WO2001018559A1

WO2001018559A1 - System and method for short range radar

Info

Publication number: WO2001018559A1
Application number: PCT/US2000/022015
Authority: WO
Inventors: Clyde Shaver
Original assignee: Preco LLC
Current assignee: Preco LLC
Priority date: 1999-09-10
Filing date: 2000-08-15
Publication date: 2001-03-15
Anticipated expiration: 2002-03-10
Also published as: AU6901700A

Abstract

An apparatus and method which uses a high frequency signal to detect objects which are located at relatively close distance to the detecting apparatus. The high frequency signal utilized can have a relatively long pulse width and requires a relatively narrow bandwidth to detect objects and determine the approximate distance of the object from the detecting apparatus. By utilizing long pulse width, low power, and narrow bandwidth signals the possibility of interference with other signals is minimized.

Description

SYSTEM AND METHOD FOR SHORT RANGE RADAR

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to the field of short range radar systems used to detect objects at relatively close distances, wherein the transmitter of the system transmits a pulse having a relatively long pulse duration. These pulses can be in the range of 5 nanoseconds and can be low power having a narrow frequency bandwidth which minimizes the possibility of interference with other high frequency signals.

Description of Related Art

It is widely understood that high frequency signals can be used to detect objects by transmitting a burst of high frequency energy (i.e. frequency in the range to millions or billions of cycles per second^'often referred to as radio frequency or RF) from a transmitting antenna. A receiving antenna is then used to detect RF energy reflected back by an object which is in the range of the burst of RF energy (RF pulse). Prior systems for radar detection of proximate objects (in the range of 0-30 ft) utilize a narrow pulse width, wide frequency band, high power signals. These prior systems transmit an RF pulse which often has a bandwidth of approximately 500Mhz or more. The problem with utilizing such a broad frequency range is that the transmitted RF pulse could interfere with a number of other signals which are being transmitted and received by other systems, such as cellular phone systems, and radio and television signals. One of the reasons prior short range radar systems use a narrow pulse is because if a wide pulse is used, the RF pulse from the transmitting antenna signal will be propagated directly to the receiving antenna for an amount of time equal to the time of the pulse. This direct transfer of energy from the transmitting antenna to the receiving antenna is sometimes referred to as the main bang. In these prior systems a problem occurs where an object is very close to the transmitting and receiving antennas. Under these circumstances the object will reflect a signal back to the receiving antenna while the receiving antenna is still receiving RF pulse directly from the transmitting antenna. In these prior systems it was very difficult or impossible for the system to recognize the presence of an object where the object was located so close to the receiving antenna that the reflected RF pulse was incident upon the receiving antenna while the main bang was still occurring. Thus, these prior systems and methods could not use a wide RF pulse having a narrow frequency bandwidth. It is axiomatic that the frequency bandwidth of the signal is inversely proportional to the time duration of the signal pulse.

The prior art systems utilizing narrow pulse width, high frequency bandwidth RF signals have rarely been used because the wide bandwidth signal is far outside of the FCC regulations which allow for a typical maximum bandwith of 150 Mhz centered on 5.8 GHz for a 5.8 GHz RF signal and less at other frequencies. One example of a prior device is a system using a digitizing receiver, such as a digital oscilloscope, as the detection engine with an ultra wide spark gap impulse transmitters. This type of system generates a very wide frequency bandwidth signal which could cause a great deal of interference with other signals, and would likely run afoul of FCC requirements. These spark gap impluse transmitters have a bandwidth of at least 2 Ghz which is far outside of FCC bandwidth requirements.

A number of variations of types of prior art short range radar systems were disclosed by McEwan in a number of U.S. Patents. One example of these is U.S. Patent No. 5,361 ,070 ULTRA- WIDEBAND RADAR MOTION SENSOR. The focus of these patents is on using relatively wide frequency bandwidth, short time pulse RF signals to detect objects, where the receiver is wide band and uses time down conversion techniques. As a review of the McEwan patents show, these prior systems suffer from many of the limitations discussed above.

