Balanced-to-balanced coaxial line impedance transformer and use thereof

Abstract

The application discloses a balanced-to-balanced coaxial line impedance transformer, and belongs to the electronic technical field.The coaxial line impedance transformer is composed of four coaxial lines with the same characteristic impedance and electrical length, the coaxial line has an inner conductor and an outer conductor, the coaxial line impedance transformer has two balanced radio frequency ports Z L and Z H , and the 2.25:1 Z H / Z L impedance transformation ratio is realized by connecting the inner conductor and the outer conductor between different ports of the four coaxial lines.The application breaks through the minimum impedance transformation ratio of 4:1 that can be realized by the prior art, can satisfy the impedance transformation requirement below 4:1, can be combined with other impedance transformers to realize the impedance transformation ratio with smaller discrete value, is helpful to the miniaturization, low insertion loss and multi-path power synthesis scheme, and can satisfy the high power and high efficiency application demand above 2kW.

Description

Technical Field

[0001] This invention belongs to the field of electronic technology, and in particular relates to a balanced-to-balance coaxial impedance converter and its applications. Background Technology

[0002] Radio frequency (RF) power amplifiers are core components of modern wireless communication systems. These high-power devices, with output power ranging up to kilowatts, are widely used in military radios, radar detection, remote control and telemetry, FM broadcasting, television signal transmission, and mobile communication base stations. For kilowatt-level power amplifiers in the MF-HF band, due to their lower operating frequency and longer wavelength, transmission line impedance transformers are often used for impedance transformation. In push-pull RF power amplifiers, balanced-to-balance transmission line impedance transformers are commonly used. In practical applications, transmission line impedance transformers are generally implemented using coaxial cables and can be designed with different impedance transformation ratios as needed, such as 4:1, 9:1, and 16:1.

[0003] Based on existing technical solutions, balance-to-balance coaxial impedance transformers can only achieve N... 2 Impedance transformation ratio of 1 (N is an integer greater than 1) (e.g., 2) 2 1, 3 2 1, 4 2 :1), its minimum achievable impedance transformation ratio is 4:1, which cannot meet the impedance transformation requirements below 4:1. Furthermore, the impedance ratios achieved by existing technical solutions are discrete values ​​with large ranges. In practical applications, the implementation of matching schemes is significantly limited, making it difficult to meet impedance matching requirements. Often, additional inductors and capacitors are needed to achieve the target impedance transformation, which is detrimental to miniaturization and low-cost design. This problem is even more pronounced in multi-channel power combining schemes. The power combining network is limited by the impedance transformation ratio, often resulting in complex and bulky matching structures, leading to greater insertion losses and making it difficult to meet the high-power, high-efficiency application requirements of 2kW and above. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a balanced-to-balance coaxial impedance transformer and its application, which can achieve an impedance ratio of 2.25:1 to meet complex design requirements.

[0005] The first objective of this invention can be achieved through the following technical solution: a balance-to-balance coaxial line impedance transformer, comprising four coaxial lines having the same characteristic impedance and electrical length; the first coaxial line having a first inner conductor and a first outer conductor; the second coaxial line having a second inner conductor and a second outer conductor; the third coaxial line having a third inner conductor and a third outer conductor; and the fourth coaxial line having a fourth inner conductor and a fourth outer conductor; the first port of the first inner conductor and the first port of the fourth inner conductor together constitute a low-impedance balance port Z. L The second port of the first inner conductor and the second port of the fourth inner conductor together constitute the high-impedance balanced port Z. H The first inner conductor's first port is connected to the first outer conductor's second port and the third inner conductor's first port, respectively; the first outer conductor's first port and the second outer conductor's first port are connected; the second outer conductor's second port and the first inner conductor's second port are connected; the fourth inner conductor's first port is connected to the fourth outer conductor's second port and the second inner conductor's first port, respectively; the fourth outer conductor's first port and the third outer conductor's first port are connected; the third outer conductor's second port and the fourth inner conductor's second port are connected; the second inner conductor's second port and the third inner conductor's second port are connected.

[0006] Preferably, the coaxial line is a two-conductor transmission line capable of transmitting TEM mode signals, including coaxial cable, coaxial device, microstrip line or stripline.

[0007] Preferably, ferrite magnetic rings or cores are individually or not provided on the four coaxial cables. The arrangement of ferrite magnetic rings or cores is not limited to the winding method between the coaxial cables and the ferrite magnetic rings or cores.

[0008] Preferably, a node C is provided between the second port of the second inner conductor and the second port of the third inner conductor, and the node C is grounded.

[0009] Preferably, a node C' is provided between the second port of the second inner conductor and the second port of the third inner conductor, and the node C' is grounded through a resistive-capacitive-inductive network.

