2.45 GHz high-gain electrically small antenna with composite right/left-handed ladder structure

Electrically small antennas are needed to lower further the cost of wireless elements. However, the antenna gain is constrained to the Harrington limit, while the impedance matching and directivity characteristics deteriorate in electrically small antennas. Using a dipole antenna loaded with a left-handed ladder structure is a promising technique for reducing the size of antennas. Reported is the design of a lumped-component loading left-handed antenna on the basis of the composite right/left-handed transmission line theory. A 4-unit cell left-handed dipole antenna with a size of 20 mm (0.16λ0) was fabricated with a T-junction balun. The actual gain of the fabricated antenna was −0.01 dBi, which was about 1 dB lower than the Harrington limit and the highest ever achieved for fabricated antennas operating at around 2.45 GHz (kr=0.502). The directivity measured in the E-plane was similar to that of typical half-wavelength dipole antennas.