JP2010183567A - Slot array antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To configure a high gain and high quality slot array antenna in which a side lobe is suppressed. <P>SOLUTION: A waveguide 30 for radiation has first and second conductive planes which are perpendicular, and a side surface which closes their end portions, and configures a guiding wave space in its inside. An array of a plurality of slots 31S is formed in front of the waveguide 30 for radiation. A disposition pitch of the slots 31S is about a half of a guide wavelength of a used frequency. A conductive plate 61 is provided so that the upper portion space of a slot is tapered by two conductive plates which forms a pair while sandwiching the slot 31S. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a slot array antenna used as an antenna for radar, communication and broadcasting.

  A slot array antenna in which a plurality of slots that resonate with transmitted and received electromagnetic waves are arranged on the side surface of a waveguide generally has a low gain and a high sidelobe level. To improve this characteristic, an amplitude aperture is used. Patent Document 1 discloses a slot array antenna having a desired distribution.

  Further, Patent Document 2 discloses a parallel plate slot antenna which uses a rectangular parallel plate waveguide and cancels reflections from each other by using two slots as radiating element units and suppresses reflection by the slots. Yes.

  Also, a radiation waveguide having a first conductor plane in which a slot array is arranged two-dimensionally and a second conductor plane parallel to the first conductor plane, and a slot for introducing electromagnetic waves into the waveguide space of the radiation waveguide Patent Document 3 discloses a slot array antenna having an introduction waveguide formed with an array.

JP-A-2-288708 Japanese Patent No. 2526393 International Publication No. 2008/018481 Pamphlet

  In the slot array antennas disclosed in Patent Document 1 and Patent Document 2, the intensity of the electromagnetic wave radiated from each slot cannot be controlled. In order to control the directivity of the antenna, a method of weighting the intensity of the electromagnetic wave radiated from each slot is effective. However, in the slot array antenna shown in Patent Documents 1 and 2, the structure In addition, since such weighting cannot be performed, directivity cannot be controlled.

  Furthermore, in Patent Documents 1 and 2, the distribution of the electromagnetic wave intensity radiated from a plurality of slots formed on one of the two conductor planes constituting the waveguide space cannot be controlled, so that optimal sidelobe control cannot be performed. There was also a problem.

  According to the slot array antenna shown in Patent Document 3, each slot of the slot array formed in the introduction waveguide has a plurality of peaks of electric field intensity distribution in the electromagnetic wave propagation direction in the emission waveguide and Since the high-order mode electromagnetic waves arranged in the vertical and horizontal directions are excited, the slot formed in the radiating waveguide shields the high-order mode tube wall current at an arbitrary position and transmits the electromagnetic waves from the first conductor plane. It becomes possible to radiate.

FIG. 1A is a diagram showing a configuration example of a slot array antenna according to Patent Document 3, and FIG. 1B is a diagram showing its coordinate system. However, in order to facilitate comparison with the embodiment of the present invention described later, in FIG. 1, the slot pattern is different from the example of the slot array antenna disclosed in Patent Document 3.
In FIG. 1A, a plurality of slots 31 are arranged vertically and horizontally on the upper surface of the radiation waveguide 30. The introduction waveguide 20 is joined to the lower surface of the radiation waveguide 30.

  A slot 21 is formed on the upper surface of the introduction waveguide 20. A radio wave absorber 34 is provided at one end of the radiation waveguide 30 on the side away from the introduction waveguide 20. The other end (the end close to the introduction waveguide 20) and the two side surfaces facing each other are short-circuited surfaces.

  However, it has been found that the slot array antenna disclosed in Patent Document 3 has a problem of side lobe under certain conditions when it is used as an antenna for a marine radar, for example.

  FIG. 2 is a diagram showing the directivity characteristics of the slot array antenna shown in FIG. 2, the horizontal axis represents the azimuth angle θ in the xz plane shown in FIG. 1B, and the vertical axis represents the radiation intensity. In FIG. 2, the curve indicated by HP is the radiation intensity of horizontal polarization, and the curve indicated by VP is the radiation intensity of vertical polarization.

  Thus, when the xz plane, that is, φ = 0 °, the sidelobe ratio at θ = 45 ° and θ = 135 ° is about −36 dB.

  On the other hand, FIG. 3 is a diagram showing the relationship between φ and radiation intensity at θ = 45 °. The horizontal axis is φ, and the vertical axis is the radiation intensity. In FIG. 3, the curve indicated by HP is the radiation intensity of horizontal polarization, and the curve indicated by VP is the radiation intensity of vertical polarization. When φ = 0 °, the radiation intensity (side lobe) at θ = 45 ° is as low as −20 dBi, but the radiation intensity at φ = ± 10 ° rises to about +10 dBi. Since the peak value of the main lobe is +32 dBi, the intensity ratio of the side lobe is increased to −22 dB.

