A type of directional bridge

Abstract

This invention discloses a directional bridge, belonging to the field of electronic circuit technology. The directional bridge includes a first port P1, a second port P2, a third port P3, and a three-layer PCB circuit board. The top layer of the circuit board includes resistors R1, R2, R3, R4, R5, R6, R7, R8, and R9, a capacitor C1, a coaxial cable H, and several ferrite beads F. The middle layer consists of Rogers 4350 and FR4 insulating dielectric layers. The bottom layer is GND (ground). This invention features a simple structure, a wide operating frequency range (0.1GHz-4.4GHz), good directivity, and is relatively simple to implement with low manufacturing costs, offering high cost-effectiveness.

Description

Technical Field

[0001] This invention belongs to the field of electronic circuit technology, and specifically relates to a directional bridge. Background Technology

[0002] Directional couplers are a crucial type of directional coupler, commonly used in vector network analyzers, where they play a vital role. Directional couplers are frequently used in microwave systems for signal sampling and combination. A key function of directional couplers is the separation of incident and reflected waves, enabling measurements of the network system. The degree of this separation (called directivity) affects the measurement accuracy of the network measurement system. Higher directivity of the directional coupler results in higher measurement accuracy. Therefore, directivity is a particularly important performance metric for directional couplers, and improving its directivity is of significant research importance.

[0003] Directional couplers are devices used in radio frequency systems to separate forward and reverse transmissions, and are key components of vector network analyzers. A common type of directional coupler is the stripline coupler. A stripline coupler is characterized by two closely spaced lines on the inner layer of a printed circuit board (PCB). However, its coupling is very low at lower frequencies, resulting in very low receiver input power at low frequencies, making it highly susceptible to signal noise and causing inaccurate measurements. Summary of the Invention

[0004] Based on existing technologies, this invention proposes a directional bridge structure design. The directional bridge is a variant of the Wheatstone bridge, achieving good directivity within an operating frequency range of 0.1 GHz to 4.4 GHz. The directional bridge exhibits better directivity than 30 dB in the 0.1 GHz to 1.5 GHz frequency range and better directivity than 20 dB in the 1.5 GHz to 4.4 GHz frequency range. Furthermore, the directional bridge circuit is relatively simple to implement, easy to fabricate, and has low cost, resulting in a high cost-performance ratio.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] A directional bridge includes a first port P1, a second port P2, a third port P3, and a three-layer PCB circuit board. The top PCB circuit board contains resistors R1, R2, R3, R4, R5, R6, R7, R8, and R9, a capacitor C1, a coaxial cable H, and several ferrite beads F. The middle PCB circuit board consists of an insulating dielectric layer. The bottom PCB circuit board is GND (ground layer). One end of resistor R1 and one end of resistor R2 are connected to the third port P3. The other end of R1 is connected in series with one end of capacitor C1. The other end of capacitor C1 and one end of resistor R9 are connected to the inner conductor of the coaxial cable H. The other end of resistor R9 is connected to the first port P1. Resistors R3, R4, R5, R6, R7, and R8 are connected in parallel. One end of the parallel connection is grounded, and the other end of the parallel connection and the other end of resistor R2 are connected to one end of the outer conductor of the coaxial cable H. The other end of the outer conductor of the coaxial cable H is grounded.

[0007] Directional directional bridges have four main technical specifications: insertion loss IL, coupling C, isolation I, and directivity D. Insertion loss IL is the ratio of the output power at the second port P2 to the input power at the first port P1; coupling C is the ratio of the output power at the third port P3 to the input power at the first port P1; and isolation I is the ratio of the output power at the second port P3 to the input power at the third port P2. The directivity D of a directional directional bridge is calculated as: D = I - (C + IL).

[0008] The first port P1 is the input terminal of the directional bridge, the second port P2 is the through terminal of the directional bridge, and the third port P3 is the coupling terminal of the directional bridge.

[0009] The coaxial cable H constitutes a transmission line transformer.

[0010] The transmission line transformers in the first port P1 to the second port P2 of the directional bridge constitute the through arm of the directional bridge, and the resistor R1 and capacitor C1 in series in the first port P1 to the third port P3 of the directional bridge constitute the coupling arm of the directional bridge.

