JP2006279525A - Antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radar antenna which is equipped with a plurality of beam-tilted sub-arrays nearly in the same structure and suppresses tilt variation and a gain decrease due to it. <P>SOLUTION: The radar antenna is equipped with a transmitting antenna including a beam-tilted sub-array as a waveguide slot array 10 and a receiving antenna which is constituted by arranging L beam-tilted sub-arrays (waveguide slot arrays 11-1 to 11-L of a receiving array 11) whose beam tilt directions are reversely symmetrical with the sub-array of the transmitting antenna so that traveling directions of radio waves of the sub-arrays are reversely symmetrical with that of the sub-array of the transmitting antenna. Sub-array groups nearly in the same structure which constitute the transmitting antenna and receiving antenna are constituted/arranged so that the traveling directions of radio waves and the directions of beam tilts to the traveling directions are reversely symmetrical with each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

      The present invention relates to an antenna suitable for application to, for example, a radar device such as a vehicle-mounted radar, and more particularly to an antenna including a plurality of sub-arrays having substantially the same structure to which beam tilt is applied. The present invention relates to an antenna that suppresses the resulting gain reduction.

      In a vehicle-mounted radar, since a small and light device is particularly required, a high frequency band such as a millimeter wave 76 GHz band is generally used. The radar antenna is also required to be light, small, and thin, and application of a planar antenna such as a microstrip antenna or a waveguide slot array is considered (for example, see Non-Patent Document 1).

      As a basic method of radar scanning, there is a mechanical scanning method that mechanically vibrates the entire antenna or the power feeding unit, but it does not require a movable part and can be controlled by electromagnetic control such as signal phase or arithmetic processing. The electronic scanning method that performs scanning equivalently is considered to be superior in terms of miniaturization of the antenna and the apparatus, wide-range high-speed scanning, and the like. A typical example of this electronic scanning method is a phased array antenna. A phased array antenna uses an array antenna in which several radiating elements are regularly arranged, and each element is equipped with a phase shifter to give a predetermined relative phase, thereby controlling the beam direction and scanning electronically. (For example, refer nonpatent literature 2).

      Furthermore, a method called DBF (digital beam forming) radar or holographic radar converts a received signal of each element of an array antenna into complex digital data, and performs a target operation by digital arithmetic processing corresponding to phase / signal synthesis of a phased array. Is known as a method suitable for high-speed and high-precision digital processing (see, for example, Non-Patent Document 3). Such).

Hereinafter, an antenna corresponding to the DBF radar will be described.
The purpose of the in-vehicle radar is to detect the preceding vehicle ahead in the horizontal direction with respect to the host vehicle. The radar antenna characteristics are narrow in order to reduce the influence of the structure on the ground surface or the road in the elevation direction. The thing of the beam is required. Further, in the horizontal direction, a wide field of view is necessary to detect the preceding vehicle or the interrupting vehicle of the self-propelled lane and the adjacent lane, and the scanning beam can obtain sharp beam characteristics by array synthesis. As a single characteristic, a wide beam characteristic is required. For this reason, the antenna aperture shape is long in the vertical direction and narrow in the horizontal direction, and is vertically long. A waveguide slot array is known as a typical element having such a characteristic condition (see, for example, Non-Patent Document 4).
Iizuka et al .; "In-vehicle millimeter-wave radar antenna", 2001 IEICE General Conference SB-1-7 Supervised by Takashi Yoshida; “Revised Radar Technology”, Corona, p119-p123, 1996 Yu Matsuo, Kuniyoshi Yamane; Radar Holography, Corona, p162-p163, 1980 Teshiro, edited by Yoneyama; “New Millimeter-wave Technology”, p112-p119, 1999

  FIG. 8 shows a basic configuration diagram of the conventional waveguide slot array (FIG. 8A) and an explanatory diagram for explaining the principle (FIG. 8B). In FIG. 8A, the waveguide slot array 1 is provided with a large number of slots 3 on the wall surface of the waveguide 2, and the waveguide slot array 1 progresses by sequentially radiating radio waves from each slot 3. In the case of a wave antenna, when the feeding electric field of each slot 3 is in-phase, a linearly polarized radiation beam is obtained in a direction perpendicular to the antenna surface (the wall surface of the waveguide 2 having the slot 3). This beam characteristic is a fan-shaped beam that is sharp in the axial direction of the waveguide 2 and wide in the direction perpendicular to the axis. Here, when used for reception, the traveling direction of the radio wave is opposite to that for transmission. However, when used for transmission, the radio wave input end is the input end 4, and the radio wave traveling direction starts from the input end 4. The axis in the traveling direction and the length direction of the waveguide 2 is referred to as a tube axis.

  The condition for in-phase power supply is obtained when the slot interval (P) is equal to the guide wavelength λg in the case of an axis perpendicular or oblique slot obtained by cutting the slot on the long side surface of the waveguide perpendicularly or obliquely to the tube axis. . On the other hand, in the case of the axial parallel slot which cuts the slot parallel to the tube axis, radiation does not occur at the center of the long side surface of the waveguide, so the slot 3 is cut by shifting left and right as shown in FIG. Since the phase is reversed on the right side or the left side, in-phase power feeding can be achieved by arranging the slot interval P as λg / 2 alternately left and right. That is, in the axial parallel slot, multiple slots can be arranged in the same waveguide length as compared with the axial vertical or oblique slot, which is advantageous in gain and beam characteristics. In the following description, the case of an axial parallel slot is assumed.

  Note that if each slot 3 is fed completely in phase (in the case of an axial parallel slot, slots 3 are alternately arranged at left and right intervals at intervals of λg / 2), a beam perpendicular to the antenna aperture can be obtained. Since the reflected waves from all the slots 3 are also added in the same phase, the reflection loss of the antenna becomes remarkably large, and a good gain cannot be obtained. For this purpose, a design method is known in which the slot interval P is slightly shifted from λg / 2 to phase cancel reflected waves to optimize the gain. However, in this case, the beam direction is slightly inclined from the true vertical, which is called beam tilt. Although it depends on the application and design, it is generally considered to give a beam tilt of about 1 to 5 °.

