A high gain 4-element Cavity Backed Substrate Integrated Waveguide (CBSIW) based antenna is proposed in this paper. The combination of low loss SIW cavities with quarter wave transformer based transmission line power divider can enhance the gain and power efficiency of the CBSIW antenna. A bow-tie shaped slot is located on rectangular shaped SIW cavity with optimum dimensions to form each element. The feed network is constructed with two quarter wave T-junction power dividers connected back-to-back to accomplish the impedance matching and optimum power distribution to the elements. The proposed CBSIW antenna exhibits a high gain of 21.9dBi with 82% of efficiency on low cost FR4 epoxy substrate. The measured results agree with simulated results obtained from commercial HFSS full-wave electromagnetic solver.