A liquid crystal phase shifter for phased array antennas

Abstract

This invention discloses a liquid crystal phase shifter for phased array antennas, belonging to the field of microwave device engineering technology. This invention solves the problems of high loss, low figure of merit, and long physical length in existing liquid crystal phase shifters. This invention combines a metal nanowire thin film with a patterned metal structure having an aperiodic metal patch array structure. The metal nanowire thin film provides additional series distributed inductance to the liquid crystal phase shifter, enabling it to achieve a larger phase shift with minimal increase in loss, thus improving the figure of merit. By incorporating the parallel distributed capacitance introduced by the aperiodic metal patch structure, the impedance mismatch and increased insertion loss caused by the series distributed inductance introduced by the metal nanowire thin film are offset, achieving enhanced signal transmission, reduced insertion loss, and a higher figure of merit.

Description

Technical Field

[0001] This invention relates to a liquid crystal phase shifter for phased array antennas, belonging to the field of microwave device engineering technology. Background Technology

[0002] Phase shifters, as key components of phased arrays, are used to control the phase of radio frequency signals and play a crucial role in phased array systems. Current mainstream phase shifters can be categorized into PIN diode phase shifters, semiconductor phase shifters, and liquid crystal phase shifters. Among these, PIN diode phase shifters can only operate at lower frequencies and cannot achieve continuous phase control, greatly limiting their applicability. While semiconductor phase shifters perform well in high-frequency bands and even millimeter-wave applications, their high cost and significant losses hinder their widespread adoption.

[0003] As an anisotropic material, liquid crystal molecules have a definite orientation along their long axes. Under the excitation of an external electric or magnetic field, the long axis of the liquid crystal molecules deflects, thus changing the dielectric constant of the liquid crystal material. Compared with other types of phase shifters, liquid crystal phase shifters offer advantages such as continuous tuning capability, high linearity, small size, and light weight. However, because the response time of a liquid crystal phase shifter is proportional to the square of the liquid crystal layer thickness (often referred to as the cell thickness), and the insertion loss (hereinafter referred to as loss) increases rapidly as the liquid crystal layer thickness decreases, liquid crystal phase shifters often struggle to simultaneously possess both a high figure of merit (FoM, defined as the ratio of phase shift to insertion loss, i.e., phase shift per unit loss) and fast response characteristics. Furthermore, existing liquid crystal phase shifters also suffer from a relatively long physical length. Summary of the Invention

[0004] This invention addresses the problems of high loss, low figure of merit, and long physical length of existing liquid crystal phase shifters by providing a liquid crystal phase shifter for phased array antennas.

[0005] The technical solution of the present invention:

[0006] One of the objectives of this invention is to provide a liquid crystal phase shifter for a phased array antenna. Specifically, the liquid crystal phase shifter comprises, from top to bottom, an upper dielectric substrate 1, a patterned metal structure 2, a liquid crystal layer 3, a metal nanowire thin film layer 4, a metal substrate 5, and a lower dielectric substrate 6.

[0007] The upper dielectric substrate 1 and the lower dielectric substrate 6 are flat plate structures made of insulating material. The liquid crystal layer 3 is located between the upper dielectric substrate 1 and the lower dielectric substrate 6. The patterned metal structure 2 is located on the lower surface of the upper dielectric substrate 1. The metal base plate 5 is located on the upper surface of the lower dielectric substrate 6, and the upper surface of the metal base plate 5 is a metal nanowire thin film layer 4.

[0008] The outer contour of the patterned metal structure 2 is spindle-shaped with narrow sides and a wide middle, and is composed of a central metal strip and metal patches that are symmetrically and periodically distributed on both sides of the central metal strip;

[0009] The metal nanowire thin film layer 4 is composed of a porous alumina thin film and metal nanowires grown in the cavities of the porous alumina thin film.

[0010] Further限定, the thickness of the upper dielectric plate 1 is h1, 0.01λ g , g , g ,

[0015] , g ,

[0014] , g , g , g , g , g , , <h1 < 0.2λ g ; the thickness of the lower dielectric plate 6 is h2, 0.01λ g <h2 < 0.2λ g ; where λ g is the dielectric wavelength corresponding to the working center frequency.

[0011] Even further限定, the insulating materials of the upper dielectric plate 1 and the lower dielectric plate 6 can be ordinary circuit board substrates or other dielectric materials with a certain hardness such as glass, silicon dioxide, and ceramics.

[0012] Even further限定, the dielectric constants of the upper dielectric plate 1 and the lower dielectric plate 6 are 5.1, and the tangent of the loss angle is 0.01.

