Antenna Theory - Half-Wave Folded Dipole

# Antenna Theory – Half-Wave Folded Dipole

A folded dipole is an antenna, with two conductors connected on both sides, and folded to form a cylindrical closed shape, to which feed is given at the center. The length of the dipole is half of the wavelength. Hence, it is called asÂ half wave folded dipole antenna.

### Frequency range

The range of frequency in which half wave folded dipole operates is around 3KHz to 300GHz. This is mostly used in television receivers.

## Construction & Working of Half-wave Folded Dipole

This antenna is commonly used with the array type antennas to increase the feed resistance. The most commonly used one is with Yagi-Uda antenna. The following figure shows a half-wave folded dipole antenna.

This antenna uses an extra conducting element (a wire or a rod) when compared with previous dipole antenna. This is continued by placing few conducting elements in parallel, with insulation in-between, in array type of antennas.

The following figure explains the working of a half-wave folded dipole antenna, when it is provided with excitation.

If the diameter of the main conductor and the folded dipole are same, then there will be four folded (two times of squared one) increase in the feed impedance of the antenna. This increase in feed impedance is the main reason for the popular usage of this folded dipole antenna. Due of the twin-lead, the impedance will be around 300Î©.

The radiation pattern of half-wave folded dipoles is the same as that of the half-wave dipole antennas. The following figure shows the radiation pattern of half-wave folded dipole antenna, which isÂ Omni-directionalÂ pattern.

Half-wave folded dipole antennas are used where optimum power transfer is needed and where large impedances are needed.

This folded dipole is the main element inÂ Yagi-Uda antenna. The following figure shows aÂ Yagi-Uda antenna, which we will study later. The main element used here is this folded dipole, to which the antenna feed is given. This antenna has been used extensively for television reception over the last few decades.

The following are the advantages of half-wave folded dipole antenna âˆ’

• Reception of balanced signals.
• Receives a particular signal from a band of frequencies without losing the quality.
• A folded dipole maximizes the signal strength.