JPH07311261A - Time-division multiplexing type multichannel radar - Google Patents

Abstract

PURPOSE:To provide a time-division multiplexing type multichannel radar in which interference between channels is reduced with a simple and low-cost structure. CONSTITUTION:A plurality of transmitting/receiving channels 11, 12 having transmitting antennas 11a, 12b, receiving antennas 11a, 12b for receiving reflected waves from an object, and mixers 11c, 12c for mixing the reflected waves received by the antennas 11a, 12b and a local oscillation signal to generate a beat signal are connected to a high frequency signal generator 13 via a high frequency signal distributor 14 having transmission switching circuits S1, S3, local oscillation switching circuits S2, S4 and a timing controller TC for turning ON, OFF the switching circuits at a suitable predetermined timing. Bias control means R1, R2, Q, etc., for varying the DC biases of the mixers 11b, 12b in the corresponding transmitting/receiving channels to increase its conversion loss when the circuits S2, S4 in the channels 11, 12 are OFF, are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time division multiplex type multi-channel radar device used in a vehicle-mounted radar device or the like.

[0002]

2. Description of the Related Art A vehicle-mounted radar device mounted on a vehicle such as a passenger car and used as a warning device for collision prevention and collision prevention,
Since the farthest distance measuring range to a target such as a preceding vehicle or an oncoming vehicle is a comparatively short distance of about several hundred meters, radiated radio waves can propagate to farther than necessary and interfere with existing microwave communication equipment. For the purpose of avoiding
The use of millimeter-wave radio waves with large propagation attenuation of about GHz is considered promising. The use of the millimeter wave band is also suitable for downsizing a radar module including an antenna size and FM signal generators and mixers arranged before and after the antenna.

Further, in this type of vehicle-mounted radar device, a value as small as several tens of centimeters is required as a shortest distance measuring range to a target such as a preceding vehicle. Therefore, the FM radar type is more preferable than the pulse radar type. Seems to be promising. Further, in this type of vehicle-mounted radar device, a plurality of transmission / reception channels may be installed for the purpose of detecting the target position with high resolution. For the purpose of avoiding mutual interference between each transmission / reception channel, a frequency division multiplexing method in which different frequency bands are allocated to each transmission / reception channel and a time division multiplexing method in which the same frequency band is allocated to each transmission / reception channel at different timings can be considered. However, from the viewpoint of reducing the manufacturing cost by narrowing the used frequency band and using common parts, it is considered that the latter configuration of the time division multiplexing multi-channel adopting the time division multiplexing method is more advantageous. .

The applicant of the present invention has proposed a time division multiplexing multi-channel radar device which has the structure of the time division multiplexing multi-channel radar device described above, in which power consumption is reduced and isolation between channels is improved. JP-A-5-2647
No. 28 disclosed.

FIG. 3 is a block diagram of the time division multiplexed radar system of the above-mentioned prior application. The high frequency oscillator circuit 110 is
20 GHz after being triangular-wave modulated by the sweep circuit 121
The FM modulated wave signal of a certain degree is generated. This FM signal is distributed to a plurality of channels by the distribution circuit 122 having an amplification function according to the instruction of the timing control circuit 120. The distribution circuit 122 having this amplification function has a circuit configuration in which high-frequency amplifiers having multi-stage FETs are arranged in parallel for the number of channels, and the bias of the FETs is turned ON / OFF for each channel in accordance with an instruction from the timing control circuit 120.
OFF control is performed and the FM signal is distributed to each channel.

The FM signal distributed by the distribution circuit 122 having an amplification function is converted into 60 G by the multiplication circuit 114.
It is multiplied to about Hz. Next, this FM signal is divided by the power division circuit 111 into a transmission FM signal and a reference signal which are emitted into space. The transmitted FM signal is circulator 1
The reflected FM signal emitted from the antenna 118 to the space after passing through 16 and reflected by the object is again transmitted to the antenna 11.
8 and sent to mixer 117 by circulator 116. Mixer 1 for each channel
17 mixes the reflected FM signal and the reference signal, generates a beat signal corresponding to the frequency difference between the signals, and outputs the beat signal to the multiplexer 124. The multiplexer 124 rearranges the beat signals sent in parallel according to the instruction of the timing control circuit 120 in serial and transmits them to the signal detection circuit 119.

