6.2.10                Radiation at Fixed Angle versus frequency

Sometimes, especially in radar applications, our aim is to control the shape of the pulse spectrum in the far zone at the particular direction from the transmitting antenna – rather than the radiation characteristic over a range of angles, at a few fixed frequencies. This would be very time-consuming to obtain with NTF transform described in Radiation and Scattering since it performs a Fourier transform of the electromagnetic field at the NTF box, followed by near-to-far transformation in the frequency domain. 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. The far-field result is then Fourier-transformed. The NTFFA post-processing allows obtaining the Fourier-transform (spectrum) of the impulse response in the far field (radiation at a fixed angle versus frequency). The results are available in the dedicated Results 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 (see figure below).

If the user lists an odd number of angle values, the last one will be ignored. The Fourier transform of the impulse response in the far field is performed for the frequency range and resolution specified by the user in the post-processings configuration dialogue for NTFFA calculations. 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.

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.

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 and User Guide 3D: Near-to-Far transformation at the fixed angle with symmetry examples.