Resonance behavior of single U-slot and dual U-slot antenna

The broadband characteristic of a microstrip patch antenna with a U-shaped slot has been confirmed by many published results, in which two different but close resonant frequencies in a single patch are combined to give a wideband operation. On the other hand, if the excited resonant frequencies are far apart, a dual-frequency operation can be achieved with the U-slot antenna. In the present work, the resonance behavior of a single U-slot microstrip patch antenna is studied. Two approximate equations for the operating frequencies of a single U-slot microstrip patch antenna are derived by analyzing the surface current distribution on the microstrip patch. The two proposed equations for the operating frequencies of a single U slot antenna are accurate within about 5%. The design simulation results of a microstrip patch antenna with two asymmetric U-shaped slots for dual-frequency operation are also presented. The two operating frequencies of the proposed antenna are found to have the same polarization and similar broadside radiation characteristics. The frequency ratio of the two operating frequencies is found to be f/sub 2//f/sub 1/=1.57. The details of the antenna design and simulation results are presented and discussed.