Planar Near-field Measurement And Diagnostic Techniques

Planar Near-field measurements have been the first choice in high-performance antenna testing. Near-field data sampling and mathematical transformation are the key factors to determine measurement accuracy and efficiency. To meet the requirement in practice, a study has been made about near-field to far-field algorithm, near-field to aperture-field algorithm, and the construction of far-field and near-field measurement system. First, the principles of planar wave expansion and the theory of probe compensation are introduced. A 2D near-field to far-field FFT transform formulas comprising probe correction are deduced. The relation of sampling parameters to spectrum discretization parameters and their selection criteria are described emphasizely. Second, a dipole array model is built and its near-field electric distributions are calculated by numerical methods. The far-field patterns are obtained from these simulated near-field measurement data. The simulated far-field patterns are in good agreement with exact analysis results. Then, on the premise of ignorance of evanescent wave, the formula of near-field to aperture-field transformation based on plane-wave spectrum is given, we can find the faults of antenna aperture according to the distribution of antenna aperture field, also we can determine the amplitude and phase of array's excitation. Last, an automation system for antenna far-field and near-field measurements is developed with Visual C. we can measure antenna's pattern, gain and so on, directly. Also, we can measure electric distributions in the near field of antenna under test, then we can gain all the information of antenna under test .The measurement results are in good agreement with the analysis results, which shows validation of the system..