An ultra-wideband 3dB directional coupler at low temperature

Abstract

The present invention discloses an ultra-wideband 3dB directional coupler at low temperature, which belongs to the technical field of passive microwave devices. It includes dielectric plates I and II of different thicknesses and a stripline, and the stripline is completely surrounded by the dielectric plates. It also includes 5 sections of coupled transmission lines, each of which has an equal line width and is bilaterally symmetrical in the overall structure. The coupler is axisymmetric in the plane. In the selection of dielectric plates, the upper and lower dielectric plates are the same, which are dielectric plates I, and the dielectric substrate of the middle layer is dielectric plate II. In addition, the specific dielectric constant of the dielectric plate and the thickness requirements of the stripline are also set. The coupler can work normally in an extremely low ambient temperature of 24K, that is, a Celsius temperature of ‑249°C, and its working parameter indicators are similar to those in a room temperature environment.

Description

Technical Field

[0001] The invention belongs to the technical field of passive microwave devices, and more specifically, relates to an ultra-wideband 3dB directional coupler at low temperature. Background Art

[0002] The ultra-wideband directional coupler is an important passive microwave device that can be used for power distribution and synthesis, and can also be used in devices such as mixers, amplifiers and attenuators. The directional coupler is a four-port device that is lossless and reciprocal under ideal conditions. The 3dB orthogonal directional coupler can divide the input signal into two output signals with equal power and a phase difference of 90°, and can be used in superheterodyne receivers. For superheterodyne receivers working in low-temperature environments, the directional coupler needs to maintain the original parameter performance unchanged in low-temperature environments. Therefore, it is of great significance to study ultra-wideband 3dB orthogonal directional couplers that can maintain their original performance unchanged at low temperatures.

[0003] The existing 3dB orthogonal directional coupler design has the following problems: For ultra-wideband orthogonal directional couplers, the operating bandwidth reaches 2-18GHz, and the phase difference between the through port and the coupled port is also maintained at 90°, but it can only work normally at room temperature. In a low-temperature environment, the working performance of the directional coupler will be significantly deteriorated and cannot be used. For low-temperature orthogonal directional couplers on the market, the operating bandwidth is relatively narrow, with a bandwidth range of 4-12GHz, and the coupling degree is too unbalanced, resulting in poor performance.

[0004] Therefore, studying the ultra-wideband 3dB orthogonal directional coupler that can work normally in low-temperature environment has great application value and practical significance. Summary of the invention

[0005] The present invention overcomes the shortcomings of the prior art and provides an ultra-wideband orthogonal directional coupler suitable for normal operation at a low temperature of 24K (-249°C). The operating frequency range of the directional coupler is 2-14GHz, the coupling degree is -3dB, and the phase difference between the through port and the coupled port is 90°. The designed 3dB ultra-wideband directional coupler can maintain working performance similar to that in room temperature at a low temperature of 24K and has a small size, which can be realized in terms of process.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: the coupler comprises:

[0007] Two dielectric plates, namely dielectric plate I1 and two dielectric plates II2, the thickness of dielectric plate II2 is different from that of dielectric plate I1; a strip line 3a, the strip line 3a is printed on the upper and lower surfaces of dielectric plate II2 by thin film technology; through the superposition of dielectric plate I1 and dielectric plate II2, the strip line is completely surrounded by the dielectric plates; another strip line 3b, the strip line 3b is printed on the upper and lower surfaces of dielectric plate II2 by thin film technology, and is parallel to the central strip of strip line 3a but keeps a certain distance, and there is no coupling between them.

[0008] 5 sections of coupled transmission lines, namely coupled transmission line Ⅰ4, coupled transmission line Ⅱ5, coupled transmission line Ⅲ6, coupled transmission line Ⅳ7, coupled transmission line V8;

[0009] In one embodiment, the line widths of the two sections of the coupled transmission line are equal, that is, each section of the coupled transmission line is symmetrical about the horizontal axis;

[0010] The coupler is symmetrical in structure, the coupled transmission line Ⅰ4 is equal to the coupled transmission line V8, and the coupled transmission line Ⅱ5 is equal to the coupled transmission line Ⅳ7; each section of the coupled transmission line serves as a separate coupled line coupler, and each section of the coupled transmission line has four ports: input end, through end, coupling end, and isolation end.

