reduced with the proposed nonideal TMS. Consequently, the developed mathematical model and the measurement methodology will benefit the accurate performance evaluation of nonideal TMAs.

A PSO-CVX Algorithm of Sum and Difference Beam Patterns for Time-Modulated Antenna Array

An integrated optimization of sum and difference beam for time-modulated linear antenna array is studied in this paper. The goal of sum and difference beam synthesis is to generate sum beam in the main band and difference beams in the first-order sideband with low side-lobe level through timing switches. The turn-on times of antenna array are achieved by solving a quadratic constraint linear programming; meanwhile, the opening times are optimized by particle swarm optimization algorithm. The results of linear array show that the sum and difference beam can be scanned within ± 40 degrees, with lower peak side-lobe level.

Efficient Shaped Pattern Synthesis for Time Modulated Antenna Arrays Including Mutual Coupling by Differential Evolution Integrated With FFT via Least-Square Active Element Pattern Expansion

The fast Fourier transform (FFT) via the least-square active element pattern expansion (LSAEPE) is generalized to speed up the computation of array patterns including mutual coupling and platform effect for time-modulated antenna arrays (TMAAs) at the central and sideband frequencies. By integrating the LSAEPE-FFT with differential evolution algorithm (DEA), the resulting DEA-LSAEPE-FFT method can realize efficient shaped pattern synthesis with accurate control of main lobe shape, sidelobe level (SLL) and sideband level (SBL). Two examples of synthesizing different shaped patterns for different TMAAs mounted on a nonuniform platform or with metal scatters are conducted to validate the effectiveness and robustness of the proposed method. Synthesis results show that the proposed method has much better accuracy performance than the conventional DEA-FFT while costing much less CPU time than that of using DEA combined with a direct summation.

An optimal compact time-modulated circular antenna array synthesis using krill herd optimization

In this paper, an optimal far-field radiation pattern synthesis by using time modulation technique is carried out for a compact circular antenna array (CAA) design using a stochastic optimization method called krill herd (KH) optimization. A compact antenna array is achieved by reducing the inter-element spacing between the array elements, which leads to the miniaturization of the size of the array. On the other hand, an improved far-field radiation characteristic is achieved with a low side lobe level (SLL) and narrow first null beam width (FNBW). A low SLL is an essential requirement to reduce the interference with the other systems operating in the same frequency band. A narrow FNBW is necessary to obtain a high directivity. In time modulation technique, ‘time’ has the most significant role. It is considered the fourth-dimensional parameter, which plays the role of an additional degree of freedom to achieve an improved radiation pattern. The time-modulated antenna array (TMAA) radiates at various harmonic frequencies for the periodic switching time sequence. In this paper, the generation of the radiation pattern at the fundamental/central frequency only is considered. The KH algorithm is a flexible and robust search algorithm. It is applied here to find out the optimum sets of switching on-time duration for each array element and to determine the optimum inter-element separation between two array elements of the 20- and 36-element time-modulated circular antenna array (TMCAA). Particle swarm optimization (PSO) and differential evolution (DE) optimization techniques are also individually applied for the same design purpose to prove the superiority of the KH algorithm–based design. Finally, statistical analysis is performed to ensure the significance of the numerical results.

Time-Modulated Antenna Array for Real-Time Adaptation in Wideband Wireless Systems—Part II: Adaptation Study

In this article, an adaptive antenna system (AAS) based on a time-modulated antenna array (TMAA) and population-based metaheuristic algorithm is presented. The algorithm is driven by the signal-to-noise ratio measurements and provides real-time adaptation of the antenna pattern. This article also addresses the issue of multiband reception with a TMAA, demonstrating that the sidebands generated from frequency-diverse signals can overlap and interfere. The effectiveness of the AAS as part of a wireless communication system is presented in three different experimental scenarios that consider gradually or rapidly changing conditions as well as the interference caused by the reception of two signals with different carrier frequencies.

Time-Modulated Antenna Array With Beam-Steering for Low-Power Wide-Area Network Receivers

The Internet of Things (IoT) denotes a concept of connected devices that communicate seamlessly over the Internet. The wireless connectivity between IoT nodes and the Internet gateways can be realized in unlicensed frequency bands upon the low-power wide-area network (LPWAN). It is foreseen that due to a massive introduction of IoT devices the unlicensed bands will experience an increased interference level which will negatively affect the communication performance. Therefore, adaptive solutions should be considered to obtain robustness. This letter presents a time-modulated antenna array (TMAA) for LPWAN receivers and demonstrates its interoperability with a commercial of-the-shelf LoRa device. According to the conducted experimental investigation, whereby the beam-steering is obtained over the sidebands inherently generated by the TMAA, both the received signal strength and the signal-to-noise ratio (SNR) are improved by means of the progressive delay applied to the time modulation functions.

