Ultra-wideband coplanar waveguide transition structure based on liquid crystal material

Abstract

The application provides a liquid crystal material-based ultra-wideband same-side coupling transition structure and relates to the field of liquid crystal devices. The strip lines in the same-side coupling transition structure are distributed on the same side of a liquid crystal layer. The coupling transition structure is composed of staggered vertical coupling strip lines which are mirror-symmetrically distributed on the upper and lower surfaces of a glass substrate. The four-port network of the design can be used to build an equivalent circuit of a directional coupler in the case of a non-uniform medium. The transmission of signals in and out of the glass layer of an electrically-controlled liquid crystal element is realized through the design of a cross-layer coupling transition structure, and the ultra-wideband working frequency band and low loss are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of liquid crystal devices, in particular to a kind of ultra-wideband same side coupling transition structure based on liquid crystal material. BACKGROUND

[0002] Coupling transition structure is a kind of design that realizes smooth transition and energy transmission between different transmission lines or different physical structures. This structure is usually used in microwave and radio frequency systems to ensure efficient and low-loss conversion of signals between different transmission media. The design of coupling transition structure is crucial to maintaining the overall performance of the system, especially in high-frequency applications. Improper transition can cause signal reflection, attenuation or interference, affecting the stability and reliability of the system.

[0003] Liquid crystals have attracted the attention of researchers for many years due to their wide range of applications in optical and non-optical fields. Due to the sensitivity of liquid crystal molecules to electromagnetic fields, they have relatively low dielectric loss, and the manufacturing cost of related devices is low, making them of great research value in microwave and millimeter wave circuits. Liquid crystals have strong electrically tunable ability, and their characteristics can be controlled by surface anchoring, external electric field or magnetic field. Under different voltages, liquid crystals exhibit different dielectric constants.

[0004] Due to the limitations of processing technology, the glass substrate encapsulating the liquid crystal cannot be metalized via, and signal transmission inside and outside the liquid crystal phase shifter can only be achieved in a coupled form. In the traditional case, in order to achieve good coupling effect, uniform medium is usually used, which is often used in the design of directional coupler with high coupling degree. The commonly used analysis method for coupled line model is the odd-even mode analysis method. The odd-even mode analysis method is to decompose the mode transmitted in the coupled line into the mode under odd mode excitation and even mode excitation. Since the coupled transmission line is a linear system, the characteristic parameters under the two excitation modes can be calculated respectively and then superimposed to obtain the overall characteristic parameters of the coupled line. The general process is to derive the odd-even mode impedance and then calculate the physical size of the coupled line. However, in the case of non-uniform medium, the odd mode phase velocity in the coupler is not equal to the even mode phase velocity. Therefore, the performance of the coupled line designed according to the traditional design method is greatly reduced, and therefore it is necessary to use an unconventional design method to design the coupled line transition structure under non-uniform medium. SUMMARY

[0005] In the case of the coupling line transition structure under the non-uniform medium involved, the uniform medium under the traditional model is replaced by a three-layer non-uniform medium of liquid crystal-glass-medium plate from top to bottom, and the dielectric constant of the liquid crystal changes with the voltage. The conventional odd-even mode analysis method cannot be applied to this kind of coupled line structure. To solve the above technical problems, the present application provides a kind of ultra-wideband same side coupling transition structure based on liquid crystal material, realizes the transmission of signal in and out of the glass layer of electrically controlled liquid crystal element, and realizes the working frequency band of ultra-wideband and lower loss.

[0006] In order to achieve the above object, the present application adopts the following technical solutions:

[0007] An ultra-wideband same-side coupling transition structure based on liquid crystal material comprises at least: staggered vertical coupling strip lines which are mirror-symmetrically distributed on the upper and lower sides of a dielectric substrate; wherein the same-side coupling structure refers to a coupling structure on the same side of a liquid crystal layer.

[0008] Preferably, the staggered vertical coupling strip lines comprise, from bottom to top, a lower metal floor, a lower dielectric substrate, a lower strip transmission line, a lower strip coupling line, a glass substrate, an upper strip transmission line, an upper strip coupling line, a liquid crystal layer, and a top metal floor.

[0009] Preferably, the overall transmission path of the signal is: first input from the input port of the feed line through the coaxial connector, coupled to the upper strip coupling line on the glass substrate by the same-side coupling structure, and then output through the coaxial connector by the coupling port at the end of the upper strip transmission line.

