MXPA99006817A - Method and apparatus for rejecting obstruction by rain in a ra system - Google Patents

Abstract

The present invention relates to a method and apparatus for detecting the presence of objects in blind spots of an operator of a vehicle. The apparatus comprises a Doppler radar system that looks to the side using a continuous wave (CW) transmission with frequency modulation (FM) operation from a frequency modulation switching technique. The radar system determines the presence, the range and the approach rate of detected targets. The radar system detects targets even when operated in adverse weather conditions and does not generate false alerts due to obstruction due to rain caused by wet roads and other humid environments. The radar system uses range techniques to reject false targets that are detected outside of a predetermined target detection zone. According to the present invention, the radar system indicates that a target is detected if and only if any part of the target is within the detection zone and (1) remains in front of the antenna for at least TH1 seconds; a range between Range-min and Range-max, and (3) is moving more quickly than the Approach Speed-min in relation to the antenna. Rejecting targets that are closer than Range-min to the antenna, the radar system reduces false alarms caused by wet foliage and other humid environments "not on the road". In one embodiment, the radar system uses a patch array antenna oriented to a diamond-shaped configuration to effectively create a spindle of linear amplitude that helps reject clogging caused by wet road surfaces.

Description

METHOD AND APPARATUS FOR REJECTING OBSTRUCTION BY RAIN IN A RADAR SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to radar systems, and more particularly to an apparatus and method for rejecting the obstruction of rain in a radar system used to detect the presence of obstacles in regions that are difficult. to see for a host vehicle operator. 2. Description of the Related Art A problem that continues to plague the operators of automotive vehicles, is the difficulty to observe the obstacles or other vehicles near the vehicle of the operators but in places or regions that are difficult to observe from the seat of the vehicles. operators inside the vehicle. These places or regions that are near a vehicle, and yet can not be observed directly from the driver's seat, are commonly referred to as "blind spots." For example, the region between the 90 ° and 170 ° angles, measured with respect to the forward direction of a vehicle in a clockwise direction (ie, generally to the right of the vehicle and slightly behind the operator's seat). ), is normally a blind spot, particularly for large vehicles such as buses and trucks. The fact that an operator is not aware of an object (usually another vehicle) in this blind spot on the right side when making a right turn or a lane change to the right, is a source of numerous accidents. Another common blind spot is the region directly towards the back of a vehicle. This region is of particular interest when the vehicle is in reverse (ie, when "going backwards"). Therefore, it is critical for the safe operation of a motor vehicle that the vehicle operator can detect obstacles (especially other vehicles) that are located at the operator's blind spots. An attempt of the prior art to solve the problem of obstacle detection in the blind spot uses mirrors to help the vehicle operator to detect the presence of obstacles that could present a risk. These mirrors have been made in a variety of ways, and with a variety of lenses. In addition, these mirrors have been mounted in different places to provide the operator with the greatest capacity to detect the presence of obstacles in particular blind spots. For example, concave mirrors are commonly mounted on the right side of a vehicle and are directed toward the blind spot on the right side. The mirrors provide the operator with some information regarding the presence of obstacles in some of the blind spots of a vehicle. However, in an inconvenient way, the mirrors are less useful at night and under adverse weather conditions. Even under the best conditions, mirrors are typically required to distort the reflex to allow the operator to see the right posterior blind spot. Some operators find it difficult to properly interpret the image presented in these mirrors (such as the convex mirrors that are commonly used as right side mirrors). In addition, the mirrors tend to reflect the lights of vehicles approaching from behind, and therefore, blind the driver of the vehicle in which the mirror is fixed. Therefore, a more complete and satisfactory solution is desired. A known alternative to the use of mirrors to detect obstacles in the blind spot of a vehicle, is to mount a camera on the vehicle to provide the operator with a visual image of the obstacles in the blind spot of the vehicle. However, this solution is complex and expensive, requiring a video camera and a video monitor. In addition, a video monitor can present a complex image that, although not distorted, can be difficult to interpret quickly under the tense conditions that arise during heavy traffic conditions. Still, monitors can be distracting. Moreover, like mirrors, these camera systems are less useful at night and under adverse weather conditions, such as rain, sleet, or snow.

Another alternative to the use of mirrors is to direct radar transmissions towards each blind spot. Then the reflections of the radar transmissions can be detected to determine the presence of obstacles in each of the blind spots. One of these systems is disclosed in U.S. Patent No. 5,325,096, issued June 28, 1994 to Alan Packett, and assigned to the owner of the present invention, which is incorporated herein by reference. These systems use a common radar transmitter-receiver that transmits a radio frequency (RF) signal to the blind spot of a vehicle. The transmitted signal is reflected by the obstacles that are present in that region of the blind spot. The frequency of the transmitted signal is compared to the frequency of a reflection of the transmitted signal that is received inside the radar system, to determine whether the reflected signal has had a Doppler shift. A Doppler change in frequency usually indicates that an obstacle is present in the blind spot. In an inconvenient manner, these Doppler radar blind spot sensors often generate false warnings (ie, detect false targets) when used in adverse weather conditions, especially when used in the rain. There are two main sources for false alarms: (l) the obstruction of rain produced by rain falling within a range close to the radar sensor; and (2) the reflections from the wet road surfaces, the wet "non-road" surfaces, and the wet foliage along the roadsides. In an inconvenient manner, prior art vehicle radar systems misinterpret the obstruction of rain, wet road surfaces, and wet foliage as dangerous objects. Accordingly, prior art radar systems falsely warn the driver about the existence of an object in the blind spot of the driver. This creates an annoying condition for the driver. The obstruction of rain, humid road conditions, and humid foliage that passes the host vehicle (ie, the vehicle equipped with the radar system), cause the radar system to falsely indicate the presence of an object at the point blind vehicle, even when there is no real threat. This can cause the operator of the host vehicle to lose faith in the reliability of the radar system, and leave the system ineffective to warn the operator of the actual threats. In addition, these indications distract and alter the operator. In accordance with the foregoing, there is a need for a simple and economical solution to the problem of detecting dangerous obstacles in blind spots of a vehicle. This solution should also be useful at night and under adverse weather conditions, and should not generate annoying conditions in response to rain clogging, wet road surfaces, and wet foliage on the sides of the road, as it passes. the host vehicle. The presence invention provides this solution. SUMMARY OF THE INVENTION The present invention is a novel method and apparatus for detecting targets in the blind spot of a host vehicle, and generating an indication to the driver of the host vehicle only when these objectives are present. The radar system detects targets even when operating in adverse weather conditions and does not generate false warnings due to obstruction of rain caused by wet roads and other wet surroundings. The radar system uses range techniques to reject false targets caused by obstruction of rain detected outside of a previously determined target detection zone. The present invention is a Doppler radar system that uses continuous wave (CW) transmission with frequency modulation (FM) operation from a frequency modulation switching technique. The radar system measures in an independent and concurrent manner the range and the approach index for a number of detected targets. In a preferred embodiment, the frequency modulation switching technique comprises the frequency change keying (FSK). A