[0010] Preferably, the RC network is a resonant network composed of one or more of the following elements: resistive elements, capacitive elements, and inductive elements.

[0011] According to another aspect of the invention, an application of a balance-to-balance coaxial line impedance converter is provided, wherein the balance-to-balance coaxial line impedance converter is applied in a push-pull power amplifier to complete a balance-to-balance impedance transformation with an impedance ratio of less than 4:1, or it is used in combination with other N:1 impedance converters to achieve an impedance transformation ratio with smaller discrete values.

[0012] Compared with the prior art, the beneficial effects of the present invention are:

[0013] 1. This invention reduces the impedance ratio to 2.25:1, breaking through the existing technology's minimum impedance transformation ratio of 4:1, and enables balanced-to-balance impedance transformation with an impedance ratio lower than 4:1 in push-pull power amplifiers.

[0014] 2. This invention can also be combined with other N:1 impedance transformers to achieve impedance transformation ratios with smaller discrete values, meet flexible design requirements, and help realize miniaturized, low insertion loss multi-channel power combining schemes. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the circuit principle of the balanced-to-balance coaxial impedance converter in Embodiment 1 of the present invention.

[0016] Figure 2 This is a schematic diagram illustrating the working principle of the balanced-to-balance coaxial impedance converter in Embodiment 1 of the present invention.

[0017] Figure 3 This is a schematic diagram of the circuit principle of the balanced-to-balance coaxial impedance converter in Embodiment 2 of the present invention.

[0018] Figure 4 This is a schematic diagram of the circuit principle of the balanced-to-balance coaxial impedance converter in Embodiment 3 of the present invention.

[0019] Figure 5 This is a schematic diagram of the circuit principle of the balanced-to-balance coaxial impedance converter in Embodiment 4 of the present invention when used alone.

[0020] Figure 6 This is a schematic diagram of the circuit principle when a balanced-to-balance coaxial impedance converter and a balanced-to-unbalanced impedance converter are used in combination in Embodiment 4 of the present invention.

[0021] Figure 7 This is a circuit diagram of the resistor-capacitor-inductor network in an embodiment of the present invention.

[0022] Figure 8 This is a comparison chart of the common-mode rejection ratio of the impedance transformers in Embodiments 1 to 3 of the present invention.

[0023] In the diagram, 1. First coaxial line; 1a1. First port of the first inner conductor; 1a2. Second port of the first inner conductor; 1b1. First port of the first outer conductor; 1b2. Second port of the first outer conductor; 2. Second coaxial line; 2a1. First port of the second inner conductor; 2a2. Second port of the second inner conductor; 2b1. First port of the second outer conductor; 2b2. Second port of the second outer conductor; 3. Third coaxial line; 3a1. First port of the third inner conductor; 3a2. Second port of the third inner conductor; 3b1. First port of the third outer conductor; 3b2. Second port of the third outer conductor; 4. Fourth coaxial line; 4a1. First port of the fourth inner conductor; 4a2. Second port of the fourth inner conductor; 4b1. First port of the fourth outer conductor; 4b2. Second port of the fourth outer conductor; 5. Resistor-capacitor-inductor network. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0025] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0026] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the accompanying drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0027] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0028] Example 1:

[0029] like Figure 1 As shown, the balanced-to-balance coaxial line impedance transformer provided by this invention consists of four coaxial lines with the same characteristic impedance and electrical length. These coaxial lines are two-conductor transmission lines capable of transmitting TEM-mode signals and have inner and outer conductors. They can be coaxial cables, coaxial adapters, microstrip lines, or striplines. Each coaxial line may or may not have a ferrite core. When a ferrite core is used, the winding method between the coaxial line and the ferrite core is not limited. In the following description, the four coaxial lines are distinguished as first coaxial line 1, second coaxial line 2, third coaxial line 3, and fourth coaxial line 4. Correspondingly, first coaxial line 1 has a first inner conductor and a first outer conductor; second coaxial line 2 has a second inner conductor and a second outer conductor; third coaxial line 3 has a third inner conductor and a third outer conductor; and fourth coaxial line 4 has a fourth inner conductor and a fourth outer conductor. Each inner and outer conductor has a first port and a second port.

[0030] Specifically, the circuit connection of the balanced-to-balanced coaxial line impedance transformer in this embodiment is as follows: the first port 1a1 of the first inner conductor and the first port 4a1 of the fourth inner conductor together constitute the low-impedance balanced port Z. L The second port 1a2 of the first inner conductor and the second port 4a2 of the fourth inner conductor together constitute the high-impedance balanced port Z. HThe first inner conductor's first port 1a1 is connected to the first outer conductor's second port 1b2 and the third inner conductor's first port 3a1, respectively; the first outer conductor's first port 1b1 is connected to the second outer conductor's first port 2b1; the second outer conductor's second port 2b2 is connected to the first inner conductor's second port 1a2; the fourth inner conductor's first port 4a1 is connected to the fourth outer conductor's second port 4b2 and the second inner conductor's first port 2a1, respectively; the fourth outer conductor's first port 4b1 is connected to the third outer conductor's first port 3b1; the third outer conductor's second port 3b2 is connected to the fourth inner conductor's second port 4a2; and the second inner conductor's second port 2a2 is connected to the third inner conductor's second port 3a2.