[0011] The second port P2 to the third port P3 of the directional bridge have the isolation characteristics of a directional bridge.

[0012] The PCB circuit board has a three-layer printed circuit board structure. The first layer is Rogers RO4350 microwave laminate material, and the second and third layers are FR4 glass fiber material.

[0013] The three-layer PCB circuit board has a cutout in the middle to accommodate the coaxial cable H and the ferrite bead F.

[0014] The coaxial cable H and the ferrite bead F sleeved on the coaxial cable H form a coaxial balun circuit. One end of the inner conductor of the coaxial cable is connected to the first port P1, and the other end is connected to the second port P2. One end of the outer conductor of the coaxial cable is connected in series with resistor R2, and the other end is grounded, thus forming a 1:1 transmission line transformer with a balun structure. The ferrite bead F is suspended at the end of the coaxial cable near the second port P2.

[0015] The SMA connectors are located at the three ports of the directional bridge. To improve the matching of the transmission line between the first and third ports, the SMA connectors at the first and third ports are tapered.

[0016] The coaxial cable H used in the transmission line transformer is part of the RG405 series cable, forming a balun transformer. The inner conductor to the outer conductor of the coaxial cable has a constant characteristic impedance of 50 ohms.

[0017] The ferrite bead F is a manganese-zinc ferrite bead with an initial relative permeability of μ = 10000.

[0018] The three-layer PCB circuit board has several vias distributed around the first port P1, the second port P2, the third port P3 and the transmission line. The components in the directional bridge are connected by the transmission line.

[0019] Resistors R3, R4, and R5 are located on the left side of the coaxial cable, while resistors R6, R7, and R8 are located on the right side. The distance between resistors R3 and R4 is 2mm, and the distance between resistors R4 and R5 is 6mm. The distance between resistors R6 and R7 is 2mm, and the distance between resistors R7 and R8 is 6mm.

[0020] This invention has the following characteristics and beneficial effects:

[0021] Directional bridges have a simple structural design and a wide operating frequency range, exhibiting good directivity within the 0.1GHz-4.4GHz frequency range. The directivity of a directional bridge is better than 30dB in the 0.1GHz-1.5GHz frequency range and better than 20dB in the 1.5GHz-4.4GHz frequency range. Directional bridge circuits are relatively simple to implement and have low manufacturing costs, offering high cost-effectiveness. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a directional bridge circuit;

[0023] Figure 2 This is a schematic diagram of a three-layer printed circuit board.

[0024] Figure 3This is a PCB diagram of a directional bridge in HFSS;

[0025] Figure 4 This is an EM simulation diagram of the directional bridge in an embodiment of the present invention. Detailed Implementation

[0026] A directional bridge includes a first port P1, a second port P2, a third port P3, and a three-layer PCB circuit board. The top PCB circuit board contains resistors R1, R2, R3, R4, R5, R6, R7, R8, and R9, a capacitor C1, a coaxial cable H, and a ferrite bead F, as shown below. Figure 1 As shown.

[0027] like Figure 2 The PCB circuit board shown is a three-layer printed circuit board structure. The first layer is Rogers RO4350 microwave laminate, and the second and third layers are FR4 glass fiber material.

[0028] Example 1

[0029] As described Figure 3 As shown, one end of resistor R1 and one end of resistor R2 are connected to the third port P3. The other end of R1 is connected in series with one end of capacitor C1. The other end of capacitor C1 and one end of resistor R9 are connected to the inner conductor of coaxial cable H. The other end of resistor R9 is connected to the first port P1. Resistors R3, R4, R5, R6, R7 and R8 are connected in parallel. One end of the parallel connection is grounded. The other end of the parallel connection and the other end of resistor R2 are connected to one end of the outer conductor of coaxial cable H. The other end of the outer conductor of coaxial cable H is grounded.

