JP6087419B2 - Array antenna and radar device - Google Patents

Description

  The present invention relates to an array antenna and a radar apparatus.

  Conventionally, a microstrip antenna having a wide directivity is known. This microstrip antenna is also used for radar devices and wireless communication devices mounted on mobile objects such as automobiles. FIG. 15 is a diagram showing a conventional microstrip antenna.

  As shown in FIG. 15, the microstrip antenna 10 includes a main feed line 12 and a radiating element 13, and the main feed line 12 and the radiating element 13 are installed as a surface pattern of a dielectric substrate. The main feed line 12 and the radiating element 13 are installed on the surface of the dielectric substrate opposite to the ground.

  As an example of this dielectric substrate, the dielectric substrate is a substrate having a predetermined relative dielectric constant. For example, a copper foil of 12 μm is formed on a dielectric having a thickness of 0.115 mm and a relative dielectric constant of 2.22. It is a bonded substrate. The main power supply line 12 is a line through which power supplied from a power source flows, and supplies high frequency to the radiating element 13. The radiating element 13 is an element connected to the main feed line 12 and radiates radio waves.

  For example, when the microstrip antenna 10 is mounted on an in-vehicle device, the radiating element 13 is often formed with an inclination of 45 degrees with respect to the main feed line 12. Moreover, the ratio of the electric power which flows into the radiation | emission element 13 among the electric power supplied to the main feeder 12 from the power supply etc. is called coupling amount. For example, assuming that the power flowing through the main feed line 12 is 100% and 20% of the power flows through the radiating element 13, the coupling amount is 20%.

JP 2010-8319 A

  However, the conventional microstrip antenna has a limit in increasing the amount of coupling, and there is a problem that a desired directivity cannot be obtained.

  Specifically, when the radiating element 13 is in a resonance state, the input impedance (Zin) of the end face of the radiating element 13 connected to the main feed line 12 is increased. For this reason, between the main feed line 12 and the end face of the radiating element 13, a reflected wave returning to the incident wave from the radiating element 13 exists in the main feed line 12 due to impedance mismatch.

  In this case, in the conventional microstrip antenna 10, the element width (W) shown in FIG. 15 is increased, and the input impedance (Zin) when the radiating element 13 is viewed from the main feed line 12 is decreased. However, there is a limit to increasing the element width, and the coupling amount is about 22% at the maximum. That is, since the power necessary for obtaining the desired directivity cannot be supplied to the radiating element, the desired directivity cannot be obtained.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and an object thereof is to provide an array antenna and a radar apparatus that can obtain desired directivity.

In order to solve the above-described problems and achieve the object, an array antenna of the present invention includes a radiating element that radiates radio waves, a main feed line that feeds power to the radiating element, the radiating element, and the main feed line. And connecting the impedance of the radiating element in the resonance state and the impedance of the main feeding line in a desired ratio, and feeding line for feeding the power fed from the main feeding line to the radiating element A plurality of antennas, wherein the plurality of antennas are arranged on the main feed line at intervals of a guide wavelength in the main feed line, and the length of the feed line is set in the order of feeding from the main feed line. The length of the first feed line that is formed to be long and is connected to the first radiation element that is earliest in the order of feeding power from the main feed line is one half of the in-tube wavelength in the main feed line. The length of Thus, the length of the second feed line connected to the second radiating element whose order of feeding from the main feed line is slower than the first radiating element is 3/4 of the in-tube wavelength in the main feed line. It becomes the length .

  According to the present invention, it is possible to obtain desired directivity.

