JP5480855B2 - Multi-beam reflect array - Google Patents

Description

  The present invention relates to a multi-beam reflectarray.

  As a technique for improving throughput in wireless communication, there is a MIMO (Multiple Input Multiple Output) method or a multi-antenna method. The MIMO scheme can improve throughput or reliability by transmitting signals simultaneously from the plurality of antennas at the same frequency.

  Figure 1 shows an overview of the MIMO scheme. The n streams 1-n are separately transmitted from the n antennas of the transmission apparatus, and are received by the n antennas of the reception apparatus via various radio propagation paths. The reception device can utilize the difference in the signal propagation path in the space to separate the received n signals into n streams 1-n and restore the transmitted information 1-n.

  As described above, the MIMO scheme is a technique that utilizes the complexity of the radio propagation path between a plurality of transmission antennas and a plurality of reception antennas. Therefore, for example, in an environment where various propagation paths exist due to an obstacle in the middle of the propagation path (in the case of a multipath environment), the signal separation of the receiving apparatus in the MIMO scheme is facilitated. However, reception power tends to be low due to scattering of radio waves by obstacles (Fig. 2). On the other hand, for example, in the case of a line-of-sight environment, the difference between the radio propagation paths becomes small, so that signal separation in the receiving apparatus becomes difficult. However, in a line-of-sight environment, the received power is not so low (Figure 3).

  Therefore, in a line-of-sight environment, it may be difficult to improve throughput by the MIMO method. In order to cope with this problem, it is conceivable to provide a relay device between the transmission device and the reception device. The receiving device receives a direct wave that reaches directly from the transmitting device and a relay wave that reaches from the transmitting device via the relay device, and separates these combined waves. By intentionally complicating the radio propagation path using the relay device, signal separation in the receiving device can be facilitated even in a line-of-sight environment. A conventional relay method using the MIMO scheme is described in Patent Document 1, for example.

  One method for easily realizing such a relay device is to use a reflector or reflector that reflects radio waves as the relay device. Such a reflector can be used not only for a MIMO receiver, but more generally when performing area improvement in a mobile communication system. However, in the case of the conventional reflector, when the size or area of the reflector is increased so that the reception level of the reflected wave is increased, the intensity of the reflected wave is increased, but the beam width of the reflected wave is reduced and the area is reduced. The area that can be improved is narrowed. When the size of the reflecting plate is small, the beam width of the reflected wave becomes relatively wide, but the reception level of the reflected wave becomes weak. For this reason, when improving an area using a reflecting plate, we are anxious about the problem that the area which satisfy | fills required quality cannot fully be expanded. These problems become more serious as the frequency of radio waves increases.

JP 2006-148482 A

  An object of the present invention is to make it possible to expand an area satisfying a required quality as compared with the conventional case when an area is improved using a reflector.

A multi-beam reflect array according to one embodiment is
A multi-beam reflectarray including at least a first and a second array group,
The first array group includes a plurality of first element arrays, the second array group includes a plurality of second element arrays,
Each of the first and second element arrays includes a plurality of elements aligned in a predetermined direction, and a phase difference between radio waves reflected by two of the plurality of elements is determined by the two elements. Proportional to the product of the spacing and the value of the trigonometric function for the angle of reflection by the element,
The reflection angle by the first array group is a multi-beam reflect array different from the reflection angle by the second array group.

  According to one embodiment, when an area is improved using a reflector, an area that satisfies the required quality can be expanded more than in the past.

The conceptual diagram of the signal transmission by MIMO system. The figure which shows the radio | wireless propagation environment which is not line-of-sight environment. The figure which shows a prospect environment. The figure for demonstrating an invention principle. The figure which shows a communication system. The figure for demonstrating a multi-beam reflect array. The figure which shows a mode that a reflected wave is formed in a desired direction. The figure which shows the mushroom structure which can be used as an element which comprises a reflect array. The enlarged plan view of a reflect array. Equivalent circuit diagram of mushroom structure. The figure which shows the relationship between patch size and a reflection phase. The figure which shows the relationship between a reflection phase and a coordinate. The figure which shows the relationship between the reflection phase converted into the range of 360 degree | times, and the position of an element. The figure which shows the positional relationship of the apparatus assumed in the simulation The figure for comparing the reflected wave by the conventional reflector, and the reflected wave by the reflector of an Example from a viewpoint of a gain and an azimuth. The figure which shows the comparative example by the spatial distribution figure of channel capacity | capacitance. The figure which shows the comparative example from a viewpoint of outage capacity | capacitance and the cumulative distribution CDF of capacity | capacitance.

