Time-modulated Antenna Arrays Research Articles

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.

An optimal far‐field radiation pattern synthesis of time‐modulated linear and concentric circular antenna array

AbstractIn this paper, an optimal far‐field radiation pattern synthesis by using time modulation technique is carried out for linear antenna array (LAA), and concentric circular antenna array (CCAA) designs using a stochastic optimization method called grey wolf optimization (GWO). An improved far‐field radiation characteristic mainly depends on the synthesis of low side lobe level (SLL) and narrow first null beam width (FNBW). A low SLL is a requirement to reduce the interference by 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 a most significant role. It is considered as the fourth‐dimensional parameter as it 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 radiation pattern only at the fundamental/central frequency and at its first two harmonic frequencies are considered. The GWO algorithm is a flexible and robust search algorithm and 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 16‐element time‐modulated linear antenna array (TMLAA) and the nine‐ring time‐modulated concentric circular antenna array (TMCCAA). The GWO algorithm‐based results show a substantial improvement in far‐field radiation pattern synthesis compared with the uniform radiation pattern and those of the methods reported in state‐of‐the‐art literature.

Time-Modulated Antenna Array for Real-Time Adaptation in Wideband Wireless Systems—Part I: Design and Characterization

This paper presents a design of a time-modulated antenna array (TMAA) with substantially wider bandwidth and higher efficiency than have already been presented in the literature. The TMAA is designed for 5.4–5.8 GHz frequency band. More than 50 MHz of channel bandwidth is achieved by utilization of ultrafast microwave switches, digital delay lines with 60 ps step, and fast control circuitry. The efficiency is improved by alternate switching between the array elements instead of switching between the array element and a matched load. Moreover, a mathematical derivation of optimal switching sequence is given. The beam steering at the first sideband frequency was obtained with a 1° step in a range from −50° to 50°. The TMAA has been evaluated by means of the radiation pattern measurements at different sideband frequencies.

Null Placement in Time-Modulated Linear Antenna Arrays of Dipole Element

ABSTRACTThis paper describes the practical implementation of time-modulated linear dipole antenna arrays (TMLDAAs) using EM simulator. Cat swarm optimization (CSO) algorithm is applied to improve the null performance of TMLDAAs by radio frequency switch. The nulls at the particular positions of the direction of arrival of a TMLDAA can be reduced effectively by the proper optimization of current excitation weights and an effective design of switch-on time intervals of each element. CSO gives the optimized value of the current excitation weights of the radiation pattern. The optimized results obtained by CSO algorithm using MATLAB simulation are practically implemented and are designed through computer simulation technology–microwave studio simulation software for half-wave dipole antenna arrays. The dipole antenna is designed to operate at a resonant frequency of 2 GHz. The antenna exhibits a frequency band from 1.8331 to 2.1285 GHz, which is applicable for wireless applications.

Radiation Performance Characteristic Optimization of Time-Modulated Circular Antenna Arrays

ABSTRACTIn this paper, memetic flower pollination algorithm (MFPA) is proposed for solving the optimal synthesis of time-modulated half symmetric circular antenna array (TMHSCAA) and time-modulated asymmetric circular antenna array (TMASCAA) by controlling the switching time sequence and the excitation phase of each element time intervals and phases. Current excitation and inter-element spacing of each element are kept uniform. A unique cost function has been formulated for both the case studies. Several low-side lobe patterns synthesized from TMHSCAA and TMASCAA have been compared with those of the conventional circular array. A 20- and 36-element TMHSCAA and TMASCAA have been taken as examples. Furthermore, a novel six-ring time-modulated concentric hexagonal antenna array (TMCHAA) design has been considered to check superiority of the MFPA. The cost function has been designed for the concurrent improvement of side lobe level (SLL) and directivity in the new geometry of TMCHAA by an appropriate fine-tuning of the switching time succession and the inter-element separation of the hexagonal ring. Numerical results show that TMHSCAA, TMASCAA, and TMCHAA can be successfully used for the synthesis of low SLLs even if the amplitude excitations and inter-element spacing are uniform. Statistical analysis is also carried out to ensure that the results are significant in terms of the statistics. The results show that MFPA can exhibit a better performance than the other algorithms like real-coded genetic algorithm, particle swarm optimization, and differential evolution for the antenna array synthesis examples.

