JP2009239574A - High-frequency sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency sensor loading a filter circuit for suppressing a reflection of higher harmonic waves to the oscillator side on a transmission line from an oscillator which produces a radiowave of the sensor to an antenna for radiating the radiowave to the outside. <P>SOLUTION: The high-frequency sensor includes: an oscillator 2 for producing a transmitting wave 1; a transmitting antenna 3 for radiating the transmitting wave to the outside; a receiving antenna 3 for receiving a reflected wave of the transmitting wave as a receiving wave; a mixer part for producing a detection signal based on the transmitting wave and the receiving wave; and a branch part for distributing and transmitting the transmitting wave produced by the oscillator to the transmitting antenna and the mixer part. A first cutoff part is provided on the transmission line connecting the oscillator with the branch part; and a second cutoff part is provided on the transmission line connecting the branch part with the mixer part. A reference potential on the transmission line is set, and a reference voltage part having a filter function of cutting off an nth-order higher harmonic wave of a high-frequency signal is disposed on the transmission line between the first cutoff part and the branch part. <P>COPYRIGHT: (C)2010,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.

  In recent years, sensors for performing object detection using high-frequency signals have been used in various fields. An oscillation circuit of a sensor using a high frequency signal generates a high frequency (hereinafter referred to as a fundamental wave) of a desired frequency for exciting an antenna element. At this time, unnecessary harmonics are generated simultaneously with the fundamental wave. In order to use the desired frequency band according to the Radio Law, it is necessary to reduce the amount of unnecessary harmonics emitted outside the other frequency bands to below the regulation value, especially for the second and third harmonics. Because it has power that cannot be ignored, measures to suppress these are necessary.

  In addition, in order to efficiently transmit the power of the fundamental wave generated by the oscillator in the high-frequency sensor, radiate the radio wave from the antenna, and stably obtain the output of the reflected wave, between the transmission lines connected to the antenna from the oscillator It is known that it is desirable to provide a reference voltage section for high-frequency signals.

In general, in order to prevent unnecessary harmonics from being radiated to the outside, a filter circuit that satisfies the filter characteristics according to the pattern shape of the transmission line in order to reduce unnecessary harmonics on the high-frequency circuit that generates a high-frequency signal (for example, Patent Documents 1 and 2) are provided.
JP 2006-352245 A JP-A-2005-315761

  However, in the filter circuit that selects the frequency by changing the length, width, and line interval of the transmission line as in Patent Document 1, if the transmission line is set to pass the desired frequency, the desired frequency In order to suppress the passage of those unnecessary harmonics, it is necessary to create a separate filter to reduce the frequency signal of the harmonics at each frequency. There is.

  Moreover, although the reference voltage part with respect to a low frequency is provided with respect to the element which comprises the mixer circuit which takes out an output signal like patent document 2, the length and width of a transmission line are further provided on the transmission line connected to an antenna. A filter circuit configured by changing the line interval is arranged.

However, although the above filter circuit suppresses radiation from the antenna to the outside by reflecting unnecessary harmonics, it can be further increased by the oscillator when the reflected harmonics are input to the oscillator. Therefore, the harmonics amplified by the oscillator cannot be suppressed by the attenuation effect of the filter and may radiate to the outside.

  Therefore, in the present invention, an unnecessary harmonic is mounted by mounting a filter circuit that suppresses reflection of harmonics to the oscillator side on the transmission line from the oscillator that generates the radio wave of the sensor to the antenna that radiates the radio wave to the outside. An object of the present invention is to provide a high-frequency sensor that suppresses reflection of waves to an oscillator and prevents unnecessary harmonics from being radiated to the outside.

  To achieve the object, an oscillator that generates a transmission wave that is a high-frequency signal, a transmission antenna that radiates the transmission wave to the outside, a reception antenna that receives a reflected wave of the transmission wave as a reception wave, and the transmission wave A high-frequency sensor comprising: a mixer unit that generates a detection signal based on the received wave and a branch unit that includes a transmission line that distributes and transmits the transmission wave generated by the oscillator to the transmission antenna and the mixer unit A first blocking unit for blocking a DC signal applied to an oscillator from entering the branch unit, a branch unit and the mixer unit on a transmission line connecting the oscillator and the branch unit; A second blocking unit configured to block the DC signal applied to the mixer unit from entering the branching unit, and to set a reference potential on the transmission line; Wave (n: 2 or more Provided is a high-frequency sensor characterized in that a reference voltage unit having a filter function for suppressing passage of an integer) through a transmission line is disposed on the transmission line between the first blocking unit and the branch unit it can.

