An antenna system composed of an activated patch backed by a ground plane and three square parasitic plates with inhomogeneous loops is analysed using the finite-difference time-domain method. Analysis of an antenna with an infinite ground plane reveals that a tilted beam of ~60° from the broadside direction is obtained with a gain of ~18 dBi. For confirmation, an antenna system with a finite-sized ground plane that approximates the antenna characteristics for the infinite ground plane is fabricated and measured. The measured results are in good agreement with the analysis results.