Multi-band reconfigurable antennas embedded with lumped-element passive components and varactors

Frequency reconfigurable dual-band antennas with varactor diodes have been demonstrated. An equivalent circuit that takes both coupling with free space and an antenna conductor embedded with lumped-elements into consideration is proposed for the design of reconfigurable antennas. By means of the equivalent circuit, reconfigurable antennas that independently control dual-band resonant frequencies were designed and fabricated with a parallel circuit with an inductor and a varactor. The lower resonant frequency was successfully controlled between 1.60 and 1.91 GHz, and the upper resonant frequency was controlled between 3.32 and 3.71 GHz. Measured gains were more than -9.8 dBi in the lower band, and more than -7.3 dBi in the upper band, respectively. To improve the gain, a reconfigurable antenna with a series circuit of an inductor and a varactor was also fabricated for the lower band. Measured gains have been improved to more than -4 dBi in the lower band.