Dual-Comb Broadband Microwave Vector Network Analyzer

We propose a dual-comb broadband microwave vector network analyzer (VNA). One of the optical frequency combs (OFCs) beats with a continuous wave (CW) light to generate the stimulus signal of the device under test, which is a multi-tone signal within a wide bandwidth. Another OFC with slightly different repetition frequency samples the scattering signal and then coherently beats with the CW light, to convert the scattering signal into the intermediate frequency (IF) signal. Thanks to the dual-comb technology, the requirement for the electrical devices is lessened. A wide measurement frequency range can be achieved by sweeping the frequency of the CW light within a narrow range, giving the credit that the multi frequencies in the stimulus signal sweep simultaneously. An electrical back end with narrow bandwidth and low sampling rate can be used to acquire the scattering parameters (S parameters), owing to the fact that the IF signal locates at the low-frequency band and has the fixed frequencies during frequency sweeping. In the experiments, the S parameters of a 25-GHz low-pass filter within 0.001-69.88 GHz is measured by the proposed VNA, utilizing a microwave signal with a frequency sweeping range of about 5 GHz and an electrical back end with a bandwidth of 200 MHz and a sampling rate of 312.5 MHz.