Radar with PRF alteration on receive

A radar system achieves unambiguous target range at a given PRI, in conjunction with unambiguous Doppler, by transmitting CW-LFM pulses and then separating the return signal into subpulses, without requiring any modifications to the transmit waveform. The CW-LFM pulses may be contiguous. The return signals are bandpass-filtered to generate the subpulses, and downconverted to a common frequency such as baseband. Each downconverted subpulse is matched-filtered to the FM slope, and the resulting matched-filtered subpulses are time-aligned. The time-aligned subpulses are Doppler-filtered to determine target velocity.

BACKGROUND

Radar, lidar, and sonar systems are in widespread use for military, commercial, and private purposes. Radar systems have well-known characteristics, in that long-range detection of small targets is known to require transmission of more power, higher-gain antennas, and/or more sensitive receivers than that or those required for short-range detection of large targets. Lidar and sonar systems have equally well known characteristics. Among the characteristics of radar systems used for detecting targets at long range are those relating to range ambiguity, which has to do with reception of signals returned from a target lying beyond the range defined by the pulse repetition interval, which may make the distant target appear to be near the radar system. Another such characteristic of radar is that of range eclipsing, which has to do with the inability of a radar receiver to receive return signals during the pulse transmission interval.

Radar, lidar and sonar systems are used, among other purposes, for volume surveillance and target tracking in both commercial and military contexts. Ideally, a radar (lidar, sonar) system would detect targets at any range within selected limits, and provide information allowing determination of the range, velocity, and azimuth and elevation position of the target. There are well-known limitations to which such systems are subject, such that the maximum range is limited by the available transmit power and the sensitivity of the receiver. Pulsed radar systems transmit their power in pulses of given duration, and “listen” for return or reflected signals during inter-pulse periods. For a given maximum transmit power, the breaking up of the radar transmissions into pulses necessarily results in transmission of less than the maximum possible total power, as transmissions cease during the inter-pulse listening periods defined by the Pulse Recurrence Frequency (PRF) and the pulse duration. The Pulse Recurrence Frequency (PRF) is the inverse of the Pulse Recurrence Interval (PRI). In order to obtain maximum range, it is desirable to transmit the maximum available total power in a continuous-wave (100% of the time) manner.

A conventional solution to range eclipsing is to vary the pulse repetition interval, so that the transmitted pulses are staggered over time, thereby allowing the receiver to periodically “see” returned signals at times which would otherwise be lost or eclipsed. The eclipsing still occurs for each individual pulse train, but the totality of the radar returns over time includes information which fills in the gaps attributable to the individual transmitted pulse trains. The tradeoff is that a longer time is required to produce all the information required for an uneclipsed view of the region. Another possible solution to range eclipsing is to reduce the duty cycle of the radar by reducing the transmitted pulse duration, to thereby reduce the duration of the eclipsing.

The reduction of the pulse duration, however, tends to reduce the transmitted energy, which reduces the range sensitivity, which again requires a longer period of integration in order to obtain the same effective range.

Another possible solution to range eclipsing is to reduce the duty cycle of the radar by increasing the pulse repetition interval, to thereby move the increased range interval to a distant range not of interest. The reduction of the duty cycle and increase in the pulse repetition interval, however, tends to consume additional radar resources resulting in a greater overall time required for completion of a surveillance scan.

Conventional range ambiguity resolution techniques require transmission of additional signals with additional dwells for resolving the range interval of the ambiguous target. The additional dwells or transmissions consume additional radar resources, resulting in a greater overall time required for completion of a surveillance scan. U.S. Pat. No. 6,639,546, issued Oct. 28, 2003 in the name of Ott et al. describes a radar system which provides unambiguous and uneclipsed range by virtue of pulse-to-pulse frequency diversity, in combination with alternating interpulse intervals and processing which fills in target information in ranges which would otherwise be eclipsed by transmitted pulses. The pulse-to-pulse frequency diversity provides a tag for each pulse that allows the individual pulses to be separately identified.

