Electro-optical-sensor for near-field measurements of large antennas

Near-field measurements are an effective tool for determining antenna far-field patterns. Small electro-optical E-field sensors offer good possibilities for these kinds of measurements, because of their small size and their little influence on the antenna under test. In this paper we present a lithiumniobate-based electro-optical field sensor with a minimum sensitivity down to 20 mV/m, which is suitable not only for antenna measurements but also for small devices, where testing power is limited, such as small enclosures like laptops or electronic control units. The functionality and accuracy of the sensor system is demonstrated with an aperture scan of a large pyramidal horn antenna. Measurements correspond well to the known theoretical description of the electric field. Additionally, far-field transforms of the measured data between 300 MHz and 3 GHz show a good agreement with direct far-field measurements at an open area test site (OATS).