Broadband 3dB power quadrature bridge and design method thereof

Abstract

The invention discloses a broadband 3dB power quadrature bridge and a design method thereof, and belongs to the field of microwave devices, the quadrature bridge comprises an input end, a straight-through end, a coupling end, an isolation end and a circuit, the quadrature bridge is characterized in that the circuit comprises three sections of symmetrical coupling lines and a section of coupling line, and after the three sections of symmetrical coupling lines are cascaded, the three sections of symmetrical coupling lines are connected in parallel. The first coupling line is in staggered connection with the first coupling line; three-layer dielectric substrate hot pressing is adopted in the structure, five-layer dielectric substrate hot pressing is not needed, the processing requirement is reduced, meanwhile, the material cost is reduced, and the cost can be greatly reduced; on the other hand, the height of the product is reduced, the tension fracture probability of the metal wall of the via hole is reduced when the product is at the limit working temperature, and the reliability is improved; the 1 / 4 wavelength coupling line only needs four stages, two stages are omitted compared with a traditional mode that a broadband quadrature bridge is achieved through an interleaving parallel technology, and the size is obviously reduced.

Description

Technical Field

[0001] The invention relates to the field of microwave devices, and in particular to a broadband 3dB power orthogonal bridge and a design method thereof. Background Art

[0002] In the design of broadband orthogonal bridges, multi-section 1 / 4 wavelength parallel coupled lines with different coupling strengths are often needed, and the multi-section 1 / 4 wavelength parallel coupled lines are divided into asymmetric multi-sections and symmetric multi-sections.

[0003] In 1965, E. G. Cristal and L. Young proposed a method of using the optimal equiripple polynomial of a 1 / 4 wavelength equivalent step impedance filter and proposed a design theoretical analysis of symmetrical multi-section couplers, which provided a design solution for the comprehensive design of symmetrical multi-section couplers, such as Figure 1 As shown, a design list of 3-section, 5-section, 7-section, and 9-section symmetrical equal ripple 3dB orthogonal bridges is given; The upper and lower dielectric layers are bonded and fixed through the semi-cured sheet and the middle microstrip line layer, which greatly improves the power capacity and has good product consistency. However, when performing multi-section coupling, under power conditions, there are requirements for the thickness of the middle layer dielectric, which leads to the need for thicker upper and lower dielectric layers when building strong coupling, while weak coupling on both sides does not require the thickness of the upper and lower dielectric layers to be too large. Considering all factors, five dielectric layers are generally used for production, such as Figure 2 As shown, from top to bottom, it includes an upper dielectric layer 1, an upper dielectric layer 2, an intermediate dielectric layer 3, a lower dielectric layer 4, and a lower dielectric layer 5. The upper dielectric layer 1 is bonded and fixed to the upper dielectric layer 2 through an upper prepreg 6, the upper dielectric layer 2 is bonded and fixed to the intermediate dielectric layer 3 through an upper prepreg 7, the lower dielectric layer 4 is bonded and fixed to the intermediate dielectric layer 3 through a lower prepreg 8, and the lower dielectric layer 5 is bonded and fixed to the lower dielectric layer 4 through a lower prepreg 9. Weak coupling 10, strong coupling 11, and weak coupling 12 belong to metal routing on the intermediate dielectric layer 3. The metal grounding layer 13 is distributed on the upper surface of the upper dielectric layer 1, the upper surface of the upper dielectric layer 2, the lower surface of the lower dielectric layer 4, and the lower surface of the lower dielectric layer 5. In actual manufacturing, the metal grounding layer is connected through metal edging or metallized vias, and the grounding layer is partially disconnected at the upper and lower positions of the strong coupling 11 through the upper surface of the upper dielectric layer 2 and the lower surface of the lower dielectric layer 4, which meets the thickness requirements of the strong coupling upper and lower dielectric layers and the weak coupling upper and lower dielectric layers. This structural design has at least the following disadvantages: 1) There are five dielectric layers, and the material cost is high; the more dielectric layers there are, the higher the product height becomes. When the hot pressing process is used, the performance requirements for the equipment become higher, and the processing requirements become higher; 2) Because the product is too high, the metal wall of the via may crack under the extreme operating temperature, reducing reliability; That is, adopting this structural design will increase the number of dielectric layers used and increase processing requirements, both of which lead to increased manufacturing costs; on the other hand, the height becomes higher and reliability decreases.

