Research And Design On Wideband Antennas

In recent years, the wireless communication system has been developing fast. As an important part of the wireless communication system, the antenna technology also has a rapid development. New technologies and new standards in wireless applications are coming out one after the other, the rapid development of communication system raises higher demand for communication equipments, such as the higher gain and wider bandwidth. Improving the bandwidth of the antenna is an important future direction of the antenna development. The wideband antenna is now been widely used in many parts of the civilian and military communication equipment, such as television, FM radio, telemetry technology and so on. In this thesis, the design principle and the status quo at home and abroad about wideband antennas are described. The work in this thesis consists of two parts. A wideband microstrip antenna at 184~241MHz is studied in the first part. A kind of conical log-spiral antenna at 4GHz~6GHz is designed in the second part.Firstly, according to the needs of practical engineering applications and the theory of the microstrip antenna, an E-shaped microstrip antenna has been designed and simulated. Due to the 3d B radiation beamwidth requirement in engineering application, a metallic cavity is introduced to adjust the 3d B radiation beamwidth of the E-shaped antenna. In order to enhance the antenna impedance bandwidth and keep the stable radiation characteristics of the antenna, a copper pillar with radius of 7mm is used to feed the antenna. Then the interactions between the impedance bandwidth and the height of the radiation patch are studied, and the effects of the impedance bandwidth cased by the changed feeding locations are discussed. Through the parameter analyses in the simulation software, the optimized values can be obtained. The measured results show that the electric characteristics of the antenna meet the application requirements in working band.Secondly, in order to realize the circularly polarized characteristics with wideband and directional radiation pattern, the conical log-spiral antenna at 4GHz~6GHz is simulated and designed based on the theory of frequency independent antenna. To achieve a good impedance bandwidth, a microstrip feeding balun is proposed. The measured results show that the antenna gain is 4.5d B and have a good 3d B radiation beamwidth which is above 80°. Compared with the traditional helical antenna, the antenna has a smaller size and a better beamwidth. The results indicate that the electric characteristics of the antenna meet the application requirements in working band.