Thus, what is needed is a system and method of short range radar apparatus which can determine the distance of an object from a transmitter and utilize relatively wide pulse width, narrow frequency bandwidth and low power signals. This type of system and method would be ideal for use as a back-up sensor for a large truck where the driver has a significant blind spot behind the truck which can pose dangers when the driver attempt to back up the vehicle. SUMMARY OF THE INVENTION

An object of the invention is to provide a reliable, simple, and sensitive short range radar, that will operate using a relatively long pulse width signal, which has a correspondingly narrow frequency bandwidth, and is less likely to interfere with other signals. This will increase the likelihood that the system will comply with the FCC's rules for an unlicensed device.

Another object of the invention is to detect high and low reflectivity targets which are within a range of approximately 0 to 50 feet of the transmitting antenna. This can provide a reliable solution to the "blind spot" problem that drivers of vehicles face. The blind spot is the area which is not easily viewable in rearview mirror of a vehicle, such as a car or truck.

Another object of the invention is to provide a short-range radar that overcomes shortcomings of other types of radar detection systems. This is accomplished by using techniques and components that other systems do not utilize. One embodiment of the invention utilizes a high repetition rate, time- down conversion receiving apparatus, and couples it with a unique complex RF signal generator and other elements to effect a system and apparatus which utilizes a wide pulse width, low power RF pulse.

One embodiment of the invention takes millions of samples across a given area adjacent to the radar system and averages the samples to give a very good signal to noise ratio (SNR). This means that the strength of the information signal is much greater than the strength of the noise which could distort or hide the information signal. By lowering the noise floor, the LDS (least discernable signal) is increased, and the necessary transmission signal is decreased. This allows the radar to pull out of the noise, signals that would normally be hidden. This helps to allow the device to operate at relatively small power levels at the transmitter, while still being able to clearly detect the reflected signals at the receiver. In one embodiment of the invention an isolation network between transmitter and receiver allows very sensitive operation to be realized. By using a long enough pulse length the transmitted RF pulse can be made to comply with the requirements of narrow bandwidth and low power transmission. As discussed above, a long pulse would normally cause an inability to detect objects at very close range, because the main bang signal would mask any return coming back in this time window. This difficulty is overcome in the present invention by pulse conditioning and detecting the trailing edge of the RF pulse initially received by the receiver, where the initial part of the initial RF pulse is due to the main bang, but the trailing edge of the initial pulse may be extended beyond where the trailing pulse would exist if initial pulse consisted of energy which was solely derived from the main pulse.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a system level block diagram of one embodiment of the invention.

Fig. 2 is a detailed block diagram of the pulsed RF dual phase transmitter block of Fig. 1.

Fig. 3 is a diagram of the radar range where an object is present. Fig. 4 is a diagram showing a transmitted RF pulse and corresponding

RF pulses which are received by the receiving antenna.

Fig. 5 is a diagram showing a transmitted RF pulse and corresponding reflected pulses which are received by the receiving antenna. Figs. 6 A and B are isometric and planar views of an embodiment of a slotted array antenna having signal shaping guides.

Fig. 7 is a diagram showing the shape of projected RF pulses from the slotted array antenna shown in Fig. 6.

Fig. 8 is a diagram showing one embodiment of a high speed gated receiver and a low noise amplifier.

DETAILED DESCRIPTION

Figure 1 shows a detailed system block diagram of one embodiment of the invention. A quartz crystal oscillator 10 is used to generate a reference signal of 20Mhz. It would be obvious to one of ordinary skill in the art that a number of other oscillators could be used to generate a different reference signal for the system. For example, another type of oscillator which could be used is an resistor/capacitor (RC) type oscillator. The signal output by the crystal oscillator 10 is then input into a pulse repetition frequency divide by circuit (PRF) select circuit 20. This circuit uses the signal output by the oscillator to output another signal with a different frequency. In the preferred embodiment the output of the PRF circuit 20 is a 5Mhz signal.

