TABLE OF CONTENTS The first form of signal processing over a number of sweeps takes place on the face of a cathode ray tube. The phosphor is repeatedly painted by the video over the width of the echo and the noise paints different areas on an A-scope or adds to the brightness of the video "painted" on a plan position indicator (PPI). The modern form is the video integrator or correlator.
The analysis of echo signals over a number of sweeps allows enough time for the recognition and filtering of the signals with different Doppler frequencies. If, for example, an S-band radar (3 GHz) has a pulse width of 1 ?s, there will be 3 000 cycles within the pulse. With a Doppler frequency of 1 000 Hz, there will be 3 000.001 cycles within the pulse, and the Doppler frequency is impossible to recognize over so short a time. If the echoes are observed over tens of milliseconds, this becomes possible. Doppler frequency processing may take place at:
| The amplitude and phase modulation of a notional carrier represent a voltage vector; |
| Polyphase signals (two or more phases) represent the video vector voltages. |
Figure 11.16 shows the complex echo video signal or modulating function sampled in range as an antenna with a Gaussian beam scans past a moving object over clutter. The clutter signal has been drawn, conventionally, with a relative phase angle of zero. In reality, clutter echoes may arrive...
