四分之一波长单极天线在左手金属材料中的实验研究(英文版)

1、Progress In Electromagnetics Research,PIER51,281293,2005 EXPERIMENTAL STUDY OF/4MONOPOLE ANTENNAS IN A LEFT-HANDED META-MATERIALQ.Sui,C.Li,L.L.Li,and F.LiInstitute of ElectricsChinese Academy of ScienceBeijing,100080,P.R.ChinaAbstractThe paper focuses on/4monopole antennas located in a meta-material

2、 that exhibits simultaneously negative values of eective permeability and permittivity within a microwave frequency band, as well as our experimental study in an anechoic chamber.The experimental results show that the electromagnetic waves radiated by the monopole are negatively refracted at the int

3、erface between the meta-material and the air at certain directions.In addition,the radiation pattern of the monopole in the meta-material is directional while it is non-directional without the meta-material.1Introduction2Experimental Setup and the Structure of Meta-Material3Experiment Results and Ex

4、planations3.1Measured S11of Monopoles in Dierent Media3.2The Frequency Band of Negative Permeability andPermittivity3.3The Radiation Pattern in x-z Plane3.4Verication of Negative Refraction4ConclusionAcknowledgmentReferencesAlso with School of Information,Beijing Broadcasting Institute,Beijing,10002

5、4, P.R.China282Sui et al.1.INTRODUCTIONIn the past few years,the meta-materials with permittivity and permeability both taking real negative values have been considered in many publications.So far,there are several experiments to verify the left-handed properties of these meta-materials.In2000,David

6、 Smith of the University of California at San Diego and his colleagues constructed therst LHM based on a periodic array of interspaced conducting nonmagnetic split-ring resonators and continuous metallicwires.1The negative permeability region begins at4.2G Hz andends at 4.6GHz.In2001,this group made

7、 another LHM at X-band and veried the negative index of refraction2predicted by Veselago.3In2002,Mehmet Bayindir et al.studied the transmission properties of LHM in free space,4which also veried the existence of negative permeability and permittivity.Also in2002,Stefan Enoch et al.studied the direct

8、ive emission of a source embedded in a slab of meta-material.5In2003,Ran Lixin,Hongsheng Chen of Zhejiang University and their colleagues made therst beam shifting experiment and T-junction waveguide experiment to verify the negative refraction 6,7.They also did an experiment to conrm negative refra

9、ctive index of a meta-material composed of-like metallic patterns.8 We constructed a large LHM and studied the transmission properties in an anechoic chamber in2003.9In this paper,a type of meta-material composed of periodical arrangement of thin copper strips and split ring resonators(SRRs is studi

10、ed.The radiation properties of a/4monopole antenna in the meta-material was measured in an anechoic chamber.2.EXPERIMENTAL SETUP AND THE STRUCTUREOF META-MATERIALThe meta-material was constructed as follows:the wire strips and SRRs were printed on two separate printed circuit boards by etching techn

11、ique.The thickness and the relative permittivity of the boards are 0.5mm and2.65,respectively.The SRRs and wire strips are0.035mm thick.The size of the square board is246×246mm2.The width and length of the strips are0.5mm and238mm respectively.There are48 strips on one board.The distance betwee

12、n the strips is5mm.The conguration of a single SRR has a geometry which is similar to the previously reported structure.2,4The details of a single SRR are shown in Figure1.It consists of two square rings separated by a gap. There are2304(48×48SRRs,which are separated by5mm,on one board of246

13、15;246mm2.Study of/4monopole antennas in meta-material283 Figure1.Single SRR with parameters l=3mm,d=t=w= 0.3mm.Three dierent media were fabricated by combining the SRR and the strip boards.The three media are as follows:Medium-1is made by placing50identical SRR boards in parallel arrangement with5m

14、m in distance,Medium-2by placing49identical strip boards in parallel arrangement with5mm in distance,and Medium-3by stacking49strip boards and50SRR boards in a periodic arrangement with2.5mm in distance.The main instruments used in our experiments were an Agilent 8722ES vector network analyzer,a mic

