The excitation of dipole antennas via a bulk current injection probe

We examine the performance of a linear and a wire biconical dipole antenna driven in their respective centers by a commercially available Bulk Current Injection (BCI) probe. The linear dipole is a 94-cm long and the biconical dipole is derived from a standard 1.4-meter wire-cage biconical antenna. To assess the performance of the probe-driven dipole antennas, we measure their complex antenna transfer functions. The antenna factor of the BCI-probe-driven 1.4-meter biconical antenna, as derived from the transfer function, is shown to be only slightly inferior to that of a conventional 1.4-meter biconical antenna. From complex 3-port scattering parameter data measured for the probe in a standard coaxial test fixture and a numerical model of a centerfed (voltage gap fed) linear dipole, we compute the complex transfer function of the probe-driven dipole and compare it with the directly measured data. The data computed with a numerical model for the center-fed dipole is in reasonably good agreement with the measured data. This would seem to be a strong indication that the probe does in fact excite current in a very local sense even on an isolated dipole antenna and even in the very uppermost region of its operating frequency range. This indicates that the action of the magnetic core is still very strong even far into the dispersion region of the core. Finally, from the measured and numerically modeled antenna transfer function data we attempt to derive the insertion loss of the probe as would be measured in the test fixture. Although reasonable agreement was obtained over a large frequency range, the predicted insertion loss was less accurate than the predicted transfer function. It is believed that this is due to the inversion of the transfer scattering parameter data and the relatively large reflection coefficient of the probe driven antenna.