Design And Research On Ultra-wideband Antenna With Wide Beam-width

With the Ultra Wideband(UWB) systems widely used in radar, navigation, electronic warfare, secure communications and civilian areas, the UWB antenna, as the critical component of UWB system in transmission and reception process, is required to meet the demands of different design on the actual situation of different applications. In the detection and location devices or interfering devices, under normal circumstances, a larger coverage area is necessary to the electronic equipment in the interference and detection area, which means the antenna must achieve the unidirectional radiation and have a wide beam width. Additionally, the operating band of the other equipment is uncertain, so the antenna in the devices should have ultra-wideband characteristic. However, due to the large operating frequency, the radiation pattern of the UWB antenna is prone to distortion with the change of operating frequency, therefore, two kinds of antennas with unidirectional radiation and a wide beam width are designed in this paper, and radiation pattern has a good consistency in the low and high bands.The spiral antenna, a common UWB antenna, can keep the excellent radiation characteristics in ultra wideband. Since the symmetric balanced characteristics of the spiral antenna and the application requirements of the unidirectional radiation pattern, the design in the paper can be divided into three parts: the spiral radiator; balance-unbalance conversion balun and metal reflective structure. In the third chapter, firstly, the parameters of the spiral antenna are optimized, and a compound spiral antenna with the good impedance characteristics in the 2~12 GHz is devised; and then, in order to meet the requirements of coaxial feed, the exponential balun has been discussed and the impedance conversion between unbalance and balance port has been realized; for achieving the wide beam width, the elliptical reflector cavity, the frustum reflector cavity and the hat-shaped reflector cavity have been designed and compared with each other; finally, an additional metal ring is designed to stabilize the radiation pattern and a resistor is loaded to improve the circular polarization. Eventually, the design requirements are achieved. In the fourth chapter, against the disadvantage of the large overall size, two different methods of making balun and radiator coplanar are designed and analysis. In the first design, a wide-band microstrip to coplanar stripline(CPS) transition has been introduced, and two spiral arms are connected to the coplanar stripline. This antenna can maintain favorable radiation characteristics at the low frequency band. In the second design, a spiral antenna operating on 2.7~12 GHz has been proposed. Utilizing the design concept of Archimedes spiral balun, the spiral arms are printed on different dielectric surface and are connected to the balun. The radiation pattern remains stable over the operating frequency band, and the vertical size of the antenna is reduced greatly. Then a closed cavity is discussed according to the shape of the antenna, which can effectively shield the interference of external electronic equipment and is benefit for assembly. The overall size of the antenna is relatively small to the former. In the end, the main work in this paper is summarized, and the further design goals are presented in light of the deficiency in the design process and test results.