Vector near-field measurement system using an electro-optic microcavity and electrical downconversion

An electro-optic (EO) field-mapping system that features a continuous-wave laser-diode optical source, an entirely fiber-coupled beam path, a resonance-assisted EO-microcavity probe, and an RF-downconversion mixing circuit is shown to be effective for extracting near-field vector RF information. The system is the first of its kind to allow amplitude and phase analysis of signals interrogated with a continuous optical beam and no polarization components in the EO-modulation section. A complete tangential-electric-field characterization in the near field of an RFID antenna - a small planar loop intended for applications in mobile-reader instruments - is presented, with a >35 dB signal-to-noise ratio attained.