Broadband coaxial cable balun device

Abstract

The invention discloses a broadband coaxial cable balun device which comprises a first coaxial unit, a second coaxial unit and a connecting unit arranged between the first coaxial unit and the second coaxial unit, the first coaxial unit is provided with an input port, the second coaxial unit is provided with two output ports, and the first coaxial unit and the second coaxial unit are connected through the connecting unit. The first coaxial unit and the second coaxial unit have a common reference ground; the first coaxial unit and the second coaxial unit are arranged on the two sides of a middle vertical line of the connecting unit in a bilateral symmetry mode, and the characteristic impedance of the first coaxial unit is the same as that of the second coaxial unit. By reasonably setting the resistance values of the capacitor and the inductor, the broadband coaxial cable balun can be realized.

Description

Technical Field

[0001] The present invention relates to the field of radio frequency technology, and in particular to a broadband coaxial cable balun device. Background Art

[0002] Balun, or balanced-unbalanced converter, is a three-port passive device used to convert balanced signals (differential signals, i.e. two signals with equal amplitudes and a phase difference of 180°) to unbalanced signals (single-ended signals). The key performance evaluation of balun mainly includes parameters such as frequency range, insertion loss, return loss, amplitude balance, and phase balance.

[0003] The coaxial cable balun is a three-port device, or a broadband RF transmission line transformer that realizes the connection between the balanced transmission line circuit and the unbalanced transmission line circuit by converting the matched input into a differential output. In practical applications, the coaxial cable is usually placed near the reference ground plane, and the inner and outer conductors form an inherent transmission line. Due to the shielding effect, the current inside the inner and outer conductors always has the same magnitude, but flows in opposite directions.

[0004] Coaxial cable baluns are currently mainly used in broadband power amplifier designs, which require a relatively wide relative bandwidth. The above-mentioned problem is particularly important in RF design, which directly limits the application of coaxial cable baluns and is an urgent problem to be solved in the microwave RF field. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a wideband coaxial cable balun device, aiming to solve the problem of high requirements of the coaxial cable balun on relative bandwidth.

[0006] The present invention is achieved through the following technical solutions:

[0007] A wideband coaxial cable balun device comprises a first coaxial unit, a second coaxial unit and a connecting unit arranged between the first coaxial unit and the second coaxial unit, wherein the first coaxial unit is provided with an input port, the second coaxial unit is provided with two output ports, and the first coaxial unit and the second coaxial unit have a common reference ground; the first coaxial unit and the second coaxial unit are arranged symmetrically on both sides of a mid-vertical line of the connecting unit, and the first coaxial unit and the second coaxial unit have the same characteristic impedance.

[0008] A further preferred embodiment of the present invention is: the first coaxial unit includes a first coaxial unit inner conductor and a first coaxial unit outer conductor arranged outside the first coaxial unit; the second coaxial unit includes a second coaxial unit inner conductor and a second coaxial unit outer conductor arranged outside the second coaxial unit; the first coaxial unit outer conductor and the second coaxial unit outer conductor both have the same characteristic impedance as the common reference ground.

[0009] A further preferred solution of the present invention is that: the first coaxial unit inner conductor is connected to the second coaxial unit inner conductor via a central conductor; and the first coaxial unit outer conductor is connected to the second coaxial unit outer conductor via a connecting unit.

[0010] A further preferred embodiment of the present invention is: the input port is connected to one side of the inner conductor of the first coaxial unit, and the same side of the outer conductor of the first coaxial unit is grounded; the two output ports of the second coaxial unit are respectively a first output port and a second output port, the first output port is connected to one side of the inner conductor of the second coaxial unit, and the second output port is connected to the same side of the outer conductor of the second coaxial unit.

[0011] A further preferred solution of the present invention is that the connection unit is a single capacitor structure or an inductor-capacitor matching structure.

[0012] A further preferred solution of the present invention is that the inductor-capacitor matching structure includes two capacitors and one inductor, the two capacitors are arranged symmetrically on both sides of the inductor, one end of each capacitor is grounded, and the other end is connected to the inductor.

[0013] The present invention discloses a broadband coaxial cable balun device, compared with the prior art:

[0014] The present invention can realize a wide-band coaxial cable balun by reasonably setting the resistance values ​​of the capacitor and the inductor; the present invention adopts the above technical solution and can realize ultra-wideband operation compared with the traditional coaxial cable balun, and has the technical effect of easy debugging. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the overall structure of the wide-band coaxial cable balun device of the present invention.

