微波技术与天线.pptx

Horn Antenna喇叭天线喇叭天线偶极子偶极子反射器反射器八木八木-宇田天线宇田天线微带（贴片）天线微带（贴片）天线微带（贴片）天线微带（贴片）天线天线阵天线阵电基本振子电基本振子介质的本征波阻抗IlI：等幅同相rqNear-Zone Fields 近区场Far-Zone(Radiation)Fields 远区场Spherical polar coordinates球坐标Antenna Pattern 天线的方向图Common Types of Antenna Patterns 天线方向图的一般类型天线方向图的一般类型Power Pattern-normalized power vs.spherical coordinate position.功率方向图：基于球坐标的归一化功率图。Field Pattern-normalized|E|or|H|vs.spherical coordinate position 场方向图：基于球坐标的归一化的电场或磁场的模值。Isotropic Pattern-an antenna pattern defined by uniform radiation in all directions,produced by an isotropic radiator(point source,a non-physical antenna which is the only nondirectional antenna).等方向性方向图等方向性方向图 由等方向性辐射源(点源,非物理上可实现的唯一的无方向性天线)产生的，在任意方向上辐射都相同的方向图,Isotropic Pattern 等方向性方向图等方向性方向图Directional Pattern-a pattern characterized by more efficient radiation in one direction than another(all physically realizable antennas are directional antennas).有向方向图有向方向图有向方向图有向方向图-在某些方向上的辐射比其他方向强的方向图(所有物理可实现的天线都是有向天线).Omnidirectional Pattern全向方向图全向方向图Omnidirectional Pattern-a pattern which is uniform in a given plane.全向方向图全向方向图-在一个给定的平面内任意方向都相同的方向图E-plane-the plane containing the electric field vector and the direction of maximum radiation.E平面-包含电场矢量和最大辐射方向的平面H-plane-the plane containing the magnetic field vector and the direction of maximum radiation.H平面-包含磁场场矢量和最大辐射方向的平面Antenna Pattern Parameters 描述方向图的参数Main Lobe-radiation lobe in the direction of maximum radiation.Minor Lobe-any radiation lobe other than the main lobe.主瓣：最大辐射方向上的波瓣主瓣：最大辐射方向上的波瓣副瓣：主瓣以外的其他波瓣副瓣：主瓣以外的其他波瓣Side Lobe：旁瓣Back Lobe-the radiation lobe opposite to the main lobe.后瓣：后瓣：与主瓣方向相反的波瓣 Half-Power Beamwidth(HPBW)-the angular width of the main beam at the half-power points.半功率波束宽度半功率波束宽度：主波束半功率点之间的夹角First Null Beamwidth(FNBW)-angular width between the first nulls on either side of the main beam.第一零点波束宽度第一零点波束宽度：主波束两边第一个零点之间的夹角？主瓣旁瓣后瓣副瓣副瓣Half power beamwidth(HPBW)First null beamwidth(FNBW)功率方向图|E|2q？主瓣？旁瓣？后瓣？副瓣？First null beamwidth(FNBW)？Half power beamwidth(HPBW)Solid Angle立体角在球面坐标下面元dA的表达式:立体角dW与面元的关系:Radiation Power Density辐射功率密度辐射的总功率：Radiation Intensity辐射强度辐射的总功率：例题1：一个理想的等方向性辐射源的辐射强度为U0，求其辐射的功率为多少，功率密度为多少？解：辐射的功率为功率密度为Directivity方向系数Directivity(D)-The ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all direction.方向系数方向系数（D）:在某方向上的辐射强度（一般取最大辐射强度）与平均辐射强度的比值例题2：理想的等方向性辐射源的方向系数为多少？解：例题3：电基本振子(电偶极子)的方向系数为多少？解：天线效率天线效率 Antenna EfficiencyPrad the total power radiated by the antenna 辐射的功率Pl the total power dissipated by the antenna in the form of ohmic losses 由于欧姆损耗而被天线消耗的功率Antenna Gain天线增益天线增益 Gain:the ratio of the intensity,in a given direction,to the radiation intensity that would be obtained if the power accepted by the antenna were radiation isotropically.The radiation intensity corresponding to the isotropically radiated power is equal to the power accepted(input)by the antenna divided by 4p.增益：天线在某个方向上的辐射强度（一般取最大辐射强度）与有同样输入功率的(无耗的)等方向性天线的辐射强度之比。G=Dh1C.A.Balanis,Antenna theory:Analysis and design,New York:John Wiley,1997.Antenna Input Impedance天线的输入阻抗ZA=RA+jXA RA：天线的电阻XA：天线的电抗RA=Rr+RLDefinition:The impedance presented by an antenna at its terminals or the ratio of the voltage to current at a pair of terminals or the ratio of the appropriate components of the electric to magnetic field at a point.