60
4 Measuring Principles and Techniques …
Fig. 4.5 Scheme of
frequency range
measurement method
The frequency analyzer, that positioned at the scheme output, represents a set of
big amount narrowband filters overlapping the whole frequency band of beats. In
one of the filters, a frequency F D is determined according to a maximum signal, and,
consequently, a distance to a target.
Maximum operational range (detection range) of radar with frequency modulation
at application of analyzer of described (parallel) type and other equal conditions not
worse than operational range of pulse radar with the same average power (energy)
of radiation.
Disadvantage of continuous-wave radar consists in difficulty of effective division of radiated and received oscillations since unlike to pulse radars in this case a
transmitter and receiver operate simultaneously. Transmitter oscillations, influencing
on receiver input, generate a constant background reducing radar detection range.
Decoupling (isolation) of transmitter and receiver in continuous-wave stations is one
of the most serious technical problems.
Minimum operating range of continuous-wave stations is less than pulse radiation
radars; in other words, a frequency method permits to measure very short ranges.
This is determined by the absence of powerful pulse of transmitter and connected
with it a dead area in range.
Single valuedness of range read-out in frequency-modulated radar is provided in
the same way as it is carried out in pulsed radars: FM period is selected in such a
way that it exceeds a signal delay time reflected from the most remote target.
Besides accurate measuring of short ranges, the pulse method has the following
advantages:
• relatively small radiating power that eliminates a breakdown danger in antennawaveguide path and reduces transmitter weight and dimensions;
• possibility of direct and single-valued measuring of target instantaneous velocity
based on Doppler effect that permits to conduct discrimination (selection) of
objects in velocity.
Discrimination in velocity capability, which opposed to pulsed radar, has a
continuous-wave radar, gives a possibility to avoid returns from local features as
having a zero velocity relatively to radar (as opposed to detected targets) and discriminate separate targets located in one resolution element with different velocities. In
aircraft airborne FM radars, it is also a possibility to suppress background returns
(clutters) based on differences in target velocities and ground relatively to airborne
radar platform.
4 Measuring Principles and Techniques …
Fig. 4.5 Scheme of
frequency range
measurement method
The frequency analyzer, that positioned at the scheme output, represents a set of
big amount narrowband filters overlapping the whole frequency band of beats. In
one of the filters, a frequency F D is determined according to a maximum signal, and,
consequently, a distance to a target.
Maximum operational range (detection range) of radar with frequency modulation
at application of analyzer of described (parallel) type and other equal conditions not
worse than operational range of pulse radar with the same average power (energy)
of radiation.
Disadvantage of continuous-wave radar consists in difficulty of effective division of radiated and received oscillations since unlike to pulse radars in this case a
transmitter and receiver operate simultaneously. Transmitter oscillations, influencing
on receiver input, generate a constant background reducing radar detection range.
Decoupling (isolation) of transmitter and receiver in continuous-wave stations is one
of the most serious technical problems.
Minimum operating range of continuous-wave stations is less than pulse radiation
radars; in other words, a frequency method permits to measure very short ranges.
This is determined by the absence of powerful pulse of transmitter and connected
with it a dead area in range.
Single valuedness of range read-out in frequency-modulated radar is provided in
the same way as it is carried out in pulsed radars: FM period is selected in such a
way that it exceeds a signal delay time reflected from the most remote target.
Besides accurate measuring of short ranges, the pulse method has the following
advantages:
• relatively small radiating power that eliminates a breakdown danger in antennawaveguide path and reduces transmitter weight and dimensions;
• possibility of direct and single-valued measuring of target instantaneous velocity
based on Doppler effect that permits to conduct discrimination (selection) of
objects in velocity.
Discrimination in velocity capability, which opposed to pulsed radar, has a
continuous-wave radar, gives a possibility to avoid returns from local features as
having a zero velocity relatively to radar (as opposed to detected targets) and discriminate separate targets located in one resolution element with different velocities. In
aircraft airborne FM radars, it is also a possibility to suppress background returns
(clutters) based on differences in target velocities and ground relatively to airborne
radar platform.