Strip line short section directional coupler

Abstract

The invention relates to a strip line short section directional coupler, relates to the technical field of communication, and is used for improving the directivity of the strip line short section directional coupler. The strip line short section directional coupler comprises a radio frequency main line, a strip line coupling circuit and a capacitance compensation circuit, the strip line coupling circuit comprises a coupling line, two beveled edge corners and two vertical lead-out strip lines, two ends of the coupling line are respectively connected with one end of one beveled edge corner, and the other end of the beveled edge corner is connected with one end of one vertical lead-out strip line; the radio frequency main line comprises an input end, a coupling main line and an output end, and the coupling main line and the coupling line are coplanar and parallel to each other; the capacitance compensation circuit comprises a metal cylinder group which is connected with an upper-layer ground wire and a lower-layer ground wire of the strip line coupling circuit, and the metal cylinder group is located on the outer side of the bevel cut edges of the two bevel cut edge corners at the two ends of the coupling line and is in bilateral symmetry about the perpendicular bisector.

Description

Technical Field

[0001] The invention relates to the field of communication technology, and in particular to a stripline short section directional coupler. Background Art

[0002] With the continuous development of communication and communication countermeasure technology, the operating frequency bands of modern communication systems and communication countermeasure systems continue to expand, and cross-band operation has become the norm. In the RF broadband transmitter system, the directional coupler is an important component. It can complete the detection of output power and standing wave, realize effective control of system output power, and can also accurately evaluate the system working efficiency by accurately detecting the power size.

[0003] For directional couplers, in the absence of reflected signals, the ratio of the signal power of the forward coupled output to the signal power of the reverse coupled output is the directivity of the coupler. The higher the directivity of the coupler, the more accurate the detection of the output RF power, thereby reducing the problem of false alarm of reflected power or uneven detection of forward and reverse power due to standing waves at the output end. Generally speaking, when the transmitter works alone, the coupler only needs a directivity of 20dB to meet the requirements of engineering use. However, in antenna array systems with a large number of elements, due to the large mutual coupling between the elements, in order to ensure that the transmitter / receiver components can work normally, in broadband systems without isolators inside the transceiver components, the coupler needs to have a directivity of at least 23dB. Some systems even require the coupler of the transceiver component to have a directivity index of more than 27dB.

[0004] In actual engineering applications, medium and large power broadband miniaturized couplers are generally used in high frequency and very high frequency bands because of their long wavelengths. In order to achieve miniaturization, transformers or transmission line coupling methods are generally used. In the very high frequency / ultra-high frequency / L band / S band, stripline couplers are generally used, mainly because of their easy processing, good indicator consistency, convenient production and debugging, and small structural size.

[0005] In order to improve the coupling directivity index, it is necessary to make the odd-mode phase velocity and the even-mode phase velocity of the coupled stripline as equal as possible. However, due to factors such as the consistency of printed circuit board materials and processing, coupling spacing, coupling line length, and a certain mismatch in impedance transition between different line segments, stripline coupling will inevitably lead to deviations between the odd-mode phase velocity and the even-mode phase velocity. The final result is poor coupling directivity.

[0006] If the coupler's directivity is not high, or if it causes a large ripple in the coupling band when working in a system with a large standing wave, the detection voltages at different frequencies will differ greatly. The power values ​​output by the amplifier at different frequencies within the working frequency band differ greatly, which will affect the reliability of the amplifier. For example, if some frequencies are the "troughs" of coupling, the coupling signal is smaller than the normal value at this time. The amplifier detection and control unit mistakenly believes that the output power is too small at this time, and will continue to increase the power output to a relatively high power level and maintain it, resulting in reduced reliability of the amplifier. In severe cases, the output power will exceed the power capacity of the external device of the amplifier, causing damage to the external device and affecting the reliability of the system. Moreover, if the power output increases beyond the rated power of the amplifier design, the power tube will work at the maximum saturated output power for a long time, and its life will be shortened and it is very easy to burn out on the spot. For example, some frequency points are coupled "peaks". At this time, the coupled signal is larger than the normal value. The power amplifier detection and control unit mistakenly believes that the output power is too large at this time, and will continue to reduce the power output to a low power level and maintain it, causing the output power of the power amplifier to be lower than the actual required value and fail to meet the system requirements. Summary of the invention

[0007] In view of the above analysis, an embodiment of the present invention aims to provide a stripline short section directional coupler to improve the directivity of the stripline short section coupler.

