Time Modulated Arrays: From their Origin to Their Utilization in Wireless Communication Systems

Abstract

Time-modulated arrays (TMAs) are electromagnetic systems whose radiated power pattern is controlled by the application of variable-width periodical pulses to the individual elements. The nonlinear nature of the array operation causes the appearance of radiation patterns at the harmonic frequencies of such periodic pulses. The technique can be used for improving the side-lobe level (SLL) topology of the radiation pattern at the central frequency and/or to profitably exploit the harmonic patterns in order to supply smart antenna capabilities. Among the latter features, the TMA harmonic beamforming takes on special importance due to its attractive trade-off performance-hardware complexity. From this perspective, TMAs are sensors capable of transforming the spatial diversity of a communication channel into frequency diversity, thus improving the performance of a wireless communication. In addition to a walk through the origins of the concept, and a brief analysis of the mathematical fundamentals, this paper organizes the prolific state of the art of TMAs in two major thematic blocks: (1) TMA design from an antenna perspective; and (2) TMA design from a signal processing perspective.

Wideband Hybrid Precoding Using Time Modulated Arrays

“…This parameter should be set according to the strength of the undesired radiation generated by the TMA. The solution to (38) in [23] is obtained with a convex solver. Here, we propose to solve (38) using a steepest descent method.…”

“…This flexibility is not possible in conventional TMAs (e.g. [15], [16], [38]) where the power distribution among the harmonic modes quickly reduces with q, i.e., F…”

Optimization Approaches in Sideband Calculations and a Non- Iterative Harmonic Suppression Strategy in 4D Arrays

“…40is not preferred to be used in an optimizer. Instead of using the direct result, the ratio of the harmonic power to the actual power is more meaningful which may be written by P H ¼ P H P H þ P 0 (41) where P 0 represents the power in main radiation given by where ϖ ¼ P H I; τ; R ÀÁ À Θ d Þ while Θ d is being the desired harmonic to main power ratio.…”

“…In the literature, TMAs have been used for direction finding and direction of arrival estimation applications [33][34][35][36][37], harmonic beam steering, adaptive beamforming and communication over sidebands [38][39][40]. Furthermore, an overview about TMAs and additional enhancements for TMA concept have been published by Maneiro-Catoria et al in 2017 [41][42].…”

A Method for Forming Distributed Beams in Time-Modulated Planar Arrays

“…TMAs have received increased research interest in recent years due to the switching methods being considerably less complex than phase-shifting and amplitude weighting methods. Research into TMAs has started to spread to multiple application domains such as signal processing [3] and communications systems [4]. Research has mainly focused on developing methods of controlling the array output.…”