The relationship between the tilt angle τ and the slot interval P is obtained by the following equation (1).
sinτ = {(P−λg / 2) / λg} / (P / λ) (1)
Here, λ: free space wavelength, λg: guide wavelength.
In the following description, the tilt direction is defined as a positive value (+).

Here, the waveguide slot array 1 has a problem that the beam direction varies depending on the frequency. From the equation (1), if the tilt angles at the frequencies Fo and F ′ = Fo + Δf are τ and τ ′, and the tilt angle variation Δτ is expressed by an approximate expression, the following expression is given.
Δτ = τ′−τ≈ (λ / λg) · (Δf / Fo) (2)
That is, it is shown that a tilt fluctuation Δτ that is substantially proportional to the frequency change Δf occurs. In the 76 GHz band (Fo = 76.5 GHz, ΔF = ± 0.5 GHz) used for the on-vehicle radar, Δτ≈ ± 0.6 ° is calculated. The guide wavelength λg varies depending on the dimensions of the waveguide 2, but here, a standard waveguide of 76 GHz band (long side: 2.54 mm) was assumed.

As a simple effect of the tilt variation on the radar performance, there is a decrease in radar gain. Assuming that the apparatus is installed so that the beam direction is horizontal at a frequency Fo = 76.5 GHz, if the beam direction fluctuates, the following gain decrease ΔG corresponding to the deviation of the tilt fluctuation Δτ from the beam peak occurs in the horizontal direction.
ΔG≈−24 · (Δτ / β) ² (3)
Where β: Radar half width.
In the in-vehicle radar, it is considered that the elevation beam width is preferably 3 to 4 °. When the radar half-value width β = 4 °, the gain drop is about 0.5 dB when the tilt fluctuation Δτ = ± 0.6 °.

  Furthermore, if the frequency cannot be specified at the time of installation of the device, for example, if the frequency at the time of installation is Fo = 76.0 GHz and the maximum fluctuation at the time of operation is 77.0 GHz (Δf = 1.0 GHz), a gain reduction of 2 dB at maximum is possible. Can happen. In-vehicle radar equipment is a priority requirement for low cost and small size, so the margin on the level is not necessarily large, and the maximum gain reduction of 2 dB is equivalent to about 10% in terms of radar maximum sensing distance performance. cause.

  In addition, since the relative movement of the beam is caused by the undulation of the road during traveling, it is necessary to allow a certain degree of angular deviation from the middle of the beam during actual operation. When the tilt variation due to the frequency is added, the gain decrease increases in proportion to the square of the angular deviation according to the equation (3). Furthermore, in order to reduce external disturbances such as road surface reflections and scattering reflections due to upper structures such as overpasses, it is desirable to suppress tilt frequency fluctuations as much as possible. As a countermeasure, first, it is conceivable to suppress the fluctuation of the frequency, but this directly leads to an increase in the price of the millimeter wave IC or the transmission / reception module, resulting in an increase in apparatus cost.

  The present invention has been made in view of the above-described conventional circumstances, and is an antenna including a plurality of subarrays having substantially the same structure to which beam tilt is applied, and an antenna that suppresses tilt fluctuations and gain reduction caused thereby. The purpose is to provide.

      In order to solve the above-described problem, the antenna of the present invention according to claim 1 is configured such that N subarrays (N is a positive integer) whose beam tilts are applied and the beam tilt directions are the same as each other. A transmitting antenna (for example, the waveguide slot array 10 in the first embodiment) arranged so that the traveling directions are the same as each other, a beam tilt is applied, and the direction of the beam tilt is N sub-arrays of the transmitting antenna. Is a receiving antenna in which M subarrays (M is a positive integer) are arranged so that the traveling direction of radio waves of the subarray is inversely symmetric with the N subarrays of the transmitting antenna (for example, in the first embodiment) And a receiving array 11) including the waveguide slot arrays 11-1 to 11-L.

      The antenna according to the present invention having the above-described configuration is configured so that the sub-array groups having substantially the same structure constituting the transmitting antenna and the receiving antenna are configured so that the traveling direction of the radio wave and the direction of the beam tilt with respect to the traveling direction are oppositely symmetric. Therefore, the tilt variation in the transmitting antenna and the receiving antenna is the same magnitude and intersects each other, and the variation as a radar beam is canceled out by the transmitting antenna and the receiving antenna, so that a directivity characteristic in a certain direction is always obtained. As a result, in the antenna including a plurality of subarrays having substantially the same structure subjected to beam tilt, tilt fluctuations and gain reduction resulting therefrom can be suppressed.

      An antenna according to a second aspect of the present invention is an antenna including N subarrays (N is a positive integer of 2 or more) to which beam tilt is applied, and R antennas out of the N (R Are arranged such that the beam tilt directions are the same, and the traveling directions of the radio waves of the subarrays are the same. N-R subarrays are configured such that the beam tilt direction is inversely symmetric with the R subarrays, and the traveling direction of the radio waves of the subarrays is inversely symmetric with the R subarrays. It arrange | positions so that it may become.

  The antenna of the present invention having the above-described configuration is configured to divide substantially the same number of sub-array groups having the same structure into two, and for each sub-array group divided into two, the direction of the radio wave and the beam tilt with respect to the direction of travel. Since the directions and configurations are arranged so as to be opposite to each other, the tilt variation of each of the sub-array groups divided into two is substantially the same size and intersects each other, and the variation as a radar beam is canceled out and is always constant. Directional directivity can be obtained, and as a result, tilt variation and a gain reduction caused by this can be suppressed in an antenna including a plurality of subarrays having substantially the same structure subjected to beam tilt.

