How does a folded dipole work

This statement "I guess the real question might be what mechanism makes a folded dipole work better than a regular dipole. A folded dipole has a 4 times higher impedance, compared to a simple dipole with the same wire diameter it has more bandwidth, but compared to a simple dipole with the much larger effective diameter you would get by use of two parallel wires on each side of an ordinary dipole I suspect there would be no bandwidth advantage. B is a folded dipole.

The open halfwave element does not contribute. A and C are equivalent as I can understand, but the feed impedance is different by a factor of 9 I would guess.

Making the wire diameter different for the two half wavelength parts of a folded dipole makes the impedance transformation different.

As I understand it, the impedance is given by the current ratio of the elements to which power is fed at the center and the elements that are shorted fed by the voltage on the tips of the fed elements. The bandwidth, as I understand it is given by the effective area of all wires. The folded dipole is also a loop antenna, but in normal configurations the electric dipole radiation is orders of magnitude larger than the magnetic dipole radiation.

The electric dipole radiation pattern has a zero in the plane of the dipole while the magnetic dipole pattern a doughnut does radiate in the plane of the folded dipole. In case you make your "folded dipole" a circle to give it the maximum possible magnetic moment, you would find that the radiation pattern is more like a magnetic dipole than an electric dipole.

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. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

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Improve this question. What actual information did you want to find out? I guess the real question might be what mechanism makes a folded dipole work better than a regular dipole. The question just seemed a bit broad initially. The folded dipole is much worse than a regular ladder line fed dipole dipole for harmonic or out-of-band operation. On even harmonic bands, it appears as a nearly dead short. It is not a good multiband antenna, and actually has excellent radiation suppression of even harmonics.

Myth 3 -A twinlead folded dipole fed with twinlead will have an impedance around ohms on the designed band. Variations in folded dipole SWR is less with changes in antenna length or frequency are less than in a regular coax fed dipole.

False: SWR variations are essentially the same. On the fundamental and odd harmonics, the dipole impedance is about 50 to ohms. That impedance is near perfect for coax, and the ladder line is still only or less. Don't be fooled by claims wide bandwidth means high loss, or that narrow bandwidth indicates high efficiency. Bandwidth is related to system Q, but system Q is not determined solely by resistive or heat losses.

System Q is really a function of stored energy to energy moved through the system. Energy can be moved through the system and exit as wasteful heat, or it can exit as useful work. Without knowing where energy is going, we should never assume bandwidth means anything other than bandwidth.

Most antennas store a majority of energy in an electric field, although small "magnetic" loops have a lot of energy in a strong, very local, magnetic field.

The folded dipole is no exception to this generalization. The folded dipole, like almost any antenna, has an electric field boundary at the wire to space transition. Current flowing into the antenna "travels" through space via displacement currents.

The folded dipole antenna or folded dipole aerial is widely used, not only on its own, but also as the driven element in other antennas like the Yagi antenna and various other types of antenna. The folded dipole antenna consists of a basic dipole, but with an added conductor connecting the two ends together.

As the ends appear to be folded back, the antenna is called a folded dipole antenna. The basic format for the folded dipole aerial is shown below. Like the basic dipole, the folded dipole antenna is a balanced antenna, and needs to be fed with a balanced feeder. Unbalanced feeders can be used provided that a balun unbalanced to balanced transformer is used.

The additional part of the folded dipole antenna is often made by using a wire or rod of the same diameter as the basic dipole section. However this is not always the case. Also the wires or rods are typically equi-spaced along the length of the parallel elements. This can be achieved in a number of ways.

Often for VHF or UHF antennas the rigidity of the elements is sufficient, but at lower frequencies spacers may need to be employed. To keep the wires apart. Obviously if they are not insulated it is imperative to keep them from shorting. In some instances flat feeder can be used. One of the main reasons for using a folded dipole antenna is the increase in feed impedance that it provides. If the conductors in the main dipole and the second or "fold" conductor are the same diameter, then it is found that there is a fourfold increase i.

Additionally the RF antenna has a wider bandwidth. It is possible to reason why there is a four fold increase in impedance for the folded dipole antenna. In a standard dipole antenna the currents flowing along the conductors are in phase and as a result there is no cancellation of the fields and as a result radiation or the signal occurs.

When the second conductor is added to make the folded dipole antenna this can be considered as an extension to the standard dipole with the ends folded back to meet each other.