Antenna
An antenna is a device that converts electrical signals in a cable (such as a coaxial cable or ladder line) into radio waves, and vice versa. An antenna is a critical part of virtually any radio system; even the best radio will not work well with a poor antenna. Many different types of antennas have been designed.
Dipoles and monopoles
A typical dipole antenna consists of two identical conductive elements such as metal wires or rods. The driving current from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the two halves of the antenna. Each side of the feedline to the transmitter or receiver is connected to one of the conductors. This contrasts with a monopole antenna, which consists of a single rod or conductor with one side of the feedline connected to it, and the other side connected to some type of ground. Outside ham radio, one well-known example of a dipole is the "rabbit ears" television antenna found on old broadcast television sets.
A dipole is the simplest type of antenna, both from a theoretical and practical standpoint. German physicist Heinrich Hertz first demonstrated the existence of radio waves in 1887 using what we now know as a dipole antenna (with capacitative end-loading). On the other hand, Guglielmo Marconi empirically found that he could just ground the transmitter (or one side of a transmission line, if used) dispensing with one half of the antenna, thus realizing the monopole antenna.
Although the term "vertical antenna" is often used to refer to a monopole antenna, either type can be vertical or horizontal; vertical dipoles are quite common, and horizontal monopoles are rarely used due to typically undesirable radiation patterns but are entirely possible.
Copyright © PBARC Wiki contributors. See the edit history of this page.
This file is licensed under Creative Commons Attribution-ShareAlike (CC BY-SA) 4.0 International.
This page contains content copied from or based on the Wikipedia article "Dipole antenna." Copyright © Wikipedia contributors. Used under CC BY-SA 3.0 Unported.