  For example, when used as an antenna for a relatively large marine radar, since the antenna is installed on a stabilizer that keeps the installation surface horizontal, the vertical inclination φ is always approximately 90 ° even if the vessel is shaken, Although the problem of side lobe as shown in FIG. 3 does not occur, when applied to a radar antenna for a small ship that does not use a stabilizer, φ = ± 10 °, θ = 45 °, θ = 135 ° (front Side lobes generated in the vicinity of ± 45 ° from the direction) are a problem.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a slot array antenna having high gain and high efficiency and suppressing side lobes.

In order to solve the above problems, the slot array antenna of the present invention is configured as follows.
(1) A slot array antenna according to the present invention includes a first conductor plane on which a slot array is formed, a second conductor plane parallel to the first conductor plane, and ends of the first and second conductor planes. A radiation waveguide composed of a conductor side surface that closes the portion, and an electromagnetic wave introduction means for introducing an electromagnetic wave into the waveguide space of the radiation waveguide,
The slot array is arranged so that the main polarization planes of the electric field radiated by coupling to the electromagnetic waves in the radiation waveguide are directed in the same direction and the polarization components orthogonal to the main polarization planes cancel each other. In the slot array antenna formed in parallel in the electromagnetic wave propagation direction (second direction) of the waveguide and the direction orthogonal to the direction (first direction),
A plurality of conductor plates standing vertically or substantially perpendicular to the first conductor plane between slots adjacent to each other in the electromagnetic wave propagation direction of the radiation waveguide in the slot array formed on the first conductor plane. It is provided with.

(2) The electromagnetic wave introduction means includes, for example, an introduction waveguide having a slot array for introducing electromagnetic waves into the waveguide space, and excitation means for exciting the electromagnetic waves in the introduction waveguide. Each slot of the slot array formed in the waveguide for the waveguide transmits high-order mode electromagnetic waves in which a plurality of magnetic field loops are arranged in the electromagnetic wave propagation direction (first direction) of the introduction waveguide to the radiation waveguide. It is arranged so as to excite it.

(3) The height of the conductor plate corresponds to, for example, approximately half the wavelength used.

(4) The slot array formed in the introduction waveguide is, for example, oriented in the electromagnetic wave propagation direction of the introduction waveguide and in the electromagnetic wave propagation direction of the radiation waveguide within a range that is within the interval between the conductor plates. It is an inclined slot inclined in a direction perpendicular to.

(5) The plurality of conductor plates are provided, for example, so that the upper space of the inclined slot is tapered with two conductor plates paired with the inclined slot interposed therebetween.

According to the present invention, the following effects can be obtained.
A radiating waveguide having a slot array and an electromagnetic wave introducing means for introducing an electromagnetic wave into the radiating waveguide serve as a slot array antenna, and the radiating waveguide of the slot array formed on the radiation surface. Predetermined with the electromagnetic wave propagation direction (x axis) of the radiating waveguide as the central axis by the action of a plurality of conductor plates standing vertically or substantially perpendicular to the radiation surface between slots adjacent to the electromagnetic wave propagation direction of the tube Side lobes appearing in a predetermined azimuth angle θ direction centered on a direction (y axis) perpendicular to the electromagnetic wave propagation direction of the radiating waveguide with an elevation angle φ of.

  In addition, the upper space of the plurality of inclined slots provided on the radiation surface of the radiation waveguide is tapered by the two conductor plates that make a pair, whereby the electromagnetic wave propagation of the radiation waveguide is achieved. The magnetic field component in the direction is suppressed, and the side lobe is suppressed.

FIG. 1A is a diagram showing a configuration example of a slot array antenna according to Patent Document 3, and FIG. 1B is a diagram showing its coordinate system. However, in order to facilitate comparison with the embodiment of the present invention, the slot pattern is different from the example of the slot array antenna disclosed in Patent Document 3. It is a figure which shows the directional characteristic of the slot array antenna shown by FIG. It is a figure which shows the relationship between (phi) and radiation intensity in (theta) = 45 degree. FIG. 4A is an external perspective view of the slot array antenna according to the first embodiment before the grid-like conductor plate is attached. FIG. 4B is a plan view of the slot array antenna. FIG. 5A is a plan view showing the positional relationship between the slots formed in the radiating waveguide 30 and the conductor plate and their dimensions. FIG. 5B is a partial perspective view showing a support structure for a plurality of conductor plates. 6A shows an example of the electromagnetic wave propagation mode in the introduction waveguide 20, and FIG. 6B shows the electromagnetic wave propagation mode in the emission waveguide together with the electromagnetic wave propagation mode in the introduction waveguide. It is a figure which shows an example. 7A is a characteristic diagram of a slot array antenna having a conventional structure without the conductor plate 41, and FIG. 7B is a slot according to the embodiment of the present invention in which the conductor plate 41 shown in FIGS. 4 and 5 is provided. It is a characteristic view of an array antenna. FIG. 8A shows the magnetic fluxes MFL1 and MFL2 blown out from the two inclined slots 31Sa and 31Sb and the resultant magnetic flux MFL0. FIG. 8B is a diagram showing a state in which a lattice for suppressing the vertical polarization generated from the slots 31Sa and 31Sb is inserted. FIG. 9A is a plan view of a type B slot array antenna, and FIG. 9B is a view of the radiating waveguide 30 viewed in the electromagnetic wave propagation direction (second direction). 10A is a plan view of a type C slot array antenna, and FIG. 10B is a cross-sectional view taken along line XX in FIG. 10A. 11A is a plan view of a type D slot array antenna, and FIG. 11B is a cross-sectional view taken along line XX in FIG. 11A. 12A is a plan view of a type E slot array antenna, and FIG. 12B is a cross-sectional view taken along line XX in FIG. It is a figure which shows the measurement result of the directivity of a type A slot array antenna. It is a figure which shows the measurement result of the directivity of a slot array antenna of type B. It is a figure which shows the actual measurement result of the directivity of a type C slot array antenna. It is a figure which shows the measurement result of the directivity of a type D slot array antenna. It is a figure which shows the measurement result of the directivity of a slot array antenna of type E.

