FM radar system

Abstract: An FM radar system of more simple construction, smaller size, lower cost and improved performance is provided in which circulators of any type in the prior art are eliminated by constructing a transceiver comprised of a transmitting part (10) and a receiving part (20), each formed on a common dielectric plate (1) and having a dedicated transmitting antenna (11) and a dedicated receiving antenna (21) respectively. The antennas comprise planar array antennas, in contrast to the solid antennas used in prior art systems. The planar array antennas are also formed on the single dielectric plate. The transmitting part comprises a plurality of transmission antennas (11) and a plurality of frequency multipliers (12) coupled to said transmission antennas. The receiving part comprises a plurality of receiving antennas (21) which are coupled to a plurality of switches through a plurality of mixers (23), frequency multipliers (22), and low noise amplifiers (24).

Description: BACKGROUND OF THE INVENTION The present invention relates to FM radar systems, and in particular, to FM radar systems for use in collision avoidance systems. A radar system which is mounted on a vehicle such as an automobile and used in conjunction with an alarm system to detect and warn of potential frontal and rear end collisions, must have high resolution and a minimum range of several decimeters. For this reason, it has been recognized that for use in collision warning systems, frequency modulated-continuous wave (FM-CW) radar systems are preferred over conventional pulsed radar systems. Further, as the longest required range of detection is roughly several hundred meters, it is preferred to utilize a beam having a frequency of about 60 GHz. The reasons for this are that beams having a frequency in the 60 GHz range are easily attenuated upon propagation, and that the use of such beams avoids interference with microwave transmission systems already in existence. An FM radar system for a vehicle usually comprises a central microwave generator for generating FM signals to be transmitted, a central microwave detector for detecting FM return signals and one or more transceivers connected to the microwave generator and the microwave detector and located in the front or rear portion of the vehicle. Such a radar system is disclosed in U.S. Patent 5,008,678. Each transceiver or sensor is formed on a dielectric substrate and comprises a plurality of transmitting antenna elements and receiving antenna elements which are separately disposed on the substrate. The antenna elements are formed as a microstrip antenna array. Additionally, microstrip phase circuits may also be formed on the substrate. The aforesaid radar system known from U.S. Patent 5,008,678 has the following disadvantage: radar signals with frequencies in the high gigahertz range (about 60 GHz) are subject to comparatively strong propagation attenuation. Radar systems working in such a frequency range are therefore particularly suited for the close-range monitoring as it is required in collision avoidance systems for vehicles. The high frequencies give rise to the problem of a suitable technology for the production of electrical components and their connection among one another. Electronic circuits on a circuit plate can be produced by microstrip technology which represents a simple and reasonably priced technology especially for highfrequency applications. Further, microstrip technology allows the production of relatively small space-saving components. However, microstrip technology is not suitable for signal transmission between individual circuit components across longer distances, e.g., in a radar system between a central generating and detecting unit and several decentral transceivers. Waveguides are suited therefor especially in the microwave range. Waveguides, however, have the disadvantage that they are rigid and inflexible as well as very elaborate and expensive to produce. Also their dimensions are relatively large and they give rise to problems with respect to their shielding. Therefore, it is the object of the invention to show a way of reducing the size and the costs in a radar system with a transceiver whose transmitter and receiver antennas are produced in microstrip technology. According to the present invention, in order to achieve this object, there is provided an FM radar device comprising: a transmitting part comprising a planar array antenna for transmitting an FM transmitting signal and a receiving part comprising a planar array antenna for receiving an FM return signal of a similar frequency band as said FM transmitting signal, said transmitting part and said receiving part each comprising one part of a transceiver of an FM radar system and being separately disposed on a common dielectric plate, characterized in that said transmitting part further comprises a frequency multiplier for multiplying the frequency of a first FM input signal supplied to a first input terminal of said transceiver in order to produce a first FM signal of raised frequency to be transmitted as said FM transmitting signal and in that said receiving part further comprises a frequency multiplier for multiplying the frequency of a second FM input signal supplied to a second input terminal of said transceiver in order to produce a second FM signal of raised frequency and