A Time Modulated Printed Dipole Antenna Array for Beam Steering Application

This paper presents time modulated beam steered antenna array without phase shifters. The beam steering is analyzed considering a two-element time modulated antenna array (TMAA) of printed dipoles with microstrip via-hole balun. The proposed array resonates at the Industrial, Scientific, and Medical (ISM) radio bands, 2.45 GHz and 5.8 GHz, and offers wide bandwidth inherited due to modified structure of ground plane. Array elements are excited by complex exponential excitation signal through broadband power divider and radio frequency (RF) switches to achieve amplitude and phase variation without phase shifters. Differential Evolution algorithm is used to modify the time sequences of the RF switches connected to the antennas to generate radiation pattern with optimum dynamic efficiency by suppressing sideband radiations. Also switch-on time instant of RF switch connected to the subsequent element is modulated to steer the beam towards different directions. The proposed prototype is fabricated followed by parametric optimization. The fabrication results agree significantly well with simulated results.

Time-Modulated Antenna Arrays for Circularly Polarized Shaped Beam Patterns

This letter presents new designs of time-modulated antenna arrays for circularly polarized shaped beams. Disk patches are used at the X-band as the elements distributed in nonuniform concentric square and circular apertures. The arrays are designed by optimizing the time-switched sequence of the elements while maintaining uniform amplitudes. The particle swarm optimization is utilized as the synthesis strategy. Two design examples for circularly polarized flat-top and isoflux patterns are presented.

Time-Modulated Antenna Array With Lossless Switching Network

In this letter, a novel architecture for a time-modulated antenna array (TMAA) based on single-pole double-throw (SPDT) switches is presented. The proposed TMAA has lossless switching network because there is no power loss during the off state. In addition to improved efficiency, this TMAA provides beam-scanning capabilities. Moreover, the proposed TMAA has a constant instantaneous directivity, which is favorable for some applications. The architecture has been implemented as an aperture-coupled patch antenna array and verified as a smart antenna in a digital wireless communication system.

Pencil beam pattern synthesis of time-modulated concentric circular antenna array using PSO with Aging Leader and Challenger

In this paper, a nine-ring time-modulated concentric circular antenna array (TMCCAA) with isotropic elements has been analyzed based on an evolutionary optimization algorithm called particle swarm optimization (PSO) with Aging Leader and Challenger (ALC-PSO) for the reduction of side lobe level (SLL) and improvement in the directivity. Some other population-based evolutionary algorithms like real-coded genetic algorithm, PSO, and differential evolution (DE) have also been applied for the sake of comparative performance study of the same optimal designs. The comparative case studies as Case-1 and Case-2 are made with three control parameters like inter-element spacing in rings, inter-ring radii, and the switching “ON” times of rings with the help of same algorithms. ALC-PSO performs the dual task of improvement of directivity values as well as minimization of SLL of TMCCAA. Experimental results show a considerable SLL reduction with respect to the uniform case. Again, the results show Case-2 outperforms Case-1 with respect to SLL and directivity. Apart from this, the powers radiated at the center/fundamental frequency, the first two sideband frequencies, and dynamic efficiency have been computed. It has been observed that as the sideband frequency increases, both the powers radiated by harmonic frequencies, sideband level decrease. The aperture size is a very important constraint for the array. Hence, in our optimized design, the maximum radius of the concentric ring array is constrained.

Single-Sideband Time-Modulated Phased Array

A new in-phase/quadrature (I/Q) complex modulation technique to realize single-sideband time-modulated phase-only weighting on an array antenna is proposed. Based on modulating rectangular pulses and trapezoidal pulses, the theories of generating a scanning beam at the single positive sideband are presented. It was found that using trapezoidal pulse modulation can obtain excellent performance in power efficiency and undesired sideband level than using rectangular pulse modulation. Unlike conventional time-modulated antenna array where each array element is connected to a RF switch, in the proposed scheme, each element is connected to an I/Q channel modulator which is composed of two Wilkinson power dividers, two RF switches, two $0/\pi $ phase shifters in RF channels, and one $\pi/2 $ fixed-phase shifter in the control circuit. By properly controlling both the phase shifters and the switches in time domain, the single-sideband modulation can be realized with the uniform amplitude and variable phase in frequency domain. The I/Q modulator acts as a phase shifter and can be used to form a phased array. In this paper, the main efforts have been paid to find the pulse sequences to suppress the spurious bands. To validate the proposed technique, simulated results of an eight-element single-sideband time-modulated linear array obtained from the array factor and full-wave analysis are reported. In the case of using rectangular pulses, the power efficiency of the scanning beam is 91.47% and the peak level of the highest undesired harmonic is $-13.98\;\mathrm{dB} $ . In the case of using trapezoidal pulses, the best values can reach 99.79% and $-27.98\;\mathrm{dB} $ .

