Non-dispersive coupling transmission line combination for filter and coupler

Abstract

The invention belongs to the technical field of passive microwave devices, and particularly relates to a non-dispersive coupling transmission line combination for a filter and a coupler, which comprises an outer conductor used as a common ground and two inner conductors used as coupling transmission lines, and the outer conductor of the common ground and the inner conductors of the coupling transmission lines are surrounded by a low-loss medium. The cross sections of all the conductors in the propagation direction are kept unchanged; the cross section of the inner conductor of the coupling transmission line is symmetrical, and the whole is circular. Under different coupling coefficients, the coupling transmission line can ensure that the inner surface of the common ground outer conductor and the outer contours of the coupling transmission line inner conductor pairs remain unchanged, can minimize the structural discontinuity generated during cascade combination of different coupling transmission lines, is beneficial to design, processing and implementation of a broadband filter and a coupler, and has wide application prospects. And the dispersion problem of the reflection coefficient of the traditional coupling line can be solved.

Description

Technical Field

[0001] The invention belongs to the technical field of passive microwave devices, and in particular, is a non-dispersive coupled transmission line combination for filters and couplers. Background Art

[0002] When two transmission lines with a common ground are close together, power coupling can occur between the transmission lines due to the interaction of the electromagnetic fields of each transmission line. Such transmission lines are called coupled transmission lines. Coupled transmission lines are widely used in microwave filters, directional couplers and other microwave circuits. Their structure is generally composed of one or more metal floors and two long straight conductor units. Depending on the different components, there can be different coupling forms.

[0003] The working mode of coupled transmission lines is related to the structure of the transmission lines. For example, the main transmission mode of strip lines is pure TEM waves, while microstrip lines cannot propagate pure TEM waves. In the design of broadband filters and directional couplers, multiple coupled line sections with different coupling coefficients are often used to combine and cascade to form an overall circuit to achieve the design purpose. In traditional designs, coupled line sections with different coupling coefficients have different cross-sectional physical dimensions, and the transition sections between sections will form a sudden change in the current path, resulting in a series of discontinuities. The above discontinuities are equivalent to frequency-dependent reactive elements in the circuit, causing dispersion responses, which in turn affect the broadband characteristics of the device.

[0004] Therefore, the study of non-dispersion coupled transmission lines has great application value and practical significance. Summary of the invention

[0005] The present invention overcomes the shortcomings of the prior art and provides a non-dispersive coupled transmission line combination for filters and couplers. Under different coupling coefficients, the coupled transmission line can minimize the structural discontinuity generated during the cascade combination, which is beneficial to the design, processing and implementation of broadband filters and couplers, and can solve the dispersion problem of the reflection coefficient of the traditional coupled line combination.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A non-dispersive coupled transmission line combination for filters and couplers comprises: an outer conductor tube, an even-mode dielectric tube, a pair of inner conductors set as inner conductor a and inner conductor b, and an odd-mode dielectric gasket. In the cross section of the transmission system, the inner conductor a and the inner conductor b are separated by the odd-mode dielectric gasket, and the three are closely fitted without an air gap in between; the inner conductor a and the inner conductor b are quasi-semicircular, and form a combined cylinder with the odd-mode dielectric gasket; the cross sections of the combined cylinder, the even-mode dielectric tube and the outer conductor tube share a common center; the dielectric constants of the even-mode dielectric ring and the odd-mode dielectric gasket are similar.

[0007] When working in even mode, the potential of inner conductor a and inner conductor b is the same. Since the thickness of odd mode gasket is relatively thin, the combined cylinder can be approximately regarded as a complete metal cylinder, so the equivalent circuit of even mode circuit is a coaxial line. According to the classical transmission line theory, the even mode impedance is only related to the dielectric constant, magnetic permeability and inner and outer diameters of the even mode medium tube.

[0008] When working in odd mode, the potentials of inner conductor a and inner conductor b are opposite, and the potential of the outer conductor tube is zero. Since inner conductor a and inner conductor b are capacitively coupled mainly through the odd mode gasket, their impedance is mainly determined by the dielectric constant, relative permeability, thickness and shape of the odd mode gasket, which is equivalent to a double wire.

[0009] When the dielectric constant and permeability of the even-mode dielectric tube and the odd-mode dielectric gasket are the same, the wave impedance and phase velocity of the even- and odd-mode transmission line systems are the same, which can prevent the occurrence of phase velocity dispersion.

