Target simulator

Abstract

The purpose of an aspect of the present disclosure is to provide a target simulator capable of accurately inspecting a millimeter wave radar, while having a configuration simpler than conventionally. In one aspect, a target simulator according to the present disclosure is provided with one antenna (102) used in common for transmission and reception, and a reflection amplitude modulator (103) that is connected to the antenna and switches an amount of reflection of a signal received from a millimeter wave radar by the antenna to return the signal to the antenna.

Description

Target Simulator

[0001] The present disclosure relates to a target simulator used to test millimeter wave radar.

[0002] In recent years, in-vehicle FMCW (Frequency Modulated Continuous Wave) millimeter-wave radar (hereinafter simply referred to as "millimeter-wave radar") has become increasingly popular for collision prevention and autonomous driving applications. Because collision prevention and autonomous driving require a high level of safety, it is expected that in the future, automobile manufacturers will specify inspection items for each vehicle model and type of millimeter-wave radar installed, and that millimeter-wave radar will become a mandatory item in legal inspections.

[0003] For example, in Japan, more than 25 million vehicles are required to undergo statutory inspections annually, and in many cases, inspections are performed by repair shops nationwide certified or designated by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT). The repair shops then submit the inspection documents they prepare to a MLIT agency, such as a transport bureau, in each prefecture, and a vehicle inspection certificate is then issued. Given this background, for millimeter-wave radar to become a mandatory item in statutory inspections, millimeter-wave radar inspection equipment must be inexpensive enough for repair shops nationwide to adopt. It would also be desirable for millimeter-wave radar inspection equipment to be inexpensive in countries other than Japan.

[0004] When testing millimeter-wave radar, a dedicated testing device is used to check whether the angle and distance of a target within the detection range can be detected with sufficient accuracy and sensitivity.To test the detection angle, it is sufficient to simply place a corner reflector simulating the target a few meters from the millimeter-wave radar.

[0005] On the other hand, when it comes to testing detection distance and detection sensitivity, even though there are long-range millimeter-wave radars in the 76 GHz band that are used worldwide and can detect targets more than 200 meters away, it is difficult to secure testing space at many maintenance workshops, etc. Therefore, a target simulator that can simulate the reflected signal from a target at any distance is required.

[0006] Patent Document 1 discloses an example of a target simulator. The target simulator of Patent Document 1 includes a receiving antenna, a transmitting antenna, a mixer, an ultra-high-speed AD / DA converter, an ultra-high-speed waveform memory, and an ultra-high-speed computing unit. The target simulator of Patent Document 1 configured in this manner can be used to inspect radars of various types, including FMCW types. However, because it uses many expensive parts (where expensive can be rephrased as having a complex configuration, high precision, or a large number of parts) that perform ultra-high-speed digital processing, it is difficult to make it low-priced (where low-priced can be rephrased as having a simple configuration, low precision, or a small number of parts, i.e., a simple configuration) that can be adopted by many repair shops.

[0007] In contrast, Patent Document 2 discloses a method for realizing a target simulator at a lower cost than Patent Document 1 by limiting the test target to FMCW radar. The target simulator in Patent Document 2 includes a receiving antenna, a transmitting antenna, a mixer, an oscillator, an amplifier, and an attenuator. The oscillator generates a local signal for the mixer. In the target simulator in Patent Document 2, the signal from the millimeter-wave radar received by the receiving antenna is mixed with the local signal in the mixer, and then the signal level is adjusted by the amplifier and attenuator before being transmitted from the transmitting antenna to the millimeter-wave radar.

[0008] Therefore, the signal transmitted from the target simulator of Patent Document 2 includes "signal components (upper and lower sidebands generated by amplitude modulation) whose frequencies are separated above and below the signal from the millimeter-wave radar by the frequency of the local signal" that are generated by mixing with the local signal in the mixer (amplitude modulation with the local signal).

[0009] In the millimeter-wave radar that receives the signal transmitted from the target simulator of Patent Document 2, an internal mixer outputs a signal having a frequency that is the difference between the frequency of the transmitted signal and the frequency of the received signal, as an FMCW radar operation. The millimeter-wave radar then determines the frequency of the output signal as the distance to the target, and detects the level of the output signal as the reflection intensity of the target.

[0010] In other words, the frequency and signal level of the local signal set in the target simulator of Patent Document 2 are reflected in the output signal from the mixer inside the millimeter-wave radar, and as a result, are reflected in the distance to the target and the signal level detected by the millimeter-wave radar.

[0011] This allows the creation of a reflected signal from a simulated target at a distance different from the actual distance at which the target simulator is placed, which can be used to test millimeter-wave radar.

[0012] Furthermore, the target simulator of Patent Document 2 does not use expensive components for ultra-high speed digital processing as in Patent Document 1, and therefore can be realized at low cost.

