8

The increased bandwidth of a folded dipole is almost entirely due to the extra thickness. Two parallel elements behave as a thicker single element. There is a small contribution too from the combination of the reactances of the transmission-line mode and radiator-mode acting in opposite directions.


8

Loaded $Q$-factor Like any resonant circuit, the bandwidth of an antenna is determined by its loaded quality factor, defined by $Q_{\ell}\overset{.}{=}\frac{X}{R}$. The lower the loaded $Q$-factor, the broader the antenna's bandwidth will be: $BW_{-3dB}=\frac{f_{res}}{Q_{\ell}}$, with $f_{res}$ the resonant frequency. Analysis of the loaded $Q_{\ell}$ of a ...


6

A little capacitive reactance is what gives you the greater bandwidth. In a regular ½λ dipole, the current that flows along the conductors are in phase. When we add the second conductor in a folded dipole, what we are really doing is extending the dipole. As a result the current in the new section flows in the same direction as those in the original dipole....


5

As explained by antenna-theory.com: Typically, the width d of the folded dipole antenna is much smaller than the length L. Because the folded dipole forms a closed loop, one might expect the input impedance to depend on the input impedance of a short-circuited transmission line of length L. However, you can imagine the folded dipole antenna as ...


5

The site above depicts a regular dipole, with a simple matching system. First, a bit about dipole impedance. The impedance of a dipole is 73 Ohms at resonance, but away from the resonant frequency the impedance is different. At frequencies lower than resonance, i.e. when the antenna is too short, it is capacitive, and its resistance is lower. The Smith ...


5

For all practical purposes, the radiation efficiency of a folded dipole versus an ordinary dipole is the same. Consider, they are essentially the same antenna. simulate this circuit – Schematic created using CircuitLab The only difference is that in the folded dipole, we've replaced the feedpoint with a short. Since the Thévenin equivalent resistance ...


4

Does a folded dipole really have "wider bandwidth"? Some sources say "yes" because that's what the textbooks say, others say "no", based on their real wold experience A little more, yes, mostly just because they are thicker than a simple dipole. The same increase in bandwidth could be achieved by making an ordinary dipole out of sections of ladder line with ...


4

It may help to consider the two arms of the folded dipole as end-shorted (ROUGHLY quarter-wave) sections of 300 ohm transmission line. Any current which attempts to flow in opposite directions on the two conductors in each arm will not radiate (which is why the transmission line works - the two currents generate opposing fields). Only a "common-mode" ...


4

Close coupling between the folded dipole's two long, parallel wires induces a nearly identical current in the "coupled" wire as is impressed on the "driven" wire. (Electromagnetics engineers will see this result as necessary because the boundary conditions on the ends of the two wires are the same.) Thus, half of the current from the power delivered to the ...


3

I had the same question for a while, more in reference to resonant loop antennas, but the same principle seems to apply to folded dipoles. Eventually I figured out what I think is going on, and the key is the length of the antenna vs. the wavelength of the signal. A folded dipole or resonant loop antenna is, electrically, a full wavelength from one side of ...


2

Read it off this chart: Interferometrist [CC BY-SA 4.0], via Wikimedia Commons A folded dipole with equal-sized conductors has 4x the impedance of an ordinary dipole. The impedance repeats every wavelength, so for example if you're interested in the impedance at 2.5 wavelengths (off the chart) it won't be far off from the impedance at 1.5 wavelengths. ...


2

The info is in the model number BM - Bluewave Marathon E - Exposed offset 139- Frequency F - Gain 5.5dBd N1 - Connector Type H - Horizontal Polarized More info can be found here - Please note you may have to download the whole book for all info.


2

Is it a "miracle antenna" that will work in any band when tuned with a suitable balanced tuner? No more than a regular dipole. A dipole of an appropriate length, fed by ladder line to reduce the standing wave losses (often called a "doublet") can be pretty close to a miraculous all-band antenna with a little care, a little luck, and a big tuner. A "folded ...


1

There are at least two ways. Firstly, you can use the antenna modeller (I prefer cocoaNEC) to estimate an impedance of the antenna at given frequency. From personal experience it doesn't work that well though. The real antenna will differ quite a bit from the model because of unknown ground properties, various metal object near antenna, etc. This method may ...


1

“ If you want an electric dipole antenna (because that is the desired radiation pattern) folded or straight dipoles should be equivalent if they use the same number of wires with the same spacing. It is probably best to use a straight dipole (maybe with many parallel wires for bandwidth) because the lower feed impedance makes it easier to eliminate common ...


1

As has been pointed out, one factor of the folded dipole that explains greater bandwidth is that it is effectively thicker. The main reason however is that it's impedance is effectively the parallel combination of a half wsve dipole and a 1/4 wave stub shorted at the far end. The reactance/susceptance of this stub varies in the opposite direction to that of ...


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