United States Patent [19]
`Tsou et al.
`
`1111111111111111111111111111111111111 111111111111111 11111111111 11111111 1111
`US005508706A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,508,706
`Apr. 16, 1996
`
`[54] RADAR SIGNAL PROCESSOR
`
`[75]
`
`Inventors: Hsi-Shen E. Tsou, Rancho Palos
`Verdes; Mark T. Core, Placentia;
`James G. Harrison, Cypress; Philip J.
`Moffa, Torrance; Gregory A. Shreve,
`Redondo Beach, all of Calif.
`
`[73] Assignee: TRW Inc., Redondo Beach, Calif.
`
`[21] Appl. No.: 173,540
`
`[22] Filed:
`
`Dec. 23, 1993
`
`Related U.S. Application Data
`
`[63] Continuation-in-part of Ser. No. 117,266, Sep. 7, 1993,
`which is a continuation-in-part of Ser. No. 767,953, Sep. 30,
`1991, Pat. No. 5,315,303.
`Int. Cl.6
`................................................... G01S 13/532
`[51]
`[52] U.S. Cl .............................................. 3411192; 342/110
`[58] Field of Search ..................................... 342/109, 110,
`342/114, 115, 128, 175, 192, 196; 364/724.01
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,270,720 12/1993 Stove ...................................... 342/114
`5,373,460 12/1994 Marks, n ........................... 3641724.01
`
`Primary Examiner-Daniel T. Pihulic
`
`[57]
`
`ABSTRACT
`
`A radar system includes a radar transceiver for generating
`transmit signals and for receiving signals reflected by tar(cid:173)
`gets. The radar system includes a mixer for combining the
`transmit signals and the reflected signals into a mixer signal.
`A radar signal processor includes a sampling device, con(cid:173)
`nected to the mixer, for sampling the mixer signal and for
`generating a sampled mixer signal. A spectrum estimation
`device, connected to the sampling device, generates a range
`profile signal including a plurality of range bins each con(cid:173)
`taining a magnitude of a spectral component. A threshold
`device, connected to the spectrum estimation device, gen(cid:173)
`erates a target space array from the range profile signal. A
`target decision device, connected to the threshold device,
`generates estimated range and speed signals for a closest
`target from the target space array.
`
`5,134,411
`
`711992 Adler ...................................... 342/128
`
`24 Claims, 18 Drawing Sheets
`
`ANTENNA
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`
`46
`
`IPR2016-00293 - Ex. 1006
`Toyota Motor Corp., Petitioner
`
`1
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`26
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`

`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 3 of 18
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`5,508,706
`
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`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 5 of 18
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`5,508,706
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`mm"i'l····t·~·,····t·j'l''"l'Jr'''''[l"''i'6'1''"''7'1''"''[1'"' 1'§'1''"'''1'1'6' 1'''1
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`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 6 of 18
`
`5,508,706
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`100
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`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 7 of 18
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`5,508,706
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`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 8 of 18
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`5,508,706
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`200
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`9
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`

`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 9 of 18
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`5,508,706
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`

`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 12 of 18
`
`5,508,706
`
`MIXER OUTPUT
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`FFT AND MAGNITUDE
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`
`13
`
`

`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 13 of 18
`
`5,508,706
`
`NOISE EQUALIZATION
`
`AVERAGING
`
`FREQUENCY
`FIG. 20
`
`FREQUENCY
`FIG. 21
`
`14
`
`

`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 14 of 18
`
`5,508,706
`
`ADAPTIVE TtflESHOLD DETERMNA TION
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`

`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 15 of 18
`
`5,508,706
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`
`U.s. Patent
`
`Apr. 16, 1996
`
`Sheet 16 of 18
`
`5,508,706
`
`FIG. 27
`
`520
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`
`17
`
`

`
`ll.s. Patent
`
`Apr. 16, 1996
`
`Sheet 17 of 18
`
`S,S08,706
`
`FIG. 28B
`
`RANGE:
`
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`
`18
`
`

`
`U.S. Patent
`
`Apr. 16, 1996
`
`Sheet 18 of 18
`
`5,508,706
`
`RANGE
`
`FIG. 280
`
`19
`
`

`
`5,508,706
`
`1
`RADAR SIGNAL PROCESSOR
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation-in-part of U.S. patent
`application Ser. No. 081117,266 filed Sep. 7, 1993, which is
`a continuation-in-part of U.S. patent application Ser. No.
