Time-Modulated Arrays: A Four-Dimensional Antenna Array Controlled by Switches

With the rapid development of modern electronic technologies, antenna arrays typically operate in very complex electromagnetic environments. However, owing to the various errors such as systematic errors and random errors, conventional antenna arrays have relatively high sidelobes. Time modulated arrays (TMAs), also known as four-dimensional (4-D) antenna arrays, introduce time as an additional dimension for generating ultra-low sidelobes at fundamental component and realizing real-time beam scanning by harmonic components. Recently, the harmonic components can also be developed for various new applications including wireless communications and radar systems. In this review, we introduce comprehensively the fundamental methodologies and recent applications of TMAs. This aims to stimulate continuing efforts for the understanding of TMAs and explore their applications in various aspects. The methods mentioned in this review include three aspects: sideband radiation suppression, power efficiency of TMAs, and applications of harmonic components. These methods either improve the existing TMAs or promote the practical applications of TMAs. First, to suppress the sideband radiation, a method using non-uniform periodical modulation is introduced. The proposed method has an advantage of low computation and can be easily used for synthesizing a real-time radiation pattern according to the environmental need. Next, a TMA structure using reconfigurable power dividers/combiner is introduced to improve the power efficiency of feeding network. Finally, three applications of harmonic component including direction finding, calibration method, and space division multiple access are separately introduced to illustrate the development potential of TMAs.