  In addition, according to one aspect of the present invention, a plurality of the reference voltage units are arranged in parallel in a direction orthogonal to a traveling direction of the n-th harmonic (n: an integer of 2 or more). A high frequency sensor can be provided.

  Further, according to one aspect of the present invention, the reference voltage unit is arranged in a direction perpendicular to the transmission line and so that at least one set faces the transmission line via the transmission line. Can provide.

  In addition, the high-frequency sensor can be provided in which the reference voltage unit is also disposed on a transmission line between the branch unit and the transmission antenna.

  In addition, according to an aspect of the present invention, it is possible to provide a high-frequency sensor characterized in that the reference voltage unit is also disposed on a transmission line between the branching unit and the second blocking unit.

In addition, according to one aspect of the present invention, it is possible to provide a high-frequency sensor characterized in that the reference voltage section is also disposed in the branch section.

In addition, according to one embodiment of the present invention, it is possible to provide a high-frequency sensor having at least one bent portion, one end connected to a transmission line and the other end connected to a ground electrode.

According to the present invention, the reference voltage unit having a filter function for suppressing the nth harmonic (n: an integer of 2 or more) of the high-frequency signal from passing through the transmission line is provided between the blocking unit and the branching unit. Therefore, unnecessary harmonics are not reflected to the oscillator, and a high-frequency sensor that does not emit unnecessary harmonics to the outside can be provided.

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 radiated to the outside, a transmission antenna 3 that radiates the transmission wave 1 to the outside, and a reflected wave of the transmission wave 1 as a reception wave 4. The receiving antenna 3 that receives the signal, the mixer unit 6 that generates the detection signal 5 based on the transmitted wave 1 and the received wave 4, and the transmitted wave 1 transmitted from the oscillator 2 to the transmitting antenna 3 and the mixer unit 6. In a high-frequency sensor provided with a branching unit 7 for distribution, a first blocking unit for preventing a DC signal 9 applied to a transmitter on a transmission line 8 between the oscillator 2 and the branching unit 7 from being transmitted to the branching unit 7 10 and a second blocking unit 13 that does not transmit the DC signal 12 applied to the mixer unit 5 to the branching unit 7 on the transmission line 11 between the branching unit 7 and the mixer unit 6. Reference to transmission line 8 connected to each part 7 Has a structure in which a pressure portion 14.

  The first cutoff unit 10 and the second cutoff unit 13 are configured by a capacitor that blocks a direct-current component and allows a desired high-frequency signal generated by an oscillator to pass therethrough, and the DC signal 9 applied to the oscillator 2 and the mixer unit 6 respectively. 12 direct current components are prevented from flowing into the antenna 3 side, and a desired high-frequency signal (hereinafter referred to as a fundamental wave) generated by the oscillator 2 can be passed.

The reference voltage unit 14 is formed of a transmission line in the transmission line 8 between the first blocking unit 10 and the branching unit 7, and one end is connected to the transmission line through which the high-frequency signal passes, and the other end is connected to the ground electrode. With this configuration, the reference potential (zero potential) for a desired high-frequency signal can be clarified, and the high-frequency signals of the transmission wave 1 and the reception wave 4 can be stably transmitted. .
Further, by providing the first cutoff unit 10 and the second cutoff unit 13, the DC signal 9 applied to the oscillator 2 and the DC signal 13 applied to the mixer unit 6 are not short-circuited by the reference voltage unit 14, The reference voltage unit 14 can be freely installed on the transmission line between the first blocking unit 10 and the branch unit 6.

  The reference voltage unit 14 is installed on the transmission line 8 to prevent unnecessary harmonics generated by the transmitter from flowing into the antenna 3 or the mixer unit 6, and at the same time, the antenna 3 and the mixer unit 6 are disabled. It also prevents unnecessary radio waves reflected by matching from being reflected to the oscillation circuit. That is, stable oscillation can be performed with less load on the oscillator.

  The reference voltage unit needs to be set to a predetermined length so that the fundamental wave is not consumed at the ground or reflected in the traveling direction of the basic transmission. When the wavelength transmitted through the transmission line on the substrate of the fundamental wave is λg1, the length of the reference voltage portion is preferably set to approximately λg1 / 4. By adopting such a configuration, one end of the reference voltage unit is connected to the ground and is short-circuited, but the other end is opened on the transmission line that transmits the fundamental wave, and the fundamental wave can be transmitted without being attenuated. it can.

