First Edition, 2012 ISBN 978-81-323-3025-7 © All rights reserved. Published by: Research World 4735/22 Prakashdeep Bldg, Ansari Road, Darya Ganj, Delhi - 110002 Email:
[email protected] Table of Contents Chapter 1 - Dipole Antenna Chapter 2 - Horn Antenna Chapter 3 - Radio Telescope Chapter 4 - Parabolic Antenna Chapter 5 - Antenna (Radio) Chapter 6 - Television Antenna Chapter 7 - Radio Masts and Towers Chapter 8 - Omnidirectional Antenna & Directional Antenna Chapter 1 Dipole Antenna A schematic of a half-wave dipole antenna that a shortwave listener might build. A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other (in line with each other), with a small space between them. The radio frequency voltage is applied to the antenna at the center, between the two conductors. These antennas are the simplest practical antennas from a theoretical point of view. They are used alone as antennas, notably in traditional "rabbit ears" television antennas, and as the driven element in many other types of antennas, such as the Yagi. Dipole antennas were invented by German physicist Heinrich Hertz around 1886 in his pioneering experiments with radio waves. Electric fields (blue) and magnetic fields (red) radiated by a dipole antenna Elementary doublet An elementary doublet is a small length of conductor (small compared to the wavelength ) carrying an alternating current: Here is the angular frequency (and the frequency), and is , so that is a phasor. Note that this dipole cannot be physically constructed because the current needs somewhere to come from and somewhere to go to.