<\/b>
The Antenna transfers the transmitter energy to signals in space with the required distribution and efficiency. This process is applied in an identical way on reception."; var txt2 ="Duplexer<\/b>
The duplexer alternately switches the antenna between the transmitter and receiver so that only one antenna need be used. This switching is necessary because the high-power pulses of the transmitter would destroy the receiver if energy were allowed to enter the receiver."; var txt3 ="Low-Noise Preamplifier<\/b>
The Low-Noise Preamplifier (LNA) amplifies the very weak backscattersignals. The low noise characteristic is very important: all following amplifiers will amplify the added noise of the LNA! The amplifier has a gain of 18...25 dB."; var txt4 ="First IF- Amplifier<\/b>
After conversion to the intermediate frequency, the signal is amplified in several IF-amplifier stages. This amplifier has got a wide bandwidth and suppress the influence of mirror-frequencies. The center frequency is relatively high, up to 450 MHz nominally."; var txt5 ="Radarscope / Monitor<\/b>
The indicator presents to the observer a continuous, easily understandable, graphic picture of the relative position of radar targets."; var txt6 ="Power Amplifier<\/b>
The Power Amplifier would typically be a klystron stage, a traveling wave tube (TWT) or solid state."; var txt7 ="First Detector<\/b>
This is a downconverting mixer stage. The function of the mixer stage is to convert the received rf energy to a lower, intermediate frequency (IF) that is easier to amplify and manipulate electronically."; var txt8 ="Second Detector<\/b>
This is a downconverting mixer stage too. The function of the mixer stage is to convert the received rf energy to a lower, intermediate frequency (IF) that is easier to amplify and manipulate electronically."; var txt9 ="Second IF- Amplifier<\/b>
After conversion to the intermediate frequency, the signal is amplified in several IF-amplifier stages. Most of the gain of the receiver is developed in the IF-amplifier stages. The overall bandwidth of the receiver is often determined by the bandwidth of the IF-stages. The center frequency is about 75 MHz nominally."; var txt10 ="Radar Signal Processor<\/b>
The signal processor is that part of the system which separates targets from clutter on the basis of Doppler content and amplitude characteristics. It convert the videosignals to radar data, to plots and tracks."; var txt11 ="Upconverter<\/b>
The Upconverter converts the transmitters waveform from intermediate frequency to high frequency transmitting signal with low power. Upconversion of exciter waveforms is similar to downconversion within the receiver."; var txt12 ="Frequency Synthesizer<\/b>
The low phase noise frequency synthesizer provides the different basic frequencies to achieve frequency agile capabilities. Older radars use an analogue synthesizer often. Recent radar systems use even phase lock loop (PLL) architecture."; var txt13 ="Upconverter<\/b>
This Upconverter provides fully coherent receiver local oscillator signals at radar frequency band as well as requisite, auxiliary high frequency clock signals. This example given needs the frequency 5.95 GHz as (fs<\/sub>\+f1.ZF<\/sub>)<\/span>, and the center frequency of first IF- amplifier."; var txt14 ="Phase Sensitive Detector<\/b>
The IF-signal is passed to a phase sensitive detector (PSD) which converts the signal to base band, while faithfully retaining the full phase and quadrature information of the Doppler signal."; var txt15 ="Analogue/Digital Converter<\/b>
The ADC converts the magnitude of the video signal to a digital data word. The resolution and the sampling rate must be very high to achieve a small range cell."; var txt16 ="Mixer / Exciter<\/b>
The first stage of cascaded mixers. The function of this mixer stage is to modulate a prospective intermediate frequency (IF) with the transmitting signals waveforms. The I- (in-phase) and Q- (quadrature) signals from the Waveform Generator are defined signals for comparing with the backscatter in the receivers synchronous detector."; var txt17 ="Waveform-Generator<\/b>
The Waveform-Generator generates the transmitting pulse in base band and low- power. Both outputsignals are complex functions. The I- (in-phase) and Q- (quadrature) signals of the synchronous detector in the receiver are performed here with a defined phase (Q-signal) and amplitude (I-signal)."; var txt18 ="Master Oscillator<\/b>
The master oscillator/frequency generator provides low phase noise local oscillators and the radar system clocks. It is a sine-wave Quartz- generator with a high stable frequency of 60 to 100 MHz often."; var txt19 ="Timing and Contol<\/b>
The synchronizer supplies the synchronizing signals that time the transmitted pulses, the A/D-Converter, and other associated circuits."; var txt20 ="Bearing Information<\/b>
An Encoder is mounted in the turntable of the antenna. It generate Azimut Change Pulses (ACP) representing the actual boresight direction of the antenna."; var txt21 ="Testpoint 1 (ACP/NRF)<\/b>
\"\""; var txt22 ="Testpoint 2<\/b> modulated Waveform,
center frequency: 75 MHz(green),
Gate (red)
\"\""; var txt23 ="Testpoint 3<\/b>
Waveform in base-band
(here the quadrature-part only)
\"\""; var txt24 ="Testpoint 4 (Control pulses)<\/b>
start waveform (cyan)
gate waveform (red)
\"\""; var txt25 ="Testpoint 5 (Clock)<\/b> 20 MHz
\"\""; var txt26 ="Testpoint 6 (Video)<\/b><\/b>
pulse modulated signal (cyan)
intrapulse modulated (green)
\"\""; var txt27 ="This line you can measure a continuous Sine frequency<\/b> e.g. 75 MHz at."; var txt28 ="This line you can measure a continuous Sine frequency<\/b> e.g. 60 MHz at, the so called Master Clock frequency."; var txt29 ="This line you can measure the full developed transmitting pulse<\/b> at. The pulses are generated in low power, e.g. 0 dB (1 mW). The pulse shape looks as like as testpoint 2 at, but the center frequency is e.g. 5.5 GHz."; var txt30 ="This line you can measure different continuous Sine frequencies<\/b> at.
(depending on the choosen carrier frequency of the transmitter)."; var txt31 ="This line you can measure a continuous Sine frequency<\/b> at.
The actual magnitude of the frequency can be calculated as sum of the carrier and both intermediate frequencies (e.g:. 5.500 \+ 450 \= 5.95 MHz). Its power has got a definite value to achieve an effective result in the following mixer."; var txt32 ="This line you can measure a continuous Sine frequency<\/b> at.<\/b>The actual magnitude of the frequency can be calculated as sum of both intermediate frequencies (e.g:. 450 \+ 75 = 525 MHz)."; var txt33 ="The transmitting pulse has got its full power here. The line is a waveguide mostly. Eventually existing testpoints are ports of directional coupler, to connect e.g. spectrum-analyzers via an attenuator."; var txt34 ="This line you could measure the weakly echo signals at. There are relicts of the transmitted pulses also. This is a waveguide coupler for coaxial semi-rigid line mostly. There aren't test points to avoid an additional attenuation of the weak signals."; -->

