What is a Loop Antenna?
A loop antenna has a continuous conducting path leading from one conductor of a two-wire transmission line, “the feed”, to the other conductor. You may think of it as a “coil that radiates”. The coil may have only a single turn. It may have arbitrary shaped perimeter, but the essence of a coil is that the defining wire encloses an area. Thus, a folded dipole is not a loop antenna in this sense, since the area inside the conductor path is vanishingly small. In a loop antenna, the magnetic field (generated by the loop current) threads the area of the loop and this provides the loop with inductance. “Symmetric” loop antennas have a plane of symmetry running along the feed and through the loop. “Planar” loop antennas lie in a single plane which also contains the conductors of the feed. “Three-dimensional” loop antennas have wire which runs in all of the x,y, and z directions (in a rectangular Cartesian system). By definition they are not planar. They may, however, be symmetric about planes
A loop antenna is an antenna that creates a continuous conducting path between one conductor of a two-wire transmission line to the other. There are three categories of loop antenna: small, medium, and large. A small loop is considered so if its circumference is less than one forth of a wavelength. Most directional receiving loops are approximately one tenth of a wavelength. A small loop is sometimes referred to as a magnetic loop, due to its increased sensitivity to the magnetic components of an electromagnetic wave. It is also less sensitive to nearby electric noise than other antennas, when properly shielded. If a small loop is brought into resonance with a tuning capacitor, its received voltage can be greatly increased. When a signal arrives along the loop’s axis, an equal amount of voltage will be induced in each limb to account for symmetry. Since the loop’s output is the difference in voltage between the two limbs, it should always be zero. If a signal arrives in the plane of th
loop antenna has a continuous conducting path leading from one conductor of a two-wire transmission line to the other conductor. You may think of it as a “coil that radiates”. The coil may have only a single turn. It may have arbitrary shaped perimeter, but the essence of a coil is that the defining wire encloses an area. Thus, a folded dipole is not a loop antenna in this sense, since the area inside the conductor path is vanishingly small. Symmetric loop antennas have a plane of symmetry running along the feed and through the loop. Planar loop antennas lie in a single plane which also contains the conductors of the feed. Three-dimensional loop antennas have wire which runs in all of the x,y, and z directions (in a rectangular Cartesian system). By definition they are not planar. They may, however, be symmetric about planes which contain the feed. It is possible for the loop antenna plane not to contain the run of the feed. This matters for situations where the feed currents are not p
