JP2021101511A - Phase shifter and phased array antenna device - Google Patents

Abstract

To provide a phase shifter using a liquid crystal material, in which a decrease in liquid crystal response speed can be prevented while the loss of a microstrip line is reduced.SOLUTION: A phase shifter includes: a microstrip line; a ground conductor layer opposing the microstrip line and provided with a slit; and a liquid crystal layer between the microstrip line and the ground conductor layer. The slit provided in the ground conductor layer is arranged such that a part or the whole of the slit overlaps with the strip line.SELECTED DRAWING: Figure 1

Description

One embodiment of the present invention relates to a phase shifter using a liquid crystal material. Further, one embodiment of the present invention relates to a phased array antenna device having a phase shifter using a liquid crystal material.

A phased array antenna device directs the direction of an antenna in one direction by controlling the amplitude and phase of each high-frequency signal when a high-frequency signal is applied to a part or all of a plurality of antenna elements. It has the characteristic that the radiation directionality of the antenna can be controlled while it is fixed to. In the phased array antenna device, a phase shifter is used to control the phase of the high frequency signal applied to the antenna element.

As the method of the phase shifter, the method of physically changing the length of the transmission line to change the phase of the high frequency signal, the method of changing the impedance in the middle of the transmission line to make the phase of the high frequency by reflection, and the phase are different. Various methods such as a method of generating a signal having a desired phase by synthesizing by controlling the gain of an amplifier that amplifies two signals and synthesizing them are adopted. In addition to these, as an example of a phase shifter, a method utilizing a property peculiar to a liquid crystal material that the dielectric constant changes depending on an applied voltage is disclosed (see Patent Document 1).

Japanese Unexamined Patent Publication No. 11-103201

A phase shifter using a liquid crystal material has a structure provided with a microstrip line. It is effective to widen the line width in order to reduce the resistance loss of the microslip line, but if only the line width is simply widened, there is a problem that the characteristic impedance is out of alignment. In this case, it is effective to increase the cell gap of the liquid crystal cell in order to maintain the matching of the characteristic impedance, but there is a problem that the speed of the phase change becomes slow.

The phase shifter according to the embodiment of the present invention includes a microstrip line, a ground conductor layer facing the microstrip line and provided with a slit, and a liquid crystal layer between the microstrip line and the ground conductor layer. ,have. The slits provided in the ground conductor layer are arranged so as to partially or wholly overlap the strip line.

The configuration of the phase shifter according to the embodiment of the present invention is shown, (A) is a plan view of a state in which the first substrate and the second substrate are overlapped, (B) is a plan view of the first substrate, and (C) is a plan view of the first substrate. The plan view of the 2nd substrate is shown. The configuration of the phase shifter according to the embodiment of the present invention is shown, and the cross-sectional structure along the line A1-A2 shown in FIG. 1 (A) is shown. The configuration of the phase shifter according to the embodiment of the present invention is shown, and (A) and (B) show a cross-sectional structure different from that of FIG. The cross-sectional structure of the phase shifter is shown, (A) and (B) are diagrams for explaining the relationship between the line width of the microstrip line and the thickness of the liquid crystal layer, and (C) relates to one embodiment of the present invention. An example of the configuration of the phase shifter is shown. An example of a configuration of a phased array antenna device in which the phase shifter according to the present embodiment is used is shown. An example of a configuration of a phased array antenna device using the phase shifter according to the present embodiment is shown, and a cross-sectional structure along the B1-B2 line shown in FIG. 5 is shown.

Hereinafter, embodiments of the present invention will be described with reference to drawings and the like. However, the present invention can be implemented in many different modes and is not construed as being limited to the description of the embodiments illustrated below. In order to clarify the description, the drawings may schematically represent the width, thickness, shape, etc. of each part as compared with the actual embodiment, but this is merely an example and limits the interpretation of the present invention. It's not a thing. Further, in the present specification and each figure, the same elements as those described above with respect to the above-mentioned figures are designated by the same reference numerals (or reference numerals having a, b, etc. added after the numbers) to provide detailed explanations. It may be omitted as appropriate. Further, the characters added with "first" and "second" for each element are convenient signs used to distinguish each element, and have no further meaning unless otherwise specified.

