JP3830848B2 - Phase modulator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a phase modulation element and a phase modulation device using liquid crystal, and in particular, the phase of a signal having a frequency in the millimeter wave band or the microwave band (hereinafter referred to as “millimeter wave signal or microwave signal”). The present invention relates to a phase modulation element and a phase modulation device that can be changed.
[0002]
[Prior art]
In recent years, development of wireless systems using millimeter wave signals or microwave signals, such as ultrahigh-speed wireless local area networks, high-speed wireless line systems, home links, inter-vehicle communication systems, etc. has been actively proposed.
[0003]
One method for performing data transmission in a wireless system is phase modulation. The phase modulation can be performed using, for example, a phase modulation device. Various types of phase modulation devices are known, and one of them uses liquid crystal.
[0004]
For example, in the phase modulation device (phase variable device) described in Japanese Patent Application Laid-Open No. 2001-237604, a meandering transmission line is provided on the inner surface of one of the two substrates constituting the cell container. The phase of the millimeter wave signal or the microwave signal that is arranged and flows through the transmission line is controlled by changing the dielectric constant of the liquid crystal layer formed in the cell container.
[0005]
In order to change the dielectric constant of the liquid crystal layer, a ground conductor is disposed around the transmission line at a predetermined interval from the transmission line. An alignment film is disposed on the inner surface of each of the two substrates constituting the cell container, and each of the substrates is disposed on the outer surface between the transmission line and the ground conductor in plan view. A plurality of electrodes (external electrodes) are arranged so as to be positioned.
[0006]
An AC bias voltage of a predetermined magnitude is simultaneously applied to each of the external electrodes arranged on the outer surface of one substrate and each of the external electrodes arranged on the outer surface of the other substrate. By doing so, the liquid crystal molecules around the transmission line are rearranged uniformly, and the dielectric constant of the liquid crystal layer around the transmission line changes uniformly. With this change, the electrical length of the transmission line changes, and as a result, the millimeter wave signal or microwave signal having a phase different from that of the millimeter wave signal or microwave signal supplied to one end of the transmission line Is output from the other end. Phase modulation can be performed.
[0007]
In addition, the publication discloses that an AC voltage for driving a liquid crystal is supplied to a transmission line together with a millimeter wave signal or a microwave signal without providing an external electrode on the outer surface of each of the two substrates constituting the cell container. There is also described a type of phase modulation apparatus that performs phase modulation. Also in this type of phase modulation apparatus, during phase modulation, liquid crystal molecules around the transmission line are uniformly rearranged to uniformly change the dielectric constant of the liquid crystal layer around the transmission line.
[0008]
[Problems to be solved by the invention]
In the phase modulation device described in the above publication, since the arrangement of liquid crystal molecules around the transmission line is uniformly controlled along the transmission line, the dielectric loss due to the liquid crystal layer is relatively large.
[0009]
An object of the present invention is to provide a phase modulation element using liquid crystal, which can reduce dielectric loss due to a liquid crystal layer.
[0010]
Another object of the present invention is to provide a phase modulation device using liquid crystal, which can reduce dielectric loss due to a liquid crystal layer.
[0011]
[Means for Solving the Problems]
According to one aspect of the present invention, (i) a first substrate provided with a millimeter-wave band or a microwave-band transmission line on one surface, and (ii) disposed opposite to the first substrate, A second electrode having a plurality of electrodes arranged on a surface facing the first substrate at a pitch of about 1/4 or less of a wavelength of a signal in the transmission line with respect to an extending direction of the transmission line; There is provided a phase modulation element having a substrate and (iii) a liquid crystal layer sandwiched between the first and second substrates and changing a dielectric constant as viewed from the transmission line by applying a voltage to the electrode. The
[0012]
According to another aspect of the present invention, (i) a millimeter wave band or a microwave band transmission line is provided on one surface, and an extension direction of the transmission line is provided on another surface facing the one surface. A first substrate having a plurality of first electrodes disposed at a pitch of approximately ¼ or less of the wavelength of a signal in the transmission line; and (ii) disposed opposite to the first substrate, A second substrate having a plurality of second electrodes overlapping the plurality of first electrodes in plan view on another surface facing the first surface facing the first substrate; and (iii) the first A phase modulation element is provided that includes a liquid crystal layer that is sandwiched between a second substrate and a voltage applied to the first and second electrodes to change a dielectric constant viewed from the transmission line.
[0013]
According to still another aspect of the present invention, (i) a millimeter wave band or a microwave band transmission line is provided on one surface, and the extension direction of the transmission line is provided on the other surface facing the one surface. A first substrate having a plurality of first electrodes disposed at a pitch of approximately ¼ or less of the wavelength of the signal in the transmission line, and (ii) disposed opposite the first substrate, A second substrate having a plurality of second electrodes overlapping the plurality of first electrodes in plan view on one surface facing the first substrate; and (iii) the first and second substrates There is provided a phase modulation element having a liquid crystal layer sandwiched between and having a dielectric constant as seen from the transmission line by applying a voltage to the first and second electrodes.
[0014]
According to still another aspect of the present invention, (A) (i) a first substrate provided with a millimeter-wave band or a microwave-band transmission line on one surface, and (ii) facing the first substrate A plurality of electrodes arranged on one surface facing the first substrate at a pitch of about 1/4 or less of the wavelength of the signal in the transmission line with respect to the extending direction of the transmission line. And (iii) a liquid crystal layer that is sandwiched between the first and second substrates and has a liquid crystal layer that changes a dielectric constant viewed from the transmission line by applying a voltage to the electrodes. A modulation element; (B) a drive circuit capable of supplying a drive signal to each of the plurality of electrodes; and (C) controlling the operation of the drive circuit to form a dielectric constant distribution in the liquid crystal layer. A phase modulation device including a control circuit capable of performing the above is provided.
