Liquid crystal phase shifter with improved performance by inverted microstrip line superposition and manufacturing method thereof

Abstract

The present invention discloses a liquid crystal phase shifter that improves the phase shift performance by superimposing inverted microstrip lines, comprising: a first dielectric layer, a second dielectric layer, a metal ground, a third dielectric layer, and a fourth dielectric layer. Inverted microstrip lines are respectively arranged on the lower surface of the first dielectric layer and the upper surface of the fourth dielectric layer. The two microstrip lines are connected through vias, and the vias pass through the second and third dielectric layers and are isolated from the metal ground. The two microstrip lines have different turning paths, and the overall length of the microstrip lines is extended within a limited area. The electric field formed between the surface where the microstrip lines are located and the metal ground causes the long axis direction of the liquid crystal molecules to deflect, realizing the function of phase shift. The present invention can achieve a large phase shift range with a small circuit board area, which is of great value for the miniaturization and high integration of radio frequency circuits; at the same time, the present invention has the advantages of simple structure, low power consumption, and low working voltage, and has a wide application prospect in the fields of wireless and satellite communications.

Description

Technical Field

[0001] The present invention relates to a method for expanding the performance of a nematic liquid crystal-based phase shifter, belonging to the technical field of microwave engineering. Background Art

[0002] As a uniaxial crystal, the average axial direction of liquid crystal molecules is represented by a director vector, and the direction of the director vector is along the long axis of the rod-shaped molecules, and is also controlled by an external electric field or magnetic field. Liquid crystal materials have tunable characteristics, that is, different bias voltages can be applied to control the direction of liquid crystal molecules, thereby controlling the dielectric constant of the liquid crystal to achieve the phase shift function of the phase shifter device. Compared with traditional phase shifter technologies, liquid crystal phase shifters have the advantages of high phase shift degree, low operating voltage, low high-frequency loss, low DC power consumption, and miniaturization. As the operating frequency band of phased array antennas develops towards microwave and even higher frequency bands, existing traditional phase shifters are difficult to meet the requirements of large-scale array antennas and high integration of payload platforms. Summary of the Invention

[0003] Object of the Invention: Aiming at the deficiencies of the above-mentioned prior art, the present invention provides a device and method for expanding the performance of a liquid crystal phase shifter by superimposing inverted microstrip lines, which can effectively reduce the size of the phase shifter while significantly expanding the phase shift range of the phase shifter with a limited circuit board area, making up for the defects of the traditional phase shifter structure.

[0004] Technical Solution: A liquid crystal phase shifter for expanding performance by superimposing inverted microstrip lines includes four dielectric plates. Two inverted microstrip lines are respectively located on the lower surface of the first dielectric plate and the upper surface of the fourth dielectric plate, and they are connected by via Via 3, and via Via 3 passes through the second dielectric plate and the third dielectric plate; the inverted microstrip line 1 (IMSL 1) and the inverted microstrip line 2 (IMSL 2) have a "paperclip"-shaped turning path, and the two turning paths have different detour curves to achieve the extension of the microstrip line length, so as to achieve the maximum phase shift range. The second dielectric plate is hollowed out in the center to form a rectangular structure, and liquid crystal is injected into the rectangular cavity to modulate IMSL 1. The third dielectric plate is also hollowed out in the center to form a rectangular structure, and liquid crystal is injected into the rectangular cavity to modulate IMSL 2; there is a metal ground between the second dielectric plate and the third dielectric plate, and the same voltage is applied between the two inverted microstrip lines and the metal ground through vias Via 1 and Via 2 respectively, so that the long axis direction of the liquid crystal molecules deflects to achieve the phase shift function.

[0005] Furthermore, PI is coated on the lower surface of the first layer board, the upper and lower surfaces of the metal ground, and the upper surface of the fourth layer board, and the thickness of the PI layer coating is about 50 - 100 nm.

