Radiophotonic module for Doppler frequency shift measurement of a reflected signal for radar type problems solving

This article describes a new method for the Doppler frequency shift (DFS) measurement of a radar microwave signal reflected from a moving object, based on radio photonics technologies. The DFS measurement device has the same structure as the sequential radiophotonic link with filtration and consists of a laser, a block of electro-optical modulators, a fiber Bragg grating (FBG), and a photodetector. The block of electro-optical modulators, in contrast to the known solutions based on a two-port Mach-Zehnder amplitude modulator, is based on two subunits, consisting of connected tandem single-port amplitude and phase modulators (TAPM). The general structure of the TAPM subunits is parallelserial. The microwave signal reflected from the object arrives at the first TAPM, which forms the measurement channel. The second and third TAPMs, connected in series, form a reference channel connected in parallel to the measurement one. The second TAPM receives a reference signal from the locator transmitter at the probing microwave frequency, after which the two-frequency radiation, spaced by twice of the probing frequency, is fed to the third TAPM, which generates from each component of the two-frequency radiation two more with a difference frequency equal to twice the maximum possible DFS. The beats of signals from the measurement and reference channels at the output of the photodetector are three high-frequency (GHz) or low-frequency (MHz) electrical signals, the frequencies and powers of which used for the DFS determination.