United States Patent 3720952

1. Apparatus for processing radar signals and the like, comprising Wideband signal receiving and transmitting antenna means; Circulator means having a first terminal connected with said antenna means, said circulator means including also second and third terminals; A first tuned microwave mixer set including a first directional filter, a plurality of first directional filter mixer units each tuned to a different discrete frequency band, and first manifold means connecting said first mixer units with said first directional filter; A second tuned microwave mixer set including a second directional filter, a plurality of second directional filter mixer units corresponding in number with said first mixer units and being tuned to the corresponding frequency bands thereof, respectively, and second manifold means connecting said second mixer units with said second directional filter; First common conductor means connecting the mixture units of the first set with the second terminal of said circulator means, said first conductor means containing series-connected series-connected switch; Second common conductor means connecting the mixture units of the second set with the third terminal of said circulator means; Local oscillator signal generator means; First gate means connecting said signal generator means with all of the mixer units of said first set; A plurality of second gate means connecting said signal generator means with the mixture units of said second set, respectively; And signal processing means having input and output terminals connected with the directional filters of said first and second sets, respectively, for controlling the operation of said switch and of said first and second gating means as a function of the inherent characteristics of signals received by said antenna means and for returning to the directional filter means of said second set a modified facsimile signal.

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International Classes:
G01S7/38; (IPC1-7): H04K3/00
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Primary Examiner:
Feinberg, Samuel
Assistant Examiner:
Montone G. E.
What is claimed is

1. Apparatus for processing radar signals and the like, comprising

2. Apparatus for processing and repeating radar signals and the like, comprising

3. An electronic countermeasure system for processing the aircraft-seeking signals generated by a hostile radar installation and for repeating to said radar installation false target echo signals, comprising

4. An electronic countermeasure system for processing an aircraft-seeking hostile radar signal within a first frequency band and for transmitting to said radar installation a processed false target echo signal having a frequency corresponding with that of the hostile radar signal, comprising

This invention relates generally to an improved electronic countermeasure system for processing the aircraft and spacecraft-seeking signals of one or more hostile radar installations and for repeating to those installations false target echo signals of corresponding frequency.

Many types of electronic countermeasure systems have been proposed in the past for protecting aircraft and spaceborne vehicles against detection by hostile radar. In general the known countermeasure systems -- in addition to being complex and quite expensive -- are often unreliable in operation and are restricted in operational capabilities. Many of the known systems include equipment that is large and massive, thus reducing the useable interior capacity and flight range of the spacecraft. Furthermore, certain types of complex countermeasure systems require manual operation and/or control by highly trained technical personnel, further increasing the size of the flight crew and the attendant problems of aircraft design.

The primary object of the present invention is to provide an improved electronic countermeasure system that is reliable and flexible in operation, that is relatively inexpensive relative to the known systems, and that lends itself to semi-automatic or fully-automatic operation.

A more specific object of the invention is to provide a countermeasure system for aircraft, seaborne and ground installations that is instrumented to perform, in real time, all the important deception repeater jamming operations. The system is operable to repeat pulse or continuous wave signals against anywhere from one to 100 hostile radars operating in either the search or track mode. The system performs also against radars provided with electronic counter-countermeasure means, such as frequency diversity, frequency jumping, and random, staggered, jittered or coded pulse repetition rate frequencies. The present invention, which makes use of programmed computer control means in response to the specific characteristics of the hostile radar signal, is operable to repeat either earlier or later in time the true target echo, whereby the repeated echo appears at a shorter or longer range on a radar display (or as recorded on a data processor). Furthermore, the present system includes doppler correction means that supply a doppler frequency correction to compensate for different simulated vehicle speeds in correlation with the repeated echo.

The system of the present invention, which repeats a signal based on the characteristics of the received signal, may be programmed to change the time of retransmission, the time base (i.e., compress or expand the time frame) or to communicate between a number of systems. In the electronic countermeasure mode of operation, all of the operational features are correlated in terms of time, frequency and phase. The system is also applicable for use in the communication mode as a link in a communication satellite network, for example.

The invention is characterized by the provision of multi-spectral component mixing program means affording precise control of time, frequency and phase. Use is made of novel microwave front end means in combination with special programmed computer control means.

