JPH0644686B2 - Array antenna - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an array antenna in which each antenna element is excited by a predetermined excitation weight.

[Technical background of the invention and its problems]

When the signal is received by the antenna, various measures are taken to remove unnecessary signals and receive only the target signal. One way to do this is to lower the side rope of the antenna. When an array antenna is used as the antenna, conventionally, each antenna element of the array antenna is provided with an excitation distribution based on the Tsiebyshev distribution, the Taylor distribution, or the like to achieve a low sidelobe.
This is effective when the direction of arrival of the unwanted signal is unknown or when the direction of arrival of the unwanted signal extends over a wide range, because the side lobe is reduced over the entire angle range except the main lobe.

However, in many cases, the direction of arrival of the unwanted signal (including the clutter that is the reflected wave from the ground or sea surface) is often known, and there is also an angular range where the unwanted signal arrives within a limited range. Often there is. In such a case, of course, it is possible to suppress the unnecessary signal by using the excitation distribution based on the Tiewisieev distribution, the Taylor distribution, etc., but the side lobe reduction is made uniform over the entire angle region other than the main lobe. Therefore, the efficiency is generally lowered. Also,
There are drawbacks such that it is not possible to particularly suppress only the unnecessary signal in a specific limited area, and it is also impossible to arbitrarily set the area of the unnecessary signal to be particularly suppressed.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an array antenna that can reduce the side lobe only in an arbitrarily designated angular region without significantly lowering the efficiency.

[Outline of Invention]

The present invention is connected to N antenna elements (N is an integer of 2 or more) and each element of the N antenna elements, here, And the constraint direction φ of the directivity and the complex constraint value B1 that are set in advance are Is a vector that is defined as

in this case, Is.

And an exciter that excites with an excitation weight Wn that is sequentially determined by.

Example of Invention

An embodiment of an array antenna according to the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for schematically explaining each antenna element of the array antenna, and shows an example in the case where each element interval is d and the number of elements N = 20. The angle θ is based on the direction perpendicular to the aperture plane of the antenna.

The excitation weight Wn (n =
A method of determining 1 ... N) will be described below.

The excitation weight Wn has an amplitude component An and a phase component θn and is represented by a complex number Wn = Anexp (jθn).

If a low side lobe region having directivity is forcibly synthesized over an arbitrary angle region, the directivity in the arrival direction of the desired signal may be affected. This is not desirable. Therefore, in order to avoid this, it is necessary to keep at least the reception level of the desired signal in the arrival direction at a constant value.

Now, considering the case where the arrival direction of the desired signal is limited to one direction, the excitation weight Wn is Need to be satisfied. Here, φ ₁ is the arrival direction of the desired signal, B ₁ is the desired complex reception level in the φ ₁ direction, N is the number of elements, d is the element spacing, k is the wavelength constant of free space, Is.

Now Using the vector representation of (T: transposed symbol).

This constraint condition can be generally set for a plurality of directions φ ₁ φ ₂ ... φ _l ... φ _{L. In} this case, the constraint condition is
From (2), It is represented by. However, Is. The equation (3) represents that the received signal _{B 1 B 2 ... B l ...} B L for a plurality of directions φ ₁ φ ₂ ... φl ... φL is the desired amplitude and phase, respectively, array weight W ₁ W ₂
... W _n ... W _N must always satisfy the condition of this expression (3).

By the way, in order to suppress the unnecessary signal, it is necessary to determine the excitation weight so that a directional null (zero point) is formed in the arrival direction.

Proceedings of the 52nd Annual Meeting of IEICE General Conference S7-1
1 describes a constrained MSN algorithm for synthesizing a null-adaptive adaptive signal in the arrival direction of an undesired signal under the condition of Expression (3). According to the algorithm, each excitation weight is determined based on the following equation with respect to the constraint condition of equation (3).

here, Is a vector display of the beam scanning signal component to each element, Is a vector representation of the received unwanted signal component, and y is the combined output of the array antenna. tν and tν + 1 are Is a function of time and is a value at times tν and tν + 1. μ is a coefficient that controls the convergence speed of the excitation weight vector in equation (4), a is a constant determined from the input signal condition, Is the unit matrix. * Is a symbol that means complex conjugate.