fixed-beam antenna transmitter-receiver transmits a radio frequency (RF) signal having a selected center frequency and at least two deflection frequencies (fl and f2). In a preferred embodiment, the center frequency of the transmitted radiofrequency signal is 24,725 GHz, and the offset frequencies are separated by approximately 1.25 MHz around the selected center frequency. The transmitted radiofrequency signal is reflected from the objects in the field of view of the antenna. The two transmission frequencies, fl and f2, when reflected from a target, generate two Doppler signals that correspond to the transmission frequencies. The reflected signals are converted down to two baseband difference signals, the signals of channel 0 and channel 1 corresponding to the transmission signals f1 and f2. The baseband signals contain the Doppler shift frequencies for the objects in the field of view of the antenna. The radar system amplifies, filters, de-multiplexes, and digitizes the returned signals to produce a stream of digital data. The digital data stream is conditioned and stored in circular buffer zones associated with the difference signals of channel 0 and channel 1. Each buffer zone is divided into four blocks of 256 words. Using this storage scheme, a block of 512 sampling points is created from two consecutively filled data blocks. A digital signal processor (DSP) performs a Fast Fourier Transform (FFT) operation on the block of 512 sampling points, to transform the signal data from the time domain to the frequency domain. The digital signal processor uses the transformed data to calculate the presence, range, and zoom ratio of the targets within the field of view of the antenna. Because the power level of the signals transmitted by the antenna is constant, the digital signal processor uses power variations in the reflected signals to detect the presence of targets. If there is more than one predetermined amount of power at the same Doppler frequency in both channel 0 and channel 1 data, it is assumed that a target is present. The digital signal processor determines the exact phase relationship between the signals of channel 0 and channel 1. The range of a target is determined by analyzing the phase difference between the two signals. The digital signal processor also calculates the movement in relation to the antenna. The digital signal processor calculates the movement in relation to the antenna using the Doppler shift in the signal returned from the target. The digital signal processor can identify and track a plurality of targets. Once the range of a target is determined, the present invention rejects targets that are not within a previously determined detection zone for a selected duration. In accordance with the present invention, the radar system indicates that an objective is detected if any part of the target is within the detection zone, and: (1) remains in front of the antenna for at least TH1 seconds; (2) it is in a range between Rangomln and Rangomax; and (3) it is moving faster than the Approach Speed in relation to the antenna. In a preferred embodiment, the Rangomin and Rangomax values comprise 0.60 meters and 3.65 meters, respectively. By rejecting targets that are closer than 0.60 meters to the antenna, false alarms due to rain obstruction are dramatically reduced. Also, by rejecting targets that are farther than 3.65 meters from the antenna, the radar system reduces false alarms caused by wet foliage and other wet surroundings "that are not the way". In addition, when rejecting targets that are farther than 3.65 meters from the antenna, the radar system will not raise the alarm when the targets are more than one lane from the host vehicle, and therefore, do not present shock threats to the vehicle host. Moreover, by orienting a square NXN patch array antenna in a diamond-shaped configuration, a decrease in natural linear amplitude is effectively created, which helps to repel clogging caused by wet road surfaces. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a preferred embodiment of the Doppler radar system that faces one side of the present invention.

Figure 2 shows a typical target detection zone used by the radar system facing one side of the present invention. Figure 2a shows a top plan view of a host vehicle having the radar system of Figure 1 deployed therein. Figure 2b shows a rear elevation view of the host vehicle of Figure 2a. Figure 3 shows a simplified block diagram of the sampling circuit used in the antenna receiver of the present invention. Figure 4 is a time diagram showing the switching time control signals used to control the sampling circuit of Figure 3. Figure 5 is a high-level flow chart of the method used to determine whether the presence of an objective Figure 6 shows a modality of the radar antenna shown in Figure 1, having antenna patch elements configured in a diamond shape, to reduce the effects of rain clogging caused by wet road surfaces. The reference numbers and the same designations in the different drawings indicate equal elements. Detailed Description of the Invention Throughout this description, the preferred embodiment and examples shown should be considered as examples, rather than limitations on the present invention. The preferred embodiment of the present invention is a method and apparatus for detecting objects in the blind spot of a host vehicle, and generating an indication to the driver of the host vehicle only when said object is present. The present invention will not generate false warnings to the driver, even when operating under rainy or otherwise adverse weather conditions. General In accordance with one embodiment of the present invention, objects are detected in the blind spot of a driver using a Doppler radar system facing one way. A block diagram of a preferred embodiment of the Doppler radar system facing one side of the present invention is shown in Figure 1. As shown in Figure 1, the side-by-side Doppler radar system 100 preferably comprises an antenna 102, a processor module ("PM") 104, and a visual display unit 106. In one embodiment, the antenna 102 and processor module 104 are enclosed in the same mechanical housing, which is preferably mounted to the side of a host vehicle (Figure 2). In one embodiment, the one-sided radar system 100 is adapted to be used, and cooperates with, a forward-facing radar system (not shown). The forward-facing radar system is used to detect and warn the host vehicle operator about potentially dangerous objects in the front path of the host vehicle (ie objects dangerously close to, and in front of, the host vehicle) . An example forward radar system is described in U.S. Patent No. 5,302,956, issued April 12, 1994 to Asbury, et al, and assigned to the owner of the present invention, which is incorporated herein by reference. to the present as a reference. The one-sided Doppler radar system 100 of the present invention warns the driver of the host vehicle about potentially dangerous targets that are present throughout the host vehicle. The radar system 100 preferably measures the ranges for the detected targets. If the radar system 100 concludes that a target is within a lane of the host vehicle, it transmits a "present target" signal to a forward-facing radar system. Normally, the forward-facing radar system will generate an appropriate warning by illuminating an indicator or sounding an alert warning. In this mode, the processor module 104 communicates with the visual display unit 106 by means of the forward-facing radar system. In an alternative way, the processor module can communicate directly with the operator by means of the visual display unit 106 (i.e., the side-by-side radar system 100 operates in a manner independent of the forward-facing radar system). The visual display unit 106 can be mounted inside the driver's compartment (e.g., in the driver's cab when the host vehicle is a truck), or can be placed in any viewing location that is convenient to the driver. As shown in Figure 1, the visual display unit 106 preferably includes at least two visual warning indicators 108, 110, and an audible warning indicator (such as a speaker) 112. The visual warning indicators 108, 110 they are very high luminance light emitting diodes (LEDs), which are normally placed on or in close proximity to a mirror on the same side of the host vehicle as the antenna 102. Accordingly, when the operator of the host vehicle sees the mirror, the operator can easily see the warning indicators 108, 110. Having the warning indicators 108, 110 fixed to an existing mirror, allows them to be seen by means of a normal movement of the head of the driver. However, the driver is not distracted or disturbed by frequent indications of obstacles that may occur under normal traffic conditions, and that are of little or no interest to the driver, unless an attempt is made to make the vehicle come in contact with the obstacle. As shown in Figure 1, in addition to the warning indicators 108, 110, an aggressive audible indicator 112 is provided, which creates an audible tone, buzzer, or buzz when an obstacle is present and the return signal