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Pulse-Doppler systems measure the range to objects by measuring the elapsed time between sending a pulse of radio energy and receiving a reflection of the object. Radio waves travel at the speed of light , so the distance to the object is the elapsed time multiplied by the speed of light, divided by two – there and back.
Pulse-Doppler signal processing separates reflected signals into a number of frequency filters. There is a separate set of filters for each ambiguous range. The I and Q samples described above are used to begin the filtering process. These samples are organized into the m × n matrix of time domain samples shown in the top half of the diagram.
Range and velocity can both be identified using medium PRF, but neither one can be identified directly. Medium PRF is from 3 kHz to 30 kHz, which corresponds with radar range from 5 km to 50 km. This is the ambiguous range, which is much smaller than the maximum range. Range ambiguity resolution is used to determine true range in medium PRF radar.
Regardless, radars that employ the technique are universally coherent, with a very stable radio frequency, and the pulse packets may also be used to make measurements of the Doppler shift (a velocity-dependent modification of the apparent radio frequency), especially when the PRFs are in the hundreds-of-kilohertz range. Radars exploiting ...
The detection made using both PRF can be compared to identify the true range. This comparison depends upon the transmitter duty cycle (the ratio between on and off). The duty cycle is the ratio of the width of the transmit pulse width T {\displaystyle \mathrm {T} } and the period between pulses 1 / P R F {\displaystyle 1/\mathrm {PRF} } .
Other difficulties arise when the interference covariance matrix is ill-conditioned, making the inversion numerically unstable. [5] In general, this adaptive filtering must be performed for each of the unambiguous range bins in the system, for each target of interest (angle-Doppler coordinates), making for a massive computational burden. [4]
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In pulsed radar and sonar signal processing, an ambiguity function is a two-dimensional function of propagation delay and Doppler frequency, (,).It represents the distortion of a returned pulse due to the receiver matched filter [1] (commonly, but not exclusively, used in pulse compression radar) of the return from a moving target.