[0015]
According to still another aspect of the present invention, (A) (i) a millimeter-wave band or a microwave-band transmission line is provided on one surface, and the transmission line is provided on the other surface facing the one surface. A first substrate having a plurality of first electrodes disposed at a pitch of approximately ¼ or less of the wavelength of the signal in the transmission line with respect to the extending direction; and (ii) facing the first substrate. A second substrate having a plurality of second electrodes disposed on another surface facing the first substrate and facing the first substrate and overlapping the plurality of first electrodes in plan view; and (iii) A phase modulation element having a liquid crystal layer sandwiched between the first and second substrates and having a dielectric constant as viewed from the transmission line by applying a voltage to the first and second electrodes; B) A drive signal can be applied to each of the plurality of first electrodes and the plurality of second electrodes. There is provided a phase modulation device comprising: a drive circuit that controls the operation of the drive circuit, and a control circuit that can form a dielectric constant distribution in the liquid crystal layer.
[0016]
According to still another aspect of the present invention, (A) (i) a millimeter-wave band or a microwave-band transmission line is provided on one surface, and the transmission line is provided on the other surface facing the one surface. A first substrate having a plurality of first electrodes disposed at a pitch of approximately ¼ or less of the wavelength of the signal in the transmission line with respect to the extending direction; and (ii) facing the first substrate. A second substrate disposed on one surface facing the first substrate and having a plurality of second electrodes overlapping the plurality of first electrodes in plan view; and (iii) the first and first A phase modulation element having a liquid crystal layer that is sandwiched between two substrates and changes a dielectric constant viewed from the transmission line by applying a voltage to the first and second electrodes, and (B) the plurality of A drive circuit capable of applying a drive signal to each of the first electrode and the plurality of second electrodes, and (C) And controls the operation of the dynamic circuit, a phase modulation apparatus that includes a control circuit capable of forming a dielectric constant distribution on the liquid crystal layer is provided.
[0017]
Here, “millimeter wave band or microwave band transmission line” in this specification means a transmission line capable of propagating a millimeter wave signal or a microwave signal. The “millimeter wave signal” means a signal having a frequency of about 30 G to 300 GHz, and the “microwave signal” means a signal having a frequency of about 3 G to 30 GHz.
[0018]
A plurality of electrodes are arranged as described above at a pitch of about 1/4 or less of the wavelength of the millimeter wave signal or microwave signal supplied to the transmission line from the outside of the phase modulation element and propagating through the transmission line, By appropriately controlling the voltage applied to these electrodes, the dielectric constant of the liquid crystal layer can be changed approximately in the period of the wavelength along the extending direction of the transmission line.
[0019]
As the dielectric constant of the liquid crystal layer changes periodically, the electrical length (characteristic impedance) of the transmission line also changes periodically. By changing the electrical length of the transmission line approximately with the period of the wavelength, a forbidden band for the millimeter wave signal or the microwave signal can be efficiently formed in the transmission line. This forbidden band is the same as the forbidden band for light (photonic band gap). In this specification, this forbidden band formed in the transmission line is also referred to as “photonic band gap” (hereinafter abbreviated as “PBG”).
[0020]
When the PBG is formed in the transmission line, the millimeter wave signal or the microwave signal propagating in the transmission line is reflected without being able to enter the PBG. By appropriately changing the formation position of the PBG, a millimeter wave signal or a microwave signal having a phase different from that of the millimeter wave signal or the microwave signal supplied to the transmission line can be generated. Phase modulation can be performed.
[0021]
This phase modulation can be performed, for example, by appropriately changing the position of the start end of the PBG in the transmission line within a region having a length equal to or shorter than the wavelength of the millimeter wave signal or microwave signal in the transmission line. Is possible.
[0022]
Compared to a conventional device that performs phase modulation by uniformly changing the arrangement of liquid crystal molecules around the transmission line along the transmission line, the dielectric loss due to the liquid crystal layer can be greatly reduced.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 schematically shows a planar shape of a phase modulation element according to the first embodiment. A phase modulation element 50 shown in the figure includes a cell container 30 having first and second substrates 10 and 20, and a liquid crystal layer (not shown) composed of liquid crystal filled in the cell container 30. Is provided.
[0024]
The first substrate 10 is formed of an electrically insulating material, and a transmission line (millimeter wave band or microwave band transmission line) 11 capable of propagating a millimeter wave signal or a microwave signal is disposed on one surface thereof. Is done. The transmission line 11 can be formed of, for example, gold (Au) or a laminate of a gold (Au) layer and a copper (Cu) layer.
[0025]
The second substrate 20 is also formed of an electrically insulating material, and a predetermined number of electrodes 21 crossing the transmission line 11 in plan view are arranged in parallel at a constant pitch on one surface thereof. Each of the electrodes 21 can be formed of a metal, a conductive metal oxide, or the like.
[0026]
The first and second substrates 10 and 20 are arranged with the transmission line 11 and the electrode 21 facing each other to constitute a cell container 30. A pad P is provided at the input end of the transmission line 11 as necessary.
[0027]
Hereinafter, the configuration of the phase modulation element 50 will be described in more detail with reference to FIGS. 2 (A) and 2 (B).
