JP2017227460A - Unnecessary radiation prevention device and unnecessary radiation prevention method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device that prevents unnecessary radiation.SOLUTION: An unnecessary radiation prevention device includes: a local oscillator for generating an output signal with a frequency varying over time on the basis of a reference signal from a reference oscillator; and a variable bandpass filter which the output signal from the local oscillator is input into and which lets a signal in a prescribed passage band pass through and output. The passage band is controlled to follow change over time of the frequency of the output signal from the local oscillator and include the frequency.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an unnecessary radiation suppressing device and an unnecessary radiation suppressing method.

A radar apparatus including a PLL (Phase Locked Loop) circuit is used. Since the radar apparatus is configured to operate the phase comparator of the PLL circuit at the frequency of the reference clock, unnecessary radiation is generated at a frequency separated from the frequency of the output signal by the frequency of the reference clock. This unnecessary radiation can be suppressed by devising such as narrowing the band of the low-pass filter in the PLL circuit.

Japanese Patent Laid-Open No. 10-209714

  However, in the case of a radar apparatus using the FM modulation method, the frequency of the output signal changes, so the frequency of unnecessary radiation generated following the frequency of the output signal also changes. In a general fixed band filter circuit, it is difficult to select and remove only unnecessary radiation whose frequency changes. Unnecessary radiation may cause detection of an erroneous target and deterioration of a signal-to-noise ratio due to an increase in noise level of a signal received by a radar.

  An object of the present invention is to provide an apparatus for suppressing unwanted radiation.

The present invention employs the following means in order to solve the above problems.
That is, the first aspect is
A local oscillator that generates an output signal of a time-varying frequency based on a reference signal from a reference oscillator;
An output signal from the local oscillator is input, and includes a variable bandpass filter that passes and outputs a signal of a predetermined passband,
The passband is controlled to include the frequency following the time change of the frequency of the output signal from the local oscillator.
Use unnecessary radiation suppression devices.

  An aspect of the disclosure may be realized by executing a program by an information processing device. That is, the disclosed configuration can be specified as a program for causing the information processing apparatus to execute the processing executed by each unit in the above-described aspect, or a computer-readable recording medium on which the program is recorded. Further, the disclosed configuration may be specified by a method in which the information processing apparatus executes the process executed by each of the above-described units. The configuration of the disclosure may be specified as a system including an information processing apparatus that performs the processing executed by each of the above-described units.

  The step of describing the program includes processes that are executed in parallel or individually even if they are not necessarily processed in time series, as well as processes that are executed in time series in the described order. Some of the steps describing the program may be omitted.

  ADVANTAGE OF THE INVENTION According to this invention, the apparatus which suppresses unnecessary radiation can be provided.

FIG. 1 is a configuration example of a radar apparatus according to the embodiment. FIG. 2 is a diagram illustrating a configuration example of a PLL circuit of the radar apparatus. FIG. 3 is a diagram illustrating an example of the output of the PLL circuit. FIG. 4 is a diagram illustrating a configuration example of a microstrip line and an example of an equivalent circuit of the microstrip line. FIG. 5 is a diagram showing the relationship between the applied voltage and the resonance frequency of the microstrip line in FIG. FIG. 6 is a diagram illustrating an example of the relationship between the frequency of a signal input to the microstrip line and the pass characteristic. FIG. 7 is a diagram illustrating an example of time dependency of the frequency of the output signal of the PLL circuit, the voltage applied to the variable capacitance element, and the peak frequency of the pass band of the band pass filter.

  Hereinafter, embodiments will be described with reference to the drawings. The configuration of the embodiment is an exemplification, and the configuration of the invention is not limited to the specific configuration of the disclosed embodiment. In carrying out the invention, a specific configuration according to the embodiment may be adopted as appropriate.

Embodiment
(Configuration example)
<Configuration example of radar device>
FIG. 1 is a configuration example of a radar apparatus according to this embodiment. The radar apparatus 1 according to the present embodiment is mounted on a vehicle and can be used to detect a target existing around the vehicle, such as another vehicle, a sign, or a guardrail. However, the radar apparatus 1 according to the present embodiment may be used for various uses other than the on-vehicle radar apparatus (for example, monitoring of an aircraft in flight or a ship being navigated). The radar device 1 is an example of an unnecessary radiation suppression device.

  The radar apparatus 1 includes a reference oscillator 101, a PLL circuit 102, a band pass filter 103, a transmission circuit 104, a transmission antenna 105, a reception antenna 106, a reception circuit 107, a band pass filter 108, a mixer 109, a BB circuit 110, and a control unit 111. Including.

