Planar Ultra Wideband Antennas with Rejected Sub-bands

A simple method for the design of a coplanar waveguide-fed ultra wideband antenna is presented. The proposed antenna has a rejection capability for a certain undesired sub-band used by other communication systems. The proposed antenna has a uniplanar configuration. The radiating element and the ground plane of the antenna are in a shape of half a circle. Two methods for rejecting the undesired sub-band are presented. In one method, a tuning strip is used at the bottom layer of the antenna facing the radiator at the feeding point, whereas in the other method a tuning slot is made at the radiator. The length of the tuning element can be used to control centre of the rejected sub-band. Results of simulations for the two methods show that the designed antennas have a bandwidth from 3.1 GHz to more than 10.6 GHz with near omnidirectional characteristics. The designed antennas have a radiation efficiency which is higher than 90% over the whole passband. The gain of the antenna at the rejected sub-band is as low as -5 dB proving the filtering characteristics of the antenna at that band.