Direct sampling of received signals in radar

A method of processing received radar signals to be integrated into a new radar receiver design comprising:

• a) designing a bandpass filter for an entire tunable bandwidth of the radar system, including choosing a sample rate to facilitate design of the bandpass filter for suppression of aliased image bands and so that a length of an inverse Fast Fourier Transform to be used in g) below is a radix-2 number, or at least a mixed-radix number with small prime factors;
• b) fabricating the bandpass filter and applying the received radar signals to the bandpass filter;
• c) sampling, by an analog-to-digital converter, the received radar signals as filtered by the bandpass filter, directly without use of any downconversion or mixing operations;
• d) transforming the received, filtered, sampled and digitized radar signals to a frequency domain with a Fast Fourier Transform to provide a received signal spectrum;
• e) selecting a portion of the received signal spectrum that matches the frequency band of a transmit pulse;
• f) compensating the selected portion of the received signal frequency spectrum for distortions in the radar receiver, including those introduced by the new bandpass filter;
• g) transforming the selected and compensated portion of the received signal spectrum back to a time domain with the inverse Fast Fourier Transform;
• h) passing the result of g) to a radar signal processor;
• i) repeating c) through h) for all receiver channels in the radar system with the analog-to-digital converters synchronized.

A method for processing in a radar system, received radar signals where the bandwidth of the transmit pulse exceeds the capability of an analog-to-digital converter comprising:

• a) partitioning the received radar signal band into subbands that are to be processed separately, including choosing a width of each subband and a sample rate to facilitate design of bandpass filters for each subband to suppress aliased images;
• b) fabricating the bandpass filters in each subband in accordance with the design, and bandpass filtering the received radar signals in each subband;
• c) choosing a length of a Fast Fourier Transform for each subband to accommodate data at an eventual sample rate for input into a radar signal processor;
• d) sampling for each subband in a respective analog-to-digital converter, the received radar signals as bandpass filtered, directly without use of any downconversion or mixing operations, wherein clocking of all the analog-to-digital converters with a master oscillator;
• e) transforming the received radar signals associated with each transmitted pulse in each subband as bandpass filtered and as sampled to a frequency domain with Fast Fourier Transforms to provide a spectrum in each subband;
• f) selecting portions of the spectrum in each subband that match the respective bandpass filters and zeroing the spectrum not in the selected portions;
• g) normalizing the spectrum in each subband by the corresponding number of analog-to-digital converter samples;
• h) compensating the normalized spectrum in each subband for distortions introduced by the bandpass filter and other microwave components;
• i) transforming the compensated, normalized spectrum in each subband back to a time domain with inverse Fast Fourier Transforms;
• j) resampling results in i) in each subband at the input sample rate of the radar signal processor;
• k) summing the resampled results in j) and inputting the resampled results to the radar signal processor;
• l) repeating c) through k) for all receiver channels in the radar system.