This letter explores geometrical optics-based raytracing in combination with modal analysis to realize an open cavity structure as an advanced variant of the resonant cavity antenna (RCA). Additional ray confinement has been ensured by determining accurate phase-locking conditions as demonstrated for the first time. Its combination with the analysis of the cavity mode has also been introduced to determine the optimum design parameters, achieving improved radiation properties. With respect to a reference RCA reported earlier, the proposed approach exhibits a remarkable improvement in gain by 4-9 dB, resulting in about 17 dBi peak value consistently over the full 18% matching bandwidth. This is resultant from an increase in aperture efficiency, typically from 27% to 74%. This is achieved without any compromise with the cross-polarization property. The sidelobe level improves over the band except in higher frequency in H-plane. The proposed concept is commercially viable, showing significantly advantageous features. © 2002-2011 IEEE.