[0028]
2A schematically shows a cross section taken along the line IIA-IIA shown in FIG. 1, and FIG. 2B schematically shows a cross section taken along the line IIB-IIB shown in FIG. Show.
[0029]
As shown in these drawings, the transmission line 11 is covered with a first alignment film 12, and each of the electrodes 21 is covered with a second alignment film 22.
[0030]
The material of each of the first and second alignment films 12 and 22 can be selected as appropriate. In addition, the alignment treatment applied to the alignment films 12 and 22 can be appropriately selected.
[0031]
However, in order to increase the responsiveness of the phase modulation element 50, a large pretilt angle (a pretilt angle measured using the alignment film surface as a reference plane) can be imparted to the liquid crystal molecules, and the polar angle anchoring energy is increased. A high alignment film is preferred. Such an alignment film can be obtained, for example, by subjecting a film formed of a polyimide material having an alkyl side chain to a rubbing treatment.
[0032]
The first substrate 10 and the second substrate 20 are integrated with each other by a sealing material 15 in which spacers (not shown) are dispersed to form a cell container 30. Each of the transmission line 11 and the electrode 21 extends to the outside of the cell container 30. As described above, the liquid crystal layer 25 is formed in the cell container 30.
[0033]
In order to obtain a highly responsive phase modulation element, it is preferable to form the liquid crystal layer 25 with a liquid crystal material having a high refractive index and a low viscosity, such as a nematic liquid crystal. If necessary, a liquid crystal (polymer dispersed liquid crystal or polymer stabilized liquid crystal) in which a polymer or an oligomer is dispersed may be used.
[0034]
The above polymer dispersed liquid crystal and polymer stabilized liquid crystal disperse several wt% to several tens wt% polymer or oligomer in the liquid crystal, and further initiate photo reaction of several wt% with respect to the polymer or oligomer. An agent is added. In this polymer-dispersed or polymer-stabilized liquid crystal, the polymer or oligomer is polymerized when irradiated with ultraviolet rays after filling into an empty cell (cell container), and a polymer network is formed in the liquid crystal layer. The layer becomes sol-gel or solid. Therefore, not only the main seal becomes unnecessary, but also the responsiveness is improved. However, since the dielectric anisotropy (Δε) decreases as the polymer ratio increases, the amount of the monomer or oligomer dispersed in the liquid crystal is preferably about 10 wt% or less.
[0035]
In order to obtain a highly responsive phase modulation element, it is preferable to reduce the cell thickness (thickness of the liquid crystal layer 25). Moreover, the cell comprised by the liquid crystal layer 25 and the cell container 30 can also be made into a hybrid alignment cell, a pi ((pi)) cell, and a vertical alignment cell as needed.
[0036]
However, in order to perform phase modulation easily and accurately, it is better not to add a chiral agent to the liquid crystal layer 25. In addition, the alignment direction of the liquid crystal molecules in a state where no voltage is applied is preferably parallel to the extending direction of the transmission line 11.
[0037]
In the phase modulation element 50, the pitch between the adjacent electrodes 21 is selected to be approximately ¼ or less of the wavelength λ of the millimeter wave signal or the microwave signal that is supplied to the transmission line 11 from the outside and propagates through the transmission line 11. Is done.
[0038]
In the phase modulation element 50 in which the electrodes 21 are arranged in this way, by controlling the voltage supplied to each electrode 21, the dielectric constant of the liquid crystal layer 25 is approximately equal to the wavelength λ along the extending direction of the transmission line 11. It can be changed with the period. Accordingly, the electrical length (characteristic impedance) of the transmission line 11 in the cell container 30 can be changed with a period of the wavelength λ.
[0039]
As a result, it becomes possible to efficiently form a PBG for the millimeter wave signal or the microwave signal in the transmission line 11. The millimeter wave signal and the microwave signal supplied to the transmission line 11 are reflected without being able to enter the PBG and are output from the phase modulation element 50.
[0040]
When the phase modulation element 50 is used in a communication device, generally, n-bit data is obtained by a 2n-phase millimeter wave signal or microwave signal whose phase angle is shifted by π / n (n represents an integer of 1 or more). Therefore, phase modulation can be performed by shifting the PBG formation position in units of λ / 4n (λ represents the wavelength of the millimeter wave signal or microwave signal supplied to the transmission line 11). preferable. For this purpose, it is preferable to arrange 4n electrodes 21 per unit length along the transmission line 11 when the wavelength λ is a unit length.
[0041]
Hereinafter, a phase modulation apparatus capable of generating a four-phase millimeter-wave signal or microwave signal with a phase angle shifted by π / 2 will be taken as an example, and the configuration and operation thereof will be specifically described with reference to FIGS. I will explain it.
[0042]
FIG. 3 schematically shows the configuration of the phase modulation apparatus according to the embodiment. The phase modulation apparatus 100 includes a driving apparatus 60, a control circuit 70, a voltage control oscillator 80 (hereinafter abbreviated as “VCO 80”), a circulator 85, and a radiator 90 in addition to the phase modulation element 50 described above. Prepare.
[0043]
The driving device 60 is controlled in operation by the control circuit 70 and generates a driving signal for driving the phase modulation element 50 and the VCO 80. The drive signal for the phase modulation element 50 is roughly classified into a drive signal supplied to each of the electrodes 21 and a drive signal supplied to the transmission line 11. Details of the drive signal supplied to the phase modulation element 50 will be described later.