further comprises a mixer for producing beat signals by mixing said second FM signal of raised frequency and said FM return signal, said beat signals being output at an output terminal of said transceiver. An advantage of the FM radar device according to the invention is that the frequencies of the signals lying at the input and output terminals of the transceiver compared to the frequency of the transmitted radar signals are substantially lower so that the use of coaxial cables for the electric connection of the transceiver becomes possible. Coaxial cables have the advantage that they are flexible and substantially cheaper than waveguides and that connecting them is uncomplicated. This is achieved by the additional arrangement of frequency multipliers and a mixer on the same substrate on which the transmitting and receiving antennas are disposed. It is advantageous that the frequency multipliers and the mixer can be produced by microstrip technology together with the antennas so that there is no substantial increase in component size. In the European Patent Application EP 0 499 270 A2, which was not prepublished, there is described a further FM radar system. Figure 4 is a block diagram of that system. As shown, a voltage of a triangular wave form is produced by sweep circuit 121, which operates under the control of timing control circuit 120. The triangular wave form voltage is supplied to a variable frequency oscillator 110 to produce a microwave FM signal. The FM signal is divided into two parts, each of which is supplied to an up-converter 112 or 113 respectively. The up-converters 112 and 113 convert each part of the divided signal to a microwave FM signal having a frequency in the range of about 20 GHz. Each of the converted FM signals is supplied to one of four frequency triple multipliers 114a-114d or one of four frequency triple multipliers 115a-115d successively through either of switches 122 or 123 which operate in sync with a timing signal supplied from the timing control circuit 120. FM mm-wave signals having a frequency of about 60 GHz, which are output successively from frequency triple multipliers 114a-114d, are supplied to antennas 118a-118d through circulators 116a-116d. The signals are then radiated from the antennas 118a-118d successively. In addition, FM mm-wave signals which are output successively from frequency triple multipliers 115a-115d, are supplied successively to a first input terminal of mixers 117a-117d. FM mm-wave signals, which are reflected from a target and received by antennas 118a-118d, are supplied successively to a second input terminal of mixers 117a-117d through circulators 116a-116d. Beat signals, which are output successively from mixers 117a-117d, are supplied to detecting circuit 119 through switching circuit 124. The operating frequencies of local oscillators of the up-converters 112 and 113 are set to different values to shift the frequency of the beat signals output from mixers 117a-117d to a frequency range high enough to reduce interference from 1/f noise. The FM radar system according to EP 0 499 270 A2 uses waveguide type circulators 116 resulting in a large-sized and expensive system. Using microstrip type circulators instead of waveguide type circulators could reduce the size of the system. However, the use of microstrip type circulators would substantially increase the costs. In addition, using microstrip type circulators, it is not possible to realize sufficient isolation in order to suppress interference between the transmitting part and the receiving part. Moreover, microstrip type circulators have a large insertion loss. Compared to the system of EP 0 499 270 A2, the present invention provides an FM radar system of more simple construction, smaller size, lower costs and improved performance by eliminating circulators of any type. By utilizing microstrip line type transmitting and receiving antennas in conjunction with frequency multipliers and mixers of the same microstrip line type on the same dielectric plate, the present invention allows realization of an FM radar system of small size and low costs. Furthermore, degradation of SN ratio of beat signals may be avoided and accuracy of detection may be improved. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a top plan view showing a construction of a transceiver of an FM radar system according to one embodiment of the present invention. Fig. 2 is a perspective illustration showing a construction of a metal box for housing a transceiver of an FM radar system in accordance with one embodiment of the present invention. Fig. 3 is a block diagram of an FM radar system according to one embodiment of the present invention. Fig. 4 is a block diagram of an FM radar system according to prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In Figs. 1 and 2, a top plan view of a transceiver of an FM radar system in accordance with one embodiment of the present invention and a perspective view of a metal box for housing the transceiver of an FM radar system in accordance with one embodiment of the present invention are shown respectively. As shown, the transceiver comprises a transmitting part 10 and a receiving part 20 formed as a microstrip circuit on a common dielectric plate 1. The common dielectric plate 1 comprises an appropriate polymer having a relatively low dielectric constant (a dielectric