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Vector Near-Field Measurements Using Optimized Electrical and Photonic Down-Conversion

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3 Author(s)
Dong-Joon Lee ; Center for Ultrafast Opt. Sci. & the Dept. of Electr. Eng. & Comput. Sci., Univ. of Michigan, Ann Arbor, MI ; Jeong-Jin Kang ; Whitaker, J.F.

A microwave vector-measurement technique based on electrooptic probing with a micro-resonator sensor and electrical down-mixing of a demodulated optical sideband is experimentally demonstrated. Detailed near-field distributions of the amplitude and phase of a radio-frequency-identification antenna are extracted and compared with field patterns obtained from an electrooptic measurement system that instead employs photonic down-conversion to create the baseband read-out signal. High-fidelity field scans with a > 35 dB signal-to-noise ratio (SNR) are obtained when using both the electrical and photonic down-conversion techniques in the measurement of a small, planar loop antenna intended for applications in mobile-reader instruments. In addition, the electrooptic-modulation sensitivity to the antenna radiation power is observed to increase by 5 dB when the optical wavelength employed with the resonant probe is shifted from the point of maximum reflected intensity to an optimized low-noise operating regime. Finally, a practical method to double the bandwidth of the electrooptic measurement during photonic down-conversion without any change in system components is introduced, enhancing the SNR to > 40 dB.

Published in:

Microwave Theory and Techniques, IEEE Transactions on  (Volume:56 ,  Issue: 12 )