[0044]
The VCO 80 operates in accordance with the drive signal supplied from the drive circuit 60, and generates a millimeter wave signal or a microwave signal having a predetermined wavelength and frequency. This signal is supplied to the circulator 85.
[0045]
The circulator 85 supplies the millimeter wave signal or the microwave signal supplied from the VCO 80 to the transmission line 11 of the phase modulation element 50 and the millimeter wave signal or the microwave signal output from the phase modulation element 50 to the radiator 90. Supply.
[0046]
The radiator 90 is an antenna, for example, and radiates a millimeter wave signal or a microwave signal supplied from the phase modulation element 50 via the circulator 85.
[0047]
In the illustrated phase modulation element 50, when the wavelength λ of the millimeter wave signal or the microwave signal supplied to the transmission line 11 is a unit length, eight electrodes 21 are arranged per unit length along the transmission line 11. Is done.
[0048]
In order to efficiently form a PBG in the transmission line 11, it is desirable to change the electrical length of the transmission line 11 over, for example, approximately four periods or more with a period of about a wavelength λ. In order to generate a four-phase millimeter-wave signal or microwave signal, it is preferable to change the start end of the PBG on the pad P side, for example, within a range of four consecutive electrodes. For these reasons, it is preferable to arrange approximately 19 or more electrodes 21 in the phase modulation element 50.
[0049]
These electrodes 21 are commonly connected every seven lines and divided into eight groups. Each group receives any one of drive signals φ1 to φ8 from the drive circuit 60. One drive signal corresponds to one group.
[0050]
When the phase modulation device 100 is driven, four of the drive signals φ1 to φ8 are at a high level, and the remaining four are at a low level. Which drive signal is set to high level and which drive signal is set to low level differ depending on which phase of the four-phase millimeter-wave signal or microwave signal to be generated is generated. A drive signal having a constant potential (for example, ground potential) is supplied from the drive circuit 60 to the transmission line 11.
[0051]
Hereinafter, with reference to FIGS. 4A to 4C and FIGS. 5A to 5B, the levels of the drive signals φ1 to φ8 supplied to the phase modulation element 50 and the phase modulation element 50 The relationship with the phase of the millimeter wave signal or the microwave signal output from will be described.
[0052]
FIG. 4A schematically shows the formation position of the PBG when the drive signals φ1 to φ4 are set to the high level and the drive signals φ5 to φ8 are set to the low level (for example, the ground potential) to drive the phase modulation element 50. Show.
[0053]
In the drawing, a high-level drive signal is supplied to each of the electrodes 21 that are hatched, and a low-level drive signal is supplied to each of the electrodes 21 that are not hatched (the same applies hereinafter). .
[0054]
When the levels of the drive signals φ1 to φ8 are controlled as described above, a region having a relatively high dielectric constant and a region having a relatively low dielectric constant are periodically formed in the liquid crystal layer 25 (see FIG. 2A). Formed. These regions are formed with a period of substantially a wavelength λ from the bottom of the electrode 21 closest to the pad P to the rear thereof (which means a direction away from the pad P along the transmission line 11; the same applies hereinafter). The length of each region along the transmission line 11 corresponds to approximately λ / 2.
[0055]
As a result, the electrical length of the transmission line 11 changes with a period of the wavelength λ from the bottom of the electrode 21 closest to the pad P to the rear thereof, and a PBG is formed here.
[0056]
When the PBG is formed in the transmission line 11, the millimeter wave signal or the microwave signal supplied to the transmission line 11 does not enter the PBG but is reflected and returns to the circulator 85 (see FIG. 3), and is emitted from here. To the container 90.
[0057]
At this time, the phase of the millimeter wave signal or microwave signal output from the phase modulation element 50 has a constant phase difference with respect to the phase of the supplied millimeter wave signal or microwave signal.
[0058]
4 (B) to FIG. 4 (C) and FIG. 5 (A) to FIG. 5 (B), the starting end of the PBG on the pad P side is almost one electrode from the state shown in FIG. The relationship between the level of each drive signal φ1 to φ8 and the position where the PBG is formed when shifting backward by approximately 2 electrodes, approximately 3 electrodes, or approximately 4 electrodes is schematically shown.
[0059]
As shown in FIG. 4B, when the phase modulation element 50 is driven by setting the drive signals φ2 to φ5 to the high level and the drive signals φ1 and φ6 to φ8 to the low level, the start end of the PBG on the pad P side Is shifted substantially one electrode rearward from the state shown in FIG.
[0060]
At this time, the millimeter wave signal or the microwave signal output from the phase modulation element 50 is a difference between two electrodes in a reciprocation, that is, 2π / 4 (= π / 2), as compared with the state of FIG. The phase difference is generated.
[0061]
As shown in FIG. 4C, when the drive signals φ3 to φ6 are set to the high level and the drive signals φ1 to φ2 and φ7 to φ8 are set to the low level to drive the phase modulation element 50, the PBG on the pad P side The starting end deviates approximately two electrodes from the state shown in FIG.
[0062]
At this time, the millimeter wave signal or the microwave signal output from the phase modulation element 50 generates a phase difference of 4π / 4 (= π) as compared with the state of FIG.
[0063]
As shown in FIG. 5A, when the drive signals φ4 to φ7 are set to the high level and the drive signals φ1 to φ3 and φ8 are set to the low level to drive the phase modulation element 50, the start end of the PBG on the pad P side However, there is a deviation of approximately three electrodes from the state shown in FIG.
