JP2009139274A - High-frequency sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency sensor mounted with a simply-formable filter circuit on a transmission line from an oscillator generating electromagnetic waves of the sensor to an antenna radiating the electromagnetic waves to the outside. <P>SOLUTION: This high-frequency sensor is provided with: the oscillator 2 generating transmission waves 1 of high-frequency signals; the transmission antenna 3 radiating the transmission waves 1 to the outside; a reception antenna receiving reflection waves generated by reflecting the transmission waves 1 by a detection object as reception waves 4; a mixer part 6 generating a detection signal 5 based on the transmission waves 1 generated by the oscillator 2 and the reception waves 4 received by the reception antenna; and a branch part 7 distributing the transmission waves 1 transmitted from the oscillator 2 to the transmission antenna 3 and the mixer part 6. The high-frequency sensor is structured such that a filter circuit 8 composed by serially connecting one or more resistors 9 is arranged on a transmission line between the oscillator 2 and the branch part 7. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a circuit configuration of a high-frequency sensor that performs high-frequency transmission / reception and detects an object.

  Currently, sensors for performing object detection using high-frequency signals are used in various fields. In sensors using high-frequency signals, it is necessary to reduce the amount of radiation to the outside of unnecessary radio waves (hereinafter referred to as spurious) in other frequency bands in order to use the desired frequency band according to the Radio Law. In particular, since a spurious signal having a frequency n times the desired frequency (n is an integer of 2 or more) generates a large signal, the spurious frequency n times the desired frequency is reduced, and radiation to the outside is reduced. Reduction is an issue.

In general, in order not to radiate spurious to the outside, a filter circuit (for example, Patent Document 1) that satisfies the filter characteristics according to the pattern shape of the transmission line in order to reduce spurious on the high-frequency circuit that generates a high-frequency signal, In addition, an antenna circuit that radiates a high-frequency signal to the outside is provided with a configuration for suppressing spurious (for example, Patent Document 2).
JP 2006-352245 A Japanese Patent Application No. 2006-217848

  Also, using a method of spatially coupling a high frequency signal to a component that does not conduct electricity such as a dielectric resonator, a structure that resonates a desired frequency with the shape (straight, thickness) of the component A method of spatially transmitting only a specific frequency is also used.

  However, in the filter circuit that selects the frequency by changing the length of the transmission line as in Patent Document 1, if the transmission line length is set so as to pass the desired frequency, it is three times the desired frequency. In order to suppress the passage of these spurious signals, it is necessary to separately create a filter for reducing the frequency signal of each spurious signal. There was a possibility that the filter circuit would become huge with increasing complexity.

In addition, the filter circuit suppresses radiation from the antenna to the outside by reflecting the spurious, but if the reflected spurious is input to the oscillator, it may be further increased by the oscillator. In addition, there is a possibility that the spurious cannot be suppressed due to the attenuation effect of the filter and radiates to the outside.

  Also, as in Patent Document 2, when the patch antenna is configured to suppress spurious radiation, when a pole antenna or horn antenna is used to change the directivity or gain of the radio wave depending on the application of the sensor Since it is impossible to suppress spurious radiation, it is necessary to provide a filter on a circuit that generates radio waves separately, and it is difficult to reduce spurious in all antennas.

  The present invention has been made to solve the problem. In the present invention, a filter circuit that can be simply configured on a transmission line from an oscillator that generates a radio wave of a sensor to an antenna that radiates the radio wave to the outside is provided. The object is to provide an on-board high-frequency sensor.

  To achieve the object, an oscillator that generates a transmission wave of a high-frequency signal, a transmission antenna that radiates the transmission wave to the outside, and a reflected wave that is generated when the transmission wave is reflected by a detected object is received as a reception wave. Receiving antenna, a transmission wave generated by the oscillator, a mixer unit that generates a detection signal based on the reception wave received by the reception antenna, a transmission antenna and a mixer that transmit the transmission wave transmitted from the oscillator A high-frequency sensor comprising: a branch portion that distributes to a portion; and a filter circuit in which at least one resistor is connected in series on a transmission line between the oscillator and the branch portion. Can provide.

  According to an aspect of the present invention, the filter circuit includes two or more resistors connected in series, and a transmission line is provided between the resistors. Can provide.

  Also, according to one aspect of the present invention, the transmission line length is approximately (2n−1) / 4 of the wavelength λg on a transmission line having a desired frequency (transmission wave frequency), where n is an integer of 1 or more. The high-frequency sensor can be provided.

  Moreover, according to one aspect of the present invention, a stub having the other end opened or short-circuited is disposed on the transmission line between the filter circuit and the branch portion so as to be orthogonal to the traveling direction of the transmission wave. It is possible to provide a high-frequency sensor characterized by the above.

