36 Facts About Radio antenna

In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves .

An Radio antenna is an array of conductors, electrically connected to the receiver or transmitter.

Radio antenna waves are electromagnetic waves which carry signals through the air at the speed of light with almost no transmission loss.

Dipole Radio antenna, which is the basis for most Radio antenna designs, is a balanced component, with equal but opposite voltages and currents applied at its two terminals.

The vertical Radio antenna is a monopole Radio antenna, not balanced with respect to ground.

Related searches

An Radio antenna lead-in is the transmission line, or feed line, which connects the Radio antenna to a transmitter or receiver.

An Radio antenna counterpoise, or ground plane, is a structure of conductive material which improves or substitutes for the ground.

An Radio antenna coupling network is a passive network used for impedance matching in between the Radio antenna and the transmitter or receiver.

The "receiving pattern" of an Radio antenna when used for reception is identical to the radiation pattern of the Radio antenna when it is driven and functions as a radiator.

The impedance match between the feedline and Radio antenna is measured by a parameter called the standing wave ratio on the feedline.

Sometimes the resulting electrical resonant frequency of such a system is described using the concept of electrical length, so an Radio antenna used at a lower frequency than its resonant frequency is called an electrically short Radio antenna.

Radiant flux as a function of the distance from the transmitting Radio antenna varies according to the inverse-square law, since that describes the geometrical divergence of the transmitted wave.

Likewise, a corner reflector can insure that all of the Radio antenna's power is concentrated in only one quadrant of space with a consequent increase in gain.

An example of a high-gain Radio antenna is a parabolic dish such as a satellite television Radio antenna.

An example of a low-gain antenna is the whip antenna found on portable radios and cordless phones.

Effective area or effective aperture of a receiving Radio antenna expresses the portion of the power of a passing electromagnetic wave which the Radio antenna delivers to its terminals, expressed in terms of an equivalent area.

Since the receiving Radio antenna is not equally sensitive to signals received from all directions, the effective area is a function of the direction to the source.

Radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles in the far-field.

The pattern of an ideal isotropic Radio antenna, which radiates equally in all directions, would look like a sphere.

Space surrounding an Radio antenna can be divided into three concentric regions: The reactive near-field, the radiating near-field and the far-field regions.

Efficiency of a transmitting Radio antenna is the ratio of power actually radiated to the power absorbed by the Radio antenna terminals.

The loss resistance and efficiency of an Radio antenna can be calculated once the field strength is known, by comparing it to the power supplied to the Radio antenna.

The power that an Radio antenna will deliver to a receiver is reduced by the same amount.

However, in the case of a directional Radio antenna used for receiving signals with the intention of rejecting interference from different directions, one is no longer concerned with the Radio antenna efficiency, as discussed above.

The directive gain of an Radio antenna can be computed from the published gain divided by the Radio antenna's efficiency.

Related searches

Orientation and physical structure of an antenna determine the polarization of the electric field of the radio wave transmitted by it.

For instance, an Radio antenna composed of a linear conductor oriented vertically will result in vertical polarization; if turned on its side the same Radio antenna's polarization will be horizontal.

Radio antenna waves reflected off the ionosphere can change the wave's polarization.

For instance, a turnstile Radio antenna mounted horizontally, from a distant location on earth, appears as a horizontal line segment, so its radiation received there is horizontally polarized.

The polarization of a commercial Radio antenna is an essential specification.

In most cases, in principle the physical length of the Radio antenna can be "trimmed" to obtain a pure resistance, although this is rarely convenient.

Physically large inductor at the base of the Radio antenna has an inductive reactance which is the opposite of the capacitative reactance that the short vertical Radio antenna has at the desired operating frequency.

Radiation pattern and even the driving point impedance of an Radio antenna can be influenced by the dielectric constant and especially conductivity of nearby objects.

Whenever both the receiving or transmitting Radio antenna are placed at significant heights above the ground, waves reflected specularly by the ground will travel a longer distance than direct waves, inducing a phase shift which can sometimes be significant.

At lower heights, the effect on the Radio antenna's impedance is very sensitive to the exact distance from the ground, as this affects the phase of the reflected wave relative to the currents in the Radio antenna.

Therefore it is usually desired for an Radio antenna to operate as a resonant element with each conductor having a length of one quarter wavelength .