This 5Mhz signal is used as a trigger signal 30 to drive the transmitter 50. The transmitter can be implemented in a number of ways as one of ordinary skill in the art would appreciate, and a wide range of trigger pulse frequencies could be used. In the preferred embodiment the 5Mhz signal is used to drive a gas-fet to produce a 5.8 Ghz RF pulse at 5Mhz having a 50% duty cycle square wave which is used as the RF trigger pulse. In the preferred embodiment the transmitter 50 is a pulsed RF dual phase transmitter. As shown in Fig. 2, this transmitter includes a RF generator having an RF oscillator which generates a high frequency signal. In the preferred embodiment this is a 5.8 Ghz signal. The 5 Mhz trigger pulse signal operates to activate RF generator to output pulses of the 5.8 Ghz signal at a rate of 5 million pulses per second, i.e. at a pulse rate of 5 Mhz PRF ( pulse repetition frequency)(i.e. the trigger pulse frequency). In the preferred embodiment the duration of each RF pulse is 12 nanoseconds. In the frequency spectrum this 12 nanosecond pulse width corresponds to a 3 db frequency bandwidth of less than 90 MHz. The 12 nanosecond pulse of RF goes from the RF oscillator to a power splitter 52 which splits the power of the RF pulse. As shown in Fig. 2, one branch of the RF pulse is then shifted in phase in the phase shifter 54. In the preferred embodiment this phase shifting changes the phase of the signal by 90 degrees. Once the phase has been shifted the power combiner 56 recombines the two signals into a complex RF signal having components with two different phases. This complex RF signal is then routed through an RF attenuator/bandwidth shaping and matching network 40. The purpose of the attenuator and matching network 40 is to allow the complex RF pulse to propagate from the output of the power combiner to the transmitting antenna 60 with as little signal reflection as possible. The goal of the matching network is to reduce the reflection coefficient going from the RF generation circuitry to the transmission antenna to zero.

The power splitter 52 and phase shifting elements 54 provide the system with the ability to output a complex signal, which can significantly aid the system in being able to obtain accurate usable information while still transmitting relatively low power RF pulses. In prior art systems the RF pulse typically transmitted only one phase component. In such systems when the RF impulse was reflected by an object which did not have a single hard boundary, such as a concrete wall, there was a possibility for the object to reflect the RF pulse back to the receiving antenna, such that the reflected pulse would have multiple components having different phases. In some circumstances these different phases could be out of phase such that the combination of the out-of- phase signals in the high speed gated receiver 140 would result in a near zero measurement, and as a result the system might fail to detect the object. One way to reduce the possibility of this occurring in the prior systems was to simply increase the power level of the transmitted RF pulse.

In the present system, however, when this dual phase RF pulse is incident on an object which reflects the pulse back to the receiving antenna at different phases, the likelihood that the summation of these different signals will be zero at the receiver is significantly reduced, because the RF pulse originally transmitted had more phase content when it was originally transmitted. Thus, this helps to reduce the need to use higher power RF pulse transmissions. In the preferred embodiment, the transmitting antenna 60 is a slotted wave guide antenna having signal shaping guides to aid in controlling the direction of the RF signal projected from the antenna. One of skill in the art would realize that a number of different antenna types and structures could also be used in a short range radar system, for example: patch, horn, spiral, cavity backed monopole antennas etc. As will be discussed below the slotted wave guide antenna with shaping guides is provides distinct advantages over the more commonly used antenna types. In the preferred embodiment, the receiving antenna 120 is identical to the transmitting antenna. This antenna receives a signal which is reflected off an object.

Fig. 3 shows the general operation of the system. The system operates by providing an RF pulse from the transmitting antenna 60. This RF pulse then propagates into the range of field 300. Where an object 310 exists in the range of field, a portion of the RF energy incident upon it will be reflected back to the receiving antenna 120. The system can then calculate how long it takes for the RF energy to travel from the transmitting antenna to the receiving antenna and based on the elapsed time, determine the location of the object relative to the transmitting and receiving antennas.

Once the signal is received by the antenna 120, it is fed into the isolation network 110. The isolation network operates to shield the receiver 140 from the initial impulse of RF pulse which is transmitted from the transmitting antenna directly to the receiving antenna when the RF pulse is initially transmitted i.e. the main bang. In the preferred embodiment, the isolation network attenuates the signal during this initial pulse by about 60-80 db. In the preferred embodiment the isolation network 110 is actually incorporated in to the circuit connection with the receiving antenna 120. The receiving antenna 120 is slotted array antenna and the connection to the back panel of the slotted array antenna can be a microstrip to waveguide probe launch. Once the signal has gone through the isolation network it is then received by the limiting low-noise amplifier 100.

