JP5025564B2 - Array antenna, array antenna arrangement method, adaptive antenna, radio wave direction detection device - Google Patents

Description

  The present invention relates to an array antenna used for a radar or the like, an array antenna arrangement method, an adaptive antenna including an array antenna, and a radio wave direction detecting device.

  Conventionally, broadband antennas typified by spiral antennas and log-peri antennas have an effective gain in a wide frequency range, but they must have an antenna diameter corresponding to the lowest frequency in the effective range. In the case of the configuration, there is a problem that a grating lobe is generated at a high frequency. When the grating lobe is generated, the suppression performance of the adaptive antenna is lowered, and the radio wave direction detection device cannot identify the true direction, which increases the error. In order to suppress such grating lobes, it is effective to arrange the antennas at unequal intervals, but it is necessary to further increase the antenna interval, the number of antennas per unit area is reduced, and the aperture efficiency is reduced. There was a problem (for example, refer to Patent Document 1).

JP 2004-56706 A

  In the conventional array antenna of the wideband antenna, it is necessary to use an antenna having a large antenna diameter corresponding to a low frequency, and there is a problem that a grating lobe is generated at a high frequency. Further, even in a system using unequal spacing, there is a problem that the antenna spacing increases and the aperture efficiency decreases.

  An object of the present invention is to provide an array antenna that suppresses grating lobes and does not reduce aperture efficiency.

The present invention is an array antenna in which phase centers of a plurality of broadband antennas having different antenna diameters are arranged on a one-dimensional axis, and the plurality of broadband antennas are arranged between two phase centers adjacent to each other on the axis. Is arranged so as to increase in order by a constant increase amount from one end of the axis toward the other end, and the broadband antenna having an antenna diameter according to the interval between the phase centers is arranged, The shift rate consisting of the ratio of the increase amount and the average value of the distance between the phase centers on the axis is set to be the reciprocal of the value obtained by subtracting 1 from the number of the broadband antennas arranged on one axis. This is an array antenna.

  The effect of the array antenna according to the present invention is that it is possible to suppress the grating lobes by arranging the wideband antennas having different antenna diameters at unequal intervals, and to arrange the wideband antennas having different antenna diameters to be filled. A wide-band array antenna with good aperture efficiency can be configured.

Embodiment 1 FIG.
1 is a front view of an array antenna according to Embodiment 1 of the present invention.
As shown in FIG. 1, an array antenna 1 according to Embodiment 1 of the present invention is composed of a plurality of wideband antennas having different antenna diameters. The wide-band antenna includes a low-frequency wide-band antenna 2 with the largest antenna diameter that can handle low-frequency frequencies, an intermediate-frequency broadband antenna 3 that can handle medium-frequency frequencies, and an antenna aperture that can handle high-frequency frequencies. Are included. Here, as a representative of the broadband antenna, a spiral antenna is used as a model, and the outer shape of the broadband antenna is indicated by a circle.

FIG. 2 schematically shows the frequency characteristics of the gain of the spiral antenna.
Here, representing the lower frequency _{F L,} a midrange frequency _{F M,} the high-pass frequency _{F H.}
Spiral antenna, as shown in FIG. 2, a wideband antenna may have a substantially constant gain at frequencies higher than the low frequency F _L. Conversely, since the low frequency F _L sufficient gain can not be obtained at lower frequencies, it must be designed antenna to be lower than the band lower frequency of required low frequency F _L. In the case of a spiral antenna, the low frequency F _L is given by equation (1) where r is the radius of the antenna. Here, c = 3 × 10 ⁸ (m / s) is the speed of light.

In equation (1) means that the circumferential length of the spiral antenna is coincident with the wavelength in the low frequency F _L. Expressed the lower frequency of the necessary bandwidth F _LN, it is necessary to set the lower frequency F _L lower than the lower frequency F _LN as shown in equation (2).

