Patent Application
20070159380
The present invention relates to millimeter-wave radar apparatuses which detects a distance from an object by receiving a reflection signal of a radiated electromagnetic wave of a millimeter-wave band reflected by the object and a millimeter-wave radar systems using the apparatuses, and more particularly, to a near-field millimeter-wave radar apparatus which observes an object present at a position away by a short distance from a vehicle and a millimeter-wave radar system using the apparatus.
A related microwave/millimeter-wave apparatus, for the purpose of obtaining its small size and low cost, is arranged so that a planar antenna is provided on the rear surface of a dielectric substrate (refer to JP-A-11-330163). More specifically, in FIG. 18 of JP-A-11-330163, a planar antenna 141 is provided on the rear surface of a dielectric substrate 1, and a semiconductor substrate 2 is provided on the front surface of the dielectric substrate 1 with metallic bumps disposed therebetween. In JP-A-11-330163, further, as an arrangement of radiating heat from an active circuit on the semiconductor substrate 2, there is disclosed an arrangement wherein a conductor 71 is provided on the rear surface of the semiconductor substrate 2 so that heat generated in the active circuit positioned on the front surface of the semiconductor substrate 2 is transmitted to the conductor 71 on the rear surface of the semiconductor via a through hole passed through the front and rear surfaces of the semiconductor substrate 2 to radiate the heat through the conductor 71 and to provide a good heat radiating performance to an active element, as shown in FIG. 7(b).
An example of related antenna integrated microwave-millimeter wave circuits has an arrangement wherein a metallic base for radiating heat to the periphery of a dielectric substrate (for example, refer to JP-A-10-233621). More specifically, in FIG. 6 of JP-A-10-233621, a microstrip antenna is made of a radiating conductor 553 and a ground conductor 552 and a metallic base 560 for reinforcement and heat radiation is provided around a dielectric substrate 551 to be electrically connected to the ground conductor 552.
The inventor, et al. of this application has studied microwave-millimeter wave radar techniques prior to this application. Use of a high frequency circuit module of microwave-millimeter wave is increasingly expanded as a module for transmitting and receiving a high frequency signal for a car-mounted radar or inter-car communication. For detecting an obstacle around a vehicle with a wide angle, a car-mounting near-field radar, in particular, is desired to be mounted at various positions such as the interiors of vehicle bumper, lamp and door mirror. However, the operation of the high frequency circuit module for car mounting is required to be ensured in a temperature range of from minus tens of degrees (e.g., about −40 degrees) to plus hundred and tens of degrees (e.g., about +110 degrees). When the high frequency circuit module is installed within such a closed space tending to have heat confined therein as the interior of bumper, lamp or door mirror, the high frequency circuit module is required to satisfy severe specifications to a temperature environment. With the arrangement of the high frequency circuit module, when it is impossible to realize an embodiment arranged to suppress a thermal resistance, a difference in temperature between the ensured-operation range of the high frequency circuit module and a temperature outside the apparatus becomes large. In particular, when the temperature outside the apparatus is high, the operation of active circuit becomes out of the operation-ensured temperature range, so that the high frequency circuit module is erroneously operated. In the case of the car-mounted radar, since the radar is treated as a sensor in a vehicle control device, the erroneous operation of the high frequency device leads to a delay in accident avoidance and thus a measure of heat radiation in the high frequency device is highly important. Further, since the bumper, lamp, or door mirror of a vehicle has a small limited space, the car-mounted radar is required not only to take the aforementioned heat radiation measure but also to have a small size. The exemplary arrangements of such a related device as to take the heat radiation measure are disclosed in JP-A-11-330163 and JP-A-10-233621.
In the case of the heat radiation arrangement having a conductor provided on the rear surface of a semiconductor substrate as shown in JP-A-11-330163, however, heat from the conductor is further required to be escaped to outside the device. To this end, a means for externally escaping heat from the conductor is additionally required, for example, by further providing a fin on the conductor. From it, the inventor, et al. of this application have uniquely found a disadvantageous problem when the device is made small in size.