In the preferred embodiment the limiting low-noise amplifier 100 operates to improve the signal to noise ratio of the RF signal by providing approximately 30 db of amplification to the received RF pulse at 5.8Ghz. This amplification serves to increase the power of the transmitted and received signal relative to noise which is also present at the input of the low-noise amplifier 100. Once the signal has gone through the low-noise amplifier, it is then propagated to the match network 150. The match network operates to ensure that there is an efficient matching of phase and impedance between the low- noise amplifier and the high speed gated receiver 140.

The high speed gated receiver 140 is driven by a trigger pulse fifty percent duty cycle 5Mhz square wave which is output by the receive trigger pulse 90. The receive trigger pulse operates in the same manner as the transmit trigger pulse, but the output of the receive trigger pulse is delayed to coincide with the amount of time it takes the RF pulse to travel from the transmitting antenna to the receiving antenna. Where the high speed gated receiver detects a signal indicating that an RF pulse was received a certain amount of time after the RF pulse was transmitted from the antenna 60, then the digital signal processor 160 will be able to calculate the distance which the signal traveled going from the transmitting antenna to the receiving antenna based on the amount of delay incurred.

The operation of the receiver of the invention is well understood by one skilled in the art. Basically, the receiver is a sample and hold receiver. The receiver operates in conjunction with the transmission part of the system. A very simple example is shown where the transmitter outputs a signal at a time tO. The receiver can then be turned on at a time tO+15 nanoseconds. If the receiver determines that there is a reflected RF pulse at the time t0+15 nanoseconds, then it can be determined that there is an object at a point equal to 7.5 nanoseconds away from the transmitting antenna. This would correspond to an object approximately 7.5 feet from the transmitting antenna. To achieve an accurate reading on the location of objects, the receiver and transmitter are used in conjunction with each other to take samples at very close time increments. For example, in the preferred embodiment a sample is taken every 200 nanoseconds (l/5Mhz = 200 nanoseconds). For range distance of 25 feet and the scan rate set at 40 Hz (25msec scan rate) in 25miliseconds with a 5Mhz PRF there are 125,000 pulses per scan. This equates to a sample every 2.4 mils. This technique is well known in the art.

An example of the transmitted and received signal samples is shown in Fig. 4. The RF pulse of 5.8 Ghz is transmitted from the transmitting antenna for a period t3 — 11. In one embodiment of the invention this period of transmission is approximately 12 nanoseconds. The RF pulse is initially received by the receiving antenna a short time, t2, after tl . The time t2 corresponds to the amount of time it takes for the RF pulse to propagate from the transmitting antenna to the receiving antenna. At a time t4 the receiving antenna receives an

RF pulse which is reflected from an object in the range of the transmitted RF pulse. The time it takes for the pulse to travel from the transmitting antenna to the receiving antenna is equal to t4 - tl . Based on the amount of time it takes for the RF pulse to be received the distance which the pulse has traveled can be calculated.

For example, if the high speed gated receiver determines that the leading edge of an RF pulse was received by the RF antenna 20 nanoseconds after it was transmitted by the transmitting antenna, then it can be determined, based on the propagation speed of the RF pulse, that the object is approximately 10 feet from the transmitting and receiving antennas. In the preferred embodiment, the transmitting and receiving antennas are located in very close proximity to each other.

