Research And Design Of Low Common-Mode Current Broadband Loop Antenna

Anechoic chamber is an important tool for wireless device performance testing.Its calibration and quiet zone evaluation are necessary to ensure the accuracy and reliability of OTA test results.The traditional calibration and evaluation method is to use dipoles as standard antennas in different frequency bands,the reuse method is not only tedious,but also difficult to ensure the accuracy of calibration.The probes of multi-probe anechoic chamber are usually dual-polarized antennas,which requires the combination of vertical and horizontal polarization antennas to calibrate.The calibration of horizontal polarization requires a loop antenna with high symmetry,which is often difficult to balance its bandwidth and symmetry.Therefore,a horizontal polarization antenna with high symmetry and wide bandwidth is proposed in this paper,it can effectively solve the problem of redundancy in the calibration process,while also taking into account the advantages of light weight,small size and easy integration,the antenna can be widely used in wireless communication field.The main research of the thesis is as follow:1.The introduction of basic theory of loop antenna.Firstly,a comprehensive overview of the radiation principle of current elements and magnetic elements is given.Then,introduce the basic parameters of the antenna,such as VSWR,radiation pattern,polarization,etc.Finally,the types of radiation elements,feeding and impedance matching of the antenna,especially the quarter-wavelength impedance converter,are studied.2.The study on loop antenna with arc element.Firstly,the calibration procedures of anechoic chamber are summarized,including ripple test and pathloss calibration.Secondly,a simple and practical loop antenna with arc element is manufactured for anechoic chamber and the symmetry is measured.After that,the drawbacks of the loop are analyzed,as well,the performance index of a novel loop antenna is proposed.3.The presentation of a broadband high symmetry loop antenna.6 planar Vivaldi arrays and one-by-six power divider are utilized to generate horizontal omnidirectional radiation.First of all,the selections of bilateral slot structure and PCB technology are explained,then the detailed design and basis of feeding structure,radiation element and transition structure are studied,and the influence of some parameters on antenna performance is analyzed.At the end,antenna proofing and testing are completed to verify the feasibility of the design method.Based on the above work,a low common-mode current broadband loop antenna is fabricated for anechoic chamber calibration.The antenna has an operating band of 2.6 ~3.2 GHz(relative bandwidth 20%)and a pattern symmetry is 0.2 dB,which basically meets the requirements of CTIA standard for calibration antenna.About 25 dB crosspolarization ratio is obtained with smaller common-mode current.Compared with the traditional calibration antenna,the loop antenna is more suitable for multi-probe anechoic chamber calibration.