Antennas 101 - Dartmouth College（天线101 -达特茅斯学院）.pdf

7/26/12 Antennas 101 Eric Hansen, KB1VUN How does radio work?   Transmitter: Convert message to radio frequency (RF) voltage   Antenna: Convert RF to propagating electromagnetic (EM) wave   Propagation path   Antenna: Convert EM wave to RF voltage   Receiver: Extract message from RF   This session: antennas Some illustrations are reproduced from the ARRL Handbook and the ARRL Antenna Handbook and are used by permission. 1 7/26/12 Figure from ARRL Antenna Handbook, 22nd edition Electromagnetic wave Figure from ARRL Antenna Handbook, 22nd edition Basic dipole antenna   Fundamental phenomenon: accelerating charges (e.g., sinusoidal current in a wire) radiate EM fields (Tx); EM field induces current in wire (Rx).   Tx is a generator connected to the feedpoint of the