Proposal and Design of a Null Reconfigurable Patch Antenna on the Basis of Multimode Method

A novel multimode method facilitating the proposal and design of a null reconfigurable patch antenna is presented in this article. First, the characteristics of a multimode antenna are theoretically investigated with respect to mode combination and excitation. It is revealed that a small frequency span between the exploited modes is required for simultaneous excitation. Then, the null formation conditions are established based on a unified equivalent circuit model, thus, proving that the desired power ratio and phase difference can be simply achieved by tuning feeding locations and working frequency without needing any additional gain attenuators and phase shifters. To demonstrate the method, a single-plane null reconfigurable antenna (NRA) on a rectangular patch is then presented by extracting the excitation coefficients. Besides, a feeding network is proposed for state switching and impedance matching. To further improve the null angle coverage and show the generality of the proposed method, a hemispherical NRA on a circular patch is employed to design an NRA whose pattern null can be reconfigured in the upper hemisphere. In final, both prototypes are fabricated and measured. A good agreement between simulated and measured results verifies the effectiveness of the proposed method and proves its potential applicability to other types of antennas.