The above described method of calculating the distance of an object from the transmitting and receiving antennas is based on the idea of using the leading edge of the signal to determine when an RF pulse is transmitted and when it is received. Using the leading edge of the RF pulse does not work well, however, in a situation where the object was located at a very close proximity to the antennas, such as 12 inches from the transmitting and receiving antennas, unless a very short RF pulse is used. For example, in the scenario discussed above a 12 nanosecond pulse was used. If the object was located one foot away from the transmitting antenna the RF pulse would be reflected from the object and received by the receiving antenna about 2 nanoseconds after the starting point of the RF pulse. This type of scenario is shown in Fig. 5. The RF pulse going from the transmitting antenna is shown during the period tl to t3. The main bang occurs from tl+t2 and continues until t3+t2. The RF pulse reflected by the object one foot from the transmitting and receiving antennas is received from time tl+to up until time t3+to. Many prior systems which are keyed to detect pulses based on the leading edge would fail to recognize the existence of an object where the leading edge of the received pulse occurs during the main bang.

In order to overcome this problem, the prior art systems use a very narrow pulse, so that even if a reflected pulse is received a couple of nanoseconds after the initial transmission of the RF pulse the main bang will have subsided, and the leading edge of the reflected signal can still be easily detected by the receiver. As discussed above the problem with using the a narrow pulse is that it will result in a signal having a broad frequency bandwidth. The present invention overcomes the problems discussed above by using the trailing edge of the reflected RF pulse to determine the propagation time of the RF pulse, where the reflected pulse overlaps with the main bang. For example the propagation time for Fig. 5 can be determined by detecting the trailing edge of the pulse at time t3+to and then subtracting the RF pulse time duration, in this case 12 nanoseconds. This calculation establishes the time at which the leading edge of the reflected RF pulse was first detected. Once leading edge of the reflected RF pulse has been determined the propagation time is obtained by subtracting the time at which the leading edge of the RF pulse was transmitted. Once the time period extends to more than two times the length of the

RF pulse width, then the system can utilize the leading edge of the reflected RF pulse.

The high speed gated receiver outputs a signal corresponding the entire scanned range at a frequency of 40hz. This means that every 25 milliseconds another range field area worth of information is output by the high speed gated receiver. The high speed gated receiver 140 operates in the manner of a standard digital oscilloscope and is widely understood in the industry as a sample and hold circuit based on an integrator function. Fig. 8 is a detailed schematic showing an embodiment of the low noise amplifier 100, the high speed gated receiver 140, and the match network, and isolation network. The input from the antenna Al is routed through the blocking capacitor C14 and through two low noise amplifiers LAI and LA2. After going through LA2 the signal is transmitted through elements C12 and C6 as well as by resistor RI and a quarter wavelength inductor Gl which is coupled to ground. The purpose for this is to act as a matching network to isolate the 5.8 Ghz signal received by the antenna. The diodes Dl and D2 operate as switching diodes to key the receiver on and off as is known and practiced in typical sample and hold methods. The diodes are keyed on and off by the RX trigger signal which is passed through inverters II and 12. The signal which is keyed on and off by the switching diodes is then routed to the amplifier A2 and output at RX video out.

In the preferred embodiment the signal output by the high speed gated receiver is input to a buffer amplifier 170 which matches the output of the receiver with the processing circuitry. The output is then transmitted to a high pass filter 180. The high pass filter 180 reduces the amount of noise in the signal and transmits the signal to the range squared amplifier 190. The range squared amplifier operates to normalize the signals received to account for signal attenuation resulting from propagation losses. For example, a signal which has been reflected off an object 15 feet from the transmitting and receiving antennas will be much smaller than a signal which has been reflected off an object which was 2 feet from the transmitting and receiving antennas.

The signal from the range squared amplifier is then transferred through the absolute value circuit 230, the video BW smoothing amplifier 220, the comparator detection control circuit 210 and then to the digital signal processor 160. The digital signal processor is driven by the constant amplitude ramp generator 130 at the same rate as the signal output from the high speed gated receiver. Thus, the digital signal processor will be able to identify which signals correspond to a certain amount of propagation delay as the RF signal travels from the transmitting antenna to the receiving antenna.