constant of about 2 is exemplary) to promote radiation of electro-magnetic waves. In addition, the common dielectric plate 1 is supported in a metal box 2. The transmitting part 10 and the receiving part 20 are separated from each other by a metal shield plate 3 to avoid interference between the respective parts 10 and 20. The transmitting part 10 comprises a transmitting -antenna 11 of a planar array type, a frequency triple multiplier 12 α-δ, input terminals 13 and 14 of a coaxial connector for receiving microwave FM signals and bias voltages respectively through coaxial cables (not shown in the Figs.), and transmission lines for forming connections between the above-listed various elements. The frequency triple multiplier 12 α-δ comprises a multiplier element 12 α, a low pass filter 12 β for rejecting mm-wave signals, a band pass filter 12 γ for rejecting higher order mm-wave and microwave signals, and a high rejection filter 12 δ for forming bias circuit and matching patterns for impedance matching. The receiving part 20 comprises a receiving antenna 21 of the planar array type, a frequency triple multiplier 22 α-δ, a mixer 23 of single balanced type, a low noise amplifier 24 for amplifying beat signals, a high rejection filter 25 forming a bias circuit, an output terminal 26 forming a coaxial connector to output beat signals, an input terminal 27 of a coaxial connector to input microwave FM signals, bias input terminals 28 and 29, and transmission lines for forming connections between the above-listed various elements. The frequency triple multiplier 22 α-δ comprises a multiplier element 22 α, a low pass filter 22 β for rejecting mm-wave signals, a band pass filter 22 γ for rejecting higher order mm-wave and microwave signals, and a high rejection filter 22 δ for forming bias circuit and matching patterns for impedance matching. In the transmitting part 10, microwave FM signals having a frequency of about 20 GHz, which are supplied to the input terminal 13 through coaxial cable, are converted to mm-wave FM signals by the frequency triple multiplier 12 α-δ for transmission by the planar array antenna 11. Matching patterns for impedance matching are formed around the frequency triple multiplier element 12 α, and bias voltage is supplied from the bias input terminal 14 to the frequency triple multiplier element 12 α through the high rejection filter 12 δ. In the receiving part 20, mm-wave FM signals received by the receiving planar array antenna 21 are supplied to an input terminal of the mixer 23 which is of single balance type. Microwave FM signals having a frequency of about 19.5 GHz are supplied to the input terminal 27 through coaxial cable and are converted to mm-wave FM signals having a frequency of about 58.5 GHz by frequency triple multiplier 22 α-δ. The mm-wave FM signals are then supplied to another input terminal of the mixer 23. Beat signals having a frequency of about 1.5 GHz which are output from the output terminal of the mixer 23, are amplified by the low noise amplifier 24 and are output to coaxial cable through the beat signal output terminal 26. Bias voltages, which are supplied to the bias input terminals 28 and 29, are supplied to frequency multiplier 22 α-δ and the low noise amplifier 24 through the high rejection filters 22 δ and 25 respectively. Fig. 3 is a block diagram showing a configuration of a mm-wave FM radar system, which includes four transceivers as shown in Figs. 1 and 2, for mounting on a vehicle. It may be noted that like elements appearing in Figs. 3 and 4 are labelled with the same reference numerals. It is believed that labelling the elements in this fashion will facilitate a comparison of the systems illustrated in Figs 3 and 4, and that duplicative descriptions relating to the various elements will be minimized. As shown in Fig. 3, each of four transceivers comprises a transmitting antenna Ta-Td, a receiving antenna Ra-Rd, a pair of frequency multipliers 114a-d and 115a-d, one mixer 117a-d, and one low noise amplifier AMPa-d. Each of the four transceivers corresponds to the transceiver shown in Fig. 1. With respect to the labelling of Figs. 1 and 3, it should be noted that frequency multipliers 114a-d and 115a-d in Fig. 3 correspond to frequency multipliers 12 and 22 in Fig. 1, and that mixers 117a-d in Fig. 3 correspond to mixer 23 in Fig. 1. In a preferred form, the four transceivers shown in Fig. 3 are mounted on front and rear portions and left and right sides of a vehicle. In addition, a common part (comprising switches 122, 123, and 124, mixers 112 and 113, detecting circuit 119, frequency oscillator 110, and timing control circuit 120) may be located together with one of the four transceivers, or located in another position apart from any of the four transceivers. It may be noted that none of the transceivers constructed as shown in Figs. 1 or 3 contain circulators, which increase both the size and cost of a collision avoidance system. The circulators are eliminated by forming dedicated transmitting antennas and dedicated receiving antennas separately, as is clear by comparison to the configuration of Fig. 4. Also, low noise amplifiers 24 for amplifying beat signals are configurated separately on the dielectric plates 1 of the transceivers (AMPa-AMPd in Fig. 3), while a single low noise amplifier is included within detecting circuit 119 following to