JPH01129508A - Multi-beam antenna - Google Patents

Abstract

PURPOSE:To obtain an antenna having the directivity of a satisfactory low side lobe characteristic by constituting a primary radiator of plural antenna elements, satisfying a constraint condition that a radiation level in the prescribed direction becomes constant, and exciting plural antenna elements by an exciting weight for minimizing the sum of power of a radiation field radiated in the direction which has satisfied said constraint condition and in the direction of a side lobe. CONSTITUTION:A primary radiator is constituted of a horn antenna 1-9 being an antenna element, and to each horn antenna 1-9, exciting weights W1-W9 are given by weighting devices 41-49. The element directivity of each antenna element is weighted, respectively, and synthesized by a synthesizer 10. In this case, a constraint condition that a radiation level in the prescribed direction becomes constant is satisfied, and by the exciting weight for minimizing the sum of power of a radiation field radiated in the direction which has satisfied this constraint condition and in the direction of a side lobe, to put it concretely, the exciting weight determined by an exciting weight vector, plural antenna elements for constituting the primary radiator are excited, and even against a physical variation of a specular system, a low side lobe characteristic is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a reflective multi-beam antenna having a primary radiator excited with a predetermined excitation weight.

(Prior art) In a multi-beam antenna, it is important to use the limited frequency band as effectively as possible, and one way to do this is to lower the side lobes of the antenna's directivity and to make sure that different beams have the same or similar characteristics. There is a method that uses frequencies.

In a reflector type multi-beam antenna, a method taken to effectively utilize frequencies by reducing side lobes is to cluster the primary radiators. A cluster is a primary reflector composed of multiple antenna elements, and by giving appropriate weights to the directivity of each antenna element and performing directivity synthesis, it is possible to obtain low sidelobe directivity. It is possible to achieve this. Several methods have been considered for determining the weights at this time, and representative methods will be explained below.

As a conventional method of determining excitation weight,
A common method is to focus on the current distribution at the aperture of the antenna. It is a well-known fact that when the edge level of the current distribution at the aperture surface is low, directivity with low side lobes can be obtained. Therefore, an aperture surface distribution with a low edge level and a lower side lobe is synthesized. It is good to set the excitation weight of each antenna element constituting the primary radiator as shown in Fig. It is effective if there are several over a wide area. However, when considering a multi-beam antenna that illuminates a long and narrow area like Japan,
There are few beams that use the same frequency, and the area that requires low sidelobes is also limited. In this case, if sidelobes are reduced by the above method, sidelobes are also suppressed in unnecessary regions, which may result in a decrease in gain, which is not an efficient method.

On the other hand, a method has been considered that focuses on the far field via a reflecting mirror, performs direct directivity synthesis, and performs sidelobe reduction only in the necessary angular region. As one of these, the Institute of Electronics and Communication Engineers Technical Research Report A-P85-
114 (February 1,986), Suzuki et al. "Study of multi-beam antenna for satellite broadcasting by 22 GHz band". This method is an application of the directional synthesis method originally considered for array antennas to determine the excitation weight of the primary radiator of a reflector-type multi-beam antenna. In this method, the excitation weight is determined so as to minimize the power level of the interference wave virtually input from the sidelobe direction, with the following constraints imposed. This method maintains the gain of main row 1,
Since sidelobes are suppressed in any predetermined direction, it is effective for multi-beam antennas that irradiate narrow areas such as in Japan.

If the wJ oscillation weight of the primary radiator is determined by a method that focuses on this far field, and the excitation weight is realized by the feed system, there will be no interference between beams in a predetermined area as shown in radiation directivity 31 in Figure 5. Low sidelobe directivity is formed. However, in reality, the reflector may become distorted due to heat, or the reflector may need to be moved to control the beam direction.
In this case, as the element directivity of each antenna element changes, the side lobe characteristics may deteriorate as shown in the directivity 32 in FIG. 5.

(Problems to be Solved by the Invention) As explained above, the low sidelobe directivity required in a reflector type multi-beam antenna cannot be achieved by the conventional method when the mirror system is completely fixed. Is it possible to achieve this? There is a problem that if the mirror system is physically changed by distorting the reflector due to heat or moving the reflector for beam control, the low sidelobe characteristics will deteriorate. .

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

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the multi-beam antenna of the present invention is a multi-beam antenna having a reflecting mirror and a plurality of primary radiators, The primary radiator is composed of multiple antenna elements, satisfies the constraint that the radiation level in a given direction is constant, and the power of the radiation field radiates in the direction that satisfies this constraint and in the side lobe/J\b direction. The object of the present invention is to include a feeding means that excites the plurality of antenna elements with an excitation weight that minimizes the sum of , and has low sidelobe characteristics even with respect to physical changes in the mirror system.