  Further, the reference voltage unit 14 has a filter function for attenuating the nth harmonic (n: an integer of 2 or more) of the high frequency signal. Therefore, a desired high-frequency signal generated by the oscillator 2 is stably transmitted or received due to the effect of setting the reference voltage, and an unnecessary n-th order harmonic is attenuated on the transmission line by a filter function, and an unnecessary n-th order is transmitted. It is possible to provide a sensor circuit in which the amount of radiation of harmonics is reduced.

In order for the reference voltage unit 14 formed of a transmission line to have a filter function, it is necessary to set the reference voltage unit 14 to a predetermined length. When the wavelength of the n-th harmonic (n: integer of 2 or more) is λn, one end is connected to the transmission line and the other end is connected to the ground, it is necessary to set the length to approximately λn / 2. That is, the reference voltage unit functions as a short stub for unnecessary harmonics. If the set length is in the range of λn / 2-0.5mm to λn / 2 + 0.5mm, it satisfies the filter function and attenuates or reflects the fundamental signal while attenuating unnecessary harmonics. It can be configured not to be allowed.
FIG. 2 shows the pass characteristic of the short stub 14 filter. As shown in FIG. 2, it can be confirmed that the second harmonic (21.05 GHz) is attenuated without attenuating the fundamental power (10,525 GHz). In FIG. 2, the reference voltage unit 14 is set to a predetermined length and the second harmonic is attenuated. However, it is easy to attenuate the desired nth harmonic by changing the length of the reference voltage unit 14. It is.

  Since the reference voltage section functions as both a reference potential setting for high frequency signals and a filter for unwanted harmonics, and the reference voltage section is composed of a transmission line on the transmission line through which the high frequency signal is transmitted. Therefore, it is not necessary to block unnecessary harmonics by a filter circuit composed of a combination of the above and a transmission line, and the entire sensor circuit can be downsized.

  FIG. 3 shows a configuration diagram in which a plurality of reference voltage units 14 are arranged. This is a case where three reference voltage units are arranged in parallel in a direction orthogonal to the transmission line. FIG. 4 shows pass characteristics when three are arranged in parallel. As shown in FIG. 4, a damping effect larger than one can be obtained by arranging a plurality in parallel. The place where the reference voltage unit is installed is an open (open) surface where the current value of the fundamental wave is 0 on the transmission line, and the arrangement interval is λg1 as the wavelength transmitted through the transmission line of the fundamental wave In this case, it is preferable to arrange them at intervals of λg1 / 2. By adopting such a configuration, all the locations where the reference voltage unit is arranged become the open surface of the fundamental wave, so that it is possible to prevent the fundamental wave from flowing into the reference voltage unit. Only the harmonics can be effectively attenuated without attenuation. When a plurality of reference voltage sections are provided, 14A, 14B, and 14C are all set to the same length to effectively attenuate the second-order harmonics, or change the length of one of the three A filter for harmonics may be configured, or all may be set for third-order harmonics. Thus, it becomes possible to have the same effect by setting many reference voltage sections for the harmonics to be attenuated.

FIG. 5 shows a reference voltage section for 2n order harmonics (n: 1 or more) and (2n-1) order harmonics (n: an integer of 2 or more) via a transmission line 8 in a direction perpendicular to the transmission line. The block diagram arrange | positioned facing is shown. 14D shown in FIG. 5 is set for the third harmonic, and 14E is set for the second harmonic. When facing each other, it is preferable to arrange them on the open face of the fundamental wave on the transmission line 8 as in the case of arranging them in parallel. Further, when facing each other, it is preferable that the positions of the transmission lines 8 in the orthogonal direction are the same, and the two reference voltage portions become open surfaces of the fundamental wave. By adopting such a configuration, even when the length of the transmission line 8 is shortened by design, a plurality of reference voltage portions can be arranged on the same open surface of the fundamental wave, which increases the size of the entire circuit. Can be prevented. FIG. 6 shows pass characteristics when 14D is the third harmonic and 14E is the second harmonic. It can be confirmed that the signal is attenuated in the frequency bands of both the second and third harmonics by the set effect of the reference voltage section.
As shown in FIG. 5, 14D may be set for the third harmonic, 14E may be set for the second harmonic, and both 14D and 14E are the same for the third harmonic and the second harmonic. If the length is set, the third or second harmonic can be concentrated and attenuated.