A Technique to Control the Harmonic Levels in Time-Modulated Antenna Arrays—Theoretical Concept and Hardware Verification Platform

This article presents techniques into prediction and control of the radiated harmonic levels in time-modulated antenna arrays (TMAs). The effect of ramping on the controlling switching waveform, due to slew in the RF switches, is analyzed first. This is followed by a novel technique for controlling and reducing the fundamental carrier component (due to the Fourier series 0 Hz term) that is always produced by TMAs. A new bespoke, steerable, TMA RF hardware test platform is presented, using three gain states to pragmatically implement the proposed carrier reduction technique. The platform implementation utilizes binary logic control interfaces to the TMA, rather than analog control interfaces. Laboratory measurements using the test platform demonstrate a 16.5 dB reduction (limited by PCB emissions) in the level of the fundamental carrier component relative to the steered first harmonic, from a possible reduction of 21.3 dB. The array gain for the first harmonic beam is 2 dBi.

Radiation Efficiency Limits in Direct Antenna Modulation Transmitters

Relative bounds on radiation efficiency are established for time-modulated antenna systems where radiation is generated by broadband conduction currents impressed using idealized non-radiating time-varying subsystems, such as those found in direct antenna modulation (DAM) transmitters. Analytical and numerical examples demonstrate that the condition of quasi-resonance, common in nearly all practical direct antenna modulation transmitters, imposes severe restrictions on the otherwise unbounded gains in effective efficiency theoretically achievable by this class of time-modulated transmitters.

Experimental investigation of beam-steering applied to 2 × 2 MIMO system with single receiving RF chain and time-modulated antenna array

AbstractMultiple antennas and multiple radio frequency (RF) chains in both the transmitter and receiver are required in conventional radio systems employing the multiple-input multiple-output (MIMO) method. This paper presents an experimental investigation of a beam-steering time-modulated MIMO receiver with a single RF chain. Implementation of the receiver is based on a time-modulated antenna array (TMAA) and a software-defined radio. The sidebands generated inherently by the TMAA are utilized as virtual spatial channels with the beam-steering functionality. Performance of the system is investigated experimentally. The bit error rate and condition number of the channel matrix are examined for different radiation patterns in order to determine favorable configurations in a given multipath environment. Obtained results show a considerable impact of the beam-steering on the performance of MIMO transmission.

Time-Modulated Antenna Array With Dual-Circular Polarization

This letter presents a time-modulated antenna array (TMAA) with a dual-circular (left-hand and right-hand) polarization. The TMAA is composed of a single-pole four-throw radio frequency switch and four linearly polarized elements arranged accordingly to the sequential rotation technique. A periodic switching of the elements leads to generation of sideband components in the frequency domain. The right-hand circular polarization (RHCP) and the left-hand circular polarization (LHCP) are synthesized over the first negative sideband frequency and the first positive sideband frequency, respectively, in wide frequency band. The TMAA used in the receiving mode provides conversion of polarization diversity into frequency diversity, therefore enabling simultaneous reception and automatic separation of two electromagnetic waves, which have the same frequency, however, mutually orthogonal senses of polarization.

Pattern Synthesis of Time-Modulated Sparse Array by an OPM-CVX Algorithm

This paper addresses the constrained multiobjective optimization problem of time-modulated sparse arrays. The synthesis objective is to find an optimal element arrangement and associated excitation strategy of sparse arrays, which realize the balance of radiation power and sideband suppression performance with minimum number of elements, and suppress side lobe level simultaneously. A novel hybrid algorithm based on orthogonal perturbation method and convex optimization (OPM-CVX) for the synthesis of time-modulated sparse antenna array is presented in this paper. In order to satisfy the main lobe beamforming and side lobe suppression of sparse arrays, the proposed method optimizes element positions with minimum array numbers by orthogonal perturbation method and optimizes excitations of array element with dynamic range ratio constraint by convex optimization. Furthermore, a trapezoidal pulse time-modulated switching function is proposed to find the balance of radiation power and sideband suppression performance. The numerical results indicate that the proposed algorithm can be an effective approach for synthesis problems of time-modulated sparse arrays.