JP6569435B2 - Array antenna - Google Patents

Description

  The present invention relates to an array antenna in which horn antenna elements are arranged one-dimensionally or two-dimensionally.

  In an array antenna in which horn antenna elements are arranged one-dimensionally or two-dimensionally, the interval between horn antenna elements needs to be less than one wavelength at the upper limit frequency of the frequency band to be used. The reason is that a grating lobe occurs in the antenna radiation pattern when the element interval is one wavelength or more. If the element interval is set to less than one wavelength in the high frequency region and an opening area with a certain extent is provided, the number of horn antenna elements increases. As the number of horn antenna elements increases, a power feeding combining circuit that feeds power to each horn and synthesizes radio waves received by the horn becomes larger. In order to reduce the size of the power feeding and synthesizing circuit, there is an array antenna including a lattice-shaped conductor that divides a horn opening into a plurality of parts (for example, see Patent Document 1).

US Patent Application Publication No. 2013/0141300

  By dividing the opening of one horn with a grid-like conductor, it can be handled as a plurality of horn antenna elements each having a sub-opening obtained by dividing the opening of one horn. However, the section conductor has only a portion close to the opening, and due to the influence of electromagnetic coupling between adjacent horn antenna elements, the phase center of each antenna element exists not on the center of the sub-opening but on the side of the horn. become. As a result, the phase center interval between adjacent horn antenna elements is alternately long and short. There is a problem that the longer interval becomes longer than one wavelength and a grating lobe is generated.

  The present invention has been made in order to solve the above-described problems, and is an array antenna in which a plurality of horn antenna elements in which a single horn opening is divided by a conductor are arranged in a one-dimensional or two-dimensional array. An object is to prevent the occurrence of grating lobes.

The array antenna according to the present invention includes at least an inner surface made of a conductive material, a horn having an opening, the opening being divided into a plurality of sub-openings, and electrically connected to the inner surface of the horn. A sub-opening barycentric line that is a straight line passing through the sub-opening barycentric center passing through the sub-opening barycentric center as a plane figure of the cross-sectional shape of each sub-opening and a section conductor made of a conductive material on the surface Are arranged in a one-dimensional or two-dimensional array, and in the conductor region surrounding all the sub-openings belonging to the horn antenna, all the sub antennas are arranged. opening a groove so as to surround without a break is provided to be adjacent in the direction in which the horn antenna is arranged, different said sub of the sub-apertures belonging to the horn antenna The distance between the opening centroid, the horn antenna is characterized in that less than minimum emission wavelength is most wavelengths shorter wave wavelengths in the radio wave radiated.

  According to the present invention, the generation of grating lobes can be prevented with an array antenna in which a plurality of horn antenna elements in which the opening of one horn is divided by a conductor are arranged in a one-dimensional or two-dimensional array.

1 is a perspective view of an array antenna according to Embodiment 1 of the present invention. 3 is an enlarged perspective view of a part of the array antenna according to Embodiment 1. FIG. It is the perspective view which expanded a part in the state before attaching the patch conductor and board | substrate of the array antenna which concerns on Embodiment 1. FIG. 3 is a plan view of the array antenna according to Embodiment 1. FIG. It is a top view in the state before attaching the patch conductor and board | substrate of the array antenna which concern on Embodiment 1. FIG. It is the top view which expanded a part in the state before attaching the patch conductor and board | substrate of the array antenna which concerns on Embodiment 1. FIG. FIG. 3 is a cutaway end view taken along line AA shown in FIG. 2. FIG. 3 is an end view of a cut portion taken along line BB shown in FIG. 2. 2 is a functional block diagram of an antenna apparatus having an array antenna according to Embodiment 1. FIG. It is a figure explaining the phase center in the array antenna which does not have the patch conductor as a comparative example. 6 is a diagram for explaining a phase center in the array antenna according to the first embodiment. FIG.

Embodiment 1
1 is a perspective view of an array antenna according to Embodiment 1 of the present invention. The array antenna 100 includes a plurality of horn antennas 10 linearly arranged in the longitudinal direction and arranged in a plurality of rows in the short direction. The aperture surfaces of the horn antenna 10 are arranged so that the array aperture surface, which is the aperture surface of the array antenna 100, becomes a flat surface. FIG. 1 shows a case where 17 horns are arranged in the longitudinal direction and 6 rows are arranged in the short direction. Note that the horn antennas 10 may be arranged in a one-dimensional array.

