Research On Broadband And Miniaturized Antennas At Low Frequency

In the field of communications, spread spectrum technique is increasingly showing its importance, which is based on broadband technology. It puts forward higher requirements on antennas in terms of broadband and miniaturization, which are known as the key components of the wireless systems. A large number of antennas are placed on a narrow work platform at the same time, so the electromagnetic interference between them will affect the quality of communication seriously. If we use a broadband antenna instead of the multiple antennas, which can cover the whole needed frequency range,the problem of the electromagnetic interference can be solved. Moreover, with the rapid development of wireless communication technology and large scale integrated circuits, all kinds of electronic equipments are miniaturized gradually. However, the antenna plays a key role in the front-end of the communication system, and therefore its miniaturization problem has become the bottle neck which restrict the development of the modern wireless communication. Therefore, in order to adapt to the development of the communication system, research on broadband and miniaturized antennas with good performance at low frequencies has become a pressing topic which has important theoretical and realistic significance.In this paper, the frequency bandwidth extension method and miniaturization technology of the antennas which work at VHF(Very High Frequency: 30-300MHz) and UHF(Ultra High Frequency: 300-3000MHz) are introduced and summarized firstly. And then we study and design the wide band antenna and miniaturized antenna for low frequency. The main contributions of this thesis are outlined as follows:Chapter I Briefly demonstrated the background of the selected topic and research significance; reviewed the development process of the research on broadband and miniaturized antenna for low frequency in recent years; expounded the basic theory of the electrically small antenna.Chapter II Introduced the main performance indexes of the antenna, furthermore, summarized the wideband technology, miniaturization technique, analytical method and optimization algorithm of the low frequency antenna which are currently used.Chapter III An improved double floor single cone antenna based on the conventional biconical antenna was designed, elaborated the design thought of the antenna detailedly, and then simulated and analyzed the influence of the various size parameters of the antenna. In order to achieve the target, the approach of antenna external broadband matching network was presented, and the genetic algorithm in the software of CST was used for the design of the wideband matching network. Finally, the antenna as well as the broadband matching network were fabricated and tested, and compared it with the traditional single cone antenna.Chapter IV According to the study of conical antenna in Chapter III, and combined with the impedance characteristics of electrically small antenna, a series of structure improvements of the single-antenna were carried on. Expanding the end of the single cone horizontally and loading a cambered top at the end of the cone can realize the purpose of broadband and miniaturization.Chapter V Concluded the whole thesis, prospected the development trend of broadband and miniaturized antenna for low frequency, and proposed possible improvement direction of the follow-up work.