[0011] In one embodiment, the coupler is symmetrical about plane AA'.

[0012] In one solution, the upper and lower dielectric plates are identical, namely dielectric plate Ⅰ1, and the dielectric substrate in the middle layer is dielectric plate Ⅱ2.

[0013] In one embodiment, the dielectric constant of the dielectric plate Ⅰ1 is 3 and the thickness is 1-3 mm.

[0014] In one embodiment, the dielectric constant of the dielectric plate II 2 is 3.2 and the thickness is 0.01-0.1 mm.

[0015] In one embodiment, the strip line uses metal copper as a conductor with a thickness of 1-5 μm.

[0016] In one embodiment, the directional coupler operates normally in an environment with an ambient temperature of 24K, ie, a Celsius temperature of -249°C.

[0017] In one embodiment, the directional coupler has similar operating parameters in a working environment of 24K, i.e. -249°C, and a room temperature of 300K, i.e. 27°C.

[0018] Beneficial effects of the present invention:

[0019] 1. Use an interlaced parallel coupled stripline structure to ensure that the coupled line can produce a strong coupling degree; and select a suitable dielectric substrate based on the condition that the dielectric constant of the dielectric plate will not change with the temperature drop under low temperature conditions. The selection of stripline materials is also based on the fact that the material has stable low-temperature characteristics under low temperature conditions. The dielectric plate and stripline design with stable low-temperature characteristics make the directional coupler have stable low-temperature characteristics, and the parameter properties will not change with the decrease in ambient temperature; the use of anti-deformation stripline structure can effectively prevent the horizontal deformation of the film material when the high temperature difference changes. Therefore, the designed directional coupler can work normally in a low-temperature environment.

[0020] 2. A coupler composed of a single coupling line can only work within a narrow bandwidth. By cascading multiple coupling transmission lines, the bandwidth of the directional coupler can be widened, which is particularly suitable for designing ultra-wideband directional couplers. The bandwidth range of the present invention is 2-14GHz, which belongs to an ultra-wideband directional coupler. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of the present invention;

[0022] Figure 2 A schematic diagram of a cross-section of an interlaced coupled stripline in the present invention;

[0023] Figure 3 It is a schematic diagram of the strip line in the present invention;

[0024] Figure 4 It is a measured parameter diagram of the imbalance between the output end and the coupled end of the 3dB coupler in the present invention at 300K under a normal temperature environment, the coupled end curve is Coupled_300K, and the through end curve is Direct_300K;

[0025] Figure 5 It is a measured parameter diagram of the imbalance between the output end and the coupled end of the 3dB coupler in the present invention at 24K in a low temperature environment, the coupled end curve is Coupled_24K, and the through end curve is Direct_24K;

[0026] Figure 6 This is a measured parameter diagram of the phase difference between the through end and the coupled end of the 3dB coupler in the present invention at 24K in a low temperature environment.

[0027] In the figure, 1-dielectric plate I, 2-dielectric plate II, 3a-main strip line, 3b-anti-deformation strip line, 4-coupled transmission line I, 5-coupled transmission line II, 6-coupled transmission line III, 7-coupled transmission line IV, 8-coupled transmission line V, 9-transmission line I, 10-transmission line II, 11-transmission line III, 12-transmission line IV. DETAILED DESCRIPTION

[0028] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Typical embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0029] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0030] Embodiment 1:

[0031] An ultra-wideband orthogonal directional coupler that works normally at low temperatures is provided. The operating frequency range of the directional coupler is 2-14GHz, the coupling degree is -3dB, and the phase difference between the through port and the coupled port is 90°. The designed 3dB ultra-wideband directional coupler can maintain working performance similar to that in room temperature at a low temperature of 24K and has a small size, which can be realized in terms of process.

