Radar detector for vehicle suitable in close range applications.

The present invention relates to a radar detector to be installed on mobile means, for short distance applications (less than 500 m), especially anti-collision-type, in particular for motor vehicles.

Discloses the use of radar to microwave in collision avoidance systems for vehicles.

The first known solutions are characterized by the use of a fixed beam in the direction of the axis of the vehicle, but they had all the serious disadvantage of generating a signal from which it was not possible to reconstruct correctly the geometry of the scene situated in front of the vehicle and cause false alarms due to the detection of objects not on the trajectory of the vehicle.

Some successively proposed known solutions have identified also, in addition to the distance and the relative speed of the obstacles located in front of the vehicle, its angular position relative to the axis thereof.

Some of these known solutions use two antennas that receive and extrapolate the angular position of the obstacle with the phase difference between the received signals.

Other known solutions use multiple frequencies to vary the maximum scattering angle of a pair of transmitting antennas.

Finally, other known solutions using multiple transmitter and receiver antennas fixed, with which simultaneously generates multiple microwave beams to cover corresponding adjacent angular sectors.

All these known solutions have significant limitations geometric discrimination and many cases of ambiguous tee in determining the position of obstacles.

Based on these considerations, in order to obtain a radar image with sufficient angular discrimination, para t need to use a single narrow beam with continuous scanning or not finished.

On the other hand, the frequency sweep by means of a network antenna, to obtain a good angular resolution, good discrimination and a distance sufficiently wide scan angle, has the disadvantage of requiring operating frequency bands extremely large (a few GHz), resulting in no difficulties both in manufacturing as the band allocation.

Regarding the scanning phase using an array antenna, it has the drawback of not allowing the achievement, at acceptable costs, a device operating in a frequency band with an antenna overall dimensions small enough to be installed in the vehicle while maintaining the desired angular discrimination.

Furthermore, the mechanical scanning entered not in itself an embodiment bulky, complex and costly due to the masses in play and, in addition, high losses in the course of radio frequency connection with the antenna.

To avoid these losses and reduce moving masses, particularly on proposed antennas of Cassegrain with the fixed radiator and fixed to the transceiver and a reflector subjected to scanning, but this type of solution considerable criticality in mechanical tolerances and assembly and performance limitations due to degradation of the radiant beam at relatively high scan angles.

It is known that the reduced dimensions can be obtained with antennas slotted waveguides, but these antennas are heavy, especially if it includes the movement of the transceiver, and require, among other machining accuracy very high.

The present invention aims to obtain a radar sensor to be installed on mobile means, for short-distance applications, especially the collision type, intended in particular for motor vehicles, which eliminates the aforesaid drawbacks.

This result has been achieved according to the invention by adopting the idea of ​​using a radar sensor comprising an antenna subjected to mechanical scanning and a transceiver pulse signal to a millimeter wavelength, and characterized in that antenna is molded type of plan network; that the transceiver forms a rigid and inseparable together with the antenna and it consists of an integrated circuit with an oscillator driven at two frequencies and with means for performing a heterodyne conversion of the reception signal; that the scanning relates to all antenna-transceiver; and in that it comprises an angular restoration module opto-electronic type, which provides the pointing angle of the antenna beam and its direction of rotation.

According to another characteristic of the invention, the radar pulses are transmitted with low repetition cycle and the oscillator is disabled at the end of the reception interval of the radar echo of the obstacle which is short of the distance predetermined maximum concerning the detection and réasctivé immediately before transmission.

The advantages obtained through the present invention consist essentially in that:<ul><li>all-antenna transceiver has a reduced inertia, a very small footprint and is advantageously applicable to any vehicle so that the transmitted beam never encounter obstacles during the entire scan;</li><li>the use of a cast type of array antenna, associated with the use of a single oscillator for transmission and generating the heterodyne frequency, can significantly reduce manufacturing costs;</li><li>the integration between the antenna and transceiver minimizes losses courses;</li><li>all-antenna transceiver, because it is housed in a molded support, provides a high rigidity and a high resistance to mechanical stresses, including the vibrations transmitted by the moving vehicle;</li><li>the entrainment movement of the entire antenna transceiver constant angular velocity is achieved with simple mechanical means of easy installation and high reliability;</li><li>the angular return module can determine with great accuracy the antenna pointing direction without having to resort to complex servo systems thereof;</li><li>transmitting a pulse signal to a millimeter wavelength allows the use of extremely compact antenna with an optimum angular discrimination for the proposed application;</li><li>disabling the oscillator inside the interval of time during which there is no interesting echo signals not entered a low power dissipation, which avoids the use of sinks;</li><li>the power and control of the transceiver signals and those detected echo is generated and processed, respectively, outside the detector using simple means commonly known, such as a control unit and processing means connected to a shielded wiring.</li></ul>

These advantages and features of the invention and others will be more and better understood by any skilled person in the light of the following description and the accompanying drawings given as a practical exemplification of the invention but not considered in the limiting sense; drawings in which: FIG. 1 shows an overall view, partly exploded, of a radar sensor according to the invention; FIG. 2 is a block diagram of the transceiver antenna system; FIG. 3 shows a time diagram of three trigger signals for starting F_{ac '} modulation F_mo and the frequency command F_fr.