[0004] Another method to realize a 3dB power bridge is to use two-stage coupling lines with a coupling degree of 8.34dB to be staggered and connected to realize 3dB strong coupling. In order to realize a broadband structure, multiple parallel coupling lines are cascaded to form two broadband 8.34dB coupling lines, and then the broadband 8.34dB coupling lines are staggered to form a 3dB broadband bridge. Since the coupling lines do not need strong coupling, they are generally made by bonding three layers of dielectric layers through prepregs. However, this structural design has at least the following problems: the broadband 8.34dB weak coupling cascade implementation requires six levels of 1 / 4 wavelength parallel coupling lines, which is relatively large in size. Summary of the invention

[0005] One of the purposes of the present invention is to provide a broadband 3dB power quadrature bridge to solve the above problems.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A broadband 3dB power orthogonal bridge comprises an input port, a through port, a coupling port, an isolation port and a circuit. The circuit comprises three sections of symmetrical coupling lines and one section of coupling line. The three sections of symmetrical coupling lines are cascaded and then staggeredly connected with the one section of coupling line.

[0007] As a preferred technical solution, the circuit is manufactured on a three-layer dielectric substrate.

[0008] The second object of the present invention is to provide a design method of the above-mentioned broadband 3dB power orthogonal bridge, the technical solution adopted is, comprising the following steps: (1) After determining the coupling strength of the coupling lines TL2, TL3, and TL4, the three coupling lines, namely, coupling lines TL2, TL3, and TL4, are regarded as a two-port network, which is assumed to be network 1, and TL1 is assumed to be network 2. (2) Assumptions , the overall scattering parameters of the two cross-series couplers are obtained by using the port excitation method, and finally: (1) (3) According to the definition of the coupling degree of the coupler, the coupling degree calculation formula is obtained: (2) (4) According to the coupling degree requirements of the orthogonal bridge, the voltage coupling coefficient of TL1 is calculated through the algorithm, thereby determining the coupling degree of TL1; As a preferred technical solution, In step (1), the selection of the coupling lines TL3 and TL4 is determined according to the size of the multi-section symmetrical parallel coupling line cascade, and the coupling degree of the coupling line TL2 is determined according to the coupling degree of the selected plate design TL2.

[0009] The present invention realizes the broadband performance and power capacity of the bridge by adopting the method of cascading three sections of symmetrical coupling lines and staggered connection of one section of coupling lines.

[0010] Compared with the prior art, the advantages of the present invention are: (1) Compared with the existing multi-section coupling line cascade technology, since the TL2 of the three-section symmetrical coupling line does not require strong coupling, the coupling degree of the four-section parallel coupling line can be achieved by hot pressing of three layers of dielectric substrates, without the need for hot pressing of five layers of dielectric substrates. The processing requirements are reduced while the material cost is reduced, which can greatly reduce the cost. On the other hand, the product height is reduced, and the probability of cracking of the via metal wall is reduced at the extreme operating temperature, thereby increasing the reliability. (2) Compared with the existing broadband 8.34 dB weak coupling cascade technology, the 1 / 4 wavelength coupling line of the present invention only requires four stages, two stages less, and the volume is significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a multi-stage symmetrical coupled line cascade equivalent circuit of the prior art of the present invention; Figure 2 This is a structural diagram of a 3dB power bridge according to the prior art of the present invention; Figure 3 It is an electrical schematic diagram of a broadband 3dB power bridge structure according to an embodiment of the present invention; Figure 4 It is a broadband 3dB power bridge structure equivalent network of an embodiment of the present invention; Figure 5 This is a structural diagram of a 3dB width power bridge according to an embodiment of the present invention; Figure 6 A schematic diagram of coupling degree C according to an embodiment of the present invention; Figure 7 The matlab coupling degree calculation diagram of the embodiment of the present invention is Figure 8 This is an ADS coupling degree simulation diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0012] The present invention will be further described below in conjunction with the accompanying drawings.

[0013] Embodiment 1: A broadband 3dB power orthogonal bridge, which achieves broadband performance of the bridge by cascading three symmetrical parallel coupled lines and staggering one parallel coupled line; its electrical schematic diagram is shown in Figure 3 As shown, Figure 3 In, Z 0e1 , Z 0e2 , Z 0e3 , Z 0e4 are the even-mode impedances of the parallel coupled lines TL1, TL2, TL3, and TL4, respectively, where Z 0e3 and Z 0e4 equal; After determining the coupling strength of the coupling lines TL2, TL3, and TL4 (the selection of the weakly coupled parallel coupling lines TL3 and TL4 is based on the size of the multi-section symmetrical parallel coupling line cascade, and the coupling degree of TL2 is designed according to the selected plate and power requirements. The coupling degree of TL2 is a selectable range, generally 4dB to 6dB. When making a specific selection, the coupling degree of TL1 is calculated according to the requirements of the coupling degree of TL2, TL3, TL4 and the orthogonal bridge. The line width calculated according to the selected dielectric substrate thickness and the coupling degree of TL2 and TL1 can meet the power requirements), the three coupling lines (coupling lines TL2, TL3, and TL4) are regarded as a two-port network to form coupler 1, assuming network 1; and the coupling line TL1 constitutes coupler 2, assuming network 2. Their equivalent circuits are as follows: Figure 4 As shown; Port 1, Port 4, Port 5, and Port 6 are the input port, straight-through port, coupled port, and isolated port of Network 1 respectively; Port 7, Port 8, Port 2, and Port 3 are the input port, straight-through port, coupled port, and isolated port of Network 2 respectively; The two networks have the following characteristics: (1) The pass-through port of network 1 is connected to the isolated port of network 2; (2) The coupling port of network 1 is connected to the input port of network 2; Figure 4 Voltage in Represents the input voltage of port n; voltage represents the reflected voltage at port n; Assume that the voltage coupling coefficients of network 1 and network 2 are k1 and k2 respectively. 2; Assume here , the overall scattering parameters of the two cross-series couplers are obtained by using the port excitation method, and finally: (1) The voltage in the formula Represents the input voltage of port n; voltage represents the reflected voltage at port n; According to the definition of the coupling degree of the coupler, the coupling degree calculation formula is obtained: (2) According to the requirements of the orthogonal bridge on the coupling degree, the voltage coupling coefficient of TL1 is calculated through the algorithm, and then the coupling degree is obtained; in actual use, the tuning simulation function can be performed according to the ADS (Advanced Design System) softness to obtain the coupling degree of TL1.

