In those cases the impedance transformation of a folded dipole can in fact aid in getting a good match. 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.
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How does a folded dipole work? Ask Question. Asked 7 years, 11 months ago. Active 1 year, 6 months ago. Viewed 5k times.
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 input impedance of the folded dipole is higher than that for a regular dipole, as will be shown in the next section. The folded dipole antenna can be made resonant at even multiples of a half-wavelength 1.
At resonance, the impedance of a half-wave dipole antenna is approximately 70 Ohms, so that the input impedance for a half-wave folded dipole antenna is roughly Ohms. Because the characteristic impedance of twin-lead transmission lines are roughly Ohms, the folded dipole is often used when connecting to this type of line, for optimal power transfer.
The radiation pattern of half-wavelength folded dipoles have the same form as that of half-wavelength dipoles.
Although the impedance of an isolated folded dipole may be around ohms, its value will be somewhat different when it is used as an element in an array or with a reflector. The folded dipole has better bandwidth characteristics than a single dipole of the same size. Its geometrical arrangement tends to behave as a short parallel stub line which attempts to cancel the off resonance reactance of a single dipole. Symmetrical and asymmetrical planar folded dipoles can also be designed and constructed using strips which can be fabricated using printed-circuit technology.
The input impedance can be varied over a wide range of values by adjusting the width of the strips. In addition, the impedance can be adjusted to match the characteristic impedance of printed-circuit transmission lines with four-to-one impedance ratios. Now study on-the-go.
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