Expression (4) is a convenient expression when the desired excitation weight is determined using the raw information of the unwanted signal in the real world.

On the other hand, from the standpoint of directivity synthesis without needing the raw information (time-dependent) of the unnecessary signal, the low sidelobe region of the directivity is expressed by a formula (4) It can be derived as follows.

Considering the case where the beam scanning signal is not supplied for simplicity, Therefore, equation (4) is Becomes (However, μs = μaa ^* ) In this equation (7), the nth excitation weight Wn (tν +
Focusing on 1), Wn (tν + 1) is It is represented by. However, Pn, 1 is the matrix shown in equation (5). (N, 1) -th element of Fn is the vector shown in equation (6) Is the nth element of.

Here, xl (tν) is the incident component of the unwanted signal wave to the l-th antenna element, and when there are M unwanted signal waves, Can be expressed as However, Am (tν), ωm, θm, and km are respectively the complex amplitude, angular frequency, arrival direction, and propagation constant of the m-th unwanted signal wave, and km = ωm / Vc (Vc: speed of light).

The combined output y (tν) of the array antenna is Therefore, in equation (8), μsxl (tν) ^* y (tν) is Becomes Further rearranging using equation (9), Becomes By the way, the directivity of the N-element array antenna with the element spacing d is as follows when the excitation weight is Wi (tν). Can be expressed as Therefore, the formula (10) is obtained by this directivity g (θ)
With, Substituting this into equation (8), the excitation weight Wn (t
ν + 1) is Becomes If the frequency and amplitude of the unwanted signal are constant regardless of time, km = k = constant, Am (tν) = A
= Constant, there is no need to use the arguments tν and tν + 1, the above equation becomes (However, μ ′s = μsA) can be expressed by a successive approximation formula.

From this equation (11), under the constraint condition shown in equation (3),
The excitation weight Wn (n is 1 to N) for improving the directivity in an arbitrary angular region can be determined successively. That is, first, using an arbitrarily set initial value W ₁ ⁽¹⁾ ... W _N ⁽¹⁾ of the excitation weight, Is used to determine g (1) (θ).

Let θ ₁ … θ _M be the angle region where you want to improve the directivity.
From the above equation, the directivity g ⁽¹⁾ (θ ₁ ) ... g in this angular range
⁽¹⁾ (θ _M ) is determined. These directivities g ⁽¹⁾ (θ ₁ ) ... g
⁽¹⁾ (theta _M) and array weight W ₁ ⁽¹⁾ ... W by substituting _N a ⁽¹⁾ into equation (11) as the initial values of directivity and array weight, sequential first array weight W ₁ ⁽²⁾ ... W _N ⁽²⁾ is determined. Similarly, the excitation weights W ₁ ⁽²⁾ ... W _N ⁽²⁾ and the directivities g ⁽²⁾ (θ ₁ ) ... g determined by these W ₁ ⁽²⁾ ... W _N ^{(2)
(2) Using} (θ _M ), the second excitation weight W ₁ ⁽³⁾ … W
_N ⁽³⁾ is determined.

Generally, this repetition is performed by exciting weights W ₁ ^{( ν +1)} ... as solutions when g ^{( ν )} (θ ₁ ) ... g ^{( ν )} (θ _M ) become zero.
If W _N ^{( ν +1)} continues ν times until W ₁ ^{( ν )} ... W _N ^{( ν )} respectively (solution converges), null (zero point) is formed in the angular region θ ₁ ... θ _M. It is possible to obtain directivity.

This directivity can be improved not only for a plurality of continuous angles but also for a plurality of discontinuous angles by arbitrarily designating the angles θ ₁ ... θ _M, and only for the angle θ ₁ . You can also do it.

