Automatic prf selection to optimize range and doppler visibility in radar tracking

Claim 2

In a moving-target-indication (MTI) radar system for tracking targets, said system having a transmitter for transmitting radar pulses at a selected transmitting frequency, F, a receiver for receiving radar return signals, and a signal processor for cancelling all radar return signals except those having a doppler shift due to a moving target, apparatus for automatically selecting a pulse repetition frequency, PRF, within a given range of PRF''s for optimum range and doppler visibility, comprising computer means for selecting said transmitting frequency, computer means for finding a band of PRF''s between velocity blind regions in said range of PRF''s, where a velocity blind region is a small band of PRF''s centered on a PRF which happens to be the same as the doppler frequency of the target being tracked, or a multiple thereof, computer means for finding a particular PRF within said band of PRF''s which does not have a range blind zone spanning the predicted range of a target being tracked, and radar synchronizing means for timing transmission of radar pulses at said particular PRF by said transmitter, each pulse consisting of electromagnetic energy at said transmitting frequency.

Claim 3

Apparatus as defined in claim 1 wherein, said computer means for finding said particular PRF includes means for causing said computer means for finding a band of PRF''s to find another band of PRF''s between velocity blind regions in said range of PRF''s upon failing to find a PRF within said band of PRF''s which does not have a blind zone spanning the predicted range of a target being tracked, and said computer means for finding a band of PRF''s includes means for thereafter causing said computer means for finding said particular PRF to search the new band of PRF''s for said particular PRF, and further includes means for terminating the resulting iterative search for a band of PRF''s and a particular PRF within said band when a particular PRF is found which does not have a blind zone spanning the predicted range of a target being tracked.

Claim 4

Apparatus as defined in claim 2 including means for selecting said frequency, F, from a plurality of predetermined frequencies, comprising clear channel sensing means connected to said receiver for sensing the magnitude of electromagnetic energy received by said receiver in a plurality of frequency channels, each of predetermined bandwidth spanning a different one of said predetermined frequencies, means for converting said magnitude of energy in each channel to a value in digital form, computer means for sorting said values in digital form in order of magnitude, and computer means for selecting a transmitting frequency corresponding to that frequeNcy of a channel having the lowest of said values of sensed electromagnetic energy.

Claim 5

Apparatus as defined in claim 3 wherein, said computer means for selecting a transmitting frequency includes means for selecting a frequency corresponding to that frequency of a channel having the next lowest of said values of sensed electromagnetic energy during the next iteration of an iterative search for a band of PRF''s and a particular PRF within said band upon said computer means for selecting a transmitting frequency, failing to find a particular PRF within said band of PRF''s which does not have a blind zone spanning the predicted range of a target being tracked in any band of PRF''s between velocity blind regions in said range of PRF''s.

Claim 6

Apparatus as defined in claim 4 wherein said computer means for finding a band of PRF''s between velocity blind regions includes means for finding a band of PRF''s by determining blind regions in accordance with the equation (PRF) 2RpF/cn + or -Delta (PRF) where n 1,2,3. . . ,c is the speed of light, and Delta (PRF) is a predetermined value included to allow for half widths of velocity blind regions for a predicted radial velocity, Rp, of a target being tracked and said selected frequency, F, a different velocity blind regions resulting for each value of n, and a different band of PRF''s allowable for tracking falling between successive velocity blind regions.

Claim 7

Apparatus as defined in claim 5 wherein said computer means for finding a particular PRF within said band of PRF''s which does not have a range blind zone spanning the predicted range, Rp, of a trarget being tracked includes means for determining the range blind zone for each PRF within said band of PRF''s until one is found not having a range blind zone spanning said target at said predicted range in accordance with the following equation Rn cn/2(PRF) where n is an integer 1,2,3. . . ,c is the speed of light, and Rn is the beginning of a blind range zone of predetermined width, delta .

Claim 8

Apparatus as defined in claim 6 wherein said means for determining a band of PRF''s by determining blind regions includes means for determining an approximation (PRF) about RPF/(2.94(10)8 + or - Delta F)n where Delta F is a percentage factor to allow for the half width, Delta (PRF), of each velocity blind region.

