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The J-pole antenna is an end-fed omnidirectional half-wave antenna that is matched to the feedline by a shorted quarter-wave parallel transmission line stub. [5] [1] [6] For a transmitting antenna to operate efficiently, absorbing all the power provided by its feedline, the antenna must be impedance matched to the line; it must have a resistance equal to the feedline's characteristic impedance.
An endfire array of multiple dipole elements along a boom with gradually decreasing lengths, back to front, all connected to the transmission line with alternating polarity. It is a directional antenna with a wide bandwidth, which makes it ideal for use as a rooftop television antenna, although its gain is much less than a Yagi of comparable size.
English: Diagram of a J-pole antenna, a vertical end-fed half-wave omnidirectional transmitting antenna used in the shortwave frequency bands. It consists of a vertical element a half wavelength ( λ / 2 {\displaystyle \lambda /2} ) long, fed in series with a quarter wavelength ( λ / 4 {\displaystyle \lambda /4} ) transmission line stub , with ...
The diagram shows the standing waves of voltage (V, red bands) and current (I, blue bands) on the antenna elements. It consists of a vertical element a half wavelength ( λ / 2 {\displaystyle \lambda /2} ) long, fed in series with a quarter wavelength ( λ / 4 {\displaystyle \lambda /4} ) transmission line stub , with the parallel wire feedline ...
If it was infinitely thin the antenna would have an infinite input impedance, but the finite width gives typical, practical half wave whips an impedance of 800–1,500 ohms. These are usually fed through an impedance matching transformer or a quarter wave stub matching section (e.g. the J-pole antenna). An advantage is that because it acts as a ...
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