JPH05283924A - Array antenna - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] Regarding an array antenna used in wireless communication, an object of the present invention is to realize an array antenna capable of narrowing the main beam width without lowering the gain. [Structure] At least one of the two local maximal points closest to each other in the angular range on either side with respect to the maximum position in the entire angular range among the maximal values serving as the target values when performing directivity synthesis An array antenna in which the level is -10 dB or more and 0 dB or less with respect to the maximum value, the levels of all other maximum points are lower than the level of this maximum point, and the amplitude and phase of the excitation current are constant with the same number of elements. The amplitude and phase of the excitation current obtained by deciding each local maximum value so as to have a value higher than the envelope value of each local maximum point in the array factor of are given to the radiating element 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for realizing an array antenna having a narrow main beam width in an array antenna used in a fixed wireless communication system or a mobile wireless communication system, in order to reduce the influence of interference waves. Is.

[0002]

2. Description of the Related Art An array antenna for a wireless communication system such as fixed wireless communication and mobile wireless communication has a structure shown in FIG. In the figure, 1 is a radiating element, 2 is a feeding circuit, 3 is an input terminal, and 4 is a main beam direction. As shown in the drawing, the antenna has N radiating elements # 1 to #N arranged in a straight line at regular intervals d. Generally, the radiation pattern f of such an array antenna is
(Θ) is represented by “Equation 6”.

[0003]

[Equation 6]

Here, θ is the angle, λ is the wavelength, and g (θ) is the radiation directivity of the radiating element. In addition, I _n and φ _n are the amplitude value and the phase value of the excitation current on the antenna element, respectively. ΣI _n exp (2πd / λsin θ in this equation
+ Φ _n ) is called the array factor. The array factor is when the directivity of the radiating element is isotropic (g (θ) = 1)
Corresponds to the radiation pattern f (θ) of the array antenna.

Conventionally, in order to maximize the gain of the antenna, the amplitude I _n and phase φ _n of the excitation current on the radiating element are set to be constant. FIG. 5B is a diagram showing an example of an array factor of a uniformly distributed array antenna having 14 elements and an element spacing of 0.5 wavelength.

[0006]

When performing fixed microwave communication or mobile communication using such an array antenna, as shown in FIG. 6, reflections caused by the surrounding environment and radio waves of the same frequency from other stations. Cause interference. When the interference wave comes from the direction away from the main beam as indicated by numeral symbol 11, the side lobe 9 may be suppressed.
On the other hand, when the interference wave comes from the direction close to the main beam as shown by numeral reference 12 in FIG. 6, it is necessary to narrow the width of the main beam to reduce the interference level as shown by numeral reference 8.2. is there.

As a simple method of narrowing the main beam in this way, a method of raising the side lobe level of an array antenna (hereinafter also referred to as Chebyshev distributed array antenna) having a constant side lobe level as shown in FIG. 7 can be considered.

However, when the Chebyshev array antenna is used to raise the entire side lobe, the power is dispersed in the side lobe, so that the gain is greatly reduced as compared with the uniform distribution array.

An object of the present invention is to provide an array antenna capable of narrowing the width of the main beam without significantly reducing the gain.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention focuses on the maximum position in the entire angular range among the maximum values that are the target values when performing directivity synthesis. At least one of the two closest local maxima in the angular range on one side is -10 with respect to its maximum value.
The level is above dB and below 0 dB, and further below -10 dB.
The levels of all local maxima other than the maxima of 0 dB or less are lower than the maxima of the levels of -10 dB or more and 0 dB or less, and the amplitude and phase of the excitation current are constant with the same number of elements. The excitation currents obtained by deciding the respective maximum values so that the values are higher than the envelope value of the respective maximum points in the array factor of the array antenna or higher than −15 dB with respect to the level of the maximum points. The amplitude and phase of are given on the radiating element.

[0011]

In the array antenna provided with the excitation coefficient of the present invention, only the first and second side lobes that most affect the main beam width are increased and the main beam width is narrowed. By doing so, the power dispersed in the side lobes becomes smaller than that in the Chebyshev distribution array, so that the gain reduction amount can be reduced while narrowing the main beam width.

[0012]

FIG. 1 shows an embodiment of the present invention. FIG. 1A shows the structure of the array antenna of the present invention.
In the figure, 1 represents a radiating element. As the radiating element, a plane antenna such as a dipole antenna, a patch antenna or a slot antenna is used. Reference numeral 2 is a feeding circuit, which is adjusted so that the amplitude and phase of the excitation current on the antenna element have predetermined values.

3 is an input terminal, 4 is a main beam direction,
Reference numerals 5.1 to 5.3 denote feed lines that give a phase difference for shaping a radiation pattern, and 6 denotes a power distributor. The excitation current distribution is adjusted by the power supply circuit shown by the broken line in the figure. The excitation amplitude distribution is given by changing the characteristic impedance of the matching line of the power distributor.