Design of a time-modulator to synthesize different patterns in time-modulated antenna arrays

This paper presents a novel technique to design a time-modulator that can be used as a discrete component to generate different patterns in time-modulated antenna array (TMAA) system. The technique quantizes the modulation period into a number of levels with equal step size between the consecutive levels and rounds off the on-time of the antenna elements to nearest quantization levels to obtain quantized on-times (QOTs) of the corresponding elements. In order to realize the time modulation technique, a representative block diagram of a time-modulator defined as “quantized time-modulator” is presented. It is shown that the effect of quantization errors on the synthesized patterns can be diminished by selecting a suitable number of quantization states by using artificial bee colony (ABC) as a global optimizer. Accordingly, two previously reported examples based on simulated annealing (SA) algorithm, optimized by using continuous search space of on-time are considered, and ABC optimized results using discrete search space of QOT are compared with those obtained by SA. Finally, a fully digitally controlled, low side lobe flat-top pattern with low dynamic range ratio of static amplitude is synthesized by considering discrete search space of QOT.

Design of digitally controlled multiple-pattern time-modulated antenna arrays with phase-only difference

An optimization approach based on differential evolution (DE) is proposed to design multiple-pattern time-modulated linear antenna arrays (TMLAAs) with phase-only control by using 5-bit digital phase shifters. The synthesized multiple patterns include a pencil beam (PB), a flat-topped beam (FTB), and a cosec squared pattern (CSP). The function of the DE is to find, simultaneously, a common, i.e., fixed, set of continuous values of switch-on time durations and discrete static excitation amplitudes for 5-bit digital attenuators, and different sets of discrete excitation phase distributions for 5-bit digital phase shifters; to generate different power patterns in the far field of the TMLAA. By perturbing the static amplitude distribution of a 20-element TMLAA in the discrete search range of “(0.2–1),” the patterns are obtained by reducing side lobe levels (SLLs) to almost −20 dB and sideband levels (SBLs) to less than −25 dB. Towards the end, the same on-time and amplitude distribution is used to produce a symmetric side lobe (S-SL) and asymmetric side lobe (A-SL) CSP, and their usefulness under a noisy signal environment is discussed.

SYNTHESIS OF SIMULTANEOUS MULTIPLE-HARMONIC-PATTERNS IN TIME-MODULATED LINEAR ANTENNA ARRAYS

In time-modulated antenna arrays (TMAAs), as a result of periodical switch-on and switch- ofi of the antenna elements, including operating frequency (termed as center frequency) signal, sideband signals are appeared at either sides of the center frequency in integer multiples of the modulation frequency. In this paper, it is shown that without using phase shifters, just by suitably controlling the on-time instants (OTIs) and on-time durations (OTDs) of a time-modulated linear antenna array (TMLAA) elements, simultaneously, along with a pencil beam pattern at the operating frequency, a shaped beam pattern can be obtained at both the flrst positive and negative harmonics of the time- modulation frequency. The important advantage of such a technique is that realization of multi-beam pattern in conventional antenna array (CAA) system generally requires complex feed network, whereas by using simple radio frequency (RF) switching circuit in the feed network of TMLAA, by virtue of the properties of harmonic radiations, synthesis of a shaped pattern at either (positive or negative) harmonic results in generating the same pattern in its opposite harmonic, and the synthesized patterns at difierent harmonics can be simultaneously used as independent communication channels. By employing a difierential evolution (DE) based optimization method, numerical results for a 16-element TMLAA with uniform excitation show that in conjunction with a pencil beam pattern at the center frequency, a ∞at-top or a cosec square pattern at flrst positive and negative sidebands of side-lobe levels (SLL) i20dB can be synthesized by suppressing the higher sideband level (SBL) to below i10dB.