FIG. 4 is a diagram for explaining the principle of the invention. Reflector R1 reflects radio waves incident at an angle of reflection alpha _0. The incident angle and the reflection angle have the same magnitude. The beam pattern B1 of the reflected wave has a wide beam width, but the gain is not large and is less than the “effective gain”. The effective gain is the gain of the beam necessary for the communication apparatus that has received the reflected wave to communicate with a quality that exceeds the required quality. In the case of the conventional method, in order to increase the gain of the beam, the size of the reflector R1 is increased like the reflector R2. As an example, the reflector R2 has an area four times that of the reflector R1. Reflector R2 also reflects radio waves incident at a reflection angle alpha ₀ is the intensity of the beam is increased. However, the beam width becomes narrow. For this reason, the range in which the communication device that has received the reflected wave can communicate with a quality higher than the required quality is narrow.

On the other hand, the reflector R34 proposed by the present application uses the reflector R3 and the reflector R4 in combination instead of the reflector R2. The reflector R3 reflects the incident radio wave at a certain reflection angle α ₁ . As an example, the reflector R3 has an area twice that of the reflector R1. The gain A3 of the reflected wave by the reflector R3 is weaker than the gain A1 of the reflected wave by the reflector R1, but exceeds the effective gain. Reflector R4 reflects radio waves incident at an angle of reflection alpha _2. As an example, the reflector R4 has an area twice that of the reflector R1. The gain A4 of the reflected wave by the reflector R4 is weaker than the gain A1 of the reflected wave by the reflector R1, but exceeds the effective gain. The reflection angle α ₂ is different from the reflection angle α ₁ . Therefore, it can be expected that communication can be performed with quality exceeding the required quality in the area covered by the reflected wave B3 by the reflector R3 and the reflected wave B4 by the reflector R4. In this way, by configuring a single reflector by using a plurality of reflectors having different reflection angles, an area satisfying the required quality can be expanded as compared with the conventional case.

  Embodiments will be described below with reference to the accompanying drawings. In the figures, similar elements are given the same reference numbers or reference signs. Examples will be described from the following viewpoints.

1． Communications system
2． Multi-beam reflect array
3． Reflection phase of element
Four. simulation

<1. Communication system>
FIG. 5 shows a communication system that can be used in the embodiment. The communication system includes a transmission device, a relay device, and a reception device. In the illustrated example, the transmission device indicates that attention is paid to a function related to transmission of a communication device capable of transmission and reception. Similarly, the receiving apparatus indicates that attention is paid to a function related to reception of a communication apparatus capable of transmitting and receiving. The receiving device receives and synthesizes the direct wave directly reaching from the transmitting device and the relay wave reaching via the relay device. As an example, it is assumed that the transmission device and the reception device communicate using a MIMO (Multiple-Input Multiple-Output) method, but the embodiment is not limited to the MIMO method, and may be used for any wireless communication method. Is possible. In the embodiment, the relay device is formed by a reflector or a reflector that reflects incident radio waves. As will be described later, the reflector used in the embodiment includes an array of a large number of elements and reflects radio waves in a plurality of directions. Therefore, the reflector may be referred to as a multi-beam reflect array, or simply referred to as a reflect array. May be.

<2. Multi-beam reflect array>
FIG. 6 shows a schematic plan view of a multi-beam reflectarray. FIG. 7 shows a schematic side view of a multi-beam reflectarray. The multi-beam reflectarray includes at least a first array group G1 and a second array group G2. The first array group G1 includes a plurality of first element arrays MG1. The second array group G2 includes a plurality of second element arrays MG2. The first sequence group G1, is reflected at the reflection angle alpha ₁ of the radio waves coming from the z-axis ∞ direction. The second sequence group G2, is reflected at a reflection angle alpha ₂ of the radio waves coming from the z-axis ∞ direction. The reflection angle α ₂ is different from the reflection angle α ₁ . In the illustrated example, only two arrangement groups G1 and G2 are shown. However, in the multi-beam reflect array, three or more arrangement groups G1, G2,. . . , GJ may exist. Furthermore, the individual array groups may be provided repeatedly or periodically in the x-axis direction and / or the y-axis direction.