On the other hand, the excitation phase distribution is represented by numeral symbols 5.1 to 5.1.
It is given by changing the length of the feeder line shown in 5.3. Regarding the phase distribution, a general phase shifter may be used instead of the feed line.

FIG. 1B is a diagram showing an example of the array factor. Here, the structural parameters are the same number of elements N = 14 and the element spacing d = 0.5 wavelength as in the case of FIG. 5 described above. The shaded area in the figure is the range of each side lobe level defined in the claims of the present invention when only the first side lobe is raised. The array factor shown by the solid line in FIG. 5 is an example in the case where the first side lobe on one side is raised to −5 dB and the other side lobe levels are kept constant at −12 dB.

This pattern falls within the side lobe level range defined by the present invention. The angle from the peak point of the main beam to the first null point A in the figure is defined as the beam width here. In FIG. 1B, the beam width is 6.2 °, and the beam width of the uniform distribution array shown in FIG.
You can see that it becomes as narrow as%.

A procedure for actually synthesizing the radiation patterns shown in FIG. 1B will be described below. The array factor of the number N of elements and the element spacing d can be generally expressed as "Equation 7".

[0018]

[Equation 7]

However, u is a normalized angle u = 2πd / λ
It is expressed as sin θ. λ is the wavelength, u _i is the angle of the i-th null point, and C is a complex constant. As can be seen from this equation, the shape of the radiation pattern is uniquely determined when the position of the null point is determined. Therefore, the target value of the m-th side lobe is f _m
^{As p} , a method of adjusting the position of each null point so that the formed pattern matches the target value can be considered.

First, a uniform distribution array antenna is used as an initial value.
Null like Chebyshev array antenna
Radial pattern with known point position and level for each sidelobe
Select the option. Now, the nth null point position is u_n, Mth
The side lobe level of f _{1, m} ^p, The angle of the peak point
u_m ^pAnd Here, “Equation 8” and “Equation 9” are set.

[0021]

[Equation 8]

[0022]

[Equation 9]

When d = 0.5λ, there are N−1 sidelobe numbers including the main beam. Therefore, the null point at the position of u _N-1 is fixed, and the position of each root is set to a small amount δu _1, δu.
The relationship between B _m and A _mn when shifted by _2, ..., δu _N-2 is “Equation 10”, and δC, δu _1, δu _2, ... _, δu _N-2 are unknowns (N−1). It is expressed in the form of simultaneous equations.

[0024]

[Equation 10]

Δu _1, δu _2, ..., Obtained by solving this equation
The level f _{2, m} ^p of each side lobe of the radiation pattern obtained when each null point is deviated by δu _N-2 is obtained.
When this level deviates from the target value, f _{1, m} ^p is further replaced by f _{2, m} ^p in “Equation 8”, and u _{n in} “Equation 9” is calculated.
Is calculated again as u _n + δu _n . By repeating this procedure, the angle of the null point when each sidelobe value matches the target value is obtained. The amplitude value and the argument of the complex coefficient of the (e ^ju ) ⁿ term when the angle of the null point is substituted into "Equation 7" and expanded are the amplitude and phase of the excitation current of the n-th element.

When the excitation current amplitude and phase distribution giving the radiation pattern of FIG. 1B is obtained by this method,
The distributions shown in (a) and (b) are obtained. When calculating the excitation coefficient, d = 0.5λ and
It is necessary to calculate “Equation 10”, but the actual element spacing of the array antenna can be set to an arbitrary value as long as the excitation coefficient is obtained.

In FIG. 3, the two side lobes near the main beam are raised to -5 dB and the other side lobes are set to -12 d.
It is a figure which shows the array factor when it is set to B. The shaded area in the figure is the range of each side lobe level defined in the claims of the present invention when the first side lobe and the second side lobe are raised. In this case, the beam width is 6.11 °, which is narrowed to about 75% of the uniform distribution array shown in FIG. Note that similar characteristics can be obtained even if the levels of the first and second side lobes are not equal.

The effect of this antenna will be described from the relationship between gain and beam width with reference to FIG. The curve plotted with ● is characteristic when one side lobe is raised and the level of other side lobe is -12 dB as shown in Fig. 1 (b), and the curve plotted with ○ is uniform. In the radiation pattern of the distributed array antenna, the characteristics when only the first side lobes are raised, and the curve plotted with ▴ shows the characteristics when the side lobe levels of the Chebyshev distributed array antenna are changed.

Here, a dipole antenna is used as the radiating element. In this case, the gain can be calculated by integrating the pattern obtained by the product of the array factor and the directivity of the dipole. In the figure, the gain is represented by a relative value when the gain of the uniform distribution array antenna is 0 dB. Also, the numerical value in the parentheses represents the level of the first side lobe. The ⊚ mark on the curve plotted with the ● marks indicates the beam width and gain of the radiation pattern shown in FIG. 1 (b).