[0013] JP-A No. 07-311257 JP-A No. 07-301669

[0014] An object of one aspect of the present disclosure is to provide a target simulator that can inspect millimeter-wave radar with high accuracy while having a simpler configuration than conventional ones.

[0015] One aspect of the target simulator of the present disclosure comprises a single antenna for both transmission and reception, and a reflection amplitude modulator connected to the antenna, which switches the amount of reflection of a signal from a millimeter wave radar received by the antenna and returns the signal to the antenna.

[0016] According to the present disclosure, it is possible to realize a target simulator that can inspect millimeter wave radar with high accuracy while having a simpler configuration than conventional ones.

[0017] Diagram showing a combination of antenna arrangements of a millimeter-wave radar and a conventional target simulatorDiagram showing a combination of antenna arrangements of a millimeter-wave radar and a conventional target simulatorDiagram showing the configuration of a target simulator in embodiment 1Diagram showing a combination of antenna arrangements of a millimeter-wave radar and a target simulator in embodiment 1Diagram showing a combination of antenna arrangements of a millimeter-wave radar and a target simulator in embodiment 1Diagram showing the configuration of a target simulator in embodiment 2Perspective view of a radio wave absorbing materialFront view of a radio wave absorbing materialDiagram showing the configuration of a target simulator in embodiment 3Diagram showing the admittance of a reflection amplitude modulator in embodiment 3Diagram showing the reflection amount switching unit in more detailPerspective view of an antenna and a reflection amplitude modulator in embodiment 3Diagram showing the configuration of a target simulator in embodiment 4Diagram showing the configuration of a target simulator in embodiment 5Diagram showing the state when the target simulator in embodiment 5 is in useDiagram showing the state when the target simulator in embodiment 5 is in use

[0018] <Inventor's Findings That Lead to the Present Disclosure> Before describing the embodiments, the inventor's findings that led to the present disclosure will be described. A millimeter-wave radar has a circuit that generates a transmission signal to a target and a circuit that processes a received signal from the target. A transmitting antenna and a receiving antenna are required to couple these two types of circuits with space. Note that some millimeter-wave radars for non-vehicle applications use a circulator to share an antenna for both transmission and reception. However, from the perspective of cost reduction, it is preferable for millimeter-wave radars for vehicle applications to avoid using circulators, which are expensive components. Furthermore, in recent years, digital beamforming technology, which uses multiple antennas to detect the direction of a target, has become mainstream in vehicle-use millimeter-wave radars, and therefore separate antennas are typically used for transmission and reception.

[0019] Here, in long-distance millimeter-wave radar, in order to increase detection sensitivity and because the angular range for azimuth detection is narrow, the gain of each antenna is set to be larger and the spacing between each antenna is set to be wider than in short-distance millimeter-wave radar.

[0020] However, when the antenna gain of each antenna is large and the antenna spacing is wide, and the distance between the vehicle equipped with the millimeter-wave radar and the target simulator is only about one meter, in a conventional target simulator having two antennas, a receiving antenna and a transmitting antenna, the reception level of the millimeter-wave radar varies greatly depending on the combination of the target simulator and the antenna arrangement for transmitting and receiving the millimeter-wave radar, resulting in a problem of deteriorating accuracy in testing the detection sensitivity of the millimeter-wave radar.

[0021] In fact, for example, in Japan, inspection equipment that can be used at a distance of one meter from the vehicle is also used in statutory inspections to check the mounting angle and illuminance of headlights, which are safety components like millimeter-wave radar. In other words, repair shops across Japan that perform statutory inspections may only be able to ensure a similar distance for millimeter-wave radar inspections, so a solution to the above problem (i.e., the problem of the deterioration of millimeter-wave radar detection sensitivity inspection accuracy at short distances) is required.

[0022] The inventors have investigated the causes of such problems.

[0023] Figures 1A and 1B show how the reception level of the millimeter-wave radar 1103 is affected by the combination of the arrangements of the transmitting antenna TX and receiving antenna RX of both the millimeter-wave radar 1103 and the target simulator 1104 when both the millimeter-wave radar 1103 and the conventional target simulator 1104 have two antennas, one for transmitting and one for receiving, and when the target simulator 1104 receives a signal transmitted from the millimeter-wave radar 1103, and the reflected signal of a simulated target created inside the target simulator 1104 is transmitted toward the millimeter-wave radar 1103 and then received again by the millimeter-wave radar 1103.

[0024] Figure 1A shows a case where both transmitting antennas TX and receiving antennas RX are arranged facing each other directly in front of each other. Figure 1B shows a case where both transmitting antennas TX and receiving antennas RX are arranged facing each other diagonally. Also, the millimeter-wave radar 1103 has two antennas, one for transmitting and one for receiving, and the target simulator 1104 has two antennas, one for transmitting and one for receiving. Also, in Figures 1A and 1B, 1105 shows the directional characteristic curve of a high-gain antenna used in long-range millimeter-wave radar.