Each of the first and second sequence group MG1, MG2 is to M1 to a plurality of elements arranged in the y-axis direction has a MN _i, similar structure to these N _i number of elements, provided iteratively Yes. i is a parameter for designating an array group or an element array. In the present example, i = 1 or 2. Each of the elements is any element that reflects radio waves, and has a mushroom structure in the illustrated example. Radio waves arrive from the z-axis ∞ direction. In the case of the first array group MG1, the radio waves are reflected at an angle α ₁ with respect to the z-axis direction. In the case of the second array group MG2, the radio waves are reflected at an angle α ₂ with respect to the z-axis direction. If the interval between adjacent elements is Δy _i , the phase difference Δφ _i and the reflection angle α _i of the reflected waves by these elements satisfy the following equation.

Δφ _i = k × Δy _i × sin (α _i )
α _i = sin ⁻¹ [(λΔφ _i ) / (2πΔy _i )]
However, k is a wave number and is equal to 2π / λ. λ is the wavelength of the radio wave. When configuring a sufficiently large reflect array compared to the wavelength, the whole according to a reflection phase difference N _i × [Delta] [phi _i of from N _i number of elements M1 aligned in the y-axis direction MN _i is, so as to be 360 degrees (2 [pi radians) In addition, it is desirable to set the reflection phase of each element. For example, when N _i = 4, Δφ _i = 360/4 = 90 degrees. Therefore, at least theoretically, by designing the elements so that the reflection phase difference between adjacent elements is 90 degrees, and arranging the four elements arranged two-dimensionally repeatedly, the angle α _i A reflect array that reflects radio waves in the direction can be realized.

  FIG. 8 shows a mushroom structure that can be used as an element in the reflect array shown in FIGS. The mushroom structure includes a ground plate 51, vias 52, and patches 53.

The ground plate 51 is a conductor that supplies a common potential to a large number of mushroom structures. Δx _i and Δy _i indicate the distance in the x-axis direction and the distance in the y-axis direction between vias in adjacent mushroom structures, respectively. Δx _i and Δy _i represent the size of the ground plate 51 corresponding to one mushroom structure. In general, the ground plate 51 is as large as an array of a large number of mushroom structures. In the first and second element arrays MG1 and MG2, Δx ₁ and Δx ₂ may be the same or different. In the first and second element arrays MG1 and MG2, Δy ₁ and Δy ₂ may be the same or different.

  The via 52 is provided to electrically short-circuit the ground plate 51 and the patch 53.

The patch 53 has a length of Wx _{i in} the x-axis direction and a length of Wy _{i in} the y-axis direction. The patch 53 is provided in parallel to the ground plate 51 at a distance t _i and is short-circuited to the ground plate 51 through the via 52. In the first and second element arrays MG1 and MG2, t ₁ and t ₂ may be the same or different.

  For simplification of illustration, only two mushroom structures are shown in FIG. 8, but a large number of such mushroom structures are provided in the x-axis and y-axis directions in the first and second arrangement groups. .

  FIG. 9 shows an enlarged plan view of the first or second array group G1, G2 as shown in FIG. Shown are four patches 53 arranged in a line along the line p, and four patches 43 arranged along the line q adjacent to the line p. The number of patches is arbitrary.

  FIG. 10 shows an equivalent circuit of the mushroom structure shown in FIGS. As shown in FIG. 9, a capacitance C is generated due to the gap between the mushroom-structured patches 53 aligned along the line p and the mushroom-structured patches 53 aligned along the line q. Furthermore, an inductance L occurs due to the mushroom structure vias 52 arranged along the line p and the mushroom structure vias 52 arranged along the line q. Therefore, the equivalent circuit of the adjacent mushroom structure is a circuit as shown on the right side of FIG. That is, in the equivalent circuit, the inductance L and the capacitance C are connected in parallel. Capacitance C, inductance L, surface impedance Zs, and reflection coefficient Γ can be expressed as follows.

