Signal coherence

  MTS systems can only work effectively if the necessary coherence of the signals of the microwave radar devices is provided. How does the coefficient of suppression of passive interference depends on the degree of coherence of signals.

  To answer this question, one should understand the physical meaning of the phenomenon.

  Cacito realngo generator    The microwave transmitter slowly goes away from the moment it is turned on (the so-called “overrun” frequency). This withdrawal is due to the heating of the resonant systems.    But it is not he who determines the quality of terrain suppression, since almost all radars have automatic frequency tuning.

  The most dangerous are the fast frequency departures during the passage of the signal from the radar to the target and the reflected signal back (coherence interval t _kg ) .    These treatments are random and can be characterized by the dispersion of frequency drift s _f ² .

  The picture shows an approximate    frequency care schedule and the interval on it t _kg .

  For the interval t _kg   fast frequency drifts cause stochastic phase fluctuations     s _j   = 2 p s _f   t _kg

  The figure shows that the output of the phase detector produces a signal proportional to the amplitude and phase of the input voltage. If the coherence of the transmitter signal is ideal, and the local object ( for example, a house) is absolutely fixed, then the reflected signal at the output of the phase detector has a constant amplitude. But if the radar channel has significant amplitude-phase instabilities, then the signal from the house becomes chaotic. In this case, the frequency spectrum band becomes large and the interference is not suppressed.

  Thus, the coefficient of suppression of passive interference P can be calculated by knowing the value of s _j   :    P = 1/2 p s _f   t _kg   adjusted for the transfer ratio.    If the value of P and the range of the radar are set, then it is easy to calculate the coherence requirements of the transmitter of continuous microwave radiation at the level of fast phase s _j    or   Frequency Care s _f .

  In pulsed radar, the requirements for transmitter coherence are lower, since its coherence interval corresponds to the entire pulse duration. But this type of radar has a local continuous oscillator. Requirements for it can be calculated by the above method.