电子科学与工程学院 95 1.2典型辐射问题的解析方法 从显
1.2典型辐射问题的解析方法
一、天线的基本原理及参数
一、天线的基本原理及参数
What is an antenna? The IEEE Standard Definitions of Terms (IEEE Std 145-1983): ●“A means for radiating or receiving radio waves” "An antenna is any device that converts electronic signals to electromagnetic waves (and vice versa)"effectively with minimum loss of signals,as shown in Fig.1. EM Waves Portion of radio wave intercepted by receiving antenna Transmitting Receiving antenna antenna Transmission Transmission line line Transmitter Receiver Electronic Electronic Figure 1.Wireless communication system
What is an antenna? The IEEE Standard Definitions of Terms (IEEE Std 145-1983): “A means for radiating or receiving radio waves” “An antenna is any device that converts electronic signals to electromagnetic waves (and vice versa)” effectively with minimum loss of signals， as shown in Fig.1. Figure 1. Wireless communication system
1.Radiation Mechanism（辐射机理 "to create radiation,there must be a time-varying current or an acceleration(or deceleration)of charge" 1.Single wire If a charge is not moving,current is not created and there is no radiation. If charge is moving with a uniform velocity: a.There is no radiation if the wire is straight,and infinite in extent. b.There is radiation if the wire is curved,bent,discontinuous,terminated,or truncated If charge is oscillating in a time-motion,it radiates even if the wire is straight. 乡 (c)Discontinuous 纱 (a)Curved 乡 (d)Terminated Ground (b)Bent 奇 乡 (e)Truncated
1. Radiation Mechanism（辐射机理） “to create radiation, there must be a time-varying current or an acceleration (or deceleration) of charge” If a charge is not moving, current is not created and there is no radiation. If charge is moving with a uniform velocity: a. There is no radiation if the wire is straight, and infinite in extent. b. There is radiation if the wire is curved, bent, discontinuous, terminated, or truncated If charge is oscillating in a time-motion, it radiates even if the wire is straight. 1. Single wire
2.Two wires "electric charges are required to excite the fields but are not needed to sustain them and may exist in their absence.This is in direct analogy with water waves." +++++ +++++ (a)Antenna and electric field lines Antenna +++++ ++++ P ● +++++ (b)Antenna and free-space wave
2. Two wires “electric charges are required to excite the fields but are not needed to sustain them and may exist in their absence. This is in direct analogy with water waves