Pulsewidth-Modulated Timed Array for Independently Controllable Harmonic Beams in Multiuser Wireless Scenario

Abstract

This article presents a novel time modulated array (TMA) or timed array, which can be a potential candidate for enabling versatile, multiuser heterogeneous wireless systems, with each user uniquely powered by a switching harmonic frequency. In the proposed timed array, each switch at the antenna element feed is controlled with a pulsewidth-modulated (PWM) signal, carrying the phase information of a triangular wave and a reference signal. This PWM timed array architecture offers precise control of the number of radiated harmonics, independent steering of individual beams, and radiated beam power levels. The user-definable beam steering makes the system an efficient candidate for dynamic multiuser applications demanding stringent scanning capabilities. The proposed timed array is experimentally validated using a $1 \times 4$ microstrip antenna array at 2.4 GHz with a PWM control signal generated by a PYNQ-Z2 field-programmable gate array (FPGA). The effect of PWM signal waveform and a systematic design methodology to achieve desired harmonics, beam direction, and power level are systematically presented in this article. Furthermore, the RF switching speed constraints and effects on PWM timed array architecture are discussed in detail.