  According to a third aspect of the present invention, there is provided an antenna of the present invention comprising N + M subarrays (N and M are each a positive integer of 2 or more) to which beam tilt is applied, wherein R out of the N The subarrays (R is the smallest positive integer of N / 2 or more) are arranged so that the beam tilt directions are the same, and the traveling directions of the radio waves of the subarrays are the same. NR of the N subarrays are configured such that the beam tilt direction is inversely symmetric to the R subarrays, and the radio wave traveling direction of the subarrays is the R subarrays. And the transmitting antennas (for example, the waveguide slot arrays 50-1 and 50-2 in the third embodiment) arranged in reverse symmetry with the S antennas among the M antennas (S is equal to or more than M / 2) The smallest positive integer) subarray The tilt directions are configured to be the same, and the sub-arrays are arranged so that the traveling directions of the radio waves are the same, and the M-S subarrays of the M are arranged in the beam tilt direction. Is configured to be inversely symmetric with the S sub-arrays, and the receiving antennas (for example, the waveguides in the third embodiment are arranged so that the traveling directions of the radio waves of the sub-arrays are inversely symmetric with the S sub-arrays). And a receiving array 51) including wave tube slot arrays 51-1 to 51-L.

  The antenna according to the present invention having the above-described configuration is divided into approximately the same number of sub-array groups having the same structure in the transmitting antenna and the receiving antenna, and the progress of radio waves is divided into the two sub-array groups divided into two. Since the direction and the direction of the beam tilt with respect to the traveling direction are configured and arranged so as to be inversely symmetric with each other, the tilt variation of each of the subarray groups divided into two is almost the same in each of the transmitting antenna and the receiving antenna. Crossing each other, fluctuations in the radar beam are offset by the transmitting antenna and the receiving antenna, and a directivity characteristic in a fixed direction is always obtained. As a result, a subarray having a substantially identical structure subjected to beam tilting is obtained. Due to tilt fluctuations in antennas with multiple It is possible to suppress the gain reduction.

      According to a fourth aspect of the present invention, in the antenna according to the first to third aspects, the subarray is preferably a traveling wave antenna that requires a fan-shaped beam and has a vertically long element shape. .

      According to a fifth aspect of the present invention, in the antenna according to any one of the first to fourth aspects, the subarray is preferably a waveguide slot antenna.

      Furthermore, the antenna of the present invention according to claim 6 is preferably the antenna according to any one of claims 1 to 4, wherein the subarray is a planar antenna of a printed antenna or a microstrip antenna.

      For example, the antenna aperture shape of a vehicle-mounted radar is required to be vertically long, narrow in the horizontal direction, and vertically long, but without tilt increase and gain reduction caused by this without increasing the cost, The present invention can be applied to such a vehicle-mounted radar.

      As described above, according to the antenna of the present invention, each subarray group having substantially the same structure that constitutes the transmission antenna and the reception antenna, or each subarray group having substantially the same structure that constitutes the transmission antenna and the reception antenna, respectively. Since the subarray groups divided into approximately the same number of two are arranged so that the traveling direction of the radio wave and the direction of the beam tilt with respect to the traveling direction are opposite to each other, each of the transmitting antenna and the receiving antenna or the transmitting antenna and the receiving antenna For each of the two sub-array groups divided into two, the tilt fluctuations are in the direction of crossing each other with substantially the same magnitude, the fluctuations as radar beams are canceled out, and a directivity characteristic in a fixed direction is always obtained. It is possible to suppress the gain reduction caused by this. That.

      Hereinafter, embodiments of the antenna of the present invention will be described in detail in the order of [Embodiment 1], [Embodiment 2], and [Embodiment 3] with reference to the drawings.

[Example 1]
FIG. 1 is a configuration diagram of an antenna according to Embodiment 1 of the present invention. FIG. 1A is a perspective view showing a relative arrangement relationship between the subarray 10 of the transmitting antenna and the receiving array 11 of the receiving antenna, and FIG. 1B is a subarray 10 and 11-i (i = 1 to L; (L is a positive integer).

      In FIG. 1, the antenna of the present embodiment is used as a radar antenna of a radar apparatus, and includes 1 + L sub-arrays having substantially the same structure to which beam tilt is applied, and is similar to the conventional example (FIG. 8) as a sub-array. This is a configuration using a waveguide slot array of axially parallel slots having the structure described above. That is, the waveguide slot array 10 is provided as a transmitting antenna, and the waveguide slot arrays 11-1 to 11-L are provided as receiving antennas.

      First, the waveguide slot array 10 of the transmitting antenna is configured to perform in-phase power feeding by arranging slots 22 at intervals of about λg / 2 on the waveguide wall surface alternately on the left and right sides. It is a traveling wave antenna that obtains a linearly polarized radiation beam (fan-shaped beam) in a direction perpendicular to the wave tube wall surface. In addition, in order to cancel the phase of the reflected wave from the slot 22, beam tilt is performed by slightly shifting the interval of the slot 22 from λg / 2. Here, the interval (pitch) P of the slot 22 is set at the center frequency Fo. P = λg / 2 + δ.

Also, as shown in the figure, the input end 24 which is the input end of the radio wave is arranged so as to be on the lower side with respect to the figure, and the traveling direction of the radio wave in the waveguide is from the lower side with respect to the figure. The direction is upward. As described in the conventional example, the tilt angle τ and the slot interval P have the relationship of Expression (1), and therefore the tilt angle τ is given by the following expression.
τ≈sinτ = (δ / P) · (λ / λg) (4)
In other words, the waveguide slot array 10 of the transmitting antenna has a tilt in the traveling direction that is upward (positive in the traveling direction) with respect to the drawing.