As used herein, when a member or region is "above (or below)" another member or region, it is directly above (or directly below) the other member or region, unless otherwise specified. Not only in some cases, but also in the case of being above (or below) the other member or region, that is, including the case where another component is included above (or below) the other member or region. .. In the following description, unless otherwise specified, in cross-sectional view, the upper side with respect to the normal position in the figure is referred to as "upper" or "upper", and the surface viewed from "upper" or "upper" is "upper surface". "" Or "upper surface side", and vice versa "lower", "lower", "lower surface" or "lower surface side".

FIG. 1A shows a plan view of the phase shifter 100 according to the embodiment of the present invention. The phase shifter 100 includes a microstrip line 106 and a ground conductor layer 108. The microstrip line 106 is formed on the first substrate 102, and the ground conductor layer 108 is formed on the second substrate 104. The first substrate 102 and the second substrate 104 are arranged so as to face each other so that the microstrip line 106 and the ground conductor layer 108 face each other. A gap is provided between the first substrate 102 and the second substrate 104, and a liquid crystal layer (not shown) is provided in the gap portion.

The ground conductor layer 108 is provided with a slit 110. The slit 110 is a region from which the ground conductor layer 108 has been removed, and is a region where the insulating surface of the second substrate 104 is exposed. The slit 110 extends substantially parallel to the microstrip line 106. The length of the slit 110 has a length that can overlap at least from one end to the other end of the microstrip line 106. The slit 110 is arranged so as to overlap the microstrip line 106.

In other words, the ground conductor layer 108 is divided into a first ground conductor layer 108a and a second ground conductor layer 108b by a slit 110 extending substantially parallel to the microstrip line 106, and the first ground conductor layer 108a It can also be said that the respective ends of the second ground conductor layer 108b are arranged so as to overlap from one end to the other end of the microstrip line 106.

The first substrate 102 and the second substrate 104 are flat plates, and the material is an insulating material such as glass, plastic, or ceramic, and has an insulating surface due to its own physical characteristics. Further, the first substrate 102 and the second substrate 104 are formed of a conductive material such as metal in addition to the above-mentioned insulating material, and an insulating surface is formed by forming an insulating film on the surface thereof. May be good.

The microstrip line 106 and the ground conductor layer 108 are formed of a conductive film such as aluminum or copper. Such a conductive film is produced on the surfaces of the first substrate 102 and the second substrate 104 by a vacuum vapor deposition method or a sputtering method. The microstrip line 106 and the ground conductor layer 108 are produced by processing such a conductive film by etching. Further, the microstrip line 106 and the ground conductor layer 108 are formed of metal foils bonded to the surfaces of the first substrate 102 and the second substrate 104 instead of the film-formed conductive film as described above. You may.

FIG. 1B shows a plan view of the first substrate 102. The microstrip line 106 is a fine wire-shaped conductor pattern and is formed on the insulating surface of the first substrate 102. The microstrip line 106 is a line to which a high frequency signal is applied and a DC bias for controlling the orientation of the liquid crystal layer is applied. The microstrip line 106 is formed with a linear line pattern as shown. Further, although not shown, the microstrip line 106 may be formed in a meander-like bent pattern.

FIG. 1C shows a plan view of the second substrate 104. The ground conductor layer 108 is provided on the insulating surface of the second substrate 104. The ground conductor layer 108 is provided with a slit 110. As described above, the slit 110 is a region from which a part of the ground conductor layer 108 has been removed, and the insulating surface of the second substrate 104 is exposed. The slit 110 is formed so as to overlap the microstrip line 106 when the first substrate 102 and the second substrate 104 are arranged so as to face each other. When the microstrip line 106 has a linear line pattern, the slit 110 is also formed with a similar linear pattern. Further, when the microstrip line 106 is formed in a meander-like pattern, the slit 110 is also formed in a meander-like pattern. The grounding conductor layer 108 is a conductive layer to which a constant potential is constantly applied, and is fixed to, for example, the grounding potential.

