天线基本原理.ppt

按一下以編輯母片標題樣式,按一下以編輯母片,第二層,第三層,第四層,第五層,*,天線設計簡介,壹、傳輸線,貳、天線設計基本原理,參、天線規格,肆、實驗與驗證課程,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：,ZL,Zin,Zin=,Zo,ZL+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,波長,=,光速,頻率*,介電常數,即,=C/f*,如,1KHz,的信號在一介電係數為,4,的電路板上傳播時其波長,(),為,=C/f*,=,3*10,8,10,3,4,=1.5,10,5,公尺,低頻的訊號波長遠大於傳輸線的長度，,l/,=0,即,l=0,，,tan(l),趨近,0,，故,Zin=ZL,故在分析低頻電路時，可以不考慮傳輸線的效應,涉及傳輸線效應，直角傳輸導線會有大的寄生電容,W,R 3W,a=1.8W,同軸線阻抗,Dinner,Douter,Z0=,138,log,Douter,Dinner,Outer,編織線愈疏則造成,insertion loss,愈大，相對的編織線愈密其,insertion loss,愈小，地網與信號線間的介電常數愈趨近於空氣,1,，衰減愈小，故使用氮氣發泡是業界常用的方式。,RF Connectors Impedance,Z0=,60lnD/d,D:,外導體內徑,d:,內導體內徑,:,絕緣介電常數,RF Connector,的上限頻率,f,u,=2c/,(D+d),/4 Transformers,Require Z0,/4,=,ZinZL,L=/4,Zin=,Z0,/4,ZL+jZ0,/4,tan(,l),Z0,/4,+jZLtan(,l),ZL,Zin,因,l=(2,/,)(/4)=,/2,Z0,/4,=ZinZL,Apply to real loads and sources,Perfect match at spot,frequency(10%-20%useable,bandwidth),Impedance Match Rule,串聯,L,並聯電容,並聯,L,串聯,C,天線設計基本原理,Sleeve Dipole Antenna,The 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 Center Driving,If the radius of wire,a,is very small,the input impedance of half wavelength dipole is 73+j 42.5 ohm,The shorter the length of dipole,the real part of impedance will be smaller,In order to match the 50 ohms coaxial cable,the length of dipole will be less than half wavelength,The imaginary part of impedance will be changed form inductance to capacitance for shorter length of dipole,The directivity of half wavelength dipole is 2.15 dBi,Whip Antenna for AMPS,This monopole antenna with higher directivity(5.162 dBi)for length 0.625 wavelength,If the length is quarter wavelength,then the directivity is 2.15 dBi,這是常見,5dBi,的作法,Radiation Pattern with Center Driving,The definition of dBi is the antenna gain which compares to that of the isotropic antenna,The definition of dBd is the antenna gain which compares to that of the dipole antenna,The directivity of half wavelength dipole is 2.15 dBi,The directivity 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,Examples,VSWR=1.5,RL=14 dB,TL=0.177 dB,VSWR=2.0,RL=9.5 dB,TL=0.512 dB,VSWR=3.0,RL=6.0 dB,TL=1.24 dB,Lower power handling for higher VSWR,The wider the bandwidth the larger the VSWR,E-Plane,Cut of antenna radiation pattern which contain the maximum field intensity and the direction of E field or electric current of antenna,H-Plane,Cut of antenna radiation pattern which contain the maximum field intensity and the direction of H field or magnetic current of antenna,Principle planes,Both E-and H-plane radiation patter,Beamwidth,Half power beamwidth,E-plane beamwidth,H-plane beamwidth,The wider beamwidth the,wider angular coverage,The wider beamwidth the,more interferences input,to the receiver,Polarization,Linear polarization,Vertical polarization,Horizontal polarization,Slant linear polarization,Circular polarization,RHCP,LHCP,Elliptical 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,