[0010] When coupled segments with different coupling coefficients can have the same physical dimensions, that is, the diameters of the outer conductor tube, the even-mode dielectric tube, and the combined cylinder are the same. In microwave engineering, different coupling coefficients refer to different combinations of even-mode impedance and odd-mode impedance. For coupled segments with determined physical dimensions, at this time, for the specified even-mode impedance, it can be achieved by adjusting the dielectric constant of the even-mode dielectric tube; after determining the dielectric constant of the even-mode dielectric tube, the dielectric constant of the odd-mode dielectric gasket is also determined; ensuring that the diameter of the combined cylinder remains unchanged, by changing the thickness of the odd-mode dielectric gasket and simultaneously changing the shape of the opposite surfaces of the inner conductor a and the inner conductor b, it is equivalent to adjusting the size of the mutual capacitance per unit length of the inner conductor a and the inner conductor b, and the odd-mode impedance can be adjusted to the target value. In order to ensure that the inner conductor a and the inner conductor b have the same functional position, the inner conductor a and the inner conductor b must maintain strict central rotational symmetry during the shape change process.

[0011] Through the above steps, a series of coupled line segments with exactly the same physical size and different coupling coefficients can be realized; the combined circuit using the above coupled line segments will have minimized structural mutations and microwave discontinuities. In the variant design, the outer conductor tube, even-mode dielectric tube and combined cylinder used in the coupled line can also be flexibly transformed into a centrally symmetrical geometric pattern such as a rectangle, square, or ellipse.

[0012] The invention has the beneficial effects of greatly reducing microwave discontinuity of the coupled line circuit and improving circuit performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the cross section of the coupling line of the present invention.

[0014] Figure 2 It is a three-dimensional schematic diagram of the coupling line in the present invention.

[0015] Figure 3 This is a schematic diagram of an equivalent circuit for even-mode excitation in the present invention.

[0016] Figure 4 The figure is a schematic diagram of connecting two coupled line segments with different coupling coefficients and odd-mode and even-mode impedances in the present invention.

[0017] Figure 5 It is a schematic diagram of another coupling line implementation method in the present invention.

[0018] In the figure, 1-outer conductor tube, 2-even mode dielectric tube, 3-combined cylinder, 3a, 3b-inner conductor, 3c-odd mode dielectric gasket, 4-common center, 5a, 5b-coupled line nodes, 3d, 3e-inner conductor, 3f-odd mode dielectric gasket. DETAILED DESCRIPTION

[0019] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments are only used to explain the present invention and do not limit the protection scope of the present invention.

[0020] Example: Figure 1 and Figure 2 As shown, a non-dispersive coupled transmission line combination for filters and couplers includes an outer conductor tube 1, an even-mode dielectric tube 2, inner conductors 3a and 3b, and an odd-mode dielectric gasket 3c. In the cross section of the transmission system, the inner conductor 3a and the inner conductor 3b are separated by the odd-mode dielectric gasket 3c, and the three are tightly fitted without an air gap in the middle; the inner conductor 3a and the inner conductor 3b are quasi-semicircular, forming a combined cylinder 3 with the odd-mode dielectric gasket 3c; the cross sections of the combined cylinder 3, the even-mode dielectric tube 2 and the outer conductor tube 1 share a common center 4, and the dielectric constants of the even-mode dielectric ring 2 and the odd-mode dielectric gasket 3c are similar.

[0021] When working in even mode, the inner conductor 3a and the inner conductor 3b have the same potential. Since the thickness of the odd mode gasket 3c is relatively thin, the combined cylinder 3 can be approximately regarded as a complete metal cylinder. Therefore, the equivalent circuit of the even mode circuit is a coaxial line. Figure 3 According to the classical transmission line theory, the even-mode impedance is only related to the dielectric constant, magnetic permeability and inner and outer diameters of the even-mode dielectric tube 2.

[0022] When working in odd mode, the potentials of the inner conductor 3a and the inner conductor 3b are opposite, and the potential of the outer conductor tube 1 is zero. Since the inner conductor 3a and the inner conductor 3b are capacitively coupled mainly through the odd mode gasket 3c, their impedance is mainly determined by the dielectric constant, relative permeability, thickness and shape of the odd mode gasket 3c, which is equivalent to a double conductor.

[0023] When the dielectric constant and magnetic permeability of the even-mode dielectric tube 2 and the odd-mode dielectric gasket 3c are the same, the wave impedance and phase velocity of the transmission line system of the odd and even modes are the same, which can prevent the occurrence of phase velocity dispersion.