In Equation (1), ε ₀ represents the dielectric constant of vacuum, and ε _r represents the relative dielectric constant of the material interposed between the patches. The element spacing is Δx _i between vias in the x-axis direction in the above example. The gap is a gap between adjacent patches, and is (Δx _i −Wx _i ) in the above example. i is a parameter for designating the element arrangement. Wx _i represents the length of the patch in the x-axis direction. That is, the argument of the arccosh function represents the ratio between the element spacing and the gap. In Equation (2), μ represents the magnetic permeability of the material interposed between the vias, and t _i represents the height of the patch 53 (distance from the ground plate 51 to the patch 53). In Equation (3), ω represents an angular frequency, and j represents an imaginary unit. In Equation (4), η represents free space impedance, and φ _i represents a phase difference.

FIG. 11 shows an example of the relationship between the size Wx _i of the patch having the mushroom structure as shown in FIG. 8 and the reflection phase. i is a parameter for designating the element arrangement (MG1 or MG2 in the example of FIG. 6). In general, the reflection phase of the mushroom structure (element) becomes 0 at the resonance frequency, and the resonance frequency is determined by the capacitance C and the inductance L described above. Therefore, in the design of the reflect array, it is necessary to appropriately set the capacitance C and the inductance L so that each element achieves an appropriate reflection phase. In the figure, solid lines indicate theoretical values, and those plotted with circles indicate simulation values by finite element method analysis. FIG. 11 shows the relationship between the patch size Wx _i and the reflection phase for each of four types of via heights or substrate thicknesses t _i . t02 represents a graph when the distance t _i is 0.2 mm. t08 represents a graph when the distance t _i is 0.8 mm. t16 represents a graph when the distance t _i is 1.6 mm. t24 represents a graph when the distance t _i is 2.4 mm. The via intervals Δx _i and Δy _i are 2.4 mm as an example.

When elements are formed with a mushroom structure as shown in FIGS. 8 and 9, the patch size Wy _{i in the} y-axis direction is the same for all elements, and the patch size Wx _{i in the} x-axis direction differs depending on the location of the element. It is not essential that the patch size Wy is common to all the elements, and it is possible to design the patch size Wy to be different for each element. However, when designing a reflectarray using a mushroom structure in which the patch size Wy is the same for all elements, the design is simplified and the patch size Wx _i in the x-axis direction can be determined according to the element location. Good. Specifically, one of the various via heights or substrate thicknesses t to be used in the design (e.g., t24) is selected, and the size of each of the multiple patches to be aligned is required at the position of the patch. It is determined according to the reflection phase. For example, when t24 is selected and the required reflection phase is 72 degrees at a certain patch position, the patch size Wx _i is about 2 mm. Similarly, the sizes of other patches are determined. Ideally, it is preferable that the patch size is designed so that the change in the reflection phase by one entire element group aligned in the reflect array is 360 degrees.

<3. Reflection phase of element>
As described with reference to FIG. 11, when designing a reflectarray, select a graph (e.g., t24) for a substrate of thickness to be used in the design, and the size of each of the multiple patches to be aligned is the position of the patch. In accordance with the required reflection phase. Ideally, the patch size and the like are designed so that the change in the reflection phase by the entire element group aligned in the reflect array is 360 degrees. However, as can be seen from the example shown in FIG. 11, there is a reflection phase that cannot be realized for theoretical and manufacturing reasons. For example, (in this example) For t16, large and the reflection phase than 144 degrees, a small reflective patch size Wx _i phase can realize there is no than 60 degrees. Even in the case of t24, it is difficult to realize a reflection phase larger than 117 degrees and a reflection phase smaller than -72 degrees. Furthermore, the gap (Δx _i −Wx _i ) becomes extremely narrow and can be manufactured when the patch size Wx _i approaches 2.4 mm due to the spacing between elements Δx _i and Δy _i being 2.4 mm. It becomes difficult. Thus, it is necessary to design the reflectarray under the constraints of the patch size that can actually be manufactured and the reflection phase that can be realized.

For convenience of explanation, it is assumed that the reflect array includes the first and second array groups G1 and G2. Furthermore, in each of the first element array MG1 included in the first array group G1 and the second element array MG2 included in the second array group G2, 60 elements aligned in the y-axis direction However, it is assumed that a structure for one cycle of the design is formed. N ₁ = N ₂ = 60. The spacing between adjacent elements is assumed to be Δy ₁ = Δx ₁ = Δy ₂ = Δx ₂ = 2.4 mm. Therefore, the structure for one period has a length of 2.4 × 60 = 144 mm. However, specific numerical values such as the number of elements and the interval between elements may be different in the first and second arrangement groups.

