The article considers typical problems of determining the Doppler frequency shift (DFS) and its sign in continuous-wave or pulse radars using microwave photonic technologies in multi-target tracking mode. The structure of the hardware-software spectrum analyzer and variants of its software for solving the above problems are proposed. The analyzer is functionally universal, however, its main purpose is to solve the problems of determining the magnitude and sign of the DFS when using a microwave photonic device based on tandem single-port amplitude and phase modulators in the radar receiver. For multi-target tracking, software of receiver is supplemented by an FFT with further analysis of all received components by scanning with an ultra-narrow band filter. The absolute error in determining the DFS from the frequency of information signals depends on the bandwidth of the software ultra-narrow band filter (units of Hz). The relative error in determining the amplitudes of information signals does not exceed ~10–3 in almost the entire range of amplitudes of the hardware high quality linear filter at the output of receiver. The ratio D of the obtained amplitudes for a pair of associated DFS information frequencies for one specific target allows you to determine its sign: if D < 1, the target is removed, if D >1 , the target is approaching. Using a method similar to the method for multi-target tracking of a continuous wave radar, typical problems of determining the DFS and its sign in pulse radars can be solved.
The article considers typical problems of determining the Doppler frequency shift (DFS) and its sign in continuous-wave radars using microwave photonic technologies in single target tracking mode. The structure of the hardware-software spectrum analyzer and variants of its software for solving the above problems are proposed. The analyzer is functionally universal, however, its main purpose is to solve the problems of determining the magnitude and sign of the DFS when using a microwave photonic device based on tandem single-port amplitude and phase modulators in the radar receiver. For the single-target continuous radar tracking mode, a hardware linear filter method with an oblique frequency response and analysis of pairwise beating frequencies is proposed. The absolute error in determining the DFS by the frequency of information signals depends on the error of beating frequencies (units of Hz).
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.
This article describes a new approach for the estimation of the direction or of the microwave signal reflected from the object, based on radio photonics technologies. The angle of arrival measurement device has the same structure as the classical fiber-optic communication channel and consists of a laser, a block of electro-optical modulators 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 parallel subunits, consisting of tandem single-port amplitude and phase modulators (TAPM). A microwave signal reflected from the object with a time delay, the value of which is determined by the AOA, is sequentially received at the radio frequency inputs of two TAPMs through the receiving antennas connected to them. In this case, the initial components of the laser carrier at the output of the TAPM subunits of both channels are completely suppressed, which significantly distinguishes the proposed solution from the known ones for the better in terms of increasing the measurement accuracy. The beats of the output signals of the TAPMs at the output of the photodetector represent a signal reflected from the object, according to the power of which the AOA can be determined.
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