Low-Profile Differential-Fed Flat-Top Beam Antenna Design Based on Independent Regional Tailoring of High-Order Mode

This paper presents a novel low-profile, single-layer, differentially-fed microstrip antenna with a flat-top beam (FTB). By incorporating a central hexagonal slot together with four elongated slots and two short slots, the proposed antenna tailors high-order modes to achieve the desired radiation characteristics. By analyzing the electric field, the distribution in various regions is decomposed and synthesized to generate a two-dimensional flat-top beam in both the E-plane and H-plane. The evolution of the antenna structure is systematically analyzed, showing how specific slot arrangements and differential feeding lead to wide beamwidth and low sidelobes. Prototypes were fabricated and measured, demonstrating a -10 dB impedance bandwidth of 2.0% (3.46–3.53 GHz), 3 dB beamwidths of 84° in E-plane and 80° in H-plane, a flat in-band average gain of 6.89 dBi, and a cross-polarization suppression above 39 dB. Compared with conventional flat-top beam antenna arrays and dielectric resonator structures, this design achieves superior flat-top effect with 3 dB beamwidth 84°/80° on the E/H plane, low profile (0.02 λo), low cost, and straightforward fabrication, without requiring complex feeding networks.