[0006] Further, after the layer to be coated is cooled, it is repeatedly rubbed with flannel along the short direction of the inverted microstrip line.

[0007] Further, the five plates are bonded together in sequence.

[0008] Further, a liquid crystal material with a measured dielectric constant is loaded into the cavity.

[0009] Further, a network analyzer is used to measure the insertion loss S of the phase shifter corresponding to the X band under the conditions of a bias voltage of 0 V and a saturation voltage 21 curve to obtain the final phase shift range.

[0010] The manufacturing method of the above liquid crystal phase shifter includes the following steps:

[0011] Step 1: Determine the initial total length of the inverted microstrip line according to the frequency points to be measured and the achieved phase shift range.

[0012] Step 2: Design the structures of two inverted microstrip lines and set the size of the via Via3 for connecting different layers of inverted microstrip lines.

[0013] Step 3: Design the structural dimensions of the coplanar waveguide for feeding.

[0014] Step 4: Set the initial sizes of the vias Via 1 and Via 2 on the first dielectric plate.

[0015] Step 5: Optimize the sizes of Via 1, Via 2, and Via 3, and finely adjust the length and width of the inverted microstrip line.

[0016] Step 6: Inject a liquid crystal material into the rectangular cavity.

[0017] Step 7: In the full-wave simulation software, set the dielectric constants of the liquid crystal in the initial state and the fully fed state, set the dielectric constants of each dielectric plate, and set the loss tangent value of the liquid crystal layer; observe the insertion loss S in the simulation results 21 curve, so that the phase shift range can be obtained at the frequency points to be measured.

[0018] Preferably, the specific steps of the manufacturing method include:

[0019] Step 1: Determine the initial total length of the microstrip line according to the frequency points to be measured and the phase shift range to be achieved.

[0020] Step 2: According to the total length of the microstrip line obtained in Step 1, on the phase shifter structure with a size of 6 mm × 6 mm, determine that the length of the inverted microstrip line on the first dielectric layer is 10.88 mm, and the length of the microstrip line on the fourth dielectric layer is 15.75 mm. When further reducing the size of the phase shifter to 4 mm × 6 mm, it can be determined that the length of the inverted microstrip line on the first dielectric layer is 20.30 mm, and the length of the microstrip line on the fourth dielectric layer is 14.10 mm;

[0021] Step 3: According to the measurement requirements, such as a 50-ohm port, determine the physical dimensions of the coplanar waveguide;

[0022] Step 4: Set the initial sizes of via Via 1 on the first dielectric layer, via Via 2 on the fourth dielectric layer, and metallized via Via 3;

[0023] Step 5: Optimize the sizes of Via 1, Via 2, and Via 3 in Step 4, and fine-tune the length and bandwidth of the inverted microstrip line by the full-wave simulation method. The fine-tuning criterion is to expand the phase shift range of the entire phase shifter structure as much as possible and ensure that the return loss is below -10 dB;

[0024] Step 6: Manufacture and assemble the entire device according to the above design;

[0025] Step 7: Inject liquid crystal into the cavity;

[0026] Step 8: Measure the transmission coefficients of the device when the external bias voltages are 0 V and V max respectively, and obtain the phase shift amounts in the two states. V max is the saturation voltage at which the liquid crystal molecules no longer deflect;

[0027] Step 9: In the measured transmission coefficient curve graph, read the phase shift amounts in the two states according to the required frequency points, and calculate the final phase shift range.

[0028] Preferably, through the design and packaging of more layers of substrates, the number of stacked inverted microstrip lines can be greater than 2.

[0029] Beneficial effects: The present invention can achieve a large phase shift range with a small circuit board area, which has important value for the miniaturization and high integration of radio frequency circuits; this liquid crystal phase shifter has advantages such as low loss, low operating voltage, and simple structure, and has a wide application prospect in the fields of satellite communication and phased array antennas. Description of the Drawings

[0030] Figure 1(a) is a top view of the first dielectric layer, Figure 1(b) is a global perspective view of the five-layer board structure of the liquid crystal phase shifter, Figure 1(c) is a schematic diagram of the upper surface of the fourth dielectric layer, and Figure 1(d) is a schematic diagram of the lower surface of the fourth dielectric layer.