is active. of the host vehicle. Figure 2 shows a typical target detection area provided by the one-sided radar system 100 of the present invention. Figure 2a shows a top plan view of a host vehicle 200 having the radar system 100 of Figure 1 deployed therein, Figure 2b shows a rear elevation view of the host vehicle 200 of Figure 1. The antenna 102 and processor module 104 are preferably enclosed within the same mechanical housing, and mounted on an appropriate side of host vehicle 200. As shown in Figure 2a, antenna 102 and processor module 104 are mounted on the right rear side of the host vehicle 200. In the example shown, the driver's seat of the host vehicle is located on the left front side of the host vehicle 200. Accordingly, the antenna 102 is mounted in such a manner as to detect the targets in the blind spot of the driver central. Typically, the objective is a motor vehicle, including motorcycles, passenger cars, and trucks. It is also considered that stationary objects, such as guardrails, tunnel walls within a predetermined distance of the antenna 102, and other extended objects, are valid targets, and will be detected by the radar system 100. Once it is done detection, a "target present" signal is generated by the radar system 100, and is produced towards the front-facing radar system or visual display 106. In one embodiment, the present objective signal remains active while the detecting the target, and then for an additional 1.5 seconds after the detection ends. Figure 2 shows the typical coverage area provided by the presently viewed side-by-side radar system 100. In general, the radar system detects an objective if any part of the target is within a "detection zone" 202 (the shaded area), and: (1) remains in front of antenna 102 for at least THL seconds; (2) it is in a range between Rangomin and Rangomax; and (3) it is moving faster than the Approach Speed in relation to antenna 102 (radially). In a preferred embodiment, THl is approximately 0.30 seconds, Rangomin is approximately 0.60 meters, Rangomax is approximately 3.65 meters, and Approach Speed, ^ is approximately 0.112 kilometers per hour. Accordingly, in the preferred embodiment, the radar system 100 will detect an objective if any part of the target is within the detection zone 202, and remains opposite the antenna 102 for at least 0.30 seconds, is in a range between 0.60 meters. and 3.65 meters, and it is moving faster than 0.112 kilometers per hour in relation to antenna 102. The Rangoraln and Rangomax cuts are implemented in the software that is executed by the processor module 104 (Figure 1). The detection zone 202 shown in Figures 2a and 2b depends on the objective. Targets that have very low reflective energies (ie, targets that reflect very little energy back to antenna 102) have reduced detection zones 202. In contrast, targets that have high reflective energies have increased detection zones 202 Doppler Radar System Sideways - Detailed Description Referring again to Figure 1, the processor module 104 performs many of the important functions of the one-sided radar system 100 of the present invention. For example, the processor module 104 generates time signals to the antenna 102, receives analog signals returned from the antenna 102, conditions the analog signals, and performs an analog-to-digital ("A / D") conversion, converting the signals analogues to the digital domain. The processor module 104 processes the data of the digital antenna using an integrated circuit specific to the application of the processor module (ASIC) 120, and a digital signal processor 122 ("DSP"). The processor module 104 communicates with the visual display unit 106 (or alternatively, with a forward-facing radar system), to indicate the alarm and integrated test failure ("BIT") conditions. The processor module 104 also includes a non-volatile random access memory ("RAM"), and a volatile random access memory circuit. As shown in Figure 1, the processor module 104 preferably comprises an antenna driver 114, an antenna receiver 116, an analog-to-digital converter 118, the application-specific integrated circuit of the processor module 120, the processor digital signals 122, a direct access memory 124, a volatile direct access memory 126, and a power supply 128. In a preferred embodiment, the digital signal processor 122 comprises a digital signal processor integrated circuit TMS320C203 manufactured by Texas Instruments The power supply 128 is designed to operate between 6.0 volts and 32.0 volts. The antenna driver 114, the antenna 102, and the antenna receiver 116 cooperate and function together as a wave transceiver in millimeters. The transceiver radiates and receives radio frequency (RF) signals, which are reflected from the objects in the field of view of the antenna 102. The reflected signals return to the antenna 102, where the antenna receiver 116"converts downwards. "the signal, to baseband signals. The baseband signals contain the "Doppler" shift frequencies for the objects in the field of view of the antenna 102. As is well known in the radar art, the frequency of a reflected received signal can be changed from the frequency of the signal transmitted on its return, due to the "Doppler" effect. The Doppler effect occurs whenever a transmitted signal is reflected from a target that has movement in relation to a transmitter-receiver. The resulting frequency change is referred to as a "Doppler shift". In accordance with the present invention, the baseband signals generated by the antenna receiver 116 include the Doppler shift frequencies for the objects in the field of view of the antenna. The antenna receiver 116 includes an analog circuit that amplifies, filters, and demultiplexes the baseband signals. The demultiplexed signals are produced towards the inputs of the analog-to-digital converter 118. In the preferred embodiment, the analog-to-digital converter 118 comprises an 18-bit analog-to-digital stereo converter. The digital data generated by the analog-to-digital converter 118 is conditioned and processed by the application-specific integrated circuit of the processor module 120 and the digital signal processor 122, to determine the presence of, and the range up to, a target . Because the power level of the signal transmitted by the antenna 102 is constant, the power variations in the signals applied to the analog-to-digital converter 118 can be attributed to the variations in power in the received signal. The digital signal processor 122 uses this fact to detect the presence of targets within the field of view of the antenna 102. If the power level of the signal produced by the analog-to-digital converter 118 exceeds a predetermined threshold (Pth ), the digital signal processor 122 concludes that a target is present. In addition, if the range indicates that the target is within a lane of the host vehicle (ie, if the range falls between the previously determined Rangomin and Rangomax values), a "present target" signal is generated on a transmission line output 130. Conveniently, the one-sided Doppler radar system 100 of the present invention precisely detects targets that are within a lane of the host vehicle, even when operating in adverse weather conditions. Instead of merely detecting the movement of the objects or objects in the field of view of the antenna (as do the blind spot sensors of the prior art), the present invention uses the range information to distinguish between rain obstruction and the valid objectives. According to the present method and apparatus, the side-by-side Doppler radar system 100 rejects all targets within the Rangomin of antenna 102. In one embodiment, Rangomin is approximately 0.60 meters. The inventors have observed that most of the false alarms caused by the obstruction of rain are due to the obstruction of rain that occurs within 0.60 meters of the antenna. Accordingly, by rejecting all detected targets within 0.60 meters of the antenna 102, the present one-sided radar system 100 conveniently eliminates false alarms due to rain obstruction. Accordingly, the present one-sided radar system 100 works much better in rainy conditions than the blind spot sensors of the prior art. The transmitter-receiver section of the present one-sided Doppler radar system 100 (ie, the antenna 102, the antenna driver 114, and the antenna receiver 116), processes the signals in a manner similar to the section of the transmitter-receiver of the forward-looking Doppler radar system of the prior art, described in U.S. Patent No. 5,302,956. For example, in a preferred embodiment, the transmitter-receiver section includes an oscillator, such as a GUNN diode of gallium arsenide (GaAs), which produces a transmission signal. The GUNN diode oscillator is coupled with a Schottky diode mixer receiver and the associated circuit of a microwave integrated circuit (MIC). The frequency of the transmission signal varies as a function of a frequency control voltage signal 406 (described in more detail below with reference to Figure 4), which is coupled with the oscillator from the specific integrated circuit of the processor module 120 application.