FIG. 1A is a diagram showing the structure of the microstrip antenna 1. FIG. 1B is a diagram showing the structure of the microstrip antenna 1. 2 is a cross-sectional view taken along the line A-A1 shown in FIG. 1A. FIG. 3 is a diagram showing a standing wave distribution in the feed line. FIG. 4 is a diagram illustrating the relationship between the length of the feed line and the coupling amount. FIG. 5 is a diagram illustrating a configuration example of an array antenna. FIG. 6 is a diagram illustrating an example of amplitude control executed to obtain desired directivity. FIG. 7 is a view showing the coupling amount distribution of the array antenna. FIG. 8 is a diagram illustrating an example of amplitude control when a conventional structure is used. FIG. 9 is a diagram showing directivity (side lobe) when designed with the conventional structure and the disclosed structure. FIG. 10 is a diagram illustrating an example in which the width of the feeder line 5 is made larger than the element width of the radiating element 4. FIG. 11 is a diagram illustrating an example in which the element length is longer than the element width. FIG. 12 is a diagram illustrating an example where the feeder line 5 is curved. FIG. 13 is a diagram illustrating an example in which a reflection suppression stub is provided. FIG. 14 is a functional block diagram of the radar apparatus. FIG. 15 is a diagram showing a conventional microstrip antenna.

  Exemplary embodiments of an array antenna and a radar apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

[Microstrip antenna]
FIG. 1A is a diagram showing the structure of the microstrip antenna 1. 1B is a cross-sectional view taken along the line A-A1 shown in FIG. 1A. FIG. 1A is an example of a plan view of the microstrip antenna 1 installed on the dielectric substrate as viewed from above the dielectric substrate.

  As shown in FIG. 1A, the microstrip antenna 1 includes a main feed line 3, a radiating element 4, and a feed line 5. Further, as shown in FIG. 1B, the main feed line 3, the radiating element 4, and the feed line 5 are installed on the surface of the dielectric substrate 2 opposite to the ground 6. The dielectric substrate 2 is a substrate having a predetermined relative dielectric constant. For example, the dielectric substrate 2 is a substrate in which a copper foil of 12 μm is bonded to a dielectric having a thickness of 0.115 mm and a relative dielectric constant of 2.22.

  The main feed line 3 is a line through which power supplied from a power source flows, and feeds a high frequency to the radiating element 4 through the feed line 5. The radiating element 4 is an element that resonates with the power supplied via the feeder line 5 to be in a resonance state and radiates radio waves. The radiating element 4 is connected to the main feed line 3 via the feed line 5.

  The feed line 5 is fed from the main feed line 3 by connecting the radiating element 4 and the main feed line 3 so that the impedance of the radiating element 4 in resonance and the impedance of the main feed line 3 are in a desired ratio. 3 is an example of a feed line that feeds the radiated power to the radiating element 4. For example, when the microstrip antenna 1 is used for an in-vehicle device or the like, the radiation element 4 is inclined 45 degrees by installing the power supply line 5 with an inclination of 45 degrees with respect to the main power supply line 3.

  Here, the feed line 5 will be specifically described. When the characteristic impedance of the feeder line 5 is Zq, the input impedance when the feeder line 5 is viewed from the main feeder line 3 is Zin, and the input impedance to the radiating element 4 in the resonance state is Zant, Zq satisfies the following expression. That is, “(Zq) squared = (Zin × Zant)”. Therefore, Zin can be calculated by dividing the square of (Zq) by Zant.

  Further, the coupling amount of the microstrip antenna 1 shown in FIG. 1A can be expressed by the following equation when expressed by the S parameter. That is, it can be expressed by “coupling amount (C) = 1− (| S11 | squared) − (| S21 | squared)”. Here, by using the impedance Zo of the main feed line and the above Zin, it is calculated as “S11 = (− Zo / Zin) / (2 + Zo / Zin)”, “S21 = 2 / (2 + Zo / Zin)”. Can do.

  As described above, in the microstrip antenna 1 shown in FIG. 1A, the input impedance (Zant) of the end face of the radiating element 4 in the resonance state becomes the maximum value, and the input impedance (Zin) viewed from the main feed line 3 to the feed line 5 ) Is the minimum value. Therefore, by installing the feed line 5 having the characteristic impedance (Zq) between the radiating element 4 and the main feed line 3, the input impedance to the radiating element 4 viewed from the main feed line 3 can be made small. .

  As a result, the input impedance from the main feed line 3 to the feed line 5 becomes small, and the power easily flows, so that the coupling amount becomes high and desired directivity can be obtained.

