A microstrip dual-band lightning protection circuit applied to Sub6G

Abstract

The present invention discloses a microstrip dual-band lightning protection circuit applied to Sub6G, which relates to the field of communication technologies. Its stub microstrip line is divided into a first stub and a second stub. The first stub connects its input microstrip line and output microstrip line; the impedances of both the input microstrip line and the output microstrip line are 50Ω; its reference ground layer includes a first ground layer and a second ground layer arranged in sequence from top to bottom; the impedance of the first stub is 75Ω, and both the input microstrip line and the output microstrip line refer to the first ground layer; the line width of the second stub is greater than that of the first stub, refers to the second ground layer, and the impedance is 75Ω; the first stub is capacitively grounded to the surface ground, and the second stub is directly connected to the surface ground; the length of the first stub is 1 / 4 of the wavelength corresponding to the center frequency of the high-frequency band among the two operating frequency bands; the total length of the first stub and the second stub is 1 / 4 of the wavelength corresponding to the frequency of the low-frequency band among the two operating frequency bands. The present invention enables the radio frequency performance of both operating frequency bands to reach the optimal state, and reduces the PCB layout space while ensuring excellent performance.

Description

Technical Field

[0001] The present invention relates to the field of communication technologies, and particularly to lightning protection measures for remote modules on the antenna side of devices such as macro base stations, pico base stations, micro base stations, and repeaters, and provides a lightning protection circuit for two operating frequency bands of sub-6G. Background Art

[0002] With the continuous development and innovation in the field of communication products, the integration of communication devices is getting higher and higher, and the applications are becoming more and more extensive. Moreover, in order to enhance the signal strength of communication devices, many communication devices are installed in open fields or on the tops of buildings, making them vulnerable to lightning damage, resulting in communication interruption and having an increasingly greater impact on human life in the information age. Therefore, in order to prevent communication devices from being damaged by lightning, most communication devices will connect lightning arresters on the transmission line between the antenna and the device to conduct the lightning pulsating current into the ground without affecting the normal transmission of radio frequency signals in communication.

[0003] The quarter-wavelength microstrip lightning arrester is a new type of lightning arrester, which is widely used in radio equipment with relatively high frequencies and relatively fixed frequency bands, such as equipment operating at 800 MHz, 900 MHz, 1.8 GHz, 2.4 GHz, etc. Its main advantages are obvious lightning protection effect and relatively high impulse current withstand. Traditional quarter-wavelength radio frequency lightning arresters have been widely used in communication radio frequency transceiver systems for many years due to their simple structure, reliability, good lightning protection effect, high power handling capacity, and maintenance-free characteristics. However, there are also some obvious disadvantages. Lightning arresters with small sizes have insufficient bandwidth; broadband lightning arresters are relatively large in size, and for devices applied to two operating frequency bands, their coverage effects are generally not ideal. Especially when the two operating frequency bands are far apart, it is difficult to ensure that the insertion loss and return loss of the two operating frequency bands can reach the optimal values. Taking the dual-band application of 900 MHz and 5.8 GHz as an example, for a traditional single-stub microstrip lightning protection circuit, a stub is made centered on the center frequency point of 3.35 GHz of the two frequency points, and the 1 / 4 wavelength corresponding to 3.35 GHz is 488 mil; the data simulation curve is as Figure 1 、 2 shown. It can be seen from the figure that the insertion loss of the two operating frequency bands reaches 2 dB, and the return loss deteriorates to -4.2 dB. Obviously, the center frequency point of 3.35 GHz cannot cover the two relatively far-apart operating frequency points, resulting in the deterioration of the operating frequency band indicators. Summary of the Invention

[0004] The present invention aims to provide a microstrip dual-band lightning protection circuit for Sub-6G, which can alleviate the above problems.

[0005] In order to alleviate the above problems, the technical solutions adopted by the present invention are as follows:

[0006] In a first aspect, the present invention provides a microstrip dual-band lightning protection circuit for Sub6G, which includes a microstrip line layer and a reference ground layer arranged in sequence from top to bottom; the microstrip line layer includes a surface ground and a T-shaped microstrip line, and the T-shaped microstrip line includes a collinear input end microstrip line and an output end microstrip line, as well as a stub microstrip line connected to the input end microstrip line and the output end microstrip line; a dielectric layer is filled between the microstrip line layer and the reference ground layer;

[0007] The stub microstrip line is divided into two segments, namely a first stub and a second stub that are joined together, and the first stub is connected to the input end microstrip line and the output end microstrip line;

[0008] The impedances of the input end microstrip line and the output end microstrip line are both 50Ω;

[0009] The reference ground layer includes a first ground layer and a second ground layer arranged in sequence from top to bottom;

[0010] The impedance of the first stub is 75Ω, and it refers to the first ground layer with both the input end microstrip line and the output end microstrip line;

[0011] The line width of the second stub is greater than that of the first stub, it refers to the second ground layer, and the impedance is 75Ω;

[0012] The first stub is capacitively grounded to the surface ground, and the end of the second stub is directly connected to the surface ground;

[0013] The length of the first stub is 1 / 4 of the wavelength corresponding to the center frequency of the high-frequency band among the two working frequency bands of Sub6G;

[0014] The total length of the first stub and the second stub is 1 / 4 of the wavelength corresponding to the center frequency of the low-frequency band among the two working frequency bands of Sub6G.

