Wireless Power Transmission (WPT) is an attractive powering method for wireless sensor nodes, battery-less sensors, and Radio-Frequency Identification (RFID) tags. The key element on the receiving side of a WPT system is the rectifying antenna (rectenna) which captures the electromagnetic power and converts it to the electric power. For maximum power transfer between the antenna and the rectifier, the antenna's input impedance should be matched to that of the rectifier circuit. In this paper a complete design method is presented to accurately calculate the impedance and the output voltage of the rectifier part in a wireless power transmission system. The presented method uses circuit analysis to calculate the input impedance of a schottky diode as a function of frequency, for different power levels. For the output voltage, the Ritz-Galerkin method is used to predict the output DC voltage across different load resistances. Moreover, the influence of the diode's parameters on the output voltage are discussed. All the simulated results are validated by measurements and by Harmonic Balance (HB) simulations.