[Specific examples of microstrip antenna]
Next, a specific example of the microstrip antenna shown in FIG. 1A will be described. FIG. 2 is a diagram showing a specific example of the microstrip antenna 1. 2 is an example of a plan view of the dielectric substrate of the microstrip antenna 1 installed on the dielectric substrate as seen from above, as in FIG. 1A. In FIG. 2, the dielectric substrate 2 is omitted.

  A microstrip antenna 1 shown in FIG. 2 includes a main feed line 3, a radiating element 4, and a feed line 5 as in FIG. 1A, and is installed on the feed line 5 with an inclination of 45 degrees with respect to the main feed line 3. . In the main feed line 3, the width is 0.2 mm, the power flows from the left to the right in FIG. 2, and the wavelength in the main feed line 3 when the power is passed, the so-called in-tube wavelength is λg.

  The radiating element 4 has an element width of 0.8 mm and an element length of λg / 2 which is half of the guide wavelength of the main feed line 3 in order to obtain a resonance state. Further, when the radiating element 4 is in a resonance state, the input impedance (Zant) at the end face (b) is maximized.

  The feed line 5 has a characteristic impedance (Zq), has a length of λg / 4, which is a quarter of the in-tube wavelength of the main feed line 3, and an arbitrary width. Here, the characteristic impedance (Zq) satisfies the above-described equation, and the coupling amount can be represented by the above-described S parameter.

  Here, the length of the feeder line 5 will be described. FIG. 3 is a diagram showing a standing wave distribution in the feed line. In FIG. 3, the horizontal axis indicates the distance from the radiating element 4 to the main feed line 3, and the vertical axis indicates the voltage. FIG. 4 is a diagram illustrating the relationship between the length of the feed line and the coupling amount. In FIG. 4, the horizontal axis indicates the length of the feeder line 5 and the vertical axis indicates the coupling amount.

  As shown in FIG. 3, when the length from the end face (b) of the radiating element 4 is 0, that is, when the distance from the end face (b) of the radiating element 4 to the main feed line 3 is 0, the radiating element 4 The voltage becomes maximum at the end face (b), and then the voltage becomes maximum every λ / 2. On the other hand, when the length from the end face (b) of the radiating element 4 is λg / 4, the voltage becomes the minimum value, and then the voltage becomes minimum every λ / 2.

  Since such a standing wave exists in the feed line 5, as shown in FIG. 4, when the length of the feed line 5 is λg / 4, the coupling amount is 80%, which is the maximum. When the length is λg / 2, the amount of coupling is minimum, and thereafter, the maximum and minimum are repeated every λg / 4. That is, the length of the feed line 5 that can increase the amount of coupling can be determined by the period of the standing wave in the feed line 5. In addition, as shown in FIG. 4, the same effect is acquired even if the element width of the radiation element 4 is 0.4 mm.

  Thus, regardless of the width of the feed line 5, the amount of power supplied to the radiating element 4 can be adjusted by adjusting the length of the feed line 5. For this reason, the coupling amount can be adjusted by adjusting the length of the feeder line 5. That is, by changing the length of the feeder line 5, Zin can be increased or decreased. That is, the feed line 5 is a line that can control the size of Zin by the length.

[Configuration of array antenna]
Next, an example of an array antenna using the microstrip antenna described in the first embodiment will be described. FIG. 5 is a diagram illustrating a configuration example of an array antenna. FIG. 5 is an example of a plan view of the array antenna viewed from above the dielectric substrate, as in FIG. 1A. In FIG. 5, the dielectric substrate 2 is omitted.

  As shown in FIG. 5, here, as an example, a case where six microstrip antennas are used will be described. Note that the number of microstrip antennas is an example, and an arbitrary number can be adopted. In the array antenna shown in FIG. 5, microstrip antennas are arranged at intervals of the guide wavelength (λg) of the main feed line. In FIG. 5, electric power flows from the left to the right in the figure. Also, element numbers 1, 2, 3, 4, 5, and 6 are set in order from the microstrip antenna close to the current source. Note that a matching element having a coupling amount of 100% is used for the radiating element of element number 6.

