Extended S-Parameter Method Including Radiation Pattern Measurements of an Antenna

Coaxial cables connected to the antenna frequently affect the characteristics of the antenna. Although the S-parameter method is one of the most effective methods of reducing the influence of the coaxial cables, it has so far only been applied to impedance measurements. We propose an extended S-parameter method that can also be applied to radiation pattern measurements of amplitude and phase. In this method, two cables are connected to an antenna, and the excitation coefficients of the two cables are obtained from the S-parameters under the condition where the unbalanced current of the coaxial cables is reduced. From array patterns generated with these excitation coefficients, we can obtain the radiation patterns with a reduced unbalanced current of the coaxial cables. We apply this method to dipole antennas and a helical antenna on a small housing. Our simulated and measured results demonstrate the validity of the proposed method and 20 dB reduction of the influence of the coaxial cables.