`071767,953 filed Sep. 30, 1991, now U.S. Pat. No. 5,315,
`303.
`
`BACKGROUND OF THE INVENTION
`
`10
`
`2
`an automotive vehicle for providing a blind spot detector, a
`true ground speed measuring device, a vehicle height mea(cid:173)
`surement device, and other various applications.
`Conventional methods for constructing a radar sensor use
`5 electronics and an antenna which are separate components.
`The electronics are typically packaged inside a sealed con(cid:173)
`ductive box for environmental protection and electromag(cid:173)
`netic shielding. The electronics and the antenna are then
`assembled. Another conventional method packages the elec-
`tronics inside a hom antenna. Still another approach utilizes
`feed assemblies in combination with reflector or lens
`antenna systems. Such designs are bulky and expensive.
`Therefore, a radar system which integrates the electronics
`and the antenna system into a compactly packaged radar
`system is desirable.
`Conventional digital radar signal processors are typically
`bulky, are unable to provide reasonable target reporting
`response times, and/or are too costly to allow use in vehicle
`20 radar systems. Other conventional vehicle radar signal pro(cid:173)
`cessors have been unable to operate in environments with
`noisy signals and with high clutter, for example clutter
`caused by roadsigns, guardrails, etc.
`Conventional, cost effective vehicle radar signal proces-
`25 sors have also encountered significant problems tracking a
`vehicle which has variable velocity, acceleration and range,
`and tracking a single vehicle when other vehicles are
`present.
`Conventional vehicle radar signal processors typically
`include relatively costly and complex processors to perform
`complex mathematical routines such as variable-point arith(cid:173)
`metic and/or perform many operations using division. Divi(cid:173)
`sion is relatively time consuming to perform using a micro-
`processor as compared with other operations.
`Therefore, an improved radar signal processor addressing
`the above shortfalls of conventional radar signal processors
`is desirable.
`
`30
`
`35
`
`1. Technical Field
`This invention relates to radar systems and, more particu- 15
`larly, to a radar signal processor for a radar system.
`2. Discussion
`Radar sensors are generally employed for detecting
`objects within a desired field. Typical sensing systems have
`been developed which employ radar, laser, infrared (IR), or
`ultrasonic principles. However, each of these systems has its
`drawbacks. Current radar sensors operate at frequencies
`which are too low to incorporate the advanced monolithic
`millimeter wave integrated circuit (MMIC) and compact
`patch antenna technology. Generally, these sensing units are
`bulky and difficult to integrate into a host system. In
`addition, current radar sensing units require a large number
`of components which make the units costly. As a result,
`these systems are limited in modularity and flexibility, and
`therefore, applications. Typical laser sensors generally suffer
`from high cost, in addition to potential health hazards.
`Furthermore, they are limited by environmental conditions
`such as fog and smoke. Infrared and ultrasonic sensors have
`limitations which include sensitivity to environmental inter-
`ferences, as well as interference from other similar sources,
`in addition to noise.
`There is a need for an effective compact, flexible and
`integrated radar sensor that can be easily integrated into
`many systems for various applications. In particular, there 40
`exists a need for a compact, low cost, flexible radar sensor
`for automotive and space and defense-related applications
`and the like. Such applications may include integrating such
`a radar sensor onto an automotive vehicle to provide a blind
`spot detector for crash avoidance purposes. For advanced 45
`vehicle designs, such as those involving four-wheel drive
`functions, there is a need for a smart sensor to determine the
`true ground speed of the vehicle for cruise control purposes,
`accurate vehicle speed measurement, and four-wheel steer(cid:173)
`ing. In addition, there exists a need for a smart sensor to 50
`determine the vehicle height and to project the road surface
`ahead for advanced adaptive suspension systems. Further(cid:173)
`more, for military applications, there exists a need for a
`compact, modular, low cost sensor for collision avoidance
`on armored vehicles, heavy robotic equipment and all types
`of transportation equipment during night operations and
`under adverse conditions such as fog and battle field smoke.
`Sensor systems have been developed and provided for
`such applications. Typical systems have generally employed
`radar, laser, infrared, and ultrasonic sensors. However, these 60
`systems have not been widely deployed because of high
`cost, poor performance, excessive size, and limited flexibil-
`ity.