(Function) The multi-beam antenna of the present invention satisfies the constraint that the radiation level in a predetermined direction is constant, and minimizes the sum of the power of the radiation field radiated in the direction that satisfies this constraint and the direction of the side lobe. The multiple antenna elements constituting the primary radiator are excited with the excitation weight to achieve low sidelobe characteristics even against physical changes in the mirror system.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram of a feeding system for a primary radiator used in a multi-beam antenna according to an 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 an antenna element.
9 is the excitation weight wt-W9 by the weighting device 41-49.
is given. The element directivity of each antenna element is weighted and combined by a combiner 10.

The combined directivity at this time needs to have a low sidelobe characteristic that does not interfere with other beams sharing the same frequency, as shown in FIG. This low sidelobe characteristic must be maintained even when the mirror system is physically changed, such as by moving a reflecting mirror for beam direction control.

−11= As an example, consider a case where the offset Cassegrain type mirror system shown in FIG. 4 is used and the beam direction is changed by driving the sub-reflector. Controlling the beam direction is necessary to prevent the beam direction from shifting due to changes in the attitude of the satellite in a multi-beam antenna. In FIG. 4, when the sub-reflector 33 is moved from the position shown by the solid line to the position 34 shown by the dotted line, the beam direction changes from the direction shown by the solid line 35 to the dotted line 36.
It changes in the direction shown by . At this time, since there are changes in the way the radio waves hit the reflecting mirror surface, the amount of phase, etc., the radiation directivity is naturally disturbed. If the excitation weight of the primary radiator is set considering only the case where the sub-reflector is fixed without moving, then
When the sub-reflector is moved, the radiation directivity is disturbed as shown by the directivity 32 in FIG. 5, and desired side lobe characteristics cannot be obtained when the sub-reflector is driven. Therefore, in order to obtain the desired low sidelobe radiation directivity even when driving the sub-reflector, we consider several states within the range in which the sub-reflector is driven, and consider the states of all mirror surfaces within the driving range. It is necessary to give each element an average excitation weight that results in a low sidelobe at . The excitation weights shown in FIG. 1 are set to the values described above.

Next, an actual method of setting excitation weights will be explained here.

When synthesizing directivity that results in a low sidelobe within a given angular region, consider the following constraint conditions so as not to adversely affect the main beam.

This equation means that when the mirror system is in the fifth height state, the reception (transmission) level in the θi direction is constrained to . Here, Wn is the excitation weight applied to the n-th horn antenna, g g (fL i.

θ, ) is the element directivity of the nth horn antenna,
(2) is the number of constraint points, and N is the number of horn antennas.

The above equation (1) is expressed as the following equation using vector matrix representation.

CTW=B ・・・・・・(2
) Here...(4) (Hereafter, blank spaces) Note that the subscript T represents complex conjugate transposition.

A constraint condition as shown in the above equation (2) is imposed on the excitation weight, and then an excitation weight that synthesizes the directivity of the low sidelobe is determined.The method will be described below.

The desired wave arrives from the direction of θ when the mirror system is in the first state of hair, and the desired wave arrives from the direction of θ when the mirror system is in the first state of hair.
Assume that J interference waves arrive. It is assumed that the desired waves arrive from the direction of the main beam in a mirror state, and the interference waves arrive from the direction of the side lobes to be suppressed. At this time, the sum of the output power of the entire primary radiator for each mirror surface state is expressed as follows.

pout=w" Rw=------
<6> Now, assuming that the noise power P generated in the n-th horn antenna is the desired wave, the interference wave, and the noise each have no correlation n, the component RnIF of R is expressed as follows: expressed.

nl+Pnn+
--------(7) However, when n to m, P. −〇, and “represents complex conjugate.

At this time, under the constraint condition of equation (2) above, the output power phase P
. If the excitation weight is determined to minimize , 1, as a result, only the desired wave component will appear in the output, and no interference wave component will occur. This is because the directivity synthesized by the excitation weights maintains the average gain in the desired wave direction in each state of the mirror system, while forming a null in the direction in which the side lobe disturbance wave is set. It corresponds to the shape.

Excitation way ut that minimizes the output power phase P The vector W is analytically given as follows.

W=TR-I C(CT IFj-I C>-1B
(8) Here, the subscript -1 represents an inverse matrix.

For example, when the sub-reflector is driven from position 33 to position 34 in the example shown in FIG. 4, the state of the mirror system is selected by selecting positions 33, 34 and several states during the drive. For each state, by assuming a desired wave and an interfering wave and solving equation (8), the directivity synthesized from the excitation weights will have side lobes suppressed on average within the driving range. . Sidelobes can be suppressed in any angular range in each state, and the amount of suppression can be freely adjusted by appropriately setting the proportional coefficients α, β, P, and J. Therefore, it can be said that the reflective multi-beam antenna having a primary radiator with excitation weights according to the present invention is very effective from the standpoint of effective frequency utilization.