[0008] An embodiment of the present invention provides a stripline short section directional coupler, comprising:

[0009] RF main line, stripline coupling circuit and capacitance compensation circuit;

[0010] The stripline coupling circuit comprises a coupling line, two chamfered corners and two vertically derived striplines, wherein two ends of the coupling line are respectively connected to one end of one of the chamfered corners, and the other end of the chamfered corner is connected to one end of one of the vertically derived striplines;

[0011] The radio frequency main line comprises an input end, a coupling main line and an output end, and the coupling main line and the coupling line are in the same plane and parallel to each other;

[0012] The capacitance compensation circuit includes a group of metal cylinders connecting the upper ground line and the lower ground line of the stripline coupling circuit. The group of metal cylinders is located outside the beveled edges of the two beveled edge corners at both ends of the coupling line and is symmetrical about the midline.

[0013] Based on the further improvement of the above-mentioned stripline short section directional coupler, the stripline coupling circuit includes a forward stripline coupling circuit and a reverse stripline coupling circuit, the forward stripline coupling circuit and the reverse stripline coupling circuit are located on both sides of the radio frequency main line and the forward stripline coupling circuit and the reverse stripline coupling circuit share the coupling main line.

[0014] Based on the further improvement of the above-mentioned stripline short-section directional coupler, the metal cylinder group includes n metal cylinders close to the input end and n metal cylinders close to the output end, and the n metal cylinders close to the input end and the n metal cylinders close to the output end are placed symmetrically with respect to the midpoint, and n is a positive integer.

[0015] Based on the further improvement of the above-mentioned stripline short section directional coupler, the center line of n metal cylinders located outside the beveled edge of one of the beveled edge corners is a straight line parallel to the beveled edge, and n is a positive integer.

[0016] Based on the further improvement of the above-mentioned stripline short section directional coupler, the length range of the central connection line is:

[0017] k1*W, wherein k1∈(0.85,0.95), and W is the width of the coupling line.

[0018] Based on the further improvement of the above-mentioned stripline short section directional coupler, the value range of the outer diameter D of a single metal cylinder is:

[0019] k2*W, wherein k2∈(0.15,0.25), and W is the width of the coupling line.

[0020] Based on the further improvement of the above-mentioned stripline short section directional coupler, the value range of the distance between the central connecting line and the bevel cut edge is:

[0021] k3*W, wherein k3∈(0.2,0.3), and W is the width of the coupling line.

[0022] Based on the further improvement of the above-mentioned stripline short section directional coupler, the center distance between two adjacent metal cylinders in the metal cylinder group has a value range of:

[0023] k4*D, wherein k4∈(1.2,2), and D is the outer diameter of a single metal cylinder.

[0024] Based on the further improvement of the above-mentioned stripline short section directional coupler, the range of the distance in the vertical direction between the center of the metal cylinder closest to the coupling main line in the metal cylinder group and the horizontal edge of the coupling line close to the coupling main line is:

[0025] k5*D, wherein k5∈(0.5,0.75), and D is the outer diameter of a single metal cylinder.

[0026] Based on the further improvement of the above stripline short section directional coupler, the metal cylinder group in the forward stripline coupling circuit and the metal cylinder group in the reverse stripline coupling circuit are placed symmetrically up and down along the horizontal center line of the coupling main line.

[0027] Based on the further improvement of the above-mentioned stripline short section directional coupler, the metal cylinder group is any one of the following:

[0028] Hollow internal vias or pads, solid internal vias or pads.

