Pulse radar detection system

#This invention relates to a short-range pulse-compression radar system particularly suitable for fabrication as an integrated circuit.

#A need exists for a short-range radar system, which, for example, is suitable for automotive and other commercial applications. Such a system would be enabled to sense the proximity of other vehicles and objects, moving or stationary, within a range radius of about 0.15 meters to 30 meters or beyond. Radar systems having automotive application have been proposed in the prior art, including systems utilizing radar for automatic braking, as well as warning the operator of the vehicle of an impending danger or obstruction such as an animal or person in the roadway.

#In addition to object range detection, it is also useful to be able to distinguish or resolve the distance between two objects in very close proximity (e.g. when they are approximately 15 centimeters apart). An intelligent radar detection system comprises a number (one or more) of sensors that operate as a transceiver for electromagnetic energy. The sensors typically transmit and receive electromagnetic energy of a defined frequency and power via an antenna over a defined spatial area. In turn, the system receives echo signals from partial reflections of any illuminated objects in that area. The ability of the sensor to resolve two or more objects closely situated in the illuminated area leads to the descriptive name of high-resolution radar (HRR).

#FIG. 1 is a block diagram of a pulse-coded, pulse-compression radar sensor according to an aspect of the present invention.

#FIG. 2 is a schematic diagram of an alternate embodiment of a transmit/receive (T/R) switch used to provide a single antenna according to an aspect of the present invention.

#FIGS. 3A through 3D show a series of timing diagrams and waveforms, including a table necessary to explain operation of the pulse-coded, pulse-compression radar sensor system as depicted in FIG. 1.

#Referring to FIG. 1 there is shown a sensor architecture of a high-resolution radar (HRR) according to an aspect of the invention. The general principle of operation of a typical radar sensor is that of object detection, position and velocity measurement. In a typical radar, a carrier signal is transmitted from the sensor via an antenna. The antenna may be fixed, or steered where the focus of the beam may be dynamically varied by electronic, or mechanical control. In Figure 1, there is shown a separate transmit antenna (Tx) 30 and a receive antenna (Rx) 31. Adjacent to the transmit antenna is an arrow designated Tx indicative of a transmitted signal. Similarly, there is an arrow showing a received signal at the receive antenna 31 designated as Rx. Thus, one can use a separate antenna for transmit and receive, but is also possible to use a single antenna to perform transmit and receive operation by adding additional switching elements without changing the principal of the described invention.

#The transmitted signal Tx is partially reflected by an object 35 at a range R from the plane of the transmit and receive antennas or from the plane of the sensor.

#The transmit operation is as follows. As shown in FIG. 1, microwave source or oscillator 10 generates a carrier signal which is a continuous wave (CW) signal. This CW signal may be either free-running, or frequency or-phase-locked to an external reference oscillator. The microwave source 10 typically would operate in the C-Band range of 4 to 8 GHz (Giga-Hertz) or in the X-Band range of 8 to 12 GHz, 18-25 GHz or higher frequencies. The ability to discriminate a range of 0.15 m (meters) requires a signal with frequency spectrum characteristics of at least 2 GHz in width, which may achieved through ‘chirping’ or modulating a CW signal over a 2 GHz frequency range, or by having a 0.5 nS (nanosecond) or shorter duration pulse. Thus, the transmitter is transmitting pulses, each pulse lasting for a duration number of frequency cycles at the above noted frequencies for C or X-Band, or other frequency-band operation. This is illustrated, for example, in the lower waveform of FIG. 3A. The microwave source is also coupled to FM modulator and frequency correction module 11. The frequency of the carrier signal that emanates from the microwave source 10 can be varied by applying a short term modulating signal that is superimposed on the carrier frequency. This short-term modulating signal is generated by the FM modulation module 11. Frequency correction may be some form of control voltage that stabilizes the frequency of the oscillator within a defined frequency range as a function of temperature or other environmental sources of variation and may be achieved using the aforementioned frequency or phase locking techniques. Such operation can be implemented by a voltage control tuning port associated with the microwave oscillator 10. Such voltage control of an oscillator is well known and a standard technique is the use of a variable reactance device whereby frequency deviation of the microwave source 10 is proportional to the magnitude of an applied DC or AC control signal. Such oscillators are sometimes referred to as voltage controlled oscillators (VCO). Many well known examples of voltage controlled oscillators which can be employed as microwave sources include use of varactor diodes or other variable controllable reactant devices. The FM modulation module 11 provides correction to the microwave source 10 and is used to vary and compensate for changes in source frequency as a function of external influence such as temperature, power supply variation and other variable parameters. Techniques for stabilizing the output frequency of a microwave source 10 according to temperature variations and so on are also well known. The output of the microwave source 10 is coupled to the input of a buffer amplifier 12. The input of the buffer amplifier 12 is coupled to the signal output of the oscillator 10 for the purpose of isolating the oscillator from variations in the output load network as a function of switching transients. The amplifier 12 may provide gain which results in an increase of the magnitude of the carrier signal at the amplifier output. The main function of the amplifier 12 is to reduce the effect of frequency pulling. Frequency pulling is an effect an oscillator undergoes as the magnitude and/or phase of the load network changes. The oscillator 10 provides a continuous wave (CW) output carrier signal. The carrier signal (transmitted pulse) used for object detection is formed by gating the oscillator or CW carrier signal for a prescribed amount of time with a pulse-forming network or pulse-former 13. Pulse-former 13 is shown in FIG. 1 as an ideal implementation of a two or three port switch network that constitutes either an absorptive single-pole single-throw (SPST) switch, or a single-pole double-throw (SPDT) switch. One of the two selected arms (3) is terminated in a matched or dissipative load 14. The usual condition of the switch is in the state where the output of the amplifier 12 is coupled and directed to the dissipative load or resistor 14. In this manner, terminal 1 or the input terminal of the pulse-former is connected to terminal 3, which is the terminal connected to the dissipative load 14. The pulse-former 13 is gated to direct energy towards position 2 of the ideal switch as a function of the transmit pulse interval, and as a function of the range gated time delay. Thus, as seen there is a switch driver module 15 coupled to the pulse-former 13 and which controls the state of the pulse-former according to desired operation.