CN115313008A

CN115313008A - Miniaturized high-power electric bridge based on multilayer PCB

Info

Publication number: CN115313008A
Application number: CN202210428927.XA
Authority: CN
Inventors: 朱建彬; 成爱强; 平培力; 钟世昌
Original assignee: CETC 55 Research Institute
Current assignee: CETC 55 Research Institute
Priority date: 2022-04-22
Filing date: 2022-04-22
Publication date: 2022-11-08

Abstract

The invention relates to a high-power bridge design of a multilayer PCB, which comprises a surface-mounted bridge and a bottom feed test rack. Adopt snakelike stripline to carry out broadside coupling, strong coupling has been realized, distribution parameters have been eliminated, the loss that installs passive circuit than traditional lumped parameter surface mounting is low, the isolation is high, the standing wave is little, system performance has been improved, select low cost's Rogers panel to carry out multilayer PCB pressfitting, adopt Rogers 4450B prepreg between board core and the board core, prevent that the PCB board is heated the distortion that each layer harmomegathus coefficient difference leads to and insulating and laminating effect, the electric bridge adopts the encapsulation form of surface mounting, design and realization of microstrip circuit and system have been convenient and optimized, and make its application aspect greatly increased, application field is more extensive.

Description

Miniaturized high-power electric bridge based on multilayer PCB

Technical Field

The invention relates to a miniaturized high-power electric bridge based on a multilayer PCB, belonging to the technical field of passive circuits.

Background

The bridge is one of key devices in a passive circuit, has functions of power division, synthesis and phase shift, is widely applied in present communication systems, can be used for beam forming in an antenna feed system, can improve input-output standing wave ratio (VSWR) in a balanced amplifier, can determine phase error in a Quadrature Phase Shift Keying (QPSK) transmitter, can also be used as a synthesizer of a power amplifier and the like, and can be conveniently integrated in the system by matching four ports of the bridge. The bridge on the market at present mainly has two kinds of forms, be traditional type bridge and surface mounting bridge respectively, traditional type bridge includes coaxial type bridge, cavity type bridge, every arm length is quarter wavelength, the size is great, and the structure singleness is difficult to realize the miniaturization, and surface mounting bridge has the miniaturization, the characteristics of high integration degree, and the application is extensive in various subassembly modules, but power capacity is little, the heat dissipation is relatively poor, how to realize high-power through selecting suitable medium material and reasonable layout is the problem that needs the solution at present urgently.

Disclosure of Invention

The invention provides a miniaturized high-power electric bridge based on a multilayer PCB, and aims to meet the requirement of a high-power radio-frequency circuit, a miniaturized surface-mounted 3dB electric bridge which meets the requirements of high power, low loss and high isolation is designed, the working frequency is 0.7-2GHz, and the miniaturized surface-mounted 3dB electric bridge can bear continuous waves of 100W.

The technical solution of the invention is as follows: a miniaturized high-power electric bridge based on a multilayer PCB structurally comprises a shell and a circuit board, wherein four end points of the shell are connected with an input end, an isolation end, a coupling end and a straight-through end, the circuit board is formed by laminating a multilayer PCB structure and sequentially comprises an upper cover plate, an upper dielectric material, an upper laminating adhesive film, an upper copper foil circuit line, a central dielectric material, a lower copper foil circuit line, a lower laminating adhesive film, a lower dielectric material and a lower cover plate from top to bottom, and the copper foil circuit line is of a strip line structure.

The multilayer PCBPCB structure laminating technology selects Rogers plates.

The upper dielectric material and the lower dielectric material are made of Rogers 4003 plates, the central dielectric material is made of Rogers 5880 plates, and the upper laminating adhesive film and the lower laminating adhesive film are made of Rogers 4450B prepregs.

The upper copper foil circuit line and the lower copper foil circuit line are printed on two sides of the middle medium substrate by adopting snake-shaped strip lines to carry out broadside coupling.

The line width of the upper copper foil circuit line and the line width of the lower copper foil circuit line are 0.9mm.

The shell is characterized in that the periphery of the outer wall of the shell is subjected to half-hole treatment, an L-shaped groove is formed, the surface of the L-shaped groove is plated with silver, the thickness of the L-shaped groove is 0.01mm, the overall shape length of the bridge is 20mm, the width of the bridge is 6mm, and the thickness of the bridge is 3mm.

The size of the bottom test frame for the bridge test is the same as that of the bridge, a dielectric copper-clad plate is adopted, the upper layer is copper foil, the dielectric material is Rogers 5880 board, the thickness is 0.254mm, and L-shaped groove digging treatment is carried out on four corners of the copper foil.

