JPS5846082B2 - array antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an array antenna in which a plurality of antenna elements are arranged in one direction or in multiple directions.

In general, in an array antenna in which antenna elements are arranged at equal intervals on a straight line or on a plane, three-dimensional surface, curved surface, etc., when the electrical length between the antenna elements becomes long, the radiation direction In addition to the main lobe, a grating lobe with almost the same intensity as the main lobe is generated in the sexual pattern.

In other words, if the spacing between antenna elements is physically constant, the electrical length increases as the frequency increases.
Grating lobes are more likely to occur.

The generation of this grating lobe is a factor that limits the effective bandwidth of the array antenna.

In addition, the presence of grating lobes in the specificity pattern can lead to misidentification of the target when the array antenna is used as a radar antenna that requires broadband characteristics or as a transmitting/receiving antenna for radio waves emitted from radar. It also becomes.

Therefore, removing or suppressing grating lobes is an important issue.

By the way, as shown in Fig. 1, the radiation directivity E of an array antenna in which N antenna elements IA having exactly the same size and electrical characteristics are arranged in a straight line M at intervals d is given by the following formula: It is expressed as

(However, λ: Free space wavelength of the frequency used, θ: Angle from the normal direction to the antenna element array straight line) In equation (1), E(θ) is a periodic function, regardless of the value of the interval d. The maximum value, ie, the main lobe, occurs at θ=0.

However, if d-λ, as shown in the radiation directivity pattern in Figure 2, E(θ) has a maximum value even in the direction of θ = ±900, and has a grating lobe with the same intensity as the main lobe. It becomes like this.

This is because the radio waves radiated from each antenna element 1A are combined in phase at the observation point, and this phenomenon occurs when the interval d is an integral multiple of the wavelength λ.

Furthermore, even if the antenna elements are arranged in two or three dimensions, the radiation directivity has the same properties as in the above case, and in either case, grating lobes occur because the antenna elements are spaced evenly. do.

Therefore, a possible method for removing or suppressing grating lobes is to arrange the antenna elements at irregular intervals or at random instead of arranging them at equal intervals.

However, with these methods, it is not easy to find an arrangement state that actually eliminates grating lobes, and the manufacturing process is also complicated.

Furthermore, even if grating lobes can be removed at a single frequency, grating lobes may appear at other frequencies, making this method extremely difficult if the frequency band is also taken into account.

In view of the above points, the present invention aims to provide an array antenna that suppresses grating lobes over a relatively wide band and expands the effective bandwidth.

The array antenna of the present invention has two antennas with different operating frequency bands.
More than one type of antenna element, specifically an antenna element that operates over the entire required frequency band, and an antenna element that operates in a band from any frequency within the required frequency band to the upper limit frequency of the required frequency band in one direction or in multiple directions. Dinner was 1 ru.

In this case, each antenna element uses one whose size is inversely proportional to the lower limit frequency of each operating frequency band.

As a result, antenna elements with different operating frequency bands operate according to the frequency used, and as the frequency used increases, the effective spacing gradually narrows, so grating lobes are suppressed at any frequency used. It will act as if it were.

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

FIG. 3 shows a first embodiment of the invention.

In this figure, antenna element 1 with radius R1 and antenna element 1 with radius R2
The antenna elements 2 are alternately arranged in a straight line to form a so-called interlaced arrangement.

Here, R1>R2, the arrangement interval of antenna element 1 is DL, and the arrangement interval of adjacent antenna elements 1 and 2 is D.
Indicated by H.

The size of each antenna element 1゜2, that is, the radii R1 and R2, is inversely proportional to its lower limit operating frequency,
Antenna element 1 covers the entire required frequency band f of the array antenna.
The antenna element 2 is configured to operate at f2 to fH (ft: lower limit frequency, fH: upper limit frequency).
(f2: Any frequency within the required frequency band, and is configured to operate in the lower limit operating frequency of the antenna element 2, fL<f2<fH).

