JPH06181410A - Antenna - Google Patents

Abstract

PURPOSE:To prevent an undesired change in the shape of a main beam and deviation in a main beam direction due to the effect of a low side lobe processing by implementing low side lobing in a desired optional direction of a beam so as to realize the radiation directivity while keeping the high gain of a main beam. CONSTITUTION:Antenna elements 1-9 of the antenna used for synthesizing beams are excited by exciting weights W1-W9 in which a restriction condition that each radiation strength of the elements in plural prescribed directions is a prescribed complex number is satisfied and the sum of sets radiation power by weighting is minimized in a direction in a restriction condition, or the direction of a side lobe to be suppressed, or the direction of a cross polarized wave to be suppressed, or in both directions, and the square of absolute values of the exciting weights W1-W9 is minimized by adjusting the phase component of the complex number.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflector antenna having a primary radiator composed of a plurality of antenna elements or an array antenna composed of a plurality of antenna elements.

[0002]

2. Description of the Related Art It is important in satellite communication and satellite broadcasting services to form a shaped beam or a multi-beam in a reflector antenna or array antenna mounted on a satellite. When forming multiple beams, it is important to use the limited frequency band as effectively as possible. As a means for that, the side lobe of the radiation directivity of the antenna is lowered and the same frequency is used between different beams. How to do it is considered.

In the reflector antenna and array antenna, it is effective to use a cluster system in which one beam is formed by a plurality of antenna elements in order to effectively use the frequency by reducing the side lobes. In this case, an appropriate excitation weight is given to each antenna element forming the cluster to combine the element directivities to realize a radiation directivity with a low side lobe. Several methods have been considered as methods for determining the excitation weight. Among them, the most effective method is "multi-beam antenna" (Japanese Patent Laid-Open No. 63-82003), "multi-beam antenna". (JP-A-1-129508).

This method is a directivity combining method originally considered for an array antenna, and pays attention to the far field and can reduce the side lobe only in a necessary area while maintaining a high gain of the main beam. To be more specific, after constraining the condition to maintain the high gain of the main lobe, the excitation weight of the element antenna is set to minimize the power sum of the interfering waves that are virtually input from the side lobe direction. To decide. According to this method, side lobes can be easily suppressed in any direction while maintaining the gain of the main lobe, so it can be said that this method is effective for a multi-beam antenna that irradiates a narrow area such as Japan.

By the method focusing on the far field, the excitation weight of the antenna element forming one beam is obtained,
If the excitation weight (excitation amplitude and excitation phase) is realized by the power feeding system, it is possible to realize the directivity of a low side lobe with less beam interference in a predetermined region. In addition, this method is practical because the excitation weight can be optimally set in consideration of the effect of antenna pointing due to cross-polarization suppression and reflector driving.

However, when the excitation weight is determined by this method, the following problems occur. That is, if one main beam direction is set as the constraint condition,
Although it is possible to maintain a high gain apparently, when the direction of the side lobe suppression region is not set symmetrically with respect to the main beam, the beam direction deviates from the predetermined direction or the shape of the main beam is desired. The shape may differ from that of.

A specific example will be described. FIG. 1 shows a parabolic antenna having a cluster-type primary radiator 10. As shown in FIG. 2, the primary radiator has four beams each formed by a cluster composed of nine horn antennas. The clusters forming the beam 1 are horn antennas 1, 2, 3, 4, 5, 6, 7, 8, 9
Composed of. The four beams are located in the far field region as shown in FIG. 3, where beam 1 and beam 4 utilize the same frequency. That is, the radiation directivity of the beam 1 must be lowered in the region of the beam 4 in order to reduce interbeam interference. Therefore, it is important to optimize the excitation weight of each antenna element by the configuration shown in FIG.

FIG. 7 shows the combined directivity of the antenna when the excitation weight is designed by setting one of the main beam directions by the conventional method. In the case of FIG. 7, beam 4
The side lobe is reduced in the area (the center of the right half of the drawing), and the constraint condition is set in one direction of the main beam (the center of the drawing).

However, in this case, the electric field intensity distribution in the main beam direction shows an elliptical shape, and the center of the ellipse does not coincide with the restraining direction. If the center of the ellipse coincides with the maximum radial direction, it indicates that the point that gives the constraint does not coincide with the maximum radial direction, and the original purpose of maintaining maximum gain in the maximum radial direction of the main beam. Does not meet.

