Antennas

There are several antenna types and ways of categorizing them. The first two antenna types are the antennas that are a body part for some animals and that are man-made. Usually people are familiar with insect antennas, but for example, the lobster—have them, too. For animals, antennas function as a sensory organ. The other understanding implies that an antenna, or aerial, is a device to send or receive signals. It is a transformer between a transmission line and free space.

The second major categorical division of antenna types is between those that transmit signals, known as transmitting antennas, and those that receive signals, called receiving antennas. Some antennas can both transmit and receive signals. Usually, transmitting antennas handle a good deal more electrical energy than receiving antennas.

There are a number of key parameters used to describe antenna properties. Chief among these relate to the directional characteristics and the resulting gain. The directivity is a measure that describes the power density the antenna radiates in the direction of its strongest emission, versus the power density radiated by an ideal isotropic radiator (which emits uniformly in all directions) radiating the same total power. An antenna's directivity is a component of its gain - a parameter which measures the degree of directivity of the antenna's radiation pattern. In laymen’s terms, gain refers to the ability of the antenna to focus scattered RF waves into a narrower, useful plane, thereby increasing signal strength. Polarization, which is the direction of the electric (not magnetic) field of an antenna is another important antenna characteristic. One more important parameter is the radiation pattern which is the angular distribution of the power radiated by an antenna. It is typically represented by a three dimensional graph and is a very important tool to both the antenna designer and the end user as it shows a quick picture of the overall antenna response.

Different antenna types are used for radio, television, and radar systems.

Antennas transmit signals of different frequencies, that’s why another way to categorize antenna types is by their frequency. For radio antennas, they can be built for frequency modulation (FM) broadcasting at 88–108 MHz (megahertz) or amplitude modulation (AM) broadcasting at 535-1605 kHz (kilohertz). For television antennas, one distinguishes between Ultra High Frequency (UHF) antennas, and Very High Frequency (VHF) antennas, or antennas that pick up both.

Antenna types can be categorized in terms of customers’ needs. The range of antennas can be categorized as short, medium, or long. For customers buying a television antenna, the decision is dependent on how close they are to the transmitting towers that they wish to pick up a signal from. If the range is well matched to the distance, it will help avoid the antenna picking up unwanted signals.

Antenna types depend on the location. Antennas can be used indoors, outdoors or installed in attics. The advantage of indoor antennas is that they are easy to install, but sometimes they do not provide the best signal, particularly for customers who are far from the place of transmission. Outdoor antennas used to be made for rooftops, but now they are being designed to be placed on the side of a house, or on a pole. An attic can be a useful installation point for those who do not want their antenna inside or outside for some reasons.

One more way to classify antenna types is by their appearance in terms of design. A directional antenna gather signals from a central location and omni directional seeks signals from towers transmitting from different locations. A non directional antenna or, an omnidirectional antenna may be used to pick up broadcast television signals or audio broadcasts from radio stations, or allow robotic devices to be operated using microwave or wireless technology. Mobile or cellular telephone services, as well as wireless Internet connections, make use of an omnidirectional antenna as part of the process of broadcasting stable signals to these devices.

In design, the omnidirectional antenna is an external or internal sending or receiving device. An internal design for the omnidirectional antenna is usually very simple, and may employ a simple design that is not unlike a dipole antenna. While compact, antennas of this type are extremely powerful, and can often pick up a stable signal for long distances. Cell phones and other small wireless devices will also have an internal antenna that makes it possible to pick up signals emitted by some type of sending equipment.

An external omnidirectional antenna is often used for controlling electronic devices, such as robotic machinery in a manufacturing plant. The antenna will be incorporated into the design of the robotics, allowing the devices to be controlled from a remote point by means of a broadcast signal on a specific frequency. Thanks to the nature of the antenna, neither the device nor the control station must be stationary in order for the signal to remain strong and stable. This makes it much easier for the device to move about the plant floor and still be under the control of the remote operator, without any difficulties.