Antenna device

Abstract

An antenna device (10) according to one aspect of the present disclosure comprises: a plurality of antenna elements (20) that are disposed with prescribed spaces therebetween; and a plurality of transmission paths (22L-24R) that respectively connect the plurality of antenna elements to a high frequency circuit (30) for distance measurement, and that transmit high frequency signals. The plurality of transmission paths include microstrip lines on a circuit board, and the microstrip lines are symmetrically wired to have an equal length for each pair of antenna elements that are line-symmetrical with respect to a center line (Lo) which passes through the center in the arrangement direction of the plurality of antenna elements and which is orthogonal to the arrangement direction.

Description

Antenna device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This international application claims the benefit of Japanese Patent Application No. 2024-150929, filed with the Japan Patent Office on September 2, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to an antenna device including a plurality of antenna elements.

[0003] As described in Patent Document 1, an antenna device for radar is known that includes multiple antenna elements arranged at predetermined intervals. This antenna device can radiate radio waves in a desired direction corresponding to the phase difference by applying a phase difference to a transmission signal and feeding power to each antenna element. Furthermore, by applying a phase difference to the received signals from each antenna element and adding them together, a receiving antenna with directivity in a desired direction can be realized.

[0004] In the above antenna device, to control the radiation direction of radio waves in a desired direction, it is necessary to accurately control the phase and amplitude of the transmission signal, or the phase of the signal added to the reception signal. For this reason, the transmission paths from the transmitting or receiving high-frequency circuit to each antenna element are all set to the same length using so-called equal-length wiring. In other words, by making the transmission paths of each antenna element equal-length wiring, changes in the phase difference of the high-frequency signals between the antenna elements due to phase fluctuations caused by frequency hopping or aging can be suppressed, making it possible to control the radiation direction and reception direction of radio waves from the antenna device in a desired direction.

[0005] Japanese Patent Application Laid-Open No. 2017-187312

[0006] In the above antenna device, the transmission path of each antenna element is usually configured as a wiring pattern, i.e., a microstrip line, on a circuit board on which circuit components such as high-frequency circuits are mounted. As a result, the transmission path and the high-frequency circuits for transmitting and receiving are integrated, making it possible to miniaturize the radar device.

[0007] However, in the above antenna device, since the transmission lines of each antenna element are wired with equal lengths, it is necessary to secure wiring area for the equal-length wiring on the circuit board, which makes it impossible to fully meet the demand for a compact radar device. It is possible to reduce the wiring area for the transmission lines by making the transmission lines of each antenna element all unequal lengths, but in this case, it is necessary to provide a separate phase adjustment circuit to offset phase fluctuations due to frequency hopping and aging. Therefore, such a solution does not allow the radar device to be compact.

[0008] One aspect of the present disclosure aims to provide an antenna device for radar having multiple antenna elements, which can reduce the effects of phase fluctuations due to frequency hopping and deterioration over time, and enable the device to be made smaller, without having to wire the transmission paths of each antenna element with equal lengths.

[0009] An antenna device according to one aspect of the present disclosure comprises a plurality of antenna elements (20) arranged at predetermined intervals, and a plurality of transmission paths (22L, 22R, 24L, 24R) that connect the plurality of antenna elements to a high-frequency circuit (30) that transmits or receives high-frequency signals for ranging, and transmit the high-frequency signals.

[0010] The multiple transmission paths include microstrip lines on a circuit board, which are symmetrically wired with equal lengths so that the microstrip lines pass through the center of the arrangement direction of the multiple antenna elements and are equal in length for each pair of antenna elements that are line-symmetrical with respect to a center line (Lo) that is orthogonal to the arrangement direction.

[0011] In symmetrical equal-length wiring, it is not necessary to make the lengths of the microstrip lines that make up the transmission paths of all antenna elements the same, and the length can be set for each pair of antenna elements that are line-symmetrical across the center line. That is, the length of the microstrip line can be set for each pair of antenna elements, for example, by shortening the transmission path of the central antenna element close to the center line and shortening the transmission path of the outer antenna element farther from the center line.

[0012] Therefore, even if the wiring area of ​​the microstrip line becomes narrower due to electronic components such as high-frequency circuits mounted on the board, the wiring area can be secured by adjusting the length of the microstrip line for each pair of antenna elements.

[0013] Therefore, according to the antenna device of the present disclosure, the wiring area required to form the transmission paths of each antenna element as microstrip lines on the substrate can be narrowed, thereby making it possible to miniaturize the substrate, and therefore it is possible to easily miniaturize the radar device configured by mounting electronic components such as high-frequency circuits on this substrate.

