A microstrip directional coupler

Abstract

The present invention relates to the field of microwave technology, and in particular to a microstrip directional coupler, comprising a dielectric substrate, a microstrip transmission line and a microstrip coupling line printed on the dielectric substrate, wherein one end of the microstrip transmission line is an input end and the other end is a straight-through end, one end of the microstrip coupling line is a coupling end and the other end is an isolation end, the bottom layer of the dielectric substrate is connected to a metal grounding layer, the microstrip coupling line is bent to increase the total length, and the microstrip coupling line forms a first coupling parallel line and a second coupling parallel line based on the bending. The present invention makes the coupling degree and directivity controllable by changing the length of the coupling parallel line and the spacing between the entire microstrip coupling line structure and the microstrip transmission line, and by changing the bending form of the microstrip coupling line, the coupling flatness can be guaranteed without affecting the directivity and coupling degree.

Description

Technical Field

[0001] The invention relates to the field of microwave technology, and in particular to a microstrip directional coupler. Background Art

[0002] In recent years, communication technology has achieved rapid development, and microwave communication equipment has also developed accordingly. Today, communication equipment tends to be miniaturized and portable, which puts higher requirements on the size reduction of passive components in communication equipment. As a key component in microwave communication systems, the technical background of directional couplers is rooted in the rapid development of communication technology in recent years; the continuous progress of microwave communication equipment has promoted the evolution of directional couplers, making them play an irreplaceable role in various high-frequency systems.

[0003] A directional coupler is a four-port network with an input port, a through port, a coupling port, and an isolation port. It transmits power to the coupling port through a certain coupling. It is an important microwave device for various high-frequency systems and is widely used in many microwave device systems such as amplitude control systems, balanced amplifiers, power distribution and synthesizers. The coupler plays the role of power distribution, combination, measurement, topology change and filtering. With the development of swept signal sources, broadband reflectometers, network analyzers and other power measurement equipment, couplers usually require high directivity to obtain suitable performance. Conventional directional couplers usually use parallel microstrip directional couplers. Due to the symmetry of the microstrip coupling line, the coupling in the undesired direction increases, which in turn leads to a decrease in directivity. Therefore, the design and research of directional couplers with high directivity is of great significance. Summary of the invention

[0004] The present invention provides a microstrip directional coupler to improve the disadvantages mentioned in the background technology.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a microstrip directional coupler, comprising a dielectric substrate and a microstrip transmission line and a microstrip coupling line printed on the dielectric substrate, the microstrip transmission line having an input end and a through end, the microstrip coupling line having a coupling end and an isolation end, the microstrip coupling line being folded and arranged on the dielectric substrate, and the microstrip coupling line having a first coupling parallel line and a second coupling parallel line located in the same straight line.

[0006] More preferably, the microstrip coupling line is composed of the first coupling connection line, the first coupling parallel line, the second coupling connection line, the third coupling connection line and the second coupling parallel line connected in sequence, the first coupling parallel line is connected to the side of the first coupling connection line away from the coupling end, the second coupling parallel line is connected to the side of the third coupling connection line away from the isolation end, and the second coupling connection line is connected to the middle section of the third coupling connection line.

[0007] More preferably, the direction parallel to the microstrip transmission line is the first direction, the direction perpendicular to the first direction is the second direction, the length value direction is the first direction, the width value direction is the second direction, and the line widths of the microstrip transmission line and the microstrip coupling line are the same.

[0008] More preferably, 0<the length of the second coupled parallel lines:the length of the first coupled parallel lines<1.

[0009] More preferably, the ratio of the length of the first coupled parallel line to the length of the second coupled parallel line is preferably (5-7):1.

[0010] More preferably, the microstrip transmission line is a straight line, and the microstrip coupling line is a bent line.

[0011] More preferably, the bending method of the microstrip coupling line is: the microstrip coupling line is led out from the coupling end, bent in the first direction, then bent in the second direction, then bent in the first direction, then bent in the second direction, and then bent in the first direction, and finally the third coupling connection line perpendicular to the first direction is led out, and connected to the isolation end through the third coupling connection line.