      On the other hand, in the waveguide slot arrays 11-1 to 11-L of the receiving array 11, similarly to the waveguide slot array 10 of the transmitting antenna, the slots are alternately spaced on the left and right sides of the waveguide wall surface at approximately λg / 2. However, as the beam tilt, the interval (pitch) P between the slots 23 is P = λg / 2−δ at the center frequency Fo, and the tilt angle is −τ. That is, the tilt is in the direction opposite to the traveling direction and has a tilt characteristic that is inversely symmetric with respect to the waveguide slot array 10 of the transmitting antenna.

      In addition, the input end 25 is placed on the upper side with respect to the drawing and is arranged in an inverse symmetry with the waveguide slot array 10 of the transmitting antenna, and the traveling direction of the radio wave in the waveguide as the sub-array is lower from the upper side with respect to the drawing. The direction will be to the side. (However, since it is used for reception, the actual traveling direction of the radio wave is the direction toward the input end 25 as opposed to the case of transmission.) With this reverse symmetrical arrangement, the waveguide slot array 11 of the reception array 11 is used. Also in the case of −1 to 11-L, the tilt direction is upward with respect to the figure, and the beam direction of transmission / reception as a radar antenna coincides upward.

By the way, the fluctuation of the beam direction due to the frequency occurs when the frequency is increased, the beam direction is in the traveling direction, and when the frequency is decreased, the beam direction is reversed in the traveling direction. This does not depend on the tilt direction (± τ) at the center frequency Fo. The transmission beam direction when the frequency changes to F = Fo + Δf is given by the following equation.
τt = τ + Δτ
Δτ≈ (λ / λg) · (Δf / Fo) (5)

The direction of the received beam is −τ + Δτ with respect to the traveling direction as the subarray, but is given by the following equation for the radar antenna due to the upside down arrangement of the transmitting antenna and the receiving antenna.
τr = − (− τ + Δτ) = τ−Δτ (6)
Therefore, the tilt fluctuations of the transmitting antenna and the receiving antenna are the same magnitude and intersect each other, so the radar beam of the radar antenna cancels the fluctuations on the transmitting side and the receiving side, and always obtains a directivity characteristic in a certain direction. Will be.

  Next, FIG. 2 shows a partial configuration diagram of a radar apparatus to which the radar antenna of this embodiment is applied. This radar apparatus is a radar apparatus using digital beam forming (DBF). In addition to the radar antenna 101 having the transmission antenna 10 and the reception array 11 of this embodiment, the transmitter (Tx) 102 and the receiver ( Rx) 103-1 to 103-L, analog / digital converters (A / D) 104-1 to 104-L, and a digital beam combining circuit 105.

  In this radar apparatus, on the transmission side, for example, a transmission wave modulated by a VCO (voltage controlled oscillator) in the transmitter 102 is transmitted via the transmission antenna 10, and on the reception side, a plurality of antennas constituting a reception array are transmitted. The reflected wave of the transmitted transmission wave is received by 11-1 to 11-L. A beat signal is generated by mixing the received signal with a local signal (VCO output) having the same frequency as that of the transmission signal, and the beat signal is converted into a digital signal by the analog / digital converters 104-1 to 104-L. Then, the digital beam synthesis circuit 105 that has captured the digital signal performs digital beam forming processing (digital signal processing such as weighting including phase calculation and addition to each beat signal) based on the amplitude and phase information of each signal. By doing so, beam forming is performed.

  Next, the effect obtained by the radar antenna of the present embodiment will be quantitatively shown with reference to FIG. 3 and FIG. Here, FIG. 3A is an explanatory diagram for explaining the frequency change of the beam directivity in the radar antenna of the present embodiment, and FIG. 3B is an explanatory diagram for explaining the frequency characteristic of the tilt variation, The result by a simulation experiment is shown. FIG. 4 is an explanatory diagram of a beam directivity frequency change (FIG. 4B) and a tilt fluctuation frequency characteristic (FIG. 4B) by a conventional radar antenna to which the present invention is not applied.

  In FIG. 3 (a), a tilt angle = 1 ° is given at a center frequency Fo = 76.5 GHz, and beam characteristics of a single unit (one subarray) in transmission and reception (in the figure, one-dot chain line and two points, respectively) (Shown by a chain line) has a slight asymmetry, but there is no problem in radar performance with respect to a radar beam obtained by combining transmission and reception (shown by a broken line in the figure).

  In addition, at F ′ = 77 GHz in which the frequency fluctuates, the single beam characteristics in transmission and reception fluctuate in directions intersecting each other, but as a radar beam direction (indicated by a solid line in the figure) that combines transmission and reception, It almost coincides with the case of the center frequency Fo. Further, as shown in FIG. 3B, the fluctuation of the radar beam has a fluctuation component that is not completely canceled because the frequency characteristic of the guide wavelength λg is not linear, but the tilt angle is within a band of ± 0.5 GHz. Is within Δτ = ± 0.007 °, indicating that it can be suppressed sufficiently smaller than the beam width.

  Further, when compared with the frequency characteristics of the beam directivity and the tilt fluctuation by the conventional radar antenna shown in FIG. 4, the conventional technique has Δτ = ± 0.6 ° with respect to the frequency fluctuation Δf = ± 0.5 GHz. The tilt variation is generated, and the effect of the present invention is clearly shown.

  Next, it will be described that the tilt variation due to the temperature change can be suppressed according to the radar antenna of the present embodiment. Although the slot interval (pitch) P and the waveguide width also change due to mechanical expansion and contraction due to temperature change, a change in tilt occurs. By applying the present invention, it is the same as the suppression of tilt change due to frequency change. The tilt fluctuation due to the temperature change can be canceled by the action.

  As described above, in FIG. 1, the interval between the slots 22 in the waveguide slot array 10 of the transmission antenna is Pt = λg / 2 + δ at the center frequency Fo, and the waveguide slot array 11− of the reception antenna (reception array 11). Beam tilt in which the interval between the slots 23 in 1 to 11-L is Pr = λg / 2−δ is performed.