[0025] In Figure 1A, the transmitting antenna TX and receiving antenna RX are located directly opposite each other, so that the millimeter-wave radar 1103 transmits, the target simulator 1104 receives, the target simulator 1104 transmits, and the millimeter-wave radar 1103 receives. When signals enter and exit the device and space, all signals pass in the direction where the antenna gain is maximized, as indicated by symbol 1106 in the figure.

[0026] 1B, the transmitting antenna TX and receiving antenna RX are diagonally opposed to each other, so all signals pass in the direction of reduced antenna gain, indicated by reference numeral 1107 in the figure. In other words, the reception level of the millimeter-wave radar 1103 is affected by the fourth power of the reduction in antenna gain, and the reception level of the millimeter-wave radar is significantly reduced, particularly in the case of long-distance millimeter-wave radars with large antenna gains and small half-widths of the antenna gains.

[0027] From the above, the inventors have come to the conclusion that when a conventional target simulator 1104 having two antennas, one for receiving and one for transmitting, is used to inspect an on-board long-range millimeter-wave radar 1103 having two antennas, the reception level of the millimeter-wave radar 1103 will vary significantly depending on the combination of the antenna arrangements of the millimeter-wave radar 1103 and the target simulator 1104, and the accuracy of the inspection of the detection sensitivity of the millimeter-wave radar 1103 will deteriorate. The present disclosure has been made based on such considerations.

[0028] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. <Embodiment 1> Fig. 2 shows the configuration of a target simulator 101 according to an embodiment. The target simulator 101 has a single antenna 102 that is used for both transmission and reception, and a reflection amplitude modulator 103 that switches the amount of reflection.

[0029] The reflection amplitude modulator 103 switches the reflection amount between, for example, "matching" and "total reflection," and also between, for example, "reflection amount -20 dB" and "reflection amount -5 dB," thereby amplitude modulating the signal from the millimeter-wave radar received by one antenna 102 and sending it back to the millimeter-wave radar via the other antenna 102.

[0030] The signal amplitude-modulated by the reflection amplitude modulator 103 contains frequency components that are above and below the frequency of the signal from the millimeter-wave radar by the modulation frequency, and therefore the target simulator 101 operates as a target simulator that can be used for an FMCW millimeter-wave radar, similar to Patent Document 2.

[0031] Furthermore, the target simulator 101 of this embodiment shown in FIG. 2 uses only one antenna 102 and one reflection amplitude modulator 103 that are used for both transmission and reception, so the target simulator can be realized at a low cost (low cost here can be rephrased as a simple configuration).

[0032] 3A and 3B show combinations of antenna arrangements of the millimeter-wave radar 201 and the target simulator 101 of this embodiment. Fig. 3A shows a case where the transmitting antenna TX of the millimeter-wave radar 201 is arranged on the upper side as viewed in the figure, and the receiving antenna RX is arranged on the lower side as viewed in the figure. In contrast, Fig. 3B shows a case where the transmitting antenna TX of the millimeter-wave radar 201 is arranged on the lower side as viewed in the figure, and the receiving antenna RX is arranged on the upper side as viewed in the figure.

[0033] As shown in Figures 3A and 3B, when the target simulator 101 has a single antenna 102 that is used for both transmission and reception, regardless of whether the transmitting antenna TX and receiving antenna RX of the millimeter-wave radar 201 are located on the top or bottom side of the figure, when signals enter and exit the device and space in a flow such that the millimeter-wave radar 201 transmits, the target simulator 101 receives, the target simulator 101 transmits, and the millimeter-wave radar 201 receives, all signals pass in the direction of approximately the same antenna gain, as indicated by the symbol 205 in the figure.

[0034] In other words, compared to using a conventional target simulator 1104 also having two antennas RX and TX, one for receiving and one for transmitting, to inspect an on-vehicle long-range millimeter-wave radar 1103 as shown in Figures 1A and 1B, using the target simulator 101 of this embodiment reduces the change in the reception level of the millimeter-wave radar 201 due to the combination of the antenna arrangement of the millimeter-wave radar 201 and the target simulator 101, making it possible to inspect the detection sensitivity of the millimeter-wave radar 201 with high accuracy.

[0035] 4, in which the same reference numerals are assigned to parts corresponding to those in Fig. 1, is a schematic diagram showing the configuration of a target simulator 301 according to embodiment 2. The target simulator 301 of this embodiment has a variable attenuator 304 in addition to a single antenna 102 used for both transmission and reception and a reflection amplitude modulator 103 that switches the amount of reflection.

