JP3280088B2 - Array antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for reducing the influence of interference waves in fixed wireless communication and mobile wireless communication. In particular, the present invention relates to an array antenna capable of suppressing a side lobe in a specific direction.

[0002]

2. Description of the Related Art In the field of wireless communication such as fixed microwave communication and mobile communication, interference by radio waves of the same frequency from other stations poses a problem. FIG. 10 shows a mechanism that causes such inter-station interference. The receiving antenna 9.1 is installed such that the direction of its main beam 10 coincides with the direction of the transmitting antenna 9.2. However, if there is a radio wave source of the same frequency in the direction of the side lobe, the radio wave becomes an interference wave 11.
Will be received. In such a case, it is necessary to suppress only the reception level in the direction in which the interference wave 11 arrives without changing the reception level in the other direction. FIG.
In the figure, reference numeral 12 indicates a state of a side lobe in which a null point is formed.

As a method of suppressing only a side lobe in a specific direction, a method has been proposed in which nulls (zero points) are formed in a specific direction by changing excitation amplitudes and phases at both ends of an array antenna (Naoki Inagaki, Zero synthesis based on the principle of directivity product "IEICE Transactions on Information and Systems, J71-B, No. 5, 1989
August). FIG. 11 shows such a configuration example.

The array antenna having the configuration shown in FIG. 11 has radiating elements 21.1 to 2-2 arranged at a constant interval d on a straight line.
1. N, of which radiating elements 21.2 to
21. N-1 is connected to the input terminal 25 via the power divider 23.3 and the power divider 23.1 connected in multiple stages. Between power distributor 23.1 and power distributor 2
Radiating elements 21.2 to 21 corresponding to 3.1. A phase shifter 22. 1 is provided between N─1 and N─1. Radiating elements 21.1, 21. N is the power distributor 23.3,
It is connected to the input terminal 25 via the attenuator 24 and the power divider 23.2. Power divider 23.2 and radiating element 2
1.1, 21. N between the phase shifters 22.
2, 22.3 are provided. Radiating elements 21.1 to 21.
As N, a dipole antenna or a planar antenna is used.

Here, the case of radiating radio waves will be described, but the input terminal 25 and the radiating elements 21.1 to 21. By reversing the signal direction between N and N, the signal can be used for reception.

FIG. 12 shows an example of the distribution of the excitation amplitude when a null point is actually formed using such an array antenna, and FIG. 13 shows an example of the distribution of the phase. The radiation pattern at this time is shown in FIG. 14, and for comparison, the radiation pattern when null point synthesis is not performed is shown in FIG. In these figures, the spacing d of the radiating elements = 0.5 wavelength, the number of elements N
= 16.

In order to provide excitation coefficients as shown in FIGS. 12 and 13, the attenuators 24 in the configuration shown in FIG. 11 use the radiating elements 21.1, 21. N level is 5dB
The phase is set by the phase shifters 22.2 and 22.3 so that the phase at both ends is ± 30 °. The other phase shifters 22.1 may be fixed.

[0008]

However, in the array antenna shown in the conventional example, when a null point is synthesized, an attenuator is used to change the excitation amplitude of the radiating elements at both ends. And the gain is reduced.
In addition, in order to dynamically change the null point direction, three elements, that is, two phase shifters and an attenuator must be adjusted, and the operation becomes complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to solve such a problem and to provide an array antenna which does not cause a decrease in gain and can be easily adjusted in a null point direction.

[0010]

SUMMARY OF THE INVENTION An array antenna according to the present invention includes a plurality of antenna elements arranged on a straight line at substantially constant intervals, and an excitation amplitude and / or an excitation phase of each of the plurality of antenna elements. And a feed circuit that sets a direction of a beam obtained by the plurality of antenna elements by giving a relative difference, wherein the feed circuit is connected to every other one of the plurality of antenna elements. One circuit, a second circuit connected to elements other than the other elements and providing substantially the same excitation amplitude difference and excitation phase difference as the first circuit, and the second circuit and the first circuit. And a phase shifter for forming a null point in the beam distribution by the plurality of antenna elements by giving a phase difference to the phase shifter.

[0011]

A description will be given of a case where radio waves are radiated from the antenna elements. Excitation currents of one input terminal are supplied to the plurality of antenna elements with an amplitude difference and a phase difference given by a feed circuit. When receiving radio waves,
The operation is the same except that the signal path is reversed.

