JPH0629719A - Phased array antenna - Google Patents

Abstract

PURPOSE:To prevent the reduction of the gain even in the case of a large angle formed between the main beam direction and a perpendicular line stood on the antenna array face by weighting the amplitude balance of an array antenna and suppressing the grating lobe or/and the side lobe at the time of beam scanning. CONSTITUTION:Phase shifters phi1, phi2,...phin are added to antenna elements A1, A2,...An respectively, and a controller CONT controls phase shifters, and a distributor CDIV weights the amplitude value of the signal to be supplied to each antenna and weights amplitude values of incoming signals from antennas to the distributor and synthesizes them and outputs the synthesis result to a transmitter-receiver TRX. Binomial distribution or Tchebycheff's weighting is proper as the weighting method. When the exciting current supplied to each antenna element or the phased array antenna is weighted, the gain is less reduced in comparison with the main beam in the front of the antenna array face even if the main beam is large deviated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase weighting method for a phased array antenna, and more particularly to a phased array antenna which suppresses side lobes and / or grating lobes to improve antenna directivity and gain.

[0002]

2. Description of the Related Art Recently, a system using an artificial satellite as a relay station has been put into practical use in order to secure a communication line between a fixed station on the ground and a moving body such as an automobile or an aircraft. Often uses a phased array antenna to automatically track satellites.
A phased array antenna is a device in which a plurality of antenna elements are arranged and the phase of a signal fed to each element is electrically changed to arbitrarily control the radiation beam direction.

FIG. 4 is a block diagram for explaining the basic concept of a phased array antenna. In the figure, A1, A2 ... An are each a plurality of antenna elements, φ1, φ2, ... φn are phase shifters added to each of the antenna elements, and DIV is the phase shifter and transceiver. It is a distributor inserted between the TRX and the TRX. Also, CONT
Is a controller, which is connected to the phase shifters φ1, φ2, ..., φn and controls the amount of phase shift of each phase shifter according to the directivity direction.

Next, the relationship between the antenna beam direction and the phase weighting will be described in detail with reference to FIG. FIG. 5 is a diagram showing an array antenna in which five antenna elements A0 to A4 are arranged at intervals d. Now, consider a case where a signal arrives from a direction (B _S ) deviated from θ ₀ from the vertical line of the antenna arrangement image. .

At this time, each antenna element has an antenna A
The radio wave arrives with a delay corresponding to the time required for the signal to propagate through the distances x ₁ , x ₂ , x ₃ , x ₄ between the vertical line drawn in the direction of arrival of the radio wave and each antenna starting from 0. To do.

Therefore, in the phased array antenna,
The phase delays of the above antennas are converted into phase shifters φ _{1 to} φ
_A larger incoming signal is obtained by correcting with _n and making the phases of all signals the same in the B _S direction and then combining them. Here, the distance xn is the distance d between the antenna elements.
Xn = nd × sin θ ₀ ···· (1) When the wavelength of the incoming signal is λ, this is expressed by the phase Ψn. When expressed, Ψn = kx ₀ = knd × sin θ ₀ (2) However, k is a wave number and k = 2π / λ.

The same applies to the case where the antenna is used as a transmitting antenna, and the signals emitted from all the antennas are controlled to have the same phase in the direction in which directivity is desired to be formed. However, when the microstrip antennas are arranged in a plane to realize a phased array antenna, the angle formed by the beam direction and the direction perpendicular to the plane is large, and the gain tends to decrease as the plane approaches. That is, FIG. 6 is a diagram for explaining this state, which is a virtual view of the beam direction of a phased array antenna using a microstrip antenna as seen from the side, and shows a perpendicular line 52 standing on the antenna array substrate 51. The direction is the front direction with respect to the array antenna substrate, and the gain in the case of forming the main beam in the direction is the largest, and the gain generally decreases as the main beam is gradually inclined in the left-right direction. This means that when the main beam is formed in the front direction, the phase shift amounts by the phase shifters attached to the respective antennas are all the same, whereas the main beam is deviated in either the left or right direction. The amount of phase shift of the signal supplied to each antenna is relatively increased, and the gain decreases as the deviation angle increases due to the phase shift error of each phase shifter. In particular, when the control of the phase shifter is digitally stepped up or down stepwise, the deviation amount error to be given to each phase shifter becomes larger than that when it continuously changes. The degree increases as the beam deflection angle increases.

As a result, as is generally known, when so-called beam steering is performed in a conventional phased array, as shown in FIG. 7, a side lobe having a level similar to that of the main beam in the direction opposite to the main beam 71. 72 is generated (hereinafter, this is referred to as a grating lobe).

The larger the beam scanning angle, the larger this grating lobe. FIG. 7 shows -6 from the front direction.
This is an example of the radiation pattern when beam scanning is performed in the 0 ° direction, but a grating lobe occurs in the direction opposite to the beam scanning direction. Therefore, since the radiation power is dispersed in both directions and is not concentrated in one direction, as the grating lobe becomes larger (in other words, the beam scanning angle becomes larger), the directional gain of the antenna not only decreases as described above. However, there is a drawback that when transmitting, it interferes with other radio stations in the grating direction, and when receiving, the noise level increases and S / N or D / U deteriorates.

