Insertion Loss Characterization of Impedance Matching Networks for Low-Power Rectennas

An impedance matching network inserted between an antenna and a rectifier is essential for rectennas, but few studies have characterized the insertion loss of the matching network if nonideal matching elements are considered. In general, the matching elements, including lumped capacitors, lumped inductors, and transmission lines, are approximated as lossless; if the overall conversion efficiency decreases, the underlying reason seldom attributes to the loss of the matching network. In this paper, we derive the insertion loss of the matching network comprising actual lumped elements and transmission lines. The loss is quantified using the operating power gain of a two-port network, which varies with different levels of input power. When the input power ranges between -30 and 0 dBm, more than 95%, 90%, and 75% of power dissipates at 900 MHz, 1.8 GHz, and 2.4 GHz, respectively, due to the use of actual matching elements. The numerical results are verified by experimental data, and all the analyses demonstrate that the loss of the matching network becomes very serious as the input power is low. These observations are explained using the contour plot of operating power gain. Accordingly, this study provides a theoretical development for rectenna designers.