Ideally, it is desirable to obtain a pattern close to a concentric circle centered on the maximum radiation direction, but in FIG. 7, the radiation pattern is biased in the vertical direction of the drawing as a result of suppressing the side lobes. However, there is a problem that unnecessary radiation may occur in the vertical direction of the drawing.

FIG. 8 shows that in the conventional combining method, the combined directivity of the antenna is not improved even when a plurality of constraint conditions are provided in the direction of the main beam. In this configuration, the four constraint conditions are symmetrically arranged in the main beam direction, and the set values of the constraint conditions are equal.

In this case, the constraint condition acts too strongly, and the main beam becomes a divided pattern, and the direction of the constraint condition has nothing to do with the maximum radiation direction.
There was a problem that the radiation directivity was far from the pattern actually requested.

[0013]

As described above, in the conventional excitation weight setting method that imposes a restraint condition on the main beam to reduce the side lobes, the main beam direction does not match the restraint direction, and There may be a problem that the beam shape does not have a desired pattern.

The present invention has been made in view of the above problems, and an excitation weight is set so that good main beam characteristics can be realized and effective side lobe reduction can be performed at the same time. To provide an antenna.

[0015]

In order to solve the above-mentioned problems, in an antenna that combines beams by a plurality of antenna elements, a constraint is set so that the radiation intensity in a plurality of predetermined directions becomes a certain constant complex value. Excitation weight that satisfies the condition and minimizes the sum of the radiated power in the direction that imposes this constraint and the side lobe to be suppressed, the cross polarization direction to be suppressed, or both directions by weighting. The antenna element is excited, and the excitation weight has a power supply circuit that is set to a value that minimizes the sum of squares of the absolute values of the excitation weights by adjusting the phase components of the complex values. . In the second invention, in the first invention, the excitation weight is an excitation weight w _n determined by an excitation weight vector W = R ^-1 C [C ^T R ^-1 C] ^-1 H, The weight vector is

[0016]

[Equation 1] And w _n represents an excitation weight for the n-th antenna element among the N antenna elements, and R is

[0017]

[Equation 2] And the element r _nm of the matrix of R is

[0018]

[Equation 3] Where i is a sampling point (i = 1, 2 ... I) within a range that constrains the radiated field strength, θ _i represents the sampled direction, and j represents side lobe suppression or cross polarization. Sampling points (j = 1, 2 ... J) within a range that requires wave suppression, θ _j represents the sampled direction, and g _n (θ _i ) is the n th antenna element whose θ _i is θ _i. Represents the radiation intensity of the normal polarization or the cross polarization radiated in the direction, α _i , β _j , and n _nm are constants, * indicates that a complex conjugate is taken, and C ^T and H are respectively

[0019]

[Equation 4] And the element of H is a complex constraint value in the direction θ _i for restraining the radiant intensity, the amplitude component of the complex constraint value is represented by h _i , the phase component is represented by φ _i , and the subscript ^T is the complex conjugate transpose of the matrix. The subscript ⁻¹ represents an inverse matrix, and the complex weight w _i is evaluated by adjusting the phase component of the complex constraint value by φ _i and is represented by the sum of squares of the absolute values of the complex weights w _i. The feature is that the function Φ is set to be the minimum.

A third invention is characterized in that, in the first invention, the minimum sum of squares of the absolute values of the excitation weights is set by using the steepest descent method.

In a fourth aspect of the invention, in the first aspect of the invention, the sum of squares of the absolute values of the excitation weights is adjusted by adjusting the amplitude component of the complex value within a certain allowable range centered on the set value. The feature is that the excitation weight is set according to the minimum value.

[0022]

In the antenna of the present invention, the excitation weight is adjusted by giving a constraint condition that it has a constant complex value in a predetermined direction. Conventionally, since the constraint condition in the predetermined direction is given by the amplitude (real number) of the synthetic radiation field, the originally unnecessary phase component is also constrained, but in the present invention, the phase component is also adjusted.

Specifically, an excitation weight group that minimizes the sum of the electric power radiated in the direction in which this constraint condition is set (main beam direction) and the direction in which the side lobes are reduced is obtained,
The excitation condition of the antenna element is determined by a value that minimizes the sum of squares of the absolute values of the excitation weights obtained by adjusting the complex-valued phase components set in the constraint conditions.

As a result, only the amplitude value in the direction in which the constraint condition is given is set as the true constraint condition, and it is possible to construct an antenna which is a synthetic radiation field with a low side lobe while maximizing the gain in the main beam direction. it can.

[0025]

EXAMPLES Examples of the present invention are shown below.

