JP4747854B2 - Array antenna - Google Patents

Description

The present invention relates to an array antenna (leakage wave antenna) having a strip line formed by periodically and repeatedly arranging a predetermined unit pattern made of a conductor on the front side of a dielectric substrate having a ground plate on the back surface. In particular, the present invention relates to an antenna having controllable directivity.
The present invention is useful for radars and communication devices that transmit or receive electromagnetic waves in the millimeter wave band or microwave band, and is very useful for reducing the size of antennas or the space required for installation.

  A configuration example of a conventional strip array antenna (leakage wave antenna) having a CRLH (Composite Right and Left Handed) transmission line on a dielectric substrate is illustrated in FIG. The CRLH line is provided with a gap that periodically divides the transmission line (main line in the X-axis direction), a stub branched from the transmission line, and the like. In this antenna, the direction of the group velocity and the phase velocity of transmitted electromagnetic waves can be opposite to each other in a certain frequency band by the action of the capacitance provided by the gap and the inductance provided by the stub. As a result, the frequency of the transmitted electromagnetic wave can be changed, so that the direction of the electromagnetic wave propagates on the main line is inclined from the positive z-axis direction to the negative x-axis direction in the figure. Electromagnetic waves can be emitted even in the angle region where θ <0. As a result, when the direction of the radiation beam is changed, the scanning range of the radiation beam can be widened. Such a principle that the phase velocity and the group velocity are opposite to each other is disclosed in detail in, for example, Non-Patent Document 1 below. However, in the prior art, unless the frequency is changed greatly, it is difficult to give the radiation beam directivity in the direction inclined in the angle region where θ <0 as described above.

  Non-Patent Document 2 below discloses a control method for variably controlling the radiation angle of a radiation beam based on predetermined electronic control while fixing the frequency of an electromagnetic wave input from a feeding point to a constant value. . In this radiation angle control method, for example, varactor diodes are arranged close to the individual gaps and stubs of the wiring pattern shown in FIG. 6 and the capacitance of each varactor diode is variably controlled to thereby adjust the radiation angle of the radiation beam. Is variably controlled.

  Non-Patent Document 3 below describes a beam scanning antenna using a reflector having an EBG structure (Electrical Band Gap structure) in which a metal patch having a via in the center is periodically arranged on a dielectric substrate (FIG. 7-). A, -B) has been proposed. This beam scanning antenna variably controls the traveling direction of the reflected wave of electromagnetic waves incident on the reflector from a predetermined direction, that is, the directivity of reflection, by changing the capacitance between the metal patches of the reflector. Therefore, the capacitance between the metal patches is variably controlled by moving the movable plate to which the metal patches are attached in the horizontal direction.

  In addition, as another control method, for example, the dielectric constant of the material through which the electromagnetic wave propagates is variably controlled by electrically controlling the permeability of the material using ferrite or the like. There is a method for variably controlling the above. That is, as such a control method, for example, the dielectric constant of the dielectric substrate constituting the target antenna is variably controlled by voltage, and thereby the radiation angle of the radiation beam of the array antenna is variably controlled to a desired angle. A control method can be considered. Examples of such a dielectric substrate material whose dielectric constant is variably controlled include liquid crystal and ferroelectric.

In the field of electromagnetic wave sensing or wireless communication, it is desirable to control the directivity of the radiation beam of the antenna without changing the frequency of the radiated electromagnetic wave.
Tatsuo Ito and two others, 'CHARACTERISTICS AND APPLICATIONS OF PLANAR NEGATIVE REFRACTIVE INDEX MEDIA', MWE2003, WS02-03 Tatsuo Ito and two others, 'Electronically-Controlled Metamaterial-Based Transmission Line as a Continuous-Scanning Leaky-Wave Antenna', 2004 IEEE MTT-S Digest TU1D-4. US Patent: US 6,552,696 B1

  However, the conventional array antenna described in Non-Patent Document 1 cannot variably control the radiation angle of the radiation beam of the antenna while keeping the frequency of the electromagnetic wave input from the feeding point constant. For this reason, an antenna that employs this method is not suitable for an antenna that emits or receives electromagnetic waves of a certain frequency, such as a millimeter wave radar.