From equation (2), in order to lower the lower frequency F _LN, it is necessary to increase the antenna size in accordance with the lower frequency F _LN. When an array antenna is configured using such a broadband antenna, a triangular arrangement as shown in FIG. 8 is generally used. When this triangular arrangement is used, the distance between the antennas in the horizontal direction can be reduced, the antennas can be arranged densely, and the aperture efficiency can be improved. For example, when receiving a radio wave having a low frequency F _L , the wavelength λ is λ = c / F _L = 2πr, and therefore the phase center of the antenna in the horizontal direction (in this case, the center of the circle. (The position of the position means the position of the phase center unless otherwise noted). The distance between them can be about the radius r of the antenna and can be reduced to 1/2 of the wavelength, so that it can be made sufficiently smaller than the half wavelength. . Therefore, there is no fear of generating a grating lobe. However, using the same antenna, for example, considering a case of receiving a radio wave of 10 times the frequency of the low frequency F _L, wavelength becomes 1/10, the antenna spacing increases to about 1.7Ramuda. When the antenna interval is increased, the same phase state is obtained in directions other than the desired direction, so that a so-called grating lobe having the same gain as the main lobe is generated.

For example, when receiving using an array antenna that generates such a grating lobe, there is a problem that unnecessary radio waves are received from directions other than the main lobe. There is a problem that becomes an interference source.
Further, when applied to an adaptive antenna, when an interference wave arrives from the grating lobe direction, the main lobe is also suppressed, and there is a problem that the S / N ratio is greatly reduced.
Further, when applied to a radio wave arrival direction detection device, if there are grating lobes having the same reception phase state, there arises a problem that the grating lobe direction corresponding to the true direction cannot be identified.

  Therefore, it has been conventionally known that it is effective to arrange the antennas at unequal intervals in order to suppress such grating lobes. However, in order to effectively suppress the grating lobes, the antennas need to be largely dispersed. For example, as shown in FIG. 9, the antenna interval increases, and the number of antennas per unit area decreases. For this reason, when the area which can arrange | position an antenna is limited, the fall of the antenna gain by the number of antenna reduction becomes a subject.

  Therefore, in the array antenna according to Embodiment 1 of the present invention, as shown in FIG. 1, spiral antennas having different antenna diameters are arranged so as to be arranged at unequal intervals. In order to efficiently arrange the antenna within the unit area, first, the low-frequency wideband antenna 2 having a large antenna diameter is arranged in a region where it can be arranged at unequal intervals. Then, the mid-band broadband antenna 3 having an intermediate antenna diameter is arranged so as to be filled at unequal intervals in the gaps in which the low-band broadband antenna 2 is arranged. Finally, the high-frequency broadband antenna 4 having the smallest antenna diameter is arranged at unequal intervals so as to fill the gap between the low-frequency broadband antenna 2 and the mid-frequency broadband antenna 3. In the array antenna according to Embodiment 1 of the present invention, three types of wideband antennas having different antenna diameters are used. However, two antenna diameters may be used, and naturally, four or more antenna diameters may be used.

  In this way, wideband antennas with different antenna diameters can be arranged at unequal intervals to suppress grating lobes, and wideband antennas with high aperture efficiency can be suppressed by placing wideband antennas with different antenna diameters. An antenna can be configured.

  Here, a spiral antenna is used as the broadband antenna, but a log-peri antenna may be used as the broadband antenna.

FIG. 5 is a diagram showing a beamformer using an array antenna composed of a plurality of wideband antennas having different antenna diameters. In FIG. 5, the low-frequency broadband antenna 2, the mid-frequency broadband antenna 3, and the high-frequency broadband antenna 4 are collectively referred to as a broadband antenna 10.
The beamformer 11 includes an array antenna 1 including a plurality of wideband antennas 10 having three types of antenna diameters, a multiplier 5 that multiplies a signal from each wideband antenna 10 by a complex load that controls phase and amplitude, and each multiplier 5. Is provided.
The beamformer 11 uses the array antenna 1 in which a plurality of wideband antennas 10 having three types of antenna diameters are arranged at unequal intervals, so that grating lobes can be suppressed during reception, thereby reducing the amount of unnecessary signals received. Can be made. Further, when this beam former 11 is used for transmission, the amount of unnecessary radiation due to the grating lobe can be reduced.