[0031] Figure 2 It is a schematic cross-sectional view of a coplanar waveguide structure.

[0032] Figure 3 It is a design schematic diagram of a microstrip line structure on a single-layer board.

[0033] Figure 4 It is a simulation result diagram of the adjustable phase shift range achieved by designing a microstrip line structure on a single-layer board.

[0034] Figure 5 It is a return loss curve diagram of the designed 6mm×6mm phase shifter structure in the X band.

[0035] Figure 6 It is a simulation result diagram of the adjustable phase shift range achieved by the designed 6mm×6mm phase shifter structure.

[0036] Figure 7 It is a return loss curve diagram of the designed 4mm×6mm phase shifter structure in the X band.

[0037] Figure 8 It is a simulation result diagram of the adjustable phase shift range achieved by the designed 4mm×6mm phase shifter structure. Detailed implementation mode

[0038] The present invention will be further described below in conjunction with specific embodiments. Specific embodiment 1:

[0040] According to Figures 1(a) to 8 as shown, the present invention provides a liquid crystal phase shifter whose performance is extended by stacking inverted microstrip lines and a manufacturing method thereof. Figures 1(a) - 1(d) It shows a schematic diagram of the overall structure of a phase shifter based on liquid crystal material. The phase shifter is characterized by including a liquid crystal injection port ①, a metallized via Via 1 ②, a coplanar waveguide for feeding ③, an inverted microstrip line ④, a via Via 3 ⑤ for connecting microstrip lines on two dielectric plates, a first-layer dielectric plate ⑥, liquid crystal ⑦, a second-layer dielectric plate ⑧, a metal ground ⑨, a third-layer dielectric plate ⑩, a fourth-layer dielectric plate and a metallized via Via2

[0041] A method for extending the performance of a liquid crystal phase shifter by stacking inverted microstrip lines includes the following steps:

[0042] Step 1: Calculate the initial length of the inverted microstrip line using the frequency points to be measured and the phase shift range to be achieved. The total length l of the microstrip line can be expressed as:

[0043]

[0044]

[0045]

[0046]

[0047]

[0048] Among them, c0 is the speed of light, l is the total length of the inverted microstrip line, and ΔΦ max is the maximum differential phase shift range, f is the frequency corresponding to the phase shift range to be measured, and ε LC1 is the effective dielectric constant of the liquid crystal when no voltage is applied, and ε LC2 is the effective dielectric constant of the liquid crystal when the voltage reaches saturation. w is the width of the inverted microstrip line, a is the thickness of the first or fourth dielectric layer, b is the thickness of the second or third dielectric layer (liquid crystal layer), and ε r is the relative dielectric constant of the first or fourth dielectric layer, and ε r⊥ represents the dielectric constant of the liquid crystal when the long axis direction of the liquid crystal is perpendicular to the electric field direction, and ε r / / represents the dielectric constant of the liquid crystal when the long axis direction of the liquid crystal is parallel to the electric field direction.

[0049] Step 2: Design the structural dimensions of the coplanar waveguide based on the selected dielectric substrate

[0050]

[0051]

[0052]

[0053]

[0054]

[0055] Among them, wt is the width of the middle conductor of the coplanar waveguide, wg is the width of the ground wires on both sides of the coplanar waveguide, g is the distance between the middle conductor and the ground wires of the coplanar waveguide, and ε r is the relative dielectric constant of the substrate material, and k, k', and ε re are intermediate variables, and Z is the characteristic impedance of the waveguide transmission line.

[0056] Step 3: The initial size of the vias for connecting microstrip lines of different layers

[0057] r via = 0.375w (11)

[0058] Among them, r via is the radius of Via 3, and w is the width of the inverted microstrip line.