[0010] Preferably, the lower strip transmission line connects the lower strip coupling line with the input port and the straight-through port, the upper strip transmission line connects the upper strip coupling line with the coupling port and the isolation port.

[0011] Preferably, the lower dielectric substrate, the lower circuit, the glass substrate, the upper circuit, and the liquid crystal layer together constitute a coupler under asymmetric non-uniform media.

[0012] Compared with the prior art, the present application has the following beneficial effects:

[0013] The present application adopts the mature process of packaging liquid crystal based on glass plate, has good air tightness and stability. By designing staggered vertical coupling strip lines which are mirror-symmetrically distributed on the upper and lower sides of a dielectric substrate, cross-layer coupling in non-uniform media is achieved, and ultra-wideband working frequency bands are achieved by broadband design of the coupling structure. The present application applies the odd-even mode analysis method to the design of a strip line directional coupler with multiple layers of media and different media layer thicknesses, and designs a same-side cross-layer transition structure based on this, greatly improving the working bandwidth of the traditional coupling transition structure and reducing the working loss. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0015] Figure 1 A three-dimensional structure schematic diagram of a liquid crystal material based ultra-wideband self-coupling transition structure for an embodiment of the present application;

[0016] Figure 2 A front view schematic diagram of a liquid crystal material based ultra-wideband self-coupling transition structure for an embodiment of the present application;

[0017] Figure 3 A top view schematic diagram of a liquid crystal material based ultra-wideband self-coupling transition structure for an embodiment of the present application;

[0018] Figure 4 A side view schematic diagram of a liquid crystal material based ultra-wideband self-coupling transition structure for an embodiment of the present application;

[0019] Figure 5 A return loss S11 schematic diagram of a phase shifter as a whole for an embodiment of the present application;

[0020] Figure 6 An insertion loss S21 schematic diagram of a phase shifter as a whole for an embodiment of the present application;

[0021] Figure 7 A coupling degree S31 schematic diagram of a phase shifter as a whole for an embodiment of the present application;

[0022] Figure 8 An isolation degree S41 schematic diagram of a phase shifter as a whole for an embodiment of the present application.

[0023] Wherein, the reference signs are: lower layer metal floor 1, lower layer dielectric substrate 2, lower layer circuit 3, lower layer strip transmission line 3-1, lower layer strip coupling line 3-2, glass substrate 4, upper layer circuit 5, upper layer strip transmission line 5-1, upper layer strip coupling line 5-2, liquid crystal layer 6, top layer metal floor 7, input port 1#, straight-through port 2#, coupling port 3#, isolation port 4#. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in details below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0025] For the coupling line transition structure in the non-uniform medium case involved in the design of the liquid crystal phase shifter, the uniform medium in the original traditional model is replaced by a three-layer non-uniform medium consisting of liquid crystal-glass-dielectric plate from top to bottom. Moreover, the dielectric constant of the liquid crystal will change with the voltage. Undoubtedly, the conventional odd-even mode analysis method is no longer applicable to the design of this coupling line structure. Due to the non-uniformity of the medium, the odd-mode phase velocity in this coupler is not equal to the even-mode phase velocity. The performance of the coupling line designed according to the traditional design method is greatly reduced. Therefore, an unconventional design method is required to design the coupling line transition structure under non-uniform medium.

[0026] The ultra-wideband same-side coupling transition structure based on liquid crystal material of this invention can be regarded as a directional coupler with high coupling requirements. Even using multiple 1 / 4-wavelength wide-side coupled striplines, achieving high coupling at the center operating frequency is difficult. Most current 3dB couplers in the literature are based on cascading two 8.34 dB stripline couplers to meet design requirements. To extend the operating bandwidth of the coupling transition structure, it is necessary to refer to the design of multi-section symmetrical directional couplers based on wide-side coupled lines, which can be equivalent to a 1 / 4-wavelength filter in a homogeneous medium. In the design, the operating center frequency is set to 12 GHz, with a relative bandwidth of 100%. The normalized even-mode impedance is calculated by referring to the table of normalized even-mode impedance values ​​for Chebyshev coupled transmission line directional couplers.

[0027] The present invention will be described in detail below with reference to the figures and specific embodiments, but this is not intended to limit the present invention.

[0028] like Figures 1-4 As shown, an ultrawideband same-side coupling transition structure based on liquid crystal material according to the present invention includes a glass plate, a liquid crystal plate, a stripline, a metal ground plane and a dielectric substrate.

