A Gain-Enhanced Differential-Fed Stacked Circular Patch Antenna With Simultaneously Controllable E-Plane and H-Plane Radiation Nulls

In this work, a differential-fed three-layer stacked circular patch antenna with enhanced gain performance is theoretically investigated for the simultaneous control of radiation nulls over both the E-plane and H-plane patterns. First, the bottom layer patch is meticulously designed based on a modified TM
₁₁
mode to meet the matching conditions. Then, the structures of the parasitic layer patches are contrived to form similar peripheral radiative current distributions compared with the bottom one, aiming to simplify the analysis process. After that, the three-layer patches are stacked in a capacitively coupled fashion, which guarantees the out-of-phase scheme between the middle layer patch and the other two-layer patches. By means of the cavity-model theorem, further investigations on the multilayer distributions of the equivalent magnetic currents for the three radiators have successfully demonstrated that the destructive interference among the currents will result in the emergence of radiation nulls for both the E-plane and H-plane patterns. As a result, the beamwidth of the antenna in the two principal planes can be narrowed, which contributes to a significant improvement in the overall gain performance. Furthermore, a thorough array factor analysis on the flexible control of the radiation nulls is highlighted with both the theoretical predictions and full-wave quantitative verifications. Finally, an experimental prototype is fabricated and measured to prove its validity. Compared with other stacked antennas with approximately the same longitudinal profiles, this design features the highest measured peak gain of 13.9 dBi, with an attractive increment of 8.0 dB pronounced.