The voltage level is controlled by the specific integrated circuit of the processor module 120 application. The voltage level applied to the oscillator is alternated between two voltage levels (F1 / F2), thus alternating the transmission frequency between two deviation frequencies (fl and f2). In the preferred embodiment, the center frequency of the signal transmitted by the antenna 102 is approximately 24,725 GHz. The two deviation frequencies (hereinafter referred to as the transmission frequency of the channel 0, fl, and the transmission frequency of the channel 1, f2) are preferably separated by approximately 2.5 MHz, and are multiplexed in time to a single output. The transmission frequency of channel 0, fl, is 24.725 GHz minus 1.25 MHz, or 24.72375 GHz. The transmission frequency of channel 1, f2, is 24.725 GHz plus 1.25 MHz, or 24.72625 GHz. As described below with In greater detail, the transmission frequencies fl and f2 are transmitted at a switched time-share rate of approximately 10 kHz. In a preferred embodiment, the antenna driver 114 comprises a voltage regulator. The voltage regulator supplies the modulated voltage levels F1 / F2 to the oscillator. In one embodiment, both voltage levels fl and f2 are varied by means of the software that is executed inside the processor module 104. Consequently, the frequencies of transmission signals can be diverted without the need for manual adjustment.

In the preferred embodiment of the present invention, the antenna 102 transmits the transmission signals, as well as receives the signals that are reflected from the objects in the field of view of the antenna 102. The Schottky diode mixer (not shown) is coupled with the retransmitted signal and the received signal. The received radiofrequency signal is thus compared to the transmitted signal. The output of the mixer is a "difference" or "down-converted" signal having a frequency equal to the difference between the frequency of the transmitted signal and the received signal. The signal switches demultiplex in time and sample the down-converted difference signals as described below with reference to Figure 3. A simplified block diagram of the sampling circuit 300 in the antenna receiver is shown in Figure 3. 116. The sampling circuit 300 controls the demultiplexion of the difference signals received by the antenna 102 and generated by the mixer. As shown in Figure 3, the sampling circuit includes a preamplifier ("pre-amp") 302, two analog signal switches 304a, 304b, two low pass filter capacitors 306, 308, and two output amplifiers 310, 312. The difference signals are input to the sampling circuit 300 on the input line 301, and are provided as inputs to the preamplifier 302. The output of the preamplifier 312 provides the signal switches 304a and 304b. In a preferred embodiment, the signal switches 304a, 304b comprise analog switches MC114053BD available from Motorola Inc .. The signal switches 304a, 304b are used to demultiplex over time the difference signals generated by the mixer at the antenna receiver 116 The preamplifier 302 amplifies the difference signals coupled from the mixer. The signal that is presented to the preamplifier 302 is a composite of the different signals that are received and mixed with the transmission signal. Typically, when the transmit signal is transmitted, a plurality of targets reflect some of the signal back to the antenna 102. Some of these targets may be stationary with respect to the antenna 102, while others may have a relative movement with respect to the antenna 102. to the antenna 102. Under the Doppler shift that occurs when a radio wave is reflected from a moving target in relation to the transmitter or the receiver, the frequency difference between the transmission signal and the reception signal can be used to determine the relative speed of the target, and to distinguish one target from another, assuming there is a difference in the relative speed of the targets. As shown in Figure 3, the output of the preamplifier 302 is coupled with both signal switches 304a, 304b. The signal switches 304a and 304b demultiplex in time the signal from the preamplifier 302, coupling the preamplifier 302 with either the audio amplifier of the channel 0, 310, and the low pass filter capacitor 306, or with the amplifier channel 1, 312 audio, and the low pass filter capacitor 308, in an alternate manner. The matched switching time control signals CH0DM 402 and CM1DM 404, coupled with the respective matched signal switches 304a, 304b from the application-specific integrated circuit of the processor module 120 over the switching time control lines 322, 324 , respectively, determine with which filter capacitor low passes 306, 308 will be coupled the output of the preamplifier 302, and the time of this coupling. Figure 4 is a time diagram showing the time of the switching time control signals CH0DM 402, CH1DM 404, with respect to the signal of the frequency control voltage 406 which is coupled with the oscillator on the signal line of frequency control voltage from the specific integrated circuit of the processor module 120 application. In the preferred embodiment of the present invention, the signal of the frequency control voltage 406 alternates between a relatively high voltage and a relatively low voltage at intervals of 51.2 microseconds. A period of the frequency control voltage signal 406 is equal to 102.4 microseconds, or has a frequency of approximately 9.7656 KHz. Accordingly, the output frequency of the transmission oscillator alternates between a relatively low frequency (fl, the transmission frequency of channel 0), and a relatively high frequency (f 2, the transmission frequency of channel 1) at intervals of 51.2 microseconds, as a function of the frequency control voltage F1 / F2 406. Referring now to FIGS. 3 and 4 simultaneously, the CHODM 402 channel selection signal in a high state, causes the output of the preamplifier 302 to be coupling with the low pass filter capacitor of channel 0 306 through signal switch 304a. The channel selection signal 1 CH1DM 404 in a high state causes the output of the preamplifier 302 to be coupled to the low pass filter capacitor of channel 1 308 through the signal switch 304b. Because the application-specific integrated circuit of the processor module 120 controls both the frequency control voltage signal (F1 / F2) 406 and the channel selection signals (CHODM 402 and CH1DM 404), the signal switches 304a , 304b are synchronized in time with the frequency control voltage signal F1 / F2. Accordingly, the signal switch 304a connects the preamplifier 302 with the capacitor of the low pass filter of channel 0 306 for slightly longer than a third of a period (38.4 microseconds), synchronized with the time when the transmission signal is in the channel frequency 0 fl (because the frequency control voltage signal 406 is high during this time). In a similar manner, the signal switch 304b connects the preamplifier 302 with the low pass filter capacitor of the channel 1 308 for slightly longer than a third of a period, synchronized with the time when the transmission signal is at the frequency of channel 1 F2 (because the frequency control voltage signal 406 is low during this time). Accordingly, the signal switches 304 a, 304 b demultiplex in time the difference signals of channel 0 and channel 1 converted downward. The alternative modalities, wherein the duration of the pulses of the selection signal of channel 0 and channel 1 402, 404 are longer or shorter, are within the scope of the present invention. The timing diagram of Figure 4 shows the pulses of the channel selection signal 0 402 and the signals of the channel selection signal 1 404 offset from the respective edges of the frequency control signal 406, to allow it to be stabilize the time of the transmission signal, and to ensure that the reception and transmission signals are at the same carrier frequency (ie, both the reception and transmission signals are at the frequency of either channel 0 of channel 1 ) when the channel 0 and channel 1 402, 404 selection signals are active. However, it should be understood that, in alternative embodiments of the present invention, these signals 402, 404 may occur anywhere in or between the rising edge and the diminishing edge of the 406 frequency control voltage signal.

