JP2624726B2 - Multi-beam antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a reflection type multi-beam antenna having a primary radiator excited by a predetermined excitation weight.

(Prior Art) In a multi-beam antenna, it is important to use a limited frequency band as effectively as possible. For this purpose, the side lobe of the directivity of the antenna is lowered, and the same frequency is used between different beams. There is a way to use it.

In a reflector type multi-beam antenna, a method that is used to effectively use the frequency by reducing the side lobe is to cluster the primary radiators. The cluster means that the primary radiator is composed of a plurality of antenna elements, and the appropriate directivity of each antenna element is weighted. Can be realized. There are several methods for determining the weight at this time, and representative methods will be described below.

As a conventional method of determining an excitation weight, a method of paying attention to a current distribution on an aperture surface of an antenna is generally used. It is a well-known fact that when the edge level of the current distribution in the aperture plane is low, a low sidelobe directivity can be obtained. In this case, the excitation weight of each antenna element constituting the primary radiator may be set. This method has a low side lobe over all angular regions except the main lobe, and is effective when there are several beams using the same frequency in a wide range. However, when considering a multi-beam antenna mounted on an artificial satellite that illuminates a narrow and narrow area like Japan, the number of beams using the same frequency is small, and the area requiring low side lobes is limited. In this case, when the side lobe is reduced by the above method, side lobe suppression is performed even in an unnecessary region, so that a decrease in gain may be caused.
Not an efficient method.

On the other hand, a method has been considered in which attention is paid to a far field via a reflecting mirror, direct directional synthesis is performed, and the side lobe is reduced only in a necessary angle region.
One of these is IEICE Technical Report A ・ P85-1
14 (February 1986), and the method described in Suzuki et al., "Study of Multi-beam Antenna for Satellite Broadcasting by 22GHz Band". This method is applied to the directivity synthesis method originally considered for array antennas and to determine the excitation wade of the primary radiator of the reflector type multi-beam antenna, so that the gain of the main lobe is not reduced. In this method, the excitation weight is determined so as to minimize the power level of the interfering wave input virtually from the side lobe direction after the above constraint condition is imposed. This method is effective for a multi-beam antenna that irradiates a narrow area such as Japan because sidelobe suppression in any given direction is performed while maintaining the gain of the main lobe.

If the excitation wade of the primary radiator is obtained by this method focusing on the far field, and the excitation weight is realized by the feed system, a low side having no interference between beams in a predetermined area as in the radiation directivity 31 in FIG. A lobe directivity is formed.
However, in actuality, it is conceivable that the reflector is distorted by heat or the reflector is moved for controlling the beam direction. In this case, the element directivity of each antenna element changes, so that the directivity 32 of FIG. Thus, the side lobe characteristics may be deteriorated.

(Problems to be Solved by the Invention) As described above, the directivity of the low side lobe required in the reflector type multi-beam antenna can be obtained by the conventional method when the mirror system is completely fixed. It can be realized, but if the mirror is distorted by heat or the mirror is moved for beam control and the mirror surface system is physically changed, the low sidelobe characteristic will deteriorate. .

The present invention has been made in view of the above, and it is an object of the present invention to provide a multi-beam antenna having good directivity with low sidelobe characteristics even when a mirror system physically changes. .

[Configuration of the Invention] (Means for Solving the Problems) In order to solve the above problems, a multi-beam antenna according to the present invention is a multi-beam antenna having a reflector and a plurality of primary radiators, The primary radiator is composed of a plurality of antenna elements, and satisfies the constraint condition that the radiation level in a predetermined direction is constant, and calculates the sum of the power of the radiation field radiated in the direction satisfying the constraint condition and the direction of the side lobe. The gist of the present invention is to provide a power supply unit that excites the plurality of antenna elements with an excitation weight that is minimized and that has low side lobe characteristics with respect to a physical change in a mirror system.

(Operation) The multibeam antenna of the present invention satisfies the constraint condition that the radiation level in a predetermined direction is kept constant, and minimizes the sum of the power of the radiation field radiated in the direction satisfying the constraint condition and in the direction of the side lobe. A plurality of antenna elements constituting the primary radiator are excited by the excitation weight to achieve low side lobe characteristics with respect to physical changes in the mirror system.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a feed system of a primary radiator used in a multi-beam antenna according to one embodiment of the present invention. In the figure, the primary radiator is constituted by horn antennas 1-9 as antenna elements, and each horn antenna 1-9 is given to an excitation weight W1-W9 by a weighter 41-49. The element directivities of the respective antenna elements are weighted and combined by the combiner 10. At this time, the combined directivity needs to have low side lobe characteristics so as not to interfere with other beams sharing the same frequency as shown in FIG. It is necessary to maintain this low side beam characteristic even when the mirror surface system is physically changed, for example, by moving a reflecting mirror for beam direction control.