  The reference oscillator 101 is an oscillator that outputs a reference frequency signal (reference signal). The reference oscillator 101 outputs a reference signal to the PLL circuit 102.

  The PLL circuit 102 is an electronic circuit that applies a feedback control to an input reference signal and outputs a signal having a predetermined frequency. The PLL circuit 102 can change the frequency of the output signal under the control of the control unit 111. The PLL circuit 102 is an example of a local oscillator. The PLL circuit 102 will be described later.

  The band-pass filter 103 is a filter that passes a signal in a predetermined band and attenuates a signal other than the predetermined band. The band pass filter 103 can change the band through which the signal is passed under the control of the control unit 111. The band-pass filter 103 may be realized by combining a high-pass filter that passes a signal of a predetermined first frequency or higher and a low-pass filter that passes a signal of a predetermined second frequency (> first frequency) or lower.

  The transmission circuit 104 is a circuit that amplifies the output of the band pass filter 103 and generates a transmission signal.

  The transmission antenna 105 transmits the transmission signal generated by the transmission circuit 104.

  The reception antenna 106 receives a signal or the like obtained by reflecting a transmission signal or the like from the transmission antenna 105 by a target or the like.

  The receiving circuit 107 is a circuit that amplifies and outputs a signal received by the receiving antenna.

  The band pass filter 108 is a filter that passes a signal in a predetermined band and attenuates a signal other than the predetermined band. The band pass filter 108 can change the band through which the signal is passed under the control of the control unit 111. The band pass filter 103 and the band pass filter 108 are examples of variable band pass filters.

  The mixer 109 multiplies the output of the receiving circuit 107 and the output of the band pass filter 108 to generate a baseband signal, and outputs the baseband signal to the BB circuit 110.

A BB (Base Band) circuit 110 performs predetermined processing on the baseband signal generated by the mixer 109.

  The control unit 111 controls the frequency of the signal output from the PLL circuit 102 and the band passed by the band pass filter 103 and the band pass filter 108. For example, the control unit 111 controls the DC voltage applied to the variable capacitance elements of the band pass filter 103 and the band pass filter 108. The band pass filter 103 and the band pass filter 108 are similarly controlled by the control unit 111. The control unit 111 is realized by, for example, a computer that includes a processor that performs signal arithmetic processing according to a computer program and a memory that stores information related to the arithmetic processing. The memory may be composed of a plurality of memories such as an auxiliary storage unit that stores computer programs and setting values, and a main storage unit that temporarily stores information used for arithmetic processing. For example, the control unit 111 controls the signal output from the PLL circuit 102 to an FM modulation signal of FM-CW radar or FCM radar. Further, the control unit 111 controls the pass bands (applied voltages) of the band pass filter 103 and the band pass filter 108 according to the timing of the FM modulation signal.

<Configuration example of PLL circuit>
FIG. 2 is a diagram illustrating a configuration example of a PLL circuit of the radar apparatus. The PLL circuit 102 of the radar apparatus 1 includes a phase comparator 201, an LPF 202, a VCO 203, and a frequency divider 204.

  The phase comparator 201 is a circuit that converts the phase difference between the reference signal input from the reference oscillator 101 and the reference signal input from the frequency divider 204 into a voltage and outputs the voltage.

An LPF (Low Pass Filter) 202 is a filter that allows a component having a frequency lower than the cutoff frequency to pass therethrough and attenuates a component having a frequency higher than the cutoff frequency. The LPF 202 smoothes the signal from the phase comparator 201.

A VCO (Voltage Controlled Oscillator) 203 is a circuit that controls the frequency of an output signal according to the voltage of the input signal.

  The frequency divider 204 is a circuit that outputs an input signal having a frequency that is 1 / integer. By controlling the frequency dividing ratio of the frequency divider 204, the frequency of the signal output from the PLL circuit 102 can be controlled. The output of the VCO 203 is input to the frequency divider 204.

<< Example of PLL circuit output >>
The PLL circuit 102 synchronizes the reference signal output from the reference oscillator 101 and the signal output from the frequency divider 204. Since the input of the division cycle 204 is the output of the VCO 203, the frequency of the output signal of the VCO 203 is a frequency divided by the frequency of the reference signal. N frequency). By changing the frequency dividing ratio of the frequency divider 203, the frequency of the output signal can be changed.