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Fully Coherent Radar

Duplexer
Low-Noise
Preamplifier
First IF-
Amplifier
Power
Amplifier
Second IF-
Amplifier
Radarsignal
Processor
Upconverter
Frequency
Synthesizer
Upconverter
Synchronous
Detector
A/D
Converter
Mixer
Waveform
Generator
Master
Oscillator
Timing and
Control

Figure 1: an easy block diagram of a fully coherent radar.

ant dup lna zf1 scr amp mx1 mx2 zf2 rdp uc1 fsy uc2 syd adc mx3 wfg mcl cnt acp acp tp1 tp2 tp3 tp4 tp5 tp6 l75 l75 cnt fxf fxf fxf fxf fxf fxf fxf
Low-Noise
Preamplifier
Second IF-
Amplifier
Timing and
Control
TP1
TP2
TP3
TP4
TP5
TP6

Figure 1: an easy block diagram of a fully coherent radar.
(Please hold the mouse-pointer over the dedicated components of the block diagram and you'll get a describing text)

The block diagram on the figure illustrates the principle of a fully coherent radar. The fundamental feature is that all signals are derived at low level and the output device serves only as an amplifier. All the signals are generated by one master timing source, usually a synthesiser, which provides the optimum phase coherence for the whole system. The output device would typically be a klystron, TWT or solid state. Fully coherent radars exhibit none of the drawbacks of the pseudo-coherent radars, which we studied in the previous section.

Functional Characteristics
Duplexer

The duplexer alternately switches the antenna between the transmitter and receiver so that only one antenna need be used. This switching is necessary because the high-power pulses of the transmitter would destroy the receiver if energy were allowed to enter the receiver.

Low Noise Preamplifier

The Low-Noise Preamplifier (LNA) amplifies the very weak backscatter signals. The low noise characteristic is very important: all following amplifiers will amplify the added noise of the LNA! The amplifier has a gain of 18...25 dB. A higher gain would be possible, but this decreases the dynamic of the receiver.

Mixer Stage

The function of the mixer stage is to convert the received rf energy to a lower, intermediate frequency (IF) that is easier to amplify and manipulate electronically. The intermediate frequency is usually 30 or 60 megahertz. It is obtained by heterodyning the received signal with a local-oscillator signal in the mixer stage. The mixer stage converts the received signal to the lower IF signal without distorting the data on the received signal.

IF-Amplifier

After conversion to the intermediate frequency, the signal is amplified in several IF-amplifier stages. Most of the gain of the receiver is developed in the IF-amplifier stages. The first IF- amplifier has got a wide bandwidth and suppress the influence of mirror-frequencies. The center frequency is relatively high, up to 450 MHz nominally. The overall bandwidth of the receiver is often determined by the bandwidth of the stages of the second IF amplifier. The center frequency is about 75 MHz nominally.

Power Amplifier

In this system the transmitting pulse is caused with a small performance in a waveform generator. It is taken to the necessary power with a Power Amplifier followingly. The Power Amplifier would typically be a klystron, Traveling Wave Tube (TWT) or solid state.

Mixer / Exciter

The first stage of cascaded mixers. The function of this mixer stage is to modulate a prospective intermediate frequency (IF) with the transmitting signals waveforms. The I- (in-phase) and Q- (quadrature) signals from the Waveform Generator are defined signals for comparing with the backscatter in the receivers synchronous detector.

Waveform-Generator

The Waveform-Generator generates the transmitting pulse in low- power. It generates the transmitting signal on an IF- frequency. It permits generating predefined waveforms by driving the amplitudes and phase shifts of carried microwave signals. These signals may have a complex structure for a pulse compression.

Phase Sensitive Detector

The IF-signal is passed to a phase sensitive detector which converts the signal to base band, while faithfully retaining the full phase and quadrature information (I & Q- processing) of the Doppler signal.

Radar Signal Processor

The signal processor is that part of the system which separates targets from clutter on the basis of Doppler content and amplitude characteristics. It generates plots and tracks from the videosignals of the receiver.

Radarscope / Monitor

The indicator presents to the observer a continuous, easily understandable, graphic picture of the position of radar targets. In recently radars the indicator would be a computerdisplay.

Publisher: Christian Wolff
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