  For each of the radiating elements with element numbers 1 to 5, the microstrip antenna shown in FIG. 1A or the like is used. Further, in order to increase the coupling amount as the element number increases, the length of the feeder line 5 is set to λg / 4 or 3λg / 4 as the element number increases. For example, the length of the feed line 5 of the microstrip antenna of element number 1 is set to λg / 2, and the length is increased by a predetermined number as the element number increases, and the feed line 5 of the microstrip antenna of element number 5 is increased. Is set to 3λg / 4. The length of each feed line 5 does not need to be increased as it goes to the element number 6, that is, the end face, and may be an appropriate length for obtaining a desired coupling amount, and set to an arbitrary length. Can do.

[simulation result]
Next, the simulation result using the array antenna shown in FIG. 5 is compared with the simulation result using the array antenna provided with six conventional microstrip antennas shown in FIG. Here, an example in which the antenna is designed so that the side lobe ratio is 30 dB will be described.

  FIG. 6 is a diagram illustrating an example of amplitude control executed to obtain desired directivity. In FIG. 6, the horizontal axis indicates the element number, and the vertical axis indicates the weighting factor. When an antenna is designed so that the side lobe ratio is 30 dB using an array antenna using six microstrip antennas, it is desirable that the radiation intensity of each element has a distribution as shown in FIG. Specifically, the weighting factor for the radiating element with element number 3 and the radiating element with element number 4 located in the middle is set to 1 which is the maximum value. Further, the weighting factor for the radiating element with the element number 1 at the start and the radiating element with the element number 6 at the end is set to a minimum value of 0.38, and the weighting factor with respect to the radiating elements with the element numbers 2 and 5 is set to 0.69. . That is, the radiation amount from the radiation element located in the middle is designed to be large.

  In the case of the array antenna using the microstrip antenna having the disclosed structure shown in FIG. 5, the coupling amount can be changed by adjusting the length of the feed line 5, so that it is shown in FIG. Thus, a desired binding amount distribution can be obtained. FIG. 7 is a view showing the coupling amount distribution of the array antenna. In FIG. 7, the abscissa indicates the element number, and the ordinate indicates the coupling amount.

  In general, in the case of an array antenna in which microstrip antennas are installed in series, the power is less at the terminal end than at the starting end near the power source. It becomes.

  In the case of the disclosed structure, a coupling amount of about 80% can be obtained by setting the length of the feed line 5 to λg / 4 or the like, and conversely, the length of the feed line 5 is set to λg / 2 or the like. As a result, a bonding amount smaller than 20% can be obtained. Therefore, by making the length of the feeder line 5 closer to λg / 4 as it is located at the terminal end as shown in FIG. 5, as shown in FIG. The amount of binding can be increased. Therefore, the radiation intensity of each microstrip antenna of the array antenna can be made the radiation intensity distribution shown in FIG.

  On the other hand, the microstrip in which the main feed line 3 and the radiating element 4 shown in FIG. 15 are directly connected can obtain a coupling amount of about 22% at the maximum as described above. Therefore, as shown in FIG. 7B, the radiating elements subsequent to the element number 3 have a coupling amount of about 22%. Therefore, the radiation intensity is as shown in FIG. FIG. 8 is a diagram illustrating an example of amplitude control when a conventional structure is used. In FIG. 8, the horizontal axis indicates the element number, and the vertical axis indicates the weight coefficient.

  When the conventional structure is used, as shown in FIG. 8, the weighting factor for the radiating element with element number 3 is 0.76, the weighting factor for the radiating element with element number 4 is 0.67, and the radiating element with element number 5 is used. The weighting factor is 0.59, and the weighting factor for the radiating element with element number 6 is 1.12.

  That is, when FIG. 6 is compared with FIG. 8, when the conventional structure is used, the radiating elements having the element numbers 1 and 2 are supplied with the amount of power necessary to obtain the desired directivity. be able to. However, since the coupling amount is about 22% at the maximum in the conventional structure, as shown in FIG. 8, the power flowing through each of the radiating elements of the element numbers 3, 4, and 5 is small. The power flowing to the matching element is increased, and the amount of radiation from the terminal matching element is maximized.

