| With the rapid development of modern wireless communication technologies such as 2G,3G,4G,Wi Max,and GPS,the requirements of the antenna with high performance is becoming more and more urgent.Antennas not only have to be low in cross-polarization,stable on gain and pattern over the operating band,but also are of low cost,wider bandwidth and more functionalities to meet various demands in the markets.The base station antennas with wide impedance bandwidth are able to working for various communication systems simultaneously,which can reduce the cost and the space usage of the base station antennas by decreasing the number of the antennas required.Recent years,wideband antennas have been widely studied,achieving over 100% impedance bandwidth.But with wideband,the antennas is unstable in gain and radiation patterns,which is unsuitable for the practical applications.In 1954,a design of a complementary antenna with combining electric dipole and magnetic dipole is proposed by Clavin.After that,some complementary antennas including electric dipole and magnetic dipole are proposed.Although,these antennas have good performance in gain and radiation pattern,the bandwidth of which is too narrow.Until 2006 a mature magneto-electric(ME)dipole antenna was proposed,which achieved low cross-polarization and low back lobe,and 43.8% impedance bandwidth.In the operating frequency band,the proposed antenna obtain a stable gain with almost identical E-plane and H-plane patterns.Circularly polarized(CP)antennas have been widely used in modern wireless communications,such as the global position system(GPS),satellite communication systems,and radio frequency identification(RFID)owing to multi-path interference suppression and polarization mismatch reduction.There are many conventional methods to realize the CP radiations,but the narrow bandwidth characteristic limits the its application severely.Therefore,it is significant to make a study of broadband CP antennas.According to some researches by many researchers,this thesis pays attention on the bandwidth and the polarization of the ME antenna.At first,a substrate integrated ME dipole for ultra-wideband(UWB)application has been designed,obtaining over 100% impedance bandwidth.Then,a wideband CP ME dipole antenna has been proposed.Wide bandwidth and good radiation pattern are achieved.The innovation of this thesis is as follows:1.A new substrate integrated ME dipole antenna has been proposed for the UWB application.The proposed antenna is composed of a bowtie patch functioning as an electric dipole and a pair of circular vertical shorted vias which are equivalent to a magnetic dipole.A ?-shaped probe feed is employed to excite the antenna,and some planar metal reflectors with shorted via holes are located at the corner of the antenna to improve matching and radiation pattern of the antenna.A prototype was fabricated and measured.The simulation and measurement results demonstrate an impedance bandwidth of 110% with SWR?2 from 3.1-10.66 GHz and a stable gain of 8.4±2.5d Bi.Good unidirectional radiation patterns with low back radiation and low cross polarization radiation are achieved across the operating bandwidth.With the use of multi-layer printed circuit board(PCB)technology,the proposed antenna is low-cost and east to fabricate.2.A novel wideband CP ME dipole antenna has been designed.In the proposed antenna,a pair of rotationally symmetric horizontal patches functions as an electric dipole,and two vertical patches with the ground act as an equivalent magnetic dipole.A ?-shaped probe is used to excite the antenna,and a metallic cavity with two gaps is designed for wideband and good performance in radiation.A prototype was fabricated and measured.The experimental results show that the proposed antenna has an impedance bandwidth of 65% for SWR?2 from 1.76 to 3.46 GHz,a 3-d B axial ratio(AR)bandwidth of 71.5% from 1.68 to 3.55 GHz,and a stable gain of 8±1 d Bi.Good unidirectional radiation characteristic and low back lobe level are achieved over the whole operating frequency band. |
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