Wideband Vector Network Analyzer Based on Direct Microwave Photonic Digitization

Abstract

Vector network analyzers (VNAs) are established as one of the indispensable tools for measuring and analyzing the characteristics of objects under test in various fields, ranging from medicine and material to geology and communication. Conventional VNAs are commonly based on microwave mixing architectures that inevitably compromise accuracy, dynamic range, and bandwidth. Spurred by the deficiencies of conventional VNAs, this paper proposes a wideband photonic vector network analyzer (PVNA) that exploits the concept of direct microwave photonic digitization. In our method, ultra-stable optical trains directly sample the response signals from the objects under test, followed by opto-electronic conversion and quantization, to ultimately obviate the intricate down-conversion procedures in traditional VNAs. The contribution of our method relies on the direct microwave photonic digitization process enabling a novel and compact PVNA architecture that extends the measurable frequency range to 110 GHz with existing commercial devices or even higher by employing a high bandwidth modulator. In any case, our technique reduces the bandwidth requirements of the optical intensity digitizers. To validate our architecture’s theoretical principle, we establish an experimental PVNA with a measurable frequency range of up to 40 GHz and a dynamic range exceeding 90 dB. The developed methodology based on direct microwave photonic digitization paves a new path to the study of broadband, low-cost, and compact VNAs.