A Study Of Wide-Band Vivaldi Antennas Fed By SIW-Microstrip Balun

In the aspect of the military field, positioning system and civil communication, there is an increase demand for wide bandwidth in the microwave and antenna field in our contemporary world. The Vivaldi antenna is a kind of travelling-wave antenna and its tapered horn radiating structure results in an infinitely wide bandwidth in theory. Therefore, it plays a significant role in many aspects, such as modern wireless communication, positioning technique, military radar technology and so on. There are too many kinds of feeding network for the vivaldi antenna. For example, the most common one is the microstrip-slot balun, which has a remarkable transmission and impedance matching characteristic in addition to lower reflection loss in the wide frequency band. However, the characteristic of the microstrip-slot balun leads to an obvious energy loss with an increase of frequency. Hence, the power which the antenna receives may decrease gradually, which results in a decrease in gain at high frequency.The rectangular waveguide is always used in radio frequency and microwave circuits, which has high power capacity and low loss. However, the planar integrated circuit is widely applied in nowadays, which limits applications of the non-planar rectangular waveguide. The substrate integrated waveguide(SIW) is a kind of slow wave device which is proposed to overcome that disadvantage. Compared with the traditional rectangular waveguide(RWG), the SIW has the similar features including high Q and power capacity factors. In addition the SIW has the advantages of light weight, small volume, simple design, low cost and easy integration, which makes a wide application. Based on the SIW, a novel feeding balun is proposed in this thesis, in order to increase the gain of the vivaldi antenna in high frequency.Based on the research done by the predecessors, the thesis is organized as follows.In the first part of this article, the SIW-microstrip fed balun is designed and simulated, which has an advantage of low cost, high performance in transmission and impedance matching. The design focuses on the linearly tapered line, which is the transition between the microstrip and the SIW to achieve a bandwidth from 6GHz to 10 GHz.Furthermore,the properties of the conventional microstrip-slot feeding balun are compared with theproposed one and the influence of the parameters on the voltage standing wave ratio, transmission constant and reflection coefficient is analyzed.In the second part of this thesis, two vivaldi antennas fed by two different kinds of balun are designed. One is the antipodal vivaldi antenna(AVA) fed by the microstrip SIW-based balun and the other is the vivaldi antenna(VA) fed by traditional, microstrip-slot feed balun. By using the software to simulate the different structures, the results show that the VA fed by the microstrip SIW-based balun, which is compared with the traditional VA, has an gain improvement at high frequency. Meanwhile it could maintain other properties unchanged compared with the traditional microstrip-slot feeding balun. In the aspect of antenna property optimization, the effect of the VA parameters on the antenna performances is analyzed.