EEE303AntennasFinalreview.pdfVIP

EEE303 Antennas Final review 概念 图床http:// 1365/tuchuang/ 线的主要特性参量 / byj r- k/ note/253737#%E6%8F%92%E5%85%A5latex%E5%85%AC%E5%BC%8F Wolfram|Alpha: Computational Knowledge Engine // [TOC] 概念 1.Antenna A structure will radiate or receive EM power in an efficient and desired manner. Advantages of radio system 1.Mobility 2.Good coverage over an area 3.Low path-loss over a long distance Loss in dB Loss=20log(distance) 2.Electric fieldE The electric field E at a given point is defined as the (vectorial) force F that would be exerted on a stationary test particle of unit charge by electromagnetic forces (i.e. the Lorentz force). A particle of charge q would be subj ect to a force F=q E The electric field (V/ m) is difined as the force per unit charge. Electric permittivity , also called dielectric constant Electric flux densityD 3.Magnetic fieldH The magnetic field,H(A/ m), is the vector field which forms closed loops around electric currents or magnets. Magnetic flux densityB Lorentz force 4.Current distributionJ Antenna design is all about how to control the current distribution J and hence to obtain the desired radiated field E. Simple case Ideal current element length Current value I For simple case: The E field has and components. The H field has j ust and component. When the angle is 90 degree. The H field reaches the maxim m. Antenna far field When the antenna size D is electrically large, , the common far-field condition is Maj or features of the far field 1.Just one E filed component: and one H field component: . 2.Both fields are inversely proportional(反比 ） to the distance r 3.E and H fields are orthogonal to each other. Power density function Intrinsic impedance(特征阻抗) 4. Antenna near field When far-field conditions are not meet, th