<< First Embodiment >>
The slot array antenna according to the first embodiment will be described with reference to FIGS.
FIG. 4A is an external perspective view of the slot array antenna according to the first embodiment before the grid-like conductor plate is attached. FIG. 4B is a plan view of the slot array antenna.

  This slot array antenna is roughly composed of an introduction waveguide 20, a radiation waveguide 30, and a lattice-shaped conductor plate 41. The introduction waveguide 20 is provided to introduce electromagnetic waves into the radiation waveguide 30 and includes an excitation means inside and a slot as described later. The radiating waveguide 30 has parallel first and second conductor planes and side surfaces that close end portions thereof, and forms a waveguide space therein. A plurality of slot arrays are formed on the upper surface of the radiation waveguide 30 in the figure, but are not shown in FIG. The introduction waveguide 20 and the radiation waveguide 30 are manufactured by punching and bending an aluminum plate as will be described later.

  As shown in FIG. 4B, a plurality of slots 31S and 31V are arranged vertically and horizontally in the first conductor plane metal plate 30a which is the front surface (upper surface in the figure) of the radiation waveguide 30. Yes. These slots include a transverse slot 31V in a direction transverse to the electromagnetic wave propagation direction (second direction) of the radiation waveguide 30 and the electromagnetic wave propagation direction (first direction) of the introduction waveguide 20. ) And inclined slots (31S) that are inclined with respect to each other.

  The radiation waveguide 30 includes a first conductor plane metal plate 30a and a second conductor plane metal plate 30b parallel to the first conductor plane metal plate 30a. The first conductor plane metal plate 30 a extends from the upper surface of the radiation waveguide 30 to a part of the lower surface via the side surface. The second conductor plane metal plate 30 b forms the main part of the lower surface of the radiation waveguide 30. The first conductor plane metal plate 30a and the second conductor plane metal plate 30b are joined together by screws.

  The introduction waveguide 20 is configured by joining an aluminum plate bent into a substantially rectangular saddle shape to the second conductor plane metal plate 30b with a plurality of screws.

  A slot 21 is formed on the top surface of the introduction waveguide 20 (the surface in contact with the second conductor plane metal plate 30b of the radiation waveguide 30). Accordingly, the second conductor plane metal plate 30b serves as both the lower surface of the radiation waveguide and the upper surface of the introduction waveguide.

  A radio wave absorber 34 is provided at one end of the radiation waveguide 30 on the side away from the introduction waveguide 20. The other end (the end close to the introduction waveguide 20) and the two side surfaces facing each other are short-circuited surfaces. The distance from the short-circuited side surface to the nearest slot in the electromagnetic wave propagation direction (first direction) of the introduction waveguide 20 (the direction orthogonal to the electromagnetic wave propagation direction of the emission waveguide 30) is λg ′ / 2. (Λg ′ is the guide wavelength in the direction perpendicular to the electromagnetic wave propagation direction in the radiation waveguide 30). In addition, the distance from the end near the introduction waveguide 20 to the slot closest to the electromagnetic wave propagation direction (second direction) of the radiation waveguide 30 is λg ″ / 2 (λg ″ is for radiation). In-tube wavelength in electromagnetic wave propagation direction in waveguide 30). Thereby, the electromagnetic wave propagation direction (x-axis direction) of the radiation waveguide 30 is used as a traveling wave type, and the direction (y-axis direction) orthogonal to the electromagnetic wave propagation direction of the radiation waveguide 30 is used as a resonance type. Thus, if the short side direction of the radiating waveguide 30 is a resonance type, a large number of slots can be arranged even if the short side is shortened, which is advantageous for downsizing.

