Radar system in which range ambiguity and range eclipsing are reduced by frequency diversity and alternation of pulse periodicity

A method for transmitting and receiving radar signals, said method comprising the steps, with the radar antenna pointed in a particular direction, of:

• generating a timing signal train including at least one sub-timing signal train, each of said sub-timing signal trains including at least first, second and third alternating and sequential pulse repetition intervals characterized by one of a β:1 and a 1:β ratio of (a) the duration from the start time of a given first pulse repetition interval to the start time of a second pulse repetition interval, said second pulse repetition interval next following said first pulse repetition interval, divided by (b) the duration from the start time of said second pulse repetition interval to the start time of a third pulse repetition interval next following said second pulse repetition interval, where β is given by 1+(α D), where α is equal to or greater than unity, and D is the duty cycle of the radar;
• in response to each said sub-timing signal train, transmitting electromagnetic radar pulses from said antenna such that the frequency of transmission in response to the first pulse of said sub-timing signal train is at a first radio frequency and the frequency of transmission in response to the second pulse of said sub-timing signal train is at a second radio frequency, different from said first radio frequency by an amount which allows subsequent separation;
• receiving, during that interpulse period immediately following said first pulse, electromagnetic radar return signals originating in response to said first pulse, to thereby generate first received signals;
• receiving, during that interpulse period immediately following said second pulse, electromagnetic radar return signals originating in response to said first pulse, to thereby generate second received signals;
• receiving, during said third pulse repetition interval, electromagnetic radar return signals originating in response to said second pulse, to thereby generate third received signals;
• concatenating said first and second received signals, with a delay therebetween no less than the duration of said second pulse, to thereby produce a concatenated return signal originating from said first radio frequency pulse, which includes information relating to the presence or absence of targets in an unambiguous range interval extending from the end of said first pulse to near the beginning of said second pulse, and extending from the end of said second pulse to near the beginning of said third pulse repetition interval, but does not include information relating to the presence or absence of targets attributable to signals received during transmission of said second pulse;
• delaying said third received signals by a time duration equal to the said second pulse repetition interval, to thereby produce a delayed third return signal including information relating to the presence or absence of targets in the interval which coincides with ranges extending at least from the beginning of said second pulse to near the beginning of said third pulse repetition interval relative to the start of said sub-pulse train;
• and
• combining the information from said concatenated return signal with the information from said delayed return signal to thereby produce signals representing the presence or absence of targets in the interval extending from said end of said first pulse to near said beginning of said third pulse repetition interval range unambiguously and range uneclipsed.

A system for transmitting and receiving radar signals, said system comprising:

• a transmitter operative for transmitting time-sequential pulses including first and second pulses at first and second mutually different frequencies, said first and second pulses being separated by a first time duration;
• a receiver operative for receiving radar return signals at said first frequency during times corresponding to said first time duration and during a second time duration that begins after transmission of the second pulse, which second time duration is different from said first time duration, and also receiving said second frequency during a third time duration;
• and
• a processor operative for processing said radar return signals to provide signals representative of targets lying in an uneclipsed range nominally corresponding to the sums of (a) the sum of said first and second time durations and (b) the duration of said second pulse.