As an example, consider a case where the beam direction is changed by driving a sub-reflector using the mirror system of the offset Cassegrain type shown in FIG. It is necessary to control the beam direction in order to prevent the beam direction from being shifted due to the attitude change of the satellite by the multi-beam antenna. In FIG. 4, when the sub-reflector 33 is moved from the position indicated by the solid line to the position indicated by the dotted line, the beam direction changes from the direction indicated by the solid line to the direction indicated by the dotted line. At this time, there is a change in how the radio wave hits the reflecting mirror surface, a change in the phase amount, and the like, so that the radiation directivity is naturally disturbed. If the excitation weight of the primary radiator is set only when the sub-reflector is fixed without moving, the radiation directivity will be disturbed as shown by the directivity 32 in Fig. 5 when the sub-reflector is moved. In addition, a desired side lobe characteristic cannot be obtained when the sub-reflector is driven. Therefore, in order to obtain the desired radiation directivity of the low side lobe even when the sub-reflector is driven, several states within the driving range of the sub-reflector are considered, and the states of all mirror surfaces within the driving range are considered. , It is necessary to give an average excitation weight to each element so as to have a low side lobe. The excitation weights shown in FIG. 1 are set to the values described above.

Next, a method of setting an actual excitation weight will be described.

When synthesizing directivity such that a low side lobe is obtained in an arbitrary angle region, the following constraint condition is considered so as not to adversely affect the main beam.

This equation means that the reception (transmission) level in the θ _i direction is restricted by b _i when the mirror system is in the _ith state. Here, W _n is the excitation weight applied to the n-th horn antenna, g _n (l _i , θ _i ) is the element directivity of the n-th horn antenna, I is the number of constraint points, and N is the number of horn antennas. .

The above equation (1) is represented by the following equation using the vector matrix representation.

here Note that the subscript T represents a complex conjugate transpose.

After imposing the constraint conditions shown in the above equation (2) on the excitation weight, an excitation weight that combines the directivity of low side lobes is determined. The method will be described.

A desired wave arrives from the direction of θ _i when the mirror system in the l _i- th state where the constraint condition is set, and an interfering wave arrives from the direction of θ _j when the mirror system is in the l _j- th state. Suppose It is assumed that the desired waves come from the direction of the main beam and the interfering waves come from the direction of the side lobe to be suppressed in the mirror state. At this time, the sum of the output power of the entire primary radiator with respect to the state of each mirror surface is expressed as follows.

Now, the noise power P _nn generated in the n-th horn antenna
Assuming that the desired signal, the interference signal, and the noise are uncorrelated, The components R _nm is expressed by the following equation.

However, when n ≠ m, P _nm = 0, and ^* represents complex conjugate.

At this time, the output power sum under the constraint condition of the above equation (2)
If the excitation weight is determined so as to minimize P _out , only the desired wave component appears in the output as a result, and no interference wave component occurs. This is such that the directivity synthesized by the excitation weight forms a null in the direction in which the side lobe interference wave is set while the gain in the desired wave direction is maintained on average in each state of the mirror system. Corresponds to being in shape.

The excitation weight vector Wopt that minimizes the output power sum P _out is analytically given as Here, the subscript -1 represents an inverse matrix.

For example, when the sub-reflector is driven from the position 33 to the position 34 in the example shown in FIG. 4, the positions of the positions 33 and 34 and some states during the drive are selected. By solving equation (8) assuming a desired wave and an interfering wave in each state, the directivity synthesized from the excitation weights is such that the side lobes are suppressed on average within the driving range. . That is, based on the predicted physical change of the mirror system, the solution of the equation (8) is uniquely obtained, and the excitation weight is fixedly set, thereby realizing the side lobe suppression. Can be performed in any angle range,
The suppression amount can be freely adjusted by appropriately setting the proportional coefficients α _i , β _j , and P _nm . Therefore, it can be said that the reflection type multi-beam antenna having the primary radiator in which the excitation weight is set according to the present invention is very effective in terms of effective frequency utilization.

