Compact microstrip antenna loaded with very high permittivity superstrate

It is noted that a superstrate (cover) layer on the top of a microstrip antenna may significantly affect the radiation properties. An adequate superstrate layer may be used to eliminate surface-wave excitation, resulting in a higher radiation efficiency. We demonstrate that, by adding a high permittivity ceramic superstrate layer, the antenna gain of a chip-resistor-loaded patch antenna, which exhibits a compact broadband characteristic, can be increased to be about the same level of a conventional patch antenna. Also, a design of a gain-enhanced compact microstrip antenna with circular polarization (CP) radiation is described. This design is achieved by cutting slits in the square patch, and the gain-enhancement is obtained by adding a high permittivity superstrate on the top of the patch antenna. Details of the experimental results are presented and discussed.