[0064]
At this time, the millimeter wave signal or the microwave signal output from the phase modulation element 50 generates a phase difference of 6π / 4 (= 3π / 2) as compared with the state of FIG.
[0065]
As shown in FIG. 5B, when the drive signals φ5 to φ8 are set to the high level and the drive signals φ1 to φ4 are set to the low level to drive the phase modulation element 50, the starting end of the PBG on the pad P side is illustrated. Although the position shown in FIG. 4 (A) deviates substantially four electrodes, the starting end of the PBG is electrically equivalent to the position shown in FIG. 4 (A).
[0066]
At this time, the millimeter wave signal or the microwave signal output from the phase modulation element 50 generates a phase difference of 2π as compared with the state of FIG. The signal is equivalent to the signal output under the state of FIG.
[0067]
As understood from FIGS. 4 (A) to 4 (C) and FIGS. 5 (A) to 5 (B), the phase of the millimeter wave signal or the microwave signal output from the phase modulation element 50 is Each time the start end of the PBG on the pad P side is shifted to the rear of about one electrode, the PBG is delayed by about λ / 4 (π / 2). A four-phase millimeter wave signal or microwave signal can be generated by appropriately changing the start end of the PBG on the pad P side within a range of four continuous electrodes.
[0068]
The phase modulation device 100 that performs phase modulation in this way is more dielectric than a device that performs phase modulation by uniformly changing the alignment of liquid crystal molecules around the transmission line along the transmission line. Body loss can be reduced easily.
[0069]
Next, a phase modulation element according to the second embodiment will be described.
[0070]
FIG. 6A schematically shows a planar shape of the phase modulation element according to the second embodiment. The phase modulation element 150 shown in the figure is structurally different from the phase modulation element 50 according to the first embodiment in that the transmission line 11 is connected to the capacitor C outside the cell container 30. Other configurations of the phase modulation element 150 are the same as those of the phase modulation element 50.
[0071]
Among the constituent elements shown in FIG. 6A, the constituent elements already shown in FIG. 1 are assigned the same reference numerals as those used in FIG. The capacitor C will be described in detail with reference to FIG.
[0072]
FIG. 6B shows an example of the capacitor C in an enlarged manner. The capacitor C shown in the figure is manufactured by forming a square wave gap in the middle of one millimeter wave band or microwave band transmission line. A transmission line between the pad P and the capacitor C is indicated by reference numeral 11a.
[0073]
The capacitor C allows the millimeter wave signal or the microwave signal to propagate between the transmission lines 11a and 11 as in the case where the capacitor C is not provided, while the transmission line is supplied when the drive signal is supplied to the electrode 21. 11 and 11a are for suppressing the functioning of the ground wire.
[0074]
The characteristics of the capacitor C can be appropriately changed according to the frequency of the millimeter wave signal or the microwave signal supplied to the phase modulation element 150.
[0075]
In the phase modulation element 150 having the capacitor C, the liquid crystal molecules in the liquid crystal layer 25 (see FIG. 2A) can be rearranged by an electric field (lateral electric field) formed between the adjacent electrodes 21. When the phase modulation element 150 is driven, a predetermined drive signal is supplied to each of the electrodes 21, and only the millimeter wave signal or the microwave signal is supplied to the transmission line 11.
[0076]
When a 2n-phase millimeter wave signal or microwave signal having a phase angle shifted by π / n is generated by controlling the orientation of the liquid crystal molecules in the phase modulation element 150 using a lateral electric field, the transmission line 11 is used. When the wavelength λ of the propagating millimeter wave signal or microwave signal is a unit length, it is preferable to arrange 4n electrodes 21 per unit length. At this time, it is preferable to make the line width of each electrode 21 narrower than the interval between adjacent electrodes 21. The liquid crystal layer 25 is preferably thin.
[0077]
In the following, taking the case of generating a four-phase millimeter wave signal or microwave signal with a phase angle shifted by π / 2 as an example, the arrangement of the electrodes 21 in the phase modulation element 150 and the method of driving the phase modulation element 150 will be described. This will be specifically described.
[0078]
When the phase modulation element 150 generates a four-phase millimeter wave signal or microwave signal, when the wavelength λ of the millimeter wave signal or microwave signal supplied to the transmission line 11 is a unit length, the transmission line 11 Eight electrodes 21 are arranged per unit length along.
[0079]
These electrodes 21 are commonly connected every seven lines and divided into eight groups. Each group receives one of the drive signals φ1 to φ8 from the drive circuit. One drive signal corresponds to one group.
[0080]
When driving the phase modulation apparatus 100, for example, six of the drive signals φ1 to φ8 are at a high level, and the remaining two are at a low level. Two of the drive signals φ1 to φ8 can be set to a low level, and the remaining six can be set to a high level.
[0081]
Which drive signal is set to high level and which drive signal is set to low level differ depending on which phase of the four-phase millimeter-wave signal or microwave signal to be generated is generated. Only the millimeter wave signal or the microwave signal is supplied to the transmission line 11.
[0082]
With reference to FIGS. 7A to 7C and FIGS. 8A to 8B, the level of the drive signal supplied to the phase modulation element 150 and the millimeters output from the phase modulation element 150 are described. The relationship with the phase of a wave signal or a microwave signal is demonstrated.
[0083]
FIG. 7A schematically shows the formation position of the PBG when the drive signals φ2 and φ4 to φ8 are set to high level and the drive signals φ1 and φ3 are set to low level (for example, ground potential) to drive the phase modulation element 150. Indicate.
