Dual-band reconfigurable antenna with a very wide tunability range

A new technique for designing dual-band reconfigurable slot antennas is presented. Dual-frequency operation is achieved by loading a slot antenna with two lumped variable capacitors (varactors) placed in proper locations along the slot. Loading the slot antenna with lumped capacitors shifts down the resonant frequencies of the first and second resonances of the antenna. However, these frequency shifts depend not only on the values of the capacitors, but also on their locations along the slot antenna. Here, it is shown that by choosing the locations of the varactors appropriately, it is possible to obtain a dual-band antenna whose first and second resonant frequencies can be controlled individually. In other words, the frequency of either the first or the second band can be fixed, while the other one is electronically tuned. Using such a design, an electronically tunable dual-band antenna is designed and fabricated using two identical varactors having a capacitance range of 0.5-2.25 pF. The antenna is shown to have a frequency ratio (f_R=f₂/f₁) ranging from 1.3 to 2.67. An important feature of this antenna is its consistent radiation pattern, polarization, and polarization purity at both bands and across its entire tunable frequency range.