In this case, the power supply circuit is composed of two substantially equivalent circuits, and a variable phase shifter is inserted into one of its inputs. The output terminal of the circuit on the side where the variable phase shifter is inserted is connected to the variable terminal. The output terminal of the circuit on the side where the phase shifter is not inserted is alternately connected to the antenna element. With such a configuration, by changing the input phase of one of the feed circuits, the excitation phase distribution on the array antenna becomes uneven.
In the radiation pattern of such an array antenna, a null point is formed in a specific direction, and the direction of the null point can be changed by changing the size of the unevenness of the distribution.

[0013]

FIG. 1 is a diagram showing a configuration of an array antenna according to an embodiment of the present invention. In the following, a case where radio waves are radiated will be described as an example. However, if the direction of input and output is reversed, radio waves can be received according to this embodiment.

In this embodiment, the radiating elements 1.... As a plurality of antenna elements arranged on a straight line at substantially constant intervals.
1-1. N, and the plurality of radiating elements 1.1 to 1.. N
Of each of the plurality of radiating elements 1.1-1. A feed circuit 2 for setting the direction of the beam obtained by N is provided. When a radio wave is radiated, an excitation current is input from one input terminal 5 to the power supply circuit 2, and the power supply circuit 2 distributes the excitation current to each of the radiating elements 1.1 to 1.. N.

The feature of the present embodiment is that the power supply circuit 2 includes the radiating elements 1.1 to 1.. N as a first circuit connected to every other element, a power divider 3.1 arranged in multiple stages and a power supply line connecting the power dividers 3.1, and a first circuit connected to elements other than this every other element. As a second circuit for providing an excitation amplitude difference and an excitation phase difference substantially equal to one circuit, there are provided a plurality of power distributors 3.2 arranged in multiple stages and a feeder line connecting them, and the second circuit The radiating elements 1.1-1. The variable phase shifter 4 is provided as a phase shifter for forming a null point in the beam distribution by N.

Radiating elements 1.1-1. As N, a planar antenna such as a dipole antenna, a patch antenna, or a slot antenna is used.

The distribution ratios of the power distributors 3.1, 3.2, 3.3, between and between them and the radiating elements 1.1 to 1..
N by adjusting the length of the feed line between the radiating elements 1.1 to 1.. The amplitude and phase of the excitation current on N can be set to desired values. Instead of setting the length of the feed line, a general phase shifter may be used.

FIG. 2 shows an example of the excitation phase distribution on the radiating element.

In the configuration shown in FIG.
When the phase amount of the radiating elements 1.1 to 1.. It is assumed that the length of each feed line is adjusted so that the excitation phase on N becomes constant. It is assumed that the excitation amplitude demultiplexing is uniform. In this case, when the phase amount of the variable phase shifter 4 is adjusted to be δφ, the radiation elements 1.1 to 1.. The phase distribution on N is a distribution having irregularities as shown in FIG. The radiation directivity f (θ) of the array antenna having the element distribution d and the number N of elements having such a phase distribution is expressed by the following equation.

[0020]

(Equation 1) Here, θ is an angle, and f ₀ (θ) is the directivity of a uniformly distributed array antenna having the same interval and the same number of elements. As is clear from this equation, if δφ = 0, f (θ) = f
₀ (θ). In the case of δφ ≠ 0, a null point is generated at an angle θ _N where cos (πd / λ sin θ + δφ / 2) = 0. At this time, the angle θ _N
Is represented by the following equation.

[0021]

(Equation 2) As is apparent from this equation, the relationship between .delta..phi and theta _N is one-to-one correspondence, it is possible to adjust the direction of the null point by the value of .delta..phi.

FIG. 3 shows the number of elements N = 16 and the element spacing d = 0.
An example of a phase distribution for five wavelengths is shown, and FIG. 4 shows the resulting radiation pattern. In this example, the variable phase shifter 4
Is set to 60 °. At this time, FIG.
42 ° while maintaining the main beam direction as shown in
A null point can be formed in the direction of.

FIG. 5 shows a phase distribution when the phase amount δφ of the variable phase shifter 4 is set to 90 °, and FIG. 6 shows a radiation pattern obtained thereby. In this case, the null point is shifted in the direction of 30 °. The positions of these null points coincide with the values obtained by Equation 2. in this way,
By adjusting only one variable phase shifter 4, the position of the null point can be freely changed.