In addition, in the case of such an arrangement as shown in JP-A-10-233621, a ground conductor and a metallic base for contributing to heat radiation in a microstrip antenna are disposed to be mutually overlapped. Thus the inventor, et al. of this application have uniquely found a problem that, when an electromagnetic wave is radiated from the microstrip antenna to outside an antenna integration millimeter-wave circuit, the metallic base disturbs the heat radiation, thus involving the deterioration of an electric wave radiation characteristic.
A typical embodiment of the present invention as an example is as follows. That is, in accordance with an aspect of the present invention, there is provided a millimeter-wave radar apparatus which includes a multilayer substrate made of a plurality of stacked layers, an active circuit provided on a first surface of the multilayer substrate, an antenna provided on a second surface of the multilayer substrate opposed to the first surface thereof for radiating an electric signal of millimeter-wave generated by the active circuit in the form of an electromagnetic wave, and a first heat transmitting plate provided on the second surface for externally radiating heat generated in the active circuit. The antenna is electrically connected with the active circuit via a first via hole formed to pass through at least part of the multilayer substrate defined by the first and second surfaces of the multilayer substrate when viewed as A.C. circuit. The heat transmitting plate is formed to pass through at least part of the multilayer substrate defined by the first and second surfaces thereof, and also is thermally connected with the active circuit via a second via hole formed as a via hole different from the first via hole.
The present invention provides a millimeter-wave radar apparatus which realizes compatibility between an improvement in the heat radiation characteristic of the apparatus and an improvement in the electronic wave radiation characteristic thereof.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.
A millimeter-wave radar apparatus in accordance with the present invention includes a multilayer substrate, an active circuit, an antenna, a thermal via hole, and a heat transmitting plate. The active circuit is realized preferably as an active element in an RF circuit. The apparatus also includes a casing for fixing the entire millimeter-wave radar apparatus to a vehicle or the like. The RF circuit and the antenna are provided on the front and rear surfaces (or first and second surfaces) of the multilayer substrate respectively, and a plurality of thermal via holes are provided in the interior of the multilayer substrate. The heat transmitting plate formed on the second surface is formed therein with an opening which acts not to deteriorate the radiation characteristic of the antenna formed on the same second surface. Heat generated in an MMIC (Monolithic Microwave Integrated Circuit) as an example of the active element of the RF circuit is transmitted through the thermal via hole and the laminated metallic layer and diffused on the surfaces of the multilayer substrate. Heat reaching the rear or second surface of the multilayer substrate is radiated from the heat transmitting plate provided on the second surface.
The thermal via hole is preferentially located under the MMIC mounted on the multilayer substrate. However, since especially the stable operation of an oscillator directly affects the performance of the radar, the oscillator is positioned on the multilayer substrate to be connected via the multilayer substrate to the heat transmitting plate with the shortest distance to the plate, thus reducing a thermal resistance. The heat transmitting plate is connected suitably to the casing of the millimeter-wave radar apparatus. However, the present invention is not limited to this example, but the casing may be formed integrally with the heat transmitting plate. Or the heat transmitting plate may be connected with the shortest distance to the mounting hole of the millimeter-wave radar apparatus, or the heat transmitting plate may form part of the casing and a hole for mounting the millimeter-wave radar apparatus may be provided in the heat transmitting plate. With such an arrangement, since a thermal resistance from the MMIC as the active circuit to the radar casing mounting hole is reduced, an increase in the operational temperature of the millimeter-wave radar apparatus can be suppressed. Thus, even the external environment temperature is high, the millimeter-wave radar apparatus can be operated continuously stably.
