A Compact Tri-Band Monopole Antenna With Single-Cell Metamaterial Loading

摘要

A compact tri-band planar monopole antenna is proposed that employs reactive loading and a “defected” ground-plane structure. The reactive loading of the monopole is inspired by transmission-line based metamaterials (TL-MTM), which enables the loaded antenna to operate in two modes. The first resonance exhibits a dipolar mode over the lower WiFi band of 2.40 GHz – 2.48 GHz, and the second resonance has a monopolar mode over the 5.15–5.80 GHz upper WiFi band. Full-wave analysis shows that the currents of the two modes are orthogonal to each other, resulting in orthogonal radiation patterns in the far field. The feature of a “defected” ground-plane, formed by appropriately cutting an ${rm L}$-shaped slot out of one of the CPW ground-planes, leads to the third resonance that covers the WiMAX band at 3.30–3.80 GHz. Air bridges at the intersection between the antenna and the CPW feedline ensure a balanced current. A fabricated prototype has compact dimensions of 20.0 mm $,times ,$23.5 mm $,times ,$1.59 mm, and exhibits good agreement between the measured and simulated $S$ parameters and radiation patterns. The measured radiation efficiencies are 67.4% at 2.45 GHz, 86.3% at 3.50 GHz and 85.3% at 5.50 GHz.