FIG. 7 shows another example of the excitation phase distribution on the radiation element, FIG. 8 shows an example of the phase distribution on the radiation element, and FIG. 9 shows an example of the radiation pattern obtained at that time.

In the excitation phase distribution shown in FIG. 7, the length of each feed line is adjusted, and the radiating elements 1.1 to 1.. Excitation phase difference between the N is set to be 2πd / λ sinθ _t, the variable phase shifter 4
Is obtained when the phase amount of δ is δφ. In this case, the direction of the main beam is offset by a theta _t from the front. FIG. 8 shows the phase distribution when δφ is set to 60 °,
FIG. 9 shows the radiation pattern. The main beam is deviated by −5 ° from the front direction, and the direction of the null point is formed at a direction substantially 45 ° from the main beam direction.

As described above, even when the phase distribution given in advance is not uniform, a null point can be generated at substantially the same point as when the phase distribution is uniform.

In the above description, the case where the excitation amplitude is uniform has been described. However, substantially the same effect can be obtained even when the amplitude distribution is not constant as in the Chebyshev distribution array or the Taylor distribution array. The variable phase shifter can be adjusted by remote control using a digital phase shifter or the like.

[0028]

As described above, the array antenna of the present invention can adjust the position of the null point of the radiation pattern without using an attenuator and by adjusting only one phase shifter. Since no attenuator is used, there is no gain reduction,
Since only one phase shifter needs to be adjusted, the interference wave can be suppressed with a simple mechanism. Therefore, the antenna can be installed in an area where the reflection objects and the interference stations are densely arranged, and the degree of freedom of arrangement of the antenna is increased. Further, since stations having the same frequency can be arranged at an arbitrary position, the line capacity can be greatly increased.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an example of an excitation phase distribution on a radiating element.

FIG. 3 is a diagram showing an excitation phase distribution when the number of elements N = 16, an element interval d = 0.5 wavelength, and a phase amount δφ = 60 °.

FIG. 4 is a view showing a radiation pattern obtained at the time of the excitation phase distribution shown in FIG. 3;

FIG. 5 is a diagram showing an excitation phase distribution when the number of elements N = 16, the element interval d = 0.5 wavelength, and the phase amount δφ = 90 °.

FIG. 6 is a view showing a radiation pattern obtained at the time of the excitation phase distribution shown in FIG. 5;

FIG. 7 is a diagram showing another example of the excitation phase distribution on the radiation element.

FIG. 8 is a diagram showing an excitation phase distribution when the number of elements N = 16, the element interval d = 0.5 wavelength, the inclination of the main beam is 5 °, and the phase amount δφ = 90 °.

FIG. 9 is a view showing a radiation pattern obtained in the case of the excitation phase distribution shown in FIG. 8;

FIG. 10 is a diagram illustrating a mechanism that causes inter-station interference.

FIG. 11 is a diagram showing a configuration of a conventional array antenna.

FIG. 12 is a diagram showing a distribution example of excitation amplitude when a null point is formed.

FIG. 13 is a diagram showing an example of phase distribution.

FIG. 14 is a diagram showing an example of a radiation pattern when nulls are formed.

FIG. 15 is a diagram showing an example of a radiation pattern when no null is formed.

[Explanation of symbols]

 9.1 Receiving antenna 9.2 Transmitting antenna 10 Main beam 11 Interference wave 21.1 to 21. N radiating element 22.1 to 22.3 phase shifter 23.1 to 23.3 power splitter 24 attenuator 25 input terminal

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-24803 (JP, A) JP-A-1-220503 (JP, A) JP-A-58-38004 (JP, A) 156611 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01Q 3/26 H01Q 3/34 H01Q 21/06 H01Q 25/02

Claims (1)

(57) [Claims] 1. A plurality of antenna elements arranged on a straight line at substantially constant intervals, and a plurality of antenna elements provided by giving a relative difference to respective excitation amplitudes and / or excitation phases of the plurality of antenna elements. A feeder circuit for setting a direction of a beam obtained by the element, wherein the feeder circuit comprises: a first circuit connected to every other element of the plurality of antenna elements; A second circuit that provides an excitation amplitude difference and an excitation phase difference substantially equivalent to the first circuit connected to elements other than the element, and between the second circuit and the first circuit. It provides a phase difference, array antenna in a direction corresponding to the phase difference, characterized in that it comprises a phase shifter for forming a null point of the distribution of the beam by the plurality of antenna elements.