[0013] Further限定, the patterned metal structure 2 is a metal thin film with a thickness of t1, which is fabricated on the lower surface of the upper dielectric plate 1 by printing or etching, where 0.0001λ g <t1 < 0.003λ g , λ g is the dielectric wavelength corresponding to the working center frequency.

[0014] Further限定, the central metal strip forming the patterned metal structure 2 is a rectangle with a width of w0 and a length the same as that of the upper dielectric plate 1, and the metal patches are rectangles, arrow shapes, or bent shapes. Where 0.001λ g <w0 < 0.2λ g , λ g is the dielectric wavelength corresponding to the working center frequency.

[0015] Further限定, the metal patch is a rectangle with a length of w1, the distance between adjacent metal patches is s, the width of the metal patch decreases sequentially from the middle of the central metal strip to both ends, and the decreasing rule is linear or exponential with position. The width of the metal patch located in the middle of the central metal strip is l1, where 0.001λ g <w1 < 0.2λ g , 0.001λ g <s < 0.15λ g , 0.001λ g<l1<0.3λ g , λ g The wavelength of the medium corresponding to the operating center frequency.

[0016] Furthermore, the metal patches located on the central metal strip have the same width l1.

[0017] Further specified, the thickness of liquid crystal layer 3 is h4, 0.0001λ. g <h4<0.05λ g , λ g The wavelength of the medium corresponding to the operating center frequency.

[0018] Furthermore, the electrical parameters of the liquid crystal material in liquid crystal layer 3 are: ε r，⊥ =2.39, ε r， / / =3.27, tanδ ⊥ =0.007, tanδ / / =0.0022.

[0019] To further define it, the length direction of the upper dielectric substrate 1 is the x-axis direction, the width direction is the y-axis direction, and the height direction is the z-axis direction.

[0020] Furthermore, the surface of the liquid crystal layer 3 has a liquid crystal alignment layer, ensuring that when there is no driving voltage, the long axis of the liquid crystal molecules in the liquid crystal layer 3 points horizontally and is perpendicular to the z-axis.

[0021] To further specify, the fabrication process of liquid crystal layer 3 is as follows:

[0022] Microspheres, gaskets, or dielectric columns are arranged between the upper dielectric substrate 1 and the lower dielectric substrate 6 to maintain a gap of height h4 between the upper dielectric substrate 1 and the lower dielectric substrate 6. Then, liquid crystal material is injected or sprayed into the gap to form a liquid crystal layer.

[0023] Further specifying, the metal substrate 5 has a metal film with a thickness of t2, which is fabricated on the upper surface of the lower dielectric substrate 6 by printing or etching, wherein 0.0001λ g <t2<0.003λ g , λ g The wavelength of the medium corresponding to the operating center frequency.

[0024] Further specifying, the thickness of the metal nanowire thin film layer 4 is h3, 0.002λ. g <h3<0.03λ g , λ g The wavelength of the medium corresponding to the operating center frequency.

[0025] Further specifying, the pore diameter of the porous alumina film used to prepare the metal nanowire thin film layer 4 is d, and the distance between the centers of adjacent pores is p.

[0026] Further specifying, the metal nanowire thin film layer 4 is prepared by sputtering a thin copper film as a seed layer on the back of a porous alumina film, growing metal nanowires in the pores by electrodeposition until the metal nanowires grow to the top of the porous alumina film, polishing to the required thickness, and obtaining the metal nanowire thin film layer 4.

[0027] Beneficial effects:

[0028] (1) This invention combines a metal nanowire thin film with a patterned metal structure having an aperiodic metal patch array structure. The metal nanowire thin film provides an additional series distributed inductance for the liquid crystal phase shifter, thereby enabling the liquid crystal phase shifter to have a larger phase shift without a significant increase in loss, thus improving the figure of merit (FoM) of the liquid crystal phase shifter. Furthermore, by combining the parallel distributed capacitance introduced by the aperiodic metal patch structure, the impedance mismatch of the liquid crystal phase shifter caused by the series distributed inductance introduced by the metal nanowire thin film is offset, as well as the resulting greater insertion loss, which limits the improvement of the figure of merit of the liquid crystal phase shifter. Ultimately, the purpose of enhancing signal transmission and reducing the insertion loss of the liquid crystal phase shifter is achieved, resulting in a higher figure of merit (FoM).

[0029] (2) The present invention utilizes a non-periodic metal patch array structure with a central metal strip loaded with metal patch structure and a metal nanowire thin film to further increase the equivalent phase shift constant of the liquid crystal phase shifter, so that the phase shift per wavelength of the liquid crystal phase shifter is large. When a fixed phase shift is achieved, the length is shorter, which is beneficial to system integration and achieves the purpose of miniaturization.