The electric bridge is arranged on the printed board and the cavity in a groove-digging way and is directly arranged on the printed board, so that surface mounting is realized.

The invention has the beneficial effects that:

(1) The invention adopts multilayer PCB laminating technology, selects the Rogers board with low cost, greatly reduces the process cost, and simultaneously increases the effective dielectric constant of the circuit by a multilayer medium filling mode, obviously reduces the volume and realizes the miniaturization purpose;

(2) The invention adopts a snakelike strip line broadside coupling structure, realizes strong coupling, eliminates distribution parameters, has low loss, high isolation and small standing wave compared with the traditional lumped parameter surface mounted passive circuit, and improves the system performance;

(3) The invention is directly installed on the printed board without grooving and installing on the printed board and the cavity, thereby realizing surface mounting, facilitating and optimizing the design and realization of the microstrip circuit and the system, greatly increasing the application level and having wider application field.

Drawings

FIG. 1 is a schematic view of an overall surface mount bridge;

FIG. 2 bottom test rack;

FIG. 3 is an internal serpentine stripline;

FIG. 4 is a diagram of a surface mount bridge multi-layer PCB structure;

FIG. 5 shows the result of standing wave simulation;

FIG. 6 is a simulation result of isolation and coupling;

FIG. 7 is a phase difference and insertion loss simulation result;

FIGS. 8-11 are power capacity simulation results for different frequency points;

fig. 12 shows the result of the heat loss simulation.

In the figure, 1 is an upper cover plate, 2 is an L-shaped groove, 3 is an L-shaped groove, 4 is a square metal plate, 5 is a side lumped port feed, 6 is an input end, 7 is an isolation end, 8 and 9 are output ends, 10 and 14 are dielectric materials, 11 and 13 are laminated adhesive films, and 12 is a central dielectric material.

Detailed Description

The technical scheme of the invention is further explained by combining the attached drawings

As shown in fig. 1, the 3dB electrical bridge described in this embodiment adopts a surface-mounted package form, the periphery of the outer wall is half-holed, the surface is plated with silver, the thickness is 0.01mm, the overall shape length of the electrical bridge is 20mm, the width is 6mm, the thickness is 3mm, 1 is an upper cover plate, and 2 is an L-shaped groove, so that the feeding portion can be in good contact and grounded.

As shown in fig. 2, the bottom test frame is similar to the bridge in size, a dielectric copper-clad plate is adopted, the upper layer is a copper foil, the dielectric substrate is a Rogers 5880 plate, the conventional thickness is 0.254mm, the copper foil is also subjected to grooving treatment, 3 is a square metal plate, 4 is a square metal plate, metal interconnection between the bridge and the test frame is realized, and 5 is a side lumped port feeding position.

As shown in fig. 3, the circuit structure adopts serpentine strip lines printed on both sides of the intermediate medium substrate for broadside coupling, and the broadside coupled bridge has the advantages of small insertion loss, high power tolerance, wide bandwidth, and the like, so that the circuit structure is often used for designing a high-power 3dB bridge, wherein 6 and 7 are respectively an input end and an isolation end, 8 and 9 are respectively two output ends, the amplitudes are equal, the phase difference is 90 degrees, the coupled line calculates a common odd-even mode model analysis method, and the characteristic impedance of the odd-even mode satisfies formula (1) and formula (2):

Z0e=1/(Ve*Ce) (1)

Z0o=1/(Vo*Co) (2)

wherein Ve and Vo are respectively the transmission speed of the even mode and the odd mode, and Ce and Co are respectively the capacitance of the unit length of the even mode and the odd mode. According to the transmission line theory, the coupling coefficient C can be derived from equation (3):

C=20Log((Ze- Zo)/( Ze+Zo) (3)

the relationship between the odd-mode and even-mode impedance and the port impedance needs to satisfy the formula (4):

Z=√(Ze*Zo) (4)

according to the formulas (3) and (4), the characteristic impedance of the even-odd mode of the 3dB bridge can be deduced to be Ze =120.91 and Zo =20.68 respectively, then the parameters of the microstrip line can be determined by analyzing and calculating the layer dielectric material and the layer thickness of the broadside coupling structure, and the characteristic impedance of the coupling strip line can be determined by the thickness and the dielectric constant of the broadside coupling interlayer dielectric material and the dielectric constant. The electrical length of the 3dB bridge is a quarter wavelength of the operating frequency, so the higher the relative dielectric constant of the slab medium, the shorter its physical length, and the easier it is to achieve miniaturization. But the higher the panel dielectric constant is simultaneously, the narrower is the line width of coupling strip line, leads to the conductor loss of coupler bigger, is unfavorable for realizing low insertion loss, is unfavorable for bearing high-power, considers the powerful bearing capacity, and this patent line width sets up to 0.9mm, is higher than theoretical calculation line width, and the power-resisting ability further improves.

