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Loop antennas are usually classified as electrically small ( C < λ / 3 ) and electrically large (C ∼ λ ). Here, C denotes the loop’s circumference. The small loops of a single turn have small radiation resistance (< 1 Ω) usually comparable to their loss resistance. Their radiation resistance, however, can be improved by adding more turns.
Short dipole antenna Real component of electric field (magntitude) Radiation pattern as function of polar angle, for different azimuthal angles
LECTURE 11: Loop Antennas (Radiation parameters of a small loop. A circular loop of constant current. Equivalent circuit of the loop antenna. The small loop as a receiving antenna. Ferrite loops.) Introduction Loop antennas form another antenna type, which features simplicity, low cost and versatility. Loop antennas can have various
Figure 1B — The far-field radiation pat-tern of a very small vertical loop, in the horizontal plane. The loop is vertical, in free space, with the plane of the loop run-ning left-to-right. The radiation is verti-cally polarized, and peaks in the plane of the loop. There is a deep null in the broadside directions. broadside to the loop.
The radiation resistance of a resonant 1-λ loop is approximately 100 Ω, when the ratio of conductor length to diameter is large. As the loop dimensions are comparable with those of a 1 / 2 -λ dipole, the radiation
Antenna Type DISCONE ALFORD LOOP Radiation Pattern Azimutm Azimuth: Figure 4 CharacterStics Pdartatbn: Linger Tyÿcd 20-80 x Gan: C" dB Bar"Wdth: or g: 1 Frequemy Limit go MHz GHz as shg.vn 80 or Frequemy Limit Lo—r: ICOIUIHz 12 GHz Antenna Type CIRCULAR LOOP (Small) SOLÆE LOOP (Sr-rail) Radiation Azimutm E E,atbm Azim Pattern Characteristics
The Log-Periodic Loop Antenna with Ground Reflector (LPLA-GR) is investigated as a new type of antenna, which provides wide bandwidth, broad beamwidth, and high gain. This antenna has smaller transverse dimensions (by a factor of 2/p) than a log-periodic dipole antenna with comparable radiation characteristics.
