# Loop Antenna

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## loop antenna

[′lüp an‚ten·ə]
(electromagnetism)
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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## 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.

### REFERENCES

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.

G. A. LAVROV

References in periodicals archive ?
For instance, you're not going to find a large loop antenna on a PCB that's, say, no larger than a postage stamp.
Nauwelaers, "Influence of Different Types of Metal Plates on a High Frequency RFID Loop Antenna: Study and Design," Advances in Electrical and Computer Engineering, vol.9, no.2, pp.3-8, 2009, doi:10.4316/AECE.2009.02001
To the best of our knowledge, five OAM generators in the RF band have been reported, including a circular phased antenna array [21,22], a helical paraboloid antenna [23], a circular polarized patch [24], a circular loop antenna [25], and an electromagnetic metasurface [26].
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.
In [11], the construction of a radio telescope is made with a particular antenna that accomplishes all the wanted characteristics, it is called magnetic loop antenna or isoloop (isolated loop).
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.
This implies that the loop antenna configuration facing each other provides more uniform distribution in sensitivity.
where [C.sub.loop] and [L.sub.loop] are the equivalent capacitance and inductance of the open loop antenna, respectively.
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.

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