[0016] Figure 2 It is a schematic diagram of a connection unit of the present invention as a single capacitor structure.

[0017] Figure 3 The connecting unit of the present invention is a schematic diagram of an inductor-capacitor matching structure.

[0018] Figure 4 FIG. 1 is a top view of an embodiment of a wide-band coaxial cable balun device with a single capacitor structure of the present invention.

[0019] Figure 5 FIG. 1 is a top view of an embodiment of a wide-band coaxial cable balun device with an inductor-capacitor matching structure of the present invention.

[0020] Figure 6 It is a cross-sectional view of the broadband coaxial cable balun device of the present invention.

[0021] Figure 7 It is a schematic diagram of the insertion loss waveform of the present invention.

[0022] Figure 8 It is a schematic diagram of the reflection coefficient waveform of the present invention.

[0023] The numbers and letters in the figure represent the corresponding component names:

[0024] Among them: 1, input port; 2, first output port; 3, second output port; 4, first coaxial unit inner conductor; 4a, first coaxial unit inner conductor on the left side; 4b, first coaxial unit inner conductor on the right side; 5, first coaxial unit outer conductor; 5a, first coaxial unit outer conductor on the left side; 5b, first coaxial unit outer conductor on the right side; 6, second coaxial unit inner conductor; 6a, second coaxial unit inner conductor on the left side; 6b, second coaxial unit inner conductor on the right side; 7, second coaxial unit outer conductor; 7a, second coaxial unit outer conductor on the left side; 7b, second coaxial unit outer conductor on the right side; 8, First coaxial unit; 9, second coaxial unit; 10, connecting unit; 11, grounding post; 12, reference common ground; 13, center conductor; 14, substrate; 15, access hole; 16, first grounding pad; 17, second grounding pad; 18, substrate surface; T1, first transmission line; T2, second transmission line; T3, third transmission line; L1, first inductor; C1, first capacitor; C2, second capacitor; C3, third capacitor; Z1, characteristic impedance of first coaxial unit; Z2, characteristic impedance of second coaxial unit; Z3, characteristic impedance of first coaxial unit to ground; Z4, characteristic impedance of second coaxial unit to ground. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0026] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0027] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "inside", "outside", etc. appear to indicate the orientation or position relationship, it is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as a limitation on the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0028] See also Figures 1 to 8 As shown, the present invention discloses a wide-band coaxial cable balun device, comprising a first coaxial unit, a second coaxial unit and a connecting unit 10 arranged between the first coaxial unit and the second coaxial unit, wherein the first coaxial unit is provided with an input port 1, the second coaxial unit is provided with two output ports, and the first coaxial unit and the second coaxial unit have a common reference ground 12; the first coaxial unit and the second coaxial unit are arranged symmetrically on both sides of a mid-vertical line of the connecting unit 10, and the first coaxial unit and the second coaxial unit have the same characteristic impedance.

[0029] The first coaxial unit 8 includes a first coaxial unit inner conductor 4 and a first coaxial unit outer conductor 5 arranged outside the first coaxial unit; the second coaxial unit includes a second coaxial unit inner conductor 6 and a second coaxial unit outer conductor 7 arranged outside the first coaxial unit; the first coaxial unit outer conductor 5 and the second coaxial unit outer conductor 7 have the same characteristic impedance as the common reference ground 12; there is a first coaxial unit characteristic impedance Z1 between the first coaxial unit inner conductor 4 and the first coaxial unit outer conductor 5, and there is a second coaxial unit characteristic impedance Z2 between the second coaxial unit inner conductor 6 and the second coaxial unit outer conductor 7; there is a characteristic impedance to ground between the first coaxial unit outer conductor 5 and the second coaxial unit outer conductor 7 and the common reference ground 12, that is, the first coaxial unit The characteristic impedance to ground is Z3, the characteristic impedance to ground of the second coaxial unit is Z4, the electrical lengths of the first coaxial unit 8 and the second coaxial unit 9 are the same, and the electrical length is 90° at the center frequency of the designed working bandwidth; the characteristic impedances of the first coaxial unit 8 and the second coaxial unit 9 are the same as each other, and are the same as the reference impedance of the input port, that is, the characteristic impedance Z1 of the first coaxial unit, the characteristic impedance Z2 of the second coaxial unit and the impedance of the input port 1 are the same; the characteristic impedances between the outer conductors of the two coaxial units and the common reference ground are the same as each other; that is, the impedances of the characteristic impedance Z3 of the first coaxial unit to ground and the characteristic impedance Z4 of the second coaxial unit to ground are the same, and the reference impedances of the two output ports are the same, that is, the reference impedances of the first output port 2 and the second output port 3 are the same.