[0029] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0030] 1. The present invention achieves the capacitance compensation effect of the short stub line by symmetrically adding a group of metal cylinders on the outside of the chamfered corner between the coupling line and the vertically derived strip line, thereby improving the consistency of the odd-mode impedance and the even-mode impedance, thereby improving the directionality of the strip line coupling.

[0031] 2. The capacitance compensation method of the grounded metal cylinder adopted in the present invention not only has the effect of matching the capacitance to the ground by the short branch line, but also can effectively reduce the electromagnetic components of the RF signals at the input and output ends of the RF main line radiated to the coupling end through space, and has the function of blocking the fluctuation of the positive and reverse coupling components caused by dielectric coupling, thereby playing an electromagnetic shielding effect and preventing the reduction of coupling directionality caused by this.

[0032] 3. The present invention can effectively enhance the mechanical strength and thermal conductivity of the multilayer printed circuit board by adopting this metal cylinder group method, and has little influence on the coupling index under high and low temperature and vibration conditions.

[0033] 4. The present invention achieves capacitance compensation effect of short branch line by adding a row of metal cylinders connecting the upper ground wire and the lower ground wire on the outside of the beveled edge corner. This compensation method can set parameters such as the number of metal cylinders, the outer diameter of the cylinder, the distance of the cylinder from the cut edge, the spacing between the centers of the cylinders, and the spacing from the center of the first metal cylinder to the edge of the coupling line as variables. The ideal optimization result can be achieved with more optimization parameters, and the coupling directionality index can be improved without affecting other technical indicators.

[0034] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components;

[0036] Figure 1a and Figure 1b The internal structure schematic diagram and the planar structure schematic diagram of the stripline stub directional coupler according to the embodiment of the present invention are respectively shown.

[0037] Figure 2 A simulation diagram of the directivity improvement effect of the stripline short section directional coupler according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0038] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0039] Figure 1a and Figure 1b The internal structure schematic diagram and the planar structure schematic diagram of the stripline short section directional coupler according to the embodiment of the present invention are respectively shown. Figure 1a and Figure 1b The embodiments of the present invention are described.

[0040] like Figure 1a and Figure 1bAs shown, the stripline short section directional coupler includes a radio frequency main line, a forward coupling circuit, a reverse coupling circuit and the compensation circuit of the present invention. The forward stripline coupling circuit and the reverse stripline coupling circuit are respectively located on both sides of the radio frequency main line. The radio frequency main line includes: an input end, a coupling main line and an output end. The structural forms of the input end and the output end both include a stripline and a gradient line with a characteristic impedance of 50 ohms. The structural form of the connection between the input end and the output end and the coupling main line adopts a gradient form. The coupling main line is generally a stripline with a characteristic impedance of 50 ohms and a dielectric thickness of h. The stripline coupling main line adopts a three-layer printed circuit board, the coupling main line is located in the middle layer (midlayer layer), and the other two layers are the upper ground line (toper layer) and the lower ground line (bottomlayer layer). The input end, the coupling main line and the output end are in a sequential series relationship to form a radio frequency main line path. This arrangement of the forward and reverse stripline coupling circuits sharing the coupling main line effectively reduces the coupling length.

[0041] The forward stripline coupling circuit includes a forward coupling line, two left and right beveled corners, and two vertically derived striplines. The two ends of the forward coupling line are each connected to the first end of a beveled corner, and the second ends of the left and right corner bevels are each connected to the first end of the vertically derived stripline. The forward coupling line is set in the middle layer of the three-layer printed circuit board, and is 0.5h away from the upper ground line and the lower ground line. The forward coupling line is parallel to the grounded metal surface of the upper ground line and the grounded metal surface of the lower ground line to form a stripline structure, and the forward coupling line is in the same plane as the coupling main line in the RF main line and runs parallel. The stripline short-section directional coupler uses a lower sideband short-section coupling far away from the forward coupling line (line length L1, center frequency f.), and generally requires the operating frequency f≤1 / 10*f. , such as Figure 1b As shown, the length of the coupling main line L2 needs to be greater than the length of the forward coupling line L1. In this embodiment, the characteristic impedance of the forward coupling line and the vertical lead-out strip line is 50 ohms.