[0031] The working principle of the balanced-to-balance coaxial impedance converter of the present invention is as follows:

[0032] Assuming it is applied to the high impedance balanced port Z H The input voltage across the two ends is V I+ and V I- At the low impedance balanced port Z L The output voltage at both ends is V O+ and V O- The node voltage at point B' where the first port 1b1 of the first outer conductor and the first port 2b1 of the second outer conductor are interconnected is V. B’ The node voltage at the interconnection point B between the first port 3b1 of the third outer conductor and the first port 4b1 of the fourth outer conductor is V. B The node voltage at point A, where the second inner conductor's second port 2a2 and the third inner conductor's second port 3a2 are interconnected, is V. A The current flowing through each inner and outer conductor of the first coaxial line 1 to the fourth coaxial line 4 is I. The voltage at critical nodes and the branch currents are as follows: Figure 2 As shown, based on the characteristics and working principle of the coaxial cable, the voltage at each node and the current in each branch have the following relationship:

[0033] V O- -V B =V I- -V O-

[0034] V O+ -V B’ =V I+ -V O+

[0035] V I+ -V I- =(V I+ -V A )+(V A -V I- )=(V B’ -V O- )+(VO+ -V B )

[0036] Combining the above three equations, we can obtain:

[0037] V I+ -V I- =3 / 2*(V O+ -V O- )

[0038] And Z L With Z H It can be obtained through the following formula:

[0039] Z L =(V O+ -V O- ) / (3*I)

[0040] Z H =(V I+ -V I- ) / (2*I)

[0041] The above three equations can be combined to obtain Z. L With Z H The relationship is:

[0042] Z H / Z L =3 2 / 2 2 =2.25:1

[0043] Z L With Z H The impedance ratio is the impedance ratio between the two balanced ports of the coaxial line impedance converter.

[0044] This invention, through the design of the above-mentioned balanced-to-balance coaxial line impedance transformer, achieves a minimum impedance transformation ratio of 2.25:1, breaking through the existing technology's minimum impedance transformation ratio of 4:1, and effectively meeting the impedance transformation requirements below 4:1.

[0045] Example 2:

[0046] This embodiment is a further improvement on Embodiment 1. In this embodiment, the main structure of the balanced-to-balance coaxial impedance transformer is roughly the same as that in Embodiment 1, except that: Figure 3As shown, node C is positioned between the second port 2a2 of the second inner conductor and the second port 3a2 of the third inner conductor, and node C is grounded. The function of the balanced-to-balanced coaxial impedance transformer is to transmit the differential-mode signal between the two balanced ports. Since common-mode signals exist in the RF path, the common-mode rejection ratio (CMRR) is commonly used to measure the network's ability to suppress common-mode signals. It is defined as the ratio of the amplification factor for the differential-mode signal to the amplification factor for the common-mode signal; a higher CMRR indicates better suppression of common-mode signals. In this embodiment, since node C is located at the center of symmetry of the entire structure, grounding node C can affect the impedance of the common-mode signal, thereby affecting the CMRR of the entire network, but it will not change the impedance transformation between the two ports of the impedance transformer.

[0047] Example 3:

[0048] This embodiment is a further improvement on Embodiment 1. In this embodiment, the main structure of the balanced-to-balance coaxial impedance transformer is roughly the same as that in Embodiment 1, except that: Figure 4 As shown, a node C' is provided between the second port 2a2 of the second inner conductor and the second port 3a2 of the third inner conductor. This node C' is grounded through the RC network 5. Specifically, the RC network 5 is a resonant network composed of resistive elements, capacitive elements, inductive elements, and one or more of these elements. The structure of the RC network is as follows... Figure 7 As shown, the order of the resistors, capacitors, and inductors in this structure does not affect the circuit function. Figure 8 The results show a comparison of the common-mode rejection ratio (CMRR) of the improved scheme based on Embodiment 1. The curves of the inverted triangle icons represent the CMRR of Embodiment 1, the curves of the square icons represent the CMRR of Embodiment 2 (node ​​C grounded), and the curves of the circular icons represent the CMRR of this embodiment (node ​​C' grounded through an RC network). The results show that at an operating frequency of 100.3MHz, the impedance transformer of this embodiment has a higher CMRR than other structures.