The digital signal processor is can be any of a wide range of simple processors as are widely available. This processor is programmed to operate in accordance with the above described methods to calculate the distance traveled by an RF pulse in the manner described above. While the system could be implement in a number of ways, the system shown in Fig. 1 shows a relatively simple configuration. Specifically, because the scan rate of processor is the same as the output rate of the receiver the processor can easily determine the amount of time that it takes for a signal to travel from the transmitting antenna to the receiving antenna. The digital signal processor is also able to determine if the amount of time that it takes for the RF pulse to travel from the transmitting antenna to the receiving antenna is greater than two times the RF pulse width. If it is not greater than two times the RF pulse width, then the digital signal processor will look to the trailing edge of the initial pulse received by the receiver to determine the travel time of the RF pulse. Based on this travel time, the digital signal processor will determine the distance from the transmitting antenna to the object which has reflected the RF pulse. Where the RF pulse is received at a time greater than two times the pulse width, then the digital signal processor will recognize that its calculations can be based off of the leading edge of the second pulse received by the receiver. Thus the leading edge is used to determine the amount of time it takes from an RF pulse to go from the transmitting to the receiving antenna.

Detail of the slotted wave guide antenna employed by one embodiment of the invention is shown in Figs. 6 A and 6B. Fig. 6 A shows an isometric view of the antenna and Fig. 6B shows a plan view of the antenna. As one of skill in the art would recognize, other antenna configurations could also be used. The operation of slotted waveguide antennas without signal shaping guides is known by one skilled in the art. The signal shaping guides 602, however, are unique and provide advantages over the prior art. The slotted waveguide antenna 600 with signal shaping guides 602 shown in Figs. 6A and 6B consists of a transmitting antenna 604 and a receiving antenna 606. Figs. 6A and 6B are generally to scale with Wl being approximately 7 inches. The actual dimensions are a matter of routine optimization and design choice. The signal shaping guides allow the shape of the RF pulse to be more accurately and easily controlled than in other antennas, and it eliminates side lobes of RF energy which often result from other antenna designs.

In the prior slotted array antennas, without the signal shaping guides, the shape of the vertical lobes of a projected RF pulse could be controlled by the dimension and locations of the slots of the slotted array antenna. To a small degree the shape of the horizontal lobe of the RF pulse could also be affected by the dimension and locations of the slots of the slotted array antenna. In prior short range radar systems this necessitated the power of the RF pulse be increased so that there would be enough energy focussed in a direction where the system sought to detect objects. Typically, the area where objects are sought to be detected is a horizontal range of about 50 degrees form the transmitting antenna.

The slotted array antenna signal shaping bodies allows for better control over the shape of the field projected by the antenna. Specifically, in the preferred embodiment the goal is for an RF pulse with projected energy in the area where objects are sought to be detected. As shown in Fig. 7, in the preferred embodiment the target design is for a vertical field of approximately 20°. In the horizontal direction, the field of the RF pulse has 50° range. The shaping of the RF lobes in the vertical direction is done by the shaping of the slots 608 of the slotted wave guide antenna as known in the art. The shaping of the RF lobes in the horizontal direction is significantly aided by using the signal shaping guides which are orientated so that the are parallel relative to alignment of the slotted array alignment, and perpendicular to the vertical projection of the RF lobe. The prior art uses a shaping of the slot arrays to affect the field of the prior art slot array antennas, however, it is more difficult to control the shape of the field projected by the antenna and there tends to be more of a vertical lobe on the slot array antenna without the signal shaping guides. These lobes can be reflected off the ground to the receiver which will cause a need for filtering, or for otherwise dealing with this reflection of energy off of the ground. The ability to control the shape of the projected field allows for there to be less power used and to create a more definitive projection of radiation. While the method and apparatus of the present invention has been described in terms of its presently preferred and alternate embodiments, those skilled in the art will recognize that the present invention may be practiced with modification and alteration within the spirit and scope of the appended claims. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Further, even though only certain embodiments have been described in detail, those having ordinary skill in the art will certainly understand that many modifications are possible without departing from the teachings thereof. All such modifications are intended to be encompassed within the following claims.

Claims

What is claimed is:

1. An apparatus for using a high frequency signal to detect objects, comprising: a power splitter which receives a high frequency pulse and divides the high frequency pulse into a first pulse component and a second pulse component; a phase shifter for shifting the phase of the first pulse component relative to the phase of the second pulse component; a power combiner which combines the first pulse component and the second pulse component into a complex high frequency pulse; a transmitting antenna coupled to the power combiner for transmitting the complex high frequency pulse; and a receiving antenna for receiving the complex high frequency pulse after it has been reflected by an object.

