Folded dipole antenna

 

 

The folded dipole antenna resonance and radiation, as well as an odd integer multiples of half wavelength (0.5, 1.5, ...) This is a real antenna, the Federal Reserve as shown in Figure 1 in the center. Input impedance of the folded dipole is higher than a regular dipole. This will be shown in the next section.

Can be folded dipole antenna resonant in even multiples of half wavelength (1.0, 2.0, ...), which can offset folded dipole feed Figure 1 (near the top or bottom edge of the folded dipole).

Half-wavelength folded dipole

Folded dipole antenna of half-wavelength antenna impedance can be found from the above formula for the ZA. ZA = 4 * the ZD. Resonance, which is about a half-wave dipole antenna impedance of 70 ohms. Therefore, the folded half-wave dipole antenna input impedance is 280 ohms.

Duplex transmission line characteristic impedance is 300 ohm folded dipole connected, usually use this type of line. This will produce the best power transfer from the transmission line antenna. Therefore, the half-wavelength folded dipole antenna is usually used for larger antenna impedance (greater than 100 ohms).

Half-wavelength folded dipole radiation pattern, the same form of half-wavelength dipole.

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A folded dipole antenna is a dipole antenna folded back, connected to each other at both ends. This form of a loop, shown in Figure 1.

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Figure 1.A folded dipole antenna length "L".

Under normal circumstances, the width of the folded dipole antenna "D" is much less than the length "L".

Form a closed loop of the folded dipole, one might expect input impedance depends in a very short short-circuit transmission line length "L" input impedance. However, you can imagine that the folded dipole antenna as two parallel short-circuit transmission line length L / 2 (midpoint separated from the feed in Figure 1). The original impedance of the folded dipole antenna impedance transmission line of length L / 2 the function.

In addition, because of the folded dipole folded, the current can be enhanced, rather than cancel each other out. Therefore, the input impedance will also depend on the impedance of the dipole antenna length "L".

Let Z_d on behalf of the length of the dipole antenna impedance to the impedance of the L Z_t on behalf of the transfer impedance line length L / 2, which is:

 

The folded dipole input impedance Z_A is:

   

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