  The joint between the first conductor plane metal plate 30a and the second conductor plane metal plate 30b is a position corresponding to a node of the tube wall current determined by the mode of the electromagnetic wave propagating in the radiation waveguide 30. It is said. This prevents leakage of radio waves at the junction (discontinuous portion) between the first conductor plane metal plate 30a and the second conductor plane metal plate 30b.

  These slots 31S and 31V are formed by, for example, an NC turret punch in a sheet metal state before the side portion is bent.

  Alternatively, a foamed low dielectric constant dielectric may be attached between the metal plates, and the dielectric may be used as a waveguide space. With this structure, a sandwich structure of a dielectric and a metal plate is formed, and the rigidity of the entire antenna can be increased.

  FIG. 5A is a plan view showing the positional relationship between the slots formed in the radiating waveguide 30 and the conductor plate and their dimensions. FIG. 5B is a partial perspective view showing a support structure for a plurality of conductor plates.

  In FIG. 5A, the slots 31S and 31V provided in the radiation waveguide 30 are 3 columns × 64 rows. The arrangement pitch Ps in the second direction (x-axis direction) of the slots 31S and 31V is 12.5 mm, which is about ¼ of the in-tube wavelength of the operating frequency 9.41 GHz. In practice, as will be described later, in order to improve the VSWR (voltage standing wave ratio) of the antenna, the dimension is slightly larger than 1/4 of the guide wavelength. The conductor plate 41 extends in the first direction (y-axis direction) at a substantially central position between the slots 31S and 31V adjacent to each other in the second direction (x-axis direction), and the front surface (first conductor) of the radiation waveguide 30. Stand perpendicular to the plane. Therefore, the arrangement pitch Pp of the conductor plates 41 is equal to the arrangement pitch Ps of the slots 31S and 31V in the second direction (x-axis direction). The height H of these conductor plates 41 is 15 to 16 mm, which is a dimension corresponding to approximately ½ wavelength at the operating frequency.

  The radiation waveguide 30 has a length L of 895.5 mm and a width A of 88.8 mm. Since the width W of the conductor plate 41 protrudes from the width A of the radiating waveguide 30 by the dimension S, the dimension is (A + 2S), and S = 3 mm, so W = 94.8 mm. The thickness t of the conductor plate 41 is 1 mm.

  In addition, by making the width of the conductor plate 41 in the first direction larger than the width of the radiation waveguide 30 in the first direction, the conductor plate 41 effectively works against electromagnetic waves that wrap around from the side of the radiation waveguide 30. Thus, the side lobe suppression effect is enhanced.

  As shown in FIG. 5B, the plurality of conductor plates 41 are connected and supported by support members 42 and 43 at positions away from the conductor plane of the radiation waveguide 30. As shown in FIG. 5 (B), the support member 42 is fitted into the notches formed near both sides of the upper side of each conductor plate 41, and the other pair of support members 43 are formed on the left and right sides of the conductor plate 41. It fits in the formed cut | notch part, respectively. The plurality of conductor plates 41 are bonded to the upper surface of the radiation waveguide 30 by an insulating bonding material or a conductive bonding material. At the same time, the plurality of conductor plates 41 and the two pairs of support members 42 and 43 are also bonded by an insulating or conductive bonding material.

  In this way, the plurality of conductor plates 41 are each formed of a metal plate, and by providing the support members 42 and 43 that connect the plurality of metal plates at positions away from the conductor plane of the radiation waveguide 30, The conductor plate 41 can be disposed on the radiation surface of the radiation waveguide 30 with high accuracy, and interference between the radiation waveguide 30 and the support members 42 and 43 can be avoided.

  In order to increase the positional accuracy of each conductor plate 41 with respect to the radiating waveguide 30, a cut portion having a width corresponding to the width A of the radiating waveguide 30 is provided at the lower side of each conductor plate 41. The lower side of the conductor plate 41 may be slightly fitted to the radiation waveguide 30.

FIG. 6A shows an example of an electromagnetic wave propagation mode in the introduction waveguide 20.
In the example of FIG. 6A, an excitation probe is provided inside the introduction waveguide 20, and power is supplied to the excitation probe from the outside via a coaxial connector. The introduction waveguide 20 is used in a resonance type in which both ends or one end thereof are short-circuited and a standing wave is generated inside. A broken line loop in the figure represents a magnetic field loop that circulates so as to surround a portion having a high electric field strength. In addition, a solid line arrow that spans between adjacent magnetic field loops represents the direction and distribution of the tube wall current. The slot 21 is arranged so as to block this tube wall current.

  In the example shown in FIG. 6A, the slot 21 is located at a position offset to the right from the center line CL-CL indicated by a one-dot chain line that faces the electromagnetic wave propagation direction (first direction) of the introduction waveguide 20 and In addition, they are arranged at a half-wavelength pitch of the in-tube wavelength λg along the electromagnetic wave propagation direction of the introduction waveguide 20.

