Tailoring the radiation pattern of patch antennas by using soft/hard surfaces

In this paper, the use of soft or hard surfaces for changing the radiation pattern of the fundamental modes of microstrip patch antennas will be introduced. Soft and hard surfaces can avoid or enhance, respectively, the propagation of electromagnetic fields in some directions. Therefore, in this paper, the authors propose the use of these surfaces for tailoring the shape of the radiation pattern in planar radiators like microstrip patch antennas. As a particular example, the fundamental mode of a circular patch antenna (TM₁₁), whose maximum is in broadside, is changed to a radiation pattern with minimum in that direction. A short-circuited ring patch whose fundamental mode is the TM₀₁ with a minimum in broadside is also changed to a radiation pattern with a maximum in that direction. Finally, a structure based in a multilayer substrate is proposed to reduce the size of the antenna. Simulations and measurements are provided to validate the results.