A low-cost high-performance hybrid integrated coaxial directional coupler and radio frequency module

Abstract

The application provides a low-cost high-performance hybrid integrated coaxial line directional coupler and radio frequency module. A single-layer double-sided printed circuit board and a metal cavity are mixed and integrated, so that the number and cost of assembly parts are greatly reduced. Meanwhile, the single-layer double-sided printed circuit board and the metal cavity cooperate with each other to form an effect similar to a coaxial coupling line, so that radiation loss is effectively suppressed, field distribution is improved, and the insertion loss, coupling flatness and isolation performance of the coupler are improved. The middle part of the dielectric on the hollowed-out circuit board is removed, the phase of the transmission signal of the coupling line is compensated, and the excellent performance of the directional coupler in coupling degree, return loss, insertion loss and isolation degree is further realized. In the case of ensuring the performance of the device, the dielectric between the transmission line and the ground is reserved, and the physical stability of the device is improved.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency microwave circuit technology, specifically relating to a low-cost, high-performance hybrid integrated coaxial directional coupler and radio frequency module. Background Technology

[0002] As a core passive component, couplers are widely used in communications, radar, and measurement and control fields due to their directional coupling, power sampling, energy distribution, and isolation functions. In 5G / 6G base stations, couplers enable transmit power monitoring, VSWR detection, and fault location, ensuring communication quality. In satellite communication systems, their high directionality isolates uplink and downlink, reducing signal distortion. In phased array radar T / R modules, couplers protect sensitive receiving devices and support target detection. In instruments such as vector network analyzers, they accurately separate incident and reflected waves, ensuring measurement accuracy. In special scenarios such as aerospace, they adapt to extreme environments, providing highly reliable passive component support and serving as a key support for high-end radio frequency and microwave systems.

[0003] Currently, most integrated directional couplers are multi-layer circuit board structures. For circuits requiring coupled-line structures, if a single-layer circuit board with single-sided metal traces is used for left-right coupling, traditional design methods limit the directional coupler's ability to achieve wide bandwidth and high performance. If a single-layer circuit board with double-sided metal traces is used for top-bottom coupling, the electric field is more distributed within the dielectric substrate because the two coupling lines are located on opposite sides of the dielectric, resulting in significant dielectric losses. Increasing the number of circuit board layers to form coupling structures on different boards, and creating through-holes in the dielectric of the boards between the coupling structures, will also multiply production costs, and this approach is mostly used in applications with narrow frequency bandwidths. For wide-bandwidth directional couplers, micro-coaxial technology is also used, but this technology has extremely high production costs and reduces isolation and coupling performance as the frequency bandwidth increases.

[0004] Patent CN109149044A discloses a dielectric integrated suspension line coupler based on a multi-layer structure. This coupler uses double-sided metal traces, forming a coupling structure by removing most of the dielectric through a third and fifth circuit board, with a through-hole formed on a fourth circuit board, resulting in a wide-edge coupling structure. This solution achieves better than 23dB return loss and isolation in the 2GHz to 5GHz frequency range, reducing dielectric loss. However, the removal involves two circuit boards, not a single layer, and the frequency multiplication factor is only 2.5. Furthermore, the use of seven circuit boards increases the cost.

[0005] Patent CN115000664A discloses a common-mode suppression dielectric-integrated suspended parallel stripline differential coupler. It embeds two layers of metal conductors—traditional double-sided parallel striplines—on metal layers G5 and G6, respectively. Simultaneously, a significant portion of the dielectric substrate is removed to reduce metal loss. Short stubs corresponding to layers G5 and G6 are connected using metallized vias to form the differential coupler. However, in this differential coupler structure, the transmission lines of metal layers G5 and G6 are in contact with each other, unlike the independent transmission lines of directional couplers. Furthermore, the research on the effectiveness of dielectric removal is not specifically aimed at directional couplers; excessive dielectric removal can affect the physical stability of the coupler.

[0006] Patent CN120691080A discloses an orthogonal directional coupler based on micro-coaxial technology. This ultra-wideband directional coupler achieves impedance matching through a coaxial structure, achieving a coupling degree of 4dB, return loss better than 15dB, directivity better than 10dB, wide operating bandwidth, and small size. However, the micro-coaxial technology used in this patent is costly, and the support strip has a significant impact on the coupler's directivity, return loss, and coupling degree.

[0007] In summary, the publicly available couplers need improvement in the following aspects:

[0008] (1) Traditional printed circuit board couplers mostly use multi-layer circuit boards to achieve wide-side coupling of upper and lower metal layers, resulting in narrow frequency bandwidth. Generally, seven or more circuit boards are required. There is little research on low-cost, high-performance coaxial directional couplers that use only a single-layer double-sided printed circuit board.