FIG. 6 is a diagram showing an adaptive antenna using an array antenna composed of a plurality of wideband antennas having three types of antenna diameters. In FIG. 6, as in FIG. 5, the low-frequency broadband antenna 2, the mid-frequency broadband antenna 3, and the high-frequency broadband antenna 4 are collectively referred to as a broadband antenna 10.
The adaptive antenna 12 controls the amplitude and phase of the received signal from the array antenna 1 and the wideband antenna 10 composed of a plurality of wideband antennas 10 having three types of antenna diameters, and suppresses interference waves in the combined signal. Adaptive signal processing means 7 for automatically controlling is provided.
When the interference wave is suppressed, a null is formed in the incident direction of the interference wave in the antenna pattern. When the array antenna has a grating lobe, there is an orientation having the same reception phase characteristics as the main lobe. For example, when an interference wave is incident from the grating lobe direction, the main lobe direction is also null. Therefore, there is a problem in that the desired wave is suppressed and the S / N ratio is consequently reduced.
However, when the array antenna 1 according to Embodiment 1 of the present invention in which a plurality of wideband antennas 10 having three different antenna diameters are arranged at unequal intervals is applied to the adaptive antenna 12, the grating lobe is suppressed. Therefore, the incident direction of the interference wave that causes performance degradation can be eliminated.
Further, since the gain can be improved by increasing the aperture efficiency, it is possible to receive with a higher S / N ratio.

FIG. 7 is a diagram illustrating a configuration of a radio wave direction detecting device using an array antenna including a plurality of wideband antennas having three types of antenna diameters. In FIG. 7, similarly to FIG. 5, the low-frequency broadband antenna 2, the mid-frequency broadband antenna 3, and the high-frequency broadband antenna 4 are collectively referred to as a broadband antenna 10.
The radio wave direction detection device 13 includes an array antenna 1 composed of a plurality of wide band antennas 10 having three types of antenna diameters, and a radio wave direction detection unit 8 that detects a radio wave arrival direction using received signals from the wide band antenna 10.
Various methods have been proposed as the radio wave direction detecting means 8, but in principle the arrival direction is detected by detecting the reception phase characteristic of the array antenna in the arrival direction as represented by the Multiple Signal Classification (MUSIC) algorithm. Looking for. For this reason, when a grating lobe is generated, a false image is generated in a direction other than the true direction, thereby causing erroneous detection and causing performance degradation.
However, when the array antenna 1 arranged at unequal intervals of a plurality of wideband antennas having different antenna diameters according to the present invention is applied to the radio wave direction detecting device 13, the grating lobe can be suppressed. Therefore, it is possible to avoid false detection caused by a false image generated in a direction other than the arrival direction, and to detect the true direction effectively.
In addition, since the gain can be improved by increasing the aperture efficiency, the radio wave direction can be detected with higher accuracy.

Embodiment 2. FIG.
FIG. 8 is a front view of an array antenna according to Embodiment 2 of the present invention.
The array antenna 1B according to the second embodiment of the present invention is composed of wideband antennas having two types of antenna diameters. The wideband antenna is a low-frequency wideband with a larger antenna diameter that can correspond to a low-frequency. The antenna 2 includes a middle-band wideband antenna 3 having a smaller antenna diameter that can correspond to a mid-frequency. Further, as an unequal interval arrangement method that can effectively suppress grating lobes, Reference Document 1 (Kazufumi Hirata and four others, “Distribution array antenna arrangement method for suppressing grating lobes”, IEICE Tech. 15, the Institute of Electronics, Information and Communication Engineers, May 2005, p. 35-40), the quantitative shift arrangement method is applied in the vertical direction and the horizontal direction.
The fixed shift arrangement can effectively suppress the grating lobe and can easily design an optimum shift amount from the conditions of the number of antennas and the viewing angle (an angle at which no grating lobe is generated).