[0015] In a preferred embodiment of the present invention, the line width and the avoidance distance from the surface ground of the input end microstrip line and the output end microstrip line are calculated according to the coplanar waveguide, so that the impedances of the input end microstrip line and the output end microstrip line are both 50Ω.

[0016] In a preferred embodiment of the present invention, the line width and the avoidance distance from the surface ground of the first stub are calculated according to the coplanar waveguide, and the line width of the first stub is smaller than that of the input end microstrip line and the output end microstrip line.

[0017] In a second aspect, the present invention provides a microstrip dual-band lightning protection circuit for Sub6G. Except that the length design method of the second stub is different from that of the microstrip dual-band lightning protection circuit described in the first aspect, other structural features are exactly the same as those of the microstrip dual-band lightning protection circuit described in the first aspect;

[0018] In the microstrip dual-band lightning protection circuit described in the second aspect, the method for designing the length of the second branch is as follows:

[0019] When there are multiple resonance points between the two operating frequency points of Sub6G, the resonance points are shifted to the right by reducing the length of the second branch, so that only one resonance point remains between the two operating frequency points on the insertion loss curve, and the length of the second branch is obtained under this condition.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] The microstrip dual-band lightning protection circuit applied to Sub6G according to the present invention does not design based on the center frequency between the two frequency bands, but conducts targeted design with the two operating frequency bands as the centers respectively, so that both operating frequency bands can reach the best state, and there will be no problem of performance degradation due to the far distance between the operating frequency bands. Moreover, by adjusting the length of the second branch, the size can be made smaller, and the PCB layout space is reduced while ensuring excellent performance.

[0022] To make the above objects, features, and advantages of the present invention more obvious and understandable, specific embodiments of the present invention are hereinafter given, and detailed descriptions are made in conjunction with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 is the insertion loss simulation curve diagram of the traditional single-branch microstrip lightning protection circuit;

[0025] Figure 2 is the return loss simulation curve diagram of the traditional single-branch microstrip lightning protection circuit;

[0026] Figure 3 is the first perspective stacked structure schematic diagram of the microstrip dual-band lightning protection circuit described in Embodiment 1;

[0027] Figure 4 is the top view schematic diagram of the microstrip line layer of the microstrip dual-band lightning protection circuit described in Embodiment 1;

[0028] Figure 5 is the second perspective stacked structure schematic diagram of the microstrip dual-band lightning protection circuit described in Embodiment 1;

[0029] Figure 6 is the insertion loss simulation curve diagram of the microstrip dual-band lightning protection circuit described in Embodiment 1;

[0030] Figure 7 is the echo loss simulation curve of the microstrip dual - band lightning protection circuit described in Embodiment 1;

[0031] Figure 8 is the insertion loss simulation curve of the microstrip dual - band lightning protection circuit after optimizing the size in Embodiment 2;

[0032] Figure 9 is the echo loss simulation curve of the microstrip dual - band lightning protection circuit after optimizing the size in Embodiment 2;

[0033] In the figure: 1 - microstrip line layer, 2 - input - end microstrip line, 3 - output - end microstrip line, 4 - first branch, 5 - second branch, 6 - surface ground, 7 - dielectric layer, 8 - first ground layer, 9 - second ground layer. Detailed implementation manners

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0035] Embodiment 1

[0036] Please refer to Figures 3 to 5 , a microstrip dual - band lightning protection circuit applied to Sub6G disclosed in this embodiment includes a microstrip line layer 1 and a reference ground layer arranged successively from top to bottom; the microstrip line layer 1 includes a surface ground 6 and a T - shaped microstrip line. The T - shaped microstrip line includes a collinear input - end microstrip line 2 and an output - end microstrip line 3, and a branch microstrip line connecting the input - end microstrip line 2 and the output - end microstrip line 3; a dielectric layer 7 is filled between the microstrip line layer 1 and the reference ground layer.

[0037] In this embodiment, the center frequency of the high - frequency band in the two working frequency bands of Sub6G is 5.8 GHz, and the center frequency of the low - frequency band is 900 MHz.