Continuous-wave linear-frequency-modulation (CW-LFM) radars use LFM waveforms with 100% duty cycle.FIG. 1Ais a simplified amplitude-range/time diagram illustrating the unambiguous range associated with a single pulse10transmission, as from a ship12, with a given PRF. InFIG. 1A, the transmitted pulse is illustrated as10, and the unambiguous range at which a return is received from a first target22is designated R1. A return from a second target24at a range greater than R1also lies within the unambiguous range at a range R2. Both targets20and22lie within the unambiguous range since there is no transmission of a second pulse, or alternatively because the pulse recurrence interval extends beyond the maximum illustrated range.

FIG. 1Bis a simplified amplitude-range/time diagram illustrating transmission of multiple pulses10a,10b,10c,10d, separated by a given pulse recurrence interval (PRI) equal to 1/PRF. InFIG. 1B, the unambiguous range extends from time0to time1/PRF, which is the time at which transmission of the second pulse10bbegins. The first ambiguous range interval extends from time1/PRF to time2/PRF, the second ambiguous range interval extends from time2/PRF to time3/PRF, and the third ambiguous range interval extends from time3/PRF to4/PRF. Targets occurring at ranges within the ambiguous range intervals will appear to be closer to the ship12than their actual range. Thus, the reflected or return signal22afrom target22occurs within the first range ambiguity, so its range may be interpreted as less than its actual range. The reflected signal from target24does not occur within the first range ambiguity interval. The maximum unambiguous range is cT/2, where c is the speed of light and T is the pulse recurrence interval. The maximum unambiguous Doppler is ±λ/4T, where λ is the free-space wavelength. Also inFIG. 1B, the reflected signals24aand24bfrom target24occur in the second and third range ambiguity intervals, respectively, so its range may be interpreted as less than its actual range. InFIG. 1B, increasing the PRF increases the maximum unambiguous Doppler but decreases the maximum unambiguous range, and decreasing PRF increases the maximum unambiguous range, but decreases the maximum unambiguous Doppler.

FIGS. 1C and 1Dare simplified amplitude/Doppler plots illustrating the measured Doppler of the returned target signals due to the transmitted pulse(s) ofFIG. 1AandFIG. 1B, respectively. In both FIGURES, it can be seen that the unambiguous Doppler region extends from 0 to PRF*λ/2. Any target Doppler velocities outside this region will fold over and be ambiguous. InFIG. 1C, no Doppler response is shown, because a single pulse cannot extract radial velocity information from the return signal. InFIG. 1D, the radial velocities of the targets22and24are shown by22E and24E, respectively. The radial velocity of target24is less than PRF*λ/2, and thus its Doppler, marked as24F, is unambiguous. The radial velocity of target22, however, exceeds this limit, and its Doppler, marked as22F, is folded over and ambiguous, therefore it may be interpreted as less than its actual Doppler.

FIG. 2illustrates a frequency-time plot of three sequential linear-FM pulses. InFIG. 2, the frequency range extends from frequency −B/2 to frequency B/2.

Various frequency-modulation schemes have been developed to allow continuous-wave transmission.

SUMMARY

A method according to an aspect of the disclosure is for radar determination of target range and velocity. The method comprises the steps of transmitting a plurality of continuous-wave linearly-frequency-modulated signals toward a target, to thereby generate return or reflected signals. The plurality of continuous-wave linearly-frequency-modulated signals may be contiguous, in that they may occur in sequence without intervening non-signal time. The method further includes the step of receiving return signals including contiguous continuous-wave linearly-frequency-modulated signals with superposed amplitude-range and frequency components associated with each target. The return signals are separated into predetermined different frequency bands, to thereby generate, within each of the frequency bands, band-limited return signal subpulses. Each of the band-limited return signal subpulses is frequency-modulated to a common frequency, such as baseband, to thereby generate a plurality of return signal subpulses at common frequencies. Each of the baseband return signal subpulses at common frequencies is matched-filtered with a linear-frequency-modulated matched filter at the common baseband frequency, to thereby generate matched-filtered return signal subpulses. The matched-filtered return signal subpulses are aligned in time, to thereby generate time-aligned matched-filtered return signal subpulses. The time-aligned matched-filtered return signal subpulses are Doppler-filtered, to thereby generate Doppler signals representing the range(s) and velocity(ies) of each target.

