Study Of Wideband And Miniaturized Antennas

As the development of modern communication, advanced techniques such as frequency hopping and frequency spreading are widely used. On the other hand, as the development of large scale integrated circuit and space technology, electronic devices become more and more compact. As a result, communication systems that are compact and wideband are demanded. As the front-end device of a communication system, wideband and compact antenna arouses more and more interests in the academic field. The contents of this dissertation can be summarized as follows:From the analysis and discussion of passive/active wideband antenna minimization technology, this paper pointed out a theory based on non-Foster circuits load antenna technology which was able to break the Bandwidth-Gain-Volume limitation. Emphasized on the design procedure of non-Foster circuit loaded antenna, which used the negative impedance characteristic of non-Foster circuit to improve the input impedance of an antenna, this paper applied wideband impedance matching circuits to extend the bandwidth of the antenna while minimized the size of the antenna. As an example, a monopole with length 0.69m was loaded with non-Foster and impedance matching circuits, achieving a working band from 30MHz to 150MHz with VSWR less than 2.0:1 while maintaining constant radiation pattern.Two omni-directional wideband antennas were designed in this dissertation to work in a wideband communication demonstration system. After a comparison between different kinds of wideband antennas, biconical antenna was chosen as the prototype of these two antennas. Based on the design of the modification of the classical biconical antenna, the working bandwidth was further extended. In order to limit the effect of feed line to the antenna performance, choking magnet ring was employed. Two prototypes of the proposed antennas were designed and fabricated, which can work from 3.2 to 3.8GHz and from 6 to 9GHz with VSWR less than 1.8 in the working band.