JP5156551B2 - FM-CW radar - Google Patents

Description

  The present invention relates to a frequency-modulated continuous wave (hereinafter referred to as “FM-CW”) composed of a voltage-controlled oscillator (hereinafter also referred to as “VCO”) composed of a Gunn diode and a varactor diode and a passive mixer. It is related to radar.

An FM-CW radar is used as a radar that measures a distance and / or relative speed with respect to a target object. This FM-CW radar includes a transmission / reception circuit and a signal processing circuit having a simple configuration, and can measure a distance and / or a relative speed with respect to a target object. For this reason, in recent years, it has been widely used as an anti-collision radar mounted on automobiles. Patent Document 1 discloses an example of FM-CW radar.
JP-A-5-297124

  FIG. 10 is a diagram illustrating a configuration of a conventional FM-CW radar. A conventional FM-CW radar includes a triangular wave generation circuit 91, a voltage controlled oscillator (VCO) 92, a directional coupler 93, a transmission / reception antenna device 94, a mixer 95, an amplifier 96, a signal processing circuit 97, Have

  The triangular wave generation circuit 91 generates a triangular wave as a modulation voltage. For example, a sawtooth wave generating circuit that generates a sawtooth wave as a modulation voltage may be used instead of the triangular wave generating circuit. The voltage-controlled oscillator 92 receives a triangular wave as a modulated wave from the triangular wave generation circuit 91 and outputs a first signal subjected to frequency modulation to the transmission / reception antenna device 94 through the directional coupler 93.

  The transmission / reception antenna device 94 includes a transmission antenna device 94a and a reception antenna device 94b, transmits a first signal from the transmission antenna device 94a to a target object, and receives a second signal reflected by the target object as a reception antenna. The signal is received using the device 94 b and output to the mixer 95.

  The mixer 95 inputs the first signal output from the directional coupler 93 and the second signal output from the transmission / reception antenna device 94, and calculates the frequency difference between the first signal and the second signal. The represented mixer output signal is output to the signal processing circuit 97 through the amplifier 96. The signal processing circuit 97 processes the mixer output signal and outputs the distance and speed between the target object and the transmission / reception device.

  In the conventional FM-CW radar, the voltage controlled oscillator is configured by, for example, an MMIC (monolithic microwave integrated circuit).

  Next, general operation of the FM-CW radar will be described. FIG. 11 shows the operation of the FM-CW radar with respect to the distance L between the target object and the transmission / reception antenna and the relative velocity V between the target object and the transmission / reception antenna. In FIG. 11, a case where modulation is performed using a triangular wave is described as an example.

  The solid line in FIG. 11A shows the time change of the frequency of the transmission signal having the center frequency f0, the frequency modulation width Δf, and the triangular wave period Tm. The dotted line in FIG. 11A shows the time change of the frequency of the received wave received after being reflected by the target object. The received signal is delayed by a time (2 · L) / c from the transmission signal when the propagation speed c of the radio wave is assumed. Further, FIG. 11A illustrates the case where the target object approaches, so that the frequency of the reception signal is higher than the frequency of the transmission signal by the Doppler shift (2 · f0 · V) / c plus side. Has shifted to.

The transmission signal and the reception signal are input to the mixer and frequency-converted in the mixer. A frequency component signal (beat signal) as shown in FIG. 11B is output from the mixer. Fb1 and fb2 shown in FIG. 11B are expressed by the following equations, respectively.
fb1 = (4 · Δf · L) / (c · Tm) + (2 · f0 · V) / c
fb2 = (4 · Δf · L) / (c · Tm) − (2 · f0 · V) / c

  As shown in the respective expressions, fb1 and fb2 are expressions including a distance L between the target object and the transmission / reception antenna and a relative speed V between the target object and the transmission / reception antenna. Therefore, the distance L and the relative speed V can be obtained by substituting the measurement values for fb1 and fb2 in the signal processing circuit.

