JP3569083B2 - Multi-beam phased array antenna - Google Patents

Description

を有する（２^Ｎ ）入力（２^Ｎ ）出力のバトラーマトリクス１０６ａ、その出力端子数に対応する固定移相器
【数２】

の（２^Ｎ ）個のアレー１０４ａ、素子アンテナの（２^Ｎ ）個のアレー
【数３】

、反射鏡１０７より構成されている。バトラーマトリクス１０６ａの出力端子の各々に固定移相器
【数４】

が接続され、その出力のそれぞれは素子アンテナ
【数５】

に接続されている。（２^Ｎ ）個の素子アンテナより構成されるアレーアンテナ１０５ａは反射鏡の焦点面１０８以外の場所に置かれている。バトラーマトリクスは入力信号を所定の位相差で出力端子に分配する分配回路として動作する。
【００１５】
アレーアンテナ１０５ａの配置にはふた通りが考えられ、反射鏡の焦点面１０８より反射鏡寄りの場合と、反射鏡より遠い場合である。図２と図１は、そのそれぞれに対応している。［Ｘ_ｆ 、Ｙ_ｆ 、Ｚ_ｆ ］は座標系１０９を表している。なお、原点は反射鏡の焦点１１０であり、Ｘ_ｆ Ｙ_ｆ 平面を反射鏡の焦点面１０８と定義している。Ｚ_ｆ 軸は反射鏡の開口面の中心を向き、焦点から反射鏡方向を正としている。ｉ番目（１≦ｉ≦２^Ｎ ）の素子アンテナの座標を［Ｘ_ｆｉ、Ｙ_ｆｉ、Ｚ_ｆｉ］とする。またｉ番目の移相器の設定値をφ_ｉ （位相遅れ）とする。
【００１６】
図１に関しては、仮に同相の信号を固定移相器のアレー１０４ａに加えるとき、素子アンテナ
【数６】

から放射される電波を反射鏡の焦点１１０に収れんさせることが、その役割である。アレーアンテナ１０５ａからは収れんする球面波１１２が放射される。すなわち、このためには移相器入力端子から素子アンテナを経て焦点に達する信号の経路長が、すべての信号経路において等しい必要がある。したがって、ｉ番目の固定移相器１０４ａ_ｉ によって与える位相遅れをφ_ｉ 、素子アンテナ１０５ａ_ｉ と焦点１１０との間の距離Ｌ_ｉ １１１（Ｌ_ｉ ＝（Ｘ_ｆｉ ^２ ＋Ｙ_ｆｉ ^２ ＋Ｚ_ｆｉ ^２ ）^１／２ ）とするとき、

が成立している必要がある。ただしｋは、自由空間における波数を表している。図１の場合のようにアレーアンテナ１０５ａが焦点面より反射鏡より遠い側にあるとき、中央の素子アンテナに接続した移相器ほど大きな位相遅れを与える必要があることがわかる。
【００１７】
図２のようにアレーアンテナ１０５ａが焦点面１０８より反射鏡寄りにあるときは、あたかも焦点１１０から電波が発射するのと等価であるように、移相器
【数７】

の値を設定する。つまり、アレーアンテナ１０５ａからは発散する球面波１１２が放射される。移相器
【数８】

の設定値は、

なる関係を満たす。このときアンテナアレーの外側の素子ほど大きな位相遅れを与えなければならないことがわかる。
【００１８】
仮想的に反射鏡の焦点から発した電波は反射鏡１０７に照射し、反射鏡１０７によって球面波から平面波１１３に変換されサービスエリアにビームが形成される。反射鏡１０７にはアレーアンテナ１０５の像が拡大して投影されていると考えることができる。バトラーマトリクス１０６ａの信号入力端子
【数９】