switching circuit 124 in the FM radar system of the prior art in Fig. 4. As a result, the same number of low noise amplifiers are required as the number of transceivers, but since such low noise amplifiers of a low frequency range are small in size and inexpensive, no serious deficiency arises. To the contrary, a number of advantages are achieved. In particular, increased accuracy of detection is achieved by locating low noise amplifiers in front of the switching circuit 124. In addition, the placement of low noise amplifiers in front of switching circuit 124 reduces propagation loss, thermal noise, and switching noise, thus improving the SN ratio of the system. In a presently preferred form, the four transceivers are enabled successively according to their order of location around a vehicle by switching circuits 122, 123, and 124, each of which operates in sync with the timing signal supplied from the timing control circuit 120. This allows the collision warning system to scan for targets existing around the vehicle. Finally, it may be noted that the distance of propagation of transmitted FM signals will be shorter compared to solid antennas such as parabolic antennas or horn-reflector antennas, since the antenna gain of a planar array antenna will be small compared to those solid antennas. Hence, the FM radar system of the present invention is especially preferable for use as a radar system for detecting obstacles near a vehicle to alert a driver of the vehicle of a potential collision. Although an example is described in which frequency triple multipliers are used, other examples could be described in which double or quadruple frequency multipliers are used. Although an example is described in which low noise amplifiers are configurated on the dielectric plate, another example could be described in which low noise amplifiers are configurated out of the dielectric plate.

Claims: An FM radar device comprising: a transmitting part (10) comprising a planar array antenna (11) for transmitting an FM transmitting signal and a receiving part (20) comprising a planar array antenna (21) for receiving an FM return signal of a similar frequency band as said FM transmitting signal, said transmitting part (10) and said receiving part (20) each comprising one part of a transceiver of an FM radar system and being separately disposed on a common dielectric plate (1), characterized in that said transmitting part (10) further comprises a frequency multiplier (12) for multiplying the frequency of a first FM input signal supplied to a first input terminal (13) of said transceiver in order to produce a first FM signal of raised frequency to be transmitted as said FM transmitting signal and in that said receiving part (20) further comprises a frequency multiplier (22) for multiplying the frequency of a second FM input signal supplied to a second input terminal (27) of said transceiver in order to produce a second FM signal of raised frequency and further comprises a mixer (23) for producing beat signals by mixing said second FM signal of raised frequency and said FM return signal, said beat signals being output at an output terminal (26) of said transceiver. The device of claim 1, wherein said transmitting part (10) and said receiving part (20) are separated from each other by a metal shield plate (3). The device of claim 1 or 2, wherein said transceiver comprises a metal box (2) supporting the dielectric plate (1) therein. The device of one of claims 1 to 3, wherein said transmitting part (10) and said receiving part (20) are formed as a microstrip circuit on said dielectric plate (1). The device of one of claims 1 to 4, wherein said input terminals (13, 27) and said output terminal (26) of said transceiver are adapted for connection to coaxial cables. The device of one of claims 1 to 5, wherein said receiving part (20) further comprises an amplifier (24) for amplifying said beat signals produced by said mixer (23), said amplified beat signals being output at said output terminal (26) of said transceiver. The device of one of claims 1 to 6, wherein said first and said second FM input signals are of different frequency and said frequency multipliers (12, 22) of said transmitting part (10) and said receiving part (20) have the same multiplication factor. An FM radar system comprising: a microwave generator (110, 111, 112, 113, 121), a microwave detector (119), a plurality of transceivers, a switching arrangement (122, 123, 124) for successively coupling said transceivers to said microwave generator (110, 111, 112, 113, 121) and said microwave detector (119), and a timing control circuit (120) for controlling synchronous operation of said microwave generator (110, 111, 112, 113, 121), said microwave detector (119) and said switching arrangement (122, 123, 124), characterized in that said transceivers each comprise an FM radar device according to one of claims 1 to 7. The system of claim 8, wherein said transceivers are located around the sides of a vehicle and are successively coupled to said microwave generator (110, 111, 112, 113, 121) and said microwave detector (119) according to an order of location of said transceivers around said vehicle.

Inventors: KOMATSU SATORU, KUDO HIROSHI, KOMATSU, SATORU, KUDO, HIROSHI
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: G01S13
IPC codes: G01S7, H01Q1, H01Q21, H01Q3, G01S13