  With such a structure, these slots 21 block the tube wall current, and electromagnetic waves having an electric field directed in the direction indicated by the straight arrow Es are emitted from each slot 21.

  FIG. 6B shows an example of an electromagnetic wave propagation mode in the introduction waveguide and an electromagnetic wave propagation mode in the radiation waveguide. 6A, the two-dot chain line loop is a magnetic field loop of a resonance mode (standing wave) in the introduction waveguide, and in FIGS. 6A and 6B, the broken line loop is a radiation guide. Each represents a magnetic field loop of electromagnetic waves excited in the wave tube.

  In the structure shown in FIG. 6B, the TEn0 mode electromagnetic wave is propagated in the waveguide space S of the radiation waveguide by the electromagnetic wave radiated from the slot 21 of the introduction waveguide 20. That is, when the in-tube wavelength of the introduction waveguide 20 is represented by λg, the slots 21 formed in the introduction waveguide 20 are arranged for each λg / 2, so that the direction of the electric field is alternately reversed. Electromagnetic waves are radiated in the direction. Therefore, the TEn0 mode is generated in the waveguide space S. Here, n is the number of peaks of the electric field strength distribution in the width direction (first direction) of the radiation waveguide 30. Hereinafter, this mode is referred to as a TE mode high-order mode.

  In the waveguide space S in the radiation waveguide shown in FIG. 6B, a broken-line loop represents a magnetic field loop that circulates so as to surround a portion having a high electric field strength. In addition, a solid line arrow that spans between adjacent magnetic field loops represents the direction and distribution of the tube wall current.

  The slot 31S formed in the radiating waveguide 30 is formed at the position where the tube wall current flowing in the first direction is blocked by the higher-order mode, and the direction of the radiated electric field is directed in the same direction. The slots 31S are inclined alternately (in series). That is, the main polarization plane of the radiation electric field is coupled to the higher-order mode electromagnetic wave in the waveguide space S so as to face the same direction, and the polarization components orthogonal to the main polarization plane cancel each other.

  The slot 31V formed in the radiating waveguide 30 is formed at a position where the tube wall current flowing in the second direction is blocked by the higher-order mode, and the direction of the radiated electric field is the same direction. The offsets d in the first direction are alternately provided so as to face. That is, the main polarization plane of the radiation electric field is coupled to the higher-order mode electromagnetic wave in the waveguide space S so as to face the same direction, and the polarization components orthogonal to the main polarization plane cancel each other.

  Since the combined vector of the electric field components of the electromagnetic waves radiated from the plurality of slots 31S and 31V faces the electromagnetic wave propagation direction (second direction) of the radiating waveguide 30, the second direction of the slot array antenna is set horizontally. When placed, this slot array antenna can be used as a horizontally polarized antenna.

  As shown in FIG. 4B, the inclination of the slot 31S formed in the radiating waveguide 30 decreases as the distance from the center of the radiating waveguide 30 in the electromagnetic wave propagation direction (second direction) increases to both ends. You may comprise so that it may become. Similarly, the offset d of the slot 31V may be configured so as to decrease as it moves away from the center of the electromagnetic wave propagation direction (second direction) of the radiating waveguide 30 toward both ends. The greater the inclination of the slot 31S, the greater the angle formed with the direction of the tube wall current to be blocked, and the greater the offset d of the slot 31V, the greater the amount of blocking the wall current, so that the radiation efficiency is increased. When the inclination angle of the slot 31S is 0, and when the offset d of the slot 31V is 0, the electromagnetic wave radiation amount is almost 0 because the tube wall current is hardly interrupted. Accordingly, by setting the inclination of the slot 31S and the offset d of the slot 31V as described above, the radiation intensity becomes maximum at the center in the longitudinal direction (second direction) of the radiation waveguide 30, and as the distance from the center increases. The radiation intensity distribution gradually decreases. Thereby, generation | occurrence | production and intensity | strength of a side lobe can be suppressed.

  In the example described above, the electromagnetic wave propagation direction (second direction) of the radiation waveguide 30 is used as a traveling wave type. However, the electromagnetic wave propagation direction (second direction) may be used as a resonance type. it can. In that case, a radio wave absorber is not provided at one end of the radiation waveguide 30 on the side away from the introduction waveguide 20, and a short-circuit surface is provided. Then, the distance from the short-circuited surface to the nearest slot in the electromagnetic wave propagation direction of the radiation waveguide may be set to ½ of the in-tube wavelength in the electromagnetic wave propagation direction in the radiation waveguide 30. The distances from the other three short-circuit planes to the slots are the same as in the traveling wave type.