  In addition, the reference voltage unit 14 is not limited to being disposed on the transmission line 8 illustrated in FIG. 1, but the transmission line 16 between the antenna 3 and the branch unit 7, and between the branch unit 7 and the mixer unit 6. You may provide in the branch part 7 comprised on the transmission line 11 or the transmission line. Further, since unnecessary harmonics are mainly generated by the oscillator 2, unnecessary radiation of the source stream is suppressed by arranging the transmission line 8 between the first cutoff unit 10 and the branching unit 7. Since it is possible to prevent unnecessary harmonics from flowing into the mixer unit 6 and to prevent unnecessary harmonics floating in the space when passing through the transmission line, it is more effective. Further, even if the reference voltage unit is arranged immediately before distributing the signal to the antenna 3 and the mixer unit 6 of the branching unit 7, the same effect can be obtained, and unnecessary harmonics reflected by the antenna 3 can be transmitted to the mixer unit 6. There is no longer any backflow back to the oscillator 2.

FIG. 7 shows a configuration diagram in which one end is installed on the transmission line 8, the reference voltage portion has a bent portion, and the other end is connected to the ground. One end of 14F in FIG. 7 is connected to the transmission line 8 in a direction orthogonal to the traveling direction of the harmonics, and once connected to the ground 16 with a bent portion.
In general, a high-frequency sensor that radiates radio waves from an antenna and detects a reflected signal is often composed of a laminated plate using a base material such as resin or ceramic, a surface that forms an oscillator and a mixer circuit, a ground surface, Divided into antenna surfaces. In that case, when providing a ground part on the surface which comprises an oscillator and a detection circuit, it connects to the ground surface in the through hole provided on the transmission line formed with the copper book, and is grounded.
In addition, a ground portion is formed around a transmission line for transmitting high frequency in order to suppress interference due to radio wave spatial propagation. Furthermore, the ground portion also does not interfere with the high-frequency transmission line, and it is necessary to ensure a certain distance in order to stably transmit the fundamental wave. Generally, the distance d secured between the transmission line and the ground is related to the substrate thickness h and the relative dielectric constant ε of the substrate, and it is desirable that d = εh or more. However, when the distance between the ground and the transmission line is set to the minimum distance where the transmission line and the ground do not interfere with each other in order to prevent the entire circuit from becoming large, the configuration in which the reference voltage portion shown in FIG. Yes, leading to miniaturization of the entire circuit.
Furthermore, as shown in FIG. 7, in order that the harmonics passing through the reference voltage unit do not interfere with the ground and sufficiently satisfy the filter function, a notch is formed in the ground along the transmission line path of the reference voltage unit. It is desirable to provide it. As long as the distance d between the notched ground and the reference voltage portion is ensured as described above, a desired filter characteristic can be obtained as in the case of the reference voltage portion constituted by a straight line.
In FIG. 7, the bent portion is formed at a right angle. However, if a length having a filter function with respect to a desired harmonic is secured, a plurality of bent portions can be provided or the same effect can be obtained with a curved line. .

As described above, the reference voltage unit is not limited to being installed on the transmission line 8 between the first blocking unit 10 and the branch unit 7, but the transmission line between the branch unit 7 and the mixer unit 6. 11, the transmission line 15 between the antenna 3 and the branching part 7 and the branching part 7 constituted by the transmission line may be provided, and in combination, unnecessary harmonics can be attenuated more effectively. An embodiment of the entire sensor circuit configuration diagram is shown in FIG. In FIG. 8, the transmission line 8 is arranged so that the reference voltage parts of the second harmonic 14H and the third harmonic 14G are opposed to each other in a direction orthogonal to the traveling direction of the harmonics, and the second harmonic is used for the transmission line 15. 14I, and the second harmonic 14J is arranged on the transmission line 11. With such a configuration, the pass characteristic shown in FIG. 9A is obtained, and the second harmonic can be effectively attenuated.
Moreover, the pass characteristics shown in FIG. 9B are obtained by designing 14H for the third harmonic, 14G for the third harmonic, 14I for the second harmonic, and 14J for the third harmonic. It is also possible to effectively attenuate the third harmonic.
In this way, it is possible to easily add a filter function to harmonics that are desired to be attenuated arbitrarily. By using a reference voltage part with a bent part and arranging the reference voltage part at a position that does not affect the fundamental wave, impedance matching of the entire sensor circuit is achieved, and the characteristics of the sensor are observed even after the entire configuration is laid out. Thus, the work of adding a filter function can be easily performed.