[0042] The vertical stripline includes two parts: one is the stripline perpendicular to the forward coupling line, and the other is the stripline to microstrip structure. In general engineering applications, the left vertical stripline in the forward stripline coupling circuit is connected to the microstrip line and the coupling adjustment circuit, and a coupling signal with a constant coupling degree within the working frequency band is obtained through the coupling adjustment network. The right vertical stripline is connected to the external circuit, generally connected to the microstrip line and then connected to a 50 ohm load resistor to the ground.

[0043] The beveled corner is the connecting part between the forward coupling line and the vertically derived strip line. Its original shape is a rectangle. According to microwave transmission theory, when RF and microwave signals are transmitted through a right-angle connection, beveled edges need to be performed on the outside of the corner. This can effectively reduce transmission reflections at the transition point and obtain excellent impedance transition matching effects.

[0044] Place n (usually 2 to 7) metal cylinder groups connecting the upper and lower ground wires of the strip line in parallel outside the two chamfered corners. The n metal cylinder groups are the compensation circuit (also called forward capacitance compensation circuit) in the embodiment of the present invention. These metal cylinder groups can be implemented by vias or pads. Figure 1b In the example, the metal cylinders are placed symmetrically about the perpendicular median Y axis. The metal cylinder group includes n metal cylinder groups on the left side of the forward coupling line and n metal cylinder groups on the right side of the forward coupling line, for a total of 2n metal cylinders. In this embodiment, the n metal cylinders have the same shape.

[0045] The reverse stripline coupling circuit includes a reverse coupling line, two left and right beveled corners, and two vertically derived striplines. The two ends of the reverse coupling line are each connected to the first end of a beveled corner, and the second ends of the left and right corner bevels are each connected to the first end of the vertically derived stripline. The reverse coupling line is set in the middle layer of the three-layer printed circuit board, and is 0.5h away from the upper ground line and the lower ground line. The reverse coupling line is parallel to the grounded metal surface of the upper ground line and the grounded metal surface of the lower ground line to form a stripline structure, and the reverse coupling line is in the same plane as the coupling main line in the RF main line and runs parallel. The stripline short section directional coupler uses a lower sideband short coupling far away from the reverse coupling line (line length L1, center frequency f.), and generally requires the operating frequency f≤1 / 10*f. , such as Figure 1b As shown, the length of the coupling main line L2 needs to be greater than the length of the reverse coupling line L1. In this embodiment, the characteristic impedance of the reverse coupling line and the vertical lead-out strip line is 50 ohms.

[0046] The vertical stripline includes two parts: one is the stripline perpendicular to the reverse coupling line, and the other is the stripline to microstrip structure. In general engineering applications, the vertical stripline on the right side of the reverse stripline coupling circuit is connected to the microstrip line and the coupling adjustment circuit, and a coupling signal with a constant coupling degree within the working frequency band is obtained through the coupling adjustment network. The vertical stripline on the left side is connected to the external circuit, generally connected to the microstrip line and then connected to a 50 ohm load resistor to the ground.

[0047] The beveled corner is the connecting part of the reverse coupling line and the vertical derived strip line. The original shape is a rectangle. According to the microwave transmission theory, the beveled corner is processed on the outside, which can effectively reduce the transmission reflection at the transition point and obtain excellent impedance transition matching effect.

[0048] Place n (usually 2 to 7) metal cylinders connecting the upper and lower ground wires of the strip line in parallel outside the two chamfered corners. The n metal cylinders are the compensation circuit (also called reverse capacitance compensation circuit) in the embodiment of the present invention. These metal cylinders are generally implemented by vias or pads. Figure 1bIn the example, the metal cylinders are placed symmetrically about the perpendicular median Y axis. The metal cylinder group includes n metal cylinders on the left side of the reverse coupling line and n metal cylinders on the right side of the reverse coupling line, for a total of 2n metal cylinders. In this embodiment, the n metal cylinders have the same shape.