`It is therefore desirable to obtain an effective, low cost,
`compact and safe to operate radar sensor. It is further 65
`desirable to obtain such a radar sensor which can be easily
`integrated into various systems. Such a system may include
`
`SUMMARY OF THE INVENTION
`
`A radar system includes a radar transceiver for generating
`transmit signals and for receiving signals reflected by tar(cid:173)
`gets. The radar system includes a mixer for combining the
`transmit signals and the reflected signals into a mixer signal.
`A radar signal processor includes a sampling device, con(cid:173)
`nected to the mixer, for sampling the mixer signal and for
`generating a sampled mixer. signal. A spectrum estimation
`device, connected to the sampling device, generates a range
`profile signal including a plurality of range bins each con(cid:173)
`taining a magnitude of a spectral component. A threshold
`device, connected to the spectrum estimation device, gen(cid:173)
`erates a target space array from the range profile signal. A
`target decision device, connected to the threshold device,
`generates estimated range and speed signals for a closest
`target from the target space array.
`In a further feature of the invention, the spectrum esti(cid:173)
`mation device includes a time window device, connected to
`the sampling device, for generating a windowed signal by
`multiplying the sampled mixer signal with a time window
`function to reduce spectral leakage. The time window func(cid:173)
`tion can be a raised cosine function. The spectrum estima(cid:173)
`tion device can further include a generating device, con(cid:173)
`nected to the time window device, for generating a
`frequency spectrum signal including a series of spectral
`components. The generating device can use a fast fourier
`transform to generate the frequency spectrum signal.
`
`55
`
`20
`
`

`
`5,508,706
`
`3
`In a further feature of the invention, the spectrum esti(cid:173)
`mation device can further include a magnitude device,
`connected to the generating device, for generating a mag(cid:173)
`nitude range profile signal including a plurality of range bins
`each containing magnitudes of the spectral components. The 5
`spectrum estimation device can further include an equaliza(cid:173)
`tion device, connected to the magnitude device, for gener(cid:173)
`ating an equalized range profile signal including a plurality
`of range bins having a noise floor substantially constant with
`respect to frequency.
`In still a further feature of the invention, the spectrum
`estimation device can further include an averaging device
`connected to the equalization device, for integrating the
`equalized range profile signal with at least one prior range
`profile signal to generate an integrated range profile signal
`and to increase signal to noise ratio thereof.
`In still another feature of the invention, the threshold
`device generates a threshold range profile signal including a
`plurality of range bins and includes a comparing device for
`comparing the range bins of the threshold range profile
`signal with range bins of the integrated range profile signal.
`The threshold device generates target flags for range bins of
`the range profile signal having a magnitude above a corre(cid:173)
`sponding range bin of the threshold range profile signal. The
`magnitude of the range bins of the threshold range profile
`signal are related to the magnitude of a plurality of adjacent
`range bins of the range profile signal. The threshold device
`can further include an averaging device with a moving
`window for averaging magnitudes of a plurality of adjacent
`range bins in the range profile signal. A multiplying device 30
`can multiply the average by a threshold constant to generate
`a detection threshold value for one range bin in the threshold
`range profile signal. An incrementing device increments the
`moving window. The control means repeatedly actuates the
`averaging device, the multiplying device, and the increment- 35
`ing device to generate detection threshold values for each
`range bin of the threshold range profile signal.
`The threshold device can further include a centroiding
`device for combining target flags in adjacent range bins and
`for generating a single target flag in a range bin central to the
`adjacent range bins.
`And still another feature of the invention, the target
`decision device includes first estimation means for executing
`an acquisition mode by performing a Hough transform to 45
`derive target range and speed for at least one target using the
`target space array.
`And still another feature of the invention, the target
`decision device includes a second estimation means for
`executing a tracking mode by performing a Hough transform 50
`to derive target range, speed and acceleration for at least one
`target using the target space array.
`Other objects, features and advantages will be readily
`apparent.