A radar system according to another aspect of the disclosure comprises a controller for generating pulses of linear frequency modulated electromagnetic signals at a given PRI, thereby giving a particular unambiguous target range at the particular PRI. A transmitter is responsive to the control means for transmitting electromagnetic signals toward a target in response to the pulses, thereby generating return signals. A receiver is provided for receiving the return signals to thereby generate received return signals. A processor is coupled to the receiver for filtering the received return signals into different frequency bands and for thereby separating the return signals into disparate-frequency subpulses to thereby generate, within each of the frequency bands, band-limited return signal subpulses. The processor also frequency-modulates each of the band-limited return signal subpulses to a common or to a baseband frequency to thereby generate a plurality of common-frequency or baseband-frequency return signal subpulses. The processor also matched-filters each of the baseband return signal subpulses with a linear-frequency-modulated matched filter response at the common or baseband frequency, to thereby generate matched-filtered return signal subpulses. The processor also aligns the matched-filtered return signal subpulses in time, to thereby generate time-aligned matched-filtered return signal subpulses, and Doppler-filtering the time-aligned matched-filtered return signal subpulses, to thereby generate Doppler signals representing the range and velocity of each target.

DETAILED DESCRIPTION

As mentioned, pulse tagging allows the various transmitted pulses to be separately identified. If a series of N orthogonal pulses or waveforms are transmitted, the maximum unambiguous range can increase by a factor of N over untagged pulses. The maximum unambiguous Doppler can be maintained or remains the same so long as the various orthogonal pulses can be cohered (given a common phase and time) for integration. Frequency modulation can be effective in providing orthogonality.

According to an aspect of the disclosure, each CW-LFM pulse of a set of contiguous LFM pulses can be viewed and treated as a group of N subpulses.FIG. 3illustrates a set310of three contiguous CW-LFM pulses311,312, and313. The three pulses are contiguous, in that the second pulse312begins at the same time t4as the end of the first pulse311, and the third pulse313starts at time t8concurrently with the end of the second pulse312. InFIG. 3, the frequency of first pulse311ranges from −B/2 at time t0to B/2 at time t4. The frequency of second pulse312ofFIG. 3ranges from −B/2 at time t4to B/2 at time t8. The frequency of third pulse313ofFIG. 3ranges from −B/2 at time t8to B/2 at time t12. Each pulse311,312, and313can be viewed as being made up or composed of a plurality of linear FM pulses, the frequency ranges of which in total range from −B/2 to B/2, for a total frequency range of B. For example, first pulse311may be viewed as being made up of N=4 subpulses311a,311b,311c, and311d, each with a frequency range of B/4. Similarly, second pulse312may be viewed as being made up of N=4 subpulses312a,312b,312c, and312d, each with a frequency range of B/4, and third pulse313may be viewed as being made up of N=4 subpulses313a,313b,313c, and313d, each with a frequency range of B/4. Each subpulse covers a different frequency range than other subpulses of the same pulse, and therefore all subpulses in a given pulse are orthogonal. For example, subpulse311aofFIG. 3has a frequency range designated f1, subpulse311bhas a frequency range designated f2, subpulse311cofFIG. 3has a frequency range designated f3, and subpulse311dofFIG. 3has a frequency range designated f4. Each subpulse has duration of (t4−t0)/N and each pulse has duration of T=(t4−t0). According to an aspect of the disclosure, linear-frequency-modulation pulses, such as pulses311,312, and313ofFIG. 3are transmitted by a radar (lidar, sonar) system. When return or reflected signals are received, the subpulses may be viewed as being “tagged” by the identifying frequency of the subpulse, and when so identified can be treated or processed as N subpulses. With particular post-reception processing, the maximum Doppler can be increased by a factor of N while maintaining the unambiguous range equal to that of the basic pulse duration. This technique may be termed PRF Alteration on Receive or PAR.