The low pass filters 306, 308 maintain the output of the signal switches 304a, 304b acting as envelope detectors. The low pass filter of channel 0 306 maintains (or "smoothes") the difference signal of channel 0 converted downwards demultiplexed in time, and the low pass filter of channel 1 308 keeps the difference signal of channel 1 converted downward demultiplexed in time. The output of each filter 306, 308 is a smooth signal having frequency components equal to the difference between the frequency of the transmission signal corresponding to the channel associated with the filter, and the frequency of each received signal during the time it is received. transmits that channel. For example, the low pass filter of channel 0 306 produces a smooth signal having a frequency equal to the difference between the transmission frequency of channel 0 and the reception frequencies of channel 0 reflected from a number of targets, as if transmitted the transmission frequency of channel 0 in a continuous waveform. The outputs of the sampling circuit 300 are coupled with the stereo analog-to-digital converter 118 (Figure 1). The analog-to-digital converter 118 includes two separate channels corresponding to the signals of channel 0 and channel 1 produced by the sampling circuit 300 on the output signal lines 328 and 330, respectively. Each channel of the analog-to-digital converter 118 converts the analog inputs from the corresponding downstream frequency channel to a stream of digital data words. In the preferred embodiment, the analog-to-digital converter 118 comprises a sigma-delta analog-to-digital converter, part number CS5330A available from Crystal Logic, Inc .. The analog-to-digital converter 118 preferably produces a series of words from 18 bit data. The first 16 bits represent the amplitude of the analog signal during a particular period of time (ie, 16-bit resolution). Accordingly, the signals reflected from the potential targets, and received by the antenna 102, are sampled, multiplexed in time, and digitized, up to a digital data stream. The digital data stream represents the received signal as a multiplexed function over time of the transmitted signal. The digital data is coupled with the application-specific integrated circuit of the processor module 120. The application-specific integrated circuit of the processor module 120 provides the time information, collects the digital data stream generated by the analog-to-digital converter 118 , and conditions the data, in such a way that they can be processed by the digital signal processor 122. More specifically, the specific integrated circuit of the processor module 120 application reads the data from the analog-to-digital converter 118, and writing the data into a memory block of the random access memory 124, which is associated with the appropriate channel (i.e., the data of the channel 0 is written to a block of memory associated with the difference signals of the channel 0, and the data of channel 1 is written to a block of memory associated with the difference signals of channel 1). In the preferred embodiment, each data sample written in the random access memory 124 is 16 bits wide (truncated by the hardware from the 18-bit analog-to-digital converter 118). The data of the channel 0 and the data of the channel 1 (associated with the transmission frequencies fl and f2, respectively) are preferably stored separately within the random access memory 124 in two circular buffer zones, each zone being buffer capable of storing 1024 words of data. Each buffer zone is divided into four blocks of 256 words. Using this storage scheme, a block of 512 sampling points is created from two consecutively filled data blocks (comprising 256 sampling points from channel 0 and 256 sampling points from the channel 1) • The digital signal processor 122 is coupled with the application-specific integrated circuit of the processor module 120, the random access memory 124, and the volatile random access memory 126. The digital signal processor 122 calculates the range up to the targets detected using the data stored in the random access memory 124. The digital signal processor 122 performs this calculation using techniques similar to those described in U.S. Patent No. 5,302,956. Because the power level of the signal transmitted by the antenna 102 is constant, the power variations in the signal generated by the analog-to-digital converter 118 can be attributed to the power variations in the received signal. If there is more than one predetermined amount of power at the same Doppler frequency in both channel 0 and channel 1 signals, it is assumed that there is a present objective. The digital signal processor 122 also determines the exact phase relationship between the signals of channel 0 and channel 1. The digital signal processor 122 determines the range of a target based on the phase difference between the two signals. The digital signal processor 122 also calculates the movement in relation to the antenna 108. The digital signal processor 122 calculates the movement in relation to the antenna 102 using the Doppler shift in the signal returned from a target. In one embodiment, the digital signal processor 122 can identify and track a plurality of targets. The objectives are distinguished by their frequency (ie, the amount of Doppler change). Before performing a window formation and a Fast Fourier Transform (FFT) operation on the 512 sampling points stored in the random access memory 124, the sampling points preferably are scaled to the largest amplitude point / tray for maximize the fixed point accuracy of the FFT operation. Then a "Blackman" window function of 512 points is applied to the buffer area of the scaled data. When there is sufficient data present in the random access memory 124, the digital signal processor 122 performs a complex FFT operation of 512 points which maps the digital representation of the time-demultiplexed reception signal from a time domain to a frequency domain. In this way, the digital signal processor 122 performs a spectral analysis of the data stored in the random access memory 124, and determines the frequencies, the phase relationships, and the relative power at each frequency. The performance of FFT operations using digital signal processors, such as the digital signal processor TMS320C203 used in the preferred embodiment of the present invention, is well known in the art. Accordingly, the result of the FFT operation is a list of frequencies and the power level associated with each of these frequencies. When the power at a particular frequency is greater than a selected threshold amount Pth, the digital signal processor 122 determines that a target is present. After the frequency spectrum data is generated, only the positive side of the spectrum needs to be considered. Noise floor estimates are calculated for eight bands of different amplitudes, covering most of the data points of the positive frequency spectrum. The digital signal processor 122 scans the frequency spectrum (within the given limits of the noise bands), looking for a single peak of the highest frequency. If this peak exceeds a "detection threshold" calculated for a given noise band, the peak is considered as a potential target. In one embodiment of the present invention, the digital signal processor 122 detects the presence of only one target (i.e., there is no requirement to scan to search for more than one peak). However, in