  FIG. 3 is a diagram illustrating an example of the output of the PLL circuit. The horizontal axis of the graph of FIG. 3 is the frequency of the output signal, and the vertical axis is the level of the output signal. In the example of FIG. 3, the highest peak of the output signal appears at the frequency of the desired signal (N times the frequency of the reference signal). The peak signal is a signal that the radar apparatus 1 wants to output. Further, from the highest peak, a peak of unnecessary radiation (portion surrounded by an ellipse in FIG. 3) appears at a position where the frequency of the reference signal is separated (portion surrounded by an ellipse in FIG. 3). These peaks of unnecessary radiation appear due to the characteristics of the PLL circuit 1. These peaks of unnecessary radiation are signals that are not desired to be output from the radar apparatus 1. The frequency of the peak of unwanted radiation changes as the frequency of the desired signal changes. Therefore, it is difficult to remove a peak of unnecessary radiation with a fixed frequency bandpass filter or the like.

<Configuration example of band-pass filter>
The band pass filter 103 and the band pass filter 108 are realized by, for example, a microstrip line. The microstrip line is a transmission line having a structure in which a linear conductor is formed on the other surface of a plate-like dielectric having a conductor formed on one surface. Here, a liquid crystal element is used as the dielectric. A variable DC voltage is applied to the liquid crystal element. The liquid crystal element can change a dielectric constant according to an applied voltage. In the microstrip line, the frequency of the electromagnetic wave that passes through changes as the dielectric constant of the dielectric changes. In the above example, the band-pass filter 103 and the band-pass filter 108 are realized using a microstrip line. However, the microstrip line is not necessarily used, and a variable capacitance element described later is mounted on a printed circuit board. It may also be configured as an integrated circuit including a variable capacitance element or the like.

  The band pass filter 103 and the band pass filter 108 are not limited to a microstrip line as long as the pass band can be changed within a desired frequency range of the output signal.

FIG. 4 is a diagram illustrating a configuration example of a microstrip line and an example of an equivalent circuit of the microstrip line. The microstrip line in FIG. 4 has a structure in which a conductor is formed on one surface and a linear conductor is formed on the other surface of the plate-like capacitance variable element. The variable capacitance element is formed such that a variable DC voltage is applied. The DC voltage applied to the capacitance variable element is controlled by the control unit 111. In the example of FIG. 4, a plurality of variable capacitance elements are arranged. The capacitance of the capacitance variable element changes by changing the applied voltage. The capacitance variable element is, for example, a liquid crystal element. By using the liquid crystal element, the variable capacitance element can be integrally formed as a part of the strip line, the control characteristics of the pass band can be improved, and unnecessary radiation can be suppressed more effectively. However, the capacitance variable element is not limited to the liquid crystal element. The capacitance variable element only needs to be an element whose capacitance changes according to an applied voltage or the like. For example, a variable capacitance diode can be used. In the microstrip line in FIG. 4, a signal is input from the left side of the linear conductor and output from the right side of the linear conductor. The equivalent circuit of the microstrip line in FIG. 4 is expressed by combining a parallel variable capacitor and coil and a serial variable capacitor and coil. The equivalent circuit is a resonance circuit composed of a capacitor and a coil, and allows a component near the resonance frequency to pass through the input signal and attenuates components other than the vicinity of the resonance frequency. The resonance frequency of the microstrip line depends on the voltage applied to the variable capacitance element. The resonance frequency of the microstrip line corresponds to the peak frequency of the pass characteristic of the passband of the bandpass filter. That is, the pass band of the band pass filter can be changed by changing the voltage applied to the variable capacitance element. In the microstrip line of FIG. 4, a signal outside the passband based on the shape and applied voltage is attenuated and output.

  FIG. 5 is a diagram showing the relationship between the applied voltage and the resonance frequency of the microstrip line in FIG. The horizontal axis of the graph of FIG. 5 is the voltage applied to the capacitance variable element of the microstrip line, and the vertical axis is the resonance frequency of the microstrip line. The microstrip line is designed so that the resonance frequency range is the desired frequency range of the output signal. A well-known method can be used to design the microstrip line. Furthermore, the resonance frequency of the microstrip line can be controlled by designing the microstrip line so that the range of the resonance frequency in which the relationship between the applied voltage and the resonance frequency is linear is the desired frequency range of the output signal. It becomes easy. In the example of the graph of FIG. 5, when the applied voltage increases in the linear region, the resonance frequency decreases.