The pitch expansion Δp of the transmitting antenna and the receiving antenna due to the temperature change T is given by the following equation.
Δp = αT (λg / 2 ± δ) ≈αTλg / 2 (7)
Here, α: linear expansion coefficient.

At this time, when the tilt angle τ of the transmitting antenna and the receiving antenna is obtained from the equation (4) with the slot interval P = λg / 2 ± δ + Δp, the following equation is obtained.
τt = (+ δ + Δp) / Pt · (λ / λg) ≈τ + Δτ
τr = − (− δ + Δp) / Pr · (λ / λg) ≈τ−Δτ
^{Δτ ≒ 2Δp · λ / λg 2} , τ ≒ 2δ · λ / λg 2 ... (8)
Therefore, the tilt variation due to expansion and contraction of the slot interval due to the temperature change of the transmission antenna and the reception antenna becomes the same magnitude and intersects each other, so that the variation is canceled on the transmission side and the reception side as the radar beam of the radar antenna. .

  Similarly, with respect to the change in the waveguide width due to the temperature change, it is similarly derived that the transmission antenna and the reception antenna have the same amount of tilt fluctuation in the opposite direction. Therefore, it has been proved that the tilt fluctuation canceling effect of the present invention is effective against expansion and contraction fluctuation due to temperature change.

  As described above, in the antenna (radar antenna) of the present embodiment, the transmission antenna using the sub-array subjected to beam tilt as the waveguide slot array 10, and the direction of the beam tilt applied to the transmission antenna is the transmission antenna. L sub-arrays (waveguide slot arrays 11-1 to 11-L of the receiving array 11) that are inversely symmetric with respect to the sub-array of the sub-array so that the traveling direction of the radio waves of the sub-array is inversely symmetric with the sub-array of the transmitting antenna. The sub-array groups having substantially the same structure constituting the transmitting antenna and the receiving antenna are arranged so that the traveling direction of the radio wave and the direction of the beam tilt with respect to the traveling direction are inversely symmetric with each other. Since it is configured and arranged in the transmitter antenna and receiver antenna (due to frequency fluctuation or temperature change) Belt fluctuation becomes a direction crossing each other at the same size, the variation of the radar beam is offset by transmit and receive antennas can always be obtained a directivity of a predetermined direction. As a result, in a radar antenna having a plurality of sub-arrays having substantially the same structure subjected to beam tilt, tilt fluctuation and gain reduction caused by this can be suppressed.

[Example 2]
Next, FIG. 5 is a configuration diagram of an antenna according to Embodiment 2 of the present invention. FIG. 5A is a perspective view showing a relative arrangement relationship between the subarray 30 of the transmitting antenna and the receiving array 31 of the receiving antenna, and FIG. 5B is a subarray 30 and 31-i (i = 1 to L; (L is a positive integer).

      In FIG. 5, the antenna (radar antenna) of this embodiment has a configuration in which 1 + L sub-arrays having substantially the same structure subjected to beam tilt are provided, and a waveguide slot array having a vertical axis slot is used as the sub-array. That is, the waveguide slot array 30 is provided as a transmitting antenna, and the waveguide slot arrays 31-1 to 31-L are provided as receiving antennas.

      First, the waveguide slot array 30 of the transmission antenna is configured to perform in-phase power feeding by arranging the slots 42 with the interval of about λg on the waveguide wall surface, and is provided on the antenna surface (waveguide wall surface having the slot 42). The traveling wave antenna obtains a linearly polarized radiation beam (fan beam) in the vertical direction. Further, in order to cancel the phase of the reflected wave from the slot 42, beam tilt is performed by slightly shifting the interval between the slots 42 from λg. Here, the interval (pitch) P between the slots 42 is set to P = It is set as λg + δ.

Also, as shown in the figure, the input end 44 that is the input end of the radio wave is arranged so as to be on the lower side with respect to the figure, and the traveling direction of the radio wave in the waveguide is from the lower side with respect to the figure. The direction is upward. Here, the tilt angle τ and the slot interval P have the following relationship.
sinτ = {(P−λg) / λg} / (P / λ) (9)
From the equation (9), the tilt angle τ is given by the following equation.
τ≈sinτ = (δ / P) · (λ / λg) (10)
In other words, the waveguide slot array 30 of the transmitting antenna has a tilt in the direction of travel that is upward (positive in the direction of travel) with respect to the drawing.

      On the other hand, also in the waveguide slot arrays 31-1 to 31-L of the receiving array 31, the slots 43 are arranged on the wall surface of the waveguide with a distance of about λg, similarly to the waveguide slot array 30 of the transmitting antenna. However, as the beam tilt, the interval (pitch) P of the slots 43 is P = λg−δ at the center frequency Fo, and the tilt angle is −τ. That is, the tilt is in the direction opposite to the traveling direction and has a tilt characteristic that is inversely symmetric with respect to the waveguide slot array 30 of the transmitting antenna.

      In addition, the input end 45 is placed on the upper side with respect to the drawing and is arranged in an inverse symmetry with the waveguide slot array 30 of the transmitting antenna, and the traveling direction of the radio wave in the waveguide as the sub-array is lower from the upper side with respect to the drawing. The direction will be to the side. (However, since it is used for reception, the actual traveling direction of the radio wave is the direction toward the input end 45 opposite to the case of transmission.) With this reverse symmetrical arrangement, the waveguide slot array 31 of the reception array 31 is used. Also in −1 to 31-L, the tilt direction is upward with respect to the figure, and the beam direction of transmission / reception as a radar antenna coincides upward.