[0024] When the coupling line segments with different coupling coefficients can have the same physical size, that is, the diameters of the outer conductor tube 1, the even-mode dielectric tube 2 and the combined cylinder 3 are the same, such as Figure 4 The coupled line segments 5a and 5b have different coupling coefficients in the coupling line segment. In microwave engineering, different coupling coefficients refer to different combinations of even-mode impedance and odd-mode impedance. For the coupled line segments with determined physical dimensions, at this time, for the specified even-mode impedance, it can be achieved by adjusting the dielectric constant of the even-mode dielectric tube 2; after determining the dielectric constant of the even-mode dielectric tube 2, the dielectric constant of the odd-mode dielectric gasket 3c is also determined; ensuring that the diameter of the combined cylinder 3 remains unchanged, by changing the thickness of the odd-mode dielectric gasket 3c and simultaneously changing the shape of the opposite surfaces of the inner conductor 3a and the inner conductor 3b, it is equivalent to adjusting the size of the mutual capacitance per unit length of the inner conductor 3a and the inner conductor 3b, and the odd-mode impedance can be adjusted to the target value. In order to ensure that the inner conductor 3a and the inner conductor 3b have the same working position, the inner conductor 3a and the inner conductor 3b need to maintain strict central rotational symmetry during the shape change process.

[0025] Through the above steps, a series of coupled line segments with exactly the same physical size and different coupling coefficients can be realized; the combined circuit using the above coupled line segments will have minimized structural mutations and microwave discontinuities. In the variant design, the outer conductor tube 1, the even-mode dielectric tube 2 and the combined cylinder 3 used in the coupled line can also be flexibly transformed into a centrally symmetrical geometric pattern such as a rectangle, a square, or an ellipse.

[0026] like Figure 4 As shown, two coupling line segments 5a and 5b with different coupling coefficients are connected together in a cascade form; wherein the cross section of the coupling line segment 5a is as shown in FIG. Figure 1 As shown, the cross section of the coupling line segment 5b is as follows Figure 5 As shown, the cross-sections of the outer conductors 1 of the coupling segments 5a and 5b are the same, the inner and outer diameters of the even-mode dielectric tubes 2 and 2a are the same, and the dielectric constants are different, so the even-mode impedances of the coupling segments 5a and 5b are different.

[0027] The inner conductor 3d, the inner conductor 3e of the coupling segment 5b and the odd-mode dielectric spacer 3f form a combined cylinder.

[0028] The diameter of the combined cylinder of the coupling line segment 5a is the same as the diameter of the combined cylinder of the coupling line segment 5b; the dielectric constant of the odd-mode dielectric gasket 3f and the even-mode dielectric tube 2a is the same. Since the shape, thickness, and dielectric constant of the odd-mode dielectric gasket 3c and the odd-mode dielectric gasket 3f are different, the odd-mode impedance of the coupling line segment 5a and the coupling line segment 5b are also different, but in the overall cross section, the coupling line segment 5a and the coupling line segment 5b have the same size, so that the minimum discontinuity can be obtained.

[0029] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A non-dispersive coupled transmission line combination for a filter and a coupler, characterized in that: The invention comprises an outer conductor tube, an even-mode dielectric tube, a pair of inner conductors set as inner conductor a and inner conductor b, and an odd-mode dielectric gasket. The inner conductor a and inner conductor b are quasi-semi-cylinders and form a combined cylinder with the odd-mode dielectric gasket. The cross sections of the combined cylinder, the even-mode dielectric tube and the outer conductor tube have a common center. The dielectric constants of the even-mode dielectric ring and the odd-mode dielectric gasket are similar.

2. A non-dispersive coupled transmission line combination for a filter and a coupler according to claim 1, characterized in that: The inner conductor a and the inner conductor b have the same cross-sectional structure and are 180-degree rotationally symmetrical, with the center of symmetry being the common center of a circle. The inner conductor a and the inner conductor b are separated by an odd-mode dielectric gasket, and the three are tightly fitted together to form a combined cylinder.

3. The non-dispersive coupled transmission line combination for a filter and a coupler according to claim 1, characterized in that: The odd-mode dielectric gasket is an isotropic dielectric sheet with uniform thickness and density distribution, and its cross-sectional shape is consistent with the shape of the inner conductor a and the inner conductor b.

4. The non-dispersive coupled transmission line combination for a filter and a coupler according to claim 1, characterized in that: The outer diameter of the even-mode dielectric tube is the same as the inner diameter of the outer conductor tube, and the inner diameter of the even-mode dielectric tube is the same as the diameter of the combined cylinder.

5. The non-dispersive coupled transmission line combination for a filter and a coupler according to claim 1, characterized in that: The even-mode dielectric tube and the odd-mode dielectric gasket have the same dielectric constant.

6. The non-dispersive coupled transmission line combination for a filter and a coupler according to claim 1, characterized in that: The shapes of the even-mode dielectric tube, the outer conductor tube and the combined cylinder are square, rectangular or elliptical.

7. The non-dispersive coupled transmission line combination for a filter and a coupler according to claim 1, characterized in that: The dielectric constants of the even-mode dielectric tube and the odd-mode dielectric gasket are the natural dielectric constants of the materials.

8. The non-dispersive coupled transmission line combination for a filter and a coupler according to claim 1, characterized in that: The dielectric constants of the even-mode dielectric tube and the odd-mode dielectric gasket are equivalent dielectric constants.

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