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This paper proposes a compact Th&#233;venin model for a rectenna. This model is then applied to design a high-efficiency radio frequency harvester with a maximum power point tracker (MPPT). The rectenna under study consists of an L-matching network and a half-wave rectifier. The derived model is simpler and more compact than those suggested so far in the literature and includes explicit expressions of the Th&#233;venin voltage (<i>V</i>_oc) and resistance and of the power efficiency related with the parameters of the rectenna. The rectenna was implemented and characterized from &#8722;30 to &#8722;10 dBm at 808 MHz. Experimental results agree with the proposed model, showing a linear current&#8211;voltage relationship as well as a maximum efficiency at <i>V</i>_oc/2, in particular 60% at &#8722;10 dBm, which is a remarkable value. An MPPT was also used at the rectenna output in order to automatically work at the maximum efficiency point, with an overall efficiency near 50% at &#8722;10 dBm. Further tests were performed using a nearby transmitting antenna for powering a sensor node with a power consumption of 4.2 &#181;W.