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A quad antenna is a self-resonant loop in a square shape; this one also includes a parasitic element.. Loop antennas may be in the shape of a circle, a square, or any other closed geometric shape that allows the total perimeter to be slightly more than one wavelength.
In 1938, George Brown et al. patented a loop antenna with rhombic shape and quarterwave sides. [2] In 1951 Clarence C. Moore, W9LZX, a Christian missionary and engineer at HCJB (a shortwave missionary radio station high in the Andean Mountains) developed and patented [3] a two-turn loop antenna which he called a "quad".
the upper half of a vertical full-wavelength loop antenna mounted on the ground (not to be confused with the visually similar but electrically different half-square antenna described below, under array antennas, [r] nor to be confused with the halo antenna, described next). The full loop is cut at two opposite points along its perimeter, and ...
A folded dipole is, technically, a folded full-wave loop antenna, where the loop has been bent at opposing ends and squashed into two parallel wires in a flat line. Although the broad bandwidth, high feedpoint impedance, and high efficiency are characteristics more similar to a full loop antenna, the folded dipole's radiation pattern is more ...
The basic concept used a loop antenna, in its most basic form simply a circular loop of wire with a circumference decided by the frequency range of the signals to be detected. When the loop is aligned at right angles to the signal, the signal in the two halves of the loop cancels out, producing a sudden drop in output known as a "null".
The loop antenna responds to the rotational component. A measuring system with a loop antenna can be designed to mostly ignore the irrotational component of the electric field. It is correct to say (1) that loop antennas are useful for measuring the magnetic field. It is incorrect to say (2) that loop antennas respond to the magnetic field.
A halo antenna is distinct from the small-loop antenna in size, [a] radiation resistance, and efficiency, but their radiation patterns are nearly the same. A halo antenna is a self-resonant antenna: Its feedpoint impedance is reactance-free / purely resistive at the design frequency.
The regenerative loop antenna can consist of a tuned signal winding on an open X frame with a feed back winding in close proximity. High effective gain is achieved, for example by placing this feedback winding in the drain circuit of a JFET (junction field effect transistor).