Fifth-Generation (5G) mobile communication demands a wide use of multi beam scanning array antennas, providing effective coverage performances at millimeter waves [1-3]. In particular, when the telecommunication channel is characterized by a reduced signal to noise ratio, an omni like radiation pattern could be generated by the beam scanning antenna system. The testing of the AUT (Antenna Under Test), in such conditions, is typically performed with low directive reference antennas. These antennas can suffer of the interaction with the feeding cable. The measurement postprocessing by the equivalent currents approach (EQC) [4-7], implemented in the MVG software INSIGHT [8], can be used for diagnostic investigations on this kind of reference antennas and to filter undesired currents on the feeding cable. In this paper the EQC approach is applied, for the first time, on diagnostic and filtering of feeding cable on a measurement of a low directive antenna for 5G tests.