[0030] (3) Compared with existing liquid crystal phase shifters, the liquid crystal phase shifter structure provided by the present invention also has the significant advantages of simple design and high efficiency. Attached Figure Description

[0031] Figure 1 This is a three-dimensional structural schematic diagram of the liquid crystal phase shifter provided by the present invention;

[0032] Figure 2 This is a side view of the liquid crystal phase shifter provided by the present invention;

[0033] Figure 3 This is a schematic diagram of the patterned metal structure.

[0034] Figure 4 The liquid crystal phase shifter S in Example 1 11 Amplitude simulation results;

[0035] Figure 5 The liquid crystal phase shifter S in Example 1 21 Amplitude simulation results;

[0036] Figure 6 The simulation results show the quality factor and phase shift per wavelength of the liquid crystal phase shifter in Example 1.

[0037] In the figure, 1-upper dielectric substrate, 2-patterned metal structure, 2-1-central metal strip, 2-2-metal patch, 3-liquid crystal layer, 4-metal nanowire thin film, 5-metal substrate, and 6-lower dielectric substrate. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. The materials, reagents, methods, and instruments used, unless otherwise specified, are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0040] Example 1:

[0041] This embodiment provides an adjustable liquid crystal phase shifter that operates in the 20-30GHz frequency band.

[0042] like Figures 1-3 As shown, the liquid crystal phase shifter, from top to bottom along the z-axis, includes an upper dielectric substrate 1, a patterned metal structure 2, a liquid crystal layer 3, a metal nanowire thin film layer 4, a metal substrate 5, and a lower dielectric substrate 6. The upper dielectric substrate 1 and the lower dielectric substrate 6 are flat structures made of insulating material. The liquid crystal layer 3 is located between the upper dielectric substrate 1 and the lower dielectric substrate 6. The patterned metal structure 2 is located on the lower surface of the upper dielectric substrate 1, and the metal substrate 5 is located on the upper surface of the lower dielectric substrate 6, with the metal nanowire thin film layer 4 forming the upper surface of the metal substrate 5. The thickness of the upper dielectric substrate 1 is h1, the thickness of the lower dielectric substrate 6 is h2, the thickness of the patterned metal structure 2 is t1, the thickness of the liquid crystal layer 3 is h4, and the thickness of the metal substrate 5 is t2. The dielectric constant of the upper dielectric substrate 1 and the lower dielectric substrate 6 is 5.1, and the loss tangent is 0.01. The electrical parameters of the liquid crystal material in the liquid crystal layer 3 are ε. r，⊥ =2.39, ε r， / / =3.27, tanδ ⊥ =0.007, tanδ / / =0.0022.

[0043] The outer contour of the patterned metal structure 2 is spindle-shaped, narrow on both sides and wide in the middle, and is composed of a central metal strip 2-1 and metal patches 2-2 that are symmetrically and periodically distributed on both sides of the central metal strip 2-1.

[0044] The central metal strip 2-1 is a rectangle with a width of w0 and a length the same as the upper dielectric substrate 1. Metal patches 2-2 are rectangles with a length of w1. The distance between adjacent metal patches is s. The width of metal patches 2-2 decreases sequentially from the middle of the central metal strip 2-1 towards both ends. Figure 3 As shown, there are 12 metal patches 2-2 located in the middle of the central metal strip 2-1, each with a width of l1. From the middle of the central metal strip 2-1, four metal patches of gradually varying lengths extend to both sides. Their purpose is to reduce the reflection of electromagnetic signals by the liquid crystal phase shifter, and their widths are l1, l2, and l3, and l4, and l5, and l6, and l7, and l8, and l9, and l1 ... 01 , l 02 , l 03 and l 04 .

[0045] The liquid crystal layer 3 is formed by arranging microspheres, spacers, or dielectric pillars between the upper dielectric layer 1 and the lower dielectric layer 6 to maintain a gap of height h4 between the upper dielectric layer and the metal nanowire thin film layer. Liquid crystal material is poured or sprayed into the gap between the upper dielectric layer and the metal nanowire thin film layer to form the liquid crystal layer. In actual processing, a liquid crystal alignment layer is made on the surfaces of the patterned metal structure layer and the metal nanowire thin film layer that are in contact with the liquid crystal to ensure that the long axis of the liquid crystal molecules is perpendicular to the z-axis when there is no driving voltage (the length direction of the upper dielectric layer 1 is taken as the x-axis direction, the width direction as the y-axis direction, and the height direction as the z-axis direction).