  In the FM-CW radar, the FM-CW radar can be operated at 76 GHz by configuring the voltage controlled oscillator with a Gunn diode. As described above, when the FM-CW radar is operated at a higher frequency, the circuit module and the device can be reduced in size and the signal resolution can be improved.

  However, when the voltage-controlled oscillator of the FM-CW radar is configured with a Gunn diode, the following problems occur. This problem will be described with reference to FIG. FIG. 4 shows a case where a triangular wave voltage is applied as a modulation voltage to a power supply terminal of a voltage controlled oscillator including a Gunn diode, and a mixer output voltage waveform output from the mixer output terminal is measured when there is no target object. A modulation voltage waveform (upper side in FIG. 4) and a mixer output voltage waveform (lower side in FIG. 4) are shown. When the target object does not exist, a waveform including a beat signal should not be output from the mixer output terminal. However, as shown in FIG. 4, a waveform following the modulation voltage (hereinafter referred to as “modulated wave superimposed signal”) is output from the mixer output terminal.

  In the FM-CW radar, if a modulated wave superimposed signal is output when there is no target object, it may be mistaken for the target object. In addition, for a target object at a long distance, the level of the detected beat signal is small, so that when the modulated wave superimposed signal is generated, the beat signal and the modulated wave superimposed signal cannot be separated, and the detection performance is improved. descend. Solving those problems has been an issue.

  The present invention is intended to solve such problems, and an object of the present invention is to provide a small FM-CW radar that improves detection performance and operates at a higher frequency.

  In order to achieve the above object, an FM-CW radar according to the present invention has a Gunn diode and a varactor diode, outputs a frequency-modulated first signal, and a first target object. A transmission / reception antenna device that transmits a first signal and receives a second signal reflected by the target object; a diode; and inputs the first signal and the second signal; A passive mixer that outputs a mixer output signal representing a frequency difference between the first signal and the second signal, a current detection circuit that detects a change in current flowing through the passive mixer, and the detected passive mixer A voltage application circuit for making the output power of the frequency-modulated signal of the voltage-controlled oscillator constant by changing the voltage applied to the Gunn diode based on the change in the flowing current , Characterized by having a.

  The FM-CW radar according to a preferred embodiment of the present invention is characterized in that the diode constituting the passive mixer is surface-mounted on a dielectric substrate.

  The FM-CW radar according to another preferred embodiment of the present invention has a directional coupler, and the voltage controlled oscillator, the passive mixer, and the directional coupler are surface-mounted on the same dielectric substrate. It is characterized by that.

  According to the present invention, the change in the current flowing through the passive mixer is detected, and the voltage applied to the Gunn diode is changed in accordance with the change in the current flowing through the passive mixer, so that the linearity between the modulation voltage and the oscillation frequency is increased. It is possible to provide an FM-CW radar that can be improved, suppress the generation of a modulated wave superimposed signal in the detection signal, and improve the detection performance.

  Further, according to the present invention, the detection performance can be improved in the FM-CW radar constituted by the Gunn diode, so that the FM-CW radar can be operated at a higher frequency. Furthermore, when surface-mount type elements are used or these elements are configured on the same dielectric substrate, an FM-CW radar that realizes downsizing of the apparatus can be provided.

Embodiments of the FM-CW radar of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an FM-CW radar according to the present invention. The FM-CW radar of the present invention includes a triangular wave generation circuit 11, a voltage controlled oscillator (VCO) 12, a directional coupler 13, a transmission / reception antenna device 14, a mixer 15, an amplifier 16, and a signal processing circuit 17. And have. The FM-CW radar of the present invention includes a current detection circuit 18 and a voltage application circuit 19.

  The triangular wave generation circuit 11 generates a triangular wave as a modulation voltage. Instead of the triangular wave generation circuit 11, for example, a sawtooth wave generation circuit that generates a sawtooth wave as a modulation voltage may be used. Hereinafter, the present invention will be described by taking the case of using the triangular wave generation circuit 11 as an example.