an alternative mode, more than one peak is detected. By counting the number of frequency peaks in which power is detected over the selected threshold Pth, the digital signal processor 122 determines how many targets are present (ie, how many targets are moving at different speeds in relation to antenna 102). The targets that move at the same relative speed, reflect signals that have the same frequency. The digital signal processor 122 also determines the phase relationship of the data of the signal of the channel 0 with the data of the signal of the channel 1. From this information, the digital signal processor can calculate the range and the relative speed of an objective. The determination of the range and the relative speed is calculated directly by multiplying the frequency and the phase difference by fixed factors, since the phase is linearly proportional to the range of the objective according to the formula, R = C * (Q ^ Tz) / (4p (f1-f2)), and the frequency is linearly proportional to the relative speed of the target according to the formula fd = 72 (Hz. Hours / 1,609 km) * V (kilometers / hour). In the range formula, R is the range to the target in meters, C is the speed of light in meters / second, fl is the frequency of the signal in channel 0 transmitted, and f2 is the frequency of the channel signal 1 transmitted. In the relative velocity formula, fd is the frequency change due to the Doppler phenomenon, and V is the relative velocity of the target with respect to the transceiver. However, in alternative modes, other means may be used to map the frequency with a relative velocity, and the phase relationship with the range. For example, a table can be used to cross-reference frequency and phase with relative speed and distance, respectively. If the data are not within the previously established limits selected, they are considered invalid, and are not taken into account. If the data is within the previously established limits, the digital signal processor 122 uses a software tracker module to create a filtered time tracking or record of the target range and the relative speed information. The digital signal processor 122 compares the new range of the target and the relative speed with the previously recorded ranges and relative speeds. If the range and relative speed of a target are consistent with the range and relative speed of a previously recorded target (ie, the difference between the range and speed of a new target and the range and speed of a target) previously recorded is within a predetermined amount), the digital signal processor 122 updates the previously recorded range and relative speed, with the newly received range and relative speed. If the new objective does not correspond to an existing objective, the range and the relative speed are stored, and in this way a new objective is defined. When the digital signal processor 122 fails to receive data that closely matches a previously recorded target, it is assumed that the previously recorded target has left the environment, and the range and relative speed are removed from the register. Therefore, in an alternative mode, the system can identify and track a multiplicity of objectives in a concurrent manner. The digital signal processor 122 generates warnings at the end of the processing cycle channel. The warning signals generated by the present radar system include the following: "there is no objective" (there is no tracked target); "target within the detection zone" 202 (Figure 2); "system malfunction" (hardware failure detected during energization or during online test procedures); and "there are inoperable conditions" (eg, heavy rain that raises the noise floor above a certain threshold, ice or mud pack covering the antenna 102, the signal level to the noise is too low, or no peak is detected for a period of time that exceeds a previously determined threshold). The warning signals generated by the digital signal processor 122 are provided on the output transmission line 130. Figure 5 is a high-level flow diagram of the method by which the digital signal processor 122 determines whether it indicates the presence of an objective. Initially, the digital signal processor 122 enters step 500 after performing a FFT operation of 512 points on the data stored in the random access memory 124 (256 sampling points of the channel 0 points, and 256 sampling points of the data from channel 1). In accordance with the preferred modality, a new FFT is calculated for every 256 new sampling points, thus producing a 50 percent overlapping FFT on the new and previously calculated sampling points. The method proceeds to step 502, to determine if there is a potential target before the antenna 102 (Figure 1). As described above, because the power of the transmitted signal is constant, the power variations in the reflected signal are used to detect the presence of a target. In step 502, the method determines whether the power level of the signal produced by the analog-to-digital converter 118 ("Pwr") exceeds a previously determined threshold (Pth). If it does, the method proceeds to step 504, to determine how long the target has been before the antenna 102. If not, the method proceeds to step 512, to obtain the next 256 sampling points for a subsequent FFT operation. In step 504, the digital signal processor 122 determines whether the target has been before the antenna 102 for a predetermined period of time. As described above, in order for the digital signal processor 122 to conclude that a target is present, the target must remain in front of the antenna 122 for at least one period of TH1 seconds. In the preferred embodiment, TH1 is approximately 0.30 seconds. In the alternative modalities, THl can assume different values, depending on the sensitivity characteristics required by the system parameters. As shown in Figure 5, if the target remains in front of the antenna 102 for at least one time period of TH1 seconds, the method proceeds to step 506 to determine whether the target is within the detection zone. Otherwise, the method proceeds to step 512. As described above with reference to Figure 2, the present one-sided Doppler radar system 100 reports on targets if and only if they remain within a previously determined detection zone. during a previously determined period of time. According to the present method and apparatus, the side-by-side Doppler radar system 100 rejects all targets within the Rangomin of antenna 102. In one embodiment, Rangomin is approximately 0.60 meters. Because most false alarms in rainy conditions are caused by the obstruction of rain that is within 0.60 meters of the antenna, the method rejects any targets that are within 0.60 meters of the antenna in step 506. rejection of all detected targets within a specified range, Rangomin, of antenna 102, the detection method of the present invention greatly reduces false alarms caused by rain obstruction. In addition, by rejecting targets that are beyond a specified range, Rangomax, of antenna 102, the detection method reduces false alarms due to obstruction caused by wet foliage and other wet conditions surrounding the antenna 102. As shown in Figure 5, if the target is not within the detection zone, the method proceeds to step 512, and obtains the next block of sampling points. However, if the target is in a range that is between Rangomin and Rangomax (ie, within the detection zone), then the method proceeds to step 508.