毎に異なった位相関係の信号が得られる。信号入力端子
【数１０】

により平面波１１３の放射方向はそれぞれ異なるが、等価的にアレー素子の間隔が拡大して反射鏡１０７に投影されているので、バトラーマトリクスとアレーアンテナを組み合わせて使用する場合と比較して、本発明では平面波１１３の放射方向は狭まるといえる。
【００１９】
次に、具体的な形状パラメータを設定し、本発明の構成のマルチビームアンテナのアンテナパタンを計算する。図３は本発明の一具体構成例で、アンテナパタン計算に用いるアンテナの形状を示している。開口径１１４が１０ｍ、焦点距離１１５が８ｍ、オフセット角１１６が４４°、開口半角１１７（焦点から反射鏡面を見込む角度の半分）が２９．７４°の反射鏡１０７があり、その焦点面１０８から１ｍ前方にアレーアンテナ１０５ａを配置している。素子アンテナは１９０ｍｍの円形開口のものとし、１９０ｍｍの間隔でアンテナを配置している。８入力８素子のバトラーマトリクスでは、隣接素子における位相差が±π／８、±３π／８、±５π／８、±７π／８のいずれかである。このような位相関係を有する信号を、式（３）で与えられる位相値に設定された移相器のアレーを介して１次放射器に与えるとき、反射鏡により形成されるアンテナパタンを計算した。形成されるアンテナパタンの断面をまとめて記したものが図４である。周波数は２．５ＧＨｚとした。図４では−１．６°、−１．１°、−０．７°、−０．２５°、０．２０°、０．６°、１．０°、１．５°の方向にピークを持つ８つのビームが形成されることがわかる。
【００２０】
従来の技術の項で、素子アンテナの間隔が１．５８３波長のときにアレーアンテナだけを用いたときに形成されるビームの方向は、±４．５°、±１３．７°、±２３．２°、±３３．５°となることを述べた。これは、周波数２．５ＧＨｚ（波長は１２０ｍｍ）のときに１９０ｍｍの間隔で素子アンテナを配置する場合に相当する。本発明の構成によれば、マルチビームが形成される領域は約１／２０に圧縮される効果が得られている。
【００２１】
【発明の効果】
バトラーマトリクスをアレーアンテナに接続し直接放射を行うとき、マルチビームが形成される領域は広く、その範囲を制御することが課題であった。バトラーマトリクスの出力に移相器アレーを接続し反射鏡の焦点面以外に配置したアレーアンテナと反射鏡より構成される系を考案し、このような系を用いることによりビームの形成される領域を圧縮することを可能とした。また反射鏡を使用したことにより、利得の向上と半値幅の狭さくという効果が得られる。本発明は送信アンテナ及び受信アンテナの双方に適用される。
【図面の簡単な説明】
【図１】本発明の実施の形態で、アレーアンテナを焦点面より反射鏡から遠い位置に配置した場合の構成である。
【図２】本発明の実施の形態のひとつで、アレーアンテナを焦点面より反射鏡寄りに配置した場合の構成である。
【図３】本発明の具体的構成の一例で、アンテナパタン計算に用いるアンテナの形状を示している。
【図４】本発明で得られるアンテナパタンの一計算例である。
【図５】バトラーマトリクスの構成を示したもので、回路は８入力８出力のものである。
【図６】バトラーマトリクスにより形成可能なアンテナビームパタンを表したもので、８入力８出力バトラーマトリクスを用いたときのものである。
【符号の説明】
【数１１】

