160
8 Coherent Radar Systems
Fig. 8.2 Block diagram of optimal coherent receiver of pulsed signals (IFO with band)
vanishes, the receiver must have a reference voltage that satisfies the following
conditions:
1. maintaining of the current phase ω 0 t of the radiated oscillation, which is ensured
by rigid phasing of reference and radiated oscillations;
2. providing Doppler frequency shift (± V ),which is possible with knowledge of
target radial velocity;
3. providing additional phase shift ϕ R + ϕ 0 that is possible with knowledge of
distance to a target and phase of reflection.
Compliance with the above conditions would mean delivering of reference voltage
to phase detector U sr = U 0 sin(ω 0 t + ϕ V − ϕ R − ϕ 0 ) obtaining at any time t
of the difference phase ϕ = 0; and the maximum voltage at the output of phase
detector when exposed by useful signal
U pd = U 0 U 0n .
(8.8)
The block diagram of the optimal coherent receiver of pulsed signals against the
background of internal noises of receiver or noise interference is shown in Fig. 8.2a.
Figure 8.2b illustrates for comparison a block diagram of non-coherent receiver.
The considered coherent signal receiving with the known frequency and phase
provides, in comparison with non-coherent reception, the following gains in the
signal-to-noise ratio:
1. The operation of multiplying the received signal and the coherent reference
voltage (8.1) removes the suppression of the weak signal by noise inherent in
the envelope detector. A phase detector, analogue to receiver mixer, is a linear
for signal-to-noise ratio and therefore ensures its constancy.
2. Precisely maintaining a zero phase shift between the signal and the reference
voltage provides suppression of the out-of-phase (relatively to the signal) noise
component. Physically, the phase of noise voltage in receiver continuously
changes according to a random law in such a way that all phases within 0
÷ 2π turn out to be equally probable. In case of non-coherent receiving, the
envelope detector, insensitive to the oscillation phase, outputs all noise voltages.
8 Coherent Radar Systems
Fig. 8.2 Block diagram of optimal coherent receiver of pulsed signals (IFO with band)
vanishes, the receiver must have a reference voltage that satisfies the following
conditions:
1. maintaining of the current phase ω 0 t of the radiated oscillation, which is ensured
by rigid phasing of reference and radiated oscillations;
2. providing Doppler frequency shift (± V ),which is possible with knowledge of
target radial velocity;
3. providing additional phase shift ϕ R + ϕ 0 that is possible with knowledge of
distance to a target and phase of reflection.
Compliance with the above conditions would mean delivering of reference voltage
to phase detector U sr = U 0 sin(ω 0 t + ϕ V − ϕ R − ϕ 0 ) obtaining at any time t
of the difference phase ϕ = 0; and the maximum voltage at the output of phase
detector when exposed by useful signal
U pd = U 0 U 0n .
(8.8)
The block diagram of the optimal coherent receiver of pulsed signals against the
background of internal noises of receiver or noise interference is shown in Fig. 8.2a.
Figure 8.2b illustrates for comparison a block diagram of non-coherent receiver.
The considered coherent signal receiving with the known frequency and phase
provides, in comparison with non-coherent reception, the following gains in the
signal-to-noise ratio:
1. The operation of multiplying the received signal and the coherent reference
voltage (8.1) removes the suppression of the weak signal by noise inherent in
the envelope detector. A phase detector, analogue to receiver mixer, is a linear
for signal-to-noise ratio and therefore ensures its constancy.
2. Precisely maintaining a zero phase shift between the signal and the reference
voltage provides suppression of the out-of-phase (relatively to the signal) noise
component. Physically, the phase of noise voltage in receiver continuously
changes according to a random law in such a way that all phases within 0
÷ 2π turn out to be equally probable. In case of non-coherent receiving, the
envelope detector, insensitive to the oscillation phase, outputs all noise voltages.