[0084]
In the drawing, a high-level drive signal is supplied to each of the electrodes 21 that are hatched, and a low-level drive signal is supplied to each of the electrodes 21 that are not hatched (the same applies hereinafter). .
[0085]
When a high level drive signal is supplied to one of two electrodes adjacent to each other and a low level drive signal is supplied to the other, a lateral electric field is formed between the two electrodes. When a drive signal of the same level is supplied to each of two adjacent electrodes, a lateral electric field is not formed between these two electrodes.
[0086]
When the levels of the drive signals φ1 to φ8 are controlled as described above, a region having a relatively high dielectric constant and a region having a relatively low dielectric constant are periodically formed in the liquid crystal layer 25 (see FIG. 2A). Formed. These regions are formed from the bottom of the electrode 21 closest to the pad P to the rear thereof, with a period of approximately wavelength λ. The length of each region along the transmission line 11 corresponds to approximately λ / 2.
[0087]
As a result, the electrical length of the transmission line 11 changes with a period of the wavelength λ from the bottom of the electrode 21 closest to the pad P to the rear thereof, and a PBG is formed here.
[0088]
A millimeter wave signal or a microwave signal having a certain phase difference with respect to the supplied millimeter wave signal or microwave signal is output from the phase modulation element 150.
[0089]
7B, FIG. 7C, FIG. 8A, and FIG. 8B show that the starting end of the PBG on the pad P side is approximately one electrode from the state shown in FIG. The relationship between the level of each drive signal φ1 to φ8 and the position where the PBG is formed when shifting backward by two electrodes, approximately three electrodes, or approximately four electrodes is schematically shown.
[0090]
As shown in FIG. 7B, when the drive signals φ1, φ3 and φ5 to φ8 are set to the high level and the drive signals φ2 and φ4 are set to the low level to drive the phase modulation element 150, the PBG on the pad P side The starting end deviates from the state shown in FIG.
[0091]
At this time, the millimeter wave signal or the microwave signal output from the phase modulation element 150 generates a phase difference of 2π / 4 (= π / 2) as compared with the state of FIG.
[0092]
As shown in FIG. 7C, when the drive signals φ1 to φ2, φ4, and φ6 to φ8 are set to the high level and the drive signals φ3 and φ5 are set to the low level to drive the phase modulation element 150, the pad P side The starting end of the PBG deviates from the state shown in FIG.
[0093]
At this time, the millimeter wave signal or the microwave signal output from the phase modulation element 50 generates a phase difference of 4π / 4 (= π) as compared with the state of FIG.
[0094]
As shown in FIG. 8A, when the drive signals φ1 to φ3, φ5, and φ7 to φ8 are set to the high level and the drive signals φ4 and φ6 are set to the low level to drive the phase modulation element 150, the pad P side The starting end of the PBG deviates from the state shown in FIG.
[0095]
At this time, the millimeter wave signal or the microwave signal output from the phase modulation element 50 generates a phase difference of 6π / 4 (= 3π / 2) as compared with the state of FIG.
[0096]
As shown in FIG. 8B, when the drive signals φ1 to φ4, φ6, and φ8 are set to the high level and the drive signals φ5 and φ7 are set to the low level to drive the phase modulation element 150, the PBG on the pad P side Although the start end of FIG. 7A is shifted substantially four electrodes rearward from the state shown in FIG. 7A, the start end of PBG is electrically equivalent to the position shown in FIG. 7A.
[0097]
At this time, the millimeter wave signal or the microwave signal output from the phase modulation element 50 generates a phase difference of 2π as compared with the state of FIG. The signal is equivalent to the signal output under the state of FIG.
[0098]
As understood from FIGS. 7A to 7C and FIGS. 8A to 8B, the phase of the millimeter wave signal or the microwave signal output from the phase modulation element 150 is Each time the start end of the PBG on the pad P side is shifted to the rear of about one electrode, the PBG is delayed by about λ / 4 (π / 2). A four-phase millimeter wave signal or microwave signal can be generated by appropriately changing the start end of the PBG on the pad P side within a range of four continuous electrodes.
[0099]
The phase modulation element 150 capable of performing phase modulation in this way is more liquid crystal than a type of device that performs phase modulation by uniformly changing the arrangement of liquid crystal molecules around the transmission line along the transmission line. Dielectric loss due to the layer can be easily reduced.
[0100]
Next, a phase modulation element according to the third embodiment will be described.
[0101]
FIG. 9 schematically shows a cross-sectional structure of the phase modulation element according to the third embodiment. The phase modulation element 250 shown in the figure includes (i) a plurality of electrodes 13 disposed on the outer surface of the first substrate 10, and (ii) electrodes on the inner surface of the second substrate 20. Is different from the phase modulation element 50 according to the first embodiment in that a plurality of electrodes 23 are arranged on the outer surface without being arranged. Other configurations of the phase modulation element 250 are the same as those of the phase modulation element 50.
[0102]
Among the constituent elements shown in FIG. 9, constituent elements excluding the electrode 13 and the electrode 23 are given the same reference numerals as those used in FIG.
[0103]
In the illustrated phase modulation element 250, each of the electrodes 13 and each of the electrodes 23 is a millimeter wave signal supplied to the transmission line 11 or each of the electrodes 21 in the phase modulation element 50 according to the first embodiment. They are arranged at a predetermined pitch less than about 1/4 of the wavelength λ of the microwave signal. These electrodes 13 and 23 both cross the transmission line 11 in plan view. One electrode 23 corresponds to one electrode 13, and the electrode 13 and the electrode 23 corresponding to each other overlap in plan view.