FIG. 2 shows a cross-sectional structure along the lines A1-A2 shown in FIG. 1 (A). The microstrip line 106 is provided on the first substrate 102, and the ground conductor layer 108 is provided on the second substrate 104. The ground conductor layer 108 is provided with a slit 110. The slit 110 is arranged at a position overlapping the microstrip line 106. The ground conductor layer 108 is arranged so that at least a part thereof overlaps with the microstrip line 106. When the grounding conductor layer divided by the slit 110 is distinguished as the first grounding conductor layer 108a and the second grounding conductor layer 108b, FIG. 2 shows two regions of the first grounding conductor layer 108a and the second grounding conductor layer 108b. Shows a structure in which the ends of the are arranged so as to overlap the microstrip line 106.

The phase shifter 100 has a function of changing the dielectric constant by controlling the orientation state of the liquid crystal layer 112 by the bias voltage applied to the microstrip line 106 and shifting the phase of the high frequency signal propagating in the microstrip line 106. Have. Therefore, the ground conductor layer 108 provided with the slit 110 is provided so that at least a part thereof overlaps with the microstrip line 106. FIG. 2 shows a case where the width D of the slit 110 is narrower than the width W of the microstrip line 106 (W> D), and both ends of the first ground conductor layer 108a and the second ground conductor layer 108b. Shows a structure that overlaps with the microstrip line 106.

3A and 3B show aspects in which the arrangement of the microstrip line 106 and the slit 110 is different from the structure shown in FIG. In FIG. 3A, the width W of the microstrip line 106 and the width D of the slit 110 are the same as those shown in FIG. 2, but the positions of the slits 110 are arranged laterally offset from the center of the microstrip line 106. The aspect is shown. FIG. 3A shows an arrangement in which the first ground conductor layer 108a does not overlap the microstrip line 106 (the ends substantially coincide with each other), and the second ground conductor layer 108b overlaps the microstrip line 106. In this case, since the width W of the microstrip line 106 and the width D of the slit 110 are the same as those shown in FIG. 2, the area where the microstrip line 106 and the ground conductor layer 108 overlap is the same.

_{FIG. 3B shows a case where the width D w of the} slit 110 is the same as or larger than the width W of the microstrip line 106 _{(W ≦ D w} ). FIG. 3B shows that the first ground conductor layer 108a does not overlap the microstrip line 106 (the end is arranged outside) and the second ground conductor layer 108b overlaps the microstrip line 106. Is shown. In other words, in FIG. 3B, the first ground conductor layer 108a is arranged at a position where it does not overlap with the microstrip line 106, and the end portion of the second ground conductor layer 108b is arranged at a position where it overlaps with the microstrip line 106. Shows the structure. The width of the slit 110 may be equal to or greater than the width of the microstrip line 106. Even in such a case, the ground conductor layer 108 is provided so that at least a part thereof overlaps with the microstrip line 106. That is, one side forming the longitudinal end of the slit 110 overlaps the entire microstrip line 106 in the longitudinal direction.

In the phase shifter 100, a control signal for controlling the orientation state of the liquid crystal layer 112 is applied to the microstrip line 106. The control signal is preferably a DC signal or a polarity inversion signal whose polarity is inverted every time a certain period of time elapses. When a control signal is applied to the microstrip line 106, the orientation of the liquid crystal molecules in the liquid crystal layer 112 changes. Since the liquid crystal molecule is a kind of polar molecule, the permittivity of the liquid crystal layer 112 changes depending on the orientation state of the liquid crystal molecule. The dielectric constant of the liquid crystal layer 112 can also be adjusted by the magnitude of the control signal. That is, the phase shifter 100 can change the dielectric constant by the control signal applied to the microstrip line 106. In the liquid crystal layer 112, the orientation of the liquid crystal molecules mainly changes in the region where the microstrip line 106 and the ground conductor layer 108 face each other, and the orientation of the liquid crystal changes in the slit 110 portion except for the influence of the wraparound electric field. do not.