  According to another aspect of the present invention, a stub having the other end opened or short-circuited so as to be orthogonal to the traveling direction of the transmission wave is disposed on the transmission line between the resistors of the filter circuit. A characteristic high-frequency sensor can be provided.

  According to the present invention, by using a resistor in the filter circuit, the attenuation increases as the frequency increases, which is a characteristic of the resistor. Since it can be converted into thermal energy by the vessel, it is possible to attenuate spurious while preventing reflection to the oscillator, and to suppress spurious emission to the outside.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a schematic configuration diagram of a high-frequency sensor of the present invention. The high-frequency sensor of the present invention includes an oscillator 2 that generates a transmission wave 1 of a high-frequency signal, a transmission antenna 3 that radiates the transmission wave 1 to the outside, and a reflected wave that is generated when the transmission wave 1 is reflected by an object to be detected. Receiving wave 4 as a received wave 4, a transmission wave 1 generated by the oscillator 2, a mixer unit 6 that generates a detection signal 5 based on the received wave 4 received by the receiving antenna, and the oscillator 2 In a high-frequency sensor comprising a branching unit 7 for distributing the transmission wave 1 transmitted from the transmission antenna 3 and the mixer unit 6, at least one or more transmission lines are provided on the transmission line between the oscillator 2 and the branching unit 7. A filter circuit 8 in which resistors 9 are connected in series is provided.

  FIG. 2 shows a schematic configuration diagram of the filter circuit 8 of the present invention. The filter circuit 8 is configured by providing at least one resistor 9 in series with respect to the traveling direction of the transmission wave 1 on a transmission line provided between the oscillator 2 and the branching unit 7. . Here, it is known that the resistor 9 generally has a constant resistance value for a low-frequency signal, but for a high-frequency signal, particularly a gigahertz band signal, the resistor 9 is shown in FIG. ), The resistance value changes according to the frequency. This is a phenomenon that occurs when an inductor (L component) is connected in series to the resistor 9 and the capacitor (C component) is connected in parallel to the two when the resistor 9 is viewed from a high frequency signal. It has become. Therefore, as shown in FIG. 3B, as the frequency of the high-frequency signal that passes through increases, the characteristics that pass through the resistor 9 are reduced, that is, the resistor 9 cannot pass through. By using the high frequency characteristics of the resistor 9, the present invention provides a filter circuit 8 having a more effective attenuation characteristic with respect to a predetermined frequency.

Here, as shown in FIG. 3B, simply by connecting the resistors 9 in series, the frequency of the transmission signal does not pass through the resistor 9 when the frequency of the transmission signal becomes high, so the amount of transmission signal to the branching unit 7 is reduced. The amount of external radiation from the transmission antenna 3 and the output signal at the mixer unit 6 are reduced. Further, if the impedance of the resistor 9 at the frequency of the transmission signal is different from the impedance of the transmission line, mismatching occurs, and the amount of transmission signal supplied to the branching unit 7 is reduced in the same manner as described above. Therefore, as shown in FIG. 2, the filter circuit 8 is provided with a matching circuit for ensuring the passage of the transmission signal at both ends of the resistor 9 and connects the matching circuit and the transmission line. By providing the matching circuit, it is possible to have an attenuation effect on the n-th harmonic (n: integer of 2 or more) of the transmission signal, which is a frequency to be reduced as a sensor, without further attenuation of the transmission signal. Therefore, it is possible to provide a sensor circuit that reduces the amount of spurious radiation.

  Furthermore, regarding the resistor 9, a resistance value that does not become a load for the transmission signal is desirable. Therefore, by reducing the resistance value of the resistor to be used, it is possible to provide the filter circuit 8 having an attenuation effect with respect to the n-order harmonics while minimizing the reduction amount with respect to the transmission signal.

  Next, a circuit when a plurality of resistors 9 are provided will be described. FIG. 4 shows a schematic configuration diagram of a filter circuit 8 using two resistors 9. When two resistors 9 are used, a transmission line is provided between the resistors 9 in series with respect to the traveling direction of the transmission signal. When there are two or more resistors 9, the attenuation characteristics of the resistors 9 are added, so that the amount of attenuation with respect to the transmission signal also increases. Therefore, by adjusting the impedance characteristics due to the fluctuation of the line width and length of the transmission line provided between the resistors 9, the frequency signal (for example, the nth-order harmonic) to be attenuated while suppressing the attenuation amount of the transmission signal is adjusted. ) Is configured to take a large attenuation.