[0049] In some embodiments, the metal cylinder in this embodiment can be either a via hole or pad with a hollow interior, or a solid via hole or pad. When the metal cylinder is hollow, the wall thickness of the metal cylinder is greater than the skin depth of the lowest operating frequency.

[0050] In some embodiments, a center line connecting the n metal cylinders located outside the beveled edge of the beveled edge corner is a straight line, and the center line is parallel to the beveled edge of the beveled edge corner.

[0051] In some embodiments, the center line of the n metal cylinders located outside the beveled edge of the beveled edge corner is a straight line, and the length L of the center line ranges from: k1*W, where k1∈(0.85,0.95), and W is the width of the forward coupling line / reverse coupling line ( Figure 1b W 50s ).

[0052] In some embodiments, the outer diameter D of a single metal cylinder has a value range of: k2*W, where k2∈(0.15,0.25), and W is the width of the forward coupling line / reverse coupling line ( Figure 1b W 50s ).

[0053] In some embodiments, the distance d1 between the center line of the metal cylinder group and the beveled edge of the beveled edge corner has a value range of: k3*W, where k3∈(0.2,0.3), and W is the width of the forward coupling line / reverse coupling line ( Figure 1b W 50s ).

[0054] In some embodiments, the center distance d2 between two metal cylinders in the metal cylinder group has a value range of: k4*D, where k4∈(1.2,2) and D is the outer diameter of a single metal cylinder.

[0055] In some embodiments, the vertical distance d3 between the center of the metal cylinder closest to the coupling main line in the metal cylinder group and the horizontal edge of the forward coupling line / reverse coupling line close to the coupling main line is in the range of: k5*D, where k5∈(0.5,0.75), and D is the outer diameter of a single metal cylinder.

[0056] In some embodiments, Figure 1bAs shown, the metal cylinder group below the horizontal center line of the X axis is symmetrical about the vertical center line Y axis. If it is dual directional coupling, the reverse coupling circuit and the reverse compensation circuit are the forward coupling circuit and the forward compensation circuit, which are symmetrical up and down along the horizontal center line of the X axis of the coupling main line and then mirrored left and right along the vertical center line Y axis, including the metal cylinder group on the left side of the reverse coupling line and the metal cylinder group on the right side of the reverse coupling line.

[0057] Figure 2 The figure shows the simulation diagram of the directivity improvement effect of the stripline short section directional coupler according to the embodiment of the present invention. Taking a certain 100MHz to 600MHz dual directional coupler as an example, Figure 2 It can be seen that the forward coupling degree dB(S(3,1)) when this patent is not adopted is shown by the dotted line in the figure, and the reverse coupling degree dB(S(3,2)) is shown by the dotted line in the figure. Its directivity is dB(S(3,1))-dB(S(3,2)), which is 16.82dB at 100MHz and 16.45dB at 600MHz. After adopting this patent, the forward coupling degree dB(S(3,1)) is shown by the solid line in the figure, and the reverse coupling degree dB(S(3,2)) is shown by the dotted line in the figure. At 100MHz, the directivity dB(S(3,1))-dB(S(3,2)) is 28.98dB, which is an increase of 12.16dB, and at 600MHz, the directivity is 28.29dB, which is an increase of 11.84dB. From the above data, it can be seen that the coupling directivity is significantly improved after adopting this patent.

[0058] Compared with the prior art, the embodiments of the present invention can achieve at least the following beneficial effects:

[0059] 1. The present invention achieves the capacitance compensation effect of the short stub line by symmetrically adding a group of metal cylinders on the outside of the chamfered corner between the coupling line and the vertically derived strip line, thereby improving the consistency of the odd-mode impedance and the even-mode impedance, thereby improving the directionality of the strip line coupling.

[0060] 2. The capacitance compensation method of the grounded metal cylinder adopted in the present invention has the effect of matching the capacitance of the short branch line to the ground, and can also effectively reduce the electromagnetic components of the RF signals at the input and output ends of the RF main line radiated to the coupling end through space, and has the function of blocking the fluctuation of the positive and reverse coupling components caused by dielectric coupling, thereby achieving an electromagnetic shielding effect and preventing the reduction of coupling directionality caused by this.