[0049] Example 4:

[0050] This embodiment provides a working scenario for the standalone application of the balanced-to-balanced coaxial impedance converter of the present invention, such as... Figure 5 As shown, the balanced-to-balanced coaxial line impedance transformer of the present invention achieves a simple impedance transformation function: at the high impedance balanced port Z... H A 50-ohm load R1 is connected. After passing through an impedance transformer with an impedance transformation ratio of 2.25:1, the 50-ohm impedance can be transformed to 50 / 2.25 = 22.2 ohms. At this time, the low-impedance balanced port Z... L The impedance is well matched with the external 22.2 ohm load R2.

[0051] Example 5:

[0052] This embodiment provides a working scenario when the balanced-to-balanced coaxial impedance converter of the present invention and a 9:1 balanced-to-unbalanced impedance converter are used in combination. For example... Figure 6 As shown, this circuit is a two-way power combining circuit. It includes two balancing-to-balancing coaxial converters with an impedance ratio of 2.25:1 (as proposed in this invention) and one balancing-to-unbalancing impedance converter with an impedance ratio of 9:1. First, the balancing-to-unbalancing impedance converter with an impedance ratio of 9:1 performs impedance transformation on the 50-ohm load at the unbalancing port, resulting in an impedance of 50 / 9 = 5.6 ohms at the balancing port. Then, the high-impedance balancing port Z of the two balancing-to-balancing coaxial converters with an impedance ratio of 2.25:1... H Connected to a 5.6-ohm balanced port, and converted to two low-impedance balanced ports Z. L Connected to the corresponding two power amplifiers, the two low-impedance balanced ports Z... L The impedance is 5.6 * 2 / 2.25 = 4.9 ohms. For a 65V LDMOS device, the maximum output power of a single channel is (65 * 2). 2 / 2 / 4.9=1724W, and the combined output power of the two amplifiers can reach over 3000W. This meets the needs of high-power, high-efficiency applications above 2kW.

[0053] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A balanced-to-balanced coaxial line impedance converter, characterized in that, It includes four coaxial cables with the same characteristic impedance and electrical length; the first coaxial cable (1) has a first inner conductor and a first outer conductor, the second coaxial cable (2) has a second inner conductor and a second outer conductor, the third coaxial cable (3) has a third inner conductor and a third outer conductor, and the fourth coaxial cable (4) has a fourth inner conductor and a fourth outer conductor; the first port (1a1) of the first inner conductor and the first port (4a1) of the fourth inner conductor together constitute the low impedance balanced port Z. L The second port of the first inner conductor (1a2) and the second port of the fourth inner conductor (4a2) together constitute the high-impedance balanced port Z. H The first inner conductor's first port (1a1) is connected to the first outer conductor's second port (1b2) and the third inner conductor's first port (3a1) respectively; the first outer conductor's first port (1b1) is connected to the second outer conductor's first port (2b1); the second outer conductor's second port (2b2) ​​is connected to the first inner conductor's second port (1a2); the fourth inner conductor's first port (4a1) is connected to the fourth outer conductor's second port (4b2) and the second inner conductor's first port (2a1) respectively; the fourth outer conductor's first port (4b1) is connected to the third outer conductor's first port (3b1); the third outer conductor's second port (3b2) is connected to the fourth inner conductor's second port (4a2); The second port (2a2) of the second inner conductor and the second port (3a2) of the third inner conductor are connected.

2. The balanced-to-balance coaxial impedance converter according to claim 1, characterized in that, The coaxial cable is a two-conductor transmission line capable of transmitting TEM mode signals.

3. A balanced-to-balance coaxial line impedance converter according to claim 1 or 2, characterized in that, Ferrite rings or cores may be individually or not provided on the four coaxial cables.

4. A balanced-to-balance coaxial line impedance converter according to claim 3, characterized in that, A node C is provided between the second port (2a2) of the second inner conductor and the second port (3a2) of the third inner conductor, and node C is grounded.

5. A balanced-to-balance coaxial impedance converter according to claim 3, characterized in that, A node C' is provided between the second port (2a2) of the second inner conductor and the second port (3a2) of the third inner conductor, and the node C' is grounded through a resistive-capacitive-inductive network (5).

6. A balanced-to-balance coaxial line impedance converter according to claim 5, characterized in that, The aforementioned RC network (5) is a resonant network composed of one or more of the following elements: resistive elements, capacitive elements, and inductive elements.

7. An application of a balanced-to-balanced coaxial line impedance converter, wherein the balanced-to-balanced coaxial line impedance converter according to any one of claims 1-6 is used alone in a push-pull power amplifier, or the balanced-to-balanced coaxial line impedance converter is used in combination with other N:1 impedance converters in a two-way power combining circuit.

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