FIG. 1 is a diagram showing the structure of a reflector antenna for setting an excitation weight according to the present invention. The reflector antenna includes a parabolic reflector 1-1 and a primary radiator 10. Here are defined in the main coordinate system (x, y, z) and the primary radiator of the coordinate system _{(x f, y f, z} f) each right-handed.

The front view of the primary radiator is shown in FIG. The primary radiator is composed of each cluster (2-1, 2-2, 2-3, 2-4) forming beams 1, 2, 3, 4;
Each cluster consists of 9 horn antennas. Part of the horn antenna is shared between adjacent beams. The cluster 2-1 forming the beam 1 is composed of horn antennas 1, 2, 3, 4, 5, 6, 7, 8, and 9.

The beam arrangement in the far field region is as shown in FIG. Here, 3-1 indicates a beam 1, 3-2 indicates a beam 2, 3-3 indicates a beam 3, and 3-4 indicates a beam 4.
From the standpoint of effective use of frequency resources, frequencies are shared, and specifically, beam 1 and beam 4 use the same frequency. Therefore, it is necessary to reduce the side lobes in the region of the beam 4 in order to prevent the radiation directivity of the beam 1 from interfering with the beam 4.

The radiation directivity for realizing a low side lobe is
As shown in FIG. 4, each element antenna has an optimal excitation weight w ₁ , w ₂ , w ₃ , w ₄ , w ₅ , w ₆ , w ₇ , w ₈ , w _9.
Then, the desired characteristics are obtained by exciting with a distributor 40 (which is a distributor in the case of transmission, but a combiner in the case of reception).

Since each excitation weight can be considered separately from the excitation amplitude which is its absolute value and the excitation phase which is its phase component, a concrete structure of the power feeding system in which the amplitude component and the phase component are separated An example is shown in FIG. Here, the excitation phase for each horn antenna is the phase shifters 11, 12, 13,
14, 15, 16, 17, 18, and 1.
The excitation amplitude for each horn antenna is the power divider 2
It is set by changing the distribution ratio of 1, 22, 23, and 24.

Here, as the phase shifter, in the case of a waveguide system, a method of changing the phase by providing a metal post or the like in the waveguide, a method of changing the phase amount by inserting a dielectric, and a size of the waveguide A method of changing the phase amount by changing the wavelength in the tube by changing the wavelength, a method of changing the waveguide length itself, etc. can be used.For the microstrip line system, in addition to the method of changing the line length, a method by line switching, The deadline method, the hybrid method, etc. can be used. As the distributor (combiner), a directional coupler or a septum type distributor can be used in the case of a waveguide system, and a T branch, a Wilkinson type distributor, a hybrid, etc. in the case of a microstrip line system. Available.

Further, the excitation weight can be changed by changing the phase amount of the phase shifter and the distribution ratio of the distributor.
It is possible to set the optimum weight according to the situation such as changing the orbital position of the satellite antenna, beam deviation, and antenna pointing operation by driving the reflector. The configuration for setting the excitation weight and the components used are not limited to this, and the present invention has the same effect in other configurations. In the example of FIG. 5, parts related to other beams are omitted. Next, a method of setting the excitation weight will be described.

First, a constraint condition is set so that the radiation intensities in a plurality of predetermined directions each have a certain constant complex value. The radiated power in the direction in which this constraint condition is imposed and the radiated power in the direction of the side lobe to be suppressed are respectively summed with a certain weighting, and each element antenna is excited by the excitation weight that minimizes this power sum. In this case, the phase component in the complex value set in each direction under the constraint condition may be freely changed. That is, among the excitation weights that minimize the sum of radiated power under the above constraint conditions, the one that optimizes a certain evaluation function by adjusting the phase component of the constraint complex value is selected as the actual excitation weight. Set.

Here, the sum of squares of the absolute values of the excitation weights is used as the evaluation function, and the optimum excitation weight minimizes this evaluation function. This is because the amplitude value in the restraint direction is constant, so the combined radiant intensity in that direction is constant, and in order to achieve this constant radiant intensity, the value that minimizes the sum of squares of the absolute values of the excitation weights is calculated. Will be there. In fact, considering that a normalized excitation weight acts such that the absolute sum of squares of the excitation weight is constant, reducing the sum of squares of the absolute values of the excitation weights means reducing the radiation gain in the restraining direction. It is nothing but raising the value.