In step 058, the present objective detection method determines whether the approach speed of the objective exceeds a specified value. As described above, the objectives are not indicated by the present invention, unless they are moved at a speed exceeding a minimum approach speed threshold (Approach Speed) in relation to the antenna 102. In the preferred embodiment, the targets are not indicated unless they are moving at least 0.112 kilometers per hour in relation to the antenna 102. In alternative modes, this speed resolution may be varied as necessary to meet the requirements of the system. If the target speed is less than the Approach Rate, the method proceeds to step 512, to obtain the next block of sampling points. However, if the target is moving at a rate that exceeds the Approach Rate, the method generates a warning that the target is within the detection zone in step 510. The target detection method shown in FIG. Figure 5 preferably comprises software executed by the digital signal processor 122 in the processor module 104. The method and apparatus of the present invention can be implemented alternatively using any convenient or desirable sequencing devices, such as state machines, discrete logic of present state-following state, or programmable gate array devices in the field. The target detection method shown in Figure 5 can be implemented in the hardware (i.e., "cabling"), or alternatively, it can be implemented using other types of programmable devices. Effects of Antenna Shape and Antenna Beam Amplitude on the Reduction of False Alarms Due to Rain Obstruction The inventors have observed, through experimentation, that a dominant contributor to rain-induced false alarm warnings is wet foliage and other wet conditions "that are not the way" around antenna 102. Wet conditions cause a normally benign obstruction to "light up" and blind radar systems of the prior art. The range method and apparatus described above with reference to Figures 1 to 5, rejects most of the obstruction created when the system 100 is used in rainy conditions. However, the inventors have observed that additional improvements in rejection of rain clogging can be achieved by narrowing the antenna beamwidth, and optimally configuring the antenna. Narrowing the amplitude of the antenna beam reduces the reflections generated by wet road surfaces and wet surfaces that are not the road. The beamwidth of the antenna should be made as small as feasible in light of the requirements of antenna size and detection area coverage. For example, in the preferred embodiment, the antenna beamwidth is +/- 7.5 ° in both azimuth and elevation. An effective means to produce a narrow beam amplitude antenna, and to lower the "side lobes" of the signal radiated by the antenna, is to use a square patch antenna array mounted diagonally with respect to the road surface (i.e. , use an antenna array "diamond shaped"). Figure 6 shows an embodiment of the antenna 102, having the antenna patch elements (e.g., elements 606 and 608) configured in a diamond shape, to reduce the effects of rain clogging. The antenna 102 shown in Figure 6 comprises a rectangular element arrangement of 6 X 6 inclined on a diagonal axis 602. The antenna 102 is mounted on the host vehicle, such that the other diagonal axis 604 of the square arrangement is parallel with the surface of the road. Note that the diagonal axis 602 is both a "diagonal" axis of the square array, and the "vertical" axis of the antenna 102, after it is mounted on the host vehicle. In a similar manner, the diagonal axis 604 is both a diagonal axis of the square array, and the "horizontal" axis of the antenna 102, after it is mounted on the host vehicle. Therefore, the cardinal planes of the antenna are oriented at 45 ° with the vertical and horizontal axes.

This diagonal orientation of the antenna 102 does not adversely affect the target detection capability of the radar system 100. However, the diagonal orientation helps to reduce false alarms due to road and surroundings other than the wet road. The diagonal orientation effectively creates a decrease in natural linear amplitude in the vertical plane, because the number of patch elements (e.g., elements 606 and 608) decreases linearly in the horizontal rows as it is traversed along the vertical axis 602 moving away from the center of the antenna array. In the example shown in Figure 6, because the number of patch elements along horizontal axis 604 decreases from 6 (in the center of the array) to 1 (in the lower part of the array) along the axis vertical 602, correspondingly the side lobes of the signals radiated by antenna 102 are lowered. In one example, the first side lobes are lowered by approximately 13dB, compared to the first side lobes of a square antenna radiation pattern (i.e. an antenna that is not inclined at an angle of 45 ° with respect to the road surface). All other side lobes decrease to even lower levels. The decrease in the side lobes helps the present radar system 100 ignore the reflected energy back to the antenna from wet roads and other humid surroundings. In addition to reducing the side lobes in the radiated signals, the diagonal orientation also creates a cross-polarized return signal. By tilting the antenna 102 to the orientation shown in Figure 6, the return electric field vector reflected by a wet surface of the path is orthogonal to the vector of the electric field transmitted by the antenna 102. The orthogonality of the return vector It is tremendously effective to reject the obstruction of rain due to the humid conditions of the road. Several alternative antenna configurations are possible. For example, the antenna elements do not need to be oriented in such a way as to create a diagonal polarization effect. The patch elements can be oriented in any desirable manner with respect to the vertical axis 602. The delineation of the entire array determines the diminishing effect on the side lobes (i.e., the delineation of the patch elements creates a decrease in natural amplitude). when configured as shown in Figure 6, however, the orientation of the patch elements themselves has no effect). In an alternative embodiment, the antenna array comprises 16 rows by 16 columns of patch elements, configured in a diamond-shaped configuration, to reduce the obstruction of rain. Various variations on this configuration are within the scope of the present invention. In summary, the method and apparatus include an element for accurately and reliably detecting objects in the blind spots of the operator of a host vehicle. The present method and apparatus preferably use a Doppler radar system mounted on the side of a host vehicle. In accordance with the present invention, an antenna transmitter-receiver transmits radiofrequency signals, and receives the reflected signals from the potential targets. Using digital signal processing techniques, the radar system determines the presence, range, and approach speeds of potential targets. The present method determines whether the detected targets are within a previously determined detection zone during a selected period of time. Only those targets that are within the detection zone are reported to the operator. In a convenient manner, the present method rejects all targets within a certain range of the antenna, thus reducing false alarms due to the obstruction of rain. The present invention uses range information to reject targets that are farther than a lane of travel from the antenna, thereby reducing false alarms caused by wet foliage. The orientation of the antenna in a diamond-shaped configuration also reduces the obstruction caused by wet road conditions. A number of embodiments of the present invention have been described. However, it will be understood that various modifications can be made without departing from the spirit and scope of the present invention. For example, the relationship between the transmission signal of channel 0 and the transmission signal of channel 1 may be such that they differ in frequency by more or less than 2.5 MHz. Additionally, the period of frequency control voltage 406 (FIG. 4) may be greater than or less than 102.4 microseconds, and may have a duty cycle greater than or less than 50 percent. As another example, the frequency modulation scheme may be somewhat different from the frequency shift keying. Also, the invention is not limited to the use of an FFT operation of 512 sampling points. FFT of virtually any size can be used to practice the present invention. In addition, the center frequency of the transmitted signal may be greater than or less than 24,725 GHz. For example, in a currently contemplated mode, the center frequency of the transmitted signal is approximately 76.5 GHz. Moreover, as described above with reference to Figure 6, several alternative patch array antennas can be used with the present invention. In accordance with the foregoing, it should be understood that the invention should not be limited by the specific embodiment illustrated, but only by the scope of the appended claims.