Further, as in the first embodiment, regarding the variation in the beam direction due to the frequency, the transmission beam direction when the frequency varies to F = Fo + Δf is given by the following equation.
τt = τ + Δτ
Δτ≈ (λ / λg) · (Δf / Fo) (11)

The direction of the received beam is −τ + Δτ with respect to the traveling direction as the subarray, but is given by the following equation for the radar antenna due to the upside down arrangement of the transmitting antenna and the receiving antenna.
τr = − (− τ + Δτ) = τ−Δτ (12)
Therefore, the tilt fluctuations of the transmitting antenna and the receiving antenna are the same magnitude and intersect each other, so the radar beam of the radar antenna cancels the fluctuations on the transmitting side and the receiving side, and always obtains a directivity characteristic in a certain direction. Will be.

Further, the pitch expansion Δp of the transmitting antenna and the receiving antenna due to the temperature change T is given by the following equation.
Δp = αT (λg ± δ) ≈αTλg (13)
Here, α: linear expansion coefficient.

At this time, when the slot angle P = λg ± δ + Δp and the tilt angle τ of the transmitting antenna and the receiving antenna is obtained from the equation (10), the following equation is obtained.
τt = (+ δ + Δp) / Pt · (λ / λg) ≈τ + Δτ
τr = − (− δ + Δp) / Pr · (λ / λg) ≈τ−Δτ
Δτ≈Δp · λ / λg ² , τ≈δ · λ / λg ² (14)
Therefore, the tilt variation due to expansion and contraction of the slot interval due to the temperature change of the transmission antenna and the reception antenna becomes the same magnitude and intersects each other, so that the variation is canceled on the transmission side and the reception side as the radar beam of the radar antenna. .

  Similarly, with respect to the change in the waveguide width due to the temperature change, it is similarly derived that the transmission antenna and the reception antenna have the same amount of tilt fluctuation in the opposite direction. Therefore, it can be proved that the tilt fluctuation canceling effect according to the present invention is effective against expansion and contraction fluctuation due to temperature change.

      As described above, in the antenna (radar antenna) of this embodiment, the transmission antenna having the waveguide slot array 30 as the sub-array subjected to the beam tilt, and the direction of the beam tilt subjected to the beam tilt is the transmission antenna. L subarrays (waveguide slot arrays 31-1 to 31-L of the receiving array 31) that are inversely symmetric with respect to the subarray of the subarray so that the traveling direction of the radio waves of the subarray is inversely symmetric with the subarray of the transmitting antenna. The sub-array groups having substantially the same structure constituting the transmitting antenna and the receiving antenna are arranged so that the traveling direction of the radio wave and the direction of the beam tilt with respect to the traveling direction are inversely symmetric with each other. Since it is configured and arranged in the transmitter antenna and receiver antenna (due to frequency fluctuation or temperature change) Belt fluctuation becomes a direction crossing each other at the same size, the variation of the radar beam is offset by transmit and receive antennas can always be obtained a directivity of a predetermined direction. As a result, in a radar antenna having a plurality of sub-arrays having substantially the same structure subjected to beam tilt, tilt fluctuation and gain reduction caused by this can be suppressed.

      In the first and second embodiments described above, the subarray is a waveguide slot array, the first embodiment uses an axial parallel slot, and the second embodiment uses a vertical axis slot. There are various types of slot patterns to be cut.

      FIG. 6 is an explanatory diagram for explaining the positional relationship of slots cut on the waveguide. In the figure, the axial parallel slot of the first embodiment uses the slot Se, and the axial vertical slot of the second embodiment uses the slot Sc. In addition, the slot Sa does not radiate because the direction of the slot and the direction of the current flowing through the waveguide wall surface coincide with each other. The present invention can be applied to the oblique slot Sd or Sf that is cut or the waveguide slot array that uses the parallel slot Sd that is cut parallel to the tube axis on the short side surface of the waveguide. In this case, the slot interval is approximately λg, and the same operations and effects as in the second embodiment are achieved.

Example 3
Next, FIG. 7 is a configuration diagram of an antenna according to the third embodiment of the present invention, and is a perspective view showing a relative arrangement relationship between a transmitting array 50 of a transmitting antenna and a receiving array 51 of a receiving antenna.

      In FIG. 7, the antenna (radar antenna) of this embodiment is provided with 2 + L sub-arrays (L is a positive integer of 2 or more) having substantially the same structure to which beam tilt is applied, and is similar to the conventional example (FIG. 8) as a sub-array. This is a configuration using a waveguide slot array of axially parallel slots having the structure described above. That is, waveguide slot arrays 50-1 and 50-2 and a distributor 106 are provided as transmitting antennas, and waveguide slot arrays 51-1 to 51-L are provided as receiving antennas.

      First, in the transmission antenna, the input signal is equally divided by the distributor 106 and fed to the waveguide slot array pairs 50-1 and 50-2 in the same phase. The waveguide slot array 50-1 is a traveling wave antenna for providing a fan-shaped beam with respect to the antenna surface by arranging slots on the wall surface of the waveguide alternately at the left and right intervals with an interval of about λg / 2. It is. In addition, in order to cancel the phase of the reflected wave from the slot, beam tilt is performed by slightly shifting the slot interval from λg / 2. Here, the slot interval (pitch) P is set to P = λg / 2 + δ at the center frequency Fo. It is said.

      In addition, as shown in the figure, the input end 64-1 which is the input end of the radio wave is arranged so as to be on the lower side with respect to the figure, and the traveling direction of the radio wave in the waveguide is lower than the figure. The direction is from the side to the upper side. Since the tilt angle τ and the slot interval P have the relationship of Expression (1), the tilt angle τ is given by Expression (4) as in the first embodiment. That is, the waveguide slot array 50-1 of the transmitting antenna has a tilt in the traveling direction upward (positive in the traveling direction) with respect to the drawing.

      On the other hand, in the waveguide slot array 50-2 of the transmitting antenna, slots are arranged on the wall surface of the waveguide alternately at the left and right intervals of about λg / 2, similarly to the waveguide slot array 50-1. As the beam tilt, the slot interval (pitch) P is P = λg / 2−δ at the center frequency Fo, and the tilt angle is −τ. In other words, the tilt is in the direction opposite to the traveling direction, and has a tilt characteristic that is opposite to that of the waveguide slot array 50-1 of the transmitting antenna.