The liquid crystal layer 112 is made of a liquid crystal material. As the liquid crystal material, a nematic liquid crystal, a smectic liquid crystal, a cholesteric liquid crystal, a discolesteric liquid crystal, a ferroelectric liquid crystal (for example, a chiral smetic liquid crystal) or the like is used. The dielectric constant of the liquid crystal layer 112 changes as the orientation state changes. The orientation state of the liquid crystal layer 112 can be controlled by a DC voltage. On the other hand, the liquid crystal layer 112 cannot follow the AC electric field generated by the high-frequency signal in which the liquid crystal molecules navigate the microstrip line 106, so that the orientation state does not change. The phase shifter 100 has a function of controlling the phase of the high frequency signal propagating on the microstrip line 106 by utilizing such characteristics.

Although not shown in FIGS. 2 and 3 (A) and 3 (B), the first substrate 102 and the second substrate 104 are provided with an alignment film for controlling the orientation state of the liquid crystal molecules in the liquid crystal layer 112. You may. Further, although not shown, a sealing material may be provided between the first substrate 102 and the second substrate 104 so as to surround the liquid crystal layer 112. Further, a spacer for keeping the distance constant may be appropriately provided between the first substrate 102 and the second substrate 104.

In the present embodiment, the phase shifter 100 is provided with a slit 110 in the ground conductor layer 108 to increase the thickness of the liquid crystal layer 112 even when the line width is widened in order to reduce the loss of the microstrip line 106. The characteristic impedance can be kept constant without changing the slit, and an increase in reflection loss can be prevented.

The characteristic impedance Z ₀ of the phase shifter 100 is proportional to (L / C) ^1/2 (Note that L is a series inductance and C is a parallel capacitance). FIG. 4A shows a phase shifter 300 having a line width W1 of the microstrip line 106 and a thickness T1 of the liquid crystal layer 112. In this structure, the ground conductor layer 108 overlaps the microstrip line 106 with a width Z1 (Z1 = W1). For this structure, FIG. 4B shows a phase shifter 302 in which the line width is doubled in order to reduce the loss of the microstrip line 106. In this structure, the ground conductor layer 108 overlaps the microstrip line 106 with a width Z2 (Z2 = W2 = W1 × 2). _{In this case, in order to make the characteristic impedance Z 0} constant with respect to the line width W2 of the microstrip line 106, it is necessary to increase the thickness of the liquid crystal layer 112 and reduce the capacitance C. Specifically, the thickness T2 of the liquid crystal layer 112 needs to be twice that of T1 (T2 = T1 × 2). However, if the thickness of the liquid crystal layer 112 is increased, there is a problem that the response speed of the liquid crystal is lowered.

On the other hand, the phase shifter 100 shown in FIG. 4C has a structure in which the ground conductor layer 108 is provided with the slit 110. While the line width of the microstrip line 106 is W2 as in FIG. 4B, the width D1 of the slit 110 is provided to be half the size of the line width W2 (D1 = W2 × 0.5). ). As a result, the total width Z11 on which the first ground conductor layer 108a overlaps and the width Z12 on which the second ground conductor layer 108b overlaps with respect to the microstrip line 106 is the same Z1 as in the case shown in FIG. 4 (A). Z1 = Z11 + Z12). Then, the characteristic impedance can be kept constant while keeping the thickness of the liquid crystal layer 112 at T1. That is, by providing the slit 110 in the ground conductor layer 108, it is not necessary to increase the thickness of the liquid crystal layer 112, and it is possible to keep the characteristic impedance constant without lowering the response speed of the liquid crystal.