In the conventional array antenna described in Non-Patent Document 2, a varactor diode is used as a variable capacitor. However, since a varactor diode generally has a large transmission loss, a varactor is used in a frequency band of several GHz or more. It is difficult to operate the diode as a desired variable capacitor. For this reason, this prior art cannot be used for an array antenna that handles electromagnetic waves in a frequency band of several GHz or more.
Further, even in a frequency band of 1 GHz or less where the radiation angle can be variably controlled, it is not always easy to ensure a sufficiently large capacity displacement ratio (change rate) with respect to a standard capacity (predetermined reference capacity) in a varactor diode. Therefore, it is not always easy to ensure a large variation range of the radiation angle.

In addition, the conventional beam scanning antenna described in Non-Patent Document 3 (FIGS. 7A and 7B) has the following problems relating to productivity, controllability, and downsizing and thinning. .
(1) As shown in FIGS. 7A and 7B, a beam scanning antenna is configured using a reflector having an EBG structure. Therefore, a separate feeding antenna for irradiating the reflector with electromagnetic waves is separately provided. It is necessary to prepare.
(2) Although the directivity of the radiation beam of the antenna can be variably controlled by moving the movable plate in the horizontal direction, each metal patch has strong theoretical and physical restrictions on the periodic positional relationship. Therefore, the position of each metal patch cannot be controlled independently. For this reason, it is impossible to introduce a beam shaping technique such as variably controlling the beam width and beam pattern to the conventional beam scanning antenna.

  Further, as described above, the dielectric constant or permeability of the dielectric substrate constituting the target antenna is variably controlled by an actively controlled electric field or magnetic field, whereby the radiation angle of the array antenna radiation beam is controlled. A control method that can be variably controlled to a desired angle can be considered, but when using a material such as a ferroelectric or ferrite whose dielectric constant changes, the power loss of the electromagnetic wave propagating through the antenna is very large. Therefore, it is difficult to ensure a large antenna gain.

  The present invention has been made to solve the above-described problems, and an object thereof is to realize a small array antenna having a wide beam-oriented scanning range that can be used even in a high frequency band of 1 GHz or higher. It is to be.

In order to solve the above problems, the following means are effective.
That is, the first means of the present invention includes a dielectric substrate, a strip line formed by arranging a plurality of identical or similar unit patterns made of conductors in a predetermined direction on the front side of the dielectric substrate, In the array antenna having a ground plate made of a conductor formed on the back surface of the body substrate, each unit pattern has a transmission line, a gap that divides the transmission line in the middle, and a stub that branches from the transmission line. It is a left-handed pattern at the operating frequency, and is composed of at least one of a dielectric, a magnetic material, a metal conductor, or a composite thereof, and is close to the strip line or unit pattern, and the strip line or unit. is disposed to cover the pattern, the height h and a movable member which can vary from stripline, mechanically acts on the movable member And an actuator for changing the height h of the movable member, the actuator, the height h from the stripline of the movable member, array antenna, at the usage frequency, the left-handed operating state, until the right-handed operation state In the range to be changed, it can be changed.

However, the unit patterns described above may be arranged in one column, or may be arranged over a plurality of columns. That is, the array antenna of the present invention may be a strip antenna having one strip line or a planar antenna having a plurality of strip lines.
The height h is a distance measured vertically from the surface of the dielectric substrate on which the unit patterns are arranged. In addition, at least from the viewpoint of ease of design and manufacturing, it is desirable to periodically arrange the unit patterns, but it is not always necessary to periodically arrange the unit patterns. .
The actuator can be configured using, for example, a piezoelectric element (piezo element) or the like. In this case, the height h can be electrically controlled. However, the height h may be variably controlled using a mechanical drive control mechanism.

  The stub may be provided only on one side of the strip line, on both sides at the same position, or the side provided along the traveling direction may be alternately reversed. The stub is usually provided at a right angle to the strip line, but the angle may be generally arbitrary. Further, the opposite part of the strip line constituting the gap may be configured to have a wide width in the direction perpendicular to the transmission direction in order to increase the capacitance. And the directivity (that is, the directivity related to the angle θ in FIG. 6) along the transmission direction around the direction perpendicular to the unit pattern (angle reference) is close to each unit. It changes based on the phase of power supplied to the pattern.

