Systems with mulitple wireless communications protocols require compact, low-cost, multiband antennas. Recently, a compact tri-band monopole antenna was proposed. It uses reactive loading, which was inspired by previous transmission-linemetamaterials (TL-MTM) work, and a "defected" groundplane. In doing so, it can meet the specifications of the WiFi and WiMAX standards while maintaining a small form factor. The antenna was developed by Jiang Zhu, Marco A. Antoniades, and George V. Eleftheriades from the University of Toronto's Edward S. Rogers Sr. Department of Electrical and Computer Engineering.
The loaded antenna can operate in two modes. The first resonance exhibits a dipolar mode over the lower WiFi band of 2.40 to 2.48 GHz. The second resonance has a monopolar mode over the 5.15-to-5.80-GHz upper WiFi band. The currents of the two modes are orthogonal to each other, resulting in orthogonal radiation patterns in the far field. The defected groundplane, which is formed by cutting an L-shaped slot out of one of the coplanar-waveguide (CPW) groundplanes, leads to the third resonance covering the WiMAX band from 3.30 to 3.80 GHz.
The 20.0-x-23.5-x-1.59-mm prototype exhibits good agreement between the measured and simulated S-parameters and radiation patterns. The measured radiation efficiencies are 67.4 percent at 2.45 GHz, 86.3 percent at 3.50 GHz, and 85.3 percent at 5.50 GHz. See "A Compact Tri-Band Monopole Antenna with Single-Cell Metamaterial Loading," IEEE Transactions On Antennas And Propagation, April 2010, p. 1031.