[0059] Step 4: Optimize the following parameters in the full-wave simulation software: the total length l of the inverted microstrip line, the width w of the inverted microstrip line, and the radii of vias Via 1, Via 2, and Via 3.

[0060] Step 5: Fabricate the phase shifter device based on the nematic liquid crystal material according to the above design parameters and the selected substrate material. First, spin coat, fix, and rub on the lower surface of the first layer board, the upper and lower surfaces of the metal ground, and the upper surface of the fourth layer board, and then bond the five-layer board in sequence. Finally, inject liquid crystal into the two cavities formed by the second dielectric board, the metal ground, and the third dielectric board respectively through the reserved small holes.

[0061] Step 6: Inject liquid crystal into the cavity through the reserved holes to ensure that the entire cavity is filled.

[0062] Step 7: Use a network analyzer to measure the insertion loss S 21 curve of the phase shifter at the bias voltage of 0 V and the saturation voltage condition in the X band to obtain the final phase shift range. Specific Embodiment 2:

[0064] As an example, the present invention expands the performance of the liquid crystal phase shifter by superimposing inverted microstrip lines and enables the phase shifter to operate in the X band. The specific structural parameters of the liquid crystal phase shifter are as follows: the width of the inverted microstrip line is w = 0.4 mm, the radii of vias Via 1, Via 2, and Via 3 are all 0.15 mm, and the thicknesses of the first dielectric board, the second dielectric board, the third dielectric board, and the fourth dielectric board are all 0.127 mm. The materials of the first dielectric board and the fourth dielectric board are Roger3003, the materials of the second dielectric board and the third dielectric board are RT / duroid 5880, and the dielectric constants of the liquid crystal material are: ε LC1 = 2.24, ε LC2 = 2.96. Based on the above structural parameters and material characteristics, the simulation results of the liquid crystal phase shifter are as Figures 5 - 8 shown. When the size of the phase shifter is 6 mm × 6 mm, the simulation results of the transmission coefficient of the phase shifter are as Figure 6 shown. At this time, the phase shift range of the phase shifter can reach about 305° at 10 GHz; for the microstrip line structure designed on a single board (such as Figure 3 ), when the size of the phase shifter remains unchanged, its phase shift range can only reach about 25° (such as Figure 4 ). To better meet the process requirements of chip production and manufacturing, we further change the size of the phase shifter to 4 mm × 6 mm, and its simulation results of the transmission coefficient are as Figure 8 shown. It can be seen that at 10 GHz, the phase shift range of the phase shifter reaches about 298°.

[0065] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A liquid crystal phase shifter that achieves performance expansion through the superposition of inverted microstrip lines, characterized in that From top to bottom, it includes: the first-layer dielectric plate, the second-layer dielectric plate, the metal ground, the third-layer dielectric plate, and the fourth-layer dielectric plate; inverted microstrip lines are respectively arranged on the lower surface of the first-layer dielectric plate and the upper surface of the fourth-layer dielectric plate, and the two inverted microstrip lines are connected by a metallized via Via 3. The via Via 3 passes through the second-layer dielectric plate and the third-layer dielectric plate and is isolated from the metal ground; the two inverted microstrip lines have different turning paths; the second-layer dielectric plate and the third-layer dielectric plate are respectively hollowed out in the center to form a rectangular cavity, and a nematic liquid crystal is injected into the rectangular cavity after the whole device is encapsulated to respectively realize the modulation of the upper and lower inverted microstrip lines; a bias voltage is applied between any one of the inverted microstrip lines and the metal ground, and by changing the voltage, the long-axis axial direction of the liquid crystal molecules is deflected to realize the adjustment of the phase of the transmitted signal.