[0007]

In the conventional time division multiplexing multi-channel radar device shown in FIG. 3, the independent operation of each channel is achieved by amplifying the amplifier switch in which FET switches are connected in multiple stages. The output signal of a single FM signal source is distributed only by the distribution circuit.
That is, when the insertion loss (including the gain in the ON state) ratio given to the high frequency signal in each of the ON state and the OFF state is insufficient, the beat signal of one transmission / reception channel leaks into the beat signal of the other transmission / reception channel. That is, there is a problem that so-called inter-channel interference occurs and the resolution in the azimuth direction deteriorates.

The plurality of antennas 118 are arranged close to each other for the purpose of improving the lateral resolution. Therefore, the FM signal reflected by the object is received not only by the channel that transmitted the FM signal but also by the antennas of other channels arranged in the vicinity. In the configuration of the multi-channel radar shown in FIG. 3, the isolation between the channels is guaranteed only by the amplification / distribution circuit. Further, the FETs of each amplification / distribution circuit tend to be miniaturized and integrated in recent years as MMICs for the purpose of cost reduction. Therefore, while the degree of integration is improved to reduce the cost and reduce the size and weight, the transmission line inside the MMIC that performs analog processing of high-frequency signals by the IC with a high degree of integration is usually of the microstrip or coplanar type. , The radiation to the space is relatively large. Therefore, the isolation of each channel tends to deteriorate depending on the degree of integration, and there is a problem that the lateral resolution cannot be ensured only by the conventional FET amplifier.

Further, in the in-vehicle FM radar device, it is not sufficient to support the operation of the vehicle simply by issuing a warning to the driver based on only the obstacle information in the distance direction. In addition, not only the distance direction but also the azimuth direction resolution is required, and the high cost is a major person who prevents the practical use of such a driver assist system. There is a strong demand. In order to meet the demands for these many on-vehicle radar application systems, we have achieved miniaturization of high-frequency circuits and cost reduction, while at the same time improving isolation between each channel of the multi-channel radar. Azimuth resolution must be further improved.

[0010]

The time division multiplex type multi-channel radar device of the present invention converts the local oscillation switching circuit by changing the DC bias of the mixer in the corresponding channel when the switching circuit is in the OFF state. The DC bias control means for increasing the loss and suppressing the originally unnecessary beat signal is provided.

[0011]

The mixer is mainly composed of a non-linear element such as a diode, and mixes the received signal and the local oscillation signal to generate a beat signal indicating the difference frequency. In such a mixer, due to the DC bias voltage (or current) applied to the non-linear element and the level of the local oscillation signal, the conversion loss generated when converting the high frequency reception signal into the intermediate frequency beat signal is caused. It fluctuates significantly. Therefore, during the period when the local oscillator switching circuit is in the ON state, the first direct current that minimizes the conversion loss of the mixer under the level of the local oscillator signal experimentally obtained as the optimum value. Bias is set. Further, in the OFF state of the local oscillation switching circuit, the level of the originally unnecessary local oscillation signal supplied to the mixer therethrough is lower than that in the ON state by the input / output isolation of the switching circuit.

Therefore, during the period in which the local oscillator switching circuit is in the OFF state, the second direct current such that the maximum conversion loss occurs in the mixer under the local oscillator signal reduced by the input / output isolation. Bias is set. As described above, by changing the DC bias of the mixer in synchronization with the on / off operation of the local switching circuit, the synergistic relationship between the local signal level and the bias voltage for an originally unnecessary beat signal. It is possible to generate extremely high conversion losses in the mixer.