Here, for the sake of simplicity, the quantitative shift arrangement will be described by taking the low-frequency wideband antennas 2 arranged in one horizontal row at the bottom of FIG. 8 as an example. In this horizontal one stage, the four low-frequency wideband antennas 2 are arranged at three types of antenna intervals. The antenna interval is increased by a certain shift amount δ _{h in} order from the left end with respect to the low-frequency wideband antenna 2 of FIG. When the average of these three antenna intervals is d ₀ , the antenna intervals are d ₀ −δ _h , d ₀ , d ₀ + δ _h from the left end. Thus the arrangement method of increasing the antenna apart by a predetermined shift amount [delta] _h is called a quantitative shift arrangement. Further, as shown in the equation (3), the ratio of the shift amount δ _h and the average d ₀ of the antenna interval is called a shift rate (S _r ).

Quantitative shift arrangement, the viewing angle is determined by the shift amount [delta] _h, the optimal shift ratio S _r to suppress the grating lobes is determined by the number of antennas. Therefore, a condition for the shift amount δ _h is determined according to the required viewing angle, and the design is made so that the optimum shift rate S _r is obtained under this condition. With respect to the derivation of optimum shift ratio S _r is omitted, given by equation when be as the number of antennas M, which is described in Reference 1 (4).

For example, in the case of FIG. 8, since the number M of antennas is 4, the shift rate _Sr is 1/3. Since the antenna diameter is sufficient in the horizontal direction of FIG. 8, the grating lobe can be effectively suppressed by arranging the low-frequency wideband antenna 2. It is also possible to increase the number of antennas in order to increase the aperture efficiency.

Next, description will be given of arranging a plurality of wideband antennas in two dimensions in the vertical direction and the horizontal direction by applying the quantitative shift arrangement. FIG. 8 shows an example in which a two-dimensional grid is formed so as to have a fixed shift arrangement in the vertical direction and the horizontal direction, and a broadband antenna is arranged at the intersection of the two-dimensional grid. Although the lateral direction of the antenna interval has already been described, similarly can be applied to quantitative shift vertically arranged, fixed shift amount in the vertical direction [delta] _y, the average of the antenna interval is d _l. At this time, similarly to the transverse direction, the optimal shift ratio S _r of the vertical direction is given by equation (5).

  When an optimum design is performed, for example, the antenna interval needs to be narrowed as shown in the vertical direction of FIG. In that case, the mid-band broadband antenna 3 may be arranged immediately above the lowermost stage in FIG. In this case, the grating lobe can be suppressed without reducing the aperture efficiency.

In addition, the antenna diameter of the low-frequency wideband antenna 2 may be larger, and one low-frequency wideband antenna 2 may occupy an intersection of two or more grids. In such a case, as shown in FIG. 9, the low-frequency wideband antenna 2 may not be arranged at the intersection. As shown in FIG. 9, when the broadband antenna is two-dimensionally arranged, the antennas may be arranged on all grids as a projection in the horizontal direction and the vertical direction. For example, when the radio wave direction detecting device is configured using the array antenna shown in FIG. 9, it can be designed to suppress the grating lobe in both the azimuth direction and the elevation direction, so that the direction detection error due to the false image is reduced. There is an effect that the direction of arrival of radio waves can be detected without occurring.
Further, in order to increase the aperture efficiency, a wide-band antenna having a small antenna diameter may be filled in the gaps in FIG.

  As described above, the array antenna according to the second embodiment has an effect that the grating lobe can be effectively suppressed by arranging the broadband antenna based on the quantitative shift arrangement. In addition, since wide-band antennas having different antenna diameters are formed on a two-dimensional grid using a quantitative shift arrangement and arranged on the intersection, it is possible to arrange with an optimum shift rate and not to lower the aperture efficiency.