  In the two central rows of the array antenna 100, the positions of the horn antennas 10 adjacent to each other in the short direction are shifted from each other in the longitudinal direction. When viewed as a whole, the central portion in the lateral direction protrudes on one side in the longitudinal direction, and is recessed on the opposite side. As shown in FIG. 1, the short direction of the array antenna 100 is the X direction, the long direction perpendicular to the short direction is the Y direction, and the direction perpendicular to the X direction and the Y direction is the Z direction. The Z direction is the direction of the array antenna 100, that is, the direction of the main lobe.

  FIG. 2 shows an enlarged perspective view of a range 50 indicated by a broken line in FIG. In FIG. 1 and FIG. 2, the dielectric substrate 2 (illustrated in FIG. 4) on which the patch conductor 1 is placed is seen through. FIG. 3 is a perspective view of the same part as FIG. 2 before the patch conductor 1 and the substrate 2 are attached. FIG. 4 shows a plan view of the array antenna according to the first embodiment with the patch conductor 1 and the substrate 2 attached. In FIG. 5, the top view in the state before attaching the patch conductor 1 and the board | substrate 2 is shown. FIG. 6 is an enlarged plan view of a range 60 indicated by a broken line in FIG. In FIG. 6, the patch conductor 1 is indicated by a broken line. FIG. 7 is a cutaway end view taken along line AA shown in FIG. FIG. 8 is an end view of the cut portion taken along line BB shown in FIG. In the cut end view, only the object existing on the plane to be cut is represented. As will be described later, FIGS. 6 and 7 show the dimensions of each part of the array antenna 100.

  As shown in FIGS. 1 to 7, the opening of the horn 6 is provided with a grid-like segmented conductor 4 for providing four sub-openings 3 having congruent sectional shapes. The cross-sectional shape of the four sub-openings 3 is a square with a corner. The section conductor 4 is a cross-shaped plate member having a predetermined thickness and width. The section conductor 4 is formed integrally with the horn frame body 5. The horn frame body 5 is a member having a function for connecting to a horn wall portion constituting the horn 6 and an adjacent horn 6. All the horn frame bodies 5 and the segment conductors 4 are integrally formed. That is, the opening side of the array antenna 100 of the first embodiment is integrally formed. This member is called an opening surface member. The opening surface member is formed by cutting a metal plate having good conductivity such as aluminum so that the opening and the sub-opening 3 are provided for each horn 6. Similarly, the other portions of the array antenna 100 are formed by cutting an aluminum plate. The array antenna 100 is formed by overlapping aluminum plates and integrated with a fastening member (not shown).

  A plurality of horns 6 may be formed respectively and arranged in an array. Alternatively, the segment conductor 4 may be formed separately from the horn frame body 5, and the segment conductor 4 may be attached to the horn frame body 5. The horn 6 and the segmented conductor 4 may not be all conductors, and may be a resin layer provided with a conductor layer. The horn 6 only needs to be made of a material having at least an inner surface thereof having conductivity. The segment conductor 4 may be made of a material having at least a surface having conductivity. It is only necessary that the inner surface of the horn 6 and the surface of the segmented conductor 3 are electrically connected.

  As can be seen from FIGS. 2 and 4, the substrate 2 on which the patch conductor 1 is mounted is attached to the opening surface of the array antenna 100. As shown in the plan view of FIG. 6, each patch conductor 1 is disposed approximately at the center of each corresponding sub-opening 3. More precisely, the opening conductor is located at a position passing through the sub-opening centroid 11 that is the center of gravity of the cross-sectional shape of the sub-opening 3 as a plane figure and passing through the sub-opening centroid line that is perpendicular to the cross-section of the sub-opening 3. A certain patch conductor 1 is arranged. A surface perpendicular to the sub-opening center of gravity line on the opening side of the sub-opening 3 is a sub-opening surface.

  Even when the aperture projection shape, which is a plane figure obtained by projecting the patch conductor 1 onto the sub-opening surface, has a missing part inside and the sub-opening center of gravity 11 exists in the missing part, the sub-opening center of gravity line passes through the patch conductor 1. And Precisely, it is assumed that the sub-opening centroid line passes through the patch conductor 1 when the sub-opening centroid 11 exists inside the smallest convex figure including the projected shape of the opening surface of the patch conductor 1. Here, the convex figure is a figure in which a point on a line segment connecting any two points in the figure exists in the figure.

  As can be seen from FIG. 7 and FIG. 8, in the square of the cross section at the portion connected to the waveguide and the square of the cross section on the opening surface side, the opening surface side is larger, and the length of the side of the opening in a curved shape Becomes bigger.

