J-antennas are ordinary half-wave whip antennas [1] . First used in 1909 for airships, [2] where they hung from its tail. A quarter-wave piece of the antenna is a resonator designed to adjust the matching of the antenna with the power cable.
Content
- 1 Features
- 1.1 Gain and radiation pattern
- 2 Design
- 3 notes
- 4 References
Features
J-antennas in their design resemble the Latin letter J and are omnidirectional half-wave antennas . The coordination of the antenna resistances with the supply line is achieved by moving the power supply along the resonator until the impedances are equal. Being a half-wave antenna, it forms a radiation pattern flattened to the ground [3] .
A J antenna emits or receives electromagnetic waves of vertical polarization. The shoulders of the antenna cavity should be upright.
Gain and radiation pattern
The gain of such omnidirectional antennas at the maximum of the radiation pattern is about 2.2 dB. [4] .
Based on such J-antennas, directional antennas can be made. For directional antennas, the reflector and director are mounted near the J-antenna in opposite places from the vibrator. The direction of the antenna radiation will occur in the direction of the director, which has a length shorter than the vibrator and reflector.
Design
J-antennas are usually made of metal pipes, coaxial or two-wire cable. [5]
Various antenna design options are possible - with a bent dipole, an elongated dipole, etc. [6] .
Elongated antennas give a gain increase of about 1.5 dB. by compressing the chart in a vertical plane.
The antenna patterns show that maximum gain is achieved in elongated antennas.
Currently, J-antennas are mainly used for amateur radio purposes. The lower part of the antenna can be grounded and used as a lightning rod. Grounding does not affect the operation of the transceiver equipment and the characteristics of the antenna, but will protect the receiver from lightning strikes. With such antennas you can work in a thunderstorm.
Notes
- ↑ Very-High-Frequency Antennas // Antennas and Antenna Systems (TM 11-314) . - US War Department. - P. 163-164.
- ↑ Beggerow, Hans Zeppelin Antenna (1909). Date of treatment January 28, 2016.
- ↑ Huggins, John S 1/4 Wave Monopole vs. 1/2 Wave J-Pole EZNEC Shootout unopened . Date of treatment January 30, 2012.
- ↑ Cebik, L. B Some J-Poles That I Have Known Part 1: Part 1: Why I Finally Got Interested in J-Poles and Some Cautions in Modeling Them . Cebik.Com. Date of treatment October 1, 2015. Archived April 22, 2014.
- ↑ Fong, Edison. The DBJ-2: A Portable VHF-UHF Roll-Up J-pole Antenna for Public Service // QST : magazine. - ARRL, Inc., 2007. - March.
- ↑ Judd, Fred. Slim Jim - 2 Meter Aerial (Neopr.) // Practical Wireless - Out of Thin Air. - S. 37-39 .