With regard to a typical tactical mission, as the vehicle with the electronic countermeasure deception jamming system approaches the hostile radar, an analysis is continuously made of all program inputs. Such information is partially derived from ancillary equipment in the vehicle, and partly from intelligence supplied prior to the mission. The date from these two sources are associated with real and non-real time. Included are such parameters as pulse repetition frequency, altitude, angle (azimuth and elevation), pulse duration, scan rate, target cross section, radar power, slant range, relative strength of main and side lobes, speed of the vehicle, and the like. The operator of the vehicle selects a predetermined program (on a tape, for example) in accordance with the prearranged tactics and new factors as they develop.

When the vehicle is within range of the hostile radar, the system repeats during real time, the radar signals in both the search and track modes. On each radar display, the false echo signal produced by the system appears at least as strong as the expected target echo (since the system operates as a one-way transmitter as distinguished from the two-way reflection radar system). If the false echo represents the radar signal repeated earlier, it appears at a short range. Furthermore, it can be made to move faster than the target echo -- i.e., it will simulate a higher speed by closing the range faster. At the same time, the doppler frequency shift (corresponding to the higher speed) is also generated. This doppler shift may be achieved at speeds ranging from a few miles per hour to speeds on the order of Mach 5 or greater.

Since the signal from the vehicle may be programmed to come down a sidelobe of the radar beam, the repeated signal will also be false in angle (for both the search and track modes). Even sophisticated monopulse tracking radars could be deceived into tracking with their side lobes.

The system is capable of automatically repeating pulse or continuous wave signals against 100 or more radars, depending on computer capacity, duty cycle, signal characteristics, electronic countermeasure techniques and tactical requirements. The operational capabilities are achieved by automatic processing of the spectral components of the radar signal. Such frequency domain operation utilizes unique techniques to control frequency and pulse transmission instantly and automatically. To this end, the frequency components are filled in or reinserted as directed by the computer program.

Other objects and advantages of the invention will become apparent from a study of the following specification when considered in conjunction with the accompanying drawing, in which:

FIGS. 1 and 2 are simplified and detailed illustrations, respectively, in block diagram form, of the wide band electronic countermeasure deception repeater jammer system of the present invention.

Referring first to FIG. 1, the wide band antenna 1 is of the equiangular (or logarithmic) spiral type broadbanded over 2 or more octaves. Such antennas are particularly suitable for high speed airborne and space vehicles. The antenna phase centers are frequency scanned by frequency scanner 2 at a programmed rate (e.g., 20 or 30 megacycles) during reception and are directed to a specific location during transmission. The frequency scanner is controlled by a programmed computer 3 to perform several functions as will be described in greater detail below. The computer, which may be of any suitable type (for example, the General Electric A-236 Real Time Computer including such units as a conventional clock, counter, ring counter, memory, address matrix, address scanner, subtractor and gate former circuits) is operable to provide the unique results of the present invention. By means of the antenna scanning means, an effective area, up to 180° solid angle, for example, may be scanned from the underside of an airplane wing during reception, and steered to a selected location within nanoseconds during transmission. For any radar mode of operation (i.e., search or track) the system of the present invention will receive, process and repeat continuous wave or radiofrequency pulses in the range covering the microwave bands generally used by radars. In describing system operation, a typical signal range from 2-9 gigacycles has been selected.

During reception (i.e., the scanning period) the radar signal passes through a crossed field amplifier 4 which serves as a passive low loss device (0.5 decibels) in the "receive" direction. The signal enters the microwave front end 5 where it is separated by duplexer 6 into two or more paths depending on the desired signal bands. In the illustrated embodiment, the signal is divided into two bands (specifically, 2-4 and 4-9 gigacycles). Signals falling in the lower and upper bands are fed to the tuned microwave mixer sets 7 and 8, respectively, depending on the signal frequency. Since the operation of the mixers 7 and 8 is identical, in the following description only the processing of the signals in the 2-4 gigacycle range will be described.

Local oscillator 9, which is also controlled by the computer 3, generates signals in the 1-2 gigacycle range that are applied to the tuned mixers 7 and 8 via the 10-gate computer-controlled oscillator gate means 10. The local oscillator 9 may be a carcinotron operating as a voltage tuned backward wave oscillator, or a travelling wave tube with regeneration. The local oscillator frequencies (in the 1-2 gigacycle range) may be obtained by modulating the carcinotron sole with white Gaussian noise at a high frequency rate, for example, in the range 10 to 30 megacycles. This technique effectively fills in "frequency holes" that might result from the use of Gaussian noise alone. The oscillator frequency spectrum then contains all frequencies over the band 1-2 gigacycles. In the illustrated embodiment, the local oscillator gate means comprise diode switches controlled by the computer 3.

