In this study, a rectenna is adopted in a microwave-based wireless power transfer system to rectify the received radio frequency (RF) to DC power. Each rectenna comprises a DC-DC converter at the DC output port to ensure a stable power supply and a Schottky diode for the DC-combining network. The results indicate that the RF-DC conversion efficiencies of the rectifier circuit and <inline-formula> <tex-math notation="LaTeX">$4\times 1$ </tex-math></inline-formula> rectenna were 71% and 71.2% when the unit-cell RF input levels were 19 dBm and 19.6 dBm, respectively. Furthermore, the DC output levels of a <inline-formula> <tex-math notation="LaTeX">$4\times8$ </tex-math></inline-formula> rectenna with and without the DC-DC converter were 28 V and 30 V, respectively, when the unit-cell RF input level was 20.2 dBm. Additionally, the RF-DC conversion efficiencies were 52.6% and 59.9% with and without the DC-DC converter, respectively. Thus, we experimentally verified that the Schottky diode combined with the DC-DC converter at the DC output port can increase the DC power combining level, making it suitable as an extendable array rectenna system.