A compact S-band front-end rectenna for wireless power transfer application

Abstract

A rectenna is used to receive transmitted power through space for wireless power transmission (WPT). This thesis presents the development of an S-band frontend microwave rectenna prototype elements operating at 2.45 GHz of industrial, scientific and medical (ISM) band. The microstrip front-end rectenna consists of an antenna and a low-pass filter (LPF). Both prototype elements were simulated. Optimized designs were fabricated and tested. For the antenna, two designs were investigated, i.e. corner-truncated square patch (CTSP) and slitted CTSP (SCTSP) fed by electromagnetic coupling. Size reduction of 37 % has been achieved through simulations for the SCTSP, compared to CTSP design at the operating frequency of 2.45 GHz. Measurement results showed that the antenna exhibits well matched impedance at the corresponding frequency of operation but with a slight shift of 123 MHz higher frequency as well as 2.5 dB higher axial ratio. SCTSP is proposed for the antenna candidate front-end rectenna. LPF was designed with elliptic function characteristic. Three designs were investigated for single element structure of 3rd order. These were stepped-impedance hairpin (SIH), meandered-gap hairpin (MGH) and over-coupled end meandered-gap hairpin (OCEMGH). Through simulations, size reduction of 28.6 % has been achieved for the MGH, compared to SIH. Both exhibit the same cutoff frequency. It was also found that higher cutoff frequency corresponds to lower insertion loss at 2.45 GHz. An impressive reduction in size of 60 % has been achieved for the OCEMGH, compared to SIH. The OCEMGH also exhibited better insertion loss at 2.45 GHz and rejection at 4.9 GHz and hence is proposed as the filter candidate for the front-end rectenna. Elliptic function LPF of 5th order was also designed. Two designs were proposed, i.e. unidentical cascaded hairpin (UCH) and identical cascaded hairpin (ICH). Simulated results showed that both filter have sharper cutoff frequencies compared to that of SIH. Measurement results showed that the five LPFs agree well with the simulated results.