This paper presents an energy harvesting system which extracts energy from radio frequency radiation for battery charging applications. It comprises of a new differential center tapped Microstrip antenna, off-chip matching circuit, on-chip novel CMOS rectifier and control circuitry in 180nm CMOS technology. For on-chip modules, thick oxide devices have been used so as to meet the charging requirements of the target batteries. The designed battery charging module charges either of 250μAh and 10μAh batteries according to the selected battery and available input power. The 250μAh battery is charged at input power of 2dBm and 10μAh battery is charged at input power of -6.5dBm. The fabricated antenna has a gain of 8.3dB and a VSWR less than 2 in the bandwidth from 844 to 970MHz. An efficient Periodic Steady State(PSS)-based power matching technique is also presented which improves the system efficiency. For 0dBm input power at 950 MHz to the antenna the proposed technique leads to 55.2% efficiency of RF to DC converter system. In addition to the integrated design a discrete rectifier using highfrequency Schottky diodes and differential microstrip antenna at the input are fabricated. The discrete system uses the proposed matching technique and exhibits efficiency of 40% for -11dBm received power by the antenna.