[0012] By regulating and allocating the lengths of the first coupling parallel line and the second coupling parallel line, the length of the first coupling parallel line is increased, so that most of the coupling energy is concentrated on the first coupling parallel line and transmitted to the coupling end, thereby improving the coupling degree;

[0013] At the same time, the length of the second coupled parallel line is the width of the microstrip transmission line. Due to the reduction in length, the energy obtained by the isolation end is reduced, the isolation is greatly reduced, the standing wave ratio is improved, and high directivity is achieved.

[0014] More preferably, the bottom layer of the dielectric substrate is connected to a metal grounding layer, and the metal grounding layer is used to shield the external electromagnetic interference of the coupler, enhance the mechanical stability of the coupler and help dissipate heat.

[0015] Compared with the prior art, the advantages of the present invention are:

[0016] The present invention achieves a coupling degree of about 25 dB in the 1.92 GHz to 2.08 GHz frequency band, a coupling flatness of less than 0.6 dB, and excellent directivity performance of better than 30 dB, and integrates the microstrip structure only on a dielectric substrate of 12 mm × 9.5 mm in size, thereby reducing size and cost;

[0017] In addition, by changing the length of the coupled parallel line and the spacing between the entire microstrip coupled line structure and the microstrip transmission line, the coupling degree and directivity can be controlled;

[0018] By changing the bending times, degree of bending, direction and other bending forms of the microstrip coupling line that can change the total length of the microstrip coupling line, it is possible to achieve a coupling degree without a significant deviation, but to adjust the coupling flatness so that the coupling flatness reaches an excellent standard;

[0019] By adopting a two-stage coupled parallel line structure, it combines many advantages such as high coupling degree, high directivity, high coupling flatness, miniaturization, and strong designability, which is of great significance in production practice activities in the RF field. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0021] Figure 1 It is a schematic diagram of the three-dimensional structure of a microstrip directional coupler proposed by the present invention;

[0022] Figure 2 It is a schematic diagram of the dimensions of a microstrip directional coupler proposed by the present invention;

[0023] Figure 3 This is one of the schematic diagrams of HFSS simulation results of a microstrip directional coupler proposed in the present invention;

[0024] Figure 4 This is the second schematic diagram of the HFSS simulation results of a microstrip directional coupler proposed by the present invention;

[0025] Figure 5 This is the third schematic diagram of the HFSS simulation results of a microstrip directional coupler proposed by the present invention;

[0026] Figure numerals: 1. input end; 2. through end; 3. coupling end; 4. isolation end; 5. microstrip transmission line; 6. microstrip coupling line; 7. dielectric substrate; 8. metal ground layer; 9. first coupling parallel line; 10. second coupling parallel line; 11. first coupling connecting line; 12. second coupling connecting line; 13. third coupling connecting line. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific embodiments. It should also be noted that, unless otherwise clearly specified and limited, terms such as: setting, installing, connecting, and connecting should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the connection of the internal lines of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] like Figure 1 As shown, the present invention proposes a microstrip directional coupler, comprising a microstrip transmission line 5, a microstrip coupling line 6 and a dielectric substrate 7, wherein the microstrip transmission line 5 and the microstrip coupling line 6 are both printed on the dielectric substrate 7, one end of the microstrip transmission line 5 is an input end 1, the other end of the microstrip transmission line 5 is a through end 2, the end of the microstrip coupling line 6 on the same side as the input end 1 is a coupling end 3, and the end of the microstrip coupling line 6 on the same side as the through end 2 is an isolation end 4.

[0029] The microstrip coupling line 6 includes a first coupling connection line 11, a first coupling parallel line 9, a second coupling connection line 12, a third coupling connection line 13 and a second coupling parallel line 10 connected in sequence, the first coupling parallel line 9 is connected to a side of the first coupling connection line 11 away from the coupling end 3, the second coupling parallel line 10 is connected to a side of the third coupling connection line 13 away from the isolation end 4, the second coupling parallel line 10 and the first coupling parallel line 9 are located on the same straight line, and the second coupling connection line 12 is connected to the middle section of the third coupling connection line 13.

