High-Efficiency Class-E Seamlessly Integrated Active-Integrated Antennas of Far-Field SWIPT Base Stations for Batteryless IoT Applications

A deep integration of active-integrated antennas (AIAs) with high transmitter efficiency (TE), high polarization purity, and low interference has presented a difficult-to-ignore challenge for designers. This fundamental problem in AIA design emerges from the lack of an impedance-matching flexibility between the antenna aperture and active element for high dc-to-RF efficiency without deteriorating the radiator’s performance. This work proposes and presents an approach for the seamless integration of AIAs based on a modified rectangular patch loaded with shorting pins. Numerical and experimental results obtained in this research demonstrate that by distributing the shorting pins in the nodes of the fundamental and second-harmonic spatial modes of the canonical patch, new degrees of freedom for flexible impedance matching can be achieved without compromising the radiator’s radiation pattern, polarization purity, and radiation efficiency. The effectiveness of the proposed design strategy is illustrated by a fabricated seamlessly integrated AIA that presents the highest active gain reported in the literature while keeping cross-polarization (CP) and harmonic-interference levels low. Based on the obtained results, the proposed design strategy is believed to have great potential for developing low-cost and high-efficiency far-field simultaneous wireless information and power transmission (SWIPT) base stations for batteryless Internet of Things (IoT) applications.

I. Introduction

In recent years, simultaneous wireless information and power transmission (SWIPT) has become a major trend in many consumer electronics and systems, such as wearables, smartphones, and tablets. SWIPT is expected to become even more prominent in the next decades due to the proliferation of the Internet of Things (IoT) [1]. However, a major drawback of developing the first generation of SWIPT-enabled networks is that most of the advancements made in this direction rely on near-field-based technologies, e.g., magnetic induction (MI)-based base stations integrating inductive charging with near-field communication (NFC) functions [2]. Although such technologies have achieved an end-to-end power transfer efficiency (PTE) as high as 75%, they are usually limited to an operating range of tens of millimeters only. Certain improvements in this regard have been achieved with resonant or metamaterial-enhanced coupling techniques but at the expense of extremely limited bandwidth and/or complex tuning mechanisms.