Research And Design Of Miniaturized Ultra-Wideband Planar Spiral Antenna

With the application of ultra-wideband system in mobile communication and national defense,antenna plays an increasingly important role in military and civil fields.Recently,electronic equipment has the characteristics of high integration and miniaturization,and its requirements for antenna are also developing towards the direction of wider frequency band,smaller size and better performance.The Archimedes plane spiral antenna is a kind of common ultra-wideband antenna,which has many remarkable advantages such as wide band,circular polarization,low profile,small size and easy to process.It has a wide range of applications in the fields of directional detection,satellite communication and electronic countermeasures.In this thesis,two miniature UWB spiral antennas and a microstrip balun operating at 0.8~ 18 GHz are proposed.The first one is a complex planar spiral antenna loaded with sine function,the diameter of it is 60 mm.The structure of high frequency area of the antenna used equiangular spiral lines,learned the excellent properties in high frequency area of equiangular spiral antenna,then connects smoothly with conical spiral arms which loaded sine function,the aim is to extend the current path,at the same time,the end of the spiral arms is more and more fine,greatly reduces the reflect current at the end of the arms.Finally,the voltage standing-wave ratio is less than 1.4 in the frequency range of 0.8~18 GHz and the AR is less than 3d B in the frequency range of 1~18 GHz.The Second one an Archimedes spiral antenna bent in the z direction.The absolute value function of sine function is introduced into the equation of z parameter of the edge curve of the dielectric plate to make the dielectric plate appear wavy,and the spiral arm of the antenna is bent in the direction of the z axis.In order to reduce the influence of the bent spiral arm on the high-frequency region,the planar Archimedes spiral antenna structure is adopted at the antenna center,and then the spiral arm is smoothly connected to the spiral arms bended in z-axis direction,which increases the current path.The diameter of it is 60 mm,compared with the traditional Archimedes spiral antenna,the size is greatly reduced,the voltage standing-wave ratio is less than 1.5 and the AR is less than 2.5d B in the frequency range of 0.8~18 GHz.Finally,a printed tapered balun is designed and manufactured.Antenna with selfcomplementing structure has stable input impedance.the theoretical value of 188.5 ?,but the actual spiral arms are limited,the input impedance of the planar spiral antenna is actually about 140 ?,but the characteristic impedance of the coaxial line is 50 ?,and the arms of the spiral antenna is balanced structure.Using balun to balance current and transform the impedance from 50 ? to 140 ?.Finally,the diameter and the height of the z-bending Archimedes spiral antenna is 60 mm and 51.5mm,and this antenna is manufactured and tested in the microwave chamber,the voltage standing-wave ratio is less than 1.8 and the AR is less than 3 d B in the frequency range of 0.8~18 GHz.