Reconfiguring UWB Monopole Antenna for Cognitive Radio Applications Using GaAs FET Switches

A novel ultrawideband (UWB) microstrip monopole antenna with reconfigurable multiband function is presented. Reconfigurability is achieved by using GaAs field effect transistor (FET) switches to connect multiple stubs of different lengths to the main feed line of the monopole. The antenna is compact and flexible in terms of the availability of different reconfiguration bands and, most importantly, the simple biasing of the GaAs FET switches will not have a severe effect on the antenna performance. Using GaAs FET switches did not degrade the antenna radiation patterns due to the simple biasing technique and the few external biasing components needed, besides these switches did not degrade the antenna gain and efficiency due to their low insertion loss and low on resistance. When the antenna was reconfigured from UWB to work into multiple frequency bands, the total peak gain improved by 20% compared to the UWB case. In addition, the total efficiency of the antenna has not been significantly reduced in any reconfigured band, whereas the out-of-band total efficiency is hugely reduced, which highlights the filtering role of the reconfiguration process. The total dc power consumption of the antenna switches is still very low (<; 33 μW), and this will lead to simple integration of the antenna in some portable communication systems or future cognitive radio front ends.