Antenna

An antenna is a device used to transmit and receive electromagnetic waves, such as radio waves and microwaves. Antennas are found in a great variety of communication devices, including radios and television sets, weather radar systems, satellite communications systems, and radio astronomy research centers.

Your local radio station uses an antenna to transmit the programs it broadcasts. Words that are spoken or music that is played within the station are converted to electrical signals. These signals are then transmitted to an antenna in the form of an electric current. Electrons inside the antenna vibrate back and forth with the same frequency as the incoming

electric current. The vibration is characteristic of the sounds produced within the station. As these electrons vibrate, they create an electromagnetic wave in the air around the antenna. That wave spreads out and travels in all directions from the antenna. The frequency of the wave is the same as the frequency of the electron vibration in the antenna and of the sounds spoken in the station.

An antenna placed in the path of these waves reverses the above process. Electromagnetic waves in the air cause electrons in the receiving antenna to begin vibrating. The frequency of vibration is the same in the receiving antenna as it is in the wave. The vibrating electrons are converted into an electrical current, which travels into your radio receiver and is converted back into sound.

Antennas come in all sizes and shapes, from the tiny units found in miniature transistor radios to the massive structures used to transmit messages to and receive messages from outer space.

[See also Microwave communication; Radar; Radio ]

an·ten·na / anˈtenə/ • n. 1. Zool. (pl. -ten·nae / -ˈtenē/ ) either of a pair of long, thin sensory appendages on the heads of insects, crustaceans, and some other arthropods. ∎  (antennae) fig. the faculty of instinctively detecting and interpreting subtle signs: he has the political antennae of a party whip.2. (pl. -ten·nas) a rod, wire, or other device used to transmit or receive radio or television signals.DERIVATIVES: an·ten·nal / -ˈtenl/ adj. (in sense 1).an·ten·na·ry / -ˈtenərē/ adj. (in sense 1).

Antenna

An antenna is a device used to transmit and receive electromagnetic waves such as radio waves and microwaves. Antennas provide the transition between a guided wave (flowing in a wire) and a free space wave (flowing in air or vacuum ). An antenna can take high frequency pulses from an electrical signal generator , focus them, and launch them into space, like the antenna at a radio station. Conversely, it can pick up waves from space, focus them, and send them to a receiver, like the antenna on your car radio. You can think of an antenna as a soap bubble pipe: pulses (soap film) travel down the transmission line (pipe stem), reach the bowl (antenna), and are electrically shaped and pushed out into free space. The horn antennas used for microwave communication are designed to let the radiation spread out gradually rather than undergo an abrupt transition from the waveguide into free space. This is known as impedance matching, and contributes to the propagation of the radiation in the same way as cupping your hands around your mouth when shouting makes your voice travel further.

Basically there are two types of antennas: those that rotate and those that are stationary. Rotating antennas usually operate as search and detection systems. They are typically found on ships, airports, or weather stations. Often, an antenna will include a reflecting element to focus the radio waves, commonly parabolic or shaped something like an orange slice.

The stationary antenna type is generally found at radio or microwave transmitting sites. This antenna configuration can be a long wire between pylons, a single pylon with a long rod at the top, or include a number of unevenly spaced rods like an outdoor television antenna. The satellite dish, an antenna with a parabolic reflector, is another common type of stationary configuration.

See also Radar.

Antenna

An antenna is a device used to transmit or receive radio waves, which are electromagnetic waves with wavelengths longer than that of infrared light. Antennas mediate between electrical signals flowing in a wire or waveguide and electromagnetic waves moving through air, water, a vacuum, or some other medium. An antenna, such as the antenna in a cell phone, can take high frequency pulses from an electrical signal generator, focus them, and launch them into space. Conversely, it can pick up waves from space, and send them to a receiver. You can think of an antenna as a soap bubble pipe: pulses (soap film) travel down the transmission line (pipe stem), reach the bowl (antenna), and are electrically shaped and pushed out into free space. The horn antennas used for microwave communication are designed to let the radiation spread out gradually rather than undergo an abrupt transition from the waveguide into free space. This is known as impedance matching.

In mechanical terms, there are basically two types of antennas: those that rotate and those that are stationary. Rotating antennas usually operate as search and detection systems. They are typically found on ships, in airports, or at weather stations. Often, an antenna will include a reflecting element to focus the radio waves, commonly parabolic or shaped something like an orange slice.

The stationary antenna type is generally found at radio or microwave transmitting sites. This antenna configuration can be a long wire between pylons, a single pylon with a long rod at the top, or a number of unevenly spaced rods like an outdoor television antenna. The satellite dish, an antenna with a parabolic reflector, is another common type of stationary configuration.

See also Radar.

antenna A long whiplike jointed mobile paired appendage on the head of many arthropods, usually concerned with the senses of smell, touch, etc. (see sensillum). In insects, millipedes, and centipedes they are the first pair of head appendages and are specialized and modified in many insects. In crustaceans they are the second pair of head appendages, the first pair (the antennules) having the sensory function, while the antennae are modified for swimming and for attachment.