Claims (13)

1. CLAIMS 1. A radar system that looks sideways, to detect the presence of an object in the blind spot of a host vehicle in which it is mounted in radar system, comprising: (a) a radar transceiver for transmitting radar signals and to detect reflected signals of the transmitted radar signals that are reflected from an object; (b) a processor block, coupled to the transceiver, to control the timing of the signals transmitted by the transceiver, and to process the reflected signals received by the transceiver, where the processor block determines the presence, the range and the approach rate of the object from which the reflected signals are reflected, and where the processor block determines whether the object is within a predetermined detection zone; and (c) an indicator, coupled to the processor block, the indicator receiving from the processor block an indication that the object is within the detection zone, where the indicator alerts an operator of the host vehicle that the object is present within the detection zone. The side-looking radar system of claim 1, wherein the radar transceiver includes: (a) an antenna; (b) an antenna driver, operatively coupled to the antenna to control transmissions from the antenna; and (c) an antenna receiver, coupled to the antenna, for processing the reflected signals, wherein the antenna receiver down-converts the reflected signals into baseband signals for further processing by the processor block. The side-looking radar system of claim 1, wherein the processor block includes: (a) an analog-to-digital (A / D) converter coupled to the radar transceiver, capable of converting the reflected signals received by the radar transceiver in a stream of digital data; (b) a processor-specific application integrated circuit (PM ASIC), coupled to the A / D converter and the radar transceiver, capable of providing timing information to the transceiver, and where the PM ASIC conditions the current of digital data to produce sample point blocks; (c) a random access memory (RAM), coupled to the PM ASIC, for storing the sample point blocks received from the PM ASIC; and (d) a digital signal processor (DSP), coupled to the PM ASIC and RAM, to carry out digital signal processing operations on the sample point blocks stored in the RAM. 4. The side-looking radar system of claim 3, wherein the A / D converter comprises an 18-bit, stereo A / D converter circuit. 5. The side-looking radar system of claim 3, wherein the PM ASIC modulates the transmitted radar signals such that they are transmitted at two frequencies, fl and f2. 6. The side-looking radar system of claim 3, wherein the PM ASIC conditions the digital data stream by associating a first block of sample point with the transmit radar signal frequency fl, and where the PM ASIC associates a second sample point block with the transmission radar signal frequency f2. The side-looking radar system of claim 6, wherein the PM ASIC stores the first sample point block in a fast circular buffer in RAM, and where the PM ASIC stores the second block of sample point in a second circular buffer in RAM. The side-looking radar system of claim 7, wherein the DSP performs a fast Fourier transform operation on the first and second sample point blocks stored in the RAM, thereby converting the point data sample from a time domain to a frequency domain. 9. A side-facing radar system for detecting objects at a blind spot of a host vehicle on which the side-facing radar system is mounted, including: (a) a Doppler radar circuit for: (1) ) transmit a modulated radar signal having a first and a second transmission frequency; (2) receiving reflections of the transmitted radar signal that are reflected from an object close to the host vehicle; (3) detecting that a change in the Doppler frequency has occurred between the transmitted radar signal and the reflected radar signal; and (4) determining the amount of energy at each Doppler frequency of the received reflections; and (b) a controller, coupled to the Doppler radar circuit, for: (1) determining whether the object from which the received reflections are reflected is within a predetermined detection zone, close to the host vehicle; and (2) provide an alert to an operator of the host vehicle only if the object is detected within the detection zone. 10. The side-by-side radar system of claim 9, wherein the controller determines whether the object is within the detection zone by placing the object in range and determining whether the object is between a predetermined minimum range and a range. predetermined maximum of the host vehicle. 11. A method for determining whether an object detected by a side-facing radar system is within a predetermined detection zone at a blind spot of a host vehicle on which the radar system is mounted, which includes the steps of : (a) transmitting a modulated radar signal having first and second transmission frequencies; (b) receiving reflections of the transmitted radar signal that are reflected from an object close to the host vehicle; (c) determining the range of the object, based on the frequency characteristics of the reflected radar signals received in step (b); (d) determining whether the object is within a predetermined detection zone close to the host vehicle; and (e) providing an alert to an operator of the host vehicle only if the object is detected within the detection zone. The method of claim 11, wherein step (d) of determining whether the object is within the detection zone comprises: (a) determining whether the amount of energy present in the reflected signals at a selected frequency exceeds one predetermined threshold energy level; (b) determining if the object has been detected for more than a predetermined period of time; (c) determining whether the object is between a predetermined minimum range and a predetermined maximum range of the host vehicle; and (d) determining whether the object is moving more rapidly than a predetermined minimum approach speed relative to the host vehicle. 13. An executable computer program in a general-purpose computing device, wherein the program is capable of determining whether an object detected by a side-facing radar system is within a predetermined detection zone in a blind spot of a host vehicle in which the radar system is mounted, comprising: (a) a first set of instructions for transmitting a modulated radar signal having first and second transmission frequencies; (b) a second set of instructions for receiving reflections of the transmitted radar signal that are reflected from an object close to the host vehicle; (c) a third set of instructions for determining the range to the object based on the frequency characteristics of the reflected radar signals; (d) a fourth set of instructions for determining whether the object is within a predetermined detection zone close to the host vehicle; and (e) a fifth set of instructions for providing an alert to an operator of the host vehicle only if the object is detected within the detection zone. Summary A method and apparatus for detecting the presence of objects in blind spots of an operator of a vehicle. The apparatus comprises a Doppler radar system that looks to the side using a continuous wave (C) transmission with frequency modulation (FM) operation from a frequency modulation switching technique. The radar system determines the presence, range and rate of approach of detected targets. The radar system detects targets even when operating in adverse weather conditions and will not generate false alerts due to obstruction due to rain caused by wet roads and other humid environments. The radar system uses range techniques to reject false targets that are detected outside of a predetermined target detection zone. According to the present invention, the radar system indicates that a target is detected if and only if any part of the target is within the detection zone and (1) remains in front of the antenna for at least TH1 seconds; (2) is in a range between Rangom? N and Rangomax; and (3) it is moving faster than the Approach Speed in relation to the antenna. Rejecting targets that are closer than Rangom to the antenna, the radar system reduces false alarms caused by wet foliage and other wet environments "not on the road". In one embodiment, the radar system uses a patch array antenna oriented to a diamond-shaped configuration to effectively create a spindle of linear amplitude that helps reject clogging caused by wet road surfaces.