The reflection phase to be realized by each of these 60 elements is determined as follows. First, it is determined what is realizable among the reflection phases necessary to realize a specific reflection angle. Between the reflection phase difference Δφ _i and the reflection angle α _i ,
Δφ _i = k × Δy _i × sin (α _i )
Therefore, a linear relationship is established between the reflection phase and the coordinates (element positions aligned in the y-axis direction).

FIG. 12 shows that such a linear relationship is established for each of the reflection angle α ₁ = 70 degrees and the reflection angle α ₂ = 45 degrees. The horizontal axis is coordinates (y-axis), and the unit is mm. The elements are aligned along the y-axis every 2.4 mm. The vertical axis represents the reflection phase. The unit is degrees, but may be radians. The reflection phase is actually expressed by an angle within the range of 360 degrees, but in order to emphasize the linear relationship, the straight line is extended as it is even for angles larger than 360 degrees. In the figure, □ marks indicate that the reflection phase can actually be set so as to realize the _first reflection angle α ₁ = 70 degrees at the coordinate position corresponding to the point. The ◯ mark indicates that the reflection phase can actually be set so as to realize the _second reflection angle α ₂ = 45 degrees at the coordinate position corresponding to the point. Furthermore, due to manufacturing or theoretical constraints, it is not possible to create an element that achieves a reflection phase in the range of about 100 degrees to 290 degrees. This is illustrated on the straight line as a region where a square mark or a round mark is not shown (an unrealizable reflection phase). An unrealizable reflection phase is determined by manufacturing and theoretical constraints, and thus does not depend on the reflection angle. For this reason, the range of the reflection phase that cannot be realized is common to both the first and second reflection angles.

FIG. 13 shows a graph in which the reflection phase is converted so that the vertical axis falls within the range of 360 degrees in the graph of FIG. 12 (vertical axis = (reflection phase) mod (360)). The horizontal axis indicates the location of each of the 60 elements M1 to M60 aligned in the y-axis direction. For the elements belonging to the first element array MG1, the reflection phase relating to the _first reflection angle α ₁ = 70 degrees is set. Specifically, the reflection phase corresponding to the square mark in FIG. 13 is set at the position of each element. Elements that do not have a corresponding reflection phase may be omitted in the first element array MG1. In this way, the first array group G1 including a plurality of first element arrays MG1 in which the reflection phases of the elements are set in the direction of the first reflection angle α ₁ = 70 ° Will be able to reflect. For the elements belonging to the second element array MG2, the reflection phase related to the _second reflection angle α ₂ = 45 degrees is set. Specifically, the reflection phase corresponding to the circle in FIG. 13 is set at the position of each element. Elements for which there is no corresponding reflection phase may be omitted in the second element array MG2. In this way, the second array group G2 including a plurality of second element arrays MG2 in which the reflection phases of the elements are set in the direction of the second reflection angle α ₂ = 45 ° Will be able to reflect.

<4. Simulation>
FIG. 14 shows the positional relationship of the devices assumed in the simulation. Assume that the transmitter Tx is at the origin and the relay device RN is at a location 10 meters away from the origin along a certain direction. The relay device RN is formed by a reflect array as shown in FIG. The relay device RN reflects the incident wave toward the area to be improved. Each of the transmission device and the reception device includes four antennas, and performs communication using a 4 × 4 MIMO scheme.

FIG. 15 shows a comparison of the reflected wave from the conventional reflector R2 and the reflected wave from the reflector R34 as shown in FIG. 6 from the viewpoint of gain and azimuth. The conventional reflector R2 is formed as a square of 1 meter square, and reflects incident waves with one reflection angle of about 90 degrees. The reflector R34 according to the embodiment also has the same size of 1 meter square, but half R3 of the reflector reflects radio waves with a reflection angle of α ₁ = 75 degrees, and half R4 has radio waves with a reflection angle of α ₂ = 90 degrees. The reflection phases of the elements in the first and second element arrays MG1 and MG2 are set so as to reflect the light. For this reason, the two patterns of the reflection angles α ₁ and α ₂ related to the embodiment have a lower gain than the pattern according to the conventional example, but the range of the azimuth angle in which the gain exceeds the effective gain (10 dB in the illustrated example) is Widened more than twice.

