Alternatively, if an antenna is placed into an electromagnetic field, it will produce an alternating voltage in response to the field. See radio frequency induction.

There are two fundamental types of antennae. The first couples to the electric field of an electromagnetic wave. It's usually a length of wire in which an electric charge moves back and forth. The second couples to the magnetic field of an electromagnetic wave. It is usually a coil or loop of wire forming an electromagnet.

Adding additional conducting rods or coils called, elements, and varying their length, spacing and orientation, an antenna with specific desired properties can be created. Typically, antennae are designed to operate at a specific frequency and to either radiate or receive energy.

The vast majority of antennae are simple vertical rods, which are inexpensive, and both radiate and receive from all directions (omnidirectional). One limitation of this antenna is that it does not radiate or receive very well in the direction in which the rod points. This is called antenna blind cone.

Antennae have practical use for the transmission and reception of rf signals (radio, tv, etc.) which can pass through (nonconducting) walls at the speed of light over great distances.

Antenna Types

• A dielectric resonator is a variation on the conventional antenna in which an insulator with a large dielectric constant is used to modify the electromagnetic field. It is claimed that the dielectric contains the antenna's near field and therefore prevents it from interfering with other nearby antennas or circuits, making it suitable for miniature equipment such as mobile phones.

• A feedhorn is an antenna system that handles the incoming waveform from the dish to the focal point. It usually comprises of a series of rings with decreasing radius in order to drive the signal to the polarizer.

• antenna height above average terrain
• antenna blind cone
• antenna effective area
• antenna theory
• electromagnetism
• log-periodic antenna
• WiFi
• Satellite television