The characteristics of the slot array antenna according to the embodiment of the present invention shown in FIGS. 4 and 5 are shown in FIGS. 7 (A) and 7 (B).
7A shows the characteristics of the conventional slot array antenna without the conductor plate 41 shown in FIG. 1, and FIG. 7B shows the present invention with the conductor plate 41 shown in FIGS. This is a characteristic of the slot array antenna according to the embodiment.

  7A and 7B, the horizontal axis represents θ, and the vertical axis represents radiation intensity. Further, the curve R0 represents the directivity characteristics of horizontal polarization at φ = 0, R1 at φ = −10 °, R2 at φ = + 10 °, and R3 at φ = + 60 °. Curve Rv is the directivity characteristic of vertical polarization at φ = 0.

  When the conductor plate 41 is not provided, as shown in FIG. 7A, relatively large side lobes are generated around φ = ± 10 ° and θ = 45 ° and 135 °. When the side lobe at the same angle when φ = + 60 ° is 0 dB, the side lobe at φ = ± 10 ° is +2 dB to +4 dB.

  On the other hand, by providing the conductor plate 41, as shown in FIG. 7B, the side lobes at φ = ± 10 ° and θ = 45 ° and 135 ° are suppressed to about −6 dB to −8 dB. I understand that Moreover, when θ = 90 ° and φ = 0, the radiation intensity in the front direction does not decrease.

  Note that the center orientation of the main lobe deviates from 90 ° because the arrangement pitch Ps of the slots 31S and 31V in the second direction (x-axis direction) is improved in order to improve the antenna VSWR (voltage standing wave ratio). Is slightly different from ¼ of the guide wavelength.

  Thus, when φ = ± 10 °, the side lobes near θ = 45 ° and 135 ° decrease because the phase of the electromagnetic wave radiated from the slots 31S and 31V is synthesized along the path along the conductor plate. It is inferred that this is caused by That is, among the electromagnetic waves radiated from the slots 31S and 31V, a part of the electromagnetic waves propagates along the surface of the conductor plate 41 in the azimuth in which the azimuth angle θ shown in FIG. Therefore, a phase difference is generated between the electromagnetic wave and the electromagnetic wave directly radiated regardless of the conductor plate 41. It is presumed that the radiation intensity to the predetermined azimuth angle θ is suppressed by this phase synthesis.

<< Second Embodiment >>
In the example shown in FIGS. 4 and 5, the plurality of conductor plates 41 are arranged so as to be in contact with the front surface (formation surface of the slots 31 </ b> S and 31 </ b> V) of the radiation waveguide 30. An example of a case where a gap exists between the front surface of the metal plate and the conductor plate 41 is shown.

  The main configuration of the slot array antenna is as shown in the first embodiment. Radiation when the gap between the upper surface of the radiation waveguide 30 shown in FIGS. 4 and 5 and the lower side of the conductor plate 41 is changed to 0 (contact), 1 mm, and 2 mm in the first embodiment. The change in intensity is shown in Table 1.

  As described above, even if the gap between the conductor plate 41 and the radiation waveguide 30 is small and not conducting in a direct current, φ = 0 °, θ = 0 °, that is, the radiation intensity in the front direction is almost reduced. do not do. It can also be seen that the side lobe radiation intensity of φ = 10 ° and θ = 135 ° has a smaller suppression effect as the gap increases. However, it can be seen that there is still a suppression effect compared to the case where the conductor plate 41 is not provided.

  The components of vertical polarization in the directions of φ = 0 ° and θ = 135 ° increase as the gap increases. When the gap is gradually increased, it can be said that there is no practical problem even if the gap exists if the radiation intensity of the vertically polarized wave does not become larger than when the conductor plate 41 does not exist.

  In the example described above, an example of an end feed type configuration in which electromagnetic waves are fed from one end of the radiation waveguide 30 by the introduction waveguide 20 is shown. The present invention can be similarly applied to a center feed type in which the introduction waveguide 20 is disposed in the lower portion of the center portion.

<< Third Embodiment >>
A slot array antenna according to a third embodiment will be described with reference to FIGS.
In the three-row two-dimensional array antenna shown in the first and second embodiments, a problem has been found that side lobes that may cause problems appear. For example, when the front direction of the antenna was swung ± 10 degrees in the vertical direction (elevation angle / depression angle direction), the side lobe rose to −22 dB in comparison with the main lobe.

  In the third embodiment, in order to solve this problem, a slot array antenna that solves the above-described problem is studied by performing the following procedure.

(1) The side lobe characteristics of the transverse slots 31V and the inclined slots 31S arranged at a half pitch (first and second embodiments) are grasped.

(2) Consider the case where the transverse slots 31V are eliminated and only the inclined slots 31S are used.

(3) A grating is provided to suppress the vertical polarization of the inclined slots 31S.