FIG. 2 shows an example of a feed system for a primary radiator that realizes the excitation weight described above. The excitation weight can be considered separately into an amplitude component and a phase component, and the amplitude component can be set by adjusting the distribution ratio of the three power dividers 21, 22, 23, and 24, and the phase component can be set by shifting. This can be done by phasers 11-19. If the power supply system is configured with a waveguide, it can be easily realized by using a method such as a metal rod inserted type as a phase shifter to change the wavelength inside the tube, and a septum type or directional coupling type as a power divider. can.

It is relatively easy to set the excitation amplitude and excitation phase using the above example.

In addition, in the above explanation, we have explained the case where the sub-reflector is driven to control the beam direction, but the same effect can be obtained even if it is the main reflector or a plane mirror installed for driving. can get. In addition, not only in beam direction control, but also in cases where distortion occurs on the mirror surface of a reflecting mirror due to the influence of heat, etc., if the distortion can be predicted, the condition can be taken into account in the calculation of equation (8) and the specified value can be determined. It is possible to maintain the low sidelobe characteristics of As described above, the present invention is effective when trying to maintain predetermined characteristics even when the mirror surface system physically changes or changes.

Further, in the above embodiments, a horn antenna was used as an example of the antenna element, but the antenna element is not limited to this, and may be a patch antenna, for example, and the number thereof is not limited, but may be any number. Can be done.

[Effects of the Invention] As explained above, according to the present invention, the constraint that the radiation level in a predetermined direction is constant is satisfied, and radiation is emitted in the direction that satisfies this constraint and in the direction of the side lobe. The excitation weight that maximizes the sum of the power of the radiation field, specifically the excitation weight vector W = [R-I
C(CT IFj-I C) -1B Excite multiple antenna elements constituting the primary radiator with the excitation weight determined by C, and achieve low sidelobe characteristics even against physical changes in the mirror system. Therefore, even if the mirror system is physically changed, the directivity with suppressed side lobes can be maintained in any angular range without reducing the gain of the main rope within the range of the change. It is extremely effective as a reflective multi-beam antenna for on-board satellites.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a feed system for 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 the feed system for a primary radiator shown in Fig. 1. Fig. 3 shows the radiation directivity of the multi-beam antenna, Fig. 4 shows how to change the beam direction by driving the sub-reflector, and Fig. 5 shows the radiation directivity when the sub-reflector is driven. FIG. 1-9... Horn antenna, 10... Combiner, 11-19... Phase shifter, 21-24... 3 power divider

Claims (2)

[Claims] (1) A multi-beam antenna having a reflecting mirror and a plurality of primary radiators, wherein the primary radiator is composed of a plurality of antenna elements and satisfies the constraint that the radiation level in a predetermined direction is constant; The plurality of antenna elements are excited with an excitation weight that minimizes the sum of the power of the radiation field radiated in the direction that satisfies this constraint condition and the direction of the side lobe, and the side lobe is low even against physical changes in the mirror system. A multi-beam antenna characterized by comprising a power feeding means having characteristics. (2) The power feeding means has an excitation weight vector W=R^
-^1C(C^TR^-^1C)^-^1B includes a feeding section that excites the plurality of antenna elements so as to substantially satisfy an excitation weight W_n determined by ^1B, and the excitation weight vector W is ▲There are mathematical formulas, chemical formulas, tables, etc.▼ where W_n represents the excitation weight for the n-th antenna element among N antenna elements, and the above R is ▲There are mathematical formulas, chemical formulas, tables, etc.▼ , the element R_n_m of the matrix of R is ▲a mathematical formula, a chemical formula, a table, etc.▼, where _i is a number (i=1, 2,...・I), θ_i represents the sampled direction, and _
j is a number (j=1, 2...J) representing the sampling point within the range that requires sidelobe suppression, and θ_j
represents its sampled direction and g_n(l, θ
) represents the directivity radiated by the n-th antenna element via the reflecting mirror, l is a number (I = 1, 2...l) representing the state in which the reflecting mirror surface is physically changed, and α_i , β_
j, P_n_m are proportional coefficients, ^* indicates complex conjugation, and C^T and B are respectively ▲There are mathematical formulas, chemical formulas, tables, etc.▼ ▲There are mathematical formulas, chemical formulas, tables, etc.▼ , b_j is a complex constraint value in the direction θ_i that constrains the radiation field intensity, the subscript T represents the complex conjugate transpose of the matrix, and the subscript -1 represents the inverse matrix. multi-beam antenna.