  FIG. 5 shows the characteristics of the filter circuit 8 of FIG. FIG. 5A shows the result of the pass characteristic of the filter circuit 8 provided with one resistor 9, and FIG. 5B shows two resistors 9 provided with a transmission line between the resistors 9. This is the result of the pass characteristics of the circuit. Here, the frequency of the transmission signal is 7 gigahertz, and the frequency signal to be reduced is a 14 gigahertz signal that is the second harmonic of the transmission signal. From the result of FIG. 5, the signal of 7 GHz that is the transmission signal is slightly attenuated by providing two resistors 9 as compared with the case of one, but 14 GHz that is the second harmonic is simply It can be confirmed that a larger amount of attenuation than that obtained by adding the attenuation amounts of the two resistors 9 can be secured. This is realized by adjusting the impedance of the transmission line provided between the resistors 9, and is approximately (2n−1) / 4 of the wavelength λg on the transmission line with respect to the transmission line width to be used. By setting the length (n is an integer equal to or greater than 1), it is possible to obtain an attenuation greater than a simple combination of attenuations and to reduce the attenuation of the transmission signal.

FIG. 6 shows the pass characteristics in the filter circuit 8 when the number of resistors 9 is three or four.
Both results pass without significant loss for the transmission signal of 7 GHz, but for 14 GHz of the second harmonic, the attenuation increases as the number increases. Therefore, it is possible to suppress the transmission of the second harmonic to the circuits after the branching unit 7. Here, in order to maintain the amount of transmission signal passing through the filter circuit 8 in which the amount of attenuation of the transmission signal increases as the number of resistors 9 increases, transmission is performed by adjusting the impedance in the matching circuit. It is also possible to provide a filter circuit 8 that retains the amount of signal passing.

  Furthermore, as in the present invention, by using an element that converts the input energy into another energy (for example, heat, light energy, etc.) like the resistor 9 in the filter circuit 8, In contrast, since it is possible to generate energy loss with respect to spurious rather than mere total reflection, it is possible to suppress reflection to the previous circuit to an oscillator, etc. It is also possible to suppress the lack of stability. Further, when a circuit for amplifying a signal is provided in the previous stage like the oscillator 2, the spurious signal may be amplified by reflecting the spurious signal, so that further spurious signal generation can be suppressed.

  Here, FIG. 1 shows a transmission / reception integrated antenna in which the transmission antenna 3 and the reception antenna are integrated to perform transmission / reception at the same time, but a transmission / reception separate antenna in which the transmission antenna 3 and the reception antenna are separated. However, it goes without saying that the above effect can be obtained. Furthermore, in this embodiment, the transmission signal is set at 7 gigahertz. However, in a high frequency signal (especially gigahertz band), there is no change in the circuit configuration according to the set frequency of the transmission signal, and the same effect can be obtained. It becomes possible.

Next, filter characteristics when the filter circuit 8 using the resistor 9 described above is combined with a stub filter 10 constituted by a transmission line will be described.
FIG. 7 shows a schematic configuration diagram in which the filter circuit 8 of the present invention and the stub filter 10 are combined. As shown in FIG. 8, the stub filter 10 is a filter circuit 8 in which one end is installed perpendicularly to the transmission direction of the transmission signal and the other end is opened or short-circuited on the transmission line through which the transmission signal is transmitted. The stub filter 10 satisfies the filter characteristics by changing the impedance of the transmission line according to the length of the stub so as to reflect the spurious. When the other end is short-circuited, the other end is in a grounded state, so that it is necessary to set a length so that a transmission signal is not transmitted to the other end.

  FIG. 7 shows a combination with the stub filter 10 using a short stub whose other end is short-circuited. In this embodiment, the stub filter 10 is installed between the filter circuit 8 and the branching unit 7. By such a grounding method, the spurious leaking slightly from the filter circuit 8 is reflected by the stub filter 10 at the subsequent stage, so that transmission of the spurious to the branching section 7 can be reliably suppressed, and the filter Since the spurious reflected by the stub is converted into other energy such as heat and light by the filter circuit 8, it is possible to further reduce the amount of reflection to the previous circuit, thereby ensuring the stability of the circuit. It is also possible to suppress an increase in spurious. Furthermore, since the stub filter 10 reflects the spurious that has already been attenuated by the filter circuit 8, it can sufficiently reflect without having a filter with high-precision filter characteristics. A filter can be constructed with a simple circuit configuration.

