dipole (half vs full)

[cyprus]

hi i want to ask what is the differnces between half wave dipole and full wave dipole ......why they prefare half wave why not full wave or 1/4 or 1,5wave i hope to hear good answers thanks

 

[safwatirteza]

Generally dipole as the name suggests has two poles and the feed is in the center. The current distribution over a dipole is a sinusoidal wave with a maximum at middle, so feeding at the center provides minimum resistance. At this point voltage is minimum. So if you consider half wavelength of sinusoid accross the complete dipole with zero at the center you will find maxima for voltages (quarter of wavelength from center on either side) but with opposite signs. Thus half a wavelength is necessary to have to optimum response from a dipole. You can always use multiple of half wavelength structure to get the same response.

Regards
Safwat

 

[vfone]

A Dipole Antenna by definition is half-wave length. If the length is different than λ/2, then the current through dipole and the antenna pattern will be changed.

Take a look to this Java Applet to see the current and pattern change when dipole dimensions are changed.

http://www.amanogawa.com/archive/DipoleAnt/DipoleAnt.html

 

[rfmw]

Sometimes a full-wave dipole is prefered if directivity is important. However full-wave dipole has high impedance (400-500Ohms), so a transformer si necessary when feeded by ordinary 50Ohm system.

 

[Element_115]

Size is an issue too. As the Name implies one is half the size as the other.

A "Full way" gets more received energy, but is bigger.