Method of operating a digital radar or sonar apparatus
View Patent ↗A radar or sonar system amplifies the signal received by an antenna of the radar system or a transducer of the sonar system is amplified and then subject to linear demodulation by a linear receiver. There may be an anti-aliasing filter and an analog-to-digital converter between the amplifier and the linear receiver. The system may also have a digital signal processor with a network stack running in the processor. That processor may also have a network interface media access controller, where the system operates at different ranges, the modulator may produce pulses of two pulse patterns differing in pulse duration and inter-pulse spacing, those pulse patterns are introduced and used to form two radar images with the two images being derived from data acquired in a duration not more than twenty times larger than the larger inter-pulse spacing, or for a radar system, larger than one half of the antenna resolution time. One or more look-up tables may be used to control the amplifier. The radar system may generate digital output which comprises greater than eight levels of radar video.
1. A method comprising:
generating a sequence of pulse signals;
converting the sequence of pulse signals to ranging signals, wherein the ranging signals are radar signals of a radar apparatus or sonar signals of a sonar apparatus;
emitting the ranging signals;
receiving passively reflected return signals in response to the ranging signals;
amplifying the return signals, wherein the amplified return signals are analog signals;
converting, by an analog-to-digital converter, the amplified return signals to digital signals;
generating, by a linear demodulator, a digital output from the digital signals representing the amplified return signals; and
processing the digital output for display and/or analysis.
2. The method of claim 1 , wherein the linear demodulator is implemented by a linear receiver comprising a plurality of linear amplifiers.
3. The method of claim 1 , further comprising filtering the amplified return signals by an anti-aliasing filter, wherein the analog-to-digital converter is a sub-sampling analog-to-digital converter.
4. The method of claim 3 , wherein the filtering comprises restricting a bandwidth of the amplified return signals to satisfy the Shannon-Nyquist-Kotelnikov sampling theorem.
5. The method of claim 3 , further comprising filtering the digital signals from the sub-sampling analog-to-digital converter.
6. The method of claim 1 , further comprising displaying a pseudo-colour representation of an amplitude of the return signals from the digital output.
7. The method of claim 1 , further comprising filtering the amplified return signals by an anti-aliasing filter, wherein the converting comprises converting the filtered amplified return signals to the digital signals.
8. The method of claim 1 , wherein the processing is performed by a digital processor, the method further comprising running a network stack on the digital processor.
9. The method of claim 1 , further comprising providing the digital output to a network unit comprising a media access controller and a physical layer interface.
10. The method of claim 1 , wherein:
the sequence of pulse signals comprises pulses of a first pulse pattern interleaved with pulses of a second pulse pattern;
the first and second pulse patterns differ in pulse duration and inter-pulse spacing; and
the processing comprises generating a first image associated with the pulses of the first pulse type and a second image associated with the pulses of the second pulse type.
11. The method of claim 10 , wherein the sequence of pulse signals comprises a plurality of the pulses of the second type interleaved between successive pulses of the first type.
12. The method of claim 1 , further comprising controlling a gain of an amplifier performing the amplifying, wherein the controlling comprises using at least one look-up table containing data for compensating for range-dependent variation of the return signals.
13. The method of claim 12 , wherein the at least one look-up table comprises multiple table regions each associated with a corresponding range.
14. The method of claim 12 , wherein the controlling comprises using a plurality of look-up tables each associated with a corresponding range.
15. The method of claim 1 , further comprising controlling a gain of an amplifier performing the amplifying, wherein the amplifier comprises a plurality of gain stages, wherein the controlling comprises using at least one look-up table containing data for at least one of the gain stages.
16. The method of claim 15 , wherein the at least one look-up table comprises multiple table regions each associated with a corresponding one of the gain stages.
17. The method of claim 15 , wherein the controlling comprises using a plurality of look-up tables each associated with a corresponding one of the gain stages.
18. The method of claim 17 , further comprising:
adding together outputs from the plurality of look-up tables; and
applying saturation logic to the added-together outputs to control the amplifier within a gain control range.
19. The method of claim 1 , further comprising applying non-linear dynamic range matching to the digital output.
20. The method of claim 1 , wherein:
the ranging signals are radar signals;
the ranging signals and the received return signals are X-band signals;
the method further comprises converting the X-band return signals to intermediate frequency return signals;
the amplifying comprises amplifying the intermediate frequency return signals;
the filtering comprises filtering the amplified intermediate frequency return signals;
the analog-to-digital converter is a sub-sampling analog-to-digital converter; and
the converting comprises sampling the filtered amplified intermediate frequency return signals at a sample rate less than the intermediate frequency.