As a result, leakage of unnecessary signals from unnecessary channels can be reduced, and isolation between channels can be ensured even when high integration is achieved by using the high frequency circuit unit as an MMIC. In particular, when a mixer using a diode is used for the mixer, the conversion efficiency is extremely sensitive to a given bias, and is suitable for the present invention. Further, since it can be extremely easily integrated with a high frequency active element such as a HEMT, it is also very suitable for downsizing and cost reduction by making the entire high frequency circuit part into one chip MMIC.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a time division multiplex type multi-channel FM radar device showing an embodiment of the present invention having two channels. In this multi-channel FM radar device, two transmission / reception channels 11 and 12 are connected to FM signal generator 1 via FM signal distributors 14 and 15.
It is configured to be connected to 3. One transmission / reception channel 11 includes a transmission / reception shared antenna 11a and a mixer 11b.
And a circulator 11c. Similarly, the other transmission / reception channel 12 has the same antenna 1
2a, a mixer 12b, and a circulator 12c. The FM signal generator 13 generates an FM signal whose frequency increases and decreases in an appropriate predetermined cycle and in an appropriate predetermined range, and outputs the FM signal to the FM signal distributor 14.

The FM signal distribution unit 14 divides the FM signal supplied from the FM signal generator 13 in the preceding stage at an appropriate ratio into power dividers D1 to D4 and the timing control circuit TC for each of the divided FM signals. A switching circuit S for time-divisionally distributing to the transmission / reception channels 11 and 12 by switching according to a control signal supplied from
1 to S4 are provided. Transmission switching circuit S1, S
3 and the local switching circuits S2 and S4 are both turned on / off by the rise and fall of the DC bias voltage.
It is mainly composed of a T amplifier. Further, the FM signal distribution unit 15, which is the other channel, is configured similarly to 14 and performs the same operation. FE inside each FM signal distributor
For details of the switching circuit mainly including the T amplifier, refer to Japanese Patent Application Laid-Open No. 5-264728, which is a prior application of the applicant of the present application, as necessary.

The mixer 11b is a transmission / reception shared antenna 11a.
90 ^o hybrid circuit HYB that superimposes the received signal supplied from the circulator 11c with the local signal supplied from the FM signal generator 13 through the switching circuit S2 and divides it into two, and the Schottky barrier mixer diode d1. and a single balanced mixer with d2. The mixer 11b further includes DC blocking capacitors C1 to C3 and a high frequency F.
The DC bias circuit includes low-pass filters L1 and L2 for blocking the M signal, resistors R1 and R2, and a switching transistor Q. Mixer 12b
Is also configured similarly to the mixer 11b.

According to an example of a typical operation of this time division multiplexing multi-channel FM radar device, the transmission switching circuit S1 and the local switching circuit S2 are simultaneously turned on in accordance with the control signal from the timing control circuit TC. Accordingly, one of the transmission / reception channels 11 becomes operational. At the same time, the transmission switching circuit S3 and the local switching circuit S4 are simultaneously turned off,
Along with this, the other transmission / reception channel 12 becomes inactive. During the above period, the FM generated by the FM signal generator 13
The signal is supplied to the transmission / reception shared antenna 11a through the switching circuit S1 and the circulator 11c and transmitted to the outside. The reflected wave generated by the external object is received by the transmission / reception shared antenna 11a and is supplied to one input terminal of the 90 ° hybrid circuit HYB of the mixer 11b through the circulator 11c. This 90 ° hybrid circuit HYB
The FM signal generated by the FM signal generator 13 is supplied to the other input terminal as the local oscillation signal through the local oscillation switching circuit S2.

During the above period, in the mixer 11b of the transmitting / receiving channel 11 in the operating state, the switching transistor Q receiving the same control signal as the control signal supplied to the local switching circuit S2 is kept in the non-conducting state. The mixer diodes d1 and d2 are supplied with a DC bias set to a value that minimizes the conversion loss from the received FM signal to the beat signal. On the other hand, in the mixer 12b of the transmission / reception channel 12 in the non-operating state, the switching transistor (Q in the mixer 11b) which receives the same control signal as the control signal supplied to the local switching circuit S4.
Is maintained in a conductive state, and a mixer diode (corresponding to d1 and d2 in the mixer 11b) is supplied with a DC bias preset to maximize the conversion loss from the received FM signal to the beat signal. To be done.

