Phase-Stabilized W-Band Planar Imaging System for Near-to-Far-Field Projection Based on Photonic Sensors

This letter presents a highly stabilized planar near-field imaging system for millimeter-wave antenna characterization based on dual electrooptic sensors. The issue of system instability, which often occurs in millimeter-wave sensing, is effectively eliminated by employing error correction techniques with field-calibrated probes. This technique compensates for the phase vibration of a radio frequency source by using an additional reference probe. Detailed stabilization techniques for the phase drift are discussed. A probe is also field-calibrated on the W-band so as to provide electric field imaging with the absolute value. W-band horn antenna characterization at 95 GHz is conducted, and the absolute field distribution is compared using the proposed system and a conventional electrical near-field system. A simulation is also conducted. The radiation far-field pattern and gain, calculated from the near-field measurements, are in good agreement with each other according to a comparison of these outcomes. Moreover, a back-projection algorithm with a far electric field as input is utilized to reconstruct the aperture fields of a horn antenna. Finally, a comparison between the measured and reconstructed near-field data with different distances between the probe and the horn antenna is made.