[0038] In this embodiment, the type of the dielectric layer 7 is selected as FR4, IT - 180A, the dielectric constant DK is 4.3, and the loss tangent DF is 0.02. The thickness of the dielectric layer 7 between the microstrip line layer 1 and the first ground layer 8 is 10 mil, the thickness of the dielectric layer 7 between the first ground layer 8 and the second ground layer 9 is 30 mil; the thickness of the microstrip line layer 1 is 2 mil, the thickness of the first ground layer 8 is 1.2 mil, and the thickness of the second ground layer 9 is 2 mil.

[0039] In this embodiment, the stub microstrip line is divided into two sections, namely the first stub 4 and the second stub 5 that are connected together. The first stub 4 is connected to the input microstrip line 2 and the output microstrip line 3. The reference ground layer includes a first ground layer 8 and a second ground layer 9 arranged in sequence from top to bottom. The first stub 4 is capacitively grounded to the surface ground 6, and the end of the second stub 5 is directly connected to the surface ground 6.

[0040] In this embodiment, the line widths of the input microstrip line 2 and the output microstrip line 3 are both 19.25 mil. Referring to the first ground layer 8, the impedance of both is 50 ohms.

[0041] In this embodiment, the length of the first stub 4 is 1 / 4 of the wavelength corresponding to the center frequency of the high-frequency band in the two operating frequency bands of Sub6G, that is, 291 mil. The width of the first stub 4 is 8.9 mil. Referring to the first ground layer 8, the impedance is 75 ohms;

[0042] In this embodiment, the line width of the second stub 5 is greater than that of the first stub 4, which is 36.2 mil.

[0043] The total length of the first stub 4 and the second stub 5 is 1 / 4 of the wavelength corresponding to the center frequency of the low-frequency band in the two operating frequency bands of Sub6G, that is, 1819 mil. Therefore, the length of the second stub 5 is 1819 mil - 291 mil = 1528 mil.

[0044] The second stub 5 refers to the second ground layer 9 through the layer, and the impedance is 75 ohms.

[0045] In this embodiment, by hollowing out the first ground layer 8 directly below the second stub 5, the second stub 5 refers to the second ground layer 9.

[0046] Position and size of the hollowed-out first ground layer 8:

[0047] Directly below the second stub 5, the length direction is flush with the second stub 5, and the width direction extends 10 mil to both sides on the basis of the width of the second stub 5; for example, if the length of the second stub 5 is 1528 mil and the width is 36.2 mil, then the size of the hollowed-out area of the first ground layer 8 is 1528 mil in length and 56.2 mil in width;

[0048] After hollowing out, the vacancy will be filled with the dielectric layer 7 (substrate), as Figure 5 shown. The second stub 5 will refer to the second ground layer 9, and the intermediate dielectric thickness is 10 mil + 1.2 mil + 30 mil = 41.2 mil.

[0049] It should be noted that:

[0050] We carried out the above calculations and processing according to the characteristic impedance calculation formula of the microstrip line, Z = {87 / [sqrt(Er + 1.41)]}ln[5.98H / (0.8W + T)], where W is the width of the microstrip line, T is the thickness of the copper foil of the microstrip line, H is the dielectric thickness, and Er is the dielectric constant of the PCB board material.

[0051] According to the formula, when the dielectric thickness is 10 mil, the width of the first stub with a characteristic impedance of 75 ohm is 8.9 mil; when the dielectric thickness is 41.2 mil, the width of the second stub with a characteristic impedance of 75 ohm is 36.2 mil;

[0052] Hollow out the first ground layer under the second stub. The purpose of making the second stub refer to the second ground layer is to widen the line width of the second stub 5 while ensuring the continuity of the 75-ohm impedance. To ensure the same impedance, the thicker the reference layer, the wider the line width; the relatively wider second stub 5 ensures the capacitive grounding of the first stub 4.

[0053] The data simulation curve of the microstrip dual-band lightning protection circuit described in this embodiment is as Figure 6 、 7 shown. It can be seen from the figure that both 900M and 5.8 GHz have been specifically matched, the insertion loss is 0.007 dB, the return loss reaches -27 dB, and the insertion loss and the input / output return loss reach the optimum.

[0054] Embodiment 2

[0055] The microstrip dual-band lightning protection circuit described in Embodiment 1 has made great progress in terms of radio frequency performance indicators compared with the traditional technology. However, its size can be further optimized. This embodiment gives a method for optimizing the size of the microstrip dual-band lightning protection circuit described in Embodiment 1.

[0056] When there are multiple resonance points between the two operating frequency points of Sub6G, the resonance points can be shifted to the right by reducing the length of the second stub, so that only one resonance point is retained between the two operating frequency points of the insertion loss curve. Under this condition, the length of the second stub 5 is obtained to achieve size optimization. That is, taking the 1 / 4 wavelength corresponding to the frequency higher than the center frequency of the low-frequency band as the total length of the first stub and the second stub. This frequency point and the corresponding stub length can still cover the low-frequency band in terms of radio frequency performance, and the length of the first stub corresponding to the high-frequency band remains unchanged. In this way, the total size of the two stubs is optimized, and the overall size of the microstrip circuit is optimized.