      In addition, the inlet end 64-2 is located on the upper side with respect to the drawing, and is disposed in an inverse symmetry to the waveguide slot array 50-1. It will be the direction to face. With this inversely symmetric arrangement, also in the waveguide slot array 50-2, the direction of tilt is upward with respect to the figure, and the direction of the transmission beam as a transmission antenna coincides upward.

      Further, the change in the beam direction due to the frequency in the waveguide slot array pair 50-1 and 50-2 of the transmission antenna will be described. With respect to the waveguide slot array 50-1, transmission when the frequency changes to F = Fo + Δf. The beam direction is given by equation (5), and the waveguide slot array 50-2 is given by equation (6). Therefore, since the tilt fluctuations of the waveguide slot array pairs 50-1 and 50-2 of the transmitting antenna have the same magnitude and intersect each other, the fluctuations of the transmitting antenna radar beams cancel each other and are always constant. Directional characteristics in the direction can be obtained.

      That is, the transmitting antenna 50 itself has the same function as the cancellation of the tilt variation based on the frequency variation or the temperature variation in the first and second embodiments by the transmitting antenna and the receiving antenna. Can be eliminated. Therefore, it is possible to use the transmission antenna 50 as a single element.

  That is, a radar antenna having N subarrays (N is a positive integer of 2 or more) subjected to beam tilting, and R out of N (R is the smallest positive integer of N / 2 or more). The subarrays are configured such that the beam tilt directions are the same, and the traveling directions of the radio waves of the subarrays are the same, and the N-R subarrays out of the N are arranged as beam tilts. Are arranged so as to be inversely symmetric with the R sub-arrays, and the traveling direction of the radio waves of the sub-arrays is inversely symmetric with the R sub-arrays. According to this configuration, the antenna can be used as an antenna capable of suppressing tilt fluctuation and gain reduction caused by the tilt even in applications other than radar.

  Further, in the receiving antenna (receiving array) 51, S of the L (S is the smallest positive integer of L / 2 or more) waveguide slot arrays 51-1, 51-3,. Are arranged so that the traveling directions of the radio waves of the waveguide slot arrays 51-1, 51-3,... Are the same. The S waveguide slot arrays 51-2, 51-4,... Are configured so that the direction of the beam tilt is inversely symmetric with the S waveguide slot arrays 51-1, 51-3,. The traveling direction of the radio waves of the M-S waveguide slot arrays 51-2, 51-4,... Is inversely symmetric with the S waveguide slot arrays 51-1, 51-3,. Arrange as follows. That is, half of the L sub-arrays (waveguide slot arrays) are given symmetrical tilt characteristics to each other, and are arranged so as to be vertically separated from each other, thereby canceling out the fluctuations in pairs of the two sub-arrays.

  In FIG. 7, the waveguide slot arrays 51-1, 51-3,... Have the same characteristics as the waveguide slot array 50-1, and the input ends 65-1, 65-3,. And the waveguide slot arrays 51-2, 51-4,... Are given the same characteristics as the waveguide slot array 50-2, and the input ends 65-2, 65-4,. However, the waveguide slot arrays having the reverse characteristics and the reverse arrangement need not be alternately arranged, and any arrangement may be employed as long as the number is almost the same.

  Further, when the number L of the waveguide slot arrays is an odd number, fluctuations that are not canceled out by one remain, but are combined as the entire reception antenna (reception array) 51. The contribution (variation amount) is 1 / L on the receiving side, and the characteristic of the radar antenna combined with the transmitting side is reduced to 1 / 2L, so that a sufficient improvement effect can be obtained.

      As described above, the antenna (radar antenna) according to the present embodiment is a radar antenna having 2 + L subarrays (L is a positive integer of 2 or more) subjected to beam tilt, and one of the two antennas. The sub-array is a waveguide slot array 50-1, the other sub-array is the waveguide slot array 50-2, and the direction of the beam tilt in the waveguide slot array 50-2 is the waveguide slot array 50-1. A transmitting antenna that is configured to be inversely symmetric and disposed such that the traveling direction of the radio wave of the waveguide slot array 50-2 is inversely symmetric with respect to the waveguide slot array 50-1, S sub-arrays (S is the smallest positive integer of L / 2 or more) are waveguide slot arrays 51-1, 51-3,..., And the beam tilt directions are the same. The wave guide slot arrays 51-1, 51-3,... Are arranged so that the traveling directions of the radio waves are the same, and LS waveguide slot arrays 51-2, 51-4 out of L pieces. ,... Are configured so that the beam tilt direction is inversely symmetric with the S waveguide slot arrays 51-1, 51-3,..., And the waveguide slot arrays 51-2, 51-4 are configured. ,... Are arranged so as to be reversely symmetric with respect to the S waveguide slot arrays 51-1, 51-3,.

      As described above, in the transmitting antenna and the receiving antenna, the sub-array groups having substantially the same structure constituting each of the sub-array groups are divided into two in substantially the same number, and the traveling direction of the radio wave and the beam tilt with respect to the traveling direction for each of the divided sub-array groups. Are arranged and arranged so that their directions are inversely symmetrical with each other, the tilt variation (due to frequency variation or temperature variation) of each of the sub-array groups divided into two is approximately the same in each of the transmitting antenna and the receiving antenna. The directions cross each other, and the fluctuations as radar beams are canceled by those of the transmitting antenna and the receiving antenna, so that a directivity characteristic in a certain direction can always be obtained. As a result, in a radar antenna having a plurality of sub-arrays having substantially the same structure subjected to beam tilt, tilt fluctuation and gain reduction caused by this can be suppressed.