  First, with the half pitch structure of (1), when the lattice is erected, there is some effect in reducing the side lobes, but it is difficult to reduce the side lobes that exit from the transverse slot 31V. From this, it was found that the effect of correcting the vertical shift of the slot is small with a simple lattice. Therefore, the transverse slot 31V that generates a side lobe due to the vertical displacement of the slot is eliminated, and only the inclined slot 31S is provided. The side lobe that exits from the inclined slot 31S is caused by the slot tilting left and right and the upper and lower ends of the slot shifting left and right.

  Here, the electromagnetic field deviation due to the inclined slot 31S is shown in FIG. FIG. 8A shows magnetic fluxes MFL1 and MFL2 blown out from the two inclined slots 31Sa and 31Sb and the resultant magnetic flux MFL0. The resultant magnetic flux MFL0 bends as shown by the curve WW and has a component in the horizontal direction (horizontal direction), so that a vertical polarization component is generated. This is a cause of side lobe generation by the inclined slot 31S.

  FIG. 8B shows a state in which a grating for suppressing the vertical polarization generated from the slot is inserted so as to correct the electromagnetic field deviation. With this grating, the horizontal component is cut off, and the magnetic field radiated from the grating is expected to be straight in the vertical direction as shown by the straight line VV, and no side lobe is expected from the straight magnetic field. it can.

The types of slot array antennas studied below are as follows.
[Type A]
1 is a conventional slot array antenna shown in FIG. 1, in which transverse slots and inclined slots are arranged at a half pitch (12.5 mm) on a radiation surface of a radiation waveguide 30. FIG.

[Type B]
FIG. 9A is a plan view of a type B slot array antenna, and FIG. 9B is a view of the radiating waveguide 30 viewed in the electromagnetic wave propagation direction (second direction). This slot array antenna is the one shown in FIG. 5 in the first embodiment. This is a type A antenna provided with a conductor plate 41 at a half pitch (12.5 mm). The grating formed by the conductor plate 41 provided in the slot array antenna of the first embodiment is hereinafter referred to as “grating a”.

[Type C]
10A is a plan view of a type C slot array antenna, and FIG. 10B is a cross-sectional view taken along line XX in FIG. 10A. Only the inclined slots 31S are arranged at the full pitch (25 mm) on the radiation surface of the radiation waveguide 30.

[Type D]
11A is a plan view of a type D slot array antenna, and FIG. 11B is a cross-sectional view taken along line XX in FIG. 11A. This slot array antenna is a type C slot array antenna in which conductor plates 51 are arranged in a lattice pattern. These conductor plates 51 are formed by bending an aluminum plate into a bowl shape, and stand perpendicular to the radiation surface of the radiation waveguide 30 so that the space above the slot 31S is sandwiched between parallel conductor surfaces. Yes. Hereinafter, the lattice formed by the conductor plates 51 is referred to as “lattice b”.

[Type E]
12A is a plan view of a type E slot array antenna, and FIG. 12B is a cross-sectional view taken along line XX in FIG. 12A. This slot array antenna is a type C slot array antenna in which conductor plates 61 are arranged in a lattice pattern. These conductor plates 61 are formed by pressing an aluminum plate, and stand on the radiation surface of the radiation waveguide 30 so that the space above the slot 31S is narrowed by a tapered conductor surface. Hereinafter, the lattice formed by the conductor plates 61 is referred to as “lattice c”.

  The grating c is composed of a plurality of conductive plates standing between slots 31S adjacent to each other in the electromagnetic wave propagation direction of the radiating waveguide 30. Of these conductor plates, a pair of conductor plates sandwiching the slot 31S constitutes a lattice with open ends. The openings of these gratings are narrowed in the electromagnetic wave propagation direction of the radiation waveguide 30.

  FIG. 13 to FIG. 17 are diagrams showing measured results of directivity characteristics of the antennas of the type A to type E slot array antennas. In each figure, the horizontal axis represents the azimuth angle from 0 degrees to 180 degrees with the front 90 degrees, and the vertical axis represents the radiation intensity with the peak value 0 dB. In both cases, the angle in the vertical direction (elevation angle and depression angle) is a characteristic of 0 degrees.

  13 shows the directivity of a type A slot array antenna, FIG. 14 shows the directivity of a type B slot array antenna, FIG. 15 shows the directivity of a type C slot array antenna, and FIG. 16 shows the type D slot. FIG. 17 shows the directivity of the type E slot array antenna.

  Table 2 shows the result of comparing the sidelobe levels in the horizontal direction for the type A to type E slot array antennas.

  In Table 2, the HFSS simulation was performed at a frequency of 9410 MHz, 3 columns × 32 elements in width, and the actual measurement was performed in 3 columns × 101 elements in relation to calculation time.

  As described above, when the type A slot array antenna is swung ± 10 degrees in the vertical direction, the ratio of the side lobe to the main lobe increases from −29 dB to −22 dB in actual measurement, whereas the type C slot array antenna Then, it only increases from -22dB to -21dB, and it turns out that there is little increase amount.