[0057] From Figure 6It can be seen that there are three resonance points between 900M and 5.8GHz. Therefore, in this embodiment, the resonance points are shifted to the right so that only one resonance point remains between the S21 curves at 900M and 5.8GHz. The measure is to reduce the stub length corresponding to 900M, that is, the total stub length. When the total stub length is reduced from 1819mil to 935mil, there is only one resonance point between 900M and 5.8GHz; 935mil is 1 / 4 wavelength of 1.8GHz. This method uses the center frequency point of 1.8G to cover the low-frequency band of 900MHz, and the length of the first stub corresponding to the high-frequency band remains unchanged. Therefore, only the length of the second stub is reduced.

[0058] The data simulation curve obtained in this embodiment is as Figure 8 , 9 shown. The insertion loss of the two working frequency bands is 0.18dB, and the standing wave is -13dB. The index has decreased slightly compared with Embodiment 1 but is still good. The length of the first stub 4 is 291mil; the length of the second stub 5 is 935mil - 291mil = 644mil; the size is reduced from the initial 1819mil to 935mil; under the condition of ensuring excellent indicators, the size has also been optimized.

[0059] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A microstrip dual-band lightning protection circuit applied to Sub6G, comprising a microstrip line layer and a reference ground layer arranged in sequence from top to bottom; The microstrip line layer includes a surface ground and microstrip lines of a T-shaped structure. The microstrip lines of the T-shaped structure include a co-linear input microstrip line and an output microstrip line, and a stub microstrip line connected to the input microstrip line and the output microstrip line. A dielectric layer is filled between the microstrip line layer and the reference ground layer. It is characterized in that The stub microstrip line is divided into two segments, namely a first stub and a second stub connected together. The first stub is connected to the input microstrip line and the output microstrip line. The impedances of both the input microstrip line and the output microstrip line are 50 Ω. The reference ground layer includes a first ground layer and a second ground layer arranged in sequence from top to bottom. The impedance of the first stub is 75 Ω, and it uses the first ground layer as the reference ground with the input microstrip line and the output microstrip line. The line width of the second stub is greater than that of the first stub. It uses the second ground layer as the reference ground and has an impedance of 75 Ω. The first stub is capacitively grounded to the surface ground, and the end of the second stub is directly connected to the surface ground. The length of the first stub is 1 / 4 of the wavelength corresponding to the center frequency of the high-frequency band among the two operating frequency bands of Sub6G. The total length of the first stub and the second stub is 1 / 4 of the wavelength corresponding to the center frequency of the low-frequency band among the two operating frequency bands of Sub6G. The input microstrip line and the output microstrip line calculate the line width and the avoidance distance from the surface ground according to the coplanar waveguide, so that the impedances of both the input microstrip line and the output microstrip line are 50 Ω. The first stub calculates the line width and the avoidance distance from the surface ground according to the coplanar waveguide, and the line width of the first stub is smaller than that of the input microstrip line and the output microstrip line.

2. A microstrip dual-band lightning protection circuit applied to Sub6G, comprising a microstrip line layer and a reference ground layer arranged in sequence from top to bottom; The microstrip line layer includes a surface ground and microstrip lines of a T-shaped structure. The microstrip lines of the T-shaped structure include a co-linear input microstrip line and an output microstrip line, and a stub microstrip line connected to the input microstrip line and the output microstrip line. A dielectric layer is filled between the microstrip line layer and the reference ground layer. It is characterized in that The stub microstrip line is divided into two segments, namely a first stub and a second stub connected together. The first stub is connected to the input microstrip line and the output microstrip line. The impedances of both the input microstrip line and the output microstrip line are 50 Ω. The reference ground layer includes a first ground layer and a second ground layer arranged in sequence from top to bottom. The impedance of the first stub is 75 Ω, and it uses the first ground layer as the reference ground with the input microstrip line and the output microstrip line. The line width of the second stub is greater than that of the first stub. It uses the second ground layer as the reference ground and has an impedance of 75 Ω. The first stub is capacitively grounded to the surface ground, and the end of the second stub is directly connected to the surface ground. The length of the first stub is 1 / 4 of the wavelength corresponding to the center frequency of the high-frequency band among the two operating frequency bands of Sub6G. When there are multiple resonance points between the two operating frequency points of Sub6G, the resonance points are shifted to the right by reducing the length of the second stub, so that only one resonance point is retained between the two operating frequency points on the insertion loss curve. Under this condition, the length of the second stub is obtained to reduce the overall size of the microstrip circuit.

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