[0046] The thickness of the metal nanowire thin film layer 4 is h3. The preparation process of the metal nanowire thin film 4 is as follows: a porous alumina film is sputter-coated with gold on one side, copper wires are led out and encapsulated as the working electrode, and copper nanowires are grown into the pores of the porous alumina film using a CHI660 electrochemical workstation with a copper sheet as the counter electrode in a copper sulfate solution via potentiostatic deposition, obtaining the desired metal nanowire thin film layer. The deposition potential is -0.4V, and the time is 30min. The concentration of copper sulfate is 0.6mol / L, and its pH is adjusted to 2 with sulfuric acid. Magnetic stirring is used during the preparation process. After deposition, the film is polished to the required thickness h3 and finally bonded to the metal substrate 5. The porous alumina film has a thickness of h5, a dielectric constant of 6.7, a loss tangent of 0.03, a pore size of d, and a center-to-center distance between adjacent pores of p.

[0047] The working principle of the adjustable liquid crystal phase shifter based on the above structure is as follows:

[0048] When electromagnetic waves propagate between the patterned metal structure 2 and the metal substrate 5, the patterned metal structure 2 and the metal substrate 5 (as well as the metal nanowire thin film layer 4) act as both boundary conductors for electromagnetic signal transmission and driving electrodes for the liquid crystal material. When a driving voltage is applied between the patterned metal structure 2 and the metal substrate 5, the metal nanowires in the metal nanowire thin film layer 4 are conductive, and the voltage applied to the metal substrate 5 is equivalent to that applied to the upper surface of the metal nanowire thin film layer 4. Therefore, the orientation of the liquid crystal molecules located between the patterned metal structure 2 and the metal nanowire thin film layer 4 will be deflected, and the deflection angle of the liquid crystal molecules can change continuously with the change of the driving voltage value, thereby causing a continuous change in the dielectric constant of the liquid crystal material in the liquid crystal layer 3. This change causes a continuous change in the capacitance formed by the patterned metal structure 2 and its opposite intermediate metal layer, which has a continuous disturbance effect on the propagation of electromagnetic waves. This continuous disturbance causes a change in the phase of the electromagnetic wave transmitted between the upper and lower layers. As the applied driving voltage value changes continuously, the phase of the transmitted electromagnetic wave also changes continuously. When the liquid crystal molecules reach full bias, the phase change reaches its maximum value, ultimately realizing a continuously adjustable liquid crystal phase shifter.

[0049] The role of the metal nanowire thin film 4 is to provide additional series distributed inductance for the liquid crystal phase shifter, thereby enabling the liquid crystal phase shifter to have a larger phase shift without a significant increase in loss, ultimately improving the figure of merit (FoM) of the liquid crystal phase shifter. However, unilaterally increasing the series distributed inductance of the liquid crystal phase shifter will lead to impedance mismatch, resulting in greater insertion loss. Therefore, the metal nanowire thin film 4 alone has a limited effect on improving the figure of merit of the liquid crystal phase shifter. To further improve the figure of merit of the liquid crystal phase shifter, this invention combines the patterned metal structure 2 with the metal nanowire thin film 4. The patterned metal structure 2 introduces additional parallel distributed capacitance to the liquid crystal phase shifter, thereby increasing the parallel distributed capacitance of the liquid crystal phase shifter. According to the characteristic impedance formula of microwave transmission lines:

[0050]

[0051] Where Z0 is the characteristic impedance of the transmission line, and L and C are the series distributed inductance and distributed capacitance per unit length of the transmission line, respectively.

[0052] Therefore, the parallel distributed capacitance introduced by the patterned metal structure 2 cancels out the impedance mismatch of the liquid crystal phase shifter caused by the metal nanowire film, thereby enhancing signal transmission and reducing the insertion loss of the liquid crystal phase shifter. Simultaneously, the introduction of the metal patch 2-2 further increases the equivalent phase shift constant of the liquid crystal phase shifter based on the metal nanowire film 4, meaning that the length of the liquid crystal phase shifter can be further reduced, thus achieving miniaturization. Of course, folding or bending the linear liquid crystal phase shifter can further reduce its size based on this invention, which is a common technique in the art.

[0053] The structural parameters of the above liquid crystal phase shifter are set as follows:

[0054] h1=0.5mm, h2=0.5mm, h3=50um, h4=6um, t1=2um, t2=2um, w0=0.083mm, w1=0.45mm,

[0055] w2=1.5mm,l1=0.383mm,l2=10.05mm,l 01 =0.123mm, l 02 =0.163mm, l 03 =0.243mm,

[0056] l 04 =0.323mm, s=0.05mm, d=50nm, p=100nm.