  The voltage controlled oscillator 12 includes a Gunn diode connected to the voltage application circuit 19 and a varactor diode connected to the triangular wave generation circuit 11. The triangular wave is input from the triangular wave generation circuit 11 as a modulation voltage and is frequency-modulated. A first signal is generated. Then, the voltage controlled oscillator 12 outputs the generated first signal to the transmission / reception antenna device 14 through the directional coupler 13.

  The transmission / reception antenna device 14 includes a transmission antenna device 14a and a reception antenna device 14b, transmits a first signal from the transmission antenna device 14a to the target object, and receives a second signal reflected by the target object as a reception antenna. The signal is received using the device 14 b and output to the mixer 15. As shown in FIG. 1, the transmission antenna apparatus 14a and the reception antenna apparatus 14b may be provided separately to constitute the transmission / reception antenna apparatus 14, or a transmission / reception antenna apparatus may be provided to The transmission / reception antenna device 14 may be configured integrally with the reception antenna device.

  The mixer 15 includes a diode and constitutes a passive mixer. The mixer 15 may include a semiconductor element having a diode function instead of the diode. The mixer 15 inputs the first signal output from the directional coupler 13 and the second signal output from the transmission / reception antenna device 14, and calculates the frequency difference between the first signal and the second signal. The represented mixer output signal is output to the signal processing circuit 17 through the amplifier 16. The signal processing circuit 17 processes the mixer output signal and outputs the distance and speed between the target object and the transmission / reception device.

  The current detection circuit 18 detects the fluctuation amount of the current flowing through the mixer 15. The voltage application circuit 19 makes the voltage variable and applies it to the voltage controlled oscillator 12 based on the fluctuation amount of the current flowing through the mixer 15 detected by the current detection circuit 18, and makes the output of the voltage controlled oscillator 12 constant. To do. The current detection circuit 18 and the voltage application circuit 19 and the operations performed by them will be described later.

  In the FM-CW radar of the present invention, a voltage controlled oscillator (VCO) 12, a mixer 15, and a directional coupler 13 are formed on a dielectric substrate 32 having a ground electrode 31 on the back surface, and are microstrip lines. You may make it comprise. FIG. 2 is a perspective view illustrating an example of the embodiment configured as described above, obliquely from above.

  The voltage-controlled oscillator 12 includes a surface-mounted Gunn diode 33 and a surface-mounted varactor diode 34. By changing the voltage applied to the power supply terminal 36, the capacitance value of the varactor diode 34 is changed, and the resonance frequency of the resonator is changed, whereby the oscillation frequency of the voltage controlled oscillator 12 can be modulated. The output of the voltage controlled oscillator 12 is connected to the directional coupler 13.

  The directional coupler 13 includes a branch line coupler 38. The output of the directional coupler 13 is connected to the transmission terminal 43 and the mixer 15. The mixer 15 includes Schottky barrier diodes 39a and 39b and a rat race circuit 41 to constitute a single balance mixer. The mixer 15 has the directional coupler 13 and the reception terminal 44 as inputs and the IF terminal 45 as an output.

  FIG. 3 is a diagram showing the relationship between the output power of the voltage controlled oscillator (VCO) 12 and the mixer current flowing through the mixer 15 when a modulation voltage of 0 to 10 V is applied to the power supply terminal 36 of the voltage controlled oscillator 12. is there. As shown in FIG. 3, when the modulation voltage increases, the output power of the voltage controlled oscillator 12 increases, and the mixer current also increases. This is because the bias point fluctuates due to increase / decrease in power output from the voltage-controlled oscillator 12 because the mixer 15 is a passive mixer including Schottky barrier diodes 39a and 39b. Here, the mixer current flowing through the mixer 15 refers to a current flowing through the Schottky barrier diode 39a, the rat race circuit 41, and the Schottky barrier diode 39b in FIG.

