Design of a novel circularly polarized (CP) rectenna (rectifying antenna) at 925MHz for wireless power transmission (WPT) applications involving wireless power transfer to low power consumption wireless device is proposed. In order to build the rectenna, a CP wide-slot antenna and a finite ground coplanar waveguide (CPW) circuit both with good impedance matching, have been developed. In addition, the size of the wide-slot antenna is smaller than the conventional slot antenna up to 60% when the meander line structure is adopted. The rectenna is the voltage-doubler rectifier with the low-pass filter (LPF) for efficiency optimization and higher order harmonics re-radiation elimination. According to the measured results, the maximum RFto- DC conversion efficiency of the rectenna achieved 75% when the RF power of 15dBm is received with a load resistance of 2k at free space. The experimental results prove that the proposed rectenna is suitable for the WPT applications.

1. INTRODUCTION

Both wireless power transmission (WPT) [1] and solar power transmission (SPT) [2] are the promising techniques for the long-distance power supply of wireless applications, such as radio frequency identification (RFID) tags [3,4], wireless embedded sensors [5-7], medical implant with biotelemetry as a communication link [8,9], etc. The rectenna (rectifying antenna) is one of the most important components for above-mentioned techniques, which has great potential to deliver, collect and convert radio frequency (RF) energy into useful direct current (DC) power for neighbored electronic devices or to recharge batteries through free space without using the physical transmission line [10]. The typical rectenna [11,12] basically consists of an antenna for receiving RF power, a low- or band-pass filter (LPF/BPF) as an input filter for selecting/suppressing energy or signal and impedance matching simultaneously, a diode as the rectifying device for RF-to-DC power conversion, a bypass capacitor as the output filter for RF block/DC pass, and a load resistance is last.