Small Loop Antennas:

Loop antennas may take many different forms such as circle, square, rectangle etc. Loop antennas are generally classified into two categories viz, electrically small and electrically large antennas. Electrically small antennas are those whose overall length is less than one tenth is number of terms in the loop times the circumference of the loop. Here we shall keep our discussion confined to small loop antennas only.

Small loops are usually not used as transmitting antennas as they have radiation resistance smaller compared to short dipoles. However many unintentional sources of radiation such as transformers, inductor, printed circuit boards etc essentially behave as small loop antennas. A small loop of current is also called a magnetic dipole and its magnetic dipole moment is equal to the product of the area with the current it carries. Thus for these types of small current loops, the shape of the loop is not important. For a given current, it is the area of the loop that determines the magnitude of the radiated fields.

Fig. 7.11 shows a small current loop of radius placed on the xy plane with its axis oriented in the z direction. The loop carries a current I₀.