Design Of The Wide Beam UWB Antennas

Wide beam width in horizon plane would be expected in antenna design for IR-UWB through-the-wall detection to cover most area of the room. At the meanwhile narrow beam width in vertical plane and little radiation in backward would also be expected, which would be useful to reduce the distortion caused by other paths.The radiation pattern could be distorted seriously in wide band, thus how to keep the radiation pattern stable is a challenge in UWB antenna design.A method to realize wide beam in ultra wide band by introducing a reflect structure is proposed in this paper. Bowtie wide beam antennas with reflector and cavity are designed respectively.In the bowtie wide beam antenna with reflector, the critical parameters of the reflector are adjusted to realize wide beam in wide band. The simulated and measured results show that the beam width of the antenna is above 120o in H plane while below 50o in E plane in 90% bandwidth. The distortion is weak within the operation band.By means of changing the fed structure gradually and the shape of bowtie slot terminal, the bowtie slot antenna with cavity keeps a beam width between 120o~170o in E plane while below 65o in H plane between 0.7GHz~2.0GHz.. The size of the antenna is decreased by 56% compared with the bowtie slot antenna with reflector.Trimming off part of the antenna could be used to decrease the size of the antenna while keeping the performance with little variation for the electric field is weak in terminal of bowtie slot. The simulated and measured results show that the antenna trimmed keeps a beam width between 115o~145o in E plane while below 50o in H plane between 1.0GHz~2.0GHz. The size of the antenna is decreased by 25% furthermore.All the UWB antennas designed and fabricated in this paper could be used in IR through-the-wall detection system for their wide beam. The bowtie slot antenna with cavity is convenient to be assembled for the antenna performance could not be affected easily by environments nearby for its close cavity structure. The size of this kind of bowtie slot antenna with cavity is also much smaller than that of antenna with reflector. The bowtie slot antenna with cavity is more practicable.