[0104]
The phase modulation element 250 is driven in the same manner as the phase modulation element 50 according to the first embodiment described above. At this time, a drive signal of the same level is supplied to the pair of electrodes 13 and 23 corresponding to each other. No drive signal is supplied to the transmission line 11.
[0105]
By driving the phase modulation element 250 in this manner, the supplied millimeter wave signal or microwave signal can be phase-modulated and output in the same manner as the phase modulation element 50 according to the first embodiment. The dielectric loss due to the liquid crystal layer can be easily reduced as compared with a type of device that performs phase modulation by uniformly changing the alignment of liquid crystal molecules around the transmission line along the transmission line.
[0106]
Next, a phase modulation element according to the fourth embodiment will be described.
[0107]
FIG. 10 schematically shows a cross-sectional structure of the phase modulation element according to the fourth embodiment. The phase modulation element 350 shown in the figure is structurally different from the phase modulation element 50 according to the first embodiment in that a plurality of electrodes 13 are arranged on the outer surface of the first substrate 10. Other configurations of the phase modulation element 350 are the same as those of the phase modulation element 50.
[0108]
Among the constituent elements shown in FIG. 10, constituent elements excluding each electrode 13 are given the same reference numerals as those used in FIG.
[0109]
In the illustrated phase modulation element 350, each of the electrodes 13 and each of the electrodes 21 is arranged at a predetermined pitch that is less than ½ of the wavelength λ of the millimeter wave signal or microwave signal supplied to the transmission line 11. . These electrodes 13 and 21 both cross the transmission line 11 in plan view. One electrode 21 corresponds to one electrode 13, and the electrode 13 and the electrode 21 corresponding to each other overlap in plan view.
[0110]
The phase modulation element 350 is also driven by the same method as the phase modulation element 50 according to the first embodiment described above. At this time, a drive signal of the same level is supplied to the pair of electrodes 13 and 21 corresponding to each other. No drive signal is supplied to the transmission line 11.
[0111]
By driving the phase modulation element 350 in this manner, the supplied millimeter wave signal or microwave signal can be phase-modulated and output in the same manner as the phase modulation element 50 according to the first embodiment. The dielectric loss due to the liquid crystal layer can be easily reduced as compared with a type of device that performs phase modulation by uniformly changing the alignment of liquid crystal molecules around the transmission line along the transmission line.
[0112]
The phase modulation element and the phase modulation device according to the embodiments have been described above, but the present invention is not limited to these embodiments.
[0113]
For example, when generating a 2n phase millimeter wave signal or microwave signal by shifting the phase angle of the millimeter wave signal or microwave signal supplied to the transmission line 11 by a value different from π / n, the unit length It is also possible to arrange more than 4n electrodes 21 per length. A two-phase (n = 1) millimeter wave signal or microwave signal can also be generated by arranging three electrodes 21 per unit length.
[0114]
The alignment film can be omitted if, for example, the first and second substrates have an alignment function for liquid crystal molecules.
[0115]
The shape of the transmission line in the cell container when viewed in a plan view is not limited to a straight line shape, and may be a comb shape, for example. It is also possible to skew the transmission line and the electrode with each other in plan view.
[0116]
The position where the PBG is formed when generating the most advanced millimeter wave signal or microwave signal among the multiple phase millimeter wave signals or microwave signals generated using the phase modulation element is the input end of the transmission line. It is not limited to the area | region ranging from the back from the electrode nearest to.
[0117]
In forming the PBG in the transmission line, it is preferable to change the electrical length of the transmission line with a period of about the wavelength of the millimeter wave signal or microwave signal supplied to the transmission line. As long as the electrical length of the transmission line changes in the above cycle, the length in a plan view of a region having a relatively large electrical length formed in the range of one cycle and the plan view of a region having a relatively small electrical length. It is not always necessary to match the above length.
[0118]
Therefore, even when the dielectric constant of the liquid crystal layer is periodically changed, the length in a plan view of the region having a relatively high dielectric constant (the length along the transmission line) and the region having a relatively low dielectric constant It is not always necessary to match the length in plan view (the length along the transmission line).
[0119]
Furthermore, the change in the dielectric constant of the liquid crystal layer is in three values of high, medium and low as long as it has a periodicity less than the wavelength of the millimeter wave signal or microwave signal supplied to the transmission line. Alternatively, it may be over 4 values. Even in this case, the PBG can be formed in the transmission line.
[0120]
When it is desired to appropriately select the frequency of the millimeter wave signal or the microwave signal that can be handled by one phase modulation device from among a plurality of values, the electrodes in the phase modulation element are electrically independent from each other, It is preferable to electrically connect the phase modulation element and the drive circuit.
[0121]
As for the phase of the millimeter wave signal or microwave signal output from the phase modulation element, a PBG is formed from below a predetermined electrode second or more counted from the input end of the transmission line, and the formation position of this PBG is fixed. The control can also be performed by appropriately selecting the value of the voltage applied to the electrode on the input end side with respect to the PBG.
[0122]
It will be apparent to those skilled in the art that other various modifications, improvements, combinations, applications, and the like are possible.
[0123]
The phase modulation element and the phase modulation device having the above-described configuration can be easily reduced in size and have a small dielectric loss due to the liquid crystal layer, and thus can be suitably used particularly for portable communication devices. Of course, the present invention can be used not only for portable communication devices but also for various communication devices. It can also be used for a survey device such as an in-vehicle radar.
