Vectorial E-field sensing using pigtailed photonic probes for aperture-field mapping of antennas

Abstract

The aperture-field mapping is very important to diagnosing the amplitude and phase distribution of the antenna under test( AUT). Since such measurements need to be done without influence to the actual field distribution near the aperture, traditional metallic near-field probes, such as horn antennas, waveguide slots, et al, are irrespective. Miniature electrooptic E-field sensors offer good possibility for such near-field or very near-field measurements, because of its small size and little perturbation to the AUT. Moreover these devices have high resolution and reduced dimensions. In this paper, we have present a simple photonic microwave probe to measure the electric field vector distribution at a distance shorter than one wavelength from the aperture plane of a antenna. The photonic E-field probe is a type of pigtailed electro-optic sensor and consists of an electro-optic crystal supported by a quartz sleeve. The probe is all-dielectric, without any metallic materials. Those physical and electrical features make the photonic sensor attractive when used as a probe for near-field antenna measurements. A patch antenna with a resonant frequency at 6.5GHz was designed and fabricated. Both amplitude and phase distribution of the two tangential E-field components are mapped by using the present photonic probe. Simulation was carried out as well, and compared with the experimental measurements. The result shows great correspondence for amplitude distribution between simulations and experiments, as well as for the phase distribution except for some random tiny fluctuations. The methods to improve the stability of measurement system are briefly discussed.