FIG. 4is a simplified block diagram of a radar system400according to an aspect of the disclosure. InFIG. 4, radar400includes a signal generating transmitter (TX)410which generates linear FM pulses of duration T, such as those ofFIG. 3, under control of a radar control computer (RCC). The linear FM pulses are applied by way of a transmit/receive (T/R) device412to an antenna illustrated by414. Those skilled in the art know that the functions represented by TX block410and T/R412may be distributed among a plurality of locations if antenna414is an array antenna. Antenna414transmits electromagnetic signals at each pulse, and in the presence of a target22or24receives return or reflected signals, as suggested by “lightning bolt” symbol406. Return signals are routed by T/R412to a receiver416, which performs conventional analog processing such as low-noise amplification, frequency filtering, and downconversion to baseband or IF frequencies. For simplicity, receiver416is assumed to also provide time and amplitude quantization such as is ordinarily provided to convert analog signals into digitized signals for further processing. The output of receiver416includes I and Q components of the return signal. The digitized return signals are applied to a processor (PROC) illustrated as a block418, also under the control of radar control computer420. Processing according to an aspect of the disclosure is performed in processor418.

FIG. 5is a simplified block diagram conceptually illustrating the nature of the processing500performed in processor418ofFIG. 4. InFIG. 5, the return signal from receiver416is applied by way of a path512in parallel or in common to a plurality of channels designated C1, C2, C3, and C4, only four of which are illustrated. Those skilled in the art will recognize that there may be more channels than four, or as few as one. InFIG. 5, each of the four channels includes a bandpass filter of a set514of bandpass filters (BPF), for separating or extracting the subpulses from each other. As an example, bandpass filter514aof set514may be tuned or set to pass return signal in the frequency range f1ofFIG. 3, bandpass filter514bof set514of bandpass filters may be tuned or set to pass return signal in the frequency range f2ofFIG. 3, bandpass filter514cof set514of bandpass filters may be tuned or set to pass return signal in the frequency range f1ofFIG. 3, and bandpass filter514dof set514of bandpass filters may be tuned or set to pass return signal in the frequency range f4ofFIG. 3. Thus, the output of BPF514ais subpulse311a, the output of BPF514bis subpulse311b, the output of BPF514cis subpulse311c, and the output of BPF514dis subpulse311d. Those skilled in the art know how to perform bandpass filtering.

It must be understood that the presence of a return signal in any channel C1, C2, C3, or C4ofFIG. 5depends upon the existence of a target at a range corresponding to the band of the subpulse. That is, in the absence of a target, return signals do not exist. Explanations of the operation of radar systems assume that targets at the appropriate ranges exist, so that a return signal is present.

