Wideband radiating ground plane with notches

Self-resonant notch antennas, fabricated using microstrip technology are very compact structures. Typically, notch antennas consist of a quarter wavelength slot cut on the edge of a semi-infinite ground plane; they are fed from a coaxial cable without the need of any balancing system. However, when a notch is cut on a finite ground plane of resonant dimensions, the shape and size of the ground plane affect the performance of the notch antenna significantly. It can be demonstrated that the interaction between the resonances of the notch and the ground plane results in a filtering effect at some frequencies. The paper uses the theory of characteristic modes to perform a modal analysis of different configurations of notch antennas on a finite ground plane. By means of this theory, the current on the surface of the antenna is expressed as a sum of real, and orthogonal, eigencurrents, that are known as characteristic modes. The filtering effect due to the interaction of the resonances can be explained with the information provided by the current distribution of the modes and their associated eigenvalues. Using a double notched radiating ground plane with two feed points, the filtering effect is reduced, and the matching is improved.