`
`40
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`55
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`4
`FIG. 2b is a block diagram which illustrates an alternate
`embodiment of a monolithic millimeter wave integrated
`circuit (MMIC) transceiver;
`FIG. 3 is a schematic diagram which illustrates a milli(cid:173)
`meter wave band microstrip patch antenna design example;
`FIG. 4 is a block diagram which illustrates the major
`functions of a digital signal processor in accordance with the
`present invention;
`FIGS. 5a-5d are assembly views of a compact radar
`10 sensor module example;
`FIG. 6 is an assembly view of a compact packaging
`system for a radar system according to the present invention;
`FIG. 7 is a view of a radar circuit fabricated on a bottom
`15 surface of a dielectric substrate;
`FIG. Sa is a top view of the radar system of FIG. 6 after
`assembly and further illustrating a frequency selective sur(cid:173)
`face having cross dipole arrays;
`FIG. Sb is an enlarged view of one alternate frequency
`20 selective surface having Jerusalem cross dipole arrays;
`FIG. 9 is an end view of the assembled radar system of
`FIGS. Sa and Sb;
`FIG. lOa is a top view of a slot radiator according to the
`25 prior art;
`FIG. lOb is a side view of the slot radiator of FIG. lOa;
`FIG. lla is a top view of a slot radiator including a
`reflector ground plane according to the prior art;
`FIG. llb is a side view of the slot radiator with the
`reflector ground plane of FIG. lla;
`FIG. l2a is a top view of a slot-coupled patch radiator
`according to the prior art;
`FIG. l2b is a side view of the slot-coupled patch radiator
`of FIG. l2a;
`FIG. 13a is a top view of a slot-coupled radiator incor(cid:173)
`porating a frequency selective surface according to the
`present invention;
`FIG. 13b is a side view of the slot-coupled radiator
`incorporating a frequency selective surface of FIG. 13a;
`FIG. l4a is a perspective view of a vehicle incorporating
`the radar system of FIG. 6 in a side view mirror and taillight
`assembly;
`FIG.l4b is a top view of the side view mirror of FIG. l4a;
`FIG. 14c is a top view of the taillight assemble of FIG.
`l4a;
`FIG. 15 is an electrical block diagram of a radar signal
`processor according to the invention;
`FIG. 16 is an electrical block diagram of a spectrum
`estimation device and an adaptive threshold device of FIG.
`15 in further detail;
`FIG. 17 illustrates a sampled mixer output signal gener(cid:173)
`ated by a data sampling device of FIG. 15;
`FIG. lS illustrates a time domain window function and a
`windowed signal generated by a time domain window
`device of FIG. 16;
`FIG. 19 illustrates a magnitude range profile signal
`including a plurality of range bins generated by a magnitude
`determining device and a fast fourier transform device of
`FIG. 16;
`FIG. 20 illustrates an equalized range profile signal gen(cid:173)
`erated by a noise equalization device of FIG. 16;
`FIG. 21 illustrates an integrated range profile signal
`including a plurality of range bins generated by an averaging
`device of FIG. 16;
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The various advantages of the present invention will
`become apparent to those skilled in the art by reading the 60
`following specification and by reference to the following
`drawings in which:
`FIG. 1 is a schematic block diagram which illustrates a
`compact millimeter wave radar sensor in accordance with
`the present invention;
`FIG. 2a is a block diagram which illustrates a monolithic
`millimeter wave integrated circuit (MMIC) transceiver;
`
`65
`
`21
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`FIG. 22 illustrates a threshold range profile signal gener(cid:173)
`ated by the adaptive threshold device of FIG. 16 and the
`integrated range profile signal;
`FIG. 23 illustrates flags generated when the integrated
`range profile signal exceeds the threshold range profile 5
`signal as performed by the adaptive threshold device of FIG.
`16;
`FIG. 24 illustrates centroiding performed on the flags
`generated in FIG. 23 by the adaptive threshold device of
`FIG. 16;
`FIG. 25 illustrates a target space array including a stack of
`past target profile signals as maintained by the adapted
`threshold device of FIG. 16;
`FIG. 26 illustrates Hough transforms performed by a 2-D
`parameter estimation device of FIG. 15 on target space
`arrays provided by the adaptive threshold device;
`FIG. 27 illustrates a 2-D range-speed histogram; and
`FIGS. 28A-28D illustrate a 3-D range-speed-acceleration
`histogram generated by a 3-D parameter estimation device 20
`ofFIG. 15.
`
`10
`
`6
`nected to the output of the automatic gain control amplifier
`32 for receiving a signal therefrom. The analog-to-digital
`converter 34 is further adapted to receive a clock signal from
`clock 37 of digital signal processor 16 and provide a digital
`output to the digital signal processor 16. Analog-to-digital
`converter 34 is a standard off-the-shelf 8-bit converter and is
`capable of handling IF signals and providing a dynamic
`range of about 48 Db. A digital-to-analog converter 36 is
`further connected to digital signal processor 16 for receiving
`an input signal therefrom. The digital-to-analog converter 36
`is adapted to provide a gain control signal to the automatic
`gain control amplifier 32 which provides a dynamic range of
`about 50 dB. The automatic gain control amplifier 32 in
`combination with the analog-to-digital converter 34, the
`digital signal processor 16, and the digital-to-analog con-
`15 verter 36 make up a dynamic range adjustment control loop
`35. Control loop 35 provides for the dynamic range required
`to process the variations in target reflections and the range
`of distance desired.