Further, the above-mentioned sequential iteration does not necessarily have to be carried out until the solution converges, and substantially the solution (excitation weight) W ₁ ^{( ν +1)} ... W before convergence if the directivity is improved. _N ^{( ν +1)}
May be used.

By the way, for example, when the excitation weight distribution (amplitude distribution and phase distribution) of a 20-element array antenna with an element spacing d = 0.5λ is set as shown in FIG. 2, that is, each antenna element is excited with the same phase and equal amplitude. In this case, the directivity is as shown in FIG.

Here, in order to improve by reducing the side lobe in the region of the directivity angle from −8.0 ° to −24.0 °, equation (11)
When the excitation weights W ₁ ... W ₂₀ are calculated by, the amplitude component and the phase component are as shown in FIG. 3 (where M = 1.
8 and set to −24.0 ° θ ₁ ... θ _M −8.0 °, and constrain the directivity value of φ ₁ = 0 ° by the formula (3)). When each antenna element is excited with the excitation weight distribution shown in FIG. 3, the directivity is as shown in FIG. The directivity of FIG. 5 does not lead to a decrease in efficiency, as is clear from comparison with FIG. 4, and is −8.0 ° to 24.0.
It can be seen that the side lobes are reduced in the region of °.

Thus, by determining the excitation weight based on the equation (11), it is possible to reduce the side lobe of the directivity at an arbitrary angle. According to this, it is possible to improve the directivity in a certain angle region as shown in FIG.
It is also possible to improve only a small part of the directivity, for example, to make the rising part (or falling part) of the directivity pattern more rapidly completed as shown by R in FIG. That is, so-called directivity shaping that improves a part of the given directivity as necessary is possible.

If the exciter connected to each antenna element is set to the excitation conditions (amplitude, phase) determined based on Eq. (11) and each antenna element is excited, the array antenna with directivity that has been corrected and improved is obtained. realizable.

In this case, an exciter that can vary the excitation conditions (amplitude, phase) is used as the exciter, and the angle setter that sets the angle (θ ₁ ... θ _M ) for low sidelobe and the condition of equation (3) are set. An arithmetic unit is connected to the setter for setting (complex reception level condition (B ₁ ... _{BL L} ) setting and its angle (φ ₁ ... φ _L ) setting), and the arithmetic unit performs the calculation of formula (11). If the excitation condition of the exciter is set on the basis of the output of this computing unit, it is possible to quickly respond to changes in environmental conditions.

When the array antenna is used as a transmission antenna, the power-distributed signal is configured to be supplied to each antenna element via an exciter, and when it is used as a reception antenna,
After passing the signal received by each antenna element through the exciter,
It may be configured to synthesize. Of course, if a transmission / reception switch is connected to the power distributor / combiner, it can be used for both transmission and reception.

Further, the present invention can be applied to an array antenna composed of two or more antenna elements. Further, the present invention can be applied to a reflector antenna having a primary radiator having two or more elements. In this case, the reflector antenna is included in the array antenna according to the present invention because it has a plurality of primary radiators.

〔The invention's effect〕

As described above, according to the present invention, it is possible to provide an array antenna having a directivity in which correction and improvement are made with respect to an arbitrary angle without causing a decrease in efficiency, and a practical effect is great. .

[Brief description of drawings]

FIG. 1 is a diagram for explaining an array antenna, FIG. 2 is a diagram showing an excitation condition when exciting each antenna element of the array antenna with the same phase and equal amplitude, and FIG. 3 is a diagram showing an array antenna according to the present invention. FIG. 4 is a diagram showing the excitation condition of each antenna element in one embodiment, FIG. 4 is a diagram showing the directivity of the array antenna when excited under the conditions shown in FIG. 2, and FIG.
It is a figure which shows the directivity of an array antenna when it excites on the conditions shown in FIG. 1, 2 ... 20 ... Antenna elements.

Claims (1)

[Claims] 1. N (N is an integer of 2 or more) antenna elements, and each element of the N antenna elements is connected to each element, And an exciter that excites with an excitation weight Wn that is sequentially determined by the array antenna.