2. The liquid crystal phase shifter according to claim 1, wherein The turning path is in the shape of a "paper clip".

3. The liquid crystal phase shifter according to claim 1, wherein Coplanar waveguides are respectively placed on the opposite sides of the inverted microstrip lines on the first-layer dielectric plate and the fourth-layer dielectric plate, and the two coplanar waveguides share a ground.

4. The liquid crystal phase shifter according to claim 1, characterized in that One ends of two inverted microstrip lines IMSL1 and IMSL2 are respectively provided with vias Via 1 and Via 2, and the coplanar waveguide is indirectly connected to the inverted microstrip line through the vias Via 1 and Via 2, and the other ends of the two inverted microstrip lines are connected by a metal via Via 3.

5. A manufacturing method of a liquid crystal phase shifter as described in claim 4, characterized in that, It includes the following steps: Step 1: Determine the initial total length of the inverted microstrip line according to the frequency points to be measured and the achieved phase shift range. Step 2: Design the structures of the two inverted microstrip lines and set the size of the via Via 3 for connecting the inverted microstrip lines of different layers. Step 3: Design the structural dimensions of the coplanar waveguide for feeding. Step 4: Set the initial sizes of the vias Via 1 and Via 2 on the first dielectric plate. Step 5: Optimize the sizes of Via 1, Via 2, and Via 3, and finely adjust the length and width of the inverted microstrip line. Step 6: Inject a liquid crystal material into the rectangular cavity. Step 7: In the full-wave simulation software, set the dielectric constants of the liquid crystal in the initial state and the fully-fed state, set the dielectric constants of each dielectric plate, and set the loss tangent value of the liquid crystal layer; observe the insertion loss S 21 curve in the simulation results, so that the phase shift range can be obtained at the frequency points to be measured.

6. The manufacturing method according to claim 5, characterized in that, The initial value of the total length of the inverted microstrip line in Step 1 is obtained through the following expression: where c0 is the speed of light, l is the total length of the inverted microstrip line, and ΔΦ max is the maximum differential phase shift range, f is the frequency corresponding to the phase shift range to be measured, and ε LC1 is the effective dielectric constant of the liquid crystal without voltage applied, and ε LC2 is the effective dielectric constant of the liquid crystal when the voltage reaches saturation, w is the width of the inverted microstrip line, a is the thickness of the first dielectric layer or the fourth dielectric layer, b is the thickness of the second dielectric layer or the third dielectric layer, and ε r is the relative dielectric constant of the first dielectric layer or the fourth dielectric layer, and ε r⊥ represents the dielectric constant of the liquid crystal when the long axis direction of the liquid crystal is perpendicular to the electric field direction, and ε r / / represents the dielectric constant of the liquid crystal when the long axis direction of the liquid crystal is parallel to the electric field direction.

7. The manufacturing method according to claim 5, characterized in that, The structural dimensions of the coplanar waveguide in Step 3 are obtained through the following expression: Among them, wt is the width of the middle conductor of the coplanar waveguide, wg is the width of the ground wires on both sides of the coplanar waveguide, g is the distance between the middle conductor of the coplanar waveguide and the ground wire, and ε r is the relative permittivity of the substrate material, k, k', and ε re are intermediate variables, Z is the characteristic impedance of the waveguide transmission line, and K and K' represent the intermediate transformation equations.

8. The manufacturing method according to claim 5, characterized in that, The initial size of the via Via 3 for connecting the microstrip lines of different layers in Step 3 is: r via ＝0.375 w (11) where r via is the radius of Via 3, and w is the width of the inverted microstrip line.

9. The manufacturing method according to claim 5, characterized in that, In Step 5, the length and width of the inverted microstrip line are finely adjusted by the full-wave simulation method. The fine-tuning standard is to make the phase shift range of the whole phase shifter reach nearly 300 degrees in the X band and ensure that the return loss of the signal is below -10 dB.

10. The manufacturing method of the liquid crystal phase shifter according to claim 5, wherein Through the design and encapsulation of more layers of substrates, the number of stacked inverted microstrip lines can be greater than 2.

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