It is a front view of the array antenna which concerns on Embodiment 1 of this invention. The frequency characteristic of the gain of a spiral antenna is typically shown. It is a front view of the array antenna which arranged the broadband antenna in the triangle. FIG. 3 is a front view of an array antenna in which wideband antennas are arranged with varying antenna intervals. It is a figure which shows the beam former using the array antenna comprised by the several wideband antenna of three types of antenna diameters. It is a figure which shows the adaptive antenna using the array antenna comprised by the several wideband antenna of three types of antenna diameters. It is a figure which shows the structure of the radio wave direction detection apparatus using the array antenna comprised with the several wideband antenna of three types of antenna diameters. It is a front view of the array antenna which concerns on Embodiment 2 of this invention. It is a front view of an array antenna when the antenna diameter of the low-frequency wideband antenna of FIG. 8 is increased.

Explanation of symbols

  1, 1B array antenna, 2 low-band wideband antenna, 3 mid-band wideband antenna, 4 high-band wideband antenna, 5 multiplier, 6 combiner, 7 adaptive signal processing means, 8 radio wave direction detecting means, 10 wideband antenna, 11 beam Former, 12 adaptive antenna, 13 radio wave direction detecting device.

Claims (5)

An array antenna in which phase centers of a plurality of wideband antennas having different antenna diameters are arranged on a one-dimensional axis,
The plurality of broadband antennas are arranged such that an interval between two phase centers adjacent to each other on the axis increases in order as the distance increases from one end of the axis to the other end,
Place the broadband antenna of the antenna diameter according to the interval between the phase centers ,
The shift rate consisting of the ratio of the increase amount and the average value of the distance between the phase centers on the axis is set to be the reciprocal of the value obtained by subtracting 1 from the number of the broadband antennas arranged on one axis. An array antenna. An array antenna in which phase centers of a plurality of wideband antennas having different antenna diameters are arranged at intersections between a plurality of parallel first axes and a plurality of second axes orthogonal to and parallel to the first axis. There,
In the plurality of wideband antennas, the interval between two phase centers adjacent to each other on the first axis is a constant first increase in order from one end of the first axis toward the other end. As the distance between two phase centers adjacent on the second axis increases from one end of the second axis toward the other end, the second increase amount increases in order. Arranged to increase,
Place the broadband antenna of the antenna diameter according to the interval between the phase centers ,
The first shift rate, which is the ratio of the first increase amount and the average value of the distance between the phase centers on the first axis, is calculated from the number of the broadband antennas arranged on one first axis. A reciprocal of the value obtained by subtracting 1 is set, and a second shift rate consisting of a ratio between the second increase amount and the average value of the intervals between the phase centers on the second axis is one. An array antenna, wherein the array antenna is set to be a reciprocal of a value obtained by subtracting 1 from the number of the wideband antennas arranged on the second axis . A plurality of first axes that are parallel to each other and spaced apart from each other by a constant first increasing amount in order from a small interval to a large interval, and are orthogonal to and parallel to the first axis and from a small interval to a large interval An array antenna arrangement method that arranges phase centers of a plurality of wideband antennas having different antenna diameters at intersections with a plurality of second axes that are separated by an interval that increases in order by a constant second increase amount,
The ratio between the first increase amount and the average value of the distance at which the first axis is separated is the reciprocal of the value obtained by subtracting 1 from the number of the wideband antennas arranged on one second axis. And setting an interval for separating the first increase amount or the first axis,
The ratio of the second increase amount and the average value of the interval at which the second axis is separated is the reciprocal of the value obtained by subtracting 1 from the number of the wideband antennas arranged on one first axis. Set the second increase amount or the interval at which the second shaft is separated,
An array antenna arrangement method comprising: firstly arranging the broadband antenna having the largest antenna diameter on the intersection, and then arranging a broadband antenna having a small antenna diameter according to the distance between the fulcrums. An adaptive antenna comprising the array antenna according to claim 1 or 2 . A radio wave direction detecting device comprising the array antenna according to claim 1 or 2 .

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