Following the growing interest in Over The Air testing of Multiple Input Multiple Output handset antenna systems, this paper presents a non-galvanic measurement tool for early antenna performance estimation in the prototyping and testing stages of the development process. The necessity for removing the coaxial cables, is here demonstrated with an example MIMO parameter - correlation. It is found by simulations, that the presence of cables not only completely changes this parameter, but the concrete cable position can also be very significant. The device proposed here, uses two parallel RF-over-fiber channels with low power consumption in wideband operation. The achieved dynamic range is up to 60 dB with acceptable isolation for two particular design frequencies and up to one hour of operation on a single battery charge. The total electrical dimensions are 40x40x10 mm, making it suitable for typical phone mock-ups. It can be used in both anechoic, as well as stirred mode chambers.