As the antenna element 1.2, it is possible to use, for example, a circular cavity on which a conductor serving as a radiating element is formed on the surface. Examples of this type of antenna element include a planar spiral antenna with a back cavity and a log-periodic antenna with a back cavity. Antennas and the like are conventionally known.

FIG. 4 shows an example of a feeding circuit for operating each antenna element 1.2 of the array antenna arranged in the first embodiment shown in FIG. 3 in the respective allocated bands.

In this figure, the duplexers 10A and IOB are low-pass filters 11 and 13 and high-pass filters 12 and 14, respectively.
, and their cutoff frequencies fC are all selected as the lower limit operating frequency f2 of the antenna element 2.

Therefore, the entire required frequency band fL-4,0 is applied to the power supply terminal 16.
When power is supplied, the antenna element 1 receives the frequency component fL-f2 extracted by the low-pass filter 11 of the duplexer 10A and the high-pass filter of the duplexer 10A, following the path indicated by the solid arrow. 12 and distributed by a distributor 15, the frequency components f2 to fH are added via a demultiplexer 10B.

That is, the antenna element 1 has the required frequency range fL to f.
H power is supplied.

Frequency components f2 to fH extracted by the high-pass filter 12 are applied to the antenna element 2 via a distributor 15, following a path indicated by a broken line arrow.

In the above configuration, at the operating frequency if within the range of fL<f<f2, only antenna element 1 is activated (therefore, the actual antenna element array spacing is DL, and f2<f
Since both antenna elements 1 and 20 operate at the operating frequency f within the range <fH, the actual antenna element array spacing is DH.

That is, in a high frequency band where grating lobes are likely to occur, the actual spacing between antenna elements becomes narrow, so grating lobes can be suppressed.

Therefore, it is possible to expand the effective bandwidth as an array antenna, and it is also possible to reduce misidentification of targets based on grating lobes.

Therefore, it is very effective when used as a radar antenna that requires broadband characteristics or as a transmitting and receiving antenna for radio waves radiated from it.

The effect of improving the effective bandwidth in the case of the first embodiment is shown in FIG.

In this figure, the horizontal axis is the effective bandwidth f/f L, and the vertical axis is DλL/λRz (where λr, = C/f L, λ2C/f, C is the speed of light) corresponding to the antenna element array spacing DK. The relationship between these values is shown using the ratio R2/R1 of the size and radius of antenna elements 1 and 2 as a parameter.

Here, the value of DλL/λR1 serves as a measure of the degree of occurrence of grating lobes, and indicates that the larger the value of DλV'λR1, the larger the grating lobes appear.

In this figure, it is assumed that, for example, if the value of DλV'λR1 is 6 or less, then the value of D is the antenna element array spacing that does not cause any problem in practice.

At this time, if R2/R1=1, that is, in the conventional case without interlace arrangement, Kf
/fL=3, but when an interlaced arrangement like the first embodiment in FIG.
Since the antenna element 2 also works in the range < f /f L, f/f L = 4, as shown by the thick line B, and it can be seen that the effective bandwidth is significantly expanded.

Note that when R2/R1 = 0.25, this is shown by thin line C, but in this case, the size of antenna element 1.2 is inappropriately set, and D is set before antenna element 2 operates.
This indicates that the value of λL/λR1 becomes 6 or more.

Therefore, it is necessary to set the value of R2/R1 by considering the value of DλL/λR1 that is practically acceptable.
If it is within the range of 0.4 to 0.8, the conventional R2/R1-
An improved effect can be obtained compared to case 1.

In the first embodiment, two types of antenna elements are arranged alternately in a straight line, but the present invention can also be applied to two-dimensional and three-dimensional antenna element arrangements.

FIG. 6a shows a second embodiment of the present invention, in which three types of antenna elements 1, 2, and 3 are arranged on the same straight line in a fixed order.

