Deflection Yoke (DY) is used for the deflection of electron beams in the cathode-ray tube. It has two coils, the horizontal deflection coil and the vertical deflection coil, where a ferrite core is used inside the vertical coil. This ferrite core wraps around the horizontal deflection coil.
External fields outside of the deflection yoke is undesirable and to be minimized. One may replace the yoke coils by its equivalent magnetic dipoles for the calculation of far fields. The presence of the ferrite core of vertical coil is to be accounted not only for the fields due to the vertical coil but also for the fields of horizontal coil. One may approximate the equivalent dipole current of the vertical deflection coil by twice of its original current by assuming that the permeability of the ferrite core is infinite. Since the most of the horizontal coil currents are shielded by this ferrite core which wraps around the horizontal coil, the neck position coils outside of the ferrite core are only accounted.
Approximated dipole fields are compared with the measured values and calculations by using a numerical moment method. When the field point is about 10 times the radius of the equivalent magnetic dipole current, the approximated fields compared with these of vertical coil in 3 percents and these of horizontal coil in 10 percents.