2. The apparatus of claim 1 further comprising: a low-noise amplifier coupled to the receiving antenna; and a receiver coupled to the low-noise amplifier.

3. The apparatus of claim 2 further comprising: a digital signal processor coupled to the receiver, wherein the digital signal processor determines the distance between the object reflecting the RF pulse and the transmitting antenna, based on detecting a trailing edge of a reflected RF pulse.

. The apparatus of claim 1 further comprising: a trigger pulse generator coupled to a pulsed RF signal generator; the pulsed RF signal generator including an RF oscillator which oscillates at a RF frequency; and wherein the RF signal generator is operative to output a pulse of the RF frequency to the power splitter in response to a signal from the trigger pulse generator.

5. The apparatus of claim 4 wherein the trigger pulse generator outputs a transmit signal at a first frequency, and wherein the RF signal generator outputs RF pulses at a rate equal to the first frequency.

6. The apparatus of claim 5 further comprising: a receiver coupled to the receiving antenna; a receive trigger pulse generator coupled to the receiver, wherein the receive pulse generator outputs a receive signal at the first frequency which drives the receiver.

7. The apparatus of claim 6 further including a delay loop which delays the operation of the of the receive trigger pulse generator relative to the transmit trigger pulse generator, and thereby delays the receive signal relative to the transmit signal.

8. The apparatus of claim 1 wherein the transmitting antenna is a slotted array antenna having signal shaping guide, and the receiving antenna is a slotted array antenna having signal shaping guides.

9. An apparatus for using a high frequency pulse to detect objects in a range, comprising: an RF pulse generator for generating RF pulses having pulse width of greater than 5 nanoseconds; a transmitting antenna coupled to the RF pulse generator which transmits the RF pulses; a receiving antenna which receives the RF pulses transmitted by the transmitting antenna where the RF pulses have been reflected by an object; a receiver coupled to the receiving antenna; and a digital signal processor which determines the distance between the object and the transmitting antenna.

10. The apparatus of claim 9 further comprising: a power splitter coupled between the RF pulse generator and the transmitting antenna, wherein the power splitter has a first output branch and a second output branch; a power combiner having a first input and a second input and a power combiner output, wherein the power splitter first output branch is coupled to the first input of the power combiner and the power splitter second output branch is coupled to the second input of the power combiner, and wherein the power combiner output is coupled to the transmitting antenna; and a phase shifter coupled between the power splitter first output branch and the first input of the power combiner.

11. The apparatus of claim 9 further comprising: a low-noise amplifier coupled between the receiving antenna and the receiver.

12. The apparatus of claim 9 wherein the digital signal processor is operative to determine the distance between the object and the transmitting antenna based on the time at which the receiver receives the trailing edge of a reflected RF pulse.

13. The apparatus of claim 9 wherein the digital signal processor is operative to determine the distance between the object and the transmitting antenna based on the time at which the receiver receives the trailing edge of a reflected RF pulse when the object is located within a first distance range from the transmitting antenna, and wherein the digital signal processor is operative to determine the distance between the object and the transmitting antenna based on the time at which the receiver receives the leading edge of a reflected RF pulse when the object is located a second distance range from the transmitting antenna.

14. The apparatus of claim 9 wherein the transmitting antenna is a slotted array antenna having signal shaping guides, and the receiving antenna is a slotted array antenna having signal shaping guides.

15. An apparatus for using a high frequency signal to detect objects, comprising: an RF pulse generator for generating RF pulses, wherein the RF pulse generator includes a RF oscillator which generates a signal at a fixed frequency; a transmitting antenna coupled to the RF pulse generator which transmits the RF pulses; a receiving antenna which is receives an RF pulse which was transmitted by the transmitting antenna and reflected by an object; and a low noise amplifier coupled to the receiving antenna, wherein the low noise amplifier amplifies a portion of the received RF pulse which corresponds to the fixed frequency.