  By surface-mounting each element constituting the voltage controlled oscillator 12, the directional coupler 13, and the mixer 15, variations in wiring connection can be reduced and high frequency characteristics can be improved. In particular, by mounting the diodes 39a and 39b constituting the mixer 15 on the surface, it is possible to obtain a remarkable effect of reducing variations in wiring connection and improving high-frequency characteristics.

  Further, by mounting the elements constituting the voltage controlled oscillator 12, the directional coupler 13, and the mixer 15 on the same dielectric substrate 32, the apparatus can be miniaturized.

  As described in the section of the problem to be solved by the invention, FIG. 4 shows a case where a triangular wave voltage is applied as a modulation voltage to the power supply terminal 36 of the voltage controlled oscillator 12 and there is no modulation voltage and no target object. Shows the output voltage waveform of the mixer output from the IF output terminal 45. When there is no target object, no beat signal should be output to the IF output terminal 45. However, as shown in FIG. 4, a modulated wave superimposed signal including a waveform following the modulated wave voltage is output from the IF output terminal 45. This is because when the output power of the voltage controlled oscillator 12 increases or decreases during the modulation, the mixer current flowing through the mixer 15 increases and decreases, thereby causing the fluctuation component of the mixer current to be output from the IF output terminal 45. It is.

  In the FM-CW radar, if a modulated wave superimposed signal is output when there is no target object, it may be mistaken for the target object. In addition, for a target object at a long distance, since the level of the detected beat signal is small, if the modulated wave superimposed signal is output, the beat signal and the modulated wave superimposed signal cannot be separated and detected. Performance decreases.

  Next, it will be described that the generation of the modulation wave superimposed signal is suppressed by the feedback operation of the current detection circuit 18 and the voltage application circuit 19 according to the present invention.

  FIG. 5 shows the voltage-controlled oscillator (VCO) 12 with the horizontal axis representing the Gunn diode applied voltage and the vertical axis representing the VCO 12 output power, and varying the modulation voltage as a parameter to change the Gunn diode applied voltage and the VCO 12 output power. It is a figure which shows the relationship. When the modulation voltage is increased at any value of the Gunn diode applied voltage, the output power of the VCO 12 increases monotonously.

  Next, for example, the modulation voltage is 0V, and the Gunn diode applied voltage is 3.7V. When the Gunn diode applied voltage is set to a constant value of 3.7 V and the modulation voltage is increased, the output power of the VCO 12 increases monotonously. On the other hand, the output power of the VCO 12 can be kept constant by lowering the Gunn diode applied voltage as the modulation voltage increases. The mixer current flowing through the mixer 15 increases as the output power of the VCO 12 increases. Therefore, the Gunn diode applied voltage is lowered as the mixer current flowing through the mixer 15 increases. This feedback operation is continued until the mixer current reaches a certain value, for example, 3 mA. When the modulation voltage decreases, the same operation as that when the modulation voltage increases is performed. This feedback operation is performed by the current detection circuit 18 and the voltage application circuit 19.

  FIG. 6 is a diagram showing the configuration of the current detection circuit 18 and the voltage application circuit 19. The current detection circuit 18 includes a detection resistor 52 and a differential amplifier 53 having an operational amplifier 54. The current detection circuit 18 is connected to the mixer 15. The voltage application circuit 19 includes a differential amplifier 55 having an operational amplifier 56 and a MOSFET 58 that applies a voltage to the Gunn diode 23. The voltage application circuit 19 is connected to the Gunn diode 23.

  The configuration and operation of the current detection circuit 18 will be described. A detection resistor 52 is connected between the mixer 15 and the power supply terminal 51, and a negative voltage is applied to the power supply terminal 51. The value of the voltage drop across the detection resistor 52 changes in accordance with the change in the mixer current flowing through the mixer 15. The value of the voltage drop detected by the detection resistor 52 is input to the differential amplifier 53 and then amplified and output to the voltage application circuit 19.

