The performance of unbiased balanced photodiodes for optical calibration of radio-frequency antenna arrays

摘要

The accurate calibration of radio-frequency (RF) antenna arrays is critical to their performance. Real-time, in situ calibration is particularly desirable and recent photonic implementations [1],[2] have stirred interest for onboard naval applications. These photonic architectures are primarily suited for large shipboard arrays [3] but may also be pertinent to the calibration of the smaller arrays found in avionic platforms. The concept is to feed each receive-mode antenna element with an optically-encoded test signal that is demodulated with unbiased photodiodes placed near every element [1],[2]. This technique provides the distinct advantage of having no metallic components near the aperture but the unbiased photodiodes will exhibit reduced performance as compared to reversed-biased photodiodes of the same type. Most notably, an unbiased photodiode will demonstrate decreased optical-to-electrical conversion efficiency and increased RF distortion.