[0124]
Since the number of electrodes per unit length provided in the cell container can be increased relatively easily, phase modulators with various performances can be easily configured. It can also be used to modulate various data such as sound data and image data, and halftone control is relatively easy. In principle, the frequency band in which phase modulation is possible is wide.
[0125]
【The invention's effect】
As described above, the phase modulation element of the present invention can reduce dielectric loss due to the liquid crystal layer even though it is an element using liquid crystal. It becomes easy to provide a phase modulation element and a phase modulation device that are small and consume less power.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a planar shape of a phase modulation element according to a first embodiment.
2A is a schematic view showing a cross section taken along the line IIA-IIA shown in FIG. 1, and FIG. 2B is a cross section taken along the line IIB-IIB shown in FIG. It is the schematic which shows a cross section.
FIG. 3 is a schematic diagram illustrating a configuration of a phase modulation apparatus according to an embodiment.
4 (A) to 4 (C) respectively show the level of each drive signal supplied to the phase modulation element shown in FIG. 3 and the position of the photonic band gap formed in the transmission line. It is the schematic which shows the relationship.
5A to FIG. 5B respectively show the level of each drive signal supplied to the phase modulation element shown in FIG. 3 and the position of the photonic band gap formed in the transmission line. It is the schematic which shows the other relationship with.
FIG. 6 is a schematic view showing a planar shape of a phase modulation element according to a second embodiment.
7A to FIG. 7C respectively show the levels of drive signals supplied to the phase modulation element shown in FIG. 6 and the positions of photonic band gaps formed in the transmission line. It is the schematic which shows the relationship.
8A to FIG. 8B respectively show the level of each drive signal supplied to the phase modulation element shown in FIG. 6 and the position of the photonic band gap formed in the transmission line. It is the schematic which shows the other relationship with.
FIG. 9 is a schematic view showing a cross-sectional structure of a phase modulation element according to a third embodiment.
FIG. 10 is a schematic view showing a cross-sectional structure of a phase modulation element according to a fourth embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... 1st board | substrate, 11 ... Transmission line, 12 ... 1st alignment film, 13 ... Electrode provided in 1st board | substrate, 15 ... Sealing material, 20 ... 2nd board | substrate, 21, 23 ... 2nd Electrodes provided on the substrate, 22 ... second alignment film, 25 ... liquid crystal layer, 30 ... cell container, 50, 150, 50B, 50C ... phase modulation element, 60 ... drive circuit, 70 ... control circuit, 80 ... Voltage controlled oscillator, 85 ... circulator, 90 ... radiator, 100 ... phase modulator.

Claims (4)

A millimeter wave band or a microwave band transmission line is provided on one surface, and a millimeter wave signal or a microwave signal in the transmission line is provided on the other surface facing the one surface with respect to the extending direction of the transmission line. A first substrate having a plurality of first electrodes arranged at a pitch of approximately ¼ or less of the wavelength;
A plurality of second electrodes, which are arranged to face the first substrate and overlap the plurality of first electrodes in plan view, on another surface facing the surface facing the first substrate. A second substrate having;
A liquid crystal layer sandwiched between the first and second substrates and having a dielectric constant seen from the transmission line changed by applying a voltage to the first and second electrodes;
A control circuit for supplying a voltage to each of the plurality of first electrodes and the plurality of second electrodes,
The first electrode and the second electrode are arranged in a region in which the length along the transmission line in a plan view is approximately four times or more the wavelength of the millimeter wave signal or microwave signal ,
The control circuit generates a periodic electric field between the first and second electrodes to form a periodic dielectric constant distribution in the liquid crystal layer, thereby forming a forbidden band in the transmission line. Phase modulation that changes the formation position of the forbidden band by appropriately controlling the voltage applied to the first and second electrodes and performs phase modulation of the millimeter wave signal or the microwave signal supplied to the transmission line Equipment . further,
A first alignment film disposed on one surface of the first substrate and covering the transmission line;
The phase modulation device according to claim 1 , further comprising: a second alignment film disposed on another surface of the second substrate. A millimeter wave band or a microwave band transmission line is provided on one surface, and a millimeter wave signal or a microwave signal in the transmission line is provided on the other surface facing the one surface with respect to the extending direction of the transmission line. A first substrate having a plurality of first electrodes arranged at a pitch of approximately ¼ or less of the wavelength;
A second substrate that is disposed to face the first substrate and has a plurality of second electrodes that overlap the plurality of first electrodes in a plan view on a surface that faces the first substrate. When,
A liquid crystal layer sandwiched between the first and second substrates and having a dielectric constant seen from the transmission line changed by applying a voltage to the first and second electrodes;
A control circuit for supplying a voltage to each of the plurality of first electrodes and the plurality of second electrodes,
The first electrode and the second electrode are arranged in a region in which the length along the transmission line in a plan view is approximately four times or more the wavelength of the millimeter wave signal or microwave signal ,
The control circuit generates a periodic electric field between the first and second electrodes to form a periodic dielectric constant distribution in the liquid crystal layer, thereby forming a forbidden band in the transmission line. Phase modulation that changes the formation position of the forbidden band by appropriately controlling the voltage applied to the first and second electrodes and performs phase modulation of the millimeter wave signal or the microwave signal supplied to the transmission line Equipment . further,
A first alignment film disposed on one surface of the first substrate and covering the transmission line;
4. The phase modulation device according to claim 3 , further comprising: a second alignment film disposed on a surface of the second substrate and covering the plurality of second electrodes .

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