FIG. 2 shows an example of a feed system of a primary radiator that realizes the above-described excitation weight. The excitation weight can be considered separately for the excitation component and the phase component. The setting of the amplitude component can be performed by adjusting the distribution ratio of the three power dividers 21, 22, 23, and 24, and the setting of the phase component is shifted. This can be performed by the phaser 11-19. When a power feeding system is configured with a waveguide, the phase shifter can be easily realized by a method such as a metal rod insertion type that changes the guide wavelength, and the power distributor can be easily realized by a septum type or directional coupling type. it can. It is relatively easy to set the excitation amplitude and the excitation phase according to the above example.

In the above description, the case where the sub-reflector is driven for beam direction directing control has been described. However, the same effect can be obtained even when the main reflector is driven or a plane mirror installed for driving. can get. In addition to the beam direction control, for example, in the case where the mirror surface of the reflecting mirror is distorted due to the influence of heat or the like, the distortion is predicted and the state is considered in the calculation of the equation (8). Can maintain the low side lobe characteristics. As described above, the present invention is effective when trying to maintain predetermined characteristics when the mirror surface system physically changes or changes.

Further, in the above embodiment, the horn antenna is described as an example of the antenna element. However, the present invention is not limited to this. For example, a patch antenna or the like may be used. Can be.

[Effects of the Invention] As described above, according to the present invention, the radiation field that satisfies the constraint condition that the radiation level in a predetermined direction is constant, and radiates in the direction satisfying the constraint condition and in the direction of the side lobe. Excitation weight that minimizes the sum of the power of the excitation, specifically the excitation weight vector Excitation weights determined by the excitation of multiple antenna elements constituting the primary radiator, and achieves low sidelobe characteristics even for physical changes in the mirror system,
Even when the mirror system is physically changed, it is possible to maintain the directivity in which side lobes are suppressed in an arbitrary angle region without lowering the gain of the main lobe within the range of the change, for example, for satellite mounting. This is extremely effective as a reflection type multi-beam antenna.

[Brief description of the drawings]

FIG. 1 is a block diagram of a feed system of a primary radiator used in a multi-beam antenna according to an embodiment of the present invention, and FIG. 2 is a specific block diagram of a feed system of a primary radiator shown in FIG. FIG. 3, FIG. 3 is a diagram showing the radiation directivity of the multi-beam antenna, FIG. 4 is a diagram for explaining the change of the beam direction by driving the sub-reflector, and FIG. FIG. 1-9: Horn antenna, 10: Combiner, 11-19: Phase shifter, 21-24: 3 power divider

Claims (2)

(57) [Claims] 1. A multi-beam antenna having a reflector and a plurality of primary radiators, wherein the primary radiator is constituted by a plurality of antenna elements and satisfies a constraint condition that a radiation level in a predetermined direction is constant. Then, the plurality of antenna elements are excited by an excitation weight that minimizes the sum of the power of the radiation field radiated in the direction satisfying the constraint condition and the direction of the side lobe, and the excitation weight is reduced with respect to the physical change of the mirror system. A multi-beam antenna comprising a feeding unit having side lobe characteristics. 2. The power supply device according to claim 1, wherein said constraint condition is defined assuming that an excitation weight for an n-th antenna element among a plurality of (N) antenna elements is Wn. Where Wn is Is satisfied, Are each Where b _i is the complex constraint value in the direction θ _i that constrains the radiation field strength, the subscript T represents the complex conjugate transpose of the matrix, and g _n (l, θ) is the n-th antenna element , And l is a number (I = 1, 2,... L) representing a state in which the reflecting mirror surface is physically changed. And the output power sum Pout of the entire primary radiator obtained by the following equation: And the The matrix element Rnm of Where _i is a number (i = 1, 2,... I) representing a sampling point within a range that constrains the radiation field intensity;
θ _i represents the sampled direction, _j is a number (j = 1, 2,... J) representing a sampling point within a range requiring side-rope suppression, and θ _j is the sampled direction. Where α _i , β _j , and P _nm are proportional coefficients, and ^* indicates that they take complex conjugate. Excitation weight vector Wopt when Pout obtained by Here, the subscript -1 represents an inverse matrix. 2. The multi-beam antenna according to claim 1, further comprising a feed unit that excites the plurality of antenna elements so as to substantially satisfy an excitation weight Wn determined by the following.