In addition, when the movable member is composed of a composite of a dielectric and a metal conductor, or a composite of a magnetic and a metal conductor, a metal conductor may be provided on the surface of the dielectric or magnetic body. Alternatively, a metal conductor may be provided inside the dielectric or magnetic material.
However, if a metal conductor that is connected over a wide area so as to cover the entire strip line or the entire unit pattern is disposed, the radiation of electromagnetic waves from the array antenna is blocked. It is not used for the structure of the movable member. When these metal conductors are used, the metal conductors are locally distributed as at least a part of the movable member, for example, locally included in a dielectric substrate.

  The movable member does not necessarily have to be disposed so as to cover the entire unit pattern. For example, only the gap may be covered from above by the movable member, only the stub may be covered from above, or both of them may be covered from above. The portion of the movable member disposed in the vicinity of the gap predominantly changes the gap capacitance, and the portion disposed in the vicinity of the stub predominantly changes the inductance of the stub.

According to a second means of the present invention, in the first means, the actuator and the movable member are individually provided for each unit pattern, and the variable control is performed for each unit pattern. It is to execute each independently.
However, the movable member described above does not necessarily have the same shape for each unit pattern.
By the above means of the present invention, the above-mentioned problem can be effectively or rationally solved.

  By moving the movable member perpendicularly to the substrate, the equivalent dielectric constant near the gap or stub can be changed, or the electrical length of the capacitor provided by the gap or the inductor provided by the stub can be changed. . That is, since the gap capacitance and the stub inductance can be changed by variably controlling the height h, the intensity and phase distribution of electromagnetic waves radiated from the array antenna can be variably controlled. it can. Therefore, according to the first means of the present invention, the directivity of the array antenna can be variably controlled by variably controlling the height h using the actuator.

  Moreover, since the fluctuation range of the height h at this time can be kept to a sufficiently small length of less than 1 mm, according to the first means of the present invention, even in a high frequency band of 1 GHz or higher, a predetermined range is obtained. It is possible to realize an array antenna with a much smaller beam than the conventional one having a wide beam-oriented scanning range with respect to the frequency. This is because the directivity of the radiation beam can be variably controlled based on the minute displacement of each movable member, so compared to the conventional method in which the directivity is variably controlled by mechanically changing the orientation of the entire array antenna. This is because a desired array antenna can be formed more compactly.

Further, according to the second means of the present invention, the capacitance and inductance can be controlled for each unit pattern, so that the beam width and beam shape of the antenna can be variably controlled.
For example, since the effective length of the antenna can be variably controlled by controlling the capacitance and inductance for each unit pattern, the beam width of the antenna can be variably controlled. At this time, the effective length of the antenna is variably controlled by providing an arrangement of unit patterns that are difficult to operate in a predetermined frequency band on the terminal end side of the antenna and forming a band gap there. That is, the effective length of the antenna can be set shorter as the arrangement length of the unit patterns (the length of the unit patterns × the number of unit patterns) that is difficult to operate in a predetermined frequency band is longer.

  Further, if the directivity is controlled for each unit pattern by variably controlling the phase for each unit pattern, a null can be formed in the beam shape of the array antenna. Further, if an appropriate radiation pattern such as a tailor distribution is employed, a beam shape with a small side lobe can be realized by controlling the capacitance and inductance for each unit pattern.

  In addition, as a material of said movable member, a fluororesin, ceramics, etc. are suitable, for example. By using these materials, the relative permittivity of the movable member can be controlled to 2 to 4, so that the array antenna can be used in a high frequency band of 1 GHz or more and has a wide beam-oriented scanning range. Can be realized at low cost.

Hereinafter, the present invention will be described based on specific examples.
However, the embodiments of the present invention are not limited to the following examples.

FIG. 1 shows a perspective view and a front view of the array antenna 100 of the first embodiment. The dielectric substrate 1 is made of a plate-like material having a thickness of about 0.13 mm formed from a tetrafluoroethylene resin (: relative dielectric constant 2.2), which corresponds to the movable member according to claim 1. Yes. The dielectric substrate 1 is connected to the array substrate 10 via the piezo element 2. The piezo element 2 can be expanded and contracted in the normal direction of the dielectric substrate 1, that is, the z-axis direction in the drawing by applying a voltage to the surface thereof. That is, the piezo element 2 corresponds to the actuator described in claim 1.
As shown in the front view of FIG. 1, the array substrate 10 is formed on the basis of a dielectric substrate 15, and a strip line 14 is formed on the upper surface of the dielectric substrate 15. A ground conductor 16 formed of a metal layer is laminated on the back surface of the dielectric substrate 15.