`An FM modulator 40 is connected to digital signal
`processor 16 for receiving a square wave signal therefrom.
`FM modulator 40 is configured for providing a triangular
`modulation waveform signal at the same periodicity as the
`square waveform. The output of FM modulator 40 is con(cid:173)
`nected to the input of the voltage controlled oscillator 20 of
`transceiver 12 for providing the frequency modulated signal
`thereto.
`Digital signal processor 16 is further connected to. an
`external interface 42. External interface 42 provides con(cid:173)
`nection to an output display 44 and input terminals 46.
`Digital signal processor 16 is manufactured by AT&T and
`has a model number DSP 16. Other suitable digital signal
`processors such as a Motorola 56001 and Texas Instruments
`TMS320C15 may also be used. Digital signal processor 16
`performs all the necessary processing and embedded intel(cid:173)
`ligence functions therein. Processor 16 includes processing
`capabilities for providing digital filtering, integrations and
`various other processing functions. In essence, digital signal
`processor 16 is adapted to provide control signals and detect
`any reflected signal from objects within the field being
`monitored and provide output responses therefrom. From
`the frequency shift and other information, the digital signal
`processor 16 provides the distance information.
`A compact voltage regulator 47 provides the +5 v DC
`supply from a 12 v DC supply. Another compact voltage
`regulator 48 provides the+ 10 v DC supply from the 12 v DC
`supply. In a different embodiment, different voltage regula(cid:173)
`tors may be used to provide the +5 v and +10 v DC from
`other voltage sources.
`FIG. 2a is a block diagram which illustrates one embodi(cid:173)
`ment of the monolithic millimeter wave integrated circuit
`(MMIC) transceiver 12. Transceiver 12 includes a voltage(cid:173)
`controlled oscillator (VCO) 20 adapted to receive the FM
`modulation signal from FM modulator 40 and provide a
`frequency modulated carrier signal therefrom. Voltage con(cid:173)
`trolled oscillator 20 includes a single high electron mobility
`transistor (HEMT) and an associated tank circuit for pro(cid:173)
`viding the carrier signal. The voltage controlled oscillator 20
`is modulated by applying, a voltage to a varactor located in
`an oscillator tank circuit. Connected to the output of the
`voltage controlled oscillator 20 is a two-stage amplifier 22
`having a first amplifier stage 21 and second amplifier stage
`23. Amplifier 22 amplifies the signal which is then trans(cid:173)
`mitted to the antenna 14 through the duplexer 24 and the
`coupler 25. The output of amplifier 22 is connected to port
`D of the coupler 25. The port E of the coupler 25 is
`connected to the port A of the duplexer 24. The transmit
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`25
`
`Turning now to FIG. 1, a schematic block diagram is
`shown therein which illustrates a compact millimeter wave
`(MMW) radar sensor 10 in accordance with the present
`invention. Radar sensor 10 employs a monolithic millimeter 30
`wave integrated circuit (MMIC) transceiver 12. The trans(cid:173)
`ceiver 12 provides MMW transmit and receive functions
`which are integrated onto a single monolithic chip 13 using
`standard photolithographic techniques known in the art.
`Transceiver 12 includes a voltage controlled oscillator 35
`(VCO) 20 which is connected to an amplifier 22. Amplifier
`22 is further connected to a coupler 25 which is connected
`to port A of duplexer 24. A pre-amplifier 28 is connected to
`port B of duplexer 24 for amplifying a reflected signal
`received by antenna 14. A balanced mixer 26 is provided 40
`which has an input connected to the output of pre-amplifier
`28. Balanced mixer 26 is further adapted to receive a leakage
`signal which is the result of the coupler 25 output of the
`transmitted signal generated by the voltage controlled oscil(cid:173)
`lator 20 and the transmit amplifier 22. Balanced mixer 26 is 45
`adapted to provide the difference between the transmit signal
`and the reflected signal. The output of balanced mixer 26 is
`an intermediate frequency (IF) known as the beat frequency
`which contains the range information. In an alternate
`embodiment, duplexer 24 and coupler 25 may be removed 50
`and replaced with a simple coupler to allow for further cost
`savings and smaller size.
