Design and Experimental Validation of a 112-Element Cross-Helix Array for Retrodirective Wireless Power Transmission

In this paper we present detailed design information and measured results of a Solar Power Satellite (SPS) power beaming array based on a 112-element cross-helix “CASSIOPeiA” Solar Power Satellite (SPS) concept, developed under the UK government DESNZ and UK space agency funded “CASSIE” research program. Designed for 2.4 GHz wireless power transmission (WPT), the array has a design goal of beaming 200 W/m² power density over 6.5 m in an anechoic chamber, transmitting 672 W of RF power with 6 W per element. Experimental validation confirmed retrodirective beam tracking across a 360° azimuth range, with limited coverage also demonstrated in elevation. The array was comprised of 7 layers, each containing 16 elements. Power beaming tests used a 144 element rectenna, able to produce an accurate power density map across the 1m² aperture, with a peak measured power density of 172 W/m², reinforcing the feasibility of high-efficiency space-based solar power (SBSP), with accurate, real time, retrodirective tracking.