[0009] (2) Couplers using single-layer double-sided printed circuit boards for coupling structures. Currently disclosed couplers are not directional couplers for left and right coupling. There is insufficient research on the dielectric in directional couplers for coupling lines, making it difficult to balance physical stability and device performance.

[0010] (3) Couplers using micro-coaxial technology have extremely high production costs. At the same time, when increasing the frequency doubling ratio, the coupling degree, directivity and return loss of the device are often affected by the support bar. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention proposes a low-cost, high-performance hybrid integrated coaxial directional coupler and RF module. Employing a hybrid integration scheme of a single-layer double-sided printed circuit board and a metal cavity significantly reduces the number of assembly components and costs. Simultaneously, the single-layer double-sided printed circuit board and the metal cavity work together to form an effect similar to a coaxial coupling line, effectively suppressing radiation loss and improving field distribution, thereby enhancing the coupler's insertion loss, coupling flatness, and isolation performance. By removing a portion of the dielectric in the middle of the transmission line on the circuit board, phase compensation is applied to the transmitted signal of the coupling line, further achieving excellent performance in coupling, return loss, insertion loss, and isolation. While ensuring device performance, the dielectric between the transmission line and ground is retained, increasing the device's physical stability.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0013] A low-cost, high-performance hybrid integrated coaxial directional coupler includes an input port, a through port, a coupling port, an isolation port, and n coupling line units that are sequentially and tightly connected along a horizontal axis of symmetry, where n is an integer and n≥2;

[0014] The coupling line unit includes a first metal shell, a first circuit board, and a second metal shell connected to each other from top to bottom, forming a metal-circuit board-metal sandwich structure; the first circuit board is a single-layer double-sided printed circuit board symmetrical about the y-axis, including ground I, a first dielectric region, a first transmission line, a second dielectric region, a second transmission line, a third dielectric region, and ground II connected in sequence through dielectric regions;

[0015] The first transmission line of the first coupling line unit is connected to the coupling port above the first transmission line and to the input port above the second transmission line; the first transmission line of the nth coupling line unit is connected to the isolation port below the first transmission line and to the through port below the second transmission line.

[0016] Furthermore, the first circuit board also adopts double-sided metal traces, which are arranged from top to bottom as an upper metal layer, a dielectric region, and a lower metal layer. In the first dielectric region, the second dielectric region, and the third dielectric region, the upper metal layer and the lower metal layer are stripped of copper. In addition, the first dielectric region and the third dielectric region retain all dielectrics, the second dielectric region retains the dielectric located in the middle, and the remaining dielectrics are removed.

[0017] Furthermore, the first metal casing is a cuboid metal structure with a first rectangular groove milled on its bottom; the first rectangular groove is in contact with the upper metal layer of the first circuit board; the second metal casing is also a cuboid metal structure with a second rectangular groove milled on its top; the second rectangular groove is in contact with the lower metal layer of the first circuit board.

[0018] Furthermore, copper is plated on the side of the first transmission line and the second transmission line that are close to each other to form a coupling line structure.

[0019] Furthermore, metal through holes are evenly distributed on the surfaces of ground I and ground II to achieve vertical connectivity of the ground structure.

[0020] Furthermore, the input port, through port, coupling port, and isolation port are all single transmission line structures.

[0021] The present invention also provides a radio frequency module that includes the above-described low-cost, high-performance hybrid integrated coaxial directional coupler.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. A hybrid integration solution of single-layer double-sided printed circuit board and metal cavity is adopted, which greatly reduces the number of assembly components and cost;

[0024] 2. The single-layer double-sided printed circuit board and the metal cavity work together to form an effect similar to a coaxial coupling line, which effectively suppresses radiation loss and improves field distribution, thereby improving the insertion loss, coupling flatness and isolation performance of the coupler.

[0025] 3. Only a portion of the medium in the middle of the transmission line on the first circuit board is hollowed out to perform phase compensation on the transmission signal of the coupling line, thereby further realizing the excellent performance of the directional coupler in terms of coupling degree, return loss, insertion loss, and isolation, and achieving good left and right coupling effect of the coupling line unit;

[0026] 4. By preserving the medium between the transmission line and ground while ensuring device performance, the physical stability of the device is increased;

[0027] 5. The number of coupling line units is adjustable. By adjusting the transmission line width, spacing, and distance to ground, directional coupler designs with different coupling degrees and frequency bands can be flexibly realized. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0029] Figure 2 This is a longitudinal cross-sectional view of the present invention;

[0030] Figure 3 This is a schematic diagram of the structure of the first circuit board in this invention;

