| With the development of wireless communication technology,the wireless communication system is developing towards the direction of high-speed and high-efficiency information transmission.As an important part of the wireless communication system for transmitting and receiving electromagnetic waves,requirement of antenna performance is becoming higher and higher.Log-periodic dipole antenna is widely used in many fields such as broadcasting,television,short-wave communication because of its wide band and high gain.It's an antenna that is expected to achieve high-efficiency and high-speed information transmission.In practical applications,antennas are usually limited by space,so it's important to study the miniaturized high-gain log-periodic dipole antenna.The characteristics of the traditional log-period dipole antenna are restricted by the dipole.It is difficult to increase the gain of the antenna without increasing the size.This thesis has conducted in research on this subject.The main work of the thesis is as follows:1.The theory of log-period dipole antenna is studied in detail.The structural design process and working characteristics are analyzed.The analytical process of equivalent circuit analysis method is derived and summarized.2.The performance of traditional log-periodic dipole antenna is restricted by dipole,on the basis of principle of log-periodic antenna,the planar inverted F antenna with magnetic current characteristics is proposed to replace the dipole and microstrip transmission line is used to replace the traditional two-wire parallel lines.Firstly,the influence of structural parameters of planar inverted F antenna on resonant characteristics is studied.Secondly,it is verified that planar inverted F antenna can play a role as director and reflector.And then,an antenna operating between 2.7GHz and 6GHz is designed.The impedance bandwidth of proposed antenna is 7%,gain is more than 10 dB within 2.7～4.5 GHz band,radiation pattern beam elevation in 28 ～ 45 °,with good bandwidth and high gain characteristics.3.On the basis of studying the impedance of plane inverted F antenna,a "case" antenna is proposed.The proposed antenna achieves 17% impedance bandwidths,elevation angle of pattern beam is 45°,in addition,impedance of the antenna is easy to adjust.Three “case” antennas fed with the coupled microstrip line,antenna operating in a band of 5.5～8.1GHz and impedance bandwidth is 38%.The maximum gain over frequency is 11 dB,and the elevation angle of the radiation pattern beam is small,and the size is about 30 degrees. |