`An antenna 14 is connected to port C of duplexer 24. The
`antenna 14 can be a microstrip patch antenna. Other antenna
`configurations will be readily apparent to those skilled in the 55
`art. The antenna 14 is adapted to transmit a high frequency
`modulated carrier signal throughout a desired field to be
`monitored. This transmitted signal may have a frequency of
`around 35 to 94 GHz. Higher frequency signal may also be
`employed. Antenna 14 is further adapted to receive a 60
`reflected signal Which is the result of the transmitted signal
`reflecting off of objects located within the field.
`An IF pre-amplifier 30 is connected to the output of the
`balanced mixer 26 for amplifying the IF output signal
`therefrom. Connected to the output of IF pre-amplifier 30 is 65
`an automatic gain control amplifier 32 which provides high
`dynamic range. An analog-to-digital converter 34 is con-
`
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`output to the antenna 14 is through port C of the duplexer 24.
`The combination of voltage controlled oscillator 20 in
`connection with the amplifier 22 forms a transmitter 50.
`Transceiver 12 further includes a two-stage pre-amplifier
`28 having a first stage 29 and second stage 27. Pre-amplifier 5
`28 is adapted to receive and amplify the reflected signals
`gathered by the antenna 14. The balanced mixer 26 is
`connected to the output of the pre-amplifier 28. Together,
`balanced mixer 26 and the pre-amplifier 28 form the receiver
`52. The duplexer 24 and the coupler 25 form a network for 10
`isolating the transmitter 50 from the receiver 52. The coupler
`provides the reference transmit signal path to the balanced
`mixer 26 of the receiver 52 and the transmit path to the
`duplexer 24 and antenna 14. The balanced mixer 26 provides
`the difference between the reference signal and the reflected
`signal to obtain an intermediate frequency (IF) known as the 15
`beat frequency. The resulting beat frequency contains the
`difference in frequency between the two signals.
`In an alternate embodiment of the MMIC transceiver 12'
`as shown in FIG. 2b, the duplexer 24 and the coupler 25 of 20
`the original implementation as shown in FIG. 2a are
`replaced with a simple coupler 31 to allow for further cost
`savings and smaller size of the MMIC transceiver. The
`voltage controlled oscillator 20 and the two-stage transmit
`amplifier 21 and 23 are basically the same as in the original 25
`transmitter except in chip layout. The two-stage amplifier 27
`and 29, and the balanced mixer 26 are similar to the original
`embodiment, except in chip layout and in that the balanced
`mixer 26 is further adapted to receive a leakage transmit
`signal which is used as the reference signal. The leakage 30
`signal is the result of the signal generated by the voltage
`controlled oscillator 20 being transmitted across a leakage
`path 39 from amplifier 23 to amplifier 29 across the new
`coupler 31. This alternate embodiment of the MMIC trans(cid:173)
`ceiver advantageously utilizes this leakage signal while 35
`providing isolation between the transmitter 50 and the
`receiver 52.
`FIG. 3 illustrates the antenna 14 designed as a millimeter
`wave band microstrip patch antenna. A plurality of radiating/
`receiving microstrip patches 54 are provided in a 4X4 array. 40
`In alternate embodiments, a 4x2 and a 4x1 array may also
`be used. Microstrip patches 54 are connected by microstrip
`feedlines 56. The antenna 14 is adapted to be etched on a
`printed circuit board and may be adapted to provide for a
`plurality of such microstrip patches 54 in various array 45
`designs. The array design essentially determines the beam
`shape which may be adapted to provide for various coverage
`requirements for different applications. The resulting
`antenna 14 is small and planar, and has a patch pattern that
`can easily be changed to adapt to various applications and 50
`mounting requirements. For automotive applications, the
`planar antenna enables incorporation of the radar sensor in
`the taillight assembly, side mirror assembly, or rear bumper
`of a vehicle. The particular antenna design example shown
`therein provides for an overall size which is less than 1.5 55
`inches by 1.5 inches. However, various shapes and sizes may
`be used, depending on the particular application.
`FIG. 4 is a block diagram which illustrates the major
`functions of the digital signal processor 16. The signal
`processing functions performed by the digital signal proces(cid:173)
`sor 16 include digital filtering and integration to remove
`clutter, reduce false alarms and to increase sensitivity. The
`embedded intelligence functions include decision logic,
`control, display, annunciation contr