  FIG. 6 is a diagram illustrating an example of the relationship between the frequency of a signal input to the microstrip line and the pass characteristic. In the graph of FIG. 6, the horizontal axis represents the frequency of the signal input to the microstrip line, and the vertical axis represents the pass characteristic of the signal passing through the microstrip line. The larger the value on the vertical axis, the higher the proportion of signals that pass through the microstrip line. In the example of FIG. 6, when the capacitance of the capacitance variable element of the microstrip line is A, the passband of the microstrip line is a region centered on the frequency X. The pass band is a region where the pass characteristic is a predetermined value or more. Similarly, when the capacitance of the variable capacitance element of the microstrip line is B, the passband of the microstrip line is a region centered on the frequency Y. When the capacitance of the variable capacitance element of the microstrip line is C, the passband of the microstrip line is a region centered on the frequency Z. Therefore, for example, when the frequency of the output signal of the PLL circuit 102 is X, a signal of the frequency X can be passed by applying a voltage so that the capacitance of the capacitance variable element is A. Furthermore, signals due to unnecessary radiation around the frequency X can be removed. The pass band of the microstrip line is controlled by the capacitance of the variable capacitance element.

(Operation example)
An operation example of the radar apparatus 1 will be described. The reference oscillator 101 of the radar apparatus 1 outputs a reference signal having a predetermined frequency to the PLL circuit 102. The PLL circuit 102 outputs a signal having a frequency based on the frequency division ratio of the frequency divider 204 as an output signal. The frequency division ratio of the frequency divider 204 is controlled by the control unit 111. The output signal of the PLL circuit 102 includes an unwanted radiation component.

  The PLL circuit 102 outputs signals to the band pass filter 103 and the band pass filter 108. The control unit 111 controls the voltage applied to the capacitance variable elements of the bandpass filter 103 and the bandpass filter 108, and the passbands of the bandpass filter 103 and the bandpass filter 108 include the frequency of the output signal of the PLL circuit 102. Like that. As a result, the signals output from the band pass filter 103 and the band pass filter 108 are signals in which the unwanted radiation component is attenuated.

  The transmission circuit 104 amplifies the signal from the band pass filter 103 and outputs it to the transmission antenna 105. The transmission antenna 105 transmits the output of the transmission circuit 104.

On the other hand, the reception antenna 106 receives a signal transmitted from the transmission antenna 105 and reflected by a target or the like. The reception circuit 107 amplifies the signal received by the reception antenna 106 and outputs the amplified signal to the mixer 109.

The mixer 109 multiplies the output of the band pass filter 108 and the output of the reception circuit 107 to generate a baseband signal, and outputs the baseband signal to the BB circuit 110. BB (Base Band) circuit 110
Performs predetermined processing on the baseband signal generated by the mixer 109. Since unnecessary radiation components are removed from the signal input to the mixer 109, detection of an erroneous target and an increase in noise level can be suppressed.

  In order to change the pass band of the band pass filter 103 and the band pass filter 108 following the frequency of the output signal of the PLL circuit 102, the unnecessary radiation signal whose frequency changes following the frequency of the output signal is removed. Can do. Further, unnecessary radiation components are removed at the subsequent stage of the PLL circuit 102, so that unnecessary radiation components are not output from the transmission antenna 105. Therefore, even in the processing for the baseband signal in the BB circuit 110, it is not necessary to perform processing for removing the influence due to the component of unnecessary radiation. In addition, since unnecessary radiation components can be removed after the PLL circuit 102, the degree of freedom in designing the spurious performance of the PLL circuit 102 is increased.

  FIG. 7 is a diagram illustrating an example of time dependency of the frequency of the output signal of the PLL circuit, the voltage applied to the variable capacitance element, and the peak frequency of the pass band of the band pass filter. FIG. 7A shows the time dependence of the frequency of the output signal of the PLL circuit 102. The frequency of the output signal of the PLL circuit 102 is controlled by the control unit 111. Here, an example of triangular wave modulation, which is an FM modulation signal of an FM-CW radar, is shown. In triangular wave modulation, the frequency of the output signal repeatedly rises and falls between frequency A and frequency B (<A). As the frequency of the output signal rises and falls, the frequency of unwanted radiation repeats rising and falling.

  FIG. 7B shows an example of the time change of the DC voltage applied to the variable capacitance element of the band pass filter 103. It is assumed that the resonance frequency of the band pass filter 103 changes as shown in the graph of FIG. 5 depending on the applied voltage. Here, when the frequency of the output signal of the PLL circuit 102 is A, the applied voltage is D, and when the frequency of the output signal of the PLL circuit 102 is B, the applied voltage is C.

