7 Non-coherent and Pseudo-coherent Radar Systems
153
within limits of ±1–3%, and this is about several megahertz), then a unit should
ensure a function of frequency adjustment (control).
After conversion at mixer output, the intermediate-frequency pulses are generated, which come to AFC unit input, which generates a voltage proportional to
deviation of intermediate frequency from its nominal value. This voltage, by influencing on control electrode of heterodyne, leads to its frequency change by reducing
an intermediate-frequency deviation from a nominal value.
From transceiver IFA output, a signal is delivered to turbulence detection unit
(TDU) of MFD. In TDU, a video signal is amplified and sent to liquid-crystal display
of MFD unit.
TDU operation principle is based on Doppler effect application. The Doppler
effect means waves frequency change registered by a receiver which happens due to
its wave source movement and a receiver. Differential frequency allocation between
radiated and reflected from a target signal is originated in TDU, and non-zero value
of this parameter testifies on movability of reflection object.
MFU—graphical and telecommunication information imaging on color liquidcrystal display from onboard systems and sensors.
As it was mentioned before, the main requirement in order to ensure the coherent
receiving consists in hard phasing of reference and radiating oscillations. For this
purpose, a hard phasing of radar HF transmitter and reference oscillations generator
is required. Different radars with inner coherence differ from each other by the
following features:
• direction of phase synchronization (transmitter synchronizes a generator of
reference oscillations or vice versa);
• synchronizing frequency (at what frequency a synchronization is performed: at
high or intermediate);
• oscillation comparison frequency in phase detector (at what frequency a comparison is performed: at high or intermediate).
Let us examine an applied in centimeter wave radars functional pseudo-coherent
diagram (Fig. 7.3) with phasing from radar transmitter and oscillations comparison are intermediate frequency of receiver. Time oscillograms in different points of
diagram are represented in Fig. 7.4.
Pulses of modulator (1) control an operation of magnetron oscillator (generator).
Part of the energy of sounding (probing) oscillation (2) of high frequency f h is mixed
with output voltage of a stable local (heterodyne) oscillator with frequency to obtain
beats of intermediate frequency f hdy at output of phasing mixer (3).
An intermediate-frequency pulse, phased relative to the radar generator, is used
for phase synchronization of coherent local oscillator, operating at intermediate
frequency. The oscillation phase of the coherent local oscillator, which acts as a
reference voltage generator for phase detector, is coupled in the described manner
with the phase of sounding pulse. Therefore, the output voltage of the coherent local
oscillator (5) can be used at receiving of reflected signals, related to this sounding
pulse. In each pulse repetition period T during the pulse duration, the coherent local
153
within limits of ±1–3%, and this is about several megahertz), then a unit should
ensure a function of frequency adjustment (control).
After conversion at mixer output, the intermediate-frequency pulses are generated, which come to AFC unit input, which generates a voltage proportional to
deviation of intermediate frequency from its nominal value. This voltage, by influencing on control electrode of heterodyne, leads to its frequency change by reducing
an intermediate-frequency deviation from a nominal value.
From transceiver IFA output, a signal is delivered to turbulence detection unit
(TDU) of MFD. In TDU, a video signal is amplified and sent to liquid-crystal display
of MFD unit.
TDU operation principle is based on Doppler effect application. The Doppler
effect means waves frequency change registered by a receiver which happens due to
its wave source movement and a receiver. Differential frequency allocation between
radiated and reflected from a target signal is originated in TDU, and non-zero value
of this parameter testifies on movability of reflection object.
MFU—graphical and telecommunication information imaging on color liquidcrystal display from onboard systems and sensors.
As it was mentioned before, the main requirement in order to ensure the coherent
receiving consists in hard phasing of reference and radiating oscillations. For this
purpose, a hard phasing of radar HF transmitter and reference oscillations generator
is required. Different radars with inner coherence differ from each other by the
following features:
• direction of phase synchronization (transmitter synchronizes a generator of
reference oscillations or vice versa);
• synchronizing frequency (at what frequency a synchronization is performed: at
high or intermediate);
• oscillation comparison frequency in phase detector (at what frequency a comparison is performed: at high or intermediate).
Let us examine an applied in centimeter wave radars functional pseudo-coherent
diagram (Fig. 7.3) with phasing from radar transmitter and oscillations comparison are intermediate frequency of receiver. Time oscillograms in different points of
diagram are represented in Fig. 7.4.
Pulses of modulator (1) control an operation of magnetron oscillator (generator).
Part of the energy of sounding (probing) oscillation (2) of high frequency f h is mixed
with output voltage of a stable local (heterodyne) oscillator with frequency to obtain
beats of intermediate frequency f hdy at output of phasing mixer (3).
An intermediate-frequency pulse, phased relative to the radar generator, is used
for phase synchronization of coherent local oscillator, operating at intermediate
frequency. The oscillation phase of the coherent local oscillator, which acts as a
reference voltage generator for phase detector, is coupled in the described manner
with the phase of sounding pulse. Therefore, the output voltage of the coherent local
oscillator (5) can be used at receiving of reflected signals, related to this sounding
pulse. In each pulse repetition period T during the pulse duration, the coherent local