Next, according to the control signal from the timing control circuit TC, the transmission switching circuit S1 and the local switching circuit S2 are simultaneously turned off, and the transmission / reception channel 11 is deactivated accordingly. At the same time, the transmission switching circuit S3 and the local switching circuit S4 are simultaneously turned on, and the transmission / reception channel 12 is activated accordingly. During this period, the FM signal generated by the FM signal generator 13 is greatly attenuated by the switching circuit S1 in the off state, so that the FM signal transmitted from the transmitting / receiving shared antenna 11a to the outside becomes weak. As a result, the reflected wave from the object generated by the FM signal transmitted from the transmission / reception shared antenna 11a to the outside becomes weaker, and the amount of the received signal of the reflected wave leaking into the mixer 11b can be ignored.

However, the FM signal transmitted from the transmitting / receiving shared antenna 12a of the transmitting / receiving channel 12 in the operating state and reflected by the object is also received by the transmitting / receiving shared antenna 11a, which is another channel adjacently installed. Therefore, the amount that this leaks into the mixer 11b in the non-operating state cannot be ignored. Further, since the local FM signal supplied to the mixer 11b through the local switching circuit S2 in the off state is an amount attenuated by about 15 dB as compared with the case where the switching circuit S2 is in the on state,
It cannot be ignored.

Therefore, if the DC bias supplied to the mixer diodes d1 and d2 is kept at the optimum value during the operation of the mixer 11b, a beat signal of a non-negligible amount is generated. In the present invention, in order to prevent such a situation, the switching transistor Q that receives the control signal supplied to the local switching circuit S2 becomes conductive, and the mixer diodes d1 and d2 receive the FM signal.
A DC bias preset to maximize the signal to beat signal conversion loss is provided.

The beat signals output from the transmission / reception channels 11 and 12 are the local switching circuits S respectively.
It is supplied to the detection circuit 15 through switching circuits S5 and S6 which are turned on / off in synchronization with 2 and S4. The detection circuit 15 processes the beat signal supplied through the switching circuits S5 and S6 based on the control signal received from the timing control circuit TC while discriminating which transmission / reception channel beat signal the reflected signal is. The distance to the object causing the noise is detected.

FIG. 3 shows the result of an experiment relating to conversion loss performed for determining the optimum DC bias voltage to be set in the mixer 11b of FIG. This experimental data shows the results of measuring the relationship between the conversion loss and the local oscillator signal level for each of three types of values A, B, and C set as the DC bias voltage.

When the local oscillator switching circuit S2 is on, the level of the local oscillator signal supplied to the mixer 11b is +5 dBm. In this state, the optimum DC bias voltage to minimize the conversion loss is A, and the conversion loss at this time is about 10 d.
It is B. When the input / output isolation of the local switching circuit S2 is -15 dB, when this is off,
The level of the originally unnecessary local signal supplied to the mixer 11b is -10 dBm. In this state, set the DC bias voltage to B
When changed to, the conversion loss becomes as large as 65 dB.
This conversion loss is about 35 dB larger than when the DC bias voltage is kept at A.

Therefore, by changing the DC bias voltage between A and B in synchronism with the ON / OFF of the local switching circuit S2, the originally unnecessary beat signal level is 35 dB compared to the conventional case. It can be reduced to some extent. This is equivalent to improving the input / output isolation of the local switching circuit S2 by about 20 dB while maintaining the DC bias voltage at A, or improving the input / output isolation of the switching circuit S5 in the subsequent stage by about 35 dB. . From the above experimental results, it was found that if the bias of the mixer is synchronized with the channel switching, the isolation between the channels is sufficiently improved.