  FIG. 16 shows a comparative example in terms of a channel capacity spatial distribution diagram. The assumed positional relationship is as shown in FIG. The outage capacity is shown for each beam (reflected wave) obtained in the cases of the “conventional example” and the “example”. In the case of the “conventional example”, only one strong reflected wave is radiated sharply, so the area with a low outage capacity occupies the majority. On the other hand, in the case of the “Example”, two strong reflected waves are reflected in different directions, and the area where the outage capacity can be improved is widened.

  FIG. 17 shows a comparative example from the viewpoint of the outage capacity and the cumulative distribution CDF of the capacity. “No reflector” corresponds to the case of receiving only the direct wave from the transmission device Tx without using the relay device. The “conventional example” corresponds to a case where an area is to be improved by using a reflector by the conventional reflector R2. “Example” corresponds to a case where an area is to be improved by using a reflector formed by the reflector R34 according to the example. As shown, in the case of the example, it can be seen that the area can be effectively improved.

  Although the present invention has been described with reference to particular embodiments, they are merely exemplary and those skilled in the art will appreciate various variations, modifications, alternatives, substitutions, and the like. For convenience of explanation, the above embodiment has been described in terms of a reflect array having mushroom-structured elements, but the present invention is not limited to such an embodiment and may be used in other situations. For example, left-handed transmission line theory, metamaterials, reflect array design using EBG (electrical band gap) structure, propagation environment improvement technology applying reflect array, reflected wave direction control technology applying reflect array, etc. It is also possible to use the present invention in various situations. Further, in the above description, the multi-beam reflectarray reflects incoming waves in a plurality of directions, but conversely, radio waves arriving from a plurality of directions may be reflected in one direction. Although specific numerical examples have been described in order to facilitate understanding of the invention, these numerical values are merely examples and any appropriate values may be used unless otherwise specified. Although specific mathematical formulas have been described to facilitate understanding of the invention, these mathematical formulas are merely examples, unless otherwise specified, and any appropriate mathematical formula may be used. The classification of the examples or items is not essential to the present invention, and the items described in two or more examples or items may be used in combination as necessary. It may be applied to the matters described in the item (unless there is a contradiction). The present invention is not limited to the above embodiments, and various modifications, modifications, alternatives, substitutions, and the like are included in the present invention without departing from the spirit of the present invention.

M1-MN element
51 Ground plate
52 Via
53 Patch α ₁ First reflection angle α ₂ Second reflection angle

Claims (3)

A multi-beam reflectarray including at least first and second array groups,
The first array group includes a plurality of first element arrays, the second array group includes a plurality of second element arrays,
Each of the first and second element arrays includes a plurality of elements aligned in a predetermined direction, and a phase difference between radio waves reflected by two of the plurality of elements is determined by the two elements. Proportional to the product of the spacing and the value of the trigonometric function for the angle of reflection by the element,
Reflection angle in the case where radio waves of a predetermined wavelength is reflected Ri by said first sequence group is different from the reflection angle in the case where radio waves of the predetermined wavelength is reflected Ri by the second sequence group, Multi-beam reflect array. A multi-beam reflectarray including at least first and second array groups,
The first array group includes a plurality of first element arrays, the second array group includes a plurality of second element arrays,
Each of the first and second element arrays includes a plurality of elements aligned in a predetermined direction,
The phase difference Δφ ₁ of the radio wave reflected by each of the two elements belonging to the first array group is expressed by Δφ ₁ = k × Δy ₁ × sin (α ₁ ), k indicates the wave number of the radio wave, Δy ₁ represents an interval between the two elements, α ₁ represents a reflection angle by the first array group ,
Wherein the phase difference [Delta] [phi ₂ of the radio wave which the second sequence of two elements each belonging to group reflected is represented by _{Δφ 2 = k × Δy 2 ×} sin (α 2), Δy 2 the spacing of the two elements Wherein α ₂ represents a reflection angle by the second array group and is different from α ₁ . The multi-beam reflect array according to claim 1 or 2, wherein the first array group and the second array group are arranged in parallel with respect to the predetermined direction.