  Next, the configuration and operation of the voltage application circuit 19 will be described. The amplified signal amplified by the differential amplifier 53 of the current detection circuit 18 and the voltage signal applied to the reference voltage terminal 25 are input to the differential amplifier 55 of the voltage application circuit 19 and then amplified and output. The signal output from the differential amplifier 55 is applied to the gate of the MOSFET 58 connected between the power supply terminal 59 and the Gunn diode 23. The signal output from the differential amplifier 55 changes the gate voltage of the MOSFET 58.

  As a result of the feedback operation of the current detection circuit 18 and the voltage application circuit 19, the output of the voltage controlled oscillator 12 becomes a certain constant value, and accordingly, the value of the mixer current flowing through the mixer 15 also becomes a certain certain value. The value of the mixer current flowing through the mixer 15 is determined by the voltage value applied to the reference voltage terminal 25.

  FIG. 7 is a diagram showing the relationship between the modulation voltage before and after the feedback operation by the current detection circuit 18 and the voltage application circuit 19 and the output power of the voltage controlled oscillator (VCO). The dotted line in FIG. 7 shows the relationship between the conventional modulation voltage in which the feedback operation by the current detection circuit 18 and the voltage application circuit 19 is not performed and the output power of the voltage controlled oscillator. Also, the solid line in FIG. 7 shows the relationship between the modulation voltage of the present invention and the output power of the voltage controlled oscillator after the feedback operation by the current detection circuit 18 and the voltage application circuit 19 is performed. As shown by the solid line in FIG. 7, after the feedback operation by the current detection circuit 18 and the voltage application circuit 19, the output power of the voltage controlled oscillator shows a flat characteristic with respect to the modulation voltage. Therefore, the output power of the voltage controlled oscillator becomes constant with respect to the modulation voltage, and the output characteristics are improved.

  FIG. 8 is a diagram showing the relationship between the modulation voltage before and after the feedback operation by the current detection circuit 18 and the voltage application circuit 19 and the oscillation frequency of the voltage controlled oscillator (VCO). The round dots in FIG. 8 indicate the values of the transmission frequencies of the conventional modulation voltage and the voltage-controlled oscillator that are not performing the feedback operation by the current detection circuit 18 and the voltage application circuit 19, and the dotted lines are linear approximation lines of the values of the round dots. Indicates. 8 indicate the values of the modulation voltage and the oscillation frequency of the voltage controlled oscillator of the present invention after the feedback operation by the current detection circuit 18 and the voltage application circuit 19, and the solid line indicates the value of the square point. The linear approximation line is shown. The index indicating the linearity of the linear approximation line represented by the conventional dotted line before the feedback operation is 8.6%, whereas the index indicating the linearity after the feedback operation is 3. At 6%, the linearity between the modulation voltage and the oscillation frequency of the voltage controlled oscillator is improved by the feedback operation. An index representing linearity is defined by | value of linear approximation−measured value | / deformation width.

  FIG. 9 is a diagram showing the relationship between the applied voltage of the Gunn diode and the oscillation frequency of the voltage controlled oscillator (VCO) using the modulation voltage as a parameter. The operation of the present invention will be described by taking the modulation voltage as a parameter. FIG. Here, the modulation voltage indicates the voltage applied to the varactor diode. The feedback operation of the present invention will be described with reference to FIGS. 8 and 5 and FIG.

  In the plot showing the relationship between the conventional modulation voltage not performing the feedback operation in FIG. 8 and the oscillation frequency of the voltage-controlled oscillator, the deviation from the linear approximation line is large around 0V and 10V. That is, in the vicinity of 0V, the increase in the actual measurement value is small compared to the linear approximation line, and in the vicinity of 8 to 10V, the increase in the actual measurement value is conversely large compared to the linear approximation line.

  For example, in the voltage controlled oscillator shown in FIG. 5, when the modulation voltage is 0V, the Gunn diode applied voltage is set to 3.7V, and a feedback operation is performed to decrease the Gunn diode applied voltage as the modulation voltage increases. .

