Highly Stable Microwave Transmission Over Optical Fiber With Accurately Characterized Absolute Delay

In distributed interferometric antenna arrays, accurate measurement and long-term stabilization of transmission delay are essential for coherent combining and accurate target localization. This paper presents a fiber-based delay measurement and stabilization system. The employed dual-tone probe enables accurate measurement of delay variations and the absolute delay simultaneously, while a phase-locked loop provides long-term delay stabilization. Experimental results demonstrate a delay measurement accuracy better than 20 fs and a stabilized delay fluctuation of 15.7 fs (standard deviation) over a 45 km fiber link for 3600 s. The proposed system realizes highly stable microwave transmission with accurately measured absolute delay, making it well-suited for coherent combining and localization in distributed antenna arrays.