  Further, with the type D slot array antenna, the side lobe was measured to be −30.4 dB while being swung in the vertical direction ± 10 degrees, whereas the type E slot array antenna was −34 dB. This is an effect obtained by narrowing the opening of the grating c in the electromagnetic wave propagation direction of the radiation waveguide 30.

  From the simulation results, the height of the grating c was set to 16 mm, which corresponds to approximately half the wavelength of the operating frequency. This is because the vertical polarization is suppressed most at 16 mm and worsens when it is longer than 16 mm. In consideration of the size, the thickness is set to 16 mm.

  The width of the grating c was 8 mm at the surface of the radiation waveguide 30 and 5 mm at the front end. This is because the sidelobe level was the best overall.

  The type E slot array antenna provided with the grating c shows the best value in the simulation by HFSS. However, in actual measurement, it does not agree with the calculation result of HFSS, and the side lobe rises. In addition, vertical polarization is larger than horizontal polarization. The value of HFSS is −50 dB or less, but the actual measurement is bad at −32 dB. As a result of the examination, it has been found that the cause of this is that the radio wave leaking from the gap between the grating c and the radiation waveguide 30 leaks as vertically polarized waves from above and below the antenna. By suppressing leakage from this gap, side lobes can be suppressed even for vertically polarized waves. Further, if the vertically polarized side lobes are reduced, the horizontally polarized side lobes are naturally further reduced.

  As shown in FIGS. 13 to 16, in the slot array antennas of type A to type D, side lobes exceeding −40 dB in each of the +45 degree azimuth and the −45 degree azimuth with the azimuth angle of 90 degrees as the center. However, in the type E slot array antenna according to the third embodiment, as shown in FIG. 17, the horizontally polarized side lobe is −40 dB or less.

  The reason why the vertical polarization is as high as −32 dB is that, as pointed out above, radio waves radiated from the gap between the radiation waveguide and the grating are converted into vertical polarization. If this gap is eliminated, side lobes of vertically polarized waves are greatly suppressed.

  In this way, in the slot array antenna according to the third embodiment, a characteristic in which side lobes are sufficiently suppressed can be obtained.

<< Other embodiments >>
In the slot array antenna shown in the first embodiment, an introduction waveguide 20 having a slot array for introducing electromagnetic waves is provided in the waveguide space of the radiation waveguide 30, and the radiation waveguide 30 is However, an excitation unit that directly supplies the electromagnetic wave from the electromagnetic propagation direction (lateral direction) may be provided to the radiation waveguide 30. That is, this excitation part may be used as an electromagnetic wave introducing means.

20 ... Introducing waveguide 21 ... Slot 30 ... Radiating waveguides 30a, 30b ... Conductor plane metal plate 31 ... Slot 31S ... Inclined slot 31V ... Transverse slot 34 ... Radio wave absorber 41, 51, 61 ... Conductor plate 42, 43 ... support members

Claims (5)

A radiation plane composed of a first conductor plane in which a slot array is formed, a second conductor plane parallel to the first conductor plane, and a conductor side surface closing an end of the first and second conductor planes. An electromagnetic wave introducing means for introducing an electromagnetic wave into the waveguide space of the radiation waveguide,
The slot array is arranged so that the main polarization planes of the electric field radiated by coupling to the electromagnetic waves in the radiation waveguide are directed in the same direction and the polarization components orthogonal to the main polarization planes cancel each other. In the slot array antenna formed in parallel in the electromagnetic wave propagation direction of the waveguide and the direction orthogonal to the direction,
A plurality of conductor plates standing vertically or substantially perpendicular to the first conductor plane between slots adjacent to each other in the electromagnetic wave propagation direction of the radiation waveguide in the slot array formed on the first conductor plane. Slot array antenna with   The electromagnetic wave introduction means includes an introduction waveguide having a slot array for introducing electromagnetic waves into the waveguide space, and excitation means for exciting the electromagnetic waves in the introduction waveguide, and the introduction waveguide Each slot of the slot array formed in the step is arranged so as to excite a higher-order mode electromagnetic wave with respect to the radiation waveguide, in which a plurality of magnetic field loops are arranged in the electromagnetic wave propagation direction of the introduction waveguide. The slot array antenna according to claim 1.   The slot array antenna according to claim 1, wherein the conductor plate has a height corresponding to approximately a half wavelength of a use frequency.   Each slot of the slot array formed in the first conductor plane is oriented in the direction orthogonal to the electromagnetic wave propagation direction and inclined in the electromagnetic wave propagation direction of the radiation waveguide within a range that is within the interval of the conductor plate. The slot array antenna according to claim 1, wherein the slot array antenna is an inclined slot.   5. The slot array antenna according to claim 4, wherein the plurality of conductor plates are two conductor plates that are paired with the inclined slot interposed therebetween, and are provided so that an upper space of the inclined slot is tapered. .

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