Kindly help me how to plot Near Field radiation pattern of an antenna in CST Studio suite?
What do you mean by a near-field radiation pattern?
The radiation pattern is usually in the far-field, and is relative to the power an omnidirectional antenna with the same input signal would send in each direction. This is independent of range. In the near-field there is no corresponding pattern, the pattern changes with distance. CST will plot the field strength at points in a sphere around the antenna, if that is what you want. You can choose which set of points it calculates at.
In Monitors, you can save near-field data as a field source.
If you are very close to the antenna, the magnetic and electric fields may not be in phase, so you will need both.
Near-field and radiation are mutually exlusive terms for antenna. The near field is oscillating quazistatic field near antenna, it is reactive power for the antenna and minus some disipations that power returns back into the antenna.
Nikolay Pavlov
What you describe is the reactive near field. Even in this region there is some radiation, the radiated power has to travel through this region. The reactive fields fall off as inverse cube and inverse square, whereas the radiation fields fall off just as the inverse of distance so carry a constant power away at each distance. Because of the different rates of fall-off, the radiation fields can be very small compared to the reactive fields close to the antenna.
There are several regions. Three are:
The reactive near field, where the fields look mostly like those of a capacitor or inductor - or both.
The radiating near field, where the radiating fields start to dominate, but the shape of the radiation pattern is not the same as in the far field.
and the far field, where the radiation pattern is constant at all larger ranges.
For an antenna more than a few wavelengths across, the far-field can be considered as starting at the distance given by twice the antenna width times the number of wavelengths across that width. commonly referred to as 2D2/lambda. The reactive near-field boundary is about 1/6 wavelength from the antenna.
Malcolm White Yes, you are right - indeed - there might be an antenna e.g. large parabolic dish which has pronononced area of radiated near field.