Claim 9

Apparatus as defined in claim 6 wherein said means for determining the range blind zone for finding range blind zones for each PRF within said band of PRF''s includes means for determining an approximation Rn about 81 (10)3n/(PRF) of the equation Rn cn/2(PRF) and the half width, delta , of each range blind zone is as predetermined.

Claim 10

In a radar system having a transmitter and a receiver for tracking targets, apparatus for automatically selecting a pulse repetition frequency, PRF, at a transmitting frequency to use for the next dwell in updating track data of a selected target, said data including predicted range, Rp, and radial velocity, Rp, and said PRF being selected to assure target visibility in range and doppler shift of radar return signals in order to be able to update said target data, said apparatus comprising computer means for calculating possible bands of PRF''s between adjacent velocity blind regions which are within upper and lower limits of PRF for said radar system using the equation (PRF) 2RpF/cn + or - Delta (PRF) where n 1,2,3 . . . ,c is the speed of light, and Delta (PRF) is a predetermined value included to allow for half widths of velocity blind regions resulting from lack of target visibility in doppler shift for said predicted radial velocity, Rp, and said selected transmitting frequenCy, F, a different velocity blind region resulting for each value of n, computer means for calculating the highest PRF within the highest of said bands of PRF''s which places said selected target outside of range blind zones at ranges between Rn and Rn+ delta , where delta , a constant known width of each blind zone, is a function of radar receiver dead time which commences concurrently with each radar pulse transmission, and Rn is the range to the nth blind zone calculated by said computer means from the equation Rn cn/2(PRF) where n 1,2,3 . . . , and c is the speed of light, signal generating means for generating a transmitting signal at said selected transmitting frequency, and radar synchronizing means for timing transmission of radar pulses at said pulse repetition frequency by said transmitter, each pulse consisting of electromagnetic energy at said selected transmit frequency.

Claim 11

In a radar system having a transmitter and a receiver for tracking targets, apparatus for automatically selecting a pulse repetition frequency, PRF, at a transmitting frequency to use for the next dwell in updating track data of a selected target, said data including predicted range, Rp, and radial velocity, Rp, and said PRF being selected to assure target visibility in range and doppler shift of radar return signals in order to be able to update said target data, said apparatus comprising computer means for calculating possible bands of PRF''s between adjacent velocity blind regions which are within upper and lower limits of PRF for said radar system using the equation (PRF) 2RpF/cn + or - Delta (PRF) where n 1,2,3 . . . ,c is the speed of light, and Delta (PRF) is a predetermined value included to allow for half widths of velocity blind regions resulting from lack of target visibility in doppler shift for said predicted radial velocity, Rp, and said selected transmitting frequenCy, F, a different velocity blind region resulting for each value of n, computer means for calculating the highest PRF within the highest of said bands of PRF''s which places said selected target outside of range blind zones at ranges between Rn and Rn+ delta , where delta , a constant known width of each blind zone, is a function of radar receiver dead time which commences concurrently with each radar pulse transmission, and Rn is the range to the nth blind zone calculated by said computer means from the equation Rn cn/2(PRF) where n 1,2,3 . . . , and c is the speed of light, signal generating means for generating a transmitting signal at said selected transmitting frequency, and radar synchronizing means for timing transmission of radar pulses at said pulse repetition frequency by said transmitter, each pulse consisting of electromagnetic energy at said selected transmit frequency.

Claim 12

Apparatus as defined in claim 9 including means for selecting said frequency, F, from one of a plurality of predetermined frequencies comprising means for sensing the magnitude of electromagnetic energy received by said receiver in a plurality of frequency channels, one channel for each of said predetermined frequencies, means for converting said magnitude of energy in each channel to a value in digital form, computational means for sorting said values in digital form in order of magnitude, and computer means for selecting said transmitting frequency, F, to be that frequency of a channel having the lowest of said values of electromagnetic energy sensed.

Claim 13

Apparatus as defined in claim 10 wherein said signal generating means comprises means for generating a plurality of signals, one for each of said predetermined frequencies, and means for gating out to said transmitter the one transmitting signal at said selected frequency.

Claim 14

Apparatus as defined in claim 11 wherein said radar synchronizing means comprises a source of clock pulses, and a counter for counting a predetermined number of clock pulses directly proportional to the reciprocal of PRF to time transmission of said radar pulses during a tracking swell, one radar pulse for each predetermined number of clock pulses.