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Based on bionics, we design and analyze the left-handed (LH) characteristics of meta-elements with leaf-shaped structure. The double negative (DNG) frequency band of the initial leaf-shaped LH structure is 5.77-6.17 GHz with a fractional bandwidth of 6.7%. Inspired by two overlapping leaves, and based on topology, we evolve the leaf-shaped LH structure into a line-line coupled double-leaf LH structure. The DNG frequency bands of the line-line coupled LH structure are 2.96-3.86 GHz and 4.14-4.18 GHz. This structure not only retains some of the radiation and reflection properties of the initial design, but also gains new electromagnetic characteristics (an additional DNG frequency band). Finally, the line-line coupled LH structure is further evolved, through mostly homeomorphic deformation, into a ring-ring coupled double-veined leaf-shaped LH structure. The DNG frequency bands are 3.05-3.81 GHz and 5.31-5.41 GHz, and the fractional bandwidth are 22.2% and 1.9%, respectively. The arc-vein branches form parallel ring-ring coupling with the margin, affecting the structure's impedance and capacitance. Similar to the line-line coupling, it can locally stretch the electromagnetic characteristics, expanding the corresponding DNG bandwidth. Through the establishment of electromagnetic topological set, we classify and analyze the topological transformation and the corresponding changes in electromagnetic characteristics. We then use formula to express the process of topological transformation intuitively. Finally, the ring-ring coupled LH structure is loaded on a microstrip antenna in several different ways, improving the antenna's radiation properties, including bandwidth, directivity, and gain.

A Double-Veined Leaf-Shaped Bionic Meta-Element and Array Loading Antennas for Radiation Beam Control