[0030] like Figure 1 As shown, the microstrip coupling line 6 is led out from the coupling end 3, first bent once in the first direction, then bent in the second direction, then bent in the first direction, then bent in the second direction, and then bent in the first direction, and finally a third coupling connection line 13 perpendicular to the first direction is led out, and connected to the isolation end 4 through the third coupling connection line 13. The total length of the microstrip coupling line 6 is increased by bending, and a microstrip coupling line 6 perpendicular to the microstrip transmission line 5 (i.e., the third coupling connection line 13 and the second coupling parallel line 10) and a microstrip coupling line 6 parallel to the microstrip transmission line 5 (i.e., the first coupling parallel line 9) are led out.

[0031] By setting the first coupling parallel line 9 and the second coupling parallel line 10, the coupling energy obtained by the microstrip coupling line 6 from the microstrip transmission line 5 can be regulated and distributed according to the lengths of the first coupling parallel line 9 and the second coupling parallel line 10, thereby realizing separate control of coupling degree and isolation degree.

[0032] In one embodiment, the length of the first coupling parallel line 9 is greater than that of the second coupling parallel line. By increasing the length of the first coupling parallel line 9, the coupling energy is concentrated on the first coupling parallel line 9 and transmitted to the coupling end 3, thereby improving the coupling degree. The length of the second coupling parallel line 10 is the line width of the microstrip transmission line 5. Due to the reduction in length, the energy obtained by the isolation end 4 is reduced, the isolation degree is greatly reduced, and the standing wave ratio is improved.

[0033] The directivity is defined as the coupling degree minus the isolation degree. Therefore, this embodiment can improve the coupling degree and reduce the isolation degree, thereby achieving high directivity.

[0034] Without changing the structure and corresponding length of the first coupled parallel line 9 and the second coupled parallel line 10, by changing the number of bends, the degree of bends, the direction of bends and other methods that can change the total length of the microstrip coupling line 6, it is possible to achieve no significant deviation in the coupling degree, but to make an adjustment in the coupling flatness so that the coupling flatness reaches an excellent standard.

[0035] By changing the height of the entire microstrip coupling line 6 structure and the spacing between the microstrip transmission line 5 and the entire microstrip coupling line 6 structure, the coupling degree can be adjusted. The shorter the distance, the higher the coupling degree, and the longer the distance, the lower the coupling degree.

[0036] When only the spacing is adjusted, only the coupling degree of the coupler is greatly affected, and other performances remain basically unchanged. Therefore, while ensuring that the spacing remains unchanged, the length of the microstrip coupling line 6 can be increased by different bending methods to compensate for the reduction in the height of the entire microstrip coupling line 6. In this way, a certain total length of the microstrip coupling line 6 can be guaranteed, so that the coupler still has the advantages of high directivity, high coupling degree, and high coupling flatness, while reducing the size of the entire dielectric substrate 7 and achieving miniaturization.

[0037] By bending the microstrip coupling line 6 , two coupling parallel lines (a first coupling parallel line 9 and a second coupling parallel line 10 ) parallel to the microstrip transmission line 5 are realized.

[0038] like Figure 1 As shown, the present invention increases the microstrip distance from the coupling end 3 to the isolation end 4 by bending the microstrip coupling line 6, adjusts the coupling effect, and can adjust the coupling flatness. The isolation end 4 leads out the longitudinal third coupling connecting line 13 and the second coupling parallel line 10 to couple with the transverse microstrip transmission line 5, and the standing wave ratio between the isolation end 4 and the coupling end 3 can be adjusted.

[0039] By this bending method, a section of the traditional microstrip line that is parallel coupled to the transverse microstrip transmission line 5 is divided into two sections of coupled parallel lines (a first coupled parallel line 9 and a second coupled parallel line 10), which can change the coupling strength between the coupling end 3 and the isolation end 4, thereby changing the coupling degree and the isolation degree, thereby greatly improving the directivity.