Table 1 shows the phase shifter 100 (Example) shown in FIG. 4 (C), the phase shifter 300 (Comparative Example 1) shown in FIG. 4 (A), and the phase shifter 302 shown in FIG. 4 (B). The result of computer simulation of the response speed of Comparative Example 2) is shown. In the simulation, the line widths of the microstrip lines were set to 1500 μm (Example), 150 μm (Comparative Example 1), and 1500 μm (Comparative Example 2), respectively, and the response speed was evaluated with respect to the presence or absence of slits in the ground conductor layer. In this case, in the example, the width of the slit was set to 1375 μn, and the thickness of the liquid crystal layer was set to 50 μm. In the comparative example, the thickness of the liquid crystal layer was set to 50 μm (Comparative Example 1) and 500 μm (Comparative Example 2).
Table 1 Evaluation of liquid crystal response speed with and without slits

As shown in Table 1, as shown in the results of Comparative Example 1 and Comparative Example 2, the response speed was increased by widening the line width of the microstrip line and increasing the thickness of the liquid crystal layer in order to make the characteristic impedance uniform. Although it is significantly reduced, in the embodiment, by providing a slit in the ground conductor layer, even when the width of the microstrip line is widened, the characteristic impedance can be matched without increasing the thickness of the liquid crystal layer, so that the response speed can be increased. It is possible to suppress the decrease.

5 and 6 show a configuration example of the phased array antenna device 200 in which the phase shifter 100 according to the present embodiment is used. FIG. 5 shows a plan view of the phased array antenna device 200, and FIG. 6 shows a cross-sectional structure corresponding to the B1-B2 line in FIG. In the following, it will be described with reference to FIGS. 5 and 6.

The phased array antenna device 200 includes a phase shifter 100 and an antenna element 114. A plurality of antenna elements 114 are arranged in a straight line, an arc shape, or a plane shape to form an antenna element array. The phase shifter 100 is provided corresponding to each of the plurality of antenna elements 114. Further, the phased array antenna device 200 has a phase control circuit (not shown). The phase control circuit has a function of outputting a signal for controlling the phase of the phase shifter 100.

Note that FIGS. 5 and 6 show a case where the phased array antenna device 200 is for transmission. The phased array antenna device 200 has a terminal portion 116 connected to each of the microstrip lines 106. Each terminal 116 is connected to the distributor 118. The distributor 118 is connected to the oscillator 120. The high frequency signal output from the oscillator 120 is distributed to the respective phase shifters 100 by the distributor 118.

The electromagnetic waves radiated from each of the plurality of antenna elements 114 have coherent properties. Therefore, electromagnetic waves radiated from each of the plurality of antenna elements 114 form a wavefront having a uniform phase. The phase of the electromagnetic wave radiated from the antenna element 114 is adjusted by the phase shifter 100. In the phase shifter 100, the phase of a high frequency signal radiated as an electromagnetic wave is controlled by a phase control circuit (not shown). Although the line width of the phase shifter 100 is widened in order to reduce the loss on the microstrip line 106, the slit 110 is provided in the ground conductor layer 108, so that the response speed of the liquid crystal is prevented from being lowered. There is. Therefore, the phased array antenna device 200 can output an electromagnetic wave having a uniform wave surface while reducing the loss in the phase shifter 100. The same effect can be obtained when the phased array antenna device 200 is used for reception.

100 ... phase shifter, 102 ... first substrate, 104 ... second substrate, 106 ... microstrip line, 108 ... ground conductor layer, 110 ... slit, 112 ... Liquid crystal layer, 114 ... antenna element, 116 ... terminal, 118 ... distributor, 120 ... oscillator, 200 ... phased array antenna device

Claims (7)

With microstrip tracks
A ground conductor layer facing the microstrip line and provided with a slit,
A liquid crystal layer between the microstrip line and the ground conductor layer,
Have,
The slit is a phase shifter characterized in that a part or the whole is arranged so as to overlap the microstrip line. The phase shifter according to claim 1, wherein the slit has a length continuous from at least one end to the other end of the microstrip line. The phase shifter according to claim 2, wherein the width of the slit is narrower than the width of the microstrip line. The third aspect of claim 3, wherein the ground conductor layer has a first side forming an end portion in the longitudinal direction of the slit and a second side facing the first side superimposing on the microstrip line. Phase shifter. The phase shifter according to claim 2, wherein the width of the slit is wider than the width of the microstrip line. The phase shifter according to claim 5, wherein the ground conductor layer has one side forming an end portion in the longitudinal direction of the slit overlapping over the entire longitudinal direction of the microstrip line. A phased array antenna device having the phase shifter according to any one of claims 1 to 6.

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