[0032] The invention comprises: a dielectric plate I (1), a dielectric plate II (2), and strip lines (3a and 3b); the strip lines (3a and 3b) are printed on the upper and lower surfaces of the dielectric plate II (2); when the two dielectric plates I (1) clamp the dielectric plate II (2) together, the strip lines (3a and 3b) are completely surrounded by the dielectric plates from top to bottom; four ports a, b, c, and d are led out perpendicular to the edge of the dielectric plate and intersect with the SMA connector lead wire; port a is an input port, port b is a straight-through port, port c is a coupling port, and port d is an isolation port. The input port and the isolation port can be interchanged, and the straight-through port and the coupling port can be interchanged.

[0033] The present invention is composed of five sections of cross-coupled coupled transmission lines, which are symmetrical in structure. The five sections of coupled transmission lines are coupled transmission line I (4), coupled transmission line II (5), coupled transmission line III (6), coupled transmission line IV (7), and coupled transmission line V (8), wherein the coupled transmission line I (4) is symmetrical with the coupled transmission line V (8), and the coupled transmission line II (5) is symmetrical with the coupled transmission line IV (7).

[0034] The five coupled transmission lines used are parallel staggered coupled transmission lines. Coupled transmission line I (4), coupled transmission line II (5), coupled transmission line III (6), coupled transmission line IV (7), and coupled transmission line V (8) can be regarded as single-section coupled line couplers. Each coupled transmission line has four ports: input end, through end, coupling end, and isolation end.

[0035] For the coupled transmission line I (4), the input end is connected to the transmission line I (9), the coupled end is connected to the transmission line III (11), the through end is connected to the input end of the coupled transmission line II (5), and the isolated end is connected to the coupled end of the coupled transmission line II (5); for the coupled transmission line II (5), the through end is connected to the input end of the coupled transmission line III (6), and the isolated end is connected to the coupled end of the coupled transmission line III (6);

[0036] For the coupled transmission line III (6), the centers of the two transmission lines thereof intersect each other, the through end is connected to the input end of the coupled transmission line IV (7), and the isolated end is connected to the coupled end of the coupled transmission line IV (7); for the coupled transmission line IV (7), the through end is connected to the input end of the coupled transmission line V (8), and the isolated end is connected to the coupled end of the coupled transmission line V (8); for the coupled transmission line V (8), the through end is connected to the transmission line II (10), and the isolated end is connected to the transmission line IV (12).

[0037] The signal line of the SMA connector contacts the transmission line I (9), the transmission line II (10), the transmission line III (11), and the transmission line IV (12) to transmit the signal.

[0038] The electrical length of each coupled transmission line of the ultra-wideband 3dB directional coupler circuit is θ=π / 2, and its physical length L is 1 / 4 of the working wavelength. According to the following formula, the physical length L of each coupled transmission line can be calculated.

[0039]

[0040] In the present invention, the dielectric constant of dielectric plate I (1) is 3, and the dielectric constant of dielectric plate II (2) is 3.2. The thickness of dielectric plate I (1) is 1-3 mm, and the thickness of dielectric plate II (2) is 0.01-0.1 mm. Because the dielectric constants of dielectric plate I (1) and dielectric plate II (2) do not change due to the decrease in temperature, in the experiment, they can work normally in an environment of 24K, thus ensuring that the parameter properties of the directional coupler are stable at low temperatures. The strip line material on the upper and lower surfaces of dielectric plate II (2) is metal copper with a thickness of 1-3 μm.

[0041] Embodiment 2:

[0042] like Figure 1As shown, a low temperature ultra-wideband 3dB directional coupler comprises: a dielectric plate I (1), a dielectric plate II (2), and strip lines (3a and 3b); the strip lines (3a and 3b) are printed on the upper and lower surfaces of the dielectric plate II (2), the two dielectric plates I (1) overlap with the dielectric plate II (2), the dielectric plate II (2) is sandwiched between the two dielectric plates I (1), and the strip lines (3a and 3b) are completely surrounded by the dielectric plates. The dielectric constant of the dielectric plate I (1) is 3, and the dielectric constant of the dielectric plate II (2) is 3.2. The thickness of the selected dielectric plate I (1) is 1-3 mm, and the thickness of the dielectric plate II (2) is 0.01-0.1 mm.