[0040] In addition, the height of the entire microstrip coupling line 6 structure can be adjusted. When the microstrip coupling line 6 structure is closer to the lateral microstrip transmission line 5, the coupling strength is stronger, and the farther away, the weaker the coupling strength. The degree of coupling can be significantly adjusted.

[0041] Embodiment 1:

[0042] like Figure 22 is a schematic diagram of the actual size of a microstrip directional coupler model proposed in an embodiment of the present invention, and illustrates the final physical size in mm. The size of the entire microstrip directional coupler is 12 mm × 9.5 mm.

[0043] The model of the microstrip directional coupler proposed in the present invention is composed of a dielectric substrate 7, a microstrip coupling line 6 printed on the upper surface of the dielectric substrate 7, a microstrip transmission line 5 and a metal grounding layer 8 on the lower surface.

[0044] Specifically, the dielectric substrate 7 is a rectangular solid dielectric.

[0045] This embodiment uses RogersRO4350 dielectric plate material, whose relative dielectric constant ε r =3.58, the length and width of the dielectric substrate 7 are 12mm and 9.5mm respectively, the thickness is 0.508mm, the line widths of the microstrip transmission line 5 and the microstrip coupling line 6 are both 1.1mm, and the structure of the present invention is resistant to high power by setting the line widths of the microstrip transmission line 5 and the microstrip coupling line 6. The upper and lower layers of the dielectric substrate 7 are closely attached to the microstrip transmission line 5, the microstrip coupling line 6 and the metal grounding layer 8 respectively.

[0046] like Figures 3 to 5 As shown in the figure, the simulation results obtained by simulating the model using 3D electromagnetic simulation software HFSS are shown in the figure. Figure 3 is the S parameter characteristic curve, Figure 4 is the directional curve, Figure 5 It is the VSWR standing wave ratio curve.

[0047] The technical indicators of directional couplers include: operating frequency band, insertion loss, coupling, directivity and isolation. A directional coupler is a microwave component, and any of its operating characteristics are related to its operating frequency. Only when the operating frequency is determined can a directional coupler that meets the requirements within the operating frequency band be designed.

[0048] Among them, insertion loss mainly refers to the signal power ratio between the main output end and the main input end, including coupling loss and heat loss of the conductor medium, and of course also includes reflection loss and radiation loss under certain conditions.

[0049] Coupling degree: describes the proportional relationship between the coupled port and the input port signal, usually expressed in dB. The greater the coupling degree, the smaller the output power of the coupled port. The size of the coupling degree is determined by the purpose of the directional coupler.

[0050] Isolation: describes the relationship between the main input port and the coupled branch isolation port. Ideally, there is no signal output at the isolation port and the isolation is infinite.

[0051] Directivity: describes the proportional relationship between the coupled port and the isolated port of the coupling branch. Directivity is the difference between coupling and isolation.

[0052] As a four-port network, the directional coupler defines the power of the signal input port as P1, the power of the through port as P2, the power of the coupled port as P3, and the power of the isolated port as P4.

[0053] Insertion loss, coupling, isolation, and directivity are represented by T (dB), C (dB), I (dB), and D (dB) respectively. Then the calculation of the four major parameters of the directional coupler can be expressed as:

[0054]

[0055]

[0056]

[0057]

[0058] Where P 1 , P 2 , P 3 , P 4 are the power of the input port 1, the through port 2, the coupled port 3, and the isolated port 4, respectively. 11 Indicates the ratio of the signal reflected from input port 1 to input port 1, which is the return loss, S 21 It represents the insertion loss of the signal from the through port 2 to the input port 1, S 31 Indicates the coupling degree of the signal from input terminal 1 to coupling terminal 3, S 41 It represents the isolation degree of the signal from the input terminal 1 to the isolation terminal 4. It is another equivalent mathematical symbol for the insertion loss T (dB), coupling degree C (dB), and isolation degree I (dB), and is often used in circuit design and simulation.