[0014] Furthermore, the antenna device of the present disclosure does not use unequal length wiring for the transmission lines of each antenna element, but uses symmetrical equal length wiring to match the lengths of the transmission lines, i.e., microstrip lines, on the substrate of a pair of antenna elements that are line-symmetrical about the center line. This makes it possible to suppress changes in the phase relationship between the high-frequency signals input and output to the pair of antenna elements, even if phase fluctuations occur due to frequency hopping or aging.

[0015] As a result, according to the antenna device of the present disclosure, the directivity of the antenna device can be controlled by, for example, the phase difference of the transmission signal supplied to each antenna element, without having to wire the transmission paths of each antenna element with equal lengths, thereby ensuring the angular accuracy of the antenna device.

[0016] Furthermore, with the antenna device of the present disclosure, it is not necessary to route the transmission lines in a serpentine manner to ensure the wiring length of each transmission line, as is the case when the transmission lines of each antenna element are wired to have equal lengths. This reduces the transmission loss of high-frequency signals that occurs in the transmission lines of each antenna element, and increases the detection distance of targets by the radar device.

[0017] 4A is a schematic diagram showing the configuration of an antenna device of an embodiment; FIG. 4B is an explanatory diagram showing the phase of a high-frequency signal input to the antenna array of an embodiment; FIG. 4C is an explanatory diagram showing measurement results of angular accuracy when the radiation direction of radio waves from the antenna device of an embodiment is changed, before and after frequency hopping; FIG. 4D is an explanatory diagram of an antenna device of a reference example in which all transmission paths connected to the antenna array are non-equal-length wiring, FIG. 4A shows the configuration of the antenna device of the reference example, and FIG. 4B shows the phase of a high-frequency signal input to the antenna array of the reference example; FIG. 4C is an explanatory diagram showing measurement results of angular accuracy when the radiation direction of radio waves from the antenna device of the reference example shown in FIG. 4 is changed, before and after frequency hopping; FIG. 4D is an explanatory diagram explaining symmetrical equal-length wiring in an antenna device of a first modified example in which the number of channels is odd; and FIG. 4E is a schematic diagram showing the configuration of an antenna device of a second modified example.

[0018] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0019] [Configuration] As shown in FIG. 1, the antenna device 10 of this embodiment includes a plurality of antenna arrays 12L, 12R, 14L, and 14R that constitute the antenna device 10, and transmission lines 22L, 22R, 24L, and 24R that connect each of the antenna arrays 12L to 14R to an MMIC 30.

[0020] The plurality of antenna arrays 12L to 14R and transmission lines 22R to 24R are configured by wiring patterns formed on the surface of the circuit board 2. The MMIC 30 is mounted on the circuit board 2.

[0021] The circuit board 2 is a component of an on-vehicle radar device and is in the form of a multilayer circuit board. The MMIC 30 is a monolithic microwave integrated circuit and is an example of a high-frequency circuit of the present disclosure. The circuit board 2 also includes wiring patterns other than the antenna device 10 and other electronic components connected to the MMIC 30.

[0022] The MMIC 30 detects targets around the vehicle by outputting high-frequency signals for ranging to the antenna arrays 12L to 14R to transmit radio waves for ranging, or by acquiring received signals from the antenna arrays 12L to 14R and processing the signals.

[0023] The multiple antenna arrays 12L to 14R are arranged at predetermined intervals. Their arrangement direction is set so that they are horizontal (i.e., the direction of arrow X shown in the figure) when the radar device is mounted on a vehicle. Therefore, by inputting transmission signals with a phase difference to the antenna arrays 12L to 14R, the horizontal beam center angle of the radio waves radiated from the antenna device 10 can be controlled by the phase difference.

[0024] Each of the antenna arrays 12L to 14R includes a plurality of antenna elements 20 arranged at equal intervals in a direction perpendicular to the arrangement direction of the antenna arrays 12L to 14R (i.e., the direction of the arrow Y shown in the figure). In this embodiment, each of the antenna arrays 12L to 14R includes four antenna elements 20, which are connected to each other via a transmission line 21. Each of the antenna elements 20 is a rectangular conductor patch.

[0025] The MMIC 30 is mounted on the circuit board 2 at one end side in the arrangement direction of the four antenna elements 20 in the antenna arrays 12L to 14R, and in the center in the arrangement direction of the antenna arrays 12L to 14R.

[0026] The transmission lines 22L to 24R are formed of wiring patterns, that is, microstrip lines, that connect the antenna elements 20 on the MMIC 30 side of each of the antenna arrays 12L to 14R to the MMIC 30.