      In the first to third embodiments described above, the subarrays in the transmission antenna and the reception antenna have been described as a basic configuration including a single-row slot array. However, in an actual radar antenna, a double-row slot array is used. It is also possible to construct a subarray. The vertical axis directivity of a single slot array, that is, the horizontal plane directivity as a radar, is a non-directional or very broad beam. When beam shaping is performed to obtain the desired beam width characteristics and directivity gain. There are many. As a general method, the horizontal beam width can be narrowed and the gain in the front direction can be increased by increasing the number of rows of the slot array.

      In the first to third embodiments, the inlet end of the waveguide slot array has a corner shape, but this is for the purpose of mounting to reduce the positive area of the device by backside feeding. Needless to say, this is not related to the basic principle of the present invention.

      Furthermore, the present invention is not limited to the waveguide slot array used in the first to third embodiments, and can be applied to all traveling wave antennas such as a planar antenna of a printed antenna or a microstrip antenna. In particular, traveling wave power supply is effective for a vertically long element that requires a fan-shaped beam, and a technique for giving a beam tilt for improving reflection is widely used. For example, a microstrip antenna designed with a beam tilt is disclosed in Iizuka et al., “In-vehicle millimeter-wave radar antenna”, 2001 IEICE General Conference SB-1-7.

1 is a configuration diagram of an antenna according to Embodiment 1 of the present invention, and FIG. 1A is a perspective view showing a relative arrangement relationship between a waveguide slot array 10 of a transmitting antenna and a receiving array 11 of a receiving antenna. (B) is a cross-sectional view of the waveguide slot arrays 10 and 11-i. 1 is a configuration diagram of a radar apparatus to which a radar antenna of Example 1 is applied. FIG. 3A is an explanatory diagram for explaining the frequency change of the beam directivity in the radar antenna of this embodiment, and FIG. 3B is an explanatory diagram for explaining the frequency characteristic of the tilt variation. It is explanatory drawing of the frequency characteristic (FIG.4 (b)) of the beam directivity by the conventional radar antenna (FIG.4 (b)), and the frequency characteristic (FIG.4 (b)) of tilt fluctuation. FIG. 5A is a configuration diagram of an antenna according to Embodiment 2 of the present invention, and FIG. 5A is a perspective view showing a relative arrangement relationship between a waveguide slot array 30 of a transmitting antenna and a receiving array 31 of a receiving antenna; (B) is a cross-sectional view of the waveguide slot arrays 30 and 31-i. It is explanatory drawing explaining the positional relationship of the slot cut | disconnected on a waveguide. It is a block diagram of the antenna which concerns on Example 3 of this invention, and is a perspective view which shows the relative arrangement | positioning relationship of the transmission array 50 of a transmitting antenna, and the receiving array 51 of a receiving antenna. FIG. 2 is a basic configuration diagram of the conventional waveguide slot array (FIG. 1A) and an explanatory diagram illustrating the principle thereof (FIG. 2B).

Explanation of symbols

1, 10, 11-1 to 11-L, 30, 31-1 to 31-L, 50-1, 50-2, 51-1 to 51-L, waveguide slot array, 2, 20, 21, 40, 41... Waveguide, 3, 22, 23, 42, 43... Slot, 4, 24, 25, 44, 45, 64-1, 64-2, 65-1 to 65- L ... Inlet, 10 ... Transmitting antenna, 11 ... Receiving antenna (receiving array), 101 ... Radar antenna, 102 ... Transmitter, 103-1 to 103-L ... Receiving , 104-1 to 104-L ... analog / digital converter, 105 ... digital beam combining circuit, 106 ... distributor

Claims (6)

A transmitting antenna in which beam tilt is applied and N subarrays (N is a positive integer) having the same beam tilt direction are arranged so that the traveling directions of radio waves of the subarray are the same;
The beam tilt is applied, and the direction of the beam tilt is M (M is a positive integer) subarrays that are inversely symmetric with respect to the N subarrays of the transmitting antenna, and the traveling direction of the radio waves of the subarrays is N of the transmitting antennas. A receiving antenna arranged to be inversely symmetric with the subarray of
An antenna comprising: An antenna having N subarrays (N is a positive integer of 2 or more) to which beam tilt is applied,
R subarrays (N is a minimum positive integer of N / 2 or more) out of the N subarrays are configured such that the beam tilt directions are the same, and the traveling directions of the radio waves of the subarrays are the same. Arrange to be the same,
The NR subarrays of the N are configured such that the beam tilt direction is inversely symmetric with the R subarrays, and the traveling direction of the radio waves of the subarrays is the R subarrays. An antenna characterized by being placed in reverse symmetry. An antenna provided with N + M subarrays (N and M are positive integers of 2 or more) each having a beam tilt,
R subarrays (N is a minimum positive integer of N / 2 or more) out of the N subarrays are configured such that the beam tilt directions are the same, and the traveling directions of the radio waves of the subarrays are the same. The NR subarrays out of the N subarrays are arranged so that the direction of the beam tilt is inversely symmetric with the R subarrays, and the radio waves of the subarrays travel. A transmitting antenna arranged such that its direction is inversely symmetric with respect to the R sub-arrays;
The S subarrays out of the M (S is the smallest positive integer greater than or equal to M / 2) are configured so that the beam tilt directions are the same, and the traveling directions of the radio waves of the subarrays are mutually different. The M-S subarrays of the M are arranged so as to be the same, and the direction of the beam tilt is inversely symmetric with the S subarrays, so that the radio waves of the subarrays travel A receiving antenna arranged such that its direction is inversely symmetric with respect to the S sub-arrays;
An antenna comprising:   The antenna according to any one of claims 1 to 3, wherein the subarray is a traveling wave antenna that requires a fan-shaped beam and has a vertically long element shape.   The antenna according to claim 1, wherein the subarray is a waveguide slot antenna. The antenna according to any one of claims 1 to 4, wherein the sub-array is a planar antenna of a printed antenna or a microstrip antenna.

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