TABLE OF CONTENTS Measurement of target doppler is directly analogous to range measurement, with time and frequency functions interchanged. In doppler measurement, however, two time and frequency scales must be considered:
The pulsewidth ? and corresponding spectral envelope width B;
The time-on-target t o and corresponding width B f of fine lines in the spectrum of the coherent pulse train.
Radars using CW or long-pulse transmissions may achieve meaningful resolution and measurement on the spectral envelope, but in most cases it is the fine-line spectrum of the coherent pulse train transmission that provides the data.
When doppler shift f d of the signal has been measured, it is related to the radial velocity of the target by
| (8.59) |  |
The purpose of doppler tracking is not always to perform this velocity measurement, but often to achieve resolution of the desired target from clutter and other targets. However, the doppler filter used for resolution provides data on radial velocity, and it is often advantageous to exploit these data in the radar system.
The optimum estimator for the doppler shift of a single pulse or sample of a signal is shown in Figure 8.26. The ? channel is formed by a filter matched to the pulse spectrum. The ? channel applies a discriminator (two filters. displaced from the center of the matched filter) to the matched-filter output, producing a bipolar pulse whose polarity and amplitude indicate the...