[0014] The bridge structure of this embodiment is as follows Figure 5 As shown, from Figure 5 It can be seen that, compared with the five-layer circuit board in the prior art, the present embodiment adopts a parallel coupling line 14, and improves the upper and lower two dielectric layers in the prior art to one dielectric layer in the upper and lower parts, namely the upper dielectric layer 15 and the lower dielectric layer 16, which are respectively fixed by the upper semi-cured sheet 17 and the lower semi-cured sheet 18, and the upper and lower grounding layers 13 are connected by metal edging or metallized vias.

[0015] According to the above design method, the inventor conducted a simulation case of a 100-500MHZ, 3dB orthogonal bridge: (1) Select the even-mode impedance Z of the TL2, TL3, and TL4 coupling lines 0e2 is 103Ω, Z 0e3 and Z 0e4 63.5Ω; (2) Use Matlab to calculate the transfer matrix A of network 1 composed of TL2, TL3, and TL4 coupling lines, and then calculate S11, i.e. k1, according to the network conversion formula (Equation 3); (3) (3) According to formula (4), calculate the even-mode impedance Z containing TL1 0e1 The voltage coupling coefficient k2; (4) in is the electrical length of the coupled line, is the wavelength at the center frequency, is the wavelength at the center frequency.

[0016] (4) Substitute k1 and k2 into equation (2) to obtain the value containing the unknown number Z 0e1 The expression of coupling degree C is: ; (5) Schematic diagram of coupling degree Figure 6 , you need to choose a suitable Z 0e1 , so that the difference between h1 and h2 (h1 represents the difference between the strongest coupling degree and the average coupling degree of 3dB in the frequency band; h2 represents the difference between the weakest coupling degree and the average coupling degree of 3dB in the frequency band) is as close as possible to 0; according to the requirements, the inventor uses the algorithm of matlab to calculate Z 0e1 We solved it and found that Z 0e1The size is 82.695, and a curve is drawn based on the result. Figure 7 As shown; (6) The obtained coupling line parameters are brought into the ADS software for simulation, and the coupling degree simulation curve is obtained as follows: Figure 8 ; It can be seen that the two are the same, which proves the feasibility of the calculation of the present invention and the feasibility of the circuit principle.

[0017] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A broadband 3dB power orthogonal bridge, comprising an input port, a through port, a coupling port, an isolation port and a circuit, characterized in that: The circuit comprises three sections of symmetrical coupling line stages and one section of coupling line. The three sections of symmetrical coupling line are cascaded and then staggeredly connected with the one section of coupling line.

2. The broadband 3dB power orthogonal bridge according to claim 1, characterized in that: The circuit is manufactured on a three-layer dielectric substrate.

3. The design method of the broadband 3dB power orthogonal bridge according to claim 1 or 2, characterized in that: The steps include: (1) After determining the coupling strength of the coupling lines TL2, TL3, and TL4, the three coupling lines, namely, coupling lines TL2, TL3, and TL4, are regarded as a two-port network, which is assumed to be network 1, and TL1 is assumed to be network 2. (2) Assumptions (where k1 and k2 are the voltage coupling coefficients of network 1 and network 2 respectively). The overall scattering parameters of the two cross-series couplers are obtained by using the port excitation method, and finally: （1） (3) According to the definition of the coupling degree of the coupler, the coupling degree calculation formula is obtained: (2) (4) According to the coupling degree requirements of the orthogonal bridge, the voltage coupling coefficient of TL1 is calculated through the algorithm, thereby determining the coupling degree of TL1.

4. The method according to claim 3, characterized in that: In step (1), the selection of the coupling lines TL3 and TL4 is determined according to the size of the multi-section symmetrical parallel coupling line cascade, and the coupling degree of the coupling line TL2 is determined according to the coupling degree of the selected plate design TL2.

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