More specifically, a millimeter-wave radar apparatus of the present invention includes a multilayer substrate made of a plurality of overlapped layers, an active circuit provided on a first surface of the multilayer substrate, an antenna provided on a second surface of the multilayer substrate opposed to the first surface thereof for radiating a millimeter-wave electric signal generated in the active circuit in the form of an electromagnetic wave, and a first heat transmitting plate provided on the second surface for externally radiating heat generated in the active circuit. The antenna is electrically connected to the active circuit through a first via hole formed so as to pass through at least part of the multilayer substrate defined by the first and second surfaces thereof when viewed as an A.C. (Alternating Current) circuit. The heat transmitting plate is formed so as to pass through at least part of the multilayer substrate defined by the first and second surfaces thereof, and is also thermally connected to the active circuit through a second via hole formed as a via hole different from the first via hole.
In this case, the active circuit and the heat transmitting plate are located suitably so that heat generated in the active circuit is transmitted to the heat transmitting plate through the second via hole, with the shortest route thereto. The active circuit and the first heat transmitting plate are provided suitably so as to be thermally connected commonly by a plurality of such second via holes. Or suitably, the heat transmitting plate has such an opening as to externally expose the antenna, the antenna is located in a region of the second surface having the opening positioned therein, and a radio wave absorber is provided so as to straddle the opening of the heat transmitting plate and the other part thereof except for the opening. The radio wave absorber has suitably a tapered shape. The radio wave absorber is also made of preferably a material containing powder which absorbs electromagnetic wave. The material contains most preferably powder of at least one of sorts of carbon, graphite, silicon carbide, and carbon nanotube.
The millimeter-wave radar apparatus of the present invention further includes preferably a casing for fixing the multilayer substrate. In this case, the multilayer substrate may be fixed to the casing through the first heat transmitting plate so as to secure a heat radiation path to externally radiate heat from the heat transmitting plate through a plurality of holes provided in the casing. Alternatively the first heat transmitting plate and the casing may be integrally formed to secure a heat radiation path to externally radiate heat from the heat transmitting plate through a plurality of holes provided in the casing.
The first heat transmitting plate and the multilayer substrate are mutually bonded preferably using at least one of a heat transmitting adhesive, a conductive adhesive, flip-chip bonding, and an anisotropic adhesive. When the both are mutually bonded, in particular, by flip-flop bonding or with use of the anisotropic adhesive, the via hole is also used as an input/output terminal. The heat transmitting plate includes preferably a heat transmitting metallic conductor. Or the heat transmitting plate may be made of a material containing a resin. In this case, at least one of a signal processing circuit and a power supply circuit in the millimeter-wave radar apparatus is mounted preferably on the heat transmitting plate.
The millimeter-wave radar apparatus of the present invention further includes preferably a polarizer for suppressing the interference of cross polarized waves. In this case, the polarizer is provided preferably on a side of the multilayer substrate opposed to the radio wave absorber opposed to the multilayer substrate with the absorber disposed between the polarizer and the multilayer substrate. The millimeter-wave radar apparatus further includes preferably a radome which covers the entire multilayer substrate and is positioned on a side of the radio wave absorber opposed to the multilayer substrate with the absorber disposed between the multilayer substrate and the radome. In this case, the thickness of the radome is set to be preferably nearly equal to an integral multiple of λ/2, where λ denotes the wavelength of the electromagnetic wave radiated from the antenna. When the millimeter-wave radar apparatus of the present invention further includes a casing for fixing the multilayer substrate, the radome is preferably fixed to the casing.
In the millimeter-wave radar apparatus of the invention, the active circuit and the antenna are electrically connected by the microstrip line and the first via hole when viewed as an A.C. circuit, and the first via hole is a pseudo coaxial line which is made of a plurality of via holes passed through at least part of the multilayer substrate and acts as a pseudo coaxial line. When λ denotes the wavelength of the electromagnetic wave radiated from the antenna, a metallic conductive layer forming a counter electrode of the microstrip line is formed preferably in the form of a landless gap pattern with a gap of λ/4 from the via hole as the center conductor of the pseudo coaxial line.