FIG. 8 shows a detailed configuration between the filter and the branching unit 7 of FIG. In this embodiment, the transmission signal is 7 GHz, and the stub filter 10 has a characteristic of reflecting a 14 GHz signal that is the second harmonic of the transmission signal (see FIG. 9).
By installing this stub filter 10 between the filter circuit 8 of the present invention and the branching section 7, it becomes possible to have both the filter characteristics of the stub filter 10 and the filter circuit 8 (see FIG. 10). The circuit 8 has a gentle characteristic with respect to the frequency of the circuit 8 and a characteristic of abruptly attenuating with respect to a specific frequency of the stub filter 10, thereby having a large attenuation effect with respect to a specific spurious. With respect to the spurious, a filter having a certain attenuation effect can be configured. Further, even when the dimensions of the filter circuit 8 and the stub filter 10 change due to a manufacturing error of a transmission line or the like, the spurious signal can be reduced as a whole because of the gentle attenuation characteristics of the filter circuit 8. Therefore, it is possible to suppress significant performance fluctuations of the filter circuit 8 due to errors or the like.

  In the above configuration, in this embodiment, the transmission signal is set to 7 gigahertz. However, as described above, the high frequency signal (especially gigahertz band) has the same characteristics, and is not limited to this frequency. However, the same effect can be obtained.

  In addition, in the sensor equipped with the filter circuit 8 as described above, spurious emission from the transmission antenna 3 can be suppressed, and an element used for the oscillator 2 and the mixer unit 6 to increase a certain frequency is used. In order to suppress transmission of a spurious signal to an element that generates a different frequency signal from a certain frequency, it becomes possible to suppress amplification and oscillation inside the sensor of the spurious signal and generation of a different spurious signal. Therefore, it is possible to more effectively reduce the emission of spurious signals from the sensor itself.

  Next, a configuration diagram in which the stub filter 10 is provided on the transmission line between the resistors 9 in the filter circuit 8 is shown in FIG. By providing the stub filter 10 on the transmission line of the resistor 9, the subsequent resistor 9 generates a loss due to energy conversion due to heat or the like with respect to a slight spurious that could not be completely reflected by the stub filter 10. Since the spurious can be reliably reduced by the subsequent resistor, transmission of the spurious to the outside can be more reliably suppressed.

  Further, by providing the stub filters 10 on both sides via the resistor 9, the spurious reflected by the stub filter 10 continues to be reflected via the resistor 9. Therefore, the spurious can be attenuated efficiently, and the emission of spurious to the outside can be further suppressed.

  In the above embodiment, the frequency is limited. However, for a high frequency such as gigahertz, the same effect can be obtained without depending on the actual value of the frequency, and the spurious can be suppressed. It becomes possible to carry out more strictly.

Schematic configuration diagram of the high-frequency sensor of the present invention Configuration diagram of a filter circuit using one resistor (A) Frequency-impedance diagram of resistor (B) Frequency-pass characteristic diagram of one resistor Configuration diagram of a filter circuit using two resistors Comparison of filter circuit pass characteristics for one and two resistors Filter circuit pass characteristics diagram for three and four resistors Schematic configuration diagram of the high-frequency sensor of the present invention provided with a stub filter Schematic configuration diagram of filter circuit and stub filter Passing characteristics of stub filter Passing characteristic diagram in FIG. Schematic configuration with a stub filter on the transmission line between resistors

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transmission wave 2 ... Oscillator 3 ... Transmission antenna 4 ... Received wave 5 ... Output signal 6 ... Mixer part 7 ... Branch part 8 ... Filter circuit 9 ... Resistor 10 ... Stub filter

Claims (5)

An oscillator that generates a high-frequency signal transmission wave;
A transmitting antenna that radiates the transmitted wave to the outside;
A receiving antenna that receives a reflected wave generated by reflecting the transmission wave by the object to be detected as a received wave;
A mixer unit that generates a detection signal based on the transmission wave generated by the oscillator and the reception wave received by the reception antenna;
A branching unit that distributes a transmission wave transmitted from the oscillator to a transmission antenna and a mixer unit;
In a high-frequency sensor equipped with
A high-frequency sensor, wherein a filter circuit in which at least one resistor is connected in series is provided on a transmission line between the oscillator and the branch portion. 2. The high frequency device according to claim 1, wherein the filter circuit includes two or more resistors connected in series, and a transmission line for suppressing attenuation of a transmission wave is provided between the resistors. Sensor. 3. The transmission line length is approximately (2n−1) / 4 (n is an integer of 1 or more) of a wavelength λg on a transmission line having a desired frequency (transmission wave frequency). The high-frequency sensor described. The stub having the other end opened or short-circuited is disposed on the transmission line between the filter circuit and the branch portion so as to be orthogonal to the traveling direction of the transmission wave. 3. The high frequency sensor according to any one of 3 above. 4. The stub having the other end opened or short-circuited so as to be orthogonal to the traveling direction of the transmission wave is disposed on the transmission line between the resistors of the filter circuit. 5. The high-frequency sensor according to item.

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