  Now, the structure of an antenna device using the array antenna 100 will be described. FIG. 9 is a functional block diagram of an antenna apparatus having an array antenna according to the first embodiment. The array antenna 100 has a plurality of horn antennas 10. A polarization adder 21 that adds circular polarization to radio waves is connected to the waveguide side of each horn antenna 10. Note that the polarization adder may add linearly polarized waves instead of circularly polarized waves. In addition, when there is no need to add polarization, no polarization adder is provided.

  The plurality of polarization adders 21 are integrated into a single waveguide by the synthesis circuit unit 22 in a stepwise manner, and are connected to the branching circuit 23. When viewed from the branching circuit 23 side, one waveguide is branched in stages in the synthesis circuit unit 22 and connected to a plurality of sets of the polarization adder 21 and the horn antenna 10. A transmitter 25 is connected to the demultiplexing circuit 23 via a transmission power supply circuit 24, and a receiver 27 is connected via a reception power supply circuit 26. The demultiplexing circuit 23 supplies the transmission signal from the transmission power supply circuit 24 to the synthesis circuit 22 and supplies the reception signal received by the array antenna 100 from the synthesis circuit 22 to the reception power supply circuit 26.

  The array antenna 100 radiates radio waves with the Z direction shown in FIG. Also, radio waves coming from the direction opposite to the Z direction can be received efficiently. Here, the wavelength of the shortest wavelength among the radio waves radiated from the array antenna 100 is referred to as the shortest radiation wavelength. The shortest radiation wavelength is expressed by a variable λ.

The length of each part will be described. Define the following variables: FIG. 6 shows a sub-opening center of gravity 11 which is a center of gravity as a figure of the sub-opening 3 in some horn antennas 10 by small white circles.
L _H : Length of one side of the horn antenna 10 P: Length of positional deviation in the X direction of the horn antennas 10 arranged in the Y direction. P≈L _H / 4.
W _L : The length of one side of the opening of the horn 6.
W _S : The length of one side of the sub-opening 3.
W ₁ : The width of the section conductor 4. W ₁ = W _L −2W _S.
W ₂ : The width of the horn frame 5. W ₂ = L _H −W _L ≧ W ₁ .
L ₁ : distance between adjacent sub-opening centroids 11 in the same horn antenna 10.
L ₁ = (L _H −W ₂ ) / 2.
L ₂ : Distance between the sub-opening centroids 11 adjacent to each other with the horn frame 5 in the X direction.
L ₂ = (L _H −W ₁ ) / 2 ≧ L ₁ .
L ₃ : Distance between the sub-opening centroids 11 adjacent to each other across the horn frame 5 in the Y direction.
L ₃ = √ (L ₂ ² + P ² ) ≧ L ₂ .
r: Diameter of the patch conductor 1
d: The depth of the groove 7.
h: thickness of the substrate 2.

The array antenna 100 determines the dimensions of each part so that the following holds.
L ₁ ≦ L ₂ ≦ L ₃ <λ (1)
λ <L _H = L ₁ + L ₂ (2)

  Equation (1) is a condition for setting the interval between the horn antenna elements to be less than the shortest radiation wavelength λ so that no grating lobe is generated. Equation (2) indicates that the length of one side of the horn antenna 10 can be made larger than the shortest radiation wavelength λ by operating the horn antenna 10 as four horn antenna elements by the segment conductor 4.

In order to describe the operation of the patch conductor 1 of the present invention, the operation of the array antenna without the patch conductor 1 and the groove 7 will be described as a comparative example. FIG. 10 is a diagram for explaining a phase center in an array antenna having no patch conductor as a comparative example. In FIG. 10, the phase center 12 of each horn antenna element is indicated by a small cross. The following is defined as a variable expressing the distance between the phase centers 12 of adjacent horn antenna elements in the comparative example.
L _1D : Distance between phase centers 12 of adjacent horn antenna elements in the same horn antenna 10.
L _2D : Distance between phase centers 12 of adjacent horn antenna elements with the horn frame 5 sandwiched in the X direction.
L _3D : Distance between phase centers 12 of adjacent horn antenna elements across the horn frame 5 in the Y direction.

When one horn 6 is divided by the segmented conductor 4 only in the vicinity of the aperture surface, the segmented conductor 4 is not only in the vicinity of the aperture, but is electromagnetically coupled to the adjacent horn antenna 10. Rather than the inner surface of the horn 6. Therefore, the interval L _1D between the phase centers 12 of adjacent horn antenna elements in the same horn 6 in the comparative example is wider than the interval L ₁ between the sub-opening centroids 11. Further, the distances L _2D and L _3D between the phase centers 12 of the horn antenna elements adjacent in the X direction or the Y direction across the horn frame body 5 in the comparative example are larger than the distances L ₂ and L ₃ of the sub-opening center of gravity 11. Narrow. Therefore, even when the relationship of equation (1) is established, the relationship is as follows.
L _2D <L _3D <λ <L _1D (3)
Equation (3) means that the phase center interval L _1D is longer than the minimum emission wavelength λ, and a grating lobe is generated.

