164
8 Coherent Radar Systems
U out =
l
2
1 + l
2
2 =
√
2U 1 .
(8.21)
With the coherent summation of two pulses by formula (8.18), the value U out =
2U 1 would have been obtained.
This particular example clearly shows that refusal from coherence leads to signal
accumulation according to the unfavorable law of powers summation: P out = n P 1 ,
inherent to noises.
So, ensuring the coherence of reference voltage of phase detector and generated sounding oscillations is an absolutely necessary condition for the efficiency of
coherent-pulse radar station.
In the considered coherent-pulse receiver of a signal with a constant phase and
a known frequency, a reference voltage (8.9) is used, rigidly phased with the oscillations of the transmitter, but having a frequency different from it (), taking into
account the radial velocity of the target. It has been shown that this method provides
efficient separation of the useful signal against the background of internal receiver
noise or noise interference.
On the other hand, this processing scheme gives a loss of 2 times in power relatively
to signal-to-noise ratio compared to the previously considered receiver of fully known
signal. This is explained by the fact that quadrature phase detectors pass both phase
(relative to signal) and 90° shifted out-of-phase noise components.
In the considered coherent-pulse receiver of a signal with constant phase and the
known frequency, a reference voltage (8.9) is used, rigidly phased with the oscillations of the transmitter, but having a different from it frequency (ω 0 ± V ), considering the radial velocity of target. It has been shown that this method provides efficient
extraction of useful signal against the background of internal receiver noise or noise
interference.
To detect a useful signal from a moving target against a different background—
against the background of reflections from stationary or slowly moving objects—it is
advisable to act differently. Keeping the rigid phasing of the reference and sounding
oscillations, the original frequency ω 0 is also left in the reference oscillation without
giving it a Doppler shift:
U = U 0rs sin ω 0 t.
(8.22)
In this case, due to multiplying of reference and receiving (8.3) oscillations inphase detector, we obtain:
U pd = U 0 U 0rs cos ϕ = U 0 U 0rs cos( V t − ϕ R − ϕ 0 ).
(8.23)
Thus, when using a reference voltage that reproduces the phase and frequency
of radar transmitter, a voltage is generated at the output of phase detector, which is
constant in time for stationary targets ( V = 0) and changes in time with the Doppler
frequency for moving targets. Measuring this frequency allows you to determine the
8 Coherent Radar Systems
U out =
l
2
1 + l
2
2 =
√
2U 1 .
(8.21)
With the coherent summation of two pulses by formula (8.18), the value U out =
2U 1 would have been obtained.
This particular example clearly shows that refusal from coherence leads to signal
accumulation according to the unfavorable law of powers summation: P out = n P 1 ,
inherent to noises.
So, ensuring the coherence of reference voltage of phase detector and generated sounding oscillations is an absolutely necessary condition for the efficiency of
coherent-pulse radar station.
In the considered coherent-pulse receiver of a signal with a constant phase and
a known frequency, a reference voltage (8.9) is used, rigidly phased with the oscillations of the transmitter, but having a frequency different from it (), taking into
account the radial velocity of the target. It has been shown that this method provides
efficient separation of the useful signal against the background of internal receiver
noise or noise interference.
On the other hand, this processing scheme gives a loss of 2 times in power relatively
to signal-to-noise ratio compared to the previously considered receiver of fully known
signal. This is explained by the fact that quadrature phase detectors pass both phase
(relative to signal) and 90° shifted out-of-phase noise components.
In the considered coherent-pulse receiver of a signal with constant phase and the
known frequency, a reference voltage (8.9) is used, rigidly phased with the oscillations of the transmitter, but having a different from it frequency (ω 0 ± V ), considering the radial velocity of target. It has been shown that this method provides efficient
extraction of useful signal against the background of internal receiver noise or noise
interference.
To detect a useful signal from a moving target against a different background—
against the background of reflections from stationary or slowly moving objects—it is
advisable to act differently. Keeping the rigid phasing of the reference and sounding
oscillations, the original frequency ω 0 is also left in the reference oscillation without
giving it a Doppler shift:
U = U 0rs sin ω 0 t.
(8.22)
In this case, due to multiplying of reference and receiving (8.3) oscillations inphase detector, we obtain:
U pd = U 0 U 0rs cos ϕ = U 0 U 0rs cos( V t − ϕ R − ϕ 0 ).
(8.23)
Thus, when using a reference voltage that reproduces the phase and frequency
of radar transmitter, a voltage is generated at the output of phase detector, which is
constant in time for stationary targets ( V = 0) and changes in time with the Doppler
frequency for moving targets. Measuring this frequency allows you to determine the