15、rowave horn antenna,and a receiving monopole with conducting ground plane.The assembled dimensions of the horn antenna are27.9cm in width,15.9cm in height, and24.4cm in length.The height of the receiving monopole above the conducting ground plane(250×250mm2is about7.5mm.As seen in Figure2,a/4mo

16、nopole with ground plane was placed in the medium.Theat conducting ground plane is made of copper of270×246mm2.The horn antenna or the receiving monopole was placed beside the medium.The Agilent8722ES was connected to the monopole in the medium and the horn antenna or the receiving monopole bes

17、ide the medium via two coaxial cables.We studied the radiation characteristics of the monopole in the meta-material by measuring the scattering parameters matrix when the monopole is in Medium-1,Medium-2,Medium-3,and the Air respectively.As seen in Figure2,we placed a/4monopole in the media.The at c

18、onducting ground plane is made of copper of270×246mm2.The horn antenna or the receiving monopole was placed beside the media.284Sui et al. Figure2.Experiment setup of monopole in meta-material.3.EXPERIMENT RESULTS AND EXPLANATIONS3.1.Measured S11of Monopoles in Dierent MediaFigure3to Figure6sho

19、ws the measured S11of the monopoles of dierent lengths in dierent media.The lengths of the monopoles are about9.3mm,7.5mm,6.2mm,and5.3mm respectively.From Figure3to6,we decide to use the monopoles of h=7.5mm and h=6.2mm in our experiments.rest of the That means the waves can3.2.The Frequency Band of

20、 Negative Permeability and PermittivityFigures7and8show the measured S21when the monopoles are in dierent media.Eachgure has four curves showing the results of the monopole(h=7.5mmin Medium-1(SRRs only,Medium-2(strips only,Medium-3(SRRs&strips,and the Air,respectively.The horn antenna was placed

21、 beside the medium.The distance between the monopole and the horn aperture is about20cm.The following facts can be derived from Figures7and8:When the monopole is in Medium-1,electromagnetic waves can not propagate within1010.5GHz,but can propagate in the rest of the frequency band.This means that th

22、e eective permeability of Medium-1 within1010.5GHz is negative.When the monopole is in Medium-2,electromagnetic waves cannot propagate in the frequency band under test,which means that the eective permittivity of Medium-2is negative.When the monopole is in Medium-3,S21at10.310.8GHz is higher than th

23、at at other frequencies.Because the meta-material consisting of50pieces of SRR boards and49pieces of strip boards isStudy of /4monopole antennas in meta-material285 S 11(V S W R Frequency (GHzFigure 3.Measured S 11of monopoles of dierent length in the Air.S 11(V S W R Frequency (GHzFigure 4.Measured

24、 S 11of monopoles of dierent lenth in Medium-1(SRRs only. S 11(V A W R Frequency (GHzFigure 5.Measured S 11of monopoles of dierent length in Medium-2(strips only. S 11(V S W R Frequency (GHzFigure 6.Measured S 11of monopoles of dierent length in Medium-3(SRRs &strips. S 21 (d B Frequency (GHzFig

25、ure 7.Measured S 21of h =7.5mm monopoles in dierent media. -70-65-60-55-50-45-40-35-30-25S 21(d B Frequency (GHzFigure 8.Measured S 21of h =6.2mm monopoles in dierent media.rather large,the attenuation of the waves in the meta-material would be very serious.Although S 21at 10.310.8GHz is not much hi

26、gher than that at some frequencies beyond 10.310.8GHz,it is reasonable to consider electromagnetic waves can propagate along the x -axis within 10.310.8GHz but cannot propagate in the rest of the frequency band,which means that both the eective permeability and the eective permittivity may be negati

27、ve within 10.310.8GHz.This conclusion is also supported by the following two experiments.3.3.The Radiation Pattern in x -z PlaneThe radiation pattern in x -z plane was measured by rotating the Medium-3around the axis of the monopole. 90270Figure 9.Normalized eld pattern of 10.6GHz.Figure 9shows the