Comparing the gains when the beam width is narrowed to 77% of the uniform distribution array antenna as shown by ⊚, it is −1.04 dB in the Chebyshev distribution array, while in the curve of ●, −. 0.56 dB and 0.
48 dB higher. As described above, this antenna has an advantage that a higher gain can be obtained than the Chebyshev array antenna with the same beam width. Similar data are obtained when the two lobes are pulled up as shown in FIG.

When the main beam width is narrowed by raising the first and second side lobes, it is necessary to make the power dispersion as small as possible in order to suppress the decrease in gain. Therefore, the side lobes other than the raised side lobes must be kept lower than the raised side lobes. The lower limit of the sidelobe level is based on the following grounds.
In FIG. 4, the data of the uniform distribution array has a relative gain of 0d.
B, the beam width is 1 and the gain is maximum in this case.

It can be seen that the -15 dB Chebyshev distribution array has substantially the same gain and beam width as the uniform distribution array. The curve plotted with a circle in FIG. 4 is the characteristic when only the first side lobe is raised in the uniform distribution array antenna, and this is almost the same tendency as when the first side lobe of the −15 dB Chebyshev distribution array is raised. is there.

When this characteristic is compared with the characteristic of the Chebyshev distributed array antenna plotted by ▴, it becomes almost the same when the beam width is 0.85 or more. Therefore, the first and second
If the components other than the side lobes are lower than -15 dB, the gain improving effect is lost. Similarly, the gain is not improved when the side lobes other than the first and second side lobes are lower than the side lobe level of the uniform distribution array. Therefore, the first
Side lobe level other than the second side lobe is -15d
It must be set above B or above the sidelobe level of a uniformly distributed array.

Generally, the first side lobe of a uniformly distributed array antenna is higher than -15 dB, so that the lower limit of the first side lobe on the unpulled side is about -15 dB as shown by the slanted line in FIG. 1 (b). For the side lobes other than, the side lobe level of the uniform distribution array is the lower limit.

In this way, the side lobe range in which the gain is higher than that of the Chebyshev distributed array antenna with the same beam width is defined.

[0036]

As described above, according to the present invention, it is possible to realize an array antenna in which the width of the main beam can be narrowed without lowering the gain. Since the interference wave in the vicinity of the main beam can be suppressed, the antenna can be installed even in the area where the reflectors are dense in the vicinity of the main beam direction, so that the degree of freedom in arranging the antenna increases. Also, since stations of the same frequency can be placed close to each other, there is an advantage that the line capacity can be greatly increased.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the excitation current amplitude and phase of the array antenna for giving the radiation characteristic shown in FIG. 1 (b).

FIG. 3 is a diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a main beam width and a gain.

FIG. 5 is a diagram showing an example of a configuration and a radiation characteristic of a conventional uniform distribution array antenna.

FIG. 6 is a diagram illustrating a problem that occurs when a conventional array antenna is used for communication.

FIG. 7 is a diagram showing an example of a radiation pattern of a conventional Chebyshev distributed array antenna.

[Explanation of symbols]

 1 Radiating Element 2 Feeding Circuit 3 Input Terminal 4 Main Beam Direction 5.1-5.3 Feeding Line for Providing Phase Difference 6 Power Distributor 7.1, 7.2 Radio Communication Antenna 8.1, 8.2 Main beam 9 Sidelobe 10 Direct wave 11 Interference wave from sidelobe direction 12 Interference wave from main beam direction

Claims (1)

[Claims] 1. An array antenna in which arbitrary N radiating elements are arranged on a straight line at a constant interval d, and for arbitrary complex number C, arbitrary N-1 real numbers u _i are substituted into "Equation 1". N-1 maximum values f _{1, m} ^p (m = 1, 2,
, N-1), the angle u _m ^p of the maximum value, and the predetermined maximum value f _m ^p , δc, δu ₁ satisfying “Expression 4” when “Expression 2” and “Expression 3” are set. , ... δu _N-2 ,
The amplitude value and the deflection angle of the complex coefficient of each (e ^ju ) ⁿ term when the equation is expanded by substituting it into “Equation 5” become the amplitude value and the phase value of the excitation current of the n-th antenna element, respectively. In the set array antenna, Where u = 2πd / λ sin θ, λ is the wavelength, and θ is the angle [Equation 3] [Equation 4] [Equation 5] At least one of the two local maximal points closest to one of the predetermined maxima f _m ^{p in} the angular range on either side with respect to the maximum is −
It is a level of 10 dB or more and 0 dB or less, and further, the levels of all the maximum points other than the maximum points of the level of -10 dB or more and 0 dB or less are lower than the levels of the maximum points of the level of -10 dB or more and 0 dB or less,
Moreover, it is higher than the envelope value of each maximum point in the array factor of the array antenna in which the amplitude and phase of the excitation current are constant with the same number of elements, or −15 with respect to the level of the maximum point.
An array antenna, wherein the maximum value f _m ^p is set so as to have a value higher than dB.