１０２_１〜_８ 高周波信号出力端子
１０３_１〜_１２ ９０°ハイブリッド
【数１２】

１０４ａ 固定移相器のアレー
１０５、１０５ａ アレーアンテナ
【数１３】

１０６、１０６ａ バトラーマトリクス
１０７ 反射鏡
１０８ 反射鏡の焦点面
１０９ 座標系
１１０ 反射鏡の焦点
１１１ ｉ番目素子アンテナと焦点の距離
１１２ 球面波
１１３ 平面波
１１４ 開口系
１１５ 焦点距離
１１６ オフセット角
１１７ 開口半角[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-beam phased array antenna.
[0002]
[Prior art]
As a feeder circuit for a multi-beam phased array antenna, reference [J. Butler and R.S. Lowe, "Beam-forming matrix simplifications of electronically scanned antennas", Electronic design, Vol. 9, pp. 170-173, Apr. 1961. Describes a high-frequency matrix circuit called a "Butler matrix". The Butler matrix is a high-frequency matrix circuit having ^2N input signal terminals and output signal terminals, and configured by connecting high-frequency hybrid circuits and fixed phase shifters in multiple stages.
[0003]
FIG. 5 shows an example of an 8-element Butler matrix 106. The circuit has high-frequency signal input terminals 101 ₁ to ₈ (4L, 3L, 2L, 1L, 1R, 2R, 3R, 4R) and high-frequency signal output terminals 102 ₁ to ₈ (A to H). ₁ to ₁₂ and fixed phase shifters 104 ₁ to ₁₆ . The signal supplied to one of the signal input terminals is finally distributed to all output ports with equal signal strength by repeating the distribution by the 90 ° hybrid and the phase setting by the fixed phase shifter. The signals appearing at the output signal terminals have a phase relationship represented by an arithmetic progression, and their tolerances are different for each input signal terminal. In the case of an 8-element Butler matrix, the tolerance, that is, the phase difference between adjacent output signal terminals, is 7π / 8 for each of the input ports 4L, 3L, 2L, 1L, 1R, 2R, 3R, 4R. , 8π, 3π / 8, π / 8, -π / 8, -3π / 8, -5π / 8, -7π / 8.
[0004]
When each of the output signals of the Butler matrix is fed to the array antenna 105 composed of the element antennas 105 ₁ to ₈ arranged at equal intervals, beams having peaks in different directions corresponding to the phase relationship of the high-frequency signal are generated. It is formed. The relationship between the beam direction Θ (based on the front direction of the array antenna) and the phase difference Δψ between adjacent elements is
sinΘ = Δψ / (kd) (1)
Given by Here, d represents the element spacing of the array antenna, and k represents the wave number of the radio wave. The beam direction Θ is determined from the condition that the radio waves emitted from the element antennas are added in phase and the radio waves are strengthened.
[0005]
FIG. 6 shows a multi-beam antenna beam pattern formed when the eight-element Butler matrix of FIG. 5 is connected to the array antenna 105 (element antennas 105 ₁ to 105 ₈ ). In the calculation, the directional characteristics of the element antenna are omnidirectional, and the distance d between the element antennas is half the wavelength. With respect to inputs to the high frequency signal input terminals 101 ₁ to ₈ (4L, 3L, 2L, 1L, 1R _, 2R, 3R, 4R), respectively, −61 °, −38.7 °, −22 °, and −7. It can be seen that eight independent beams are formed in the directions of 2 °, 7.2 °, 22 °, 38.7 °, 61 °.
[0006]
In FIG. 6, beams radiated from the element antenna of FIG. 1 are named 4L, 3L, 2L, 1L, 1R, 2R, 3R, and 4R beams in order from the top. Further, when the interval between the element antennas is expanded to, for example, 1.583 wavelengths, beams are formed in directions of ± 4.5 °, ± 13.7 °, ± 23.2 °, and ± 33.5 °.
[0007]
The Butler matrix, when the number of input or output terminal and 2 ^N, the number of components constituting the circuit is on the order of _{^{2 N · log 2 (2 N}} ), multi-beam circuit scale even in multi-element array antenna Is characterized by not increasing explosively. Therefore, there is a great merit when used as a multi-beam forming circuit requiring multiple beams. However, the range of the formed beam is quite wide, and as can be seen from FIG. 6, when the distance between the element antennas is half a wavelength, the distance between the two outermost beams is 61 ° − (− 61 °) = 122 °. Become. Even if the distance between the element antennas is increased to 1.583 wavelengths, the distance between the two outermost beams is 67 °.
[0008]
[Problems to be solved by the invention]
For example, there is a case where it is desired to form a multi-beam in a narrow area such as several degrees so that a limited area of the earth from a geostationary satellite is set as a service area. When the Butler matrix is used alone, the range over which multiple beams are formed is quite large. Increasing the spacing between the element antennas can reduce the beam forming range, but there is a limit to increasing the overall size of the array antenna.
[0009]
An object of the present invention is to provide an antenna capable of forming a multi-beam in a narrow area by using a Butler matrix capable of forming a large number of beams with a small circuit scale as a feed circuit of a multi-beam phased array.
[0010]
[Means for Solving the Problems]
The present invention provides a configuration in which an array of phase shifters is provided between a Butler matrix and an element antenna, the antenna array is placed at a position off the focal plane of the reflector, and the antenna array is combined with the reflector using the antenna array as a primary radiator. Is the most main feature.
[0011]
The conventional method of connecting an antenna element to a Butler matrix and radiating radio waves directly to the space is to insert an array of phase shifters between the Butler matrix and the element antenna, and to use the array antenna as a primary radiator to transmit radio waves. The difference is that the mirror is used by irradiating it.
[0012]
In general, a Butler matrix is used by connecting to an array antenna in which element antennas are arranged linearly or in a plane as described above. At this time, the radio wave radiated from the array antenna is a plane wave having an equal phase plane. In the present invention, an array of phase shifters is connected to the subsequent stage of the Butler matrix, and a radio wave radiated from the array antenna is converted into a spherical wave by adding a specific phase distribution in the array of the phase shifters. The spherical wave radiated from the array antenna is applied to a reflecting mirror, converted from the spherical wave into a plane wave again by the reflecting mirror, and applied to a service area.
[0013]
Equation (1) shows that, when the phase difference Δψ between adjacent elements is the same, the beam direction 小 さ く becomes smaller as the distance d between the element antennas is larger. According to the configuration of the present invention, it can be considered that the array antenna used as the primary radiator is enlarged and projected on the reflecting mirror. In other words, this is equivalent to increasing the distance d between the element antennas, and an effect that a multi-beam can be formed in a narrow area is obtained as compared with the conventional method using the Butler matrix alone.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
1 and 2 show two cases of the embodiment of the present invention. The invention provides a high-frequency input terminal