[0061] 3. The present invention can effectively enhance the mechanical strength and thermal conductivity of the multilayer printed circuit board by adopting this metal cylinder group method, and has little influence on the coupling index under high and low temperature and vibration conditions.

[0062] 4. The present invention achieves capacitance compensation effect of short branch line by adding a row of metal cylinders connecting the upper ground wire and the lower ground wire on the outside of the beveled edge corner. This compensation method can set parameters such as the number of metal cylinders, the outer diameter of the cylinder, the distance of the cylinder from the cut edge, the spacing between the centers of the cylinders, and the spacing from the center of the first metal cylinder to the edge of the coupling line as variables. The ideal optimization result can be achieved with more optimization parameters, and the coupling directionality index can be improved without affecting other technical indicators.

[0063] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A stripline short section directional coupler, characterized in that: It includes a radio frequency main line, a stripline coupling circuit and a capacitance compensation circuit; The stripline coupling circuit comprises a coupling line, two chamfered corners and two vertically derived striplines, wherein two ends of the coupling line are respectively connected to one end of one of the chamfered corners, and the other end of the chamfered corner is connected to one end of one of the vertically derived striplines; The radio frequency main line comprises an input end, a coupling main line and an output end, and the coupling main line and the coupling line are in the same plane and parallel to each other; The capacitance compensation circuit includes a group of metal cylinders connecting the upper ground line and the lower ground line of the stripline coupling circuit. The group of metal cylinders is located outside the beveled edges of the two beveled edge corners at both ends of the coupling line and is symmetrical about the midline.

2. The stripline short section directional coupler according to claim 1, characterized in that: The stripline coupling circuit includes a forward stripline coupling circuit and a reverse stripline coupling circuit, wherein the forward stripline coupling circuit and the reverse stripline coupling circuit are located at two sides of the radio frequency main line and the forward stripline coupling circuit and the reverse stripline coupling circuit share the coupling main line.

3. The stripline short section directional coupler according to claim 1, characterized in that: The metal cylinder group includes n metal cylinders close to the input end and n metal cylinders close to the output end, the n metal cylinders close to the input end and the n metal cylinders close to the output end are placed symmetrically about the perpendicular bisector, and n is a positive integer.

4. The stripline stub directional coupler according to claim 1, characterized in that: A line connecting the centers of n metal cylinders located outside the beveled edge of a beveled edge corner is a straight line parallel to the beveled edge, and n is a positive integer.

5. The stripline stub directional coupler according to claim 4, characterized in that: The length range of the center line is: k1*W, wherein k1∈(0.85,0.95), and W is the width of the coupling line.

6. The stripline stub directional coupler according to claim 1, characterized in that: The value range of the outer diameter D of a single metal cylinder is: k2*W, wherein k2∈(0.15,0.25), and W is the width of the coupling line.

7. The stripline stub directional coupler according to claim 4, characterized in that: The value range of the distance between the center line and the bevel cut edge is: k3*W, wherein k3∈(0.2,0.3), and W is the width of the coupling line.

8. The stripline stub directional coupler according to claim 1, characterized in that: The value range of the center distance between two adjacent metal cylinders in the metal cylinder group is: k4*D, wherein k4∈(1.2,2), and D is the outer diameter of a single metal cylinder.

9. The stripline stub directional coupler according to claim 1, characterized in that: The range of the distance in the vertical direction between the center of the metal cylinder closest to the coupling main line in the metal cylinder group and the horizontal edge of the coupling line close to the coupling main line is: k5*D, wherein k5∈(0.5,0.75), and D is the outer diameter of a single metal cylinder.

10. The stripline stub directional coupler according to claim 2, characterized in that: The metal cylinder group in the forward stripline coupling circuit and the metal cylinder group in the reverse stripline coupling circuit are symmetrically placed up and down along the horizontal center line of the coupling main line.

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