[0027] The transmission lines 22L to 24R pass through the center of the arrangement direction of the antenna arrays 12L to 14R and are wired so that the lengths of each pair of antenna arrays 12L-12R and 14L-14R are equal, and are line-symmetrical with respect to a center line Lo perpendicular to the arrangement direction. In other words, the microstrip lines constituting the transmission lines 22L to 24R are wired symmetrically with equal lengths, with the center line Lo as the center.

[0028] Incidentally, wiring patterns 26 are provided around the microstrip lines constituting each of the transmission paths 22L to 24R so as to sandwich the microstrip lines. The wiring patterns 26 are connected through vias 28 to a ground pattern provided on the back surface or intermediate layer of the circuit board 2.

[0029] [Effect] As described above, in the antenna device 10 of this embodiment, the transmission lines 22L to 24R that connect the antenna elements 20 on one end of the antenna arrays 12L to 14R to the MMIC 30 are configured with microstrip lines on the circuit board 2. The microstrip lines are wired symmetrically with equal lengths around the center line Lo that passes through the center of the arrangement direction of the antenna arrays 12L to 14R.

[0030] Therefore, according to the antenna device 10 of this embodiment, it is not necessary to make the lengths of all of the microstrip lines constituting the transmission paths 22L to 24R the same, and the length can be set for each pair of antenna arrays 12L-12R and 14L-14R that are line-symmetrical with respect to the center line Lo. In other words, as shown in Fig. 1, it is possible to shorten the transmission paths 22L and 22R of the central antenna arrays 12L and 12R and lengthen the transmission paths 24L and 24R of the outer antenna arrays 14L and 14R.

[0031] Therefore, even if the wiring area for the transmission lines 22L to 24R on the circuit board 2 becomes narrower due to the implementation of the MMIC 30 or other electronic components, the wiring area can be secured by adjusting the length of each of the transmission lines 22L-22R and 24L-24R.

[0032] Therefore, according to the antenna device 10 of this embodiment, it is possible to reduce the wiring area required to form the transmission paths 22L to 24R of the respective antenna arrays 12L to 14R on the circuit board 2, thereby reducing the size of the circuit board 2. Therefore, it is possible to easily reduce the size of the radar device configured using the circuit board 2.

[0033] Furthermore, in the antenna device 10 of this embodiment, the transmission paths of each of the antenna arrays 12L to 14R are not all wired with unequal lengths, but rather, the lengths of the transmission paths of a pair of antenna arrays 12L-12R and 14L-14R that are line-symmetrical with respect to the center line Lo are made to match by symmetrical wiring with equal lengths.

[0034] For this reason, although it is not possible to align the phases of the high-frequency signals input and output in all of the antenna arrays 12L to 14R, as with the equal-length wiring shown by the dotted lines in Figure 2, it is possible to align the phases of the high-frequency signals between the above pair of antenna arrays, as shown by the solid lines in Figure 2.

[0035] Therefore, according to the antenna device 10 of this embodiment, the phase relationship between the input and output high frequency signals in the pair of antenna arrays 12L-12R, 14L-14R can be prevented from fluctuating due to frequency hopping or aging.

[0036] Furthermore, since fluctuations in the phase relationship of the high-frequency signals input and output in the pair of antenna arrays 12L-12R, 14L-14R can be suppressed, the angular accuracy of the antenna device 10 can be suppressed from decreasing due to frequency hopping or deterioration over time, as shown in Figure 3.

[0037] In other words, Figure 3 shows the measurement results of the angular accuracy when the phase difference of the transmission signals input to each antenna array 12L to 14R in the antenna device 10 of this embodiment is adjusted to change the directivity of the antenna device 10 within a horizontal angle range of -60 to +60 degrees.

[0038] As a result, it was found that the angular accuracy did not change significantly before and after frequency hopping of the transmission signal, and that the antenna device 10 of this embodiment can be fully used as an antenna device for a radar device.

[0039] As a comparative example of angular accuracy, an antenna device 11 with non-equal length wiring as shown in Fig. 4A was fabricated, and the angular accuracy was measured in the same manner as above. The measurement results are shown in Fig. 5.

[0040] As shown in Figure 5, even if the phase difference of the transmission signals input to each of the antenna arrays 12L to 14R is adjusted so that the desired angular accuracy can be obtained with the transmission signals before frequency hopping, it was found that the angular accuracy significantly deteriorates when the transmission signals are frequency hopped. It was also found that in this case, the angular accuracy deteriorates more significantly on the -60° and +60° sides away from the central angle than at the central angle where the horizontal angle is 0°.

[0041] This is because, in the non-equal length wiring of FIG. 4A, the transmission paths 34L, 32L, 32R, and 34R become longer in the order of the antenna arrays 14L, 12L, 12R, and 14R, and as shown in FIG. 4B, the phase difference of the input signals input to each of the antenna arrays 12L to 14R also shifts.

