Miniaturized Bandwidth Reconfigurable Yagi-Uda Antenna for Wireless Applications

We propose a miniaturized Yagi-Uda antenna with a reconfigurable operating bandwidth. The antenna miniaturization and bandwidth enhancement are achieved based on manipulating the shape and the position of the antenna reflector and director. Indeed, by coupling effects, three resonances are combined to broaden the impedance bandwidth without affecting much the radiation characteristics. On the other hand, the reconfigurability function is ensured based on the insertion of one varactor diode onto the antenna reflector. The measured results reveal that the proposed design has the merits of a miniaturized one-layer design with 75% size reduction compared with the conventional antenna, a measured peak gain of 4.57 dBi, a peak efficiency of 97%, a smoothly tunable relative bandwidth of 10% to 30%, and a simple DC-bias network with less lumped components. The proposed antenna may find its use in some wide-band unidirectional wireless applications covering the bandwidth 0.99 GHz to 1.34 GHz, for instance, in cognitive radio applications where the operating bandwidth can be reconfigured, accordingly.