[0030] The input port 1 is connected to one side of the inner conductor 4 of the first coaxial unit, and the same side of the outer conductor 5 of the first coaxial unit is grounded; the two output ports of the second coaxial unit are the first output port 2 and the second output port 3, respectively, the first output port 2 is connected to one side of the inner conductor 6 of the second coaxial unit, and the second output port 3 is connected to the same side of the outer conductor 7 of the second coaxial unit; the input port 1 is connected to the leftmost side 4a of the outer conductor of the first coaxial unit, the rightmost side 4b of the inner conductor of the first coaxial unit is connected to the leftmost side 6a of the inner conductor of the second coaxial unit, and the rightmost side 6b of the inner conductor of the second coaxial unit is connected to the first output port 2; the leftmost side 5a of the outer conductor of the first coaxial unit is connected to the grounding column 11; the rightmost side 5b of the outer conductor of the first coaxial unit is connected to the connecting unit 10, the connecting unit 10 is connected to the leftmost side 7a of the outer conductor of the second coaxial unit, and the rightmost side 7b of the outer conductor of the second coaxial unit is connected to the second output port 3.

[0031] See also Figure 2 and Figure 3 As shown, Figure 2 and Figure 3 Two filling conditions of the connection unit 10 are shown. The connection unit 10 is a single capacitor structure or an inductor-capacitor matching structure. The inductor-capacitor matching structure includes two capacitors and one inductor. The two capacitors are arranged symmetrically on both sides of the inductor. One end of each capacitor is grounded and the other end is connected to the inductor. Figure 2 As shown, when the connecting unit 10 is a single capacitor structure, there is only the first capacitor C1; Figure 3 As shown, when the connecting unit 10 is an inductor-capacitor matching structure, one end of the second capacitor C2 and the third capacitor C3 are connected to both sides of the first inductor L1, and the other end is grounded.

[0032] Figure 4 and Figure 5The top view of the wideband coaxial cable balun device made by the embodiment is shown. The entire coaxial cable balun device is formed on a substrate surface 18 of a single substrate 14. The substrate 14 is usually made of ceramic, such as alumina. The substrate 14 is supported by a reference common ground 12. An access hole 15 is located near the leftmost side of the first coaxial unit 8. The grounding post 11 extends from the reference common ground 12 and has a bonding surface substantially at the same level as the substrate surface 18. The first transmission line T1 is formed near the access hole 15 and leads to the input port 1. The conductor 4 is connected to the first transmission line T1, the second transmission line T2 is formed in the middle of the rightmost side of the substrate 14 and leads to the first output port 2, the second coaxial unit inner conductor 6 is connected to the second transmission line T2, the third transmission line T3 is formed on the rightmost side of the second coaxial unit 9 and leads to the second output port 3, the second coaxial unit outer conductor 7 is connected to the second transmission line T2, the first coaxial unit inner conductor 4 and the second coaxial unit inner conductor 6 are connected by the center conductor 13; the first coaxial unit outer conductor 5 and the second coaxial unit outer conductor 7 are connected by the connecting unit 10.

[0033] like Figure 4 As shown, when the connecting unit 10 is a single capacitor structure, the first capacitor C1 is formed between the first coaxial unit outer conductor 5 and the second coaxial unit outer conductor 7; Figure 5 As shown, when the connecting unit 10 is an inductor-capacitor matching structure, a first inductor L1 is formed between the first coaxial unit outer conductor 5 and the second coaxial unit outer conductor 7, a second capacitor C2 is formed between the first coaxial unit outer conductor 5 and the first grounding pad 16, and a third capacitor C3 is formed between the second coaxial unit outer conductor 7 and the second grounding pad 17.

