Consideration of bandwidth of the small EBG-resonator antenna using the in-phase highly-reflecting surfaces

The drawback of the small EBG-resonator antenna using a square-patch in-phase highly-reflecting surface (HRS), proposed in Li and Esselle (2008), is its narrow bandwidth. The theoretical method is cleared for analyzing the effect of the bandwidth of the in-phase HRS on the bandwidth of the EBG-resonator antenna in this paper. To enhance the gain bandwidth of the antenna according to the theoretical rule, a double-layer mushroom-type in-phase HRS surface, whose reflection phase decreases much slower with frequency than that of the square-patch HRS, is designed. Results of an antenna application with wider bandwidth at 11.9 GHz are shown.