A novel null steering method in a multi-mode circular microstrip patch antenna is presented in this letter. A stacked patch configuration, capable of exciting three different radiating modes, namely TM11, TM21, and TM31, is investigated. When two or three modes are excited simultaneously, up to three nulls can be formed in the upper hemisphere, and by tuning the amplitude ratio of these modes, a continuous null steering pattern is realized. It is shown that a full hemispherical null steering of ±90° range can be achieved using the proposed method. The null steering capability with different dielectric permittivities is also presented.
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