The output signal from the tuned microwave mixer set 7, which represents the sum and difference frequency components, is filtered through unit 7 (which passes spectral components in the range 4-7 gigacycles) and is applied to the microwave amplifier 11. At the input to amplifier 11 (which may be a traveling wave tube), the signal level is approximately -90 decibels. For a nominal gain of 25 decibels, the amplifier output is on the order of -65 decibels. Preferably the amplifier 11 is provided with instantaneous automatic gain control for suppressing ring-around action.

The output from the amplifier is applied to the balanced mixer 12 for mixing with a signal that is supplied by the computer-controlled local oscillator 13 via hybrid junction 14 as programmed by the computer. The local oscillator frequency band covers the range of 4.1-7.1 gigacycles. The output signal from mixer 12, is amplified by the broadband intermediate frequency amplifier 15 at 100 ± 60 megacycle bandwidth. Selection of the IF bandwidth is based on the smallest anticipated time delay inherent in the system (on the order of 0.05 to 0.1 microseconds). The local oscillators 9 and 13 may time share a single local oscillator component controlled by computer 3.

The derived 100 ± 60 megacycle broadband signal is fed through the fixed and variable delay lines 16 and 17, and the delayed signal is amplified by the intermediate frequency amplifier 18 and is applied to one input of the balanced mixer 19. As indicated by the broken line 20, the variable delay line 17 is associated with a doppler correcting means 21 that is conventional in the art and includes a variable speed means, servomotor amplifier means, a motor, a generator, a differential generator and an attenuator. While the amplifier 15, the fixed and variable delay means 16 and 17, the amplifier 18, and the doppler means 21 constitute conventional matching components, the delay lines (generally quartz) may be modified in accordance with the anticipated pulse repetition frequency, the simulated vehicle speed (correlated with the doppler frequency shift of the repeated pulse) and the tactical considerations envisioned. In this respect, the range of corrections applicable on doppler frequency shifts will vary from 0.1 to 15 microseconds or higher to cover a range of speeds from 80 miles per hour to Mach 13 or higher. A typical length of the quartz line (for a 500 microsecond delay) is equivalent to about 40 miles in range. The operation and structure of the doppler correcting means will be described in greater detail below. Pulse repetition information is also supplied by the IF amplifier 15 to the computer 3 via conductor 22. The programmed computer automatically utilizes the spacing between consecutive pulses for timing and delay purposes. Consequently, a received signal with random, jittered, staggered or coded pulse repetition frequency will be processed in such a manner that the repeated signal will appear as a valid target return to the hostile radar.

In the balanced mixer 19, the 100 ± 60 megacycle signal is mixed with the 4.1 to 7.1 gigacycle signal supplied by oscillator 13 via hybrid junction 14 as controlled by the computer program. The reconverted output of the mixer 19, having a typical level of -65 decibels, is now a broadband delayed signal. This signal is amplified by microwave amplifier 23 (which comprises, for example, a traveling wave tube) and appears as an approximately -40 decibel signal level that is attenuated by attenuator 24 which supplies a standard level to microwave amplifier 25. This latter amplifier brings the output signal to a level suitable for processing by the microwave front end means 5. Instantaneous automatic gain control may be supplied to microwave amplifier 23 to prevent ring around effects.

The delayed signal that is applied to the mixer set 8 of the front end 5 is filtered to supply spectral components in the 4-7 gigacycle range that are mixed with the 1-2 gigacycle local oscillator signals supplied via the computer controlled gates 10.

The resultant signal, which represents a reconstituted facsimile of the original radar signal that is delayed in time and corrected for a predetermined doppler shift, is then passed through duplexer 6 to the crossed-field amplifier 4 which provides a nominal power gain of approximately 20 decibels. As directed by the computer program, the signal is amplified by the amplifier 4 and is repeated from antenna 1 to a selected location or radar site.

