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Development of Rectenna for Estimating Received Power Level Using Second Harmonic Wave

This paper proposes a novel rectenna that can estimate the received power level by using the second-harmonic power generated by the rectenna. The proposed rectenna consists of two rectifier circuits for fundamental waves (main rectifier circuits), a branch line coupler (BLC), a dual-band pass filter (DBPF), and a rectifier circuit for second-harmonic waves (feedback rectifier circuit). The feedback rectifier circuit rectifies the second harmonic wave extracted by BLC and DBPF, and the second harmonic power level is read as the rectified dc voltage. We estimate the received power level of each rectenna element from the read dc voltage level and feedback them to the transmitting array antenna. In this paper, we describe the design method and the results of the simulation and measurement of the proposed rectenna. The proposed rectenna has the rf-dc conversion efficiency of 75.3 % and the output dc voltage of 0.99 V of the feedback rectifier circuit at the input power of 34.7 dBm. Our results show that the output dc voltage of the feedback rectifier circuit is determined by the input power, resulting in the received power estimation.