A millimeter-wave radar system in accordance with the present invention includes a millimeter-wave radar apparatus arranged to be mounted in a vehicle. The millimeter-wave radar system is arranged to observe an obstacle to the vehicle. In this case, the millimeter-wave radar apparatus includes a multilayer substrate made of a plurality of overlapped layers, an active circuit provided on a first surface of the multilayer substrate, an antenna provided on a second surface of the multilayer substrate opposed to the first surface for radiating a millimeter-wave electric signal generated by the active circuit as an electromagnetic wave, and a first heat transmitting plate provided on the second surface for externally radiating heat in the active circuit. The antenna is electrically connected to the active circuit through a first via hole formed to pass through at least part of the multilayer substrate between the first and second surfaces thereof when viewed as an A.C. circuit. The heat transmitting plate is thermally connected to the active circuit through a second via hole different from the first via hole and formed to pass through at least part of the multilayer substrate between the first and second surfaces thereof. As in the aforementioned millimeter-wave radar apparatus, the active circuit and the heat transmitting plate are located to preferably transmit heat generated in the active circuit to the heat transmitting plate through the second via hole with the shortest route, and the active circuit and the first heat transmitting plate are preferably thermally connected commonly by a plurality of the second via holes.
The present invention will be explained in detail in connection with several embodiments as the preferred examples of embodying the present invention, by referring to the accompanying drawings.
A circuit for RF control is provided within the casing and above the multilayer substrate having the RF circuit board mounted thereon. The RF circuit and the RF control circuit are connected by a wire. In the arrangement of the present embodiment, since the RF control circuit and the RF circuit are vertically arranged into a row, the horizontal-direction width of the casing can be reduced.
Since the car-mounted radar handles a microwave or millimeter wave having a short wavelength, a small change in the length of the antenna caused by a temperature variation affects its radar characteristic. However, since the antenna and the heat transmitting plate are provided as separated members on one surface of the multilayer substrate in the present invention, heat generated in the active circuit is concentrated not on the antenna but on the heat radiating plate having a thermal resistance lower than the antenna. Thus, a change in the length of the antenna caused by a temperature variation affects the radar characteristic. Considering also the fact that the antenna characteristic is deteriorated by the thermal concentration on the antenna, the present invention proposes an arrangement of providing the antenna and the heat radiating plate as separated members.
Since millimeter wave has a large transmission line passage loss, it is necessary to minimize the length of a transmission line between the oscillator and the antenna. To this end, when the RF circuit and the antenna are mounted on the front and back surfaces of the multilayer substrate, the oscillator and the amplifiers in the RF circuit are positioned so as to minimize the length of the millimeter-wave transmission line. At the same time, however, it is also required to realize a heat radiation structure.
In the present invention, since a thin ceramic multilayer substrate is employed, it is advantageous to provide the heat radiating plate on the antenna side close in distance to the MMIC because of short wiring.
Further, the polarizer 10, which can advantageously suppress the orthogonal polarization of the antenna 3 and reduce the side lobe of the radiation characteristic, is located in front of the antenna. The support base 9 is provided to limit a distance between the polarizer 10 and the antenna 3. For securing the resistance to environment and reliability of the antenna 3, the radome 11 is provided in front of the antenna so as not to come into direct contact with its ambient environment. The thickness of the radome is set to an integral multiple of ½ of the electromagnetic wave radiated from the antenna 3 so as to allow the electromagnetic wave to be efficiently transmitted through the radome.
In the present embodiment, since the heat transmitting plate 4 is used also as the RF circuit control board 23, the millimeter-wave radar 100 (casing) can be made thin in thickness. Accordingly, when the radar is mounted in a vehicle, the radar can be mounted even in a location having a narrow radar installation space such as parts of the vehicle around its front side. Further, heat issued from the top of the RF circuit 2 tends to be easily escaped to outside the casing advantageously.