As described above, F transmitted and received by each transmission / reception channel
The present invention has been described by taking the operation mode of receiving the reflected wave of the M signal as an example. However, it is obvious that the present invention can be applied to the case where each transmission / reception channel adopts an operation mode of receiving a reflected wave transmitted by another transmission / reception channel in order to improve the resolution of the position of the object in the azimuth direction. In the latter operation mode, the transmission switching circuit of each channel and the local switching circuit are turned on / off with a time lag.

Also, the case where the transmission signal from the antenna is an FM signal has been illustrated. However, the present invention can be applied to a Doppler radar device that detects a relative velocity with respect to an object by regarding the transmission signal as a signal having a constant frequency instead of the FM signal and regarding the frequency change amount of the received reflected wave as the Doppler shift amount. it is obvious.

Further, in the embodiment, the case of using the transmission / reception shared antenna has been illustrated. However, it is obvious that the present invention can be applied to the case where a dedicated transmitting antenna and a dedicated receiving antenna are used.

[0029]

As described in detail above, the time division multiplex type multi-channel radar device of the present invention is synchronized with the local switching circuit in each transmission / reception channel and the DC bias of the mixer in the corresponding channel. Since the conversion loss is increased / decreased by the above, it is possible to prevent inter-channel interference due to an unnecessary beat signal under a very simple and inexpensive structure.

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration of a time division multiplex type multi-channel FM radar device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing measurement data of conversion loss performed to determine a DC bias voltage to be set in the mixer of FIG.

FIG. 3 is a block diagram showing a configuration of a conventional time division multiplex type multi-channel FM radar device.

[Explanation of symbols]

 11,12 Transmit / receive channel 11b, 12b Mixer 13 FM signal generator 14 FM signal distributor 15 Detector S1, S3 Transmit switching circuit S2, S4 Local switching circuit

Claims (6)

[Claims] 1. A transmitting antenna, a receiving antenna for receiving a reflected wave from an object, and a mixer for mixing a reflected wave received by the receiving antenna and a part of a local oscillator signal to generate a beat signal. A transmission / reception channel including a transmission switching circuit installed in the front stage of the transmission antenna, a local switching circuit installed in the front stage of the mixer, and on / off of these switching circuits at appropriate predetermined timings. In a time division multiplex type multi-channel radar device connected to a high frequency signal generator through a high frequency signal distributor having a timing control circuit, the local switching circuit in each transmission / reception channel is turned off. DC bias control for increasing the conversion loss by changing the DC bias of the mixer in the corresponding transmission / reception channel in some cases A time division multiplex type multi-channel radar device comprising means. 2. A high frequency signal generator, switching means for inputting a signal output from the high frequency signal generator, switching to a plurality of output terminals, and outputting the plurality of output terminals, the switching means corresponding to a plurality of output terminals of the switching means. Is arranged
By mixing a plurality of antennas for transmitting high-frequency signals toward an object, arranged corresponding to the plurality of antennas, reflected by the object, and a signal related to the transmission signal and the reception signal received by the antenna, A plurality of mixers for generating beat signals, bias means for independently applying a bias to each of the plurality of mixers, and a control stage for controlling the bias of the mixers in synchronization with the switching timing of the pre-switching means A radar device comprising: 3. The transmission switching circuit and the local switching circuit according to claim 1, wherein:
A time division multiplex type multi-channel radar device comprising an amplifier that is turned on / off by increasing / decreasing a DC bias. 4. The detector according to claim 1, further comprising a detection unit that detects a distance from a frequency of a beat signal generated by the mixer of each transmission / reception channel to an object that has generated the reflected wave. Characteristic time division multiplex type multi-channel radar device. 5. The method according to claim 1, wherein each of the transmitting antenna and the receiving antenna is a multi-beam antenna.
A time division multiplex type multi-channel radar device characterized by being an antenna. 6. The transmitter according to claim 5, wherein each of the transmitting antenna and the receiving antenna is a primary radiator,
A time division multiplex type multi-channel radar device having a common reflector for the primary radiator and forming a multi-beam antenna.