[0057] Based on the above structural parameters and material properties, the simulation results of this liquid crystal phase shifter are as follows: Figure 4-6 As shown in the figure, for both liquid crystal molecule alignment and bias states, within the operating frequency band of 20-30 GHz, S 11 All impedance values ​​are less than -10dB, achieving good impedance matching. Furthermore, the insertion loss is less than 4dB over the operating frequency band, the quality factor (FoM) is greater than 120° / dB, and the phase shift per wavelength is greater than 360° / λ0. These performance characteristics far surpass those of currently disclosed liquid crystal phase shifter specifications. These results demonstrate that the liquid crystal phase shifter design method proposed in this patent can bring considerable and beneficial effects.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A liquid crystal phase shifter for a phased array antenna, characterized by, From top to bottom, the upper layer dielectric plate, the patterned metal structure, the liquid crystal layer, the metal nanowire film layer, the metal bottom plate and the lower layer dielectric plate are included. The upper layer dielectric plate and the lower layer dielectric plate are flat structures made of insulating materials, the liquid crystal layer is located between the upper layer dielectric plate and the lower layer dielectric plate, the patterned metal structure is located on the lower surface of the upper layer dielectric plate, the metal bottom plate is located on the upper surface of the lower layer dielectric plate, and the upper surface of the metal bottom plate is the metal nanowire film layer. The patterned metal structure has a spindle shape with narrow sides and a wide middle, and is composed of a central metal strip and metal patches on both sides of the central metal strip. The central metal strip and the metal patches are an integral structure. The central metal strip has a width of... w 0. A rectangle with the same length as the upper dielectric substrate; the metal patches on both sides of the central metal strip are symmetrically distributed about the central metal strip; the metal patches are periodically distributed along the length of the central metal strip; all metal patches are of equal length and the distance between adjacent metal patches is equal; The metal nanowire film layer is composed of a porous alumina film and metal nanowires grown in the pores of the porous alumina film.

2. The liquid crystal phase shifter of claim 1, wherein, The thickness of the upper dielectric plate is h 1, 0.01 h 1 < 0.2 The thickness of the lower dielectric plate is h 2, 0.01 h 2 < 0.2 Wherein is the dielectric wavelength corresponding to the operating center frequency.​​ 3. The liquid crystal phase shifter of claim 1, wherein, The patterned metal structure is a metal thin film with a thickness of t 1, which is printed or etched on the lower surface of the upper dielectric plate, wherein 0.0001 t 1<0.003 , is the dielectric wavelength corresponding to the operating center frequency.​ 4. The liquid crystal phase shifter of claim 1, wherein, The metal patch is rectangular, arrowhead-shaped or bent-shaped, the center metal strip width w 0 satisfies: 0.001 w 0<0.2 is the medium wavelength corresponding to the operating center frequency.​​ 5. The liquid crystal phase shifter of claim 4, wherein, The metal patch is a rectangle with a length of w 1 and a distance between adjacent metal patches of s 1, the width of the metal patch decreases from the middle to both ends, the decrease rule is linear change with position or exponential change with position, the total width of the central metal strip in the middle of the patterned metal structure and the metal patches on both sides is l 1, wherein 0.001 <0.2 w 1 0.001 <0.15 s 0.001 1 0.3 l , , is the medium wavelength corresponding to the working center frequency.

6. The liquid crystal phase shifter of claim 1, wherein, The liquid crystal layer thickness is h 4, 0.0001 h 4 < 0.05 is the medium wavelength corresponding to the operating center frequency.​​ 7. The liquid crystal phase shifter of claim 1, wherein, The thickness of the metal backplane is t 2, is made on the upper surface of the lower medium plate by printing or etching, wherein 0.0001 , t 2 < 0.003 , is the medium wavelength corresponding to the operating center frequency.

8. The liquid crystal phase shifter of claim 1, wherein, The thickness of the metal nanowire thin film layer is h 3, 0.002 , h 3 < 0.03 , is the dielectric wavelength corresponding to the operating center frequency.

9. The liquid crystal phase shifter of claim 1 or 8, wherein, The pore diameter of the porous alumina thin film in which the metal nanowire thin film layer is prepared is d , and the distance between the centers of adjacent pores is p .

10. The liquid crystal phase shifter of claim 9, wherein, The preparation method of the metal nanowire film layer is as follows: a thin copper film is sputtered on the back of the porous alumina film as a seed layer, metal nanowires are grown in the pores by electro-deposition until the metal nanowires grow to the top of the porous alumina film, and the metal nanowire film layer is polished to the desired thickness.

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