Novel Method to Improve the Signal-To-Noise Ratio in Far-Field Results Obtained from Planar Near-Field Measurements

A method to reduce the noise power in a far-field pattern without modifying the desired signal is proposed. An important signal-to-noise-ratio improvement may thereby be achieved. The method is used when the antenna measurement is performed in the planar near-field, where the recorded data are assumed to be corrupted with white Gaussian and space-stationary noise, because of the receiver´s additive noise. Back-propagating the measured field from the scan plane to the plane of the antenna under test (AUT), the noise remains white Gaussian and space-stationary, whereas the desired field is theoretically concentrated in the aperture antenna. Thanks to this fact, a spatial filtering may be applied, canceling the field that is located out of the AUT´s dimensions and that is only composed of noise. Next, a planar-field-to-far-field transformation is carried out, achieving a great improvement compared to the pattern obtained directly from the measurement. To verify the effectiveness of the method, two examples are presented using both simulated and measured near-field data.