[0036] Variable attenuator 304 has radio wave absorbing material 305 that surrounds the periphery of the space through which the radio waves pass, and a drive unit (not shown) that drives radio wave absorbing material 305. Variable attenuator 304 surrounds the periphery of the space through which the radio waves pass with radio wave absorbing material 305 and moves radio wave absorbing material 305 to change the size of the space through which the radio waves pass, thereby attenuating radio waves (signals) 306 passing through the space.

[0037] For example, foamed or non-foamed resin with carbon or magnetic powder dispersed therein, or non-foamed resin with a carbon or magnetic layer attached to the surface thereof can be used as the radio wave absorber 305. In addition, a wide range of composites of materials that cause loss to millimeter waves can also be used as the radio wave absorber 305.

[0038] Fig. 5A is a perspective view of the radio wave absorber 305, and Fig. 5B is a front view of the radio wave absorber 305 as seen from the direction of the antenna 102. As shown in Fig. 5A and 5B, the radio wave absorber 305 of the variable attenuator 304 of this embodiment has a structure in which a space through which radio waves pass (radio wave transmission path) is sandwiched between an upper radio wave absorber 403 and a lower radio wave absorber 404 each having a "crocodile tooth" shaped cross section, so that the space through which radio waves pass can be adjusted in a range from approximately zero to infinity while maintaining matching with the passing radio waves.

[0039] The variable attenuator 304 in FIG. 4 can reduce the amount of attenuation to approximately zero by making the space through which the radio waves pass larger than that of a single antenna 102, and can make the amount of attenuation infinite by completely closing the space through which the radio waves pass.

[0040] Therefore, by adjusting the variable attenuator 304, the target simulator 301 of this embodiment shown in Figure 4 can simulate a wide range of targets, from large reflecting targets at short distances of 10 meters or less to small reflecting targets at long distances of 200 meters or more. Furthermore, by moving the radio wave absorbing material 305, the size of the space through which the radio waves pass can be adjusted, and since the radio wave absorbing material 305 can be continuously moved by a mechanical mechanism, the variable attenuator 304 can also adjust the attenuation amount with an accuracy of about 0.1 dB. As a result, the variable attenuator 304 of this embodiment can achieve the wide variable range and small variable amount of attenuation required, for example, in statutory inspections, without using expensive millimeter-wave semiconductor components.

[0041] 6, in which the same reference numerals are assigned to parts corresponding to those in Fig. 4, is a schematic diagram showing the configuration of a target simulator 501 according to embodiment 3. The target simulator 501 of this embodiment has a single antenna 102 that is used for both transmission and reception, a reflection amplitude modulator 103 that switches the amount of reflection, and a variable attenuator 304 that attenuates radio waves passing through space.

[0042] The reflection amplitude modulator 103 of this embodiment has a reflection amount switching unit 505, a transmission line 506 between one antenna 102 and the reflection amount switching unit 505, a transmission line 507 of the reflection amount switching unit 505, two diodes 508, a matching termination line 509 formed by extending the transmission line 507 of the reflection amount switching unit 505 by a predetermined length, a current limiting resistor 510 for the two diodes 508, and a terminal 511 for supplying a drive current to the two diodes 508.

[0043] The two diodes 508 only need to perform an on / off switching operation between their terminals depending on the amount of current flowing, and for example, Schottky barrier diodes, PIN diodes, Zener diodes, or other types of diodes can be used as the two diodes 508. Furthermore, each of the two diodes 508 may be a composite diode having multiple diodes inside, with two more diodes connected in parallel or in series with opposite polarities.

[0044] The two transmission lines 506 and 507 have the same characteristic impedance, as does the matching termination line 509. Furthermore, by utilizing the transmission loss of the line, the matching termination line 509 has a predetermined length such that the round-trip transmission loss is, for example, −20 dB or less even when the tip of the matching termination line 509 is totally reflected.

[0045] Next, the operation of the reflection amplitude modulator 103 of this embodiment will be described with reference to Figures 7A and 7B. Figure 7A is an admittance chart, and Figure 7B is a diagram showing the reflection amount switching unit 505 of Figure 6 in more detail.

[0046] First, using the admittance chart of FIG. 7A, the movement locus of admittance when viewed from each position on the transmission line 507 of the reflection amount switching unit 505 in FIG. 6 toward the matching termination line 509 will be described.

[0047] 7A, symbol a indicates the admittance seen from position 604 toward matching termination line 509 when no diode is connected to transmission line 507. Symbol b indicates the admittance seen from position 604 toward matching termination line 509 when the admittance of the inter-terminal capacitance of one diode 602 is added to admittance a. Symbol L indicates the distance less than 1 / 4 wavelength on transmission line 507 where the two diodes are connected.

[0048] Here, the wavelength refers to the wavelength on the transmission line 507 at the center frequency of the operating frequency band of the millimeter-wave radar under test. Specifically, if the operating frequency band of the millimeter-wave radar is 76 to 77 GHz, the center frequency is 76.5 GHz. A millimeter wave with a center frequency of 76.5 GHz has a free space wavelength of 3.92 mm, and if the wavelength shortening rate of the transmission line 507 is 1 / 1.5, the wavelength on the transmission line 507 is 3.41 mm.