[0031] Figure 4 This is a schematic diagram of a low-cost, high-performance hybrid integrated coaxial directional coupler according to Embodiment 1 of the present invention;

[0032] Figure 5This is a top view of the first circuit board in Embodiment 1 of the present invention;

[0033] Figure 6 This is a phase comparison diagram of the first and second transmission lines before and after the dielectric is removed from the single-section coupling line unit in Embodiment 1 of the present invention. Figure 6 (a) is before the medium is removed. Figure 6 (b) is after the medium has been removed;

[0034] Figure 7 This is a performance diagram of a low-cost, high-performance hybrid integrated coaxial directional coupler provided in Embodiment 1 of the present invention;

[0035] Figure 8 This is a schematic diagram of a low-cost, high-performance hybrid integrated coaxial directional coupler according to Embodiment 2 of the present invention;

[0036] Figure 9 This is a performance diagram of a low-cost, high-performance hybrid integrated coaxial directional coupler provided in Embodiment 2 of the present invention.

[0037] The markings in the diagram are as follows: Input port 1, through port 2, coupling port 3, isolation port 4, first metal casing 5, first circuit board 6, second metal casing 7, ground I 8, first dielectric area 9, first transmission line 10, second dielectric area 11, second transmission line 12, third dielectric area 13, ground II 14, metal via 15. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The specific implementation methods of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] like Figure 1 As shown, this invention provides a low-cost, high-performance hybrid integrated coaxial directional coupler, comprising an input port 1, a through port 2, a coupling port 3, an isolation port 4, and n coupling line units connected sequentially and tightly along a horizontal axis of symmetry, where n is an integer and n≥2. The input port 1, through port 2, coupling port 3, and isolation port 4 are all single-transmission-line structures.

[0040] Example 1;

[0041] like Figure 2As shown, the coupling line unit includes a first metal shell 5, a first circuit board 6, and a second metal shell 7 connected to each other from top to bottom, forming a metal-circuit board-metal sandwich structure; the first metal shell 5 is a cuboid metal structure with a first rectangular groove milled on its bottom; the first rectangular groove is in contact with the upper metal layer of the first circuit board 6; the second metal shell 7 is also a cuboid metal structure with a second rectangular groove milled on its top; the second rectangular groove is in contact with the lower metal layer of the first circuit board 6.

[0042] like Figure 3 As shown, the first circuit board 6 is a single-layer double-sided printed circuit board symmetrical about the y-axis, including ground I 8, first dielectric region 9, first transmission line 10, second dielectric region 11, second transmission line 12, third dielectric region 13, and ground II 14 connected sequentially through dielectric regions. The first circuit board 6 also uses double-sided metal traces, with an upper metal layer, dielectric region, and lower metal layer arranged from top to bottom. At the first dielectric region, second dielectric region, and third dielectric region, the upper and lower metal layers have copper removed; and all dielectrics are retained in the first and third dielectric regions, while the dielectric in the middle of the second dielectric region is retained, and the remaining dielectrics are removed. The first transmission line 10 and the second transmission line 12 are copper-plated on the side closest to each other, forming a coupling line structure. Metal vias 15 are evenly distributed on the surfaces of ground I 8 and ground II 14 to achieve vertical connectivity of the ground structure.

[0043] like Figure 4 , 5 As shown, in this embodiment, n is 15, that is, it includes 15 coupling line units. The first transmission line 10 of the first coupling line unit is connected to the coupling port 3 above, and the second transmission line 12 is connected to the input port 1 above. The first transmission line 10 of the 15th coupling line unit is connected to the isolation port 4 below, and the second transmission line 12 is connected to the through port 2 below.

[0044] The number of coupling line units and the required odd-mode impedance value for each coupling line unit can be theoretically calculated. In this embodiment, a Rogers 5880 printed circuit board with a dielectric thickness of 0.127 mm and upper and lower metal thicknesses of 0.035 mm are selected. By adjusting the widths of the first transmission line 10 and the second transmission line 12, the spacing between the transmission lines, and the distance to ground on both sides, the odd-mode impedance of the transmission lines can be controlled to meet the calculation results. The structural parameters given in Embodiment 1 are preferred parameters; adjusting the structural parameters can achieve the required actual performance.

[0045] Figure 6 A phase comparison of the first and second transmission lines before and after removing the dielectric from a single-section coupling line unit of a low-cost, high-performance hybrid integrated coaxial directional coupler provided in Example 1. Figure 6 (a) Before media removal Figure 6After the medium is removed in (b), it can be seen that removing part of the medium in the second medium region J2 can compensate the phase of the transmission line signal, thereby improving the isolation of the signal. Furthermore, the medium is retained in the first medium region J1 and the third medium region J3, which improves the physical stability of the device.

