TABLE OF CONTENTS The time delay t d between transmission and reception of a radar signal is related to the target range R by
| (8.47) |  |
Measurement of the time delay is accomplished in two steps: the centroid, or other definable point on the received waveform, is located; the delay between that point in the transmission and its reception is then measured and converted to output data. Estimation of the signal centroid involves the implementation of Figures 8.1 and 8.2 in the time coordinate: formation of time weighting functions f 1( t) and f 2( t) combining them into ?( t), and ?( t), applying them to the input signal a( t), and determining the resulting error signal ?/ ?. These are the same operations as performed on beam patterns for angle measurement, but the process is much more easily implemented in the time domain, using range gates, correlators, or digital operations on samples in time.
The optimum estimator for the centroid of a signal consists of a matched filter, a differentiator, and a zero-crossing detector (Figure 8.20). A narrow impulse, formed when the differentiator output passes through zero, marks the peak of the matched-filter output, which appears with a fixed delay from the centroid of the input signal. The time delay of this impulse, relative to an equivalent event in the generation of the transmitted signal, can...
