A 360° Electrically Null-Steering Antenna

A design of null-scanning antennas operated at 2.45 GHz is proposed. The proposed antenna is composed of two stacked microstrip arrays, and each array can generate omnidirectional radiation patterns in the horizontal plane. For the bottom array with a corporate feed network, the phases of the radiated fields are constant in the whole azimuth plane. As regards the top array, it is excited with a series feed network, and the phases of the radiated fields have a linear variation against the azimuth angle. When the two arrays are simultaneously activated with the same amplitude, the resultant radiation patterns can generate a null at a specific azimuth angle. Moreover, the null can be continuously steered in the whole 360° plane by controlling the differences between the excitation phases of the two arrays. An antenna prototype integrated with the required circuits is fabricated, and its measured results indicate that a null depth of more than 23 dB is obtained when the null is steered. Simulated results validate the experiments.