A single objective approach for suppressing sideband radiations of ultra-low side lobe patterns in time-modulated antenna arrays

In this paper, a novel optimization method based on single objective, that is, minimization of sideband radiation (SBR) of ultra-low side lobe, narrow beam patterns in time modulated antenna arrays (TMAAs) is proposed. The proposed method utilizes the weighting vectors of the low side lobe Dolph-Chebyshev/Taylor series patterns as the dynamic excitation coefficients of the desired pattern at fundamental radiation. Differential evolution algorithm is employed to distribute the static amplitudes and switch-on time durations in such a way that in the optimization process, dynamic excitation distribution remains the same. Static amplitudes are perturbed in a predefined search range of (0.25, 1), whereas the weighted values of switch-on time durations are obtained by dividing dynamic excitation coefficients by static amplitudes. The technique greatly simplifies the difficulties of multi-objective TMAA synthesizing problem by reducing it to a single-objective optimization problem. Numerical examples for a 32-element linear array are presented to produce ultra low side lobe Taylor and Dolph-Chebyshev pattern with low value of maximum sideband radiation (SBRmax). The optimization results of the proposed method are also compared with those obtained by other optimization techniques, which have been reported previously.

Pattern Synthesis with Specified Broad Nulls in Time-Modulated Circular Antenna Arrays

This article presents an approach for the synthesis of time-modulated circular array patterns with specified null width constraints. The time-modulated circular antenna arrays with uniform amplitude excitations are designed through the differential evolution algorithm with their excitation phases, and the switch-on time intervals of each element of the time-modulated circular arrays are the variables to be optimized. Several examples synthesized from the time-modulated circular array with the prescribed null width and depth are compared with some published results of the conventional circular array. Simulation results illustrate the achievable performance of the approach in successfully synthesizing patterns with desirable broad nulls, even if the amplitude excitations are uniform.

Adaptive Nulling with Time-Modulated Antenna Arrays Using a Hybrid Differential Evolution Strategy

A flexible approach based on a hybrid differential evolution strategy was developed for adaptive pattern nulling with time-modulated linear antenna arrays. The hybrid differential evolution strategy adjusts only the least significant bits of the digital phase shifters and the on—off time sequence to minimize the total output power; deep nulls can then be placed in the direction of the interferences without much compromise of the shape of the main beam. Thanks to the new design freedom introduced in time-modulated antenna arrays, this adaptive nulling approach exhibits better performance over the traditional phase-only, amplitude-only, and phase-amplitude adaptive nulling methods, in terms of the practical implementation, nulling depth, and pattern deterioration. Numerical examples are presented to demonstrate the effectiveness and robustness of the proposed approach.

Shaped patterns synthesis in time-modulated antenna arrays with static uniform amplitude and phase excitations

A novel approach for the synthesis of shaped beam patterns in time-modulated antenna arrays (TMAAs) with static uniform amplitude and phase excitations is proposed in this paper. Based on the sideband radiation in TMAAs, shaped beam patterns can be realized by only controlling the switch-on time sequences of the TMAAs. Differential evolution (DE) algorithm is adopted to optimize the time modulation parameters to obtain the desired flat-top and cosecant-squared beams and to suppress the sidelobe levels (SLLs). Simulation results of a time-modulated linear array (TMLA) and a time-modulated semicircular array (TMSA) demonstrate the effectiveness of the proposed approach for the synthesis of shaped beam patterns from TMAAs.

Design of a novel monopulse antenna system using the time-modulated antenna arrays

A novel monopulse antenna for a tracking radar system is proposed using the time modulated antenna array technique. The time modulation technique applied in the antenna arrays overcomes the usual need for compromise between sum and difference beams and avoids the need for implementation of two separate feed networks. The time modulated antenna array also relaxes the error tolerance of the tracking accuracy from the amplitude and phase errors, due to the new design freedom of “time” which can be controlled precisely and quickly. Moreover, the position of the target can be recovered by two reflected echoes from one previously transmitted pulse, thus the tracking errors resulting from the excitation errors and receiver noise in conventional antenna arrays can be greatly alleviated. Numerical results show that with the aid of time modulation technique, one sum beam and two difference beams can be simultaneously obtained either for the boresight or off-boresight target tracking. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.

Mutual-Coupling Compensation in Time-Modulated Antenna Arrays for Flat-Top Pattern Synthesis

A method that can be used to compensate for the mutual-coupling effect in time-modulated antenna arrays for synthesizing flat-top patterns is proposed in this article. Based on the measured complex embedded element patterns, the differential evolution algorithm is employed to optimize time sequences and phase excitation of each element in the array and to suppress the sideband level, leaving the amplitude excitations to be uniform. A −20-dB sidelobe level flat-top pattern is successfully synthesized in which the ripple level of the mainlobe is lower than 0.5 dB and the sideband level is lower than −10 dB. An S-band eight-element printed dipole with a double-layered structure linear array is used in the experiment to verify the proposed method, and the measured results are in good agreement with the simulated results.