In electromagnetics, optimization problems generally require high computational resources and involve a large number of unknowns. They are usually characterized by non-convex functionals and continuous spaces suitable for strategies based on Differential Evolution (DE). In such a framework, this paper is aimed at presenting an overview of Differential Evolution-based approaches used in electromagnetics, pointing out novelties and customizations with respect to other fields of application. Starting from a general description of the evolutionary mechanism of Differential Evolution, Differential Evolution-based techniques for electromagnetic optimization are presented. Some hints on the convergence properties and the sensitivity to control parameters are also given. Finally, a comprehensive coverage of different Differential Evolution formulations in solving optimization problems in the area of computational electromagnetics is presented, focusing on antenna synthesis and inverse scattering.

Differential Evolution as Applied to Electromagnetics

The proliferation of wireless services is driving innovative phased array solutions that are able to provide better cost/performance tradeoffs. In this context, the use of irregular array architectures provides a viable solution. This paper reviews and highlights some of the most recent advances in this field, including clustered, thinned, sparse, and time-modulated arrays, and their proposed design methodologies.

Unconventional Phased Array Architectures and Design Methodologies—A Review

In this paper, the synthesis of simultaneous multibeams through time-modulated linear arrays is studied. Unlike classical phased arrays where the antenna aperture is usually shared to generate multiple beams, the periodic on-off sequences controlling the static excitations are properly defined by means of an optimization strategy based on the Particle Swarm algorithm to afford desired multiple patterns at harmonic frequencies to make practical application of these harmonic beams which are typically regarded as an undesirable effect in time-modulated arrays. The synthesis of simultaneous broadside sum and difference patterns, flat-top and narrow beam patterns, and steered multibeams is enabled as assessed by a set of selected results reported and discussed to show the potentialities of the proposed method. Comparisons with previously published results are reported, as well.

Harmonic Beamforming in Time-Modulated Linear Arrays

Time and frequency modulated arrays have numerous application areas including radar, navigation, and communications. Specifically, a time modulated array can create a beampattern with low sidelobes via connecting and disconnecting the antenna elements from the feed network, while the frequency modulated frequency diverse array produces a range-dependent pattern. In this paper, we aim to introduce these advanced arrays to the signal processing community so that more investigations in terms of theory, methods, and applications, can be facilitated. The research progress of time/frequency modulated array studies is reviewed and the most recent advances are discussed. Moreover, potential applications in radar and communications are presented, along with their technical challenges, especially in signal processing aspects.

An Overview on Time/Frequency Modulated Array Processing

In this paper, a novel technique for electronic beam steering in time modulated linear array (TMLA) is proposed. The beam steering technique is realized at the flrst sideband by controlling the switch-on time sequences of each element in the TMLA without using phase shifters. The difierential evolution (DE) algorithm is employed to improve the gain and suppress the sidelobe levels (SLLs) at both the center frequency and the flrst sideband, simultaneously. An S-band 8-element double-layered printed dipole linear array was used to verify the technique experimentally. Measured results are compared with numerical data, and good agreement is reported. Moreover, some simulation results on the binary phase shift keying (BPSK) modulated signals arriving from difierent directions received by the proposed approach are presented, which validates the application of the proposed beam steering technique.

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A Novel Electronic Beam Steering Technique in Time Modulated Antenna Array

A novel approach for estimating the direction of arrivals (DOAs) in time modulated linear arrays (TMLAs) with unidirectional phase center motion (UPCM) scheme is proposed in this paper. Based on the fact that the main beams of the patterns at different sidebands can be directed at different directions, the corresponding received signals can be used to compose a received data space. Thus, the spatial locations of the far-field sources can be estimated by using multiple signal classification (MUSIC) algorithm. Simulation results of the DOA estimation in an 8-element TMLA with the UPCM scheme validate the proposed approach, where the performance such as the accuracy and resolution of the DOA estimation is obtained through Monte-Carlo simulations. As compared to the DOA estimation based on conventional uniform linear arrays (ULAs), a much better resolution performance is obtained.

Direction of Arrival Estimation in Time Modulated Linear Arrays With Unidirectional Phase Center Motion

The time modulated (TM) linear arrays with variable aperture sizes (VAS) are applied to the airborne pulsed Doppler (PD) radar system in this paper. The VAS arrays which have great flexibility in the control of the aperture excitations are employed to synthesize low/ultra-low sidelobe patterns in the PD radar system, and the optimized time sequences obtained via the differential evolution (DE) algorithm is used to minimize the average power loss due to the time modulation. Numerical simulation results of the signals transmitted and received by PD radar based on the VAS arrays show that the time modulation changed the waveforms of the signals in time domain but the received signals also contain the correct range and velocity information of the moving target.

A Study on the Application of Time Modulated Antenna Arrays to Airborne Pulsed Doppler Radar

In this paper, an additional degree of freedom "time" is introduced into conventional linear arrays with unequal element spacing forming the time modulated unequally spaced linear arrays (TMUSLAs). The differential evolution (DE) algorithm is adopted to optimize the positions and switch-on times of elements in the TMUSLAs to suppress the sidelobe levels (SLLs), sideband levels (SBLs) and constrain the beamwidth, simultaneously. Numerical results show that lower SLLs and SBLs are obtained by the proposed method than those by the published results.

Sidelobe Suppression in Time Modulated Linear Arrays with Unequal Element Spacing

The invention discloses antenna array phase control technology based on time modulation and a system realizing method thereof. By adopting the technology, an antenna array can realize spatial electric scanning of beams without using a phase shifter. The basic proposal of the invention comprises the antenna array, a complex programmable logic device, a high-speed radio-frequency switch, a receiver, and the like. Based on the proposal, by reasonably designing the working time sequence of each antenna unit, the technology and the method can realize the electric scanning of the antenna array beams in the space under the condition that the phase shifter is not needed to move the phase for each antenna unit and realize a directional diagram according with the requirement of side lobe level. By reasonably adding a frequency mixer, a filter, an amplifier and the like into the receiver, three beams and double-beam synchronous electric scanning can be conveniently realized. Because the phase shifter is not adopted, the volume of the system can be further reduced, and the complexity of the system can be reduced. Because the electric scanning of the antenna array beams can be conveniently realized, the technology and the method can be widely applied to radar and wireless communication systems.

Gang Li

Papers

A Novel Electronic Beam Steering Technique in Time Modulated Antenna Array

Direction of Arrival Estimation in Time Modulated Linear Arrays With Unidirectional Phase Center Motion

A Study on the Application of Time Modulated Antenna Arrays to Airborne Pulsed Doppler Radar

Sidelobe Suppression in Time Modulated Linear Arrays with Unequal Element Spacing

Antenna array phase control technology based on time modulation and system realizing method thereof