The separated subpulses311a,311b,311c, and311dat the outputs of the bandpass filters of set514of bandpass filters ofFIG. 5are individually downconverted to an intermediate frequency or to baseband. The downconversion is accomplished in a set516of multipliers or frequency converters. Downconversion to an intermediate frequency or to baseband are well known in the art. InFIG. 5, subpulses corresponding to311afrom BPF514aare applied to a multiplier516aand are multiplied by a signal designated LO1to convert the subpulse to baseband. If subpulse311ais already at baseband, no conversion is needed, and multiplier516amay be dispensed with. Subpulses311b,311c, and311dare applied to multipliers516b,516c, and516d, respectively, together with LO2, LO3, and LO4signals, respectively, to convert to baseband or to the selected intermediate frequency. For simplicity in explanation, conversion to baseband is assumed, but intermediate frequencies may be used.FIGS. 6A through 6Gtogether represent the frequency conversion to baseband as may be performed by set516of multipliers ofFIG. 5.FIG. 6Arepresents subpulse311aat baseband, with a frequency range of f1.FIG. 6Brepresents pulse311bin frequency range f2, and arrow610represents the conversion to the frequency range f1.FIG. 6Crepresents pulse311cin frequency range f3, and arrow612represents the conversion to the frequency range f1.FIG. 6Drepresents pulse311din frequency range f4, and arrow614represents the conversion to the frequency range f1. The result of the frequency conversion is to adjust the frequency ranges of the various subpulses to a common frequency range. However, the timing of the various pulses is not common, in that they occur sequentially rather than simultaneously.

The various subpulses converted to a common frequency which are produced at the output of the set516of frequency converters or multipliers ofFIG. 5are applied to a set518of filters matched to linear FM with a bandwidth of B/N and pulse width T/N. Matched filtering is well known in the art. The baseband signal or pulses from downconverter516aare applied to a matched filter518a, the baseband signal or pulses from downconverter516bare applied to a matched filter518b, the baseband signal or pulses from downconverter516care applied to a matched filter518c, and the baseband signal or pulses from downconverter516dare applied to a matched filter518d.FIG. 7is a simplified illustration of the matched filtering for each subpulse. Since all of the subpulses being matched-filtered in set518of matched filters are at baseband, the frequency range of each matched filter of set518ofFIG. 5is the same as that of all the other matched filters of set518. All of the pulses arriving at set518of matched filters ofFIG. 5originated from transmission of linear-FM signals, so the slope or rate of change of frequency as a function of time is the same for all subpulses of a pulse. Reference toFIG. 3shows that each subpulse, as for example subpulse311a, has a frequency range or bandwidth of B/4 (for the case of N=4). Consequently, the characteristic of each matched filter of set518of matched filters has a frequency slope of B/4 Hz in a time equal to T/N, as illustrated inFIG. 7.

As mentioned, the presence of a return signal assumes the presence of a target at the appropriate range. The output of set518of matched filters ofFIG. 5will produce a matched-filter response from one of the filters for each target in response to each transmitted pulse. Thus, a matched filter of set518will produce one match signal for each target in response to each transmitted pulse.FIG. 8illustrates pulse-to-pulse outputs from a single matched filter of set518of matched filters in the presence of a single target. InFIG. 8, the output of one matched filter of set518is illustrated as including a set510of a plurality of match peaks810a,810b,810c, spaced apart in time by pulse recurrence interval T. If the target is in radial motion relative to the radar set, the period between successive ones of the matched-filter pulses of set810will change by an amount related to the radial velocity of the target.

FIG. 9is a plot of frequency versus time illustrating the division of the single transmitted LFM pulse into multiple orthogonal subpulses. Because each of the subpulses extends for the duration of the original LFM pulse, the maximum unambiguous range is maintained while performing PAR processing. It can also be seen that the PRI is increased by a factor equal to the number of subpulses per pulse, thereby increasing the maximum unambiguous Doppler. Also, it can be seen that the bandwidth for each of the subpulses is equal to the bandwidth of the original pulse divided by a factor equal to the number of subpulses per pulse, thereby decreasing the range resolution by this factor.