As shown in fig. 4, the bridge adopts a multilayer PCB lamination technology, copper foils, prepregs and patterned core boards (copper clad laminates) are sequentially laminated, and then bonded into a whole under high temperature and high pressure, considering the problem of high-power heat dissipation, two materials, namely Rogers 4003 (10, 14) and Rogers 5880 (12), with good heat dissipation are selected, and Rogers 4450B prepregs (11, 13) are used between the core boards to prevent the distortion and the insulation and bonding caused by the difference of expansion and shrinkage coefficients of the layers after the PCB is heated.

Fig. 5-8 are simulation results of S parameters of the bridge, and it can be seen from the figure that the ports are well matched, the standing wave ratio is below 1.4, the isolation is below-17 dB, the coupling is about 3dB, the phase difference between the 3 port and the 4 port is about 90 degrees, and the average insertion loss is about 0.5.

Fig. 9-11 show the simulation results of the power capacity of the bridge, and the input port is fed with 100W power to simulate the field strengths at different frequency points of 0.7GHz, 1.2GHz and 2GHz, and it can be seen from the figure that the maximum field strength is smaller than the air breakdown field strength of 3e6V/m, and the bridge is considered to be capable of withstanding 100W high power.

Fig. 12 shows the simulation result of heat dissipation of the bridge, which deduces that 5W of power in 100W continuous wave is converted into heat according to the insertion loss of the bridge about 0.5dB, i.e. about 5% of power is dissipated, and then thermodynamic simulation is performed according to the thermal conductivity of Rogers 5880 of 0.2W/m/° c and the thermal conductivity of Rogers 4003 of 0.71W/m/° c, so that the temperature is increased by 30 degrees as can be seen from the graph by giving the initial operating temperature of the bridge of 70 degrees, and the temperature is within the temperature tolerance range of the bridge.

Claims

1. A miniaturized high-power electric bridge based on a multilayer PCB is characterized by comprising a shell and a circuit board, wherein four end points of the shell are connected with an input end, an isolation end, a coupling end and a straight-through end, the circuit board is formed by laminating a multilayer PCB structure, an upper cover plate, an upper dielectric material, an upper laminating adhesive film, an upper copper foil circuit line, a central dielectric material, a lower copper foil circuit line, a lower laminating adhesive film, a lower dielectric material and a lower cover plate are sequentially arranged from top to bottom, and the copper foil circuit line is of a strip line structure.

2. A multi-layer PCB based miniaturized high power electrical bridge according to claim 1, wherein said multi-layer PCB structure is laminated using rogers board.

3. The multi-layer PCB-based miniaturized high-power bridge as claimed in claim 2, wherein the upper dielectric material and the lower dielectric material are Rogers 4003 plates, the central dielectric material is Rogers 5880 plates, and the upper laminating adhesive film and the lower laminating adhesive film are Rogers 4450B prepregs.

4. The multi-layer PCB-based miniaturized high-power electrical bridge as claimed in claim 1, wherein the upper and lower copper foil circuit lines are printed on both sides of the middle dielectric substrate by using serpentine strip lines for broadside coupling.

5. The miniaturized high power bridge based on multi-layer PCB of claim 1 or 4, wherein the line width of the upper copper foil circuit line and the lower copper foil circuit line is 0.9mm.

6. The miniaturized high-power electric bridge based on the multilayer PCB as claimed in claim 1, wherein the periphery of the outer wall of the shell is processed by half-hole processing, and is provided with an L-shaped groove with silver-plated surface, the thickness is 0.01mm, the overall external length of the electric bridge is 20mm, the width is 6mm, and the thickness is 3mm.

7. The miniaturized high-power electric bridge based on the multilayer PCB as claimed in claim 1, wherein the bottom test rack for the electric bridge test has the same size as the electric bridge, a dielectric copper-clad plate is adopted, the upper layer is copper foil, the dielectric material is Rogers 5880 plate material, the thickness is 0.254mm, and L-shaped groove digging processing is carried out on four corners of the copper foil.

8. The multi-layer PCB-based miniaturized high-power bridge as claimed in claim 1, wherein the bridge is mounted on the printed board directly by grooving the printed board and the cavity, thereby realizing surface mounting.