定义：天线终端的阻抗Rr：辐射电阻 RL：损耗电阻辐射电阻Radiation ResistancePr：天线的辐射的功率I：终端电流例题：求电基本振子的辐射电阻。解：Definition:The polarization of the wave transmitted by the antenna.定义：天线辐射波的极化。Antenna Polarization 天线极化 辐射波的极化Definition:The polarization of radiated wave is defined as that property of an electromagnetic wave describing the time varying direction and relative magnitude of the electric-field vector;specifically,the figure traced as a function of time by the extremity of the vector at a fixed location in space,and the sense in which it is traced,as observed along the direction of propagation.定义：沿电磁波传播方向观察的电场矢量随时间的变化方式。Linear polarization 线性极化Circular Polarization 圆极化Elliptical Polarization 椭圆极化 左旋极化（left hand polarization）逆时针极化（CCW）椭圆极化 右旋极化：right hand polarizatoin 顺时针极化（CW）极化的数学表达式线性极化：线性极化：圆极化：圆极化：CCWLeft hand polarizationCWright hand polarization椭圆极化椭圆极化Bandwidth带宽Definition:The range of frequencies within which the performance of the antenna,with respect to some characteristic,conforms to a specified standard.定义：使天线的特性（输入阻抗、方向图、波束宽度、极化、旁瓣电平、增益、辐射效率等）能够达到某种要求的频率范围表达方式：1.10:1带宽：indicates that the upper frequency is 10 times greater than the lower.2.5%带宽:indicates that the frequency difference of acceptable operation is 5%of the center frequenty of the bandwith.Effective Length有效长度Definition:the ratio of the magnitude of the open-circuit voltage developed at the terminals of the antenna to the magnitude of the electric field strength in the direction of the antenna polarization.Alternatively,the effective length is the length of a thin straight conductor oriented perpendicular to the given direction and parallel to the antenna polarization,having a uniform current equal to that at the antenna terminals and producing the same far-field strength as the antenna in that direction.定义：平行于天线极化方向，垂直于给定方向，并在该给定方向上产生相等远区场，同时又具有均匀电流（值为终端电流值）分布的细直导体的长度。一长度为2h（hl）中心馈电的短振子，其电流分布为：I(z)=I0(1-|z|/h)，其中I0为输入电流，也等于波腹电流Im。试求：.短振子的辐射场（电场、磁场）；.辐射电阻及方向系数；.有效长度。例题解：hhyzdzrr辐射的功率为辐射电阻为方向系数为：有效长度电基本振子电基本振子短振子短振子有效长度为 h接收天线理论Reciprocity in antenna theory states that if antenna#1 is a transmitting antenna and antenna#2 is a receiving antenna,then the ratio of transmitted to received power will not change if antenna#1 becomes the receiving antenna and antenna#2 becomes the transmitting one.互易性：天线#1是发射天线，天线#2是接收天线，当把天线#1作为发射天线，天线#2作为接收天线时，发射功率和接收功率之比保持不变。有效面积（口径）Effective Area(Aperture)Definition:The effective antenna area(aperture)is the ratio of the available power at the terminals of the antenna to the power flux density of a plane wave incident upon the antenna,which is polarization matched to the antenna.If there is no specific direction chosen,the direction of maximum radiation intensity is implied.定义：在入射波与天线极化匹配的情况下，天线终端的资用功率与天线接收的入射波的能流密度之比。天线的噪声温度Antenna Noise TemperatureK:波尔兹曼常数（Boltzmanns constant）1.38 10-23T:绝对温度 Df:带宽线天线Linear Wire AntennasHalf-wavelengthFull-wavelengthxyzEqEjErjqhhxzrrqhhxzrrh=0.25lh=0.5lh=0.75lh=l