[0049] Symbol c indicates the admittance seen from position 605, where admittance b has moved by distance L on transmission line 507 in a direction away from matching termination line 509, toward matching termination line 509. Symbol d indicates the admittance when the admittance of the inter-terminal capacitance of the other diode 603 is added to admittance c.

[0050] 7A, since transmission line 507 and matching termination line 509 are matched, "a" is at the center of the admittance chart, but when the admittance of one diode 602 is connected in parallel to "a," the admittance moves to "b." Next, when the position on transmission line 507 from which the admittance on the matching termination line 509 side is viewed is moved by a distance L less than a quarter wavelength, the admittance becomes "c." Then, when the admittance of the other diode 603 is connected in parallel to "c," the admittance moves to "d."

[0051] In other words, by appropriately selecting the spacing L of less than a quarter wavelength on the transmission line 507, the admittance d can be returned to the center of the admittance chart, i.e., the matched state position, by the admittances of the two diodes, one and the other.

[0052] Furthermore, when the diode current flows and the diodes 602 and 603 are switched on, the terminals of the diodes 602 and 603 are short-circuited, and therefore the admittance seen from the other diode 603 toward the matching termination line 509 moves to an infinite position, regardless of the capacitance between the terminals of the one diode 602 and the other diode 603.

[0053] From the above, by configuring the reflection amplitude modulator 103 as in this embodiment, it is possible to realize a reflection amplitude modulator 103 that has a high modulation degree that is not affected by the terminal capacitance of the diode, even if an inexpensive diode with a terminal capacitance of approximately 0.1 pF to 0.2 pF is used, thereby realizing a low-cost target simulator 501.

[0054] The reason for setting the distance L to less than a quarter wavelength is that it is possible to maximize the frequency range in which the admittance d in the admittance chart (FIG. 7A) is close to matching. This also maximizes the frequency range in which a high modulation degree can be obtained. Furthermore, even if the reflection amount switching unit 505 is connected in multiple stages, the frequency range in which a high modulation degree can be obtained can be expanded.

[0055] FIG. 8, in which the same reference numerals are assigned to parts corresponding to those in FIG. 6, shows a perspective view of a target simulator 501 of this embodiment in which one antenna 102 for both transmission and reception and a reflection amplitude modulator 103 are configured using a printed circuit board and a conductor plate.

[0056] 8, in this embodiment, one antenna 102 (102-1, 102-2) and reflection amplitude modulator 103 are integrally configured. A more specific description will be given. On a printed circuit board 702, a ground conductor 703 of the printed circuit board 702, one antenna conductor 102-1 using a board conductor, transmission lines 506 and 507, two diodes 508, a matching termination line 509, a current limiting resistor 510 of the diode 508, a terminal 511 that supplies a drive current to the diode 508, and the other antenna conductor 102-2 are formed.

[0057] The antenna conductor 102-1 and the antenna conductor 102-2 are electrically connected by soldering or other means at a position 711 where the ends of both conductors meet.

[0058] The structure shown in FIG. 8 configures the antenna 102 and reflection amplitude modulator 103 of FIG. 6 using fewer components, such as a printed circuit board 702, the other antenna conductor 102-2, two diodes 508, and a current-limiting resistor 510, so that the target simulator 501 can be realized at a lower cost.

[0059] 9, in which the same reference numerals are assigned to parts corresponding to those in Fig. 4, is a schematic diagram showing the configuration of a target simulator 801 according to embodiment 4. The target simulator 801 of this embodiment includes a plurality of partial target simulators 803, each of which is made up of a single antenna 102 used for both transmission and reception and a reflection amplitude modulator 103, a reflector 804 that passes a portion of the signal 306 from the millimeter-wave radar and a portion of the signal from the partial target simulator 803 and reflects them in a direction different from the direction in which the signal is passed, and a radio wave absorber 805 that absorbs the signal reflected by the reflector 804.

[0060] In the target simulator 801, a signal 306 from the millimeter wave radar is partially transmitted by a reflector 804, and partially reflected in a direction different from the transmission direction. Here, a partial target simulator 803 is disposed in the direction different from the transmission direction.

[0061] Each of the multiple partial target simulators 803 returns a signal that has been reflected amplitude modulated at a modulation frequency corresponding to only one of the multiple chirp velocities possessed by the millimeter wave radar toward the reflector 804.

[0062] 9, in the target simulator 801 of this embodiment, a partial target simulator 803 is also placed at the final position where the signal 306 from the millimeter-wave radar passes through multiple reflectors 804. The signals reflected and amplitude-modulated by each partial target simulator 803 at the corresponding modulation frequency are combined by passing through and being reflected again by the reflector 804 and are sent back toward the millimeter-wave radar.

