最新天线基本原理PPT课件.ppt

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1、天线基本原理壹、傳輸線 根據傳輸線理論，一段無損耗傳輸線，輸入阻抗可表成：ZLZinZin=ZoZL+jZ0tan(l)Z0+jZLtan(l)Z0:特性阻抗Zin:輸入阻抗:相位常數,與訊號波長的關係為=2/l:傳輸長度l天線設計基本原理SleeveDipoleAntennaThe current distribution of sleeve antenna is like the dipole antenna這是目前業界最常見的SLEEVE偶極天線銅管/4約22mm=C/f*約8.8cm/4約22mm實作驗證要不斷嘗試錯誤方有心得此線長會有影響Dipole Antenna with Cen

2、ter DrivingIf the radius of wire,a,is very small,the input impedance of half wavelength dipole is 73+j 42.5 ohmThe shorter the length of dipole,the real part of impedance will be smallerIn order to match the 50 ohms coaxial cable,the length of dipole will be less than half wavelength The imaginary p

3、art of impedance will be changed form inductance to capacitance for shorter length of dipoleThe directivity of half wavelength dipole is 2.15 dBiWhip Antenna for AMPSThis monopole antenna with higher directivity(5.162 dBi)for length 0.625 wavelengthIf the length is quarter wavelength,then the direct

4、ivity is 2.15 dBi這是常見5dBi的作法Radiation Pattern with Center DrivingThe definition of dBi is the antenna gain which compares to that of the isotropic antennaThe definition of dBd is the antenna gain which compares to that of the dipole antennaThe directivity of half wavelength dipole is 2.15 dBiThe dir

5、ectivity of 1.25(2x0.625)wavelength dipole 5.16 dBi這是場型圖，請注意不同gain值的場型VSWR:Return loss(RL)Transmission Loss(TL)參、天線規格:VSWR與Return Loss的關係是互換關係，若VSWR是2.0:1,則相對於Return Loss是約-10dB，其意是發射出去有90%的功率，反射回來有10%，反射愈多，幅射效率愈差ExamplesVSWR=1.5,RL=14 dB,TL=0.177 dBVSWR=2.0,RL=9.5 dB,TL=0.512 dBVSWR=3.0,RL=6.0 dB,T

6、L=1.24 dBLower power handling for higher VSWRThe wider the bandwidth the larger the VSWRE-Plane Cut of antenna radiation pattern which contain the maximum field intensity and the direction of E field or electric current of antennaH-Plane Cut of antenna radiation pattern which contain the maximum fie

7、ld intensity and the direction of H field or magnetic current of antennaPrinciple planesBoth E-and H-plane radiation patterBeamwidthHalf power beamwidthE-plane beamwidth,H-plane beamwidthThe wider beamwidth the wider angular coverageThe wider beamwidth the more interferences input to the receiverPol

8、arizationLinear polarizationVertical polarization,Horizontal polarization,Slant linear polarizationCircular polarizationRHCP,LHCPElliptical polarization Transmit Receive Polarization Loss vertical horizontal infinity horizontal vertical infinity RHCP LHCP infinity LHCP RHCP infinity RHCP or LHCP linear 3 dB linear RHCP or LHCP 3 dB vertical vertical 0 dB RHCP LHCP infinity horizontal horizontal 0 dB 45度slant Linear V or H 3 dB Polarization loss结束语结束语谢谢大家聆听！谢谢大家聆听！20