Left-Handed Dipole Antennas and Their Implementations

A new type of dipole antenna using a left-handed transmission line is proposed. The antenna is composed of a transmission line loaded periodically with shunt inductors and series capacitors. The placement of capacitors into one side only of the line leads to currents of different amplitude on the two sides. Because out-of-phase currents have different amplitudes, they do not completely cancel in the far field, and as a result radiate. Numerical investigation of a wire model shows a unique feature of left-handed transmission lines, which is a reduced wavelength with decreasing frequency. Measured results of two antennas are presented. One is a short dipole antenna working at n=-1, based on conventional resonance numbering. The antenna of 0.18 wavelengths in free space has a gain of -3.9 dBi and bandwidth of 1.7% for |S₁₁ |<-10 dB. The other is a meandered dipole antenna working at n=-9. Polarization orthogonal to a right-handed one is achieved by the induced current of |-9| half wavelengths on the meander having 0.77 wavelengths in free space