Pattern Transformation of Low-Profile Multi-Mode Antenna for a Phased Array With Simultaneous Wide-Angle Scanning and High-Gain Properties

In this article, a novel multi-mode design approach for pattern transformation of low-profile multi-mode microstrip patch antenna (MPA) has been proposed and developed, aiming to simultaneously achieve the wide-angle scanning and high-gain properties for a phased array. Herein, the TM₀₀, TM₀₁, TM₂₀, and TM₂₁ modes of the MPA are employed. Firstly, the working principle about how to move these four modes closely to each other in resonant frequency is deeply studied, the results prove that the shorting pins and slots could be loaded on the radiator for frequency reallocation of these four modes. Secondly, the radiation pattern transformation of the MPA at TM₀₀, TM₂₀, and TM₂₁ modes are deeply investigated, which demonstrates that the non-broadside beam of its TM₂₁ mode could be reshaped into the broadside one, and the omnidirectional pattern of its TM₀₀ mode could be reshaped into the dual beam at yoz-plane. Most importantly, the radiation pattern of its TM₂₀ mode could be rotated into the dual-beam with co-polarized Eθ component at yoz-plane. With these arrangements, the broadside-beam and dual-beam could be excited under same frequency at different modes. Thirdly, based on these two beams with different phases at two ports, the antenna element has successfully gained the improved beam scanning and gain performance simultaneously. Fourthly, the proposed multi-mode array is arranged in a triangular grid. By controlling the phase difference between these ports, the antenna could achieve both wide-beam scanning and high gain. Experimental results show that the antenna element has an impedance bandwidth (|S₁₁| < -10 dB) from 3.52 to 3.82 GHz. Besides, the beam scanning angle reaches to ±70° for the array, while keeping the compact size of about 3.9 × 1.3 × 0.043λ₀³ and achieving an improved gain of 15.02 dBi, which is about 2.4 dB higher than the traditional counterpart.