Far Field Parameters
Go to the Setup tab in the main window and select the Far-Field panel, Fig. 1.
The far field can be computed after having calculated the current distribution previously. Thus, the parameters set in the Far-Field panel have no effect in the determination of the currents and can be modified at any time. However, the far field must be recalculated every time these parameters are modified.
There are four options for radiation pattern calculations:
The far field is calculated in angular ranges that cover the entire 3D space, which allows us to obtain 3D radiation lobes. The steps for the Theta (zenith) and Phi (azimuth) angles can be set in the Theta [deg] and Phi [deg] boxes.
The far field is calculated at a vertical slice for a given Phi (azimuth) angle. The step for the Theta (zenith) angle can be set in the Theta [deg] box, while the fixed Phi can be set in the Phi [deg] box.
The far field is calculated at a horizontal slice for a given Theta (zenith) angle. The step for the Phi (azimuth) angle can be set in the Phi [deg] box, while the fixed Theta can be set in the Theta [deg] box.
The far field is calculated for the specified ranges of angles Theta (zenith) and Phi (azimuth). The start, step, and stop values for Theta and Phi can be set in the Theta [deg] and Phi [deg] boxes.
Additionally, the following parameters can be set:
This can be any point used as a phase reference, its coordinates do not affect the shape of the radiation pattern. The 3D radiation pattern will be plotted centered at this point.
It is the distance from (X0,Y0,Z0) to an observation point in the far-field region. A normalized far-field pattern can be obtained by setting Distance = 1.
The zenith and azimuth angles, Theta and Phi, are shown in Fig. 2, where it is also shown de Distance R from the structure to an observation point in the far-field zone. These three numbers (R,Theta,Phi) define the spherical coordinates of the far-field point.
To calculate the directivity, the average radiated power from a structure or the Radar Cross Section (RCS), a full radiation pattern covering the whole of space should be defined. For this reason, the Theta and Phi angles should vary in the following ranges when the Custom option is chosen:
:: If the environment is free space (there is no ground plane):
0 <= Theta <= 180 deg.
0 <= Phi <= 360 deg.
:: If the environment has a ground plane:
0 <= Theta <= 90 deg.
0 <= Phi <= 360 deg.
These angular ranges allow the Average Power Density to be computed averaging the power density or Poynting vector in all directions in 3D space. If there is a ground plane, directions must be considered in half-space.
When a real ground plane or an infinite substrate slab is set, and the Vertical, Horizontal or Custom option is chosen not in the ranges mentioned above, the calculated directivity, average power density and RCS will be meaningless quantities.