Low measurement uncertainties in thefrequency range 30 MHz to 1 GHz using acalculable standard dipole antenna and national reference ground plane

Abstract

Using a pair of calculable standard dipole antennas above a large specially constructed ground plane it is demonstrated over the frequency range of 30 – 500 MHz that the antenna factor can be attributed to the standard antenna with an uncertainty as low as ±0.1 dB. The uncertainty is derived from a comparison of measured and predicted insertion loss between two antennas. The insertion loss and antenna factor of the NPL calculable dipole antenna are calculated by two different methods. The results agree to better than ±0.05 dB. By the correct choice of equipment and operating methods it is possible to obtain an agreement between measured and predicted values of insertion loss to better than ±0.2 dB. A detailed analysis of uncertainties is given. At 1 GHz the difference increased to ±0.8 dB because of the large size of the feed arrangement relative to the dipole length. Whereas in the past an accurate prediction of the antenna factor of resonant dipoles has been claimed, here it is shown that similar accuracy can be achieved for bandwidths of 200%. This makes it possible to use dipole antennas as broadband calculable standards with which to accurately calibrate broadband antennas and evaluate the performance of EMC test sites.