The frequency-aligned, matched-filtered pulses ofFIGS. 6A and 6Ethrough6G are not, in general, concurrent in time. From each of the matched filters of set518of matched filters ofFIG. 5the frequency-aligned, matched-filtered pulses, each of which may be similar to the plot ofFIG. 8, flow to a corresponding time alignment function of a set520of time alignment blocks520a,520b,520c, and520d. The functions of the time alignment blocks520a,520b,520c, and520dare illustrated inFIGS. 10A,10B,10C,10D,10E,10F, and10G. Time alignment is well known in the art, and should require no additional explanation. More particularly, each time alignment block of set520ofFIG. 5receives one of the frequency-aligned, matched-filtered pulses, and translates it to a common time. For example, the frequency-aligned, matched-filtered pulse resulting from subpulse311aofFIG. 10Ais applied to time alignment block520aofFIG. 5, and is only time converted if not at reference time t0. The frequency-aligned, matched-filtered pulse resulting from subpulse311bofFIG. 10Bis applied to time alignment block520bofFIG. 5, and time converted to begin at reference time t0, as suggested by arrow1001. The frequency-aligned, matched-filtered pulse resulting from subpulse311cofFIG. 10Cis applied to time alignment block520cofFIG. 5, and time converted, as suggested by arrow1002, to begin at reference time t0. Finally, the frequency-aligned, matched-filtered pulse resulting from subpulse311dofFIG. 10Dis applied to time alignment block520dofFIG. 5, and time converted, as suggested by arrow1003, to begin at reference time t0.

The result of the time alignment of the various pulses in set520of time alignment blocks ofFIG. 5is a set of time- and frequency-aligned matched-filtered pulses, such as those illustrated as311a,311b,311c, and311dofFIGS. 11A,11B,11C, and11D, respectively. Doppler filtering is performed on the pulses ofFIGS. 11A through 11Din block522ofFIG. 5, in the direction illustrated by the Doppler Filtering arrows inFIGS. 11A through 11D. In the indicated locations, there are no target returns, so Doppler filtering, while possible, will not result in meaningful information. However, when performed at and near the indicated pulse region, the subpulse-to-subpulse Doppler filtering produces time offset information resulting from the radial motion of the target. Such Doppler processing is well known in the art and requires no further explanation. The Doppler information is made available on path590ofFIG. 5.

FIG. 12represents the information available as a result of the processing in the radar system ofFIG. 5. More particularly, the target return signal amplitude is represented along the amplitude axis, at a time along the Time axis related to the range of the target, and with a particular Doppler along the Doppler axis. Such plots are well known. While a particular ordering of the processing steps has been illustrated inFIG. 5, with some restrictions, other orderings of these steps are possible, and will yield identical results. For example, matched filter processing can occur after Doppler filtering has been performed. Restrictions on orderings include the requirements that frequency-alignment, bandpass filtering, and time alignment (in any order) should occur prior to Doppler filtering.

The table ofFIG. 13tabulates various radar parameters, and in two columns compares the corresponding values for a traditional CW-LFM radar and a CW-LFM radar according to aspects of the disclosure.

Unambiguous range, unlike unambiguous Doppler, cannot be improved by the methods of the disclosure once the PRI is set. Typically, the PRI would be set to provide as large an unambiguous range as possible, and to improve the unambiguous Doppler according to aspects of the disclosure.

The use of the disclosure allows greatly increased maximum unambiguous Doppler without trading off maximum unambiguous range. There is ordinarily a tradeoff between range resolution and maximum unambiguous Doppler. Because the method of the disclosure is performed on receive, the tradeoff can be performed many times.

FIG. 14is a simplified block diagram illustrating how multiple PRIs are simultaneously generated. InFIG. 14, a plurality of PAR processing blocks1412,1414,1416, . . . ,1418of a set1410of PAR processing blocks are fed in common with return signals by way of path512. Each PAR processing block of set1410corresponds generally with the processing500ofFIG. 5. PAR processing block1412processes with N1 subpulses per pulse (subpulses/pulse), PAR processing block1414processes with N2 subpulses per pulse, PAR processing block1416processes with N3 subpulses per pulse, . . . , and PAR processing block1418processes with Nk subpulses per pulse. Thus, the value of N1 in PAR processing block1412might be selected to equal four, in which case PAR processor1412corresponds exactly with processor500ofFIG. 5. Each other PAR processor ofFIG. 14would have a different number of bandpass filters to thereby define a different number of subpulses. Each PAR processor of set1410ofFIG. 14produces different unambiguous Doppler information.