  As a result, there is a difference in gain between the array antennas using the conventional structure and the disclosed structure. FIG. 9 is a diagram showing directivity (side lobe) when designed with the conventional structure and the disclosed structure. In FIG. 9, the horizontal axis indicates the angle between the main feed line 3 and the radiating element 4, and the vertical axis indicates the gain.

  As shown in FIG. 9, when the conventional structure is used, the radiation intensity distribution of each radiating element cannot be the radiation intensity distribution shown in FIG. 6, but the radiation intensity distribution shown in FIG. The difference between the lobe and the main lobe is 12.2 dB, and the desired directivity cannot be obtained. On the other hand, as shown in FIG. 9, when the disclosed structure is used, the radiation intensity distribution of each radiating element can be the radiation intensity distribution shown in FIG. 6, so the sidelobe ratio can be set to 30 dB. And desired directivity can be obtained. Further, the amount of coupling can be changed while suppressing unnecessary cross knitting wave components by feeding power straight to the radiating element 4.

  Next, another structure of the microstrip antenna will be described with reference to FIGS. In any of FIGS. 10 to 13, in order to bring the radiating element 4 into a resonance state, the length of one end of the radiating element 4 is set to λg / 2 which is half of the guide wavelength of the main feed line 3. It is preferable to do. In order to obtain the maximum amount of coupling, it is preferable to set the distance between the main feed line 3 and the radiating element 4, that is, the length of the feed line 5 to λg / 4 or 3λg / 4.

  FIG. 10 is a diagram illustrating an example in which the width of the feeder line 5 is made larger than the element width of the radiating element 4. As shown in FIG. 10, the width of the feeder line 5 may be larger than the element width of the radiating element 4. FIG. 11 is a diagram illustrating an example in which the element length is longer than the element width. As shown in FIG. 11, the radiating element 4 shown in FIG. 2 and the like can be connected to the feed line 5 in a state where it is rotated by 90 degrees. In addition, the position where the feeder line 5 is connected in FIG. 11 is preferably a position where the end face of the radiating element has a length of λg / 2. That is, the feed line 5 is preferably connected to the end face of the radiating element having a length of λg / 2. FIG. 12 is a diagram illustrating an example where the feeder line 5 is curved. As shown in FIG. 12, the feed line 5 that connects the main feed line 3 and the radiating element 4 may be bent instead of a straight line.

  10 to 12, the feed line 5 having the characteristic impedance (Zq) is installed between the radiating element 4 and the main feed line 3 so as to be viewed from the main feed line 3. Further, the input impedance to the radiating element 4 can be made small. Therefore, in any structure, the radiation intensity of each radiating element can be made to have the radiation intensity distribution shown in FIG. 6, so that desired directivity can be obtained. Moreover, since various types of lines can be used for the feed line 5, a highly versatile microstrip antenna can be provided.

  Further, the feed line 5 may be connected to the center of the end face of the radiating element 4 or may be connected to any position on the end face to be connected. That is, it can be connected to any position as long as the input impedance to the radiating element 4 seen from the main feed line 3 can be seen small.

  FIG. 13 is a diagram illustrating an example in which a reflection suppression stub is provided. As shown in FIG. 13, by installing the reflection suppression stub 9 in the main feed line 3, it is possible to suppress the reflected wave with respect to the incident wave incident on the feed line 5 from the main feed line 3. That is, since the value of S11 described above can be reduced, the gain of the antenna is increased. The position where the reflection suppression stub is installed is preferably a position where the reflected wave has an opposite phase in order to cancel the reflected wave. As an example of the position where the reflected wave has the opposite phase, the position of λg / 4 corresponds.

  Next, a radar apparatus using the array antenna shown in FIG. 5 will be described. FIG. 14 is a functional block diagram of the radar apparatus. Here, a radar apparatus mounted on a vehicle is assumed.

  A radar apparatus 200 illustrated in FIG. 14 includes a radar antenna 100. The radar antenna 100 includes array antennas 20, 30, 31, and 32. The array antenna 20 is a transmission antenna and has the same structure as the array antenna shown in FIG. Array antennas 30, 31, and 32 are receiving antennas, and may have the same structure as the array antenna shown in FIG. 5 or a conventional structure using the microstrip antenna shown in FIG.

