Research And Design Of Miniaturized UWB-MIMO Antenna

When electromagnetic waves propagate in a complex environment,influenced by factors such as ground building or atmosphere,light will be reflected,deflected or transmitted to receiving end.This phenomenon is called multipath effect which leads to multipath fading.For communication systems,multipath fading is an unfavorable factor which reduce reception quality of the communication system.Installing multiple antennas at both ends of the transceiver,MIMO(Multiple-Input Multiple-Output)technology make full use of multipath fading.It can not only break through the bottleneck of the Shannon capacity,but also increase the capacity of the channel by many times.However,with the increase of number of antennas,the problem of how to miniaturized antenna systems and reduce the coupling of antenna units cannot be ignored.In recent years,UWB(Ultrawideband)technology has become mainstream technology in wireless communication field because of its advantages such as wide frequency band(3.1-10.6 GHz),low power consumption,high speed and strong anti-interference ability.Because UWB technology can provide 100-500Mb/s,and MIMO technology can increase transmission rate,combining UWB and MIMO,that is MIMO technology can achieve high speed of 1Gb/s.There are some other systems which frequencies exist in 3.1-10.6GHz may severely affect the UWB system,such as 3.5 GHz WiMAX(Worldwide Interoperability for Microwave Access),5.5 GHz WLAN(Wireless Local Area Networks)and 7.5 GHz X-band.In order to alleviate their interference with the UWB-MIMO system,designing UWB-MIMO antennas with notched-band or stop-band characteristics is the most effective solution.Therefore,research and design of miniaturized UWB-MIMO antenna with multiple notched bands and high isolation characteristics has theoretical and practical significance.This paper mainly researches and designs an UWB-MIMO antenna and multiple notched UWB-MIMO antennas.Simulation analysis and processing tests are carried out.Test results show that the antennas have good performance.The specific research contents include the following aspects:1)Combining working principles of decoupling and impedance matching,a compact monopole UWB-MIMO antenna is proposed.It consists of two similar microstrip-fed circular monopole radiators and two symmetric inverted T-shaped slots curved in the ground for better impedance matching.An I-shaped metal ground stub not only reduce ports mutual coupling,but also improve impedance matching at low frequency band which is useful for miniaturization.The results of simulation and measurement show that the antenna has good characteristics of compact structure,wide working bandwidth,stable gain and omnidirectional radiation.2)No more than three notched frequency bands are realized for most UWB-MIMO antennas.To solve this problem,a polarization diversity quad-notched band UWB-MIMO antenna and a pattern diversity quad-notched band UWB-MIMO antenna are investigated.Firstly,a quad-notched band UWB antenna is introduced.It comprises of a U-shaped radiator,a tapered microstrip-fed feed-line,and semielliptical ground plane.By inserting a pair of L-shaped slots,CSRR(Complementary Split-Ring Resonators)on the radiator and adding a pair of C-shaped stubs symmetrically around the feed-line,four notched bands are achieved to filter 3.5GHz WiMAX,5.25GHz lower WLAN,5.8GHz upper WLAN,and 7.5GHz X-band.Placing these two antennas vertically to each other,a polarization diversity UWB-MIMO antenna is formed which has quad-notched bands and high isolation.Put above two quad-band notched UWB antennas horizontally to each other,then a pattern diversity quad-notched bands UWB-MIMO antenna is designed.Port isolation is enhanced with three metal strips on the ground plane.The results indicate that these two quad-band notched UWB-MIMO antennas can cover UWB frequency band and mitigate interference from WiMAX,lower WLAN,upper WLAN,and X-band.Moreover,both antennas have characteristics of high isolation,gentle gain and good radiation.3)Miniaturization of antenna element is the most direct method to reduce antenna size.If decoupling unit can improve impedance matching of low frequency band,the antenna can also be miniaturized.Combining these two methods,based on half-cutting method,two multiple notched UWB-MIMO antennas are studied.Taking a beveled rectangle monopole antenna as an original model,two beveled rectangular elements are obtained by half-cutting segmentation.The UWB-MIMO antenna with three notched bands is composed of these two beveled rectangular elements,a common ground plane and a T-shaped stub which is used to reduce mutual coupling and improving impedance matching.By etching three inverted L-shaped slots of different lengths on the radiating patch,three notched bands for 3.5GHz WiMAX,5.5GHz WLAN and 8.1GHz X band are realized.The quad-notched band UWB-MIMO antenna is also composed of these two beveled rectangular elements and a common ground plane.Compared with the former antenna,some improvements have made.The quad-notched band UWB-MIMO antenna replaces the original FR4 substrate with Rogers R04003C substrate which has a better performance.And the original T-shaped stub was replaced with a T-like stub.To obtain quad notched band of 3.4GHz WiMAX,5.3GHz lower WLAN,5.8 GHz upper WLAN and 8GHz X band,an inverted L-like meander slot and two inverted L-shaped slots are etched on the radiator,and a pair of C-shaped stub is placed symmetrically beside the feeding line.The results of test demonstrate that the design methods are correct and feasible for these two multiple notched-band UWB-MIMO antennas which are based on half-cutting method.