Referring now to FIG. 2, the duplexer 6 of the microwave front end includes a filter diplexer 40 that separates the incoming signal into two or more paths (specifically, those including the bands 2-4 gigacycles and 4-9 gigacycles in the described embodiment). The operation of each band path is substantially identical. The duplexer 6 includes circulators 41 and 42 associated with the respective bands. The 2-4 gigacycle range signals from the filter diplexer 40 are applied, via circulator 41 and nanosecond switch 43, to the input directional filter manifold 44 having a termination 45. The filter manifold coveys the signal to a plurality of directional filter mixers 46-49 which serve as tuning elements and mixers to separate the signal into discrete overlapping narrow band channels. If needed, ancillary equipment may be provided to afford adjustability as desired. Similarly the 4-9 gigacycle range signals from filter diplexer 40 are applied, via circulator 42 and nanosecond switch 53, to the input directional filter manifold 54 having a termination 55. The switching operations of switches 43 and 53 during both the reception and repeating periods are controlled by computer 3. During reception switches 43 and 53 and the diode switch associated with the output 110 of oscillator gate 10 are closed while the diode switches associated with gates 101-109 are open. During repeating, switches 43 and 53 and gate switch 110 are open, while gate switches 101-109 are closed as determined by the computer program. The switches 43 and 53 provide nanosecond operation.

Thus, in the reception period, for a signal in the 2-4 gigacycle range, the local oscillator signal band (1-2 gigacycles) is fed to all tuned mixer elements in such a manner that mixer outputs are produced only in those elements that are tuned to the radar input signal. The mixer output signal, which consists of the sum and difference products, is routed via waveguide or stripline channels (with suitable interfacing joints, if desired) to the output directional filter manifold 60 having a termination 61. The signal passes through directional filter 62 which filters out spectral components in the range of 4-7 gigacycles. Filter 62 is designed with proper bandpass or band rejection skirts to channel out only 4-7 gigacycle components. The spectral output is now passed through filter diplexer 63 to microwave amplifier 11.

In a similar manner, a signal in the 4-9 gigacylce range is processed from circulator 42 via switch 53 to the input directional filter manifold 54. The signal is applied to one or more of the directional filter mixers 66, 67, 68, 69 and 70 (in accordance with signal frequency) and is mixed with the 1-2 gigacycle local oscillator signal gated via diode switch gate 110. The resulting mixer output signal is then routed via waveguide or stripline channels to the output directional filter manifold 72 having a termination 73. The signal is filtered through directional filter 74 which passes the 4-7 gigacycle spectrum components to microwave amplifier 11 via diplexer 63.

The tuning ranges of the directional filter-mixers are as follows:

During During reception transmission filter-mixer 46 134 2.0-2.5 gigacycle filter-mixer 47 135 2.5-3.0 gigacycle filter-mixer 48 136 3.0-3.5 gigacycle filter-mixer 49 137 3.5-4.0 gigacycle filter-mixer 66 138 4.0-5.0 gigacycle filter-mixer 67 139 5.0-6.0 gigacycle filter-mixer 68 140 6.0-7.0 gigacycle filter-mixer 69 141 7.0-8.0 gigacycle filter-mixer 70 142 8.0-9.0 gigacycle

Thus the signal supplied to microwave amplifier 11 contains 4-7 gigacycle spectral components representative of the radar signal in the range 2-9 gigacycles. As noted before, it is amplified by amplifier 11 and is converted in balanced mixer 12 with the local oscillator 4.1-7.1 gigacycle signal supplied via hybrid junction 14 as programmed by computer 3. The resulting signal is amplified by intermediate frequency amplifier 15 with a passband of 100 ± 60 megacycles, and is fed to computer 3 and fixed delay line 16.