  FIG. 7C shows an example of the time change of the peak frequency of the pass band of the band pass filter 103. The peak of the pass band of the band pass filter 103 is the resonance frequency of the band pass filter 103. The peak of the pass band of the band pass filter 103 changes as the applied voltage changes. When the applied voltage is D, the peak frequency of the passband is A. When the applied voltage is C, the peak frequency of the pass band is B. The frequency of the peak of the pass band substantially matches the frequency of the output signal of the PLL circuit 102. The control unit 111 controls the voltage applied to the variable capacitance element in accordance with the change in the frequency of the PLL output signal, so that the peak frequency of the pass band matches the frequency of the output signal of the PLL circuit 102. Thereby, the band pass filter 103 can attenuate the component of unnecessary radiation included in the output signal of the PLL circuit 102. The same applies to the band pass filter 108. The radar apparatus 1 can suppress unnecessary radiation from the transmission antenna 105 due to the FM modulation signal of the radar by the band pass filter 103.

Here, in the PLL circuit 102, the frequency of the output signal depends on the voltage input to the VCO 203. In the band pass filter 103 and the band pass filter 108, the resonance frequency depends on the voltage applied to the variable capacitance element. Further, it is required that the frequency of the output signal of the PLL circuit 102 matches the resonance frequency of the band pass filter 103 and the band pass filter 108. Therefore, the voltage applied to the variable capacitance element may be set using the voltage input to the VCO 203. Thereby, the frequency of the output signal of the PLL circuit 102 and the resonance frequencies of the band pass filter 103 and the band pass filter 108 can be synchronized with each other more easily.

(Operation and effect of this embodiment)
The radar apparatus 1 attenuates components of unnecessary radiation generated in the PLL circuit 102 by providing the band-pass filter 103 and the band-pass filter 108 on the output side of the PLL circuit 102. By removing unnecessary signals in the local system (Lo system: a system through which a signal output from a local oscillator such as a PLL circuit passes), it is not necessary to remove noise in subsequent signal processing (for example, processing in the BB circuit 110). In addition, an increase in noise level as the radar apparatus 1 can be suppressed. When the frequency of the output signal of the PLL circuit 102 changes with time, the radar apparatus 1 changes the passbands of the bandpass filter 103 and the bandpass filter 108 so as to follow the frequency of the output signal. Attenuate components. The radar apparatus 1 can effectively suppress unnecessary radiation even when the frequency of the output signal changes with time.

<Computer-readable recording medium>
A program for causing a computer or other machine or device (hereinafter, a computer or the like) to realize any of the above functions can be recorded on a recording medium that can be read by the computer or the like. The function can be provided by causing a computer or the like to read and execute the program of the recording medium.

  Here, a computer-readable recording medium is a recording medium that stores information such as data and programs by electrical, magnetic, optical, mechanical, or chemical action and can be read from a computer or the like. Say. In such a recording medium, elements constituting a computer such as a CPU and a memory may be provided to cause the CPU to execute a program.

  Examples of such a recording medium that can be removed from a computer or the like include a flexible disk, a magneto-optical disk, a CD-ROM, a CD-R / W, a DVD, a DAT, an 8 mm tape, and a memory card.

  Moreover, there are a hard disk, a ROM, and the like as a recording medium fixed to a computer or the like.

1 Radar equipment
101 Reference oscillator
102 PLL circuit
103 Band pass filter
104 Transmitter circuit
105 Transmitting antenna
106 Receiving antenna
107 Receiver circuit
108 Bandpass filter
109 mixer
110 BB circuit
111 Control unit
201 Phase comparator
202 LPF
203 VCO
204 divider

Claims (5)

A local oscillator that generates an output signal of a time-varying frequency based on a reference signal from a reference oscillator;
An output signal from the local oscillator is input, and includes a variable bandpass filter that passes and outputs a signal of a predetermined passband,
The passband is controlled to include the frequency following the time change of the frequency of the output signal from the local oscillator.
Unwanted radiation suppression device. The local oscillator generates an output signal of the modulation frequency of the FMCW radar;
The unnecessary radiation suppression device according to claim 1, wherein the variable bandpass filter controls the passband following the modulation frequency. The variable bandpass filter includes a liquid crystal element connected to a voltage variable power source.
The unnecessary radiation suppression device according to claim 1 or 2. The local oscillator has a PLL (Phase Locked Loop) circuit,
The PLL circuit includes a VCO (Voltage Controlled Oscillator) to which a signal for controlling the frequency of the output signal from the local oscillator is input,
A signal for controlling a pass band of the variable band pass filter is controlled based on a signal input to the VCO.
The unnecessary radiation suppression device according to any one of claims 1 to 3. Based on the reference signal from the reference oscillator, generate an output signal with a time-varying frequency,
The generated output signal is passed through a variable bandpass filter whose passband is controlled so as to include the frequency following the time change of the frequency of the output signal.
Unnecessary radiation suppression method.