[0059] Depend on Figure 3 It can be seen that the microstrip directional coupler described in the present invention has a coupling degree of about 25 dB in the frequency band of 1.92 GHz to 2.08 GHz, a flatness of less than 0.6 dB, and an isolation degree better than 55 dB.

[0060] Depend on Figure 4 It can be seen that the directivity of the microstrip directional coupler of the present invention in the frequency band of 1.92 GHz to 2.08 GHz is better than 30 dB, and has the characteristic of high directivity.

[0061] Depend on Figure 5It can be seen that the standing wave ratio of the coupling end 3 and the isolation end 4 of the microstrip directional coupler described in the present invention is in the range of 1.6 to 1.65 in the frequency band of 1.92 GHz to 2.08 GHz, and the standing wave ratio of the input end 1 and the through end 2 is in the range of 1.1 to 1.15, which meets the requirements of industrial technical indicators.

[0062] The present invention will be of great significance in the practical application of radio frequency front end due to its advantages such as high directivity, small size, high coupling flatness, etc.

[0063] In some embodiments, the end of the microstrip coupling line 6 on the same side as the through end 2 is the coupling end 3, the end of the microstrip coupling line 6 on the same side as the input end 1 is the isolation end 4, and the coupling end 3 is sequentially connected to the first coupling connection line 11, the first coupling parallel line 9, the second coupling connection line 12, the third coupling connection line 13 and the isolation end 4.

[0064] Although the present disclosure has been shown and described with reference to specific exemplary embodiments of the present disclosure, it should be understood by those skilled in the art that various changes in form and details may be made to the present disclosure without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents. Therefore, the scope of the present disclosure should not be limited to the above-mentioned embodiments, but should be determined not only by the appended claims, but also by the equivalents of the appended claims.

Claims

1. A microstrip directional coupler, characterized in that: It comprises a dielectric substrate and a microstrip transmission line and a microstrip coupling line printed on the dielectric substrate, wherein the microstrip transmission line has an input end and a through end, the microstrip coupling line has a coupling end and an isolation end, the microstrip coupling line is folded and arranged on the dielectric substrate, and the microstrip coupling line has a first coupling parallel line and a second coupling parallel line located in the same straight line; The microstrip coupling line is composed of a first coupling connection line, the first coupling parallel line, the second coupling connection line, a third coupling connection line and the second coupling parallel line connected in sequence, the first coupling parallel line is connected to a side of the first coupling connection line away from the coupling end, the second coupling parallel line is connected to a side of the third coupling connection line away from the isolation end, and the second coupling connection line is connected to a middle section of the third coupling connection line.

2. A microstrip directional coupler according to claim 1, characterized in that: The direction parallel to the microstrip transmission line is the first direction, the direction perpendicular to the first direction is the second direction, the length direction of the microstrip transmission line is the first direction, the width direction of the microstrip transmission line is the second direction, and the line widths of the microstrip transmission line and the microstrip coupling line are the same.

3. A microstrip directional coupler according to claim 2, characterized in that: 0<the length of the second coupled parallel lines: the length of the first coupled parallel lines<1.

4. A microstrip directional coupler according to claim 3, characterized in that: The ratio of the length of the first coupling parallel line to the length of the second coupling parallel line is (5-7):

1.

5. The microstrip directional coupler according to claim 1, characterized in that: The microstrip transmission line is a straight line, and the microstrip coupling line is a bent line.

6. The microstrip directional coupler according to claim 2, characterized in that: The bending method of the microstrip coupling line is as follows: the microstrip coupling line is led out from the coupling end, bent in the first direction, then bent in the second direction, then bent in the first direction, then bent in the second direction, then bent in the first direction, and finally the third coupling connection line perpendicular to the first direction is led out, and connected to the isolation end through the third coupling connection line.

7. The microstrip directional coupler according to claim 1, characterized in that: The bottom layer of the dielectric substrate is connected to a metal grounding layer, and the metal grounding layer is used to shield the external electromagnetic interference of the coupler, enhance the mechanical stability of the coupler and help heat dissipation.

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