[0030] The SMA connectors are located at the three ports of the directional bridge. The inner conductor of the SMA connector at the first port P1 serves as the input excitation, and the outer conductor of the SMA connector is grounded. The inner conductor of the SMA connector at the third port P3 serves as the excitation for the coupling port, and the outer conductor of the SMA connector is grounded. The inner conductor of the SMA connector at the second port P2 is connected to the inner conductor of the coaxial cable H.

[0031] The first port P1, the second port P2, and the third port P3 of the directional bridge all use SMA type connectors as microwave connectors to connect the circuit.

[0032] The resistor R9 connects the inner conductor H of the coaxial cable and the inner conductor of the first port P1, adjusting the balance of the directional bridge circuit.

[0033] The three-layer PCB circuit board has several vias distributed around the first port P1, the second port P2, the third port P3 and the transmission line. The components in the directional bridge are connected by the transmission line.

[0034] The three-layer PCB circuit board has cutouts in the middle to accommodate the coaxial cable H and the ferrite bead F. The ferrite bead F is a manganese-zinc ferrite bead with an initial relative permeability of μ = 10000.

[0035] As described Figure 1 As shown, ports P1 to P2 of the directional bridge form a through arm, which is constructed from a transmission line transformer and connected via a coaxial cable H. The characteristic impedance Z0 of the coaxial cable H is constant at 50 ohms. Resistor R1 and capacitor C1 are connected in series from the first port P1 to the third port P3 of the directional bridge, forming a coupling arm. R1 is a 0402 packaged surface-mount SMT resistor, and C1 is a 0603 packaged surface-mount capacitor.

[0036] The S-parameters of the main channel and coupling loss in the 0.1GHz-4.4GHz frequency range can be calculated using the following formula:

[0037]

[0038] Where R1...R8 are the resistance values ​​of the corresponding resistors.

[0039] Then, the insertion loss IL of the directional bridge at the operating frequency is:

[0040]

[0041] Then, the coupling degree C of the directional bridge at the operating frequency is:

[0042]

[0043] The Figure 3 The PCB is a three-layer printed circuit board. The first layer is Rogers RO4350 microwave laminate with a relative permittivity of ε1 = 3.66 and a relative permeability of μ1 = 1. The second and third layers are FR4 glass fiber material. FR4 has a relative permittivity of ε2 = 4.4 and a permeability of μ2 = 1. The thickness of the first layer is 0.254 mm, the second layer is 1 mm, and the third layer is 0.254 mm. The metal sheet between the layers is 0.023 mm thick. The use of FR4 glass fiber material improves the mechanical strength of the directional bridge.

[0044] Resistors R3, R4, and R5 are located on the left side of the coaxial cable, while resistors R6, R7, and R8 are located on the right side. The distance between resistors R3 and R4 is 2mm, and the distance between resistors R4 and R5 is 6mm. The distance between resistors R6 and R7 is 2mm, and the distance between resistors R7 and R8 is 6mm.

[0045] The coaxial cable H and a ferrite magnetic ring F fitted onto the coaxial cable form a coaxial balun circuit. The coaxial cable H is 6 cm long, with an inner conductor diameter of 0.29 mm, an outer conductor diameter of 1.19 mm, and a PTFE insulating dielectric layer diameter of 0.93 mm. The dielectric layer has a relative permittivity of ε3 = 1.96 and a relative permeability of μ3 = 1. The ferrite magnetic ring F has a diameter of 1 cm, a relative permeability of μ4 = 10000, and a relative permittivity of ε4 = 12.

[0046] One end of the coaxial cable H has an inner conductor connected to resistor R9, and an outer conductor connected to resistors R2, R3, R4, R5, R6, R7, and R8. The other end has an inner conductor connected to the second port SMA connector, and the other end of the outer conductor grounded. A ferrite core F is suspended at the end of the coaxial cable near port P2, at a distance of 0.5mm from the second port P2.

[0047] HFSS (High Frequency Structure Simulator) is a high-performance simulation software for arbitrary 3D passive devices in the full-wave electromagnetic field (EM) band. The circuit of the aforementioned directional bridge is connected in series according to the connection method required by this patent, and a three-dimensional simulation is performed in HFSS software. Figure 3 The figure shows the simulation results of the directional bridge after cascading in HFSS software.