[0063] Here, when the signal waves pass through and reflect again at the reflector 804, some signal waves are generated that travel in directions other than those returned to the millimeter-wave radar. However, these signal waves are absorbed by the radio wave absorber 805, so that unnecessary multiple reflections between the reflector 804 and the partial target simulator 803 are suppressed, thereby enabling the generation of high-quality target simulation signals.

[0064] 10 is a schematic diagram showing the configuration of a target simulator 901 according to embodiment 5. The target simulator 901 according to this embodiment includes a cylindrical body 903 having a radio wave absorber 902 on its inner surface, the variable attenuator 304 described in embodiment 2, and the target simulator 801 described in embodiment 4. Note that the target simulator 101 described in embodiment 1 may be used instead of the target simulator 801.

[0065] In a target simulator that amplitude-modulates a signal from a millimeter-wave radar and returns it, as in Patent Document 2 and the present disclosure, frequencies are generated that are above and below the signal from the millimeter-wave radar by the frequency of the modulated signal. Therefore, at the moment when the millimeter-wave radar is transmitting at the lower or upper limit frequency of the legally occupied band, the frequency component generated by amplitude modulation in the target simulator exceeds the legally occupied band of the millimeter-wave radar, causing radio interference to other wireless devices.

[0066] 10 , which has a radio wave absorber 902 on its inner surface, can be integrated with the variable attenuator 304 and target simulator 801 to reduce the radio waves leaking from the entire target simulator 901 to a level that does not interfere with other radio wave devices. In other words, by absorbing the radio waves generated by the target simulator 801 simulating a target and traveling in directions other than those returned to the millimeter-wave radar with the radio wave absorber 902 on the inner surface of the cylindrical body 903, the only radio waves that reach the exit of the cylindrical body 903 are those components traveling in the direction of the millimeter-wave radar, and therefore the strength of the radio waves leaking from the entire target simulator can be significantly attenuated.

[0067] In addition, by using the cylindrical body 903 with the tip pressed against the front of the millimeter-wave radar mounted on the vehicle, the strength of the radio waves leaking from the gap between the cylindrical body 903 and the millimeter-wave radar can be further reduced.

[0068] 11A and 11B show a configuration example in which a target simulator 901 of this embodiment is used to inspect a vehicle equipped with a millimeter-wave radar. As shown in Fig. 11A, the target simulator 901 of this embodiment can be attached to a tripod so that it can be used to inspect the vehicle. Fig. 11B is a diagram showing how a millimeter-wave radar 1005 mounted on a vehicle 1004 is inspected using the target simulator 901 attached to the tripod.

[0069] 11B, according to the target simulator 901 of this embodiment integrated with the cylindrical body 903, it is possible to use the target simulator by bringing the cylindrical body 903 into close contact with the millimeter-wave radar 1005 so as to surround the millimeter-wave radar 1005. Therefore, in a target simulator that amplitude-modulates the signal from the millimeter-wave radar, it is possible to reduce the amount of frequency components outside the legally occupied band of the millimeter-wave radar that leaks to the outside to a level that does not interfere with other radio wave devices.

[0070] <Summary> According to the present disclosure, it is possible to realize a target simulator 101 at low cost that can accurately test the detection sensitivity of a long-range millimeter-wave radar 201 having two antennas TX and RX for transmission and reception.

[0071] That is, the target simulator 101 of the present disclosure has a single antenna 102 that is used for both transmission and reception, thereby significantly suppressing changes in the reception level of the millimeter-wave radar 201 that are caused by the combination of the antenna arrangements of the millimeter-wave radar 201 and the target simulator 101. Therefore, it is possible to maintain high accuracy in the inspection of the long-distance millimeter-wave radar 201 using the target simulator 101.

[0072] Note that the target simulator 101 has a single antenna 102 that is used both for transmission and reception, so the received signal from the millimeter-wave radar 201 and the transmitted signal from the target simulator 101 pass through the same transmission path. Therefore, the target simulator 101 of the present disclosure is provided with a reflection amplitude modulator 103 that generates a transmitted signal from the target simulator 101, which is a simulated target signal, by amplitude modulating the amount of reflection of the received signal from the millimeter-wave radar 201. In other words, by having a single antenna 102 that is used both for transmission and reception and a reflection amplitude modulator 103 that switches the amount of reflection, the target simulator 101 of the present disclosure can solve the problem of conventional target simulators, such as reduced accuracy in testing the detection sensitivity of millimeter-wave radar at short distances.

[0073] Furthermore, the target simulator 301 of the present disclosure is equipped with a variable attenuator 304 that attenuates the passing radio waves by changing the size of the space through which the radio waves pass in both directions while maintaining compatibility with both the radio waves transmitted from the millimeter-wave radar 201 and the radio waves transmitted from the target simulator 301. This allows the target simulator 301 to be realized at a lower cost than when a bidirectional variable attenuator using a semiconductor is used.