  Further, unnecessary harmonics may be generated not only by the oscillator 2 but also by a diode constituting the mixer unit 6. In that case, by arranging a plurality of reference voltage sections in 14J (in some cases, a plurality of reference voltage sections), there is an effect of suppressing unnecessary harmonics generated in the mixer section 6 from flowing back and radiating from the antenna 3.

  Furthermore, the reference voltage section is configured with an impedance higher than the impedance of the transmission line that transmits the fundamental wave, so that the transmission line of the reference voltage section is formed by a transmission line that is narrower than the transmission line that transmits the fundamental wave, and is transmitted. Since the contact area between the line and the reference voltage section is reduced, attenuation with respect to the fundamental wave can be reduced, and the circuit can be miniaturized.

  In the above configuration, in this embodiment, the fundamental wave is set to 10.525 GHz. However, the high frequency signal (particularly the GHz band) has the same characteristics, and is not limited to this frequency. Furthermore, even if transmission and reception are integrated with respect to the antenna, the same effect can be obtained by changing the position where the reference voltage unit is installed, even if transmission and reception are separate.

Schematic configuration diagram of the high-frequency sensor of the present invention Passing characteristics diagram of filter circuit with one reference voltage section Configuration diagram with three reference voltage units arranged in parallel Passing characteristic diagram of filter circuit with three reference voltage parts arranged in parallel Configuration diagram in which the reference voltage section is placed facing the transmission line Passing characteristic diagram of filter circuit with reference voltage section placed opposite to transmission line Configuration diagram in which the reference voltage part is arranged with a bent part Overall configuration of sensor circuit (A) Passing characteristic diagram when three reference voltages for the second harmonic are arranged and one reference voltage for the third harmonic are arranged. (B) Three reference voltages for the third harmonic are arranged. Passing characteristic diagram when one reference voltage section for second harmonic is placed

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transmission wave 2 ... Oscillator 3 ... Transmission and reception antenna 4 ... Reception wave 5 ... Output signal 6 ... Mixer part 7 ... Branch part 8, 11, 15 ... Transmission line 9, 12 ... DC signal 10 ... First interruption | blocking part 13 ... 2nd interruption | blocking part 14, 14A, 14B, 14C, 14D, 14E, 14F, 14G, 14H ... Reference voltage part 16 ... Ground

Claims (7)

An oscillator that generates a transmission wave that is a high-frequency signal;
A transmitting antenna that radiates the transmitted wave to the outside;
A receiving antenna that receives a reflected wave of the transmitted wave as a received wave;
A mixer unit that generates a detection signal based on the transmission wave and the reception wave;
A branching unit comprising a transmission line for distributing and transmitting the transmission wave generated by the oscillator to the transmission antenna and the mixer unit;
A high-frequency sensor comprising
On the transmission line connecting the oscillator and the branching section, a first blocking section that blocks the DC signal applied to the oscillator from entering the branching section;
On the transmission line connecting the branching unit and the mixer unit, a second blocking unit for blocking the entry of the DC signal applied to the mixer unit to the branching unit,
A reference voltage unit having a filter function for setting a reference potential on the transmission line and suppressing an nth-order harmonic (n: an integer of 2 or more) of the high-frequency signal from passing through the transmission line is the first blocking unit. And a high-frequency sensor disposed on a transmission line between the branch portion. The high-frequency sensor according to claim 1, wherein a plurality of the reference voltage units are arranged in parallel in a direction orthogonal to the transmission line. 3. The high-frequency sensor according to claim 1, wherein the reference voltage unit is arranged in a direction perpendicular to the transmission line and so that at least one set faces the transmission line via the transmission line. 4. The high-frequency sensor according to claim 1, wherein the reference voltage unit is also disposed on a transmission line between the branch unit and the transmission antenna. 5. 5. The high-frequency sensor according to claim 1, wherein the reference voltage unit is also disposed on a transmission line between the branching unit and the second blocking unit. The high-frequency sensor according to claim 1, wherein the reference voltage unit is also disposed in the branching unit. 7. The high-frequency circuit according to claim 1, wherein the reference voltage unit has at least one bent portion, and has one end connected to a transmission line and the other end connected to a ground electrode.

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