Step-like structure and EBG structure to improve the performance of patch antennas on high dielectric substrate

Applications of microstrip antennas on high dielectric constant substrate are of growing interest due to their compact size and conformability with monolithic microwave integrated circuit (MMIC). However, there are some drawbacks with the use of high dielectric constant substrate such as narrow bandwidth, low efficiency and poor radiation patterns, which result from the pronounced excitation of surface waves. Several methods were previously used to overcome these drawbacks by manipulating the antenna substrate. One approach suggested was to lower the effective dielectric constant of substrate under the patch using micromachining techniques. A shortcoming of this approach is the larger patch size than that on the unperturbed substrate. Another approach is to surround the patch with a complete band-gap structure or synthesized low dielectric constant substrate so that the surface wave can be reduced. In this paper, a step-like substrate and electromagnetic band-gap (EBG) structure is applied to the patch antennas separately to overcome the undesirable features of the high dielectric constant substrate without sacrificing any of the desirable features, namely, small size and bandwidth. Both numerical and experimental results are presented to demonstrate the validity of these two approaches.