[0074] In particular, target simulators used in confined spaces, such as those required for legal inspections, are required to be able to simulate a wide range of targets, from large reflecting targets located at distances of less than 10 meters to small reflecting targets located at distances of more than 200 meters, with an accuracy of approximately 0.1 dB. Therefore, implementing a bidirectional variable attenuator operating in the millimeter wave band with such performance using semiconductors would require a very complex and expensive circuit configuration, making it difficult to reduce the price of the target simulator. In contrast, the target simulator 301 disclosed herein surrounds the space through which the radio waves pass with radio wave absorbing material 305, and the opening through which the radio waves pass is adjusted by moving the radio wave absorbing material 305. This allows the wide variable range and small variable attenuation required for legal inspections to be achieved without using expensive millimeter wave semiconductor components.

[0075] Furthermore, the target simulator 501 of the present disclosure allows for the realization of a diode-based reflective amplitude modulator 103 with good modulation depth at low cost. The reflective amplitude modulator 103 can be constructed by utilizing the switching characteristics of the diode, which equivalently switches on and off between its terminals. However, because the terminal capacitance, which is the sum of the diode's junction capacitance and package capacitance, is equivalently connected in parallel with the diode, the diode does not achieve a completely switched-off state even when the diode current is zero. This reduces the modulation depth of the reflective amplitude modulator. Therefore, to realize a reflective amplitude modulator 103 with good modulation depth, a diode with an extremely small terminal capacitance that results in a small admittance (i.e., a large impedance) at the frequency used is required. However, to achieve this, a semiconductor process for lateral structure diodes is required to achieve a capacitance of 0.01 pF to 0.05 pF, especially in the millimeter-wave radar band. Furthermore, lateral structure diodes have a lower breakdown voltage than vertical structure diodes, so a dedicated design is required for each signal level of the application, resulting in a very expensive design.

[0076] In contrast, the target simulator 501 of the present disclosure includes first and second diodes 602, 603 connected to a transmission line 507 and a matched termination line 509 extending the transmission line by a predetermined length, and the first and second diodes 602, 603 are connected between the transmission line 507 and a ground conductor 703 at a distance less than a quarter wavelength on the transmission line 507 at the center frequency of the operating frequency band. Incidentally, in the case of a long-range radar, the operating frequency band is, for example, 76 to 77 GHz, and the center frequency is 76.5 GHz. In the case of a short-range radar, the operating frequency band is, for example, 77 to 81 GHz, and the center frequency is 79 GHz.

[0077] As a result, even when a diode used in the microwave band with a terminal capacitance of approximately 0.1 pF to 0.5 pF is used, the admittance between transmission line 507 and ground conductor 703 due to the terminal capacitance of one diode 602 can be canceled by the admittance between transmission line 507 and ground conductor 703 due to the terminal capacitance of the other diode 603. As a result, when viewed from the end of transmission line 507, it is equivalent to the first and second diodes 602 and 603 having no terminal capacitance, and as a result, it is equivalent to the transmission line 507 being connected only to matched termination line 509, and the reflection amplitude becomes zero.

[0078] When the diode current flows and the diodes 602, 603 are switched on, the terminals of the diodes 602, 603 are short-circuited, and the reflection amplitude is 1 regardless of the inter-terminal capacitance. Therefore, in the target simulator 501 of the present disclosure, even when low-cost diodes 602, 603 having inter-terminal capacitance that cannot be ignored in the millimeter wave band are used for the reflection amplitude modulator 103, a high modulation degree can be achieved without being affected by the inter-terminal capacitance of the diodes 602, 603, and therefore a low-cost target simulator 501 can be realized.

[0079] Furthermore, the target simulator 801 of the present disclosure can be used in an FMCW radar that switches between multiple chirp rates. Recent FMCW radars include a type that switches the chirp rate (the rate at which the frequency changes). In this type of millimeter-wave radar, each time the chirp rate is switched, the conversion coefficient used to calculate the distance to the target from the frequency output from the mixer inside the millimeter-wave radar is changed to detect the distance. Only when a target is detected at the same distance at any chirp rate is the target determined to be a true target and not a false detection due to noise detected. Therefore, a target simulator used in this type of millimeter-wave radar must transmit a signal amplitude-modulated at frequencies corresponding to the multiple chirp rates switched by the millimeter-wave radar. However, if the signal from the millimeter-wave radar is amplitude-modulated with a single signal containing all frequency components corresponding to the multiple chirp rates, intermodulation occurs between the included frequency components. As a result, many unnecessary frequency components are mixed into the signal transmitted from the target simulator, making it impossible to accurately simulate the target.