[0042] Other Embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modifications.

[0043] [First Modification] In the above embodiment, the number of antenna arrays 12L to 14R, i.e., the number of channels (hereinafter, channels will also be referred to as CH), is described as four, but this number of CHs can be changed as appropriate and may be an even number of CHs or an odd number of CHs.

[0044] If the number of antenna arrays is an odd number of channels, for example, antenna arrays 12, 14L, and 14R, the lengths of transmission paths 22, 24L, and 24R may be set so that the phases of the high-frequency signals input to each antenna array 12, 14L, and 14R are as shown in Figure 6.

[0045] That is, symmetrical equal-length wiring can be achieved by making the lengths of the transmission paths 24L, 24R of the antenna arrays 14L, 14R arranged symmetrically on either side of the antenna array 12 on the center line Lo the same, and making the lengths of the transmission paths 22 of the antenna array 12 different.

[0046] [Second Modification] In the above embodiment, the antenna arrays 12L to 14R are all described as having the same configuration, but as shown in Figure 7, it is possible to have the antenna arrays 12L-12R and 14L-14R that are line-symmetrical with respect to the center line Lo have the same configuration.

[0047] In other words, the number and shape of the antenna elements 20 constituting the antenna arrays 12L to 14R need only be the same for each pair of antenna arrays that are symmetrical about the center line Lo, and may be configured differently from the other antenna arrays.

[0048] Furthermore, by wiring the transmission lines 22L to 24R of the antenna arrays 12L to 14R in symmetrical, equal-length wiring, it is possible to increase the free space on the circuit board 2 compared to conventional equal-length wiring. Therefore, as shown in FIG. 7, electronic components 40, 50 may be mounted between the transmission lines 22L to 24R.

[0049] Furthermore, multiple functions possessed by one component in the above embodiments may be realized by multiple components, or one function possessed by one component may be realized by multiple components. Furthermore, multiple functions possessed by multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Furthermore, part of the configuration of the above embodiments may be omitted. Furthermore, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0050] [Technical Ideas Disclosed in the Specification] [Item 1] An antenna device comprising: a plurality of antenna elements (20) arranged at predetermined intervals; and a plurality of transmission paths (22L, 22R, 24L, 24R) that respectively connect the plurality of antenna elements to a high-frequency circuit that transmits or receives a high-frequency signal for ranging, and transmit the high-frequency signal, wherein the plurality of transmission paths include microstrip lines on a circuit board, and the microstrip lines pass through the center of the arrangement direction of the plurality of antenna elements and are wired symmetrically with equal lengths so that each pair of the antenna elements that are line-symmetrical with respect to a center line (Lo) that is orthogonal to the arrangement direction has an equal length.

[0051] [Item 2] The antenna device according to Item 1, wherein the plurality of antenna elements are each connected to other antenna elements arranged in a direction perpendicular to the arrangement direction to form a plurality of antenna arrays (12L, 12R, 14L, 14R), and the plurality of transmission paths are configured to connect the plurality of antenna arrays and the high-frequency circuit.

[0052] [Item 3] The antenna device according to Item 2, wherein at least a pair of antenna arrays that are line-symmetric with respect to the center line among the plurality of antenna arrays have the same configuration.

[0053] [Item 4] The antenna device according to Item 3, wherein at least a portion of the pair of antenna arrays has a different structure from the other antenna array.

Claims

1. An antenna device comprising: a plurality of antenna elements (20) arranged at predetermined intervals; and a plurality of transmission paths (22L, 22R, 24L, 24R) that respectively connect the plurality of antenna elements to a high-frequency circuit that transmits or receives high-frequency signals for ranging, and transmit the high-frequency signals, wherein the plurality of transmission paths include microstrip lines on a circuit board, and the microstrip lines pass through the center of the arrangement direction of the plurality of antenna elements and are wired symmetrically with equal lengths so that each pair of antenna elements that are line-symmetrical with respect to a center line (Lo) that is perpendicular to the arrangement direction has the same length.

2. The antenna device according to claim 1, wherein each of the plurality of antenna elements is connected to other antenna elements arranged in a direction perpendicular to the arrangement direction to form a plurality of antenna arrays (12L, 12R, 14L, 14R), and the plurality of transmission paths are configured to connect the plurality of antenna arrays to the high-frequency circuit.

3. The antenna device according to claim 2, wherein at least a pair of said antenna arrays that are line-symmetric with respect to said center line have the same configuration.

4. The antenna device according to claim 3, wherein at least a portion of the pair of antenna arrays has a structure different from that of the other antenna array.

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