Funding is requested for a three year program that will: 1) complete development of a small-scale, portable solid-state retrodirective wireless power transmission (WPT) demonstration system; 2) use the solid-state phased array transmitter and rectenna (rectifier + antenna) developed in task 1 for ground testing to determine the phase control of the transmitter. This program will provide a path for the first US non-laboratory demonstration of beamed power in which the transmitted beam will be controlled by a pilot beam from the receiving antenna (a retrodirective system). The program will demonstrate key components of an integrated microwave wireless power transmission system: a phased array transmitter, rectifying receiving antenna (rectenna) and the retrodirective control system. The transmitter will operate at a frequency of 5.8 GHz and will consist of 4 panels, which will allow beam steering in two dimensions. The array will consist of 640 elements, arranged in 10 subarrays with 64 elements in each subarray. Microstrip patch antenna will be used for low cost fabrication, lightweight, planar structure, and good performance. The patch antennas will be located on one side of the ground plane and the microwave and electronic circuits will be on the other side. The signals are coupled from the circuits to antenna elements through equal-phase microstrips. The distributing microstrip circuits and power dividers are fed by a coaxial line connected to the center of the subarray. The beam control subsystem will use photonics to distribute reference phase information. A circular polarized rectenna will be constructed. Since the power density level at the rectenna array will be fairly low for the proposed experiment, techniques using low breakdown voltage diodes or multi-antenna rectenna elements per diode will be investigated. The ability of the retrodirective phase control system to maintain tight beam steering can be measured by the use of simple receivers located around the rectenna. The measured performance will be compared with theoretical predictions for error sources (phase jitter, phase bias, mechanical misalignment, and amplitude variations) systematically introduced into the system. Beam patterns including side lobes and grating lobes will be measured. The project will provide a practical demonstration of wireless power transmission as an enabling technology for space solar power for both terrestrial and extraterrestrial application. The program will be coordinated and managed by the Center for Space Power (CSP) at Texas A&M University (TAMU) and conducted by a team that includes researchers from the Department of Electrical Engineering and the Johnson Space Center (JSC). NASA support for this program will include laboratory and test facilities at NASA Johnson Space Center.