[0080] Therefore, the target simulator 801 of the present disclosure splits the signal 306 from the millimeter-wave radar 201 into multiple signals by using a reflector 804 that passes some of the signals and reflects some of the signals in a direction different from the direction of the passing signal. The target simulator 801 then amplitude-modulates each of the split signals at a frequency corresponding to a different chirp speed using different partial target simulators 803, and then combines the signals again by passing them through the reflector 804 before returning them to the millimeter-wave radar 201. The target simulator 801 also prevents unnecessary multiple reflections by using a radio wave absorber 805 to absorb signals reflected in a direction different from the direction of the passing signal when combined. This prevents intermodulation between frequency components corresponding to multiple chirp speeds, making it possible to realize a target simulator 801 that can accurately simulate targets even with the above-mentioned millimeter-wave radar that switches chirp speeds.

[0081] Furthermore, the target simulator 901 of the present disclosure can achieve performance with minimal radiation of unnecessary radio waves. When a signal from a millimeter-wave radar 1005 is amplitude-modulated, the modulated signal also contains frequency components outside the band occupied by the millimeter-wave radar. If these frequency components leak to the outside, they can interfere with other radio-wave devices. Here, the target simulator 901 of the present disclosure includes a cylindrical body 903 having a radio wave absorber 902 on its inner surface, so that the cylindrical body 903 can be used in a state where it is sandwiched between the millimeter-wave radar 1005 attached to the vehicle 1004 and the target simulator 101 (301, 501, 801). In other words, the cylindrical body 903 significantly reduces the external leakage of radio waves transmitted and received between the millimeter-wave radar 1005 and the target simulator 101 (301, 501, 801), thereby realizing a usage mode that does not interfere with external radio-wave devices.

[0082] The above-described embodiments are merely examples of specific embodiments for carrying out the present disclosure, and the technical scope of the present disclosure should not be interpreted as being limited by these embodiments. In other words, the present disclosure can be carried out in various forms without departing from the gist or main features thereof.

[0083] The disclosures of the specification, drawings and abstract contained in Japanese Patent Application No. 2024-092318, filed on June 6, 2024, are incorporated herein by reference in their entirety.

[0084] As described above, the target simulator of the present disclosure has the effect of being able to accurately test the detection sensitivity of, for example, an FMCW-type long-range millimeter-wave radar for vehicle use at low cost (simple configuration), and is widely applicable as a target simulator used to test millimeter-wave radar.

[0085] 101, 301, 501, 801, 901, 1104 Target simulator 102 Antenna 102-1, 102-2 Antenna conductor 103 Reflection amplitude modulator 201, 1005, 1103 Millimeter wave radar 1106, 1107 Antenna gain direction 205, 1105 Antenna gain direction 304 Variable attenuator 305, 403, 404 Radio wave absorbing material 306 Signal (radio wave) 505 Reflection amount switching unit 506, 507 Transmission line 508, 602, 603 Diode 509 Matching termination line 510 Current limiting resistor 511 (Current supply) terminal 604, 605 Admittance observation position 702 Printed circuit board 703 Ground conductor 803 Partial target simulator 804 Reflector 805, 902 Radio wave absorber 903 Cylindrical body 1004 Vehicle equipped with millimeter wave radar

Claims

1. A target simulator comprising: a single antenna for both transmission and reception; and a reflection amplitude modulator connected to said antenna, which switches the amount of reflection of a signal received by said antenna from a millimeter wave radar and returns the signal to said antenna.

2. A target simulator as described in claim 1, further comprising a variable attenuator that has radio wave absorbing material surrounding the space through which radio waves pass, and that attenuates the radio waves passing through the space by moving the radio wave absorbing material to change the size of the space.

3. The target simulator according to claim 1, wherein the reflection amplitude modulator comprises at least first and second diodes connected to a transmission line, and a matched termination line extending the transmission line by a predetermined length, the first and second diodes being connected between the transmission line and a ground conductor at an interval of less than a quarter wavelength on the transmission line at the center frequency of the operating frequency band of the millimeter-wave radar, and a drive current for the first and second diodes is supplied from the side of the matched termination line opposite to the side connected to the transmission line.

4. A target simulator comprising a plurality of target simulators as defined in claim 1, and a reflector that passes a portion of the signal from the millimeter wave radar and a portion of the signal from the plurality of target simulators as defined in claim 1 and reflects a portion of the signal in a direction different from the direction of passage, wherein the plurality of target simulators as defined in claim 1 are each arranged in a different position and perform reflection amplitude modulation at a different modulation frequency.

5. The target simulator according to claim 4, further comprising a radio wave absorber that absorbs signals reflected by the reflector.

6. The target simulator according to claim 1, further comprising a cylindrical body having a radio wave absorber on its inner surface.

7. The target simulator according to claim 4, further comprising a cylindrical body having a radio wave absorber on its inner surface.

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