Observation of reverse Doppler effect in a composite right/left-handed transmission line

In this paper, we demonstrate the reverse Doppler effect associated with the left-handed medium by a simple transmission line circuit implantation. The left-handed medium is analogized with the composite right/left-handed transmission line at microwave frequency. Virtual moving source is realized in the composite right/left-handed medium by electrically trigged voltage-controlled sequential switching of transmission-line taps along the transmission line. By analyzing the frequency spectrum of the output signals, we found that the frequency shift supported the reverse Doppler effect in such left-handed transmission line system.