The computer 3 performs three distinct functions. First, it stores the pulse repetition frequency information in the memory storage section. Secondly, it controls the timing of all system functions, such as starting, stopping and switching. Finally, it processes pulse repetition frequency information (whether regular or irregular). The storage and timing functions are accomplished in a conventional manner and need not be described in detail. For the processing of the pulse repetition rate frequency, however, novel means are provided for utilizing the difference in time between consecutive pulses to determine a gate width which will cause certain pulses to be repeated at such a time that the hostile radar is deceived (that is to cause the radar to accept the pulse as one of its own reflected signals). Thus, the computer clock 90 times all units of the computer at a given rate (for example, at a 1 megacycle rate). Thus, the signal supplied to computer 3 from the intermediate frequency amplifier 15 via conductor 22 starts a counter 91 which is gated by ring counter 92 operating at a nominal rate of 2 megacycles. The counter 91 resets ring counter 92 which shifts from gate 1 to gate 2 and so forth to gate n. The outputs on lines 1, 2 ... n (corresponding to the gates) are committed to the memory 93. Words t1, t2... tn are called from memory 93 by the address matrix 94 when actuated by the address scanner 95. The address scanner is essentially an addition unit which gates the lines 1, 2 ... n from the memory so that words t1, t2 ... tn will be allowed through subtractor 96. The subtractor puts out differences Δ t1, Δt2 ... Δtn between consecutive pulse intervals into gate former 97 which forms 1 more pulse than the word. Thus a zero time difference produces 1 pulse, 1 unit time difference produces 2 pulses, 2 units produces 3 pulses, and so forth. These pulse outputs from the gate former modulate the crossed field amplifier 4 which repeats the radiofrequency signal in these several pulses so that the hostile radar selects only its own radiofrequency pulse signal and throws out all the other pulses. In this manner, it is possible to repeat effectively against radar with irregular pulse repetition rate frequencies, e.g., staggered, jittered, random, coded signals and the like.

The fixed delay line 16 consists of one or more sections which cover the radar pulse repetition frequency signal range with anticipated pulse intervals. Variable delay line 17 supplies a fine adjustment for the total delay and a rate of change of delay to represent the range rate of the repeated echo. With respect to this latter function, doppler correcting network 21 operates as follows. The variable speed drive 120 is set for the airborne or spaceborne vehicle in which it is installed. The drive output feeds servo amplifier 121 that drives motor 122. The motor, which is calibrated in terms of equivalent feet of delay line, is mechanically linked with variable delay line 17, generator 123, and differential generator 124. As part of the servo loop, the generator smooths out variations in motor speed (whereby the speed is maintained constant) such that the rate of change of the variable delay line is a true equivalent of the input speed information (i.e., the range rate). Differential generator 124 transforms the rate of change of delay line into a doppler voltage which is passed to attenuator 125 and then to microwave amplifier 23 (specifically, to the helix of a travelling wave tube). This results in a phase change of the delayed radiofrequency signal that is correlated with the desired speed of the vehicle at all times.

The delayed intermediate frequency at 100 ± 60 megacycles is mixed in balanced mixer 19 with the 1.4-7.1 gigacycle local oscillator signal band generated by local oscillator 13 and gated by hybrid junction 14. This reconversion produces delayed spectral components which are attenuated and further amplified in microwave amplifier 23.

The delayed signal is routed via filter diplexer 127 to directional filters 128 and 129 which filter out the 4-7 gigacycle spectral components. This signal appears in input directional filter manifolds 130 and 131 having terminations 132 and 133, respectively. The signal is routed to directional filter mixers 134-137 in the 2-4 gigacycle path and to directional filter mixers 138-142 in the 4-9 gigacycle path. Then one or more of the filter-mixer units will be activated with the local oscillator band 1-2 gigacycle signal depending on those diode switch gates 101-109 which have been selected by the computer 3. The resulting mixer output from the activated unit now represents a reconstituted facsimile of the original radar signal delayed in time and corrected for a predetermined doppler shift. The signal (or signals) are then routed, via the output directional filter manifolds 143 and 144 with termination 145 and 146, respectively, to circulators 41 and 42 and to filter diplexer 40. In accordance with the computer program, the delayed and doppler-corrected signal is amplified in amplifier 4 which may be modulated with additional pulse gates as previously described. The signal is now repeated and beamed via wide band antenna 1 to a selected location or radar site.

It is apparent that the system of the present invention constitutes a wide-band, multi-spectral component mixer, duplexer system with computer program control of timing, frequency and phase. The system repeats signals earlier or later with the correct doppler frequency and when feasible, will repeat also at a false angle. The operation may be performed on 100 or more radars, depending on computer capacity and system factors. The system performs satisfactorily even for sophisticated radars using frequency diversity, frequency jumping, monopulse tracking, random, jittered, staggered or coded pulse repetition rate frequency, and so forth.

While in accordance with the provisions of the Patent Statutes, the preferred form and embodiment of the invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made in the apparatus described without deviating from the invention set forth in the following claims.