16. An apparatus for using high frequency pulses to detect objects in a range, comprising: an RF pulse generator for generating RF pulses having pulse width of greater than 5 nanoseconds; a transmitting antenna coupled to the RF pulse generator which transmits the RF pulses; a receiving antenna which is receives the RF pulses transmitted by the transmitting antenna where the RF pulses have been reflected by an object; a receiver coupled to the receiving antenna; a digital signal processor which determines the distance between the object and the transmitting antenna, wherein the digital signal processor is operative to determine the distance between the object and the transmitting antenna based on the time at which the receiver receives the trailing edge of a reflected RF pulse; a power splitter coupled between the RF pulse generator and the transmitting antenna, wherein the power splitter has a first output branch and a second output branch; a power combiner having a first input and a second input and a power combiner output, wherein the power splitter first output branch is coupled to the first input of the power combiner and the power splitter second output branch is coupled to the second input of the power combiner, and wherein the power combiner output is coupled to the transmitting antenna; a phase shifter coupled between the power splitter first output branch and the first input of the power combiner; and a low-noise amplifier coupled between the receiving antenna and the receiver.

17. An method for using high frequency pulses to detect objects, comprising the steps of: generating an RF pulse; transmitting the RF pulse; receiving the RF pulse when it is reflected by an object; detecting the trailing edge of the reflected RF pulse; and determining the distance between the transmitting point of the RF pulse and the object reflecting the pulse based on the detection of the trailing edge of the reflected pulse.

18. The method of 17 further comprising the steps: splitting the RF pulse into a first RF pulse component and a second RF pulse component; shifting a phase of the first RF pulse component relative a phase of the second pulse component; and recombining the first RF pulse component with the second RF pulse component.

19. The method of claim 17 further comprising the step of routing the reflected RF pulse through a low noise amplifier.

20. A method for using a high frequency RF pulse to detect an object, comprising the steps of: generating an RF pulse; using a transmitting antenna to transmit the RF pulse; using the receiving antenna to receive the RF pulse when it is reflected by an object; detecting the trailing edge of a reflected RF pulse; calculating the amount of time it takes for the RF pulse to travel from the transmitting antenna to the receiving antenna based on the detecting the trailing edge of the reflected RF pulse.

21. A method for using high frequency pulses to detect an object, comprising the steps of: generating an RF pulse; splitting the RF pulse into a first RF pulse component and a second RF pulse component; shifting a phase of the first RF pulse component relative a phase of the second pulse component; and recombining the first RF pulse component with the second RF pulse component to create a complex pulse; transmitting the complex RF pulse; and receiving the complex RF pulse when it is reflected by an object.

22. The method of 21 further comprising the steps: detecting the trailing edge of the reflected complex RF pulse; determining the distance between the transmitting point of the complex RF pulse and the object reflecting the complex RF pulse based on the detection of the trailing edge of the reflected pulse.

23. The method of claim 21 further comprising the step of routing the reflected RF pulse through a low noise amplifier.

24. A method for using high frequency pulses to detect objects, comprising the steps of: generating an RF pulse; transmitting the RF pulse; receiving the RF pulse when it is reflected by an object, and routing the reflected RF pulse through a low noise amplifier.

25. The method of 24 further comprising the steps: detecting the trailing edge of the reflected RF pulse; determining the distance between the transmitting point of the

RF pulse and the object reflecting the RF pulse based on the detection of the trailing edge of the reflected pulse.

26. The method of claim 24 further comprising the following steps done prior to transmitting the RF pulse: splitting the RF pulse into a first RF pulse component and a second RF pulse component; shifting a phase of the first RF pulse component relative a phase of the second pulse component; and recombining the first RF pulse component with the second RF pulse component.

27. A slotted waveguide antenna including: a housing made of conducting material, wherein said housing has a first face said first face having disposed therein a plurality of slots; and a first signal shaping guide protruding from said first face, such that the signal shaping guide limits the range of a signal projected from said plurality of slots when an electrical impulse is conducted by the conducting material of the housing.

28. The slotted waveguide antenna of claim 27 further including a second signal shaping guide protruding from said first face, such that the second signal shaping guide limits the range of a signal projected from said plurality of slots when an electrical impulse is conducted by the conducting material of the housing.