FIG. 2 shows a plan view of the array substrate 10. The strip line 14 is formed by a periodic arrangement of unit patterns U in the x-axis direction. The unit pattern U includes a transmission line 11 that is continuous in the x-axis direction and a stub 12 that is branched from the transmission line 11 and extends in the y-axis direction. An end portion of the stub 12 is formed wider in the x-axis direction than a portion in the middle of branching from the transmission line 11.
Further, the gap G1 is formed by a gap between the facing part 11a and the facing part 11b that are wide in the y-axis direction of the transmission line 11.
In this way, the strip line 14 is formed by a periodic arrangement of the unit patterns U in the x-axis direction, the right end portion (P ₁ ) in the figure is the feeding point, and the left end portion (P ₂ ) in the figure is the feed point. It is a terminal point.

  The height h in FIG. 1 indicates the distance from the top surface of the dielectric substrate 15 that forms the base of the array substrate 10 to the back surface of the dielectric substrate 1, and is measured in the z-axis direction. The height h can be freely variably controlled by the expansion / contraction operation of the piezo element 2 (actuator) whose applied voltage can be variably controlled as described above.

FIG. 3 shows the dependency characteristics regarding the directivity height h of the array antenna 100. This directivity is measured by changing the height h in three ways: h = 0.1 mm, 0.05 mm, and 0.025 mm. The frequency of the feed power was 76.5 GHz. The peak position (angle θ) of the radiation pattern at this time is θ≈0 ° (in the z-axis direction) when h = 0.05 mm, θ≈ + 25 ° when h = 0.1 mm, and h = 0. At 025 mm, θ≈−28 °.
For example, in this way, in this array antenna 100, the direction of the radiation beam can be variably controlled by variably controlling the height h by the actuator.

  FIG. 4 shows a perspective view of the array antenna 200 of the second embodiment. This array antenna 200 is an improvement of the array antenna 100 of the first embodiment, and the array substrate 10 is made of the same material and the same structure as that used for the array antenna 100 of the first embodiment. . However, although the configuration of each unit pattern U is the same, the number of repetitions of the unit pattern U in the x-axis direction is 11 units.

  The array antenna 200 is characterized in that the dielectric substrate 1 of the array antenna 100 is divided and arranged in correspondence with each unit pattern U. That is, in the array antenna 200, the dielectric substrate 1 of the array antenna 100 is divided into a total of 11 pieces of 1a to 1k and arranged in the x-axis direction. Further, along with this division, the piezo elements 2 (actuators) of the array antenna 100 are also arranged individually corresponding to the respective dielectric substrates 1a to 1k. For example, the piezo element 2k is an actuator for translating the dielectric substrate 1k in the z-axis direction. The same applies to the piezo elements 2a to 2j.

(Operation and effect of Example 2)
The height h of each dielectric substrate 1a-1k can be variably controlled by variably controlling the voltage applied to each piezoelectric element 2a-2k. Then, by executing the variable control of the height h independently for each unit pattern, the following actions and effects can be obtained.

(1) Change the beam width of the antenna freely For example, the capacitance component of the gap and the inductance component of the stub can be variably controlled by using the actuator described above. The frequency can be controlled to be inactive. In this case, a band gap can be formed on the termination side of the array antenna, that is, on the opposite side of the feeding point, by the unit pattern in the non-operating state. The length can be variably controlled. At that time, the shorter the effective length of the array antenna, the wider the beam width of the array antenna, so that the antenna beam width can be variably controlled. However, the effective length is the length of the portion of the array of unit patterns constituting the antenna that actually acts effectively as an antenna. This length is the length of each unit pattern. It can be determined based on each radiation amount.

  FIG. 5 illustrates a beam shape (azimuth-gain characteristic) in the z-axis direction of the array antenna 200. For example, when the frequency of the feeding power is 76.0 GHz, the height h of the dielectric substrates 1a to 1c is 0.1 mm, and the height h of the dielectric substrates 1d to 1k is 0.025 mm, respectively, FIG. A beam shape as shown in (c) is obtained. When the height h of the dielectric substrates 1a to 1g is 0.1 mm and the height h of the dielectric substrates 1h to 1k is 0.025 mm at the same frequency, a beam as shown in FIG. A shape is obtained. Further, when the heights h of the dielectric substrates 1a to 1k are all 0.1 mm at the same frequency, a beam shape as shown in FIG. 5A is obtained.