In the millimeter-wave radar 100, according to an operational program written in the recording circuit 34, the digital circuit 33 activates a CPU (Central Processing Unit) or a DSP (Digital Signal Processing), and the analog circuit 31 drives a radar sensing part of the RF circuit 2 through the A/D and D/A conversion circuit 32. The RF circuit 2 receives a reflected signal including a Doppler signal from the antenna 3, generates an intermediate frequency IF signal containing the Doppler signal, and transmits the IF signal to the analog circuit 31. The IF signal is amplified and waveform-shaped to a certain extent by the analog circuit 31, sampled by the A/D and D/A conversion circuit 32, and then processed by the digital circuit 33. The digital circuit 33, according to the program of the recording circuit 34, calculates a relative speed, a relative distance, a relative angle, and so on on the basis of a reflected wave from an obstacle. These calculated results are recorded in the recording circuit 34 and also transmitted externally from the input/output circuit 36.
The active circuits of the oscillator 14, the power amplifier 15, and the receiver 16 are mounted on the multilayer substrate 1 by soldering or with a conductive adhesive. When these active circuits 7 are mounted face-up, the millimeter-wave signal is transmitted to the transmission line of the multilayer substrate 1 via a bonding wire or ribbon line. As the transmission line of the millimeter-wave signal between the RF circuit 2 and the antenna 3, a pseudo coaxial line 18 using a via hole is used. The IF signal generated by the receiver 16 is again transmitted to the analog circuit 31 via the power and signal lines 19.
Although not shown, the active circuit can also be mounted on the multilayer substrate 1 in the form of a flip chip. In the case of the flip chip mounting, a multiplicity of bump metals are provided to increase the surface area of contact with the heat radiating via hole 5. Further, an active circuit having a small amount of heat generation is employed. When the active circuit is mounted in the form of a flip chip, a wire bonding step can be eliminated and thus its productivity can advantageously be increased.
As has been explained in the foregoing, in accordance with the respective embodiments of the present invention, heat generated in the active circuits of the RF circuit provided on the front surface of the multilayer substrate can be transmitted to the rear side of the substrate through the via holes, further from the heat transmitting plate to the casing, and externally radiated from the mount part of the casing. The heat transmitting plate and the oscillator as a key to the stable operation of the millimeter-wave radar are connected with the shortest distance therebetween with the multilayer substrate disposed therebetween, its thermal resistance can be advantageously reduced. Further, when the wave radiation characteristic of the antenna is improved with use of the radio wave absorber and the polarizer by suppressing the inter-antenna interference, diffracted waves, and the cross polarized waves of the antenna, the position of the obstacle can be accurately measured. In addition, when the radome is used, even a resistance to environment can also be improved, and the reliability of the millimeter-wave radar in addition to the temperature characteristic thereof can be improved.
With the arrangement of providing the RF circuit and the antenna on the front and rear surfaces of the multilayer substrate, when an opening is provided in the heat transmitting plate according to the radiation characteristic of the antenna, the multilayer substrate and the heat transmitting plate can also be made small even when the substrate and the plate are laminated or mounted each other. Thus the miniaturization of the millimeter-wave radar can be realized while maintaining the radiation characteristic. For this reason, even when the millimeter-wave radar of a light weight having a small shape and an improved temperature characteristic is provided in a small-sized closed space such as a door mirror, the radar can stably scan.
As a result, the radar system using a plurality of the millimeter-wave radars can easily grasp environmental conditions outside of a car on a real-time basis. In other words, there are provided car obstacle monitoring sensors which can provide many surrounding situations to the driver in every driving operation of congestion drive, cornering, route change drive, etc. and can prevent a car accident beforehand.
The apparatus can grasp driver's driving pattern in the surrounding environment. That is, there are provided car obstacle monitoring sensors which can statistically derive a safe drive index to the driving. Thus on the basis of the derived safe drive index, driver's car insurance fee can be reduced or a decision to an actual accident can be made from objective view.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-302432 | Oct 2005 | JP | national |
