Novel design of dual-band reconfigurable antennas using lumped-elements and varactors located inside antenna's conductor

A frequency reconfigurable dualband antenna is demonstrated, where the antenna's conductor consists of a radiating conductor, lumped and distributed elements, and varactors. An analytical expression for current distribution, input impedance, and radiated power is derived by connecting electromagnetic fields inside and outside the antenna's sphere for an electrically small antenna. With the formulae, input impedances are numerically estimated, and dual resonant frequencies are shown to be controlled almost independently by varying the value of a shunt inductor or a series inductor. The reconfigurable antenna is fabricated, where the varied reactances for the inductors are realized with series resonant circuits consisting of an inductor and a varactor. Measured upper and lower resonant frequencies are shown to be controlled by the applied voltage to the varactor between 2.60 and 2.91 GHz, and between 5.10 and 5.32 GHz, where the other resonant frequencies are almost identical.