(2 ^N ) input (2 ^N ) output Butler matrix 106 a having a fixed phase shifter corresponding to the number of output terminals thereof

Of ^{(2 N)} pieces of the array 104a, ^{(2 N)} pieces of the array ## EQU3 ## element antennas

, And a reflecting mirror 107. A fixed phase shifter for each of the output terminals of the Butler matrix 106a

Are connected, and each of the outputs is an element antenna

It is connected to the. An array antenna 105a composed of (2 ^N ) element antennas is placed at a place other than the focal plane 108 of the reflector. The Butler matrix operates as a distribution circuit that distributes an input signal to an output terminal with a predetermined phase difference.
[0015]
There are two possible arrangements of the array antenna 105a, and there are a case where the reflector is closer to the reflector than the focal plane 108 of the reflector and a case where it is farther than the reflector. FIG. 2 and FIG. 1 correspond to each. [X _f , Y _f , Z _f ] represents the coordinate system 109. Note that the origin is the focus 110 of the reflector _defines the X f _{Y f} plane as the focal plane 108 of the reflector. The _Zf axis points toward the center of the opening surface of the reflector, and the direction from the focal point to the reflector is positive. Let the coordinates of the i-th (1 ≦ i ≦ 2 ^N ) element antenna be [X _fi , Y _fi , Z _fi ]. The set value of the i-th phase shifter is φ _i (phase delay).
[0016]
Referring to FIG. 1, if an in-phase signal is added to the fixed phase shifter array 104a, the element antenna

The function is to converge the radio waves radiated from the reflector 110 at the focal point 110 of the reflector. A converging spherical wave 112 is emitted from the array antenna 105a. That is, for this purpose, the path length of the signal reaching the focal point from the phase shifter input terminal via the element antenna needs to be equal in all the signal paths. Therefore, the phase delay given by the i-th fixed phase shifter 104a _i is φ _i , and the distance L _i 111 (L _i = (X _fi ² + Y _fi ² + Z _fi ² ) ¹ ) between the element antenna 105a _i and the focal point 110. ^{/ 2} )

Must be established. Here, k represents a wave number in free space. When the array antenna 105a is farther from the reflector than the focal plane as in the case of FIG. 1, it is understood that the phase shifter connected to the central element antenna needs to have a larger phase delay.
[0017]
When the array antenna 105a is closer to the reflector than the focal plane 108 as shown in FIG. 2, the phase shifter ## EQU7 ## is equivalent to the emission of radio waves from the focal point 110.

Set the value of. That is, the diverging spherical wave 112 is radiated from the array antenna 105a. Phase shifter [Equation 8]

The setting value of

Satisfy the following relationship. At this time, it is understood that a larger phase delay must be given to an element outside the antenna array.
[0018]
A radio wave virtually emitted from the focal point of the reflecting mirror irradiates the reflecting mirror 107 and is converted from a spherical wave to a plane wave 113 by the reflecting mirror 107 to form a beam in the service area. It can be considered that the image of the array antenna 105 is projected on the reflecting mirror 107 in an enlarged manner. Signal input terminal of Butler matrix 106a

A signal having a different phase relationship is obtained every time. Signal input terminal [Equation 10]