  The array antenna 20 will be described as an example. The array antenna 20 generates a 45-degree oblique polarization used in automobile radar. As shown in FIG. 5, the array antenna 20 includes six rectangular radiating elements 4 formed on one side of the main feed line 3 at an angle of 45 degrees with respect to the line 3. 4 is connected to the main feed line 3 via the feed line 5. The interval (w) between the radiating elements 4 is the guide wavelength λg of the main feed line 3 at the operating frequency, and the length of each radiating element 4 is set to about half the guide wavelength λg. Further, all the sides of the open ends of the projecting radiating elements 4 are parallel to each other. Further, the length of each feed line 5 that connects the radiating element 4 and the main feed line 3 is set to ¼ of the in-tube wavelength λg of the main feed line 3.

  In the radar apparatus 200 shown in FIG. 14, the output of the oscillator 90 that generates a carrier wave in the GHz band is pulse-modulated by the mixer 40 with the signal generated by the pulse generator 80. Next, the pulse signal passes through the band pass filter 60 and is transmitted to the array antenna 20 for transmission. Then, the radio waves reflected from the front object are received by the array antennas 30, 31, and 32. The received signals of these antennas are input to the demodulators 50, 51, 52 and demodulated into baseband pulse signals by the carrier wave output from the oscillator 90. Then, the signal processing unit 70 obtains the phase difference between the pulse signals received by the array antennas 31 and 32 and the phase difference between the pulse signals received by the array antennas 30 and 32. The radar apparatus can obtain the azimuth angle and the elevation angle by using these two phase differences, and can detect the distance from the radar apparatus to the front object and the position of the front object. In addition, since the calculation method which calculates | requires an azimuth and an elevation angle using two phase differences can use various general calculation methods, detailed description is abbreviate | omitted. Moreover, the FM-CW method etc. can also be employ | adopted for the measurement of distance.

  As described above, the microstrip antenna, array antenna, and radar apparatus according to the present invention are suitable for obtaining desired directivity.

DESCRIPTION OF SYMBOLS 1 Microstrip antenna 2 Dielectric board 3 Main feed line 4 Radiating element 5 Feed line 9 Reflection suppression stub

Claims (3)

A radiating element that radiates radio waves;
A main feed line for feeding power to the radiating element;
The radiating element and the main feed line are connected, the impedance of the radiating element in resonance and the impedance of the main feed line are set to a desired ratio, and the power fed from the main feed line is radiated. A plurality of antennas having a power feed line for feeding power to the element;
Wherein the plurality of antennas, the main intervals of the guide wavelength in the feed line disposed on the main feed line, wherein is formed so that the length of the feeder line becomes longer in the order to be fed from the main feed line ,
The length of the first feed line connected to the first radiating element that is fed in the earliest order from the main feed line is ½ of the guide wavelength in the main feed line, and the main feed line The length of the second feed line connected to the second radiating element whose order of feeding from the line is slower than the first radiating element is three-quarters of the guide wavelength in the main feed line. An array antenna.   The radiating element of the last antenna fed from the main feed line among the plurality of antennas is a matching element that radiates the radio wave using fed power. Array antenna. A radar device that detects a distance to an object or a direction to an object using a reflected wave with respect to a radiated wave radiated from an antenna,
The antenna is
A radiation element that radiates radio waves; a main feed line that feeds power to the radiation element; and the radiation element and the main feed line connected to each other, so that the impedance of the radiation element in resonance and the main feed line A plurality of antennas having an impedance and a desired ratio, and a power feed line that feeds power fed from the main power feed line to the radiation element;
Wherein the plurality of antennas, the main intervals of the guide wavelength in the feed line disposed on the main feed line, wherein is formed so that the length of the feeder line becomes longer in the order to be fed from the main feed line ,
The length of the first feed line connected to the first radiating element that is fed in the earliest order from the main feed line is ½ of the guide wavelength in the main feed line, and the main feed line The length of the second feed line connected to the second radiating element whose order of feeding from the line is slower than the first radiating element is three-quarters of the guide wavelength in the main feed line. A radar device characterized by the above.

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