As a specific method for obtaining the excitation weight that minimizes the sum of squares of the absolute values of the excitation weight,
All the methods dealt with in the optimization of nonlinear functions can be used. Among them, the method of steepest descent (Method of steepest
The optimal weight can be obtained easily and quickly by using descent). The method of setting the excitation weight will be described below using mathematical expressions. The excitation weight is an excitation weight w determined by the following excitation weight vector W.
_n . W = R ^-1 C [C ^T R ^-1 C] ^-1 H (1) The relationship between the excitation weight vector W and the excitation weight w _n is as follows.

[0036]

[Equation 5]

Here, w _n represents an excitation weight for the n-th antenna element of the N antenna elements and can be considered separately for the amplitude component and the phase component. R in the equation (1) is a correlation matrix and is represented by the following equation.

[0038]

[Equation 6] Here, the elements r _nm of the matrix R are as follows.

[0039]

[Equation 7]

Here, i is a sampling point (i = 1, 2 ... I) within the range in which the radiant field strength is constrained, θ _i represents the sampled direction, and j requires side lobe suppression. Sampling points within the range (j = 1, 2 ...
J), θ _j represents the sampled direction, and g _n (θ _i ) represents the radiation intensity radiated by the n-th antenna element in the θ _i direction. α _i , β _j , and n _nm are constants,
* Indicates to take a complex conjugate. Furthermore, C ^{T in} equation (1)
And H are a constraint matrix and a response vector, respectively, and are represented as follows.

[0041]

[Equation 8]

The element of H is a complex constraint value in the direction θ _i for restraining the radiation intensity, and its amplitude component is h _i and its phase component is φ _i . The subscript T represents the complex conjugate transpose of the matrix,
Subscript ^-1 represents the inverse matrix.

The excitation weight given by the equation (1), under the constraint C ^T W = H, the sum of the radiation power P = W ^T
It is obtained by minimizing RW. This is derived using Lagrange's undetermined coefficient method. The excitation weight obtained here restrains the main beam and realizes radiation directivity with low side lobes. Here, the element h _i exp (j of the response vector H constrained by the constraint condition
Even if the phase component φ _i is changed in φ _i ), the gain of the radiation field in the constraint direction does not change. Therefore, the excitation weight can be optimized by using the degree of freedom of this phase component. Here, the evaluation function Φ for optimization is set by the excitation weight w _i as follows.
The sum of squares of the absolute value of.

[0044]

[Equation 9] Phase quantity {φ _i } of response vector that minimizes evaluation function Φ
Is obtained by the following iterative calculation by the steepest descent method.

[0045]

[Equation 10]

Here, the subscript k indicates the number of repeated calculations, and μ is the step amount. By converging the solution by the equation (8), the above-mentioned optimum weight is obtained.
The optimization by the steepest descent method is easy to calculate and requires a short calculation time. This is convenient in terms of design efficiency because it is not necessary to change the setting value of the constraint direction one after another in order to obtain the optimum phase amount and to repeat the calculation.

An example of radiation directivity by the antenna of the present invention is shown in FIG. As is clear from this figure, a level of -40 dB or less is achieved in the direction of side lobe reduction, and the main beam is a good radiation that is not affected by the side lobe reduction such as deviation of the beam direction or change in shape. The directivity is realized. Further, as compared with the radiation patterns of FIGS. 7 and 8, it can be seen that a radiation pattern that is almost isotropic can be synthesized without being biased in the vertical and horizontal directions of the drawings.

Generally, the inter-beam interference level required for frequency sharing in a multi-beam antenna is -27 dB or less in satellite communication and -35 dB or less in satellite broadcasting in the case of the most severe FM modulation. It can be said that the radiation directivity sufficiently satisfies this condition. Here, by adjusting the direction in which the constraint condition is set to the irradiation coverage, it is possible to form a shaped beam having the same shape as the irradiation coverage.

With the antenna having the excitation weight set as described above, the side lobe can be reduced in any desired direction, and the radiation directivity can be realized while maintaining the high gain of the main beam. Here, by setting a plurality of restraint conditions in the main beam, it is possible to prevent a deviation in the main beam direction and an inadvertent change in the shape of the main beam due to the influence of the side lobe reduction. It is also easy to shape the beam according to the shape of the irradiation area of the beam.
Furthermore, the excitation weight is set so that the gain in the restraining direction is maximized, which is convenient for high gain and miniaturization of the antenna. From the above, it can be said that the present invention is very effective for a multi-beam antenna mounted on a satellite and a shaped beam antenna. Although the embodiments of the present invention have been described above, the same effects can be obtained even if the following modifications are made in the embodiments.