Although the radiation directions of the plane waves 113 are different from each other, the distance between the array elements is equivalently enlarged and projected onto the reflecting mirror 107, so that the present invention is compared with the case where the Butler matrix and the array antenna are used in combination. Then, it can be said that the radiation direction of the plane wave 113 is narrowed.
[0019]
Next, specific shape parameters are set, and the antenna pattern of the multi-beam antenna having the configuration of the present invention is calculated. FIG. 3 shows an example of a specific configuration of the present invention, showing the shape of an antenna used for calculating an antenna pattern. There is a reflecting mirror 107 having an opening diameter 114 of 10 m, a focal length 115 of 8 m, an offset angle 116 of 44 °, and an opening half angle 117 (half the angle from the focal point to the reflecting mirror surface) of 29.74 °. An array antenna 105a is arranged 1 m ahead. The element antenna has a circular opening of 190 mm, and the antennas are arranged at intervals of 190 mm. In an 8-input, 8-element Butler matrix, the phase difference between adjacent elements is any of ± π / 8, ± 3π / 8, ± 5π / 8, ± 7π / 8. When a signal having such a phase relationship is applied to a primary radiator through an array of phase shifters set to a phase value given by Expression (3), an antenna pattern formed by a reflector is calculated. . FIG. 4 collectively shows the cross sections of the formed antenna pattern. The frequency was 2.5 GHz. In FIG. 4, peaks appear in the directions of -1.6, -1.1, -0.7, -0.25, 0.20, 0.6, 1.0, and 1.5. It can be seen that eight beams having are formed.
[0020]
In the related art section, the directions of beams formed when only the array antenna is used when the interval between element antennas is 1.583 wavelengths are ± 4.5 °, ± 13.7 °, ± 23. 2 °, ± 33.5 °. This corresponds to a case where element antennas are arranged at intervals of 190 mm when the frequency is 2.5 GHz (the wavelength is 120 mm). According to the configuration of the present invention, the effect of compressing the region where the multi-beam is formed to about 1/20 is obtained.
[0021]
【The invention's effect】
When a Butler matrix is connected to an array antenna to perform direct radiation, the area in which multiple beams are formed is wide, and it has been a problem to control the area. A system consisting of an array antenna and a reflector arranged outside the focal plane of the reflector by connecting a phase shifter array to the output of the Butler matrix is devised, and by using such a system, the area where the beam is formed can be defined. It is possible to compress. Also, the use of the reflecting mirror has the effect of improving the gain and narrowing the half-value width. The invention applies to both transmitting and receiving antennas.
[Brief description of the drawings]
FIG. 1 is a configuration according to an embodiment of the present invention when an array antenna is arranged at a position farther from a reflector than a focal plane.
FIG. 2 shows an embodiment of the present invention, in which an array antenna is arranged closer to a reflector than a focal plane.
FIG. 3 shows an example of a specific configuration of the present invention, showing an antenna shape used for antenna pattern calculation.
FIG. 4 is a calculation example of an antenna pattern obtained by the present invention.
FIG. 5 shows the configuration of a Butler matrix, and the circuit has eight inputs and eight outputs.
FIG. 6 shows an antenna beam pattern that can be formed by a Butler matrix, when an 8-input 8-output Butler matrix is used.
[Explanation of symbols]
(Equation 11)

102 ₁ to ₈ high frequency signal output terminals 103 ₁ to ₁₂ 90 ° hybrid

104a fixed phase shifter array 105, 105a array antenna

106, 106a Butler matrix 107 Reflecting mirror 108 Reflecting mirror focal plane 109 Coordinate system 110 Reflecting mirror focal point 111 Distance between i-th element antenna and focal point 112 Spherical wave 113 Plane wave 114 Aperture system 115 Focal length 116 Offset angle 117 Opening half-angle

Claims (2)

A reflector,
A distribution circuit having a plurality of high-frequency input terminals and a plurality of high-frequency output terminals, and distributing a signal of each input terminal to each output terminal with a predetermined phase difference with equal signal strength,
A phase shifter array connected to the output of the distribution circuit and having an input / output terminal corresponding to 1: 1;
An element antenna array connected to the output of the phase shifter array and located on a plane other than the focal plane of the reflecting mirror,
The distribution circuit is 2 ^N (N is a natural number) input terminals and 2 ^N Butler matrix circuit with output terminals
Said element antenna array is located between said reflector and its focal point,
The phase shifter array has an i-th (1 ≦ i ≦ 2 ^N) ) _Is [X _fi , Y _fi , Z _fi ], the set value of the i-th phase shifter is φ i , and the distance L i between the i-th element antenna and the focal point is L i = (X _fi ² + Y _fi ² + Z _fi ² ) ^1/2 , where k is the wave number in free space,

A multi-beam phased array antenna, wherein the amount of phase shift is set so that A reflector,
A distribution circuit having a plurality of high-frequency input terminals and a plurality of high-frequency output terminals, and distributing a signal of each input terminal to each output terminal with a predetermined phase difference with equal signal strength,
A phase shifter array connected to the output of the distribution circuit and having an input / output terminal corresponding to 1: 1;
An element antenna array connected to the output of the phase shifter array and located on a plane other than the focal plane of the reflecting mirror,
The distribution circuit is 2 ^N (N is a natural number) input terminals and 2 ^N Butler matrix circuit with output terminals
The element antenna array is located on the opposite side of the reflector with respect to the focal plane of the reflector,
The phase shifter array has an i-th (1 ≦ i ≦ 2 ^N) ) _Is [X _fi , Y _fi , Z _fi ], the set value of the i-th phase shifter is φ _i , and the distance L i between the i-th element antenna and the focal point is L i = (X _fi ² + Y _fi ² + Z _fi ² ) ^1/2 , where k is the wave number in free space,

A multi-beam phased array antenna, wherein the amount of phase shift is set so that

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