[0043] The thickness of the dielectric plate I (1) is selected to be 1.524 mm, and the thickness of the dielectric plate II (2) is selected to be 0.025 mm. The strip line material is selected to be copper metal, and the copper metal is plated on the upper and lower layers of the dielectric plate II (2) using thin film technology. The thickness of the copper metal can be selected in the range of 1-3 μm, and 2 μm is selected in the embodiment of the present invention.

[0044] like Figure 2 As shown, it is a cross-sectional schematic diagram of each single-section coupled line coupler. The electrical length of each single-section coupled line coupler is θ=π / 2, and the physical length is 5.2 mm. w represents the width of the coupled line of each single-section coupled line coupler, w o Represents the distance between the two coupled lines of each single-section coupled line coupler. Each coupled transmission line acts as a separate coupled line coupler.

[0045] The w of the single-section coupled line coupler I (4) is 1.89 mm, and w o is 2.87 mm; the w of the two coupling lines that make up the single-section coupling line coupler II (5) is 1.5 mm, and w o is 1.61 mm; the w of the single-section coupled line coupler III (6) is 0.38 mm, w o is 0.17 mm; the w of the single-section coupled line coupler IV (7) is 1.5 mm, w o is 1.61mm; the w of the single-section coupled line coupler V(8) is 1.89mm, w o It is 2.87mm.

[0046] like Figure 3 As shown, the present invention requires a total of 4 transmission lines, and their lengths and widths are exactly the same, with a length of 3 mm and a width of 1.98 mm.

[0047] The working frequency band of the present invention is 2-14 GHz, and the bandwidth is 12 GHz. The coupling loss and isolation parameters are obtained by testing in a low temperature environment. As shown in the figure, the present invention can ensure normal operation in a 24K working environment and can be used stably.

[0048] It should be understood that the detailed description of the technical solutions of the present invention by means of the preferred embodiments is illustrative rather than restrictive. A person skilled in the art may modify the technical solutions described in the embodiments, or replace some of the technical features by equivalents, based on reading the specification of the present invention; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ultra-wideband 3dB directional coupler at low temperature, characterized in that: The coupler comprises: 3 dielectric plates, including 2 outer dielectric plates I (1) and 1 inner dielectric plate II (2), wherein the dielectric plate II (2) and the dielectric plate I (1) have different thicknesses; a planar stripline I (3a) and a planar stripline II (3b), wherein the planar stripline I (3a) and the planar stripline II (3b) are made of metal materials and are printed on the upper and lower surfaces of the dielectric plate II (2) by thin film circuit processing; the stripline is completely surrounded by the dielectric plates by superposition of the dielectric plate I (1) and the dielectric plate II (2); The planar stripline 1 (3a) includes five coupled transmission lines, namely coupled transmission line I (4), coupled transmission line II (5), coupled transmission line III (6), coupled transmission line IV (7) and coupled transmission line V (8); The line widths of the two sections of the coupled transmission line are equal, that is, each section of the coupled transmission line is symmetrical about the horizontal axis; The coupler is symmetrical in structure. The coupled transmission line I (4) is equal to the coupled transmission line V (8), and the coupled transmission line II (5) is equal to the coupled transmission line IV (7). Each section of the coupled transmission line is used as a separate coupled line coupler. Each section of the coupled transmission line has four ports: an input end, a through end, a coupled end, and an isolated end. The directional coupler is rotationally symmetrical at the center point; The upper and lower dielectric plates of the directional coupler are identical, namely dielectric plate I (1), and the dielectric substrate of the middle layer is dielectric plate II (2); The dielectric constant of the dielectric plate I (1) is 3, and the thickness can be selected in the range of 1-3 mm; The dielectric constant of the dielectric plate II (2) is 3.2, and the thickness can be selected in the range of 0.01-0.1 mm; The planar strip line 1 (3a) and the planar strip line 2 (3b) use metal copper as conductor, and the thickness is selected in the range of 1-5 μm; The directional coupler has good temperature stability, and its working parameter indicators in the working environment of 24K (-249°C) and the room temperature environment of 300K (27°C) are similar; The planar strip line 1 (3a) and the planar strip line 2 (3b) are decoupled from each other, that is, there is no energy exchange between them; the planar strip line 2 (3b) plays a role in resisting film deformation caused by strong temperature changes.

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