[0048] Simulation results are as follows Figure 4 As shown, the directional bridge exhibits good directivity within the operating frequency range of 0.1GHz-4.4GHz. The directivity of the directional bridge is better than 30dB in the 0.1GHz-1.5GHz frequency range and better than 20dB in the 1.5GHz-4.4GHz frequency range.

Claims

1. A directional bridge, characterized in that, It includes a first port P1, a second port P2, a third port P3, and a three-layer PCB circuit board; The top PCB of the three-layer PCB circuit board includes resistors R1, R2, R3, R4, R5, R6, R7, R8, and R9, capacitor C1, coaxial cable H, and several ferrite beads F; the middle PCB circuit board consists of an insulating dielectric layer; and the bottom PCB circuit board is a ground layer. One end of resistor R1 and one end of resistor R2 are connected to the third port P3. The other end of R1 is connected in series with one end of capacitor C1. The other end of capacitor C1 and one end of resistor R9 are connected to the inner conductor of coaxial cable H. The other end of resistor R9 is connected to the first port P1. Resistors R3, R4, R5, R6, R7 and R8 are connected in parallel. One end of the parallel connection is grounded. The other end of the parallel connection and the other end of resistor R2 are connected to one end of the outer conductor of coaxial cable H. The other end of the outer conductor of coaxial cable H is grounded.

2. A directional bridge according to claim 1, characterized in that, The directional bridge has four technical specifications: insertion loss IL, coupling degree C, isolation degree I, and directivity D; The insertion loss IL is the ratio of the output power of the second port P2 to the input power of the first port P1; the coupling C is the ratio of the output power of the third port P3 to the input power of the first port P1; and the isolation I is the ratio of the output power of the second port P3 to the input power of the third port P2. The directionality of a directional bridge is D = I - (C + IL).

3. A directional bridge according to claim 1, characterized in that, The first port P1 is the input terminal of the directional bridge, the second port P2 is the through terminal of the directional bridge, and the third port P3 is the coupling terminal of the directional bridge. The coaxial cable H constitutes a transmission line transformer; The transmission line transformers in the first port P1 to the second port P2 of the directional bridge constitute the through arm of the directional bridge, and the resistor R1 and capacitor C1 in series in the first port P1 to the third port P3 of the directional bridge constitute the coupling arm of the directional bridge. The second port P2 to the third port P3 of the directional bridge have the isolation characteristics of a directional bridge.

4. A directional bridge according to claim 1, characterized in that, The three-layer PCB circuit board has a three-layer printed circuit board structure. The first layer is Rogers RO4350 microwave laminate material, and the second and third layers are FR4 glass fiber material.

5. A directional bridge according to claim 1, characterized in that, The three-layer PCB circuit board has a cutout in the middle to accommodate the coaxial cable H and ferrite beads F.

6. A directional bridge according to claim 1, characterized in that, The coaxial cable H and the ferrite bead F sleeved on the coaxial cable H form a coaxial balun circuit, and the coaxial cable H forms a 1:1 transmission line transformer with a balun structure; the ferrite bead F is suspended at one end of the second port P2 of the coaxial cable.

7. A directional bridge according to claim 1, characterized in that, The SMA connectors are located at the three ports of the directional bridge, with the first and third ports having a tapered structure.

8. A directional bridge according to claim 1, characterized in that, The ferrite bead F is a manganese-zinc ferrite bead with an initial relative permeability of μ = 10000.

9. A directional bridge according to claim 1, characterized in that, The three-layer PCB circuit board has several vias distributed around the first port P1, the second port P2, the third port P3 and the transmission line. The components in the directional bridge are connected by the transmission line.

10. A directional bridge according to any one of claims 1 to 9, characterized in that, Resistors R3, R4, and R5 are located on the left side of the coaxial cable, while resistors R6, R7, and R8 are located on the right side of the coaxial cable. The distance between resistors R3 and R4 is 2mm, and the distance between resistors R4 and R5 is 6mm. The distance between resistors R6 and R7 is 2mm, and the distance between resistors R7 and R8 is 6mm.

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