Near-Field Antenna Pattern Measurements in Highly Reflective Environments

The far-field pattern of an antenna under test is determined from the near-field measurements in a highly reflective environment. The proposed post-processing effectively combines time gating and spatial filtering of the radiated fields. Time gating utilizes frequency diversity, while spatial filtering makes use of probe diversity and source localization. Different probe locations are used to form a virtual array, which focuses the fields at the antenna volume. The possible scatterers are illuminated as little as possible. The weighting coefficients for the virtual array are found by solving a field synthesis problem. The effects of time gating and spatial filtering are analyzed separately. A measurement setup is described in a highly reflective chamber involving fully spherical measurements with probes in up to 120 different positions and with 1001 frequencies. Time gating yields better results, but a combination of both methods is necessary to achieve an estimated accuracy of -30 dB for the considered S-band and -40 dB for the considered Ku-band antenna.