Electrically small antennas for wireless communications applications are prone to excite common mode currents on cables connected to them for measuring their performance. A miniature RF-optical transducer enables an optical fibre connection to the antenna, thereby eliminating the large distortion associated with the unwanted radiation from a coaxial cable. This opto-electric field sensor system operates from 300 kHz to 10 GHz. Results of a small UWB monopole antenna with coaxial cable and with optical fibre are compared.