Aperture field analysis of gain enhancement method for microstrip antennas

In this paper, the electric field distribution on the top surface of a layered microstrip antenna structure is investigated. A new explanation of the gain enhancement method is given using the aperture antenna theory. The superstrate rearranges the field distribution in the aperture. The gain increment comes from the rearranged aperture field phase. Quasi-circular contours are observed. A superstrate with limited size should thus be circular. The field declines very rapidly from the center. A circular superstrate with radius R=4/spl lambda//sub 0/ is big enough for a typical patch antenna to get the desired gain increment. Field oscillations are observed in x direction. When the limited superstrate is cut just at a local minimum field point, the edge diffraction can be minimized. Approximate formulas are given to describe the field decline and predict the local maximum field points and the local minimum field points.