wifi_antenna_design_and_application.ppt

Antenna Wireless 1886 HertZ 提出天線理論 1901 Marconi 把天線應用於生活上Antenna TheoryRadiation MechanismCreate radiation(a.) There must be a time-varying current or acceleration charge(b.) The wire must be curved、bent、discontinuous、 terminated or truncated Radiation MechanismField regions of an antennaRadiation PatternDef：The radiation pattern is a graphical representation of radiation properties of the antenna as a function of space coordinates Classification1.Isotropic Pattern2.Directional Pattern3.Omnidirectional Patter• Main lobe (major lobe) • Side lobe • Back lobe • Half power beamwidth(FNBW) • First null beamwidth(FNBW) Radiation PatternCurrent distribution on TLØ 天線是TL的變形Current distribution on DipolesAntenna Parameter1. Radiation Power(輻射功率)2. Radiation Intensity(輻射強度)3. Radiation Resistance(輻射電阻)4. Directivity(方向性)DipoleDipoleDipole• XZ plane  E plane• XY plane  H planeRadiation PatternDipole radiation patternHalf-wavelength DipoleD=1.64IsotropicD=1Dipole radiation patternVertical electric dipole above ground plane修正項Vertical electric dipole above ground planeVertical electric dipole above ground plane有適當的h提高天線效能將金屬板放置天 線後適當距離範例MonopoleFolded MonopolePIFA電感性，阻抗匹配用PIFAPIFA變形Ø 全向性Ø 線性極化PIFATwo-Element ArrayAFEFAFEFTwo-Element ArrayEFAFTOTALCase (a)AFEFEFAFTOTALAFEFCase (b)Ø 往相位落後方向發射及接收EFAFTOTALAFEFCase (c)Ø 往相位落後方向發射及接收N-Element ArrayBroadside ArrayØ 每根天線具相同相位及電流Endside ArrayØ 往相位落後方向發射及接收Ø Endside Array  集中火力Ø Endside Array應用於雷達Ø Broadside Array  左右分散攻擊Patch AntennaØ Light weight、Small volume、Low costØ Easy to integrate with MMICØ Linear and circular polarizationAdvantagesDisadvantagesØ Narrow bandwidth (high Q)Ø Low GainØ Low efficiencyFringing effectØ 模擬與量測會有差，起因為未考慮邊緣效應(fringing effect)Patch antenna Patch antenna Microstrip line feedØ 可利用此達到較佳的阻抗匹配Chip AntennaØ High dielectric constantØ Reduce the antenna sizeUWB ( Ultra Wideband ) Ø 10m的短距離高速通訊Ø 寬頻 Ø 高傳輸速率Ø 低功率消耗(省電)UWB ( Ultra Wideband ) UWB Spectrum UWB vs IEEE802.11aUWB Antenna UWB Antenna Ø 深度t及寬度w可用來達到最佳的阻抗匹配UWB Antenna Ø 角度越大共振長度越短進入VSWA=2的頻率點就往高頻走UWB Antenna Ø 半徑越大共振長度越長進入VSWA=2的頻率點就往低頻走。