[0034] Figure 6 It is a cross-sectional view of a coaxial cable balun device, wherein a grounding post 11 extends from a common reference ground 12, which usually serves as a grounding function; a coupling effect is achieved between the first coaxial unit 8 and the second coaxial unit 9 by using a connecting unit 10, and a wide-band coaxial cable balun can be achieved by reasonably setting the resistance distribution of the capacitor and the inductor;

[0035] The value of input port 1 is 50Ohm; the value of all output ports, namely the first output port 2 and the second output port 3, is 25Ohm; the characteristic impedance Z1 of the first coaxial unit and the characteristic impedance Z2 of the second coaxial unit are 50Ohm; the characteristic impedance Z3 of the first coaxial unit to ground and the characteristic impedance Z4 of the second coaxial unit to ground are 200Ohm; the electrical length of the first coaxial unit 8 and the second coaxial unit 9 is 90° at 1GHz; the first inductance L1, the first capacitor C1, the second capacitor C2 and the third capacitor C3 are 190nH, 1896pF, 7000pF and 198pF respectively.

[0036] The above circuit schematic is simulated using ADS simulation software, and the S parameter curve obtained by simulation is as follows: Figure 7 and 8 As shown, Figure 7 and Figure 8 is the transmission phase diagram in the embodiment obtained by simulation, Figure 7 The middle dashed line is the insertion loss when the connection unit 10 is a single capacitor structure, and the solid line is the insertion loss when the connection unit is an inductor-capacitor matching structure. The upper trace refers to the internal coaxial conductor at the balun output, and the lower trace refers to the external coaxial conductor at the balun output. Figure 8 The dashed line is the reflection coefficient when the connection unit is a single capacitor structure, and the solid line is the reflection coefficient when the connection unit is an inductor-capacitor matching structure. Figure 7 and Figure 8 It can be clearly seen that a good single-capacitor balun performance is only possible between 200MHz and 800MHz, while a good inductor-capacitor matching balun performance is possible between 250MHz and 1500MHz. Reasonable adjustment of the resistance values ​​of capacitors and inductors can achieve a wider bandwidth design.

[0037] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A wideband coaxial cable balun device, characterized in that: The invention comprises a first coaxial unit (8), a second coaxial unit (9) and a connecting unit (10) arranged between the first coaxial unit (8) and the second coaxial unit (9), wherein the first coaxial unit is provided with an input port (1), the second coaxial unit is provided with two output ports, and the first coaxial unit and the second coaxial unit have a common reference ground (12); the first coaxial unit and the second coaxial unit are arranged symmetrically on both sides of a vertical center line of the connecting unit (10), and the first coaxial unit and the second coaxial unit have the same characteristic impedance.

2. The broadband coaxial cable balun device according to claim 1, characterized in that: The first coaxial unit comprises a first coaxial unit inner conductor (4) and a first coaxial unit outer conductor (5) arranged outside the first coaxial unit; the second coaxial unit comprises a second coaxial unit inner conductor (6) and a second coaxial unit outer conductor (7) arranged outside the first coaxial unit; the first coaxial unit outer conductor (5) and the second coaxial unit outer conductor (7) both have the same characteristic impedance as a common reference ground (12).

3. The broadband coaxial cable balun device according to claim 2, characterized in that: The first coaxial unit inner conductor (4) and the second coaxial unit inner conductor (6) are connected via a central conductor (13); the first coaxial unit outer conductor (5) and the second coaxial unit outer conductor (7) are connected via a connecting unit (10).

4. The broadband coaxial cable balun device according to claim 3, characterized in that: The input port (1) is connected to one side of the inner conductor (4) of the first coaxial unit, and the same side of the outer conductor (5) of the first coaxial unit is grounded; the two output ports of the second coaxial unit are respectively a first output port (2) and a second output port (3), the first output port (2) is connected to one side of the inner conductor (6) of the second coaxial unit, and the second output port (3) is connected to the same side of the outer conductor (7) of the second coaxial unit.

5. The broadband coaxial cable balun device according to claim 1, characterized in that: The connection unit (10) is a single capacitor structure or an inductor-capacitor matching structure.

6. The broadband coaxial cable balun device according to claim 5, characterized in that: The inductor-capacitor matching structure includes two capacitors and an inductor. The two capacitors are arranged symmetrically on both sides of the inductor. One end of each capacitor is grounded, and the other end is connected to the inductor.

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