Multiple PRFs can be simultaneously used to perform the tradeoff multiple times between range resolution and maximum unambiguous Doppler. However, both range resolution and maximum unambiguous Doppler cannot both be increased simultaneously. Instead, the multiple PRFs provide different views of the targets present. For example, with a few subpulses, we may discern that two targets are present in range, but we are not sure if any of their velocities are ambiguous. For the same targets, with many subpulses, we may only see one target in range, but can resolve two targets in Doppler and can ascertain that their Dopplers are unambiguous up to a much higher velocity than before. The particular application of the radar system will determine how these different views of the target are combined. Thus, since PRF/PRI is determined on receive, we can simultaneously perform multiple tradeoffs to get various views of any targets present in range and Doppler.

A method according to an aspect of the disclosure is for radar determination of target range and velocity. The method comprises the steps of transmitting (406) a plurality of contiguous continuous-wave linearly-frequency-modulated signals (311,312,313) toward a target (22,24), to thereby generate return or reflected signals. The method further includes the step of receiving (416) return signals including contiguous continuous-wave linearly-frequency-modulated signals with superposed amplitude-range and frequency components associated with each target. The return signals are separated (514) into predetermined different frequency bands (t0-t1, t1-t2, t2-t3, . . . ), to thereby generate, within each of the frequency bands, band-limited return signal subpulses (311a,311b,311c, . . . ). Each of the band-limited return signal subpulses (311a,311b,311c, . . . ) is frequency-modulated for conversion to a common frequency (FIGS. 6Athrough G), such as baseband, to thereby generate a plurality of return signal subpulses at common frequencies (f1). Each of the baseband return signal subpulses at common frequencies is matched-filtered (518) with a linear-frequency-modulated matched filter at the common or baseband frequency (f1), to thereby generate matched-filtered return signal subpulses (FIGS. 6A,6E,6F,6G). The matched-filtered return signal subpulses are aligned in time (520), to thereby generate time-aligned matched-filtered return signal subpulses (FIGS. 10A,10E,10F; and10G). The time-aligned matched-filtered return signal subpulses (FIGS. 10A,10E,10F; and10G) are Doppler-filtered (522), to thereby generate Doppler signals (1210) representing the range(s) and velocity(ies) of each target (22,24).

A radar system according to an aspect of the disclosure comprises a controller (420) for generating pulses (Pulse #1, pulse #2, . . . ) of linear frequency modulated electromagnetic signals at a given PRI, thereby giving a particular unambiguous target range at the particular PRI. A transmitter (410) is responsive to the control means for transmitting electromagnetic signals toward a target in response to the pulses, thereby generating return signals. A receiver (412,418) is provided for receiving the return signals to thereby generate received return signals. A processor (418) is coupled to the receiver for filtering the received return signals into different frequency bands (310) and for thereby separating the return signals into disparate-frequency subpulses (311a,311b, . . . ) to thereby generate, within each of the frequency bands, band-limited return signal subpulses. The processor (418) also frequency-modulates each of the band-limited return signal subpulses to a common or to a baseband frequency (FIGS. 6A through 6G) to thereby generate a plurality of common-frequency or baseband-frequency return signal subpulses. The processor (418) also match-filters (FIG. 7) each of the baseband return signal subpulses with a linear-frequency-modulated matched filter response at the common or baseband frequency, to thereby generate matched-filtered return signal subpulses. The processor (418) also aligns the matched-filtered return signal subpulses in time (FIGS. 10A through 10G), to thereby generate time-aligned matched-filtered return signal subpulses, and Doppler-filtering the time-aligned matched-filtered return signal subpulses (311b,311c, . . . ), to thereby generate Doppler signals representing the range and velocity of each target.