Balun Design for CISPR 16-1-5 Calibration and Reference Test Site Verification

The CISPR 16-1-5 standard requires site insertion loss (SIL) measurements for the validation of test sites. These measurements are made with tuned linear dipole antennas driven from coaxial transmission lines via balancing networks (baluns) and can incorporate attenuators in order to reduce reflections. Some latitude exists in the design of such a balun/attenuator combination. In particular, an attenuator on the balanced side of the balun (between the dipole elements and the balun) may be implemented as center-grounded or floating. It is shown that in that in the first case the attenuator causes balun/attenuator combination to behave more nearly as a 180° power divider, but in the second case as a current balun. These two statements are true regardless of the topology of the original balun. Thus, the floating attenuator might have some application in the implementation of a broadband current balun for vertical-polarization measurements.