FIG. 11 is a diagram for explaining the phase center in the array antenna according to the first embodiment. By providing the patch conductor 1 and the groove 7, the phase center 12 becomes substantially the same position as the sub-opening gravity center 11. The following is defined as a variable expressing the distance between the phase centers 12 of adjacent horn antenna elements in the first embodiment.
L _1S : Distance between phase centers 12 of adjacent horn antenna elements in the same horn antenna 10.
L _2S : Distance between phase centers 12 of adjacent horn antenna elements across the horn frame 5 in the X direction.
L _3S : Distance between phase centers 12 of adjacent horn antenna elements across the horn frame 5 in the Y direction.

The distances L _2S and L _3S between the phase centers 12 of the horn antenna elements adjacent to each other in the X direction or the Y direction across the horn frame 5 in the first embodiment are _{equal to} the distances L ₂ and L ₃ of the sub-opening center of gravity 11. It will be almost the same. The interval L _1S between the phase centers 12 of adjacent horn antenna elements in the same horn 6 in the first embodiment is substantially the same as the interval L ₁ between the sub-opening centroids 11. That is, the following relationship is established.
L _1S <L _2S <L _3S <λ (4)
Equation (4) means that the phase center intervals L _1S, L _2S, and L _3S are shorter than the minimum radiation wavelength λ, and no grating lobe is generated. Incidentally, generally greater than the width W ₁ of it is partitioned conductor 4 the width W ₂ of the horn frame body 5, the relation of _L 1 _<L 2 _{<L 3} is satisfied, the phase center 12 subaperture centroid L _1s = L _2s when it is slightly on the inner surface side of the horn 6 than 11. Further, it is only necessary that the phase center 12 exists in the vicinity of the sub-opening center of gravity 11 such that MAX (L _1S , L _2S , L _3S ) <λ holds.

  In the present invention, the phase center 12 of the sub-opening approaches the sub-opening center of gravity 11 mainly due to the action of the patch conductor 1. The patch conductor 1 is a circular thin plate. The diameter r of the patch conductor 1 is about ¼ of the minimum radiation wavelength λ. The patch conductor 1 is disposed outside the sub opening 3 in the Z direction and substantially at the center of the sub opening 3 on the XY plane. If the diameter r of the patch conductor 1 is ½ of the minimum emission wavelength λ, the radio wave having the minimum emission wavelength λ resonates with the patch conductor 1. In the resonated state, all radio waves enter the patch conductor 1 and are not radiated to the outside of the horn 6. If the diameter r of the patch conductor 1 is reduced, the resonance is weakened and radio waves can be emitted to the outside. In addition, the patch conductor 1 having a diameter r of less than ½ of the minimum radiation wavelength λ acts to attract radio waves to the patch conductor 1, that is, to bring the phase center 12 closer to the sub-opening center of gravity 11. The position and diameter r of the patch conductor 1 are appropriately determined in consideration of the position of the phase center 12 and the radiation efficiency. When radiating radio waves having a plurality of wavelengths, the position and the diameter r of the patch conductor 1 are determined in consideration of all the wavelengths of the radiated radio waves. The diameter r of the patch conductor 1 determined in this way is a value less than ½ of the minimum radiation wavelength λ.

  The planar shape of the main surface of the patch conductor 1 is preferably circular, but may not be circular. Although a convex figure is desirable, it may not be a convex figure. In the case of a plane figure that is not circular, the length of the longer side of the smallest rectangle that surrounds the plane figure affects the resonance between the patch conductor 1 and the radio wave. The smallest rectangle that encloses a plane figure is called the smallest rectangle. The length of the longer side of the smallest package rectangle is called the smallest package length. If the minimum package length of the patch conductor 1 is ½ of the minimum radiation wavelength λ, the radio wave and the patch conductor 1 resonate. The shape and the minimum package length of the patch conductor 1 are determined so that the resonance is moderately weakened and the radio wave is appropriately attracted to the patch conductor 1. The minimum envelope length determined in this way is less than ½ of the minimum radiation wavelength λ.