Reduced to its essential structure and with reference to the accompanying drawings, a radar sensor for a vehicle for short distance applications according to the invention consists of:<ul><li>(A) - an antenna 1 to plan the cast type network, consisting of a microstrip circuit (microstrip) for the supply elements (patch) 10 radiating in a narrow beam of the order of one or two degrees azimuth angle and a few degrees of elevation angle;</li><li>(B) - a transceiver 2 millimeter wave, placed in direct contact with the rear face of the antenna 1 and secured thereof by means of a weld connection between the connection track to the transceiver and the center of the antenna feed circuit, comprising:<ul><li>an oscillator driven at two frequencies, arranged to generate sequentially the frequency F₀ and that transmission F₀ - F₁ necessary for mixing, required for the heterodyne conversion in reception phase;</li><li>a directional coupler for sampling the heterodyne signal;</li><li>a fast switch for the formation of the transmission pulse, a duration of the order of ten nanoseconds;</li><li>a mixer in which, by beating between the radar echo signal and that the frequency F₀ - F₁, a signal is generated at an intermediate frequency F_I;</li><li>an amplifier which supplies the output signal for the successive processing;</li></ul></li><li>(C) - a molded member 3 supporting the whole antenna-transceiver 1.2, which is accommodated in a holder casing, not shown in the drawing for reasons of simplification, and provided with means, for example two pivots placed on the axis of rotation Z of said assembly, to allow the horizontal scan: said shell to be appropriately fixed to the vehicle and being provided with a radome 6 in low-loss material in the wave field millimeter and with an extension and a suitable form not to degrade the beam to maximum angles of the scan;</li><li>(D) - the means of entrainment mechanical motion of the antenna-transceiver with a 1.2 micromotor 4 DC, a worm gear motor 41 and 42 teeth wheel chopper dales, a cam 43, keyed on the shaft of said wheel 42, a roller 44 mounted fast, crazy on the aforementioned support 3 and kept in contact with the active profile of the cam 43. Advantageously, the profile of said cam 43 is made in such a way to impose a said set 1.2 reciprocating law trapezo dale, around the Z axis, with the linear portion, that is to say angular velocity constant, within the useful scanning angle;</li><li>(E) - an angular return module 5 with an optical encoder of incremental type, which provides a reference pulse, along the longitudinal axis of the vehicle, and the indication of the antenna rotation: said encoder being keyed on the axis Z of rotation of the antenna or, more advantageously, the rotary disk provided on the support 3 of the whole antenna-transceiver 1.2 and integral with its pivots.</li></ul>

According to the invention, said transmitter-receiver is constituted by a hybrid circuit millimeter waves, which uses as a waveguide structure of a microstrip or a ribbed waveguide (stripline) symmetrical, produced by metallization (by photolithography example) with a dielectric thin film with embedded active components (MIC) possibly monolith (MMIC).

Advantageously, said transceiver 2 is constituted by a single integrated monolithic circuit type.

In another preferred embodiment, the whole antenna-transceiver 1,2 is formed on a single substrate eg by photoetching or deposition increase.

According to the invention, it is intended to exclude the transmission signal near the dead point, that is to say to establish the transmission during movement at a constant angular speed of the whole antenna-transceiver , so as to allow a substantially constant pulse rate and thus avoiding a signal density increase in specific areas and providing a homogenous image of the surrounding space.

Advantageously, the rate is not perfectly constant that is done deliberately vary the repetition period of the pulses following a cyclical pseudo-random law that minimizes the probability of mutual interference between multiple radars operating in the same area : the cycle of variation being shorter than the period required to cover an angle equal to the width of the antenna main beam, the power radiated by the latter results practically constant with the pointing direction.

Hereinafter is described an operation mode can be a radar sensor according to the invention. Once activated power, derived from the main power supply of the vehicle via an external processing unit and control the micromotor 4 starts rotating continuously and the worm wheel transmission mechanism transmits the 41.42 desired reciprocating scanning movement to the whole antenna-transceiver. Simultaneously, the angular playback module 5 also starts to transmit the position pulses to the processing unit and control.

Once the angle pointing into the useful field, the trigger pulse for the transceiver 2 are empowered and, as can be seen in Fig. 3 of the accompanying drawings, it occurs that:<ul><li>Turning on the oscillator (signal F_ac high) with frequency control switched on F₀ transmission frequency (F signal_fr above). </li><li>Brief waiting period t for the stabilization of the amplitude and frequency of the oscillation frequency millimeter.</li><li>F modulation trigger activation_mo which causes the transmission of the pulse RF (radio frequency).</li><li>Switching frequency of the oscilloscope on the frequency heterodyne F₀-F₁ (F signal_fr low).</li><li>Maintaining the operation of the oscilloscope for receiving radar returns to the maximum distance concerned.</li><li>Turning off the oscilloscope Service (F signal_ac low).</li><li>Switching the frequency control on the transmission frequency F₀ (signal F_fr above).</li><li>Maintain the retirement of the oscillator pending the setting next step and repeating the cycle.</li></ul>

The repetition of the transmission-reception cycle is carried out until it reaches the other end of the scanning, when the external unit, as a result of the reading of the pointing angle on the line of the encoder, inhibits the trigger for the transceiver.

The radar echo signal relating to each transmitted pulse, is easily synchronized with the antenna pointing data 1 and is available for the production of images and for the successive processing.