Antenna Theory - Introduction To Short Dipole & How Radiation Are Created From It?

A short dipole is one in which the field is oscillating because of the oscillating voltage and current. It is called so, because the length of the dipole is short and the current is almost constant throughtout the entire length of the dipole. It is also called as Hertzian Dipole which is a hypothetical antenna and is defined as a short isolated conductor carrying uniform alternating current.


The dipole has two equal charges of opposite sign oscillating up and down in a harmonic motion. The charges will move towards each other and electric filed lines were created. When the charges meet at the midpoint, the field lines cut each other and new field are created. This process is spontaneous and so more fields are created around the antenna. This is how radiations are obtained from a short dipole.


A short dipole that does have a uniform current is known as elemental dipole. Such a dipole will generally be considerably shorter than the tenth wave length maximum specified for a short
dipole. Elemental dipole is also called as elementary dipole, elementary doublet and hertzian dipole.


When the length of the short dipole is vanishingly small, then such a dipole is called a infinitesimal dipole. If dl be the infinitesimally small length and I be the current,then Idl is called as the current element.


A short dipole is initially in neutral condition and the moment a current starts to flow in one direction, one half of the dipole require an excess of charge and the other a deficit because a current is a flow of electrical charge. Then, there will be a voltage between the two halves of the dipole. When the current changes its direction this charge unbalance will cause oscillations. Hence an oscillating current will result in an oscillating voltage. Since, in such dipole, electric charge oscillates, it may be called as Oscilllating electric dipole.