  This will be described with reference to FIG. 9. With the modulation voltage of 0V, the frequency changes diagonally upward to the left as the modulation voltage increases from the Gunn diode applied voltage of 3.7V. Accordingly, the increase in frequency increases near the modulation voltage 0V, and the increase in frequency decreases conversely near the modulation voltage 10V, so that an operation for improving linearity is performed.

It is a figure which shows the structure of the FM-CW radar of this invention. 1 is a perspective view showing an embodiment in which a voltage controlled oscillator (VCO), a directional coupler, and a mixer configured by surface-mount elements are formed on a dielectric substrate. FIG. It is a figure which shows the relationship between the output electric power of a voltage control type | mold oscillator (VCO) at the time of making a modulation voltage variable, and a mixer current. It is a figure which shows a modulation voltage waveform and the output voltage waveform of a mixer when there is no target object. It is a figure which shows the relationship between a Gunn diode applied voltage and the output power of a voltage control type | mold oscillator (VCO) by using a modulation voltage as a parameter. It is a figure which shows the structure of a current detection circuit and a voltage application circuit. It is a figure which shows the relationship between the modulation voltage before and behind a feedback operation | movement, and the output electric power of a voltage controlled oscillator (VCO). It is a figure which shows the relationship between the modulation voltage before and behind a feedback operation | movement, and the transmission frequency of a voltage controlled oscillator (VCO). It is a figure which shows the relationship between the Gunn diode applied voltage and the oscillation frequency of a voltage control type | mold oscillator (VCO) by using a modulation voltage as a parameter. It is a figure which shows the structure of the conventional FM-CW radar. It is a figure explaining the general operation | movement of FM-CW radar.

Explanation of symbols

11: Triangular wave generation circuit, 12: Voltage controlled oscillator (VCO), 13: Directional coupler, 14: Transmission / reception antenna device, 14a: Transmission antenna device, 14b: Reception antenna device, 15: Mixer, 16: Amplifier, 17 : Signal processing circuit, 18: Current detection circuit, 19: Voltage application circuit, 23: Gunn diode, 25: Reference voltage terminal, 31: Back ground electrode, 32: Dielectric substrate, 33: Surface mount type Gunn diode, 34: Surface mount type varactor diode, 35: power supply terminal, 36: power supply terminal, 37: via hole, 38: branch line coupler, 39a, 39b: surface mount type Schottky barrier diode, 41: rat race circuit, 42: power supply terminal, 43: transmission terminal, 44: reception terminal, 45: IF output terminal, 51: power supply terminal, 52: detection resistor, 53: difference Amplifier: 54: operational amplifier, 55: differential amplifier, 56: operational amplifier, 58: MOSFET, 59: power supply terminal, 91: triangular wave generation circuit, 92: voltage controlled oscillator (VCO), 93: directional coupler, 94: Transmission / reception antenna device, 94a: transmission antenna device, 94b: reception antenna device, 95: mixer, 96: amplifier, 97: signal processing circuit

Claims (3)

A voltage controlled oscillator having a Gunn diode and a varactor diode and outputting a frequency-modulated first signal;
A transmitting / receiving antenna device for transmitting the first signal to a target object and receiving a second signal reflected by the target object;
A passive mixer having a diode, inputting the first signal and the second signal, and outputting a mixer output signal representing a frequency difference between the first signal and the second signal;
A current detection circuit for detecting a change in current flowing through the passive mixer;
A voltage application circuit for making the output power of the frequency-modulated signal of the voltage controlled oscillator constant by changing the voltage applied to the Gunn diode based on the detected change in the current flowing through the passive mixer When,
An FM-CW radar characterized by comprising:   The FM-CW radar according to claim 1, wherein the diode constituting the passive mixer is surface-mounted on a dielectric substrate.   The FM-CW according to claim 1, further comprising a directional coupler, wherein the voltage controlled oscillator, the passive mixer, and the directional coupler are surface-mounted on the same dielectric substrate. Radar.

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