Here, each antenna element 1.2.30 radius is R1, R2
, R3 (where R□>R2>R3), and the operating frequency bands are fL~fH, f2~fH, and f3~f, respectively.
H (however, f L < f 2 < f 3 < fH).

Note that the radii R1, R2, and R3 are the radius of each antenna element 1.2.
The magnitude is set to be inversely proportional to the lower limit operating frequencies fL, f2, and f3 of 3.

FIG. 6 shows a third embodiment of the present invention, in which two types of antenna elements 1.2 are arranged so that they are all adjacent to different types of antenna elements, that is, the antenna elements 1.2 are located at the vertices of an equilateral triangle, respectively. The figure shows the case where they are placed on the same plane.

Note that the antenna element 1.20 radius and operating frequency band may be determined in the same manner as in the first embodiment.

FIG. 6C shows a fourth embodiment of the present invention, in which three types of antenna elements 1, 2, and 3 are arranged so that each antenna element is located at the apex of a square.

Note that the radius and operating frequency of each antenna element may be the same as in the second embodiment.

The configuration of the feeder circuit also needs to be changed depending on the type of antenna element used, but when three types of antenna elements 1.2.3 are used as in the second and fourth embodiments shown in FIGS. 6a and 6C. An example of the configuration of the power supply circuit is shown in FIG.

In this figure, the required frequency range fL ~
When fH power is supplied, the duplexer 21 causes fL-f2
the frequency component of f −f and the frequency component of f3~
The fH frequency is divided into three components.

The frequency components f2 to f3 are further distributed to the duplexer 22.24 via the two-way divider 25, and the frequency components f3 to fH are further distributed to the antenna element 3 and the duplexer 23.24 through the two-way divider 26. It is distributed to 24 people.

As a result, the antenna element 3 is fed with frequency components f3 to fH, and the antenna element 2 is fed with frequency components f2 through the duplexer 24.
The antenna element 1 receives power from the frequency component of ~fH, and receives power from the entire required frequency band fl-fH via the duplexer 23.

In addition, in each of the above embodiments, a circular antenna element is illustrated, but the antenna element is not limited to a circular one, and may have other shapes.
Also, although we have shown the case where the antenna elements are in contact with each other,
They may be arranged close to each other at regular intervals.

As mentioned above, according to the present invention, it is possible to realize an array antenna that can suppress grating lobes and expand the effective bandwidth regardless of the frequency used.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an example of a conventional array antenna, Fig. 2 is a graph showing its radiation directivity pattern, and Fig. 3 is a schematic diagram showing an example of a conventional array antenna.
The figure is a schematic configuration diagram showing the first embodiment of the array antenna according to the present invention, FIG. 4 is a block diagram showing an example of the feeder circuit used in the first embodiment, and FIG. 5 is for explaining the effects of the embodiment. 6A is a schematic diagram showing the second embodiment of the present invention, and FIG.
is a schematic configuration diagram showing the fourth embodiment, and FIG. 7 is a schematic diagram showing the fourth embodiment.
FIG. 2 is a block diagram showing an example of a power feeding circuit used in an example. 1.2.3...Antenna element, IOA, 10B
, 21.22.23.24... duplexer, 11,
13...Low pass filter, 12.14...
...High pass filter, 15.25.26...
·Distributor.

Claims (1)

[Claims] 1. A first antenna element that has a radial size R1 that is inversely proportional to the lower limit frequency of the required frequency band and that operates over the entire required frequency band, and a lower limit operating frequency that is any frequency within the required frequency band. and a second antenna element having a radial size R2 inversely proportional to the operating frequency and operating in a band from the lower limit operating frequency to the upper limit frequency of the required frequency band, alternately in one direction or in multiple directions. Alternatively, the arrangement interval of the first antenna elements is approximately R1+R2, and R2//R1 is 0.4 to 0.
An array antenna characterized by setting 8.