Half-Elliptical UWB Planar Monopole with Reconfigurable Slot Antenna for Cognitive Radio Front-End

In this paper, a half-elliptical disc ultra-wideband (UWB) monopole antenna integrated with a reconfigurable rectangular slot antenna is presented. It consists of a half-elliptical disc radiator to operate in the UWB mode whereas the etched rectangular slot on the half-elliptical patch is designed to operate as a reconfigurable narrowband slot antenna which is fed through a microstrip line from the back side of the patch. Both the antennas are placed in such a way that they are isolated to each other. Frequency reconfigurability has been achieved by inserting three lumped elements (two PIN diodes and a varactor diode) in the slot. An approximate transmission line model of the proposed slot antenna is derived to calculate the proper positioning of the diodes, and the design has been verified through numerical simulations. The simple compact proposed antenna covers a wide frequency range from 0.75 to 12GHz. Additionally, a wide tuning range from 0.8 to 2.9GHz (with the frequency ratio of 3.625:1) has been achieved. This compact integrated antenna is a good choice to be implemented in Cognitive Radio (CR) devices.