28、measured result of normalized eld pattern of 10.6GHz.The reference angle 0.means that the normal direction of the boards is along the x -axis.The radiation pattern of the monopole in Medium-3is directional while it is non-directional in the Air,which was also observed in 5.The maximum radiation dire

29、ction is perpendicular to the normal direction of the board.Because both the eective permeability and permittivity are negative at this direction,the waves radiated by the monopole can pass through Medium-3.When the angle changes from 0to ±90,the eective permeability changes to be positive grad

30、ually while the eective permittivity remains negative.The electromagnetic waves changeto non-propagable gradually.It is clear that the meta-material is anisotropic.In theory,the radiation pattern in x-z plane of monopole with large ground plane in the air should be a circle.Because the ground plane

31、is not very large in our experiment,the measured pattern is approximately a circle and because the framework that holds the strip and SRR boards remains when we tested the monopole without the meta-material,there are pits at45±10and135±10.3.4.Verication of Negative RefractionAccording to V

32、.G.Veselagos prediction,when a beam of radiation is incident on an interface between right-handed material(RHMand left-handed material(LHM,the refracted ray is bent on the same side of the normal as the incident ray.As shown in Figure10,if the transmitting monopole is in the LHM,the radiation beam s

33、hould bend downwards.In order to verify the negative refraction,we moved the receiving monopole antenna up and down and measured the S21 at dierent position.In our experiment,the distance between the transmitting monopole and the receiving one is about30.5cm.Figure11shows the measured S21of10.6GHz i

34、n the test of Figure10.It is because both the eective permeability and permittivity of Medium-3may be negative within10.310.8GHz that we choose the frequency of10.6GHz for the sake of illustration.Figure11has four curves showing the S21when the transmitting monopoles(h=7.5mm and h=6.2mmare in Medium

35、-3and the Air,respectively. Figure10.Experimental setup for refraction received by monopole. H (cmFigure11.Measured S21s received by monopole.From Figure11,the maximum S21emerges at about H=3cm to H=4cm when the monopole is in Medium-3,while at about H=0cm to H=0.5cm when the monopole is in the Air.

36、That means that the electromagnetic waves radiated by the monopole antenna in the meta-material are refracted downwards of the interface between Medium-3and the Air.Indeed,if the electromagnetic waves were not refracted downwards,the maximum S21could not emerge at the lower position than the conduct

37、ing ground plane of the transmitting monopole.The role of electromagnetic waves diraction at the edge of the ground plane was also considered.The diractive electriceld below the ground plane of the monopole in the air was calculated.10The ground plane is250×250mm2,and the calculated result alon

38、g the route of the receiving monopole was shown in Figure12.The diractive electriceld decreases when the position moves downwards below the plane.Therefore,we conclude that the maximum power detected below the ground plane(at H=3cm to4cmwhen the monopole is in Medium-3is due to the negative refracti

39、on instead of the diraction.Study of /4 monopole antennas in meta-material Normalized diffractive electric field 1.0 291 h=7.5mm h=6.2mm 0.8 0.6 0.4 0.2 0.0 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 H (cm Figure 12. Normalized diractive electric eld. 4. CONCLUSION The propagation characteristics of the elect

40、romagnetic waves radiated by a monopole antenna located inside a meta-material or in the air are studied in our experiments. From the experiments, the following facts can be concluded: 1. The eective permeability of the medium made of SRRs could be negative within 1010.5 GHz. Both the eective permit

41、tivity and the eective permeability of the meta-material with SRRs and strips could be negative within 10.310.8 GHz at certain direction. 2. The radiation pattern of the monopole in the meta-material is directional while it is non-directional without the meta-material. 3. The incident beam was refra

42、cted on the same side of the normal to the interface between meta-material and the air as the incident ray. ACKNOWLEDGMENT The authors wish to thank Professor T. M. Grzegorczyk and referee for valuable correspondence. This work was supported by the National Natural Science Foundation of China. (Gran

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