For example, although the present embodiment has described the case of a multi-beam antenna using a reflector antenna, the present invention is also applicable to the case of forming a multi-beam or a shaped beam in an array antenna that directly radiates without using a reflector. , The same effect can be obtained.

Further, although the above embodiment has described the case where the radiation directivity with the low side lobe is realized, the present invention can be applied to the case where the cross polarization is reduced. In this case, when the sum of the radiated powers is obtained, the radiated powers in the cross polarized waves are combined with the powers in the normal polarized waves for setting the restraining direction for optimization.

Further, the present invention can realize an antenna in which desired radiation characteristics are effective over the frequency band by obtaining the optimum weight in consideration of the characteristics at each frequency in a certain frequency band. Similarly, when antenna pointing is performed by driving a reflecting mirror, the optimization weight can be obtained in consideration of changes in the mirror surface system and the shape of the antenna.
This is very important in the actual operation of the antenna.

Further, in the embodiment of the present invention, the excitation weight for minimizing the evaluation function Φ by adjusting the phase component of the complex set value in the constraint direction is set, but by adjusting the amplitude component in addition to the phase component, In addition, the degree of freedom in design is increased, and a better excitation weight can be set. Here, if the adjustable region of the amplitude component is within a certain allowable range centered on the value of the amplitude of the complex set value, a gain close to the gain set by the constraint condition can be realized. By such an operation, it can be said that the gain in the direction in which the constraint condition is set can be increased as a whole, and as a result, a better radiation directivity can be realized. Such a method is very effective because an antenna with a high gain is required for a satellite antenna or the like.

In the embodiment of the present invention, the procedure of minimizing the evaluation function Φ by changing the phase component of the complex constraint value is performed from the viewpoint of maximizing the gain in the constraint condition direction. Therefore, from the viewpoint of lowering the side lobe, it is certain that the excitation weight minimizes the side lobe level when the phase of the complex constraint value is set, but the phase is changed. In this case, the side lobe level changes, and the excitation weight set in the above procedure is not necessarily optimum from the viewpoint of lowering the side lobe. Therefore, this time, select an amount related to the sidelobe level as the evaluation function, and use the phase value of the complex constraint value that gives the excitation weight set in the above procedure as the initial value, and allow the decrease in the gain value in the constraint direction. You can optimize as much as you can. The excitation weight set by this method can provide an excitation weight that achieves better characteristics in achieving the two purposes of increasing the gain in the restraining direction and reducing the side lobe.

As described above, according to the present invention, it is possible to reduce the side lobes in any desired direction and to realize the radiation directivity maintaining the high gain of the main beam. Here, by setting a plurality of restraint conditions in the main beam, it is possible to prevent a deviation in the main beam direction and an inadvertent change in the shape of the main beam due to the influence of the side lobe reduction. It is also easy to shape the beam according to the shape of the irradiation area of the beam. Furthermore, the excitation weight is optimized to increase the gain in the restraining direction, which is convenient for high gain and miniaturization of the antenna.

[0056]

According to the present invention, it is possible to provide an antenna in which an excitation weight is set so that good main beam characteristics can be realized and effective side lobe reduction can be performed at the same time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a reflector antenna according to an embodiment of the present invention.

FIG. 2 is a front view of a primary radiator of a reflector antenna according to an embodiment of the present invention.

FIG. 3 is a beam arrangement diagram of a reflector antenna according to an embodiment of the present invention.

FIG. 4 is a diagram showing a concept of directivity synthesis of a primary radiator of a reflector antenna in an embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a primary radiator of a reflector antenna according to an embodiment of the present invention.

FIG. 6 is a diagram showing a combined directivity when an excitation weight is set by the method of the present invention.

FIG. 7 is a diagram showing a combined directivity when the excitation weight is set by the conventional method.

FIG. 8 is a diagram showing a combined directivity when an excitation weight is set by a conventional method.

[Explanation of symbols]

 1-9 ... Horn antenna 11-19 ... Phase shifter 21-24 ... Power distributor

Claims (2)

[Claims] 1. A weighted power of a first radiation power in the main radiation direction and a second radiation power in a radiation direction different from the main radiation direction with a radiation intensity in the main radiation direction being a predetermined value. An antenna constructed by giving excitation weights of a plurality of antenna elements so that the sum becomes a minimum, wherein the excitation weights are adjusted so that the direction giving the maximum radiation intensity and the main radiation direction coincide with each other. . 2. In order to adjust the excitation weight, the phase component of a predetermined value of the radiation intensity in the main radiation direction is adjusted so that the sum of squares of the plurality of excitation weights is minimized. The antenna according to claim 1.