(2) Suppressing unwanted side lobe radiation If the variable control of the height h is executed independently for each unit pattern, the side lobe level can also be suppressed. That is, by using the actuator, it is possible to control the distribution of each radiation amount of the unit pattern to an appropriate distribution that exerts a sidelobe suppression action such as the well-known Taylor distribution. The amount of radiation of the side lobe of the array antenna can be reduced.

(3) Null is formed in a desired direction. Further, if variable control of the height h is executed independently for each unit pattern, each directivity of the unit pattern is controlled in a plurality of different directions, Nulls can be formed in directions that deviate from those directions, thereby reducing the reception of signals from any direction. For example, when nulls are to be formed in the front direction of the antenna, the beam direction of half of the unit pattern is directed toward the backward wave (ie, the direction of the left-handed beam) and the remaining half of the unit pattern The pattern beam may be directed toward the forward wave (ie, the direction of the right-handed beam). Thereby, reception of the signal from the front direction can be reduced.

  However, for example, when controlling the directivity of unit patterns in two different directions, each unit pattern belonging to a set of unit patterns to be radiated in one direction is not necessarily continuous on the unit pattern array. There is no need to arrange them together. That is, unit patterns that give different directivities may be arranged alternately, or a set of unit patterns that radiate in one direction may be combined into a continuous set on the array. The plurality of directions may be three directions or four or more directions.

[Other variations]
The embodiment of the present invention is not limited to the above-described embodiment, and other modifications as exemplified below may be made. Even with such modifications and applications, the effects of the present invention can be obtained based on the functions of the present invention.
(Modification 1)
For example, in each of the embodiments described above, the dielectric is moved as the movable member, but a metal piece may be placed inside these dielectrics. In that case, it is possible not only to control the dielectric constant but also to control the electrical length of the gap and stub at the same time, so that the change of the beam angle θ with respect to the movement of the dielectric can be set more sensitively. . Therefore, if such a modification is made, it is possible or easier to secure a wider range of change in the beam direction, or to further downsize the actuator.

(Modification 2)
In the above embodiment, the movable member is translated in the vertical direction (z-axis direction), but the movement of the movable member may be a translational reciprocating motion or a rotational motion. The height h can be variably controlled by any form of motion.

  The present invention is useful for wireless communication and electromagnetic wave sensing. For example, an object search for a wireless communication device, an obstacle sensor used in a vehicle accident prevention system, an auto cruise control system, or other objects around the vehicle. It can be used as a means.

The perspective view and front view of the array antenna 100 of Example 1. FIG. Plan view of array substrate 10 of array antenna 100 The graph which shows the dependence characteristic regarding the height h of the directivity of the array antenna 100 The perspective view of the array antenna 200 of Example 2. FIG. A graph illustrating the beam shape (azimuth-gain characteristic) of array antenna 200 Explanatory drawing explaining the characteristic of the conventional strip array antenna Plan view of other conventional beam scanning antennas Sectional view of other conventional beam scanning antennas

100: Array antenna 1: Dielectric substrate (movable member)
2: Piezo element (actuator)
10: Array substrate 12: Stub 14: Strip line 15: Dielectric substrate U: Unit pattern G1: Gap

Claims (2)

From a dielectric substrate, a strip line formed by arranging a plurality of identical or similar unit patterns made of conductors in a predetermined direction on the front side of the dielectric substrate, and a conductor formed on the back surface of the dielectric substrate An array antenna having a ground plate comprising:
Each unit pattern has a transmission line, a gap that divides the transmission line in the middle, and a stub that branches off from the transmission line, and is a pattern that becomes a left-handed system at a used frequency,
It is composed of at least one of a dielectric, a magnetic material, a metal conductor, or a composite thereof , and is disposed so as to be close to the strip line or the unit pattern and cover the strip line or the unit pattern. is, the height h that can change the movable member from the strip line,
An actuator that mechanically acts on the movable member to change the height h of the movable member;
The actuator is capable of changing the height h of the movable member from the strip line in a range in which the array antenna changes from a left-handed operating state to a right-handed operating state at a use frequency. An array antenna. The array antenna according to claim 1, wherein the actuator and the movable member are individually provided for each unit pattern, and the variable control is performed independently for each unit pattern.