[0010]

The present invention has been made in view of the above circumstances, and provides a phased array antenna that does not cause a decrease in gain even if the angle formed by the main beam direction and the perpendicular line standing on the antenna array surface is large. The purpose is to

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a phased array antenna for inputting or outputting a signal to a plurality of antenna elements and a phase shifter provided corresponding thereto through a distributor. The feature is that the amplitude balance is weighted to suppress the grating lobe and / or the side lobe at the time of beam scanning, and the amplitude balance of the array antenna is Chebyshev weighted.

[0012]

The present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, A ₁ , A ₂ , ... A _n are each a plurality of antenna elements, φ ₁ , φ _2, ... φ _n are phase shifters added to each of the antenna elements, and CONT is the shifter. It is a controller for controlling the phaser. The CDIV is a distributor having the function of characterizing the present invention. The amplitude value of the signal supplied to each antenna is weighted, and the amplitude value of the incoming signal input from the antenna to the distributor is weighted. It has a function of post-combination and output to the transceiver TRX. That is, the conventional distributor in the phased array antenna system simply distributes the electric power evenly, whereas the present invention is characterized in that the amplitude value is weighted with strength and weakness.

As a weighting method, for example, binomial distribution, Chebyshev weighting, etc. may be suitable. Chebyshev weighting is a method that has been conventionally used as a side lobe suppressing means in a beam direction fixed array antenna, and is described in detail in Chapter 5 of Ohmsha, "Antenna Engineering Handbook" edited by the Institute of Electronics and Communication Engineers, for example. ing.
Briefly explaining the Chebyshev distribution, this method keeps the sidelobe level of the array antenna below a certain allowable value, and in order to minimize the beam width at this time, the amplitude value of the excitation signal supplied to each antenna element is changed. This is a so-called weighting method in which the position is changed according to the position of the array. For example, FIG. 2 shows the amplitude value weighting for each antenna when the number of antenna elements is 6 and the side lobe is made equal to −30 dB with respect to the main beam.
An example of the term distribution is shown by the dotted line.

As described above, the present invention adopts the Chebyshev weighting or binomial distribution weighting method conventionally used for side lobe suppression in the phased array antenna to scan the main beam over a wide range. This is a reduction in gain reduction. That is, for example, as shown in FIG. 2, the current amplitude value of the signal supplied to each antenna element is given a light weight depending on the antenna array position, and becomes smaller as the distance to both sides increases. By weighting the excitation current supplied to each antenna element of the phased array antenna in this way, even if the main beam is largely deviated, the decrease in gain is less than that of the main beam in front of the antenna array surface.

FIG. 3 is a pattern characteristic diagram of a phased array antenna embodying the present invention, in which the gain difference between the case where the main beam 30 is formed in the central direction and the case where the main beam 31 is formed in the −60 degree direction. Is small, and it is understood that the gain hardly decreases.

Further, it is an effect of the present invention that the side lobe 32 with respect to the main beam 31 is suppressed to be relatively small. In the embodiment, a method has been described in which the divider DIV is used to set the amplitude balance of the array antenna to a desired value. However, as another method, the phase shifters φ ₁ , φ ₂ ,. -It may not be necessary to explain that the desired amplitude balance may be realized by using φ _n or the like. Furthermore, in the present embodiment, only the example in which the Chebyshev is weighted for the amplitude balance of the array antenna has been described.
In short, it is clear that the effect is the same regardless of what method is applied to the present invention as long as the side lobe is suppressed when beam scanning is not performed.

[0017]

As described above, the present invention can be applied to the phased array antenna only by applying the side lobe suppression method of the normal non-beam scanning array antenna, and the directional gain in beam scanning, especially in wide-angle beam scanning can be obtained. Or, it has a remarkable effect on the improvement of the operation gain.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention.

FIG. 3 is a diagram showing antenna directional characteristics when the present invention is implemented.

FIG. 4 is a block diagram of a conventional phased array antenna.

FIG. 5 is a diagram showing the principle of a phased array antenna.

FIG. 6 is a diagram illustrating a reduction in gain of a conventional phased array antenna pattern.

FIG. 7 is a characteristic diagram showing a conventional phased array antenna pattern.

[Explanation of symbols]

A ₁ , A ₂ , …… A _n ··· Antenna element φ ₁ , φ ₂ , …… φ _n ··· Phase shifter CDIV ··· Chebyshev distributor CONT ·· .... controller C _1, C _2, the amplitude output of ...... C _n ······ Chebyshev distributor

Claims (2)

[Claims] 1. A grating at the time of beam scanning by weighting the amplitude balance of the array antenna in a phased array antenna in which a signal is input to or output from a plurality of antenna elements and a phase shifter provided corresponding thereto through a distributor. A phased array antenna characterized by suppressing a lobe, a side lobe, or both. 2. The phased array antenna according to claim 1, wherein the amplitude balance of the array antenna is Chebyshev weighted.