[0029] like Figure 2 As shown, the LCD panel is encapsulated with a glass plate. From bottom to top, each layer is as follows: lower metal ground plane 1, lower dielectric substrate 2, lower circuit 3, glass substrate 4, upper circuit 5, liquid crystal layer 6, and top metal ground plane 7. The lower circuit 3 consists of a lower stripline transmission line 3-1 and a lower stripline coupling line 3-2. The upper circuit 5 consists of an upper stripline transmission line 5-1 and an upper stripline coupling line 5-2. The lower stripline transmission line (3-1) connects the lower stripline coupling line (3-2) to input port 1# and through port 2#. The upper stripline transmission line 5-1 connects the upper stripline coupling line 5-2 to coupling port 3# and isolation port 4#.

[0030] The ultra-wideband same-side coupling transition structure has metal ground planes on both the top and bottom, namely the lower metal ground plane 1 and the upper metal ground plane 7, to maintain the independence of the device. The lower circuit 3 is located between the lower dielectric substrate 2 and the glass substrate 4, and is connected as one unit by an adhesive layer. The upper circuit 5 is located on the upper side of the glass substrate 4. The lower circuit 3 and the upper circuit 5 are mirror images of each other, forming a reciprocal four-port network. The liquid crystal layer 6 is located on the upper side of the upper circuit 5. The lower dielectric substrate 2, the lower circuit 3, the glass substrate 4, the upper circuit 5, and the liquid crystal layer 6 together constitute a coupler under an asymmetric and non-uniform dielectric. The lower dielectric substrate 2 is made of Rogers 3003, with a thickness of 1.127 mm and a stripline width of 0.1 mm.

[0031] like Figure 1 and Figure 4 As shown, this same-side coupling transition structure uses two interleaved coupled striplines cascaded to improve coupling. The signal is input from the coaxial input port 1#, transmitted through the lower stripline transmission line 3-1 to the lower stripline coupling line 3-2, transmitted in the coupling region to the upper stripline coupling line 5-2, and output from the coupling port 3# through the upper stripline transmission line 5-1. The four ports are the input port 1#, the through port 2#, the coupling port 3#, and the isolation port 4#. The through port 2# is located at the end of the lower stripline transmission line 3-1, opposite to the input port 1#, and is used to test the coupling energy loss. The isolation port 4# is located at the beginning of the upper stripline transmission line 5-1, on the same side as the input port 1#, and is used to characterize the decoupling power.

[0032] Figures 4-8 The overall S-parameters of the device under different liquid crystal dielectric constants are shown, where represents the return loss, insertion loss, coupling, and isolation of the device.

[0033] The parts of this invention not described in detail are well-known to those skilled in the art.

[0034] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. An ultrawideband same-side coupling transition structure based on liquid crystal material, characterized in that, At least including: Interlaced vertically coupled strips distributed on the upper and lower sides of the dielectric substrate in a mirror-symmetrical manner; where, same-side coupling structure refers to coupling structure on the same side of the liquid crystal layer; The staggered vertically coupled stripline includes, from bottom to top, a lower metal ground plane (1), a lower dielectric substrate (2), a lower stripline transmission line (3-1), a lower stripline coupling line (3-2), a glass substrate (4), an upper stripline transmission line (5-1), an upper stripline coupling line (5-2), a liquid crystal layer (6), and a top metal ground plane (7).

2. The ultra-wideband same-side coupling transition structure based on liquid crystal material according to claim 1, characterized in that, The overall signal transmission path is as follows: First, the feed line is input from the power input port through the coaxial connector, and then coupled to the upper strip coupling line (5-2) on the glass substrate (4) by the same-side coupling structure. Then, the signal is output through the coaxial connector through the coupling port located at the end of the upper strip transmission line (5-1).

3. The ultra-wideband same-side coupling transition structure based on liquid crystal material according to claim 1, characterized in that, The lower stripline transmission line (3-1) connects the lower stripline coupling line (3-2) to the input port and the through port, and the upper stripline transmission line (5-1) connects the upper stripline coupling line (5-2) to the coupling port and the isolation port.

4. The ultra-wideband same-side coupling transition structure based on liquid crystal material according to claim 1, characterized in that, The lower dielectric substrate (2), the lower circuit (3), the glass substrate (4), the upper circuit (5), and the liquid crystal layer (6) together constitute a coupler under an asymmetric and non-uniform dielectric.

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