  One of the causes that the phase center 12 approaches the wall surface side of the horn 6 is that the adjacent horn antennas 10 are electromagnetically coupled because the horn frame 6 between the horn antennas 10 is a conductor. In order to electromagnetically isolate the horn antenna 10, a groove 7 is provided so as to surround the horn 6, that is, the four sub-openings 3 without interruption. The depth d of the groove 7 is in the range of about 1/5 to about 3/10% of the minimum emission wavelength λ. When the array antenna 100 radiates only radio waves having the minimum radiation wavelength λ, if the depth of the groove 7 is d = λ / 4, the radio waves are opposite in phase on both sides of the groove 7 and cancel each other. Becomes weaker. When radiating radio waves of a plurality of wavelengths, the depth of the groove 7 is determined in consideration of the degree of electromagnetic coupling with radio waves of a plurality of wavelengths. The depth d of the groove 7 thus determined is in the range of about 1/5 to about 3/10% of the minimum radiation wavelength λ.

  Since the patch conductor 1 is mounted on the dielectric substrate 2, the patch conductor 1 is separated from the opening surface in the Z direction by the thickness h of the substrate 2. By adjusting the dielectric constant and thickness h of the substrate 2, the reflection characteristics of the horn antenna 10 can be adjusted. The dielectric constant and thickness h of the substrate 2 are determined so that the reflection is as small as possible. The patch conductor 1 may be placed on the horn antenna 10 side of the dielectric substrate 2.

  The shape of the sub-opening 3 as a planar figure is a square with a corner. To take a corner is to exclude a portion including the vertex of a corner by a curve or a straight line from a range determined from the vertex of the corner. The range excluding the corners is appropriately determined. It is not necessary to take a corner at all. Squares with corners are also called squares. The shape of the sub-opening section as a plane figure is preferably a square, but may be a rectangle, another kind of quadrangle, or a polygon other than a quadrangle. A rectangle, square or polygon with a corner is also called a rectangle, square or polygon.

  In this embodiment, the opening of the horn 6 is divided into four sub-openings 3 having a congruent square shape. The number of divisions may be any number other than 4, such as 2, 3, 6, 9. In the case of dividing into four, it is desirable that all the sub-openings have a congruent shape, but all the sub-openings may not be congruent.

  The present invention can be modified and omitted from the embodiments within the spirit of the invention.

1 Patch conductor (opening conductor)
2 Substrate 3 Sub-aperture 4 Section conductor 5 Horn frame 6 Horn 7 Groove 10 Horn antenna 11 Sub-opening center of gravity 12 Phase center 21 Polarization adder 22 Synthesizing circuit 23 Demultiplexing circuit 24 Transmitting power supply circuit 25 Transmitter 26 Receiving power supply Circuit 27 Receiver 50 Range 60 Range 100 Array antenna

Claims (7)

A horn having at least an inner surface made of a conductive material and having an opening;
The opening is divided into a plurality of sub-openings, electrically connected to the inner surface of the horn, and at least the surface is a segmented conductor made of a conductive material;
A plurality of opening conductors arranged at positions passing through a sub-opening centroid as a plane figure of a cross-sectional shape of each of the sub-openings and passing through a sub-opening centroid line that is a straight line perpendicular to the cross-section of the sub-opening; The horn antennas provided are arranged in a one-dimensional or two-dimensional array,
In the conductor region surrounding all the sub-openings belonging to the horn antenna, a groove is provided so as to surround all the sub-openings seamlessly,
The distance between the sub-opening centroids of the sub-openings that are adjacent in the direction in which the horn antennas are arranged and belong to different horn antennas is the wavelength of the shortest wave among the radio waves radiated by the horn antenna An array antenna characterized by being smaller than the minimum radiation wavelength. The opening conductor is a plate-like shape arranged in parallel to a sub-opening surface that is a plane perpendicular to the sub-opening barycenter line,
2. The array antenna according to claim 1, wherein the length of the longer side of the rectangle having the smallest area surrounding the planar shape of the main surface of the opening conductor is less than half of the minimum radiation wavelength.   The dielectric material which mounted the said opening part conductor arrange | positioned at the array opening surface which is a plane in which the opening surface of all the said horn antennas is arrange | positioned was provided. Array antenna.   The array antenna according to claim 2, wherein the shape of the main surface of the opening conductor is circular.   The array antenna according to any one of claims 1 to 4, wherein the segmented conductor divides the opening into four sub-openings having a congruent cross-sectional shape.   The array antenna according to any one of claims 1 to 5, wherein the sub-opening has a square cross-sectional shape. The array antenna according to any one of claims 1 to 6, wherein a depth of the groove is in a range of 1/5 to 3/10 of the minimum emission wavelength .

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