Loop Antenna

Also found in: Wikipedia.

loop antenna

[′lüp an‚ten·ə]
A directional-type antenna consisting of one or more complete turns of a conductor, usually tuned to resonance by a variable capacitor connected to the terminals of the loop. Also known as loop.

Loop Antenna


(frame antenna), a directive antenna in the shape of one or more flat rings of wire forming a circular, square, or rectangular frame. It was proposed in 1913 by K. Braun.

In most cases, the perimeter of the loop is very small compared with the operating wavelength; thus, the input impedance of the antenna has the characteristics of an inductance. By connecting a loop antenna with a variable capacitor, it is possible to obtain an oscillatory circuit that is tuned to the operating wavelength. When the dimensions of the loop are small, the amplitude and phase of the current oscillations in the loop are practically constant over the entire perimeter. In a transmitting loop antenna, the direction of the current in the opposite elements of the loop is reversed, and the radiated electromagnetic waves are therefore shifted by exactly 180° in phase. As a result, the radiation in the direction perpendicular to the plane of the loop is completely canceled. In other directions the cancellation is incomplete, and the maximum radiation intensity corresponds to the directions lying in the plane of the loop.

The strength of an electric field E of an electromagnetic wave at some point located a great distance d from a transmitting loop antenna is calculated from the formula

where l is the current in the loop, n is the number of turns, S is the area of the loop, λ is the operating wavelength, and ɸ is the angle between the plane of the loop and the direction to the point under consideration. The electromotive force ∊ induced in a receiving loop antenna is calculated from the formula

where E is the component of the electric field strength of the received wave parallel to the plane of the loop and ɸ is the angle between the plane of the loop and the direction of arrival of the wave. In the plane perpendicular to the plane of the loop, the polar diagram of the antenna has the shape of a figure eight. The directivity factor is equal to 1.5. Loop antennas sometimes have dimensions comparable with λ. In this case, the polar diagram has multiple lobes and the direction of maximum radiation (or reception) is changed.

Loop antennas are primarily used as the receiving antennas for radio direction finders, including radio compasses, and for radio broadcast receivers operating in the low-, medium-, and high-frequency ranges.


Shuster, A. Ia. Sudovye radionavigatsionnye pribory. Leningrad, 1973.
Drabkin, A. L., V. L. Zuzenko, and A. G. Kislov. Antenno-fidernye ustroistva, 2nd ed. Moscow, 1974.
Lavrov, A. S., and G. B. Reznikov. Antenno-fidernye ustroistva. Moscow, 1974.


References in periodicals archive ?
Tenders are invited for Supply of 3 Loop Antenna system with coupling and decoupling network (CDN) etc.
There is no imaginary component of the input impedance because the Alford loop is a resonant loop antenna.
iSIGN will be supplying the Smart Antennas from its existing inventories and will be, at the request of RMT, removing the standard stick antenna, so that RMT can use their Loop Antenna in order to meet airport requirements.
nivalis at the cave; however, if they were passing through the loop antenna configuration they were not detected with any regularity via the PIT tag system.
The loop antenna can be designed in various shapes, such as a circle, a square, a rectangle, a triangle and others.
The total HP radiation pattern can be regarded as a superimposition of the loop antenna patterns.
High frequency (HF) loop antenna is the perfect solution to guarantee communications on the battlefield for harsh environment conditions when satellite communications are not available.
Cahill, "Pattern shaping using a reactively loaded wire loop antenna," Proc.
The radio comes with an AC/DC adapter, FM dipole antenna, AM loop antenna, a print user manual and a CD with a voice recording of user guide.
The proposed shielded loop antenna feeding line design not only reduces the common mode current but also acts as antenna balancing (antenna balun), removing the need for an extra balun.
A loop antenna is essentially an inductor made up of coils of ferrite rods tuned with a parallel capacitor at the wanted frequency.
6 flare on Feb 18, obtained with a simple loop antenna plugged into a computer's sound card.