[0046] Figure 7 This invention provides S-parameter simulation results for a low-cost, high-performance hybrid integrated coaxial directional coupler, as described in this embodiment. The invention has universal applicability to the port; in Embodiment 1, the port is set as a conventional port and tested using an SMA connector. Within the frequency range of 0.4 GHz to 15.2 GHz, the frequency doubling ratio is 38, the coupling fluctuates around 20 dB with a fluctuation range of ±1 dB, the insertion loss is only 0.5 dB, the return loss is better than 25 dB, the isolation is better than 45 dB, and the directivity is better than 25 dB.

[0047] Example 2;

[0048] This embodiment also provides a low-cost, high-performance hybrid integrated coaxial directional coupler, with a structure basically the same as that of Embodiment 1, the difference being: Figure 8 As shown, in this embodiment, the coupling line unit is designed to be 3.

[0049] The number of coupling line units and the required odd-mode impedance value for each coupling line unit can be theoretically calculated. In this embodiment 1, a Rogers 5880 printed circuit board with a dielectric thickness of 0.127 mm and upper and lower metal thicknesses of 0.035 mm are selected. By adjusting the width of the first transmission line 10 and the second transmission line 12, the spacing between the transmission lines, and the distance to the ground on both sides, the odd-mode impedance of the transmission lines can be controlled to meet the calculation results. The structural parameters given in embodiment 2 are preferred parameters; adjusting the structural parameters can achieve the required actual performance.

[0050] Figure 9 The following are the S-parameter simulation results for a low-cost, high-performance hybrid integrated coaxial directional coupler provided in Embodiment 2 of the present invention. The present invention has universal applicability to the ports; the ports in Embodiment 2 are set as ideal ports. Within the frequency range of 5 GHz to 32 GHz, the frequency bandwidth is large, the frequency doubling ratio is 6.4, the coupling fluctuates around 20 dB with a fluctuation range of ±1 dB, the insertion loss is only 0.1 dB, the return loss is better than 28 dB, the isolation is better than 38 dB, and the directivity is better than 20 dB.

[0051] Example 3;

[0052] This embodiment provides a radio frequency module that includes the low-cost, high-performance hybrid integrated coaxial directional coupler provided in Embodiment 1 or Embodiment 2.

[0053] The above embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Although the invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the invention do not depart from the spirit and scope of the invention and should be covered within the scope of the claims of the invention.

Claims

1. A low-cost, high-performance hybrid integrated coaxial directional coupler, characterized in that, It includes an input port, a through port, a coupling port, an isolation port, and n coupling line units that are connected in close succession along the horizontal axis of symmetry, where n is an integer and n≥2; The directional coupler includes a first metal shell, a first circuit board, and a second metal shell connected sequentially from top to bottom, forming a metal-circuit board-metal sandwich structure. The first metal shell is a cuboid metal structure with a first rectangular groove milled on its bottom. The first rectangular groove is in contact with the upper metal layer of the first circuit board. The second metal shell is also a cuboid metal structure with a second rectangular groove milled on its top. The second rectangular groove is in contact with the lower metal layer of the first circuit board. The first circuit board is a single-layer double-sided printed circuit board symmetrical about a horizontal axis of symmetry. The first circuit board includes, in a direction perpendicular to the horizontal axis of symmetry, ground I, a first dielectric region, a first transmission line, a second dielectric region, a second transmission line, a third dielectric region, and ground II. The first transmission line of the first coupling line unit is connected to the coupling port above the first transmission line and to the input port above the second transmission line; the first transmission line of the nth coupling line unit is connected to the isolation port below the first transmission line and to the through port below the second transmission line. The first circuit board also uses double-sided metal traces, which are arranged from top to bottom as an upper metal layer, a dielectric region, and a lower metal layer. The upper and lower metal layers have the same structure. In the first dielectric region, the second dielectric region, and the third dielectric region, the upper and lower metal layers are stripped of copper. Furthermore, in the corresponding area of ​​each coupling line unit, only the middle dielectric located between the first transmission line and the second transmission line is retained, and the rest of the dielectric is removed. The sidewalls of the first and second transmission lines on the upper and lower metal layers that are close to each other are plated with copper to form a coupling line structure. Metal through-holes are evenly distributed on the surfaces of Ground I and Ground II on the upper and lower metal layers to achieve vertical connectivity of the ground structure. The input port, through port, coupling port, and isolation port are all single transmission line structures.

2. A radio frequency module, characterized in that, It includes the low-cost, high-performance hybrid integrated coaxial directional coupler as described in claim 1.

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