6.2.11                Impulse response in the far-field

Sometimes, especially in radar applications, our aim is to control the shape of the pulse in the far zone at the particular direction from the transmitting antenna. That is why QuickWave offers another post-processing allowing the far field radiation analysis, called NTF Fixed Angle (NTFFA). The NTFFA post-processing activates near-to-far field transformation in the time domain, directly from the time-domain fields at the NTF box, for a set of fixed directions and then performs the Fourier transform of the far-field result, as previously described. The first stage of the NTFFA post-processing delivers the impulse response in the far field, for a set of fixed directions. The results, as time domain variations of Etheta and Ephi are available via 1D Fields window. The directions for the near-to-far field transformation are defined by the user, when configuring the NTFFA post-processing in the Input Interface, as pairs of Phi and Theta angles, with Z axis considered as a reference axis:

If the user lists an odd number of angle values, the last one will be ignored. The scaling of the far fields is the same as for Fields at 1m option of the NTF post-processing.

It should be noted that each pair of Phi and Theta angles defined for NTFFA calculations creates a separate post-processing called NTFFA_1_2, NTFFA_3_4, etc., and all of them are available in the Choose NTFFA Postprocessing dialogue in the 1D Fields window.

Similarly to NTF post-processing, the NTFFA post-processing also requires the NTF box. Remember that for correct near-to-far field calculation, the NTF box must fully surround the structure and be itself surrounded by a homogeneous medium terminated with absorbing boundaries (except for symmetry and ground planes). A majority of NTFFA applications are in air, however, calculation in dielectrics, and even in lossy dielectrics, may be of interest. That is why the NTFFA post-processing in QW-3D has been especially adapted to such cases; for more detail refer to Radiation pattern in an arbitrary isotropic medium.

Note that the NTFFA post-processing is available in QW-3D but not in QW-V2D.

The use of NTFFA post-processing has been exemplified and discussed on User Guide 3D: Near-to-Far transformation at the fixed angle with symmetry examples example.