A broadband balun

Abstract

The present invention discloses a broadband balun, which includes a printed short - circuit type two - wire balun and a shielding cavity. The two - wire balun is provided with three - layer circuits. The middle - layer circuit includes a first impedance compensation transformation section and a low - impedance open - circuit coupling section which are electrically connected. The two side circuits include a short - circuit double - line section, a second impedance compensation transformation section and a two - wire output section which are electrically connected in sequence. The short - circuit double - line section corresponds to the middle - layer circuit. The shielding cavity is set as a 1 / 4 - wavelength short - circuit - open - circuit cavity. The short - circuit double - line section is arranged in the shielding cavity, and the symmetry line coincides with the axis of the shielding cavity. The short - circuit position of the two - wire balun is connected to the short - circuit position of the shielding cavity. The present invention can solve the balanced feeding problems of antenna forms such as directly - fed broadband planar spiral type, conical spiral type and dipole - excited back - cavity type, realize the compression of the transverse dimension, eliminate problems such as beam tilt and pattern distortion, improve the producibility of the product and reduce the production cost.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic fields and microwave technologies, and particularly to a broadband balun. Background Art

[0002] The balanced feeding technology is a technology for solving the conversion between the unbalanced mode and the balanced mode of electromagnetic propagation, commonly known as the "balun" technology. At present, there are many types of baluns for antenna feeding. In the case of relatively low frequencies, broadband balanced feeding mostly uses a transmission line transformer to achieve, with a bandwidth up to the range of DC to 2 GHz. However, at higher frequencies, the magnetic loss of the transmission line transformer is large, and the distributed inductance effect is difficult to control, so it has little use in engineering. At higher frequencies, broadband balanced feeding technologies mostly use short-circuit type two-wire baluns, coplanar waveguide baluns, parallel cavity baluns, series cavity baluns, and planar integrated baluns, among which:

[0003] (1) The short-circuit type two-wire balun is the main body of the broadband vibrator-like antenna feeding, with a bandwidth generally between 4:1 and 7:1. Its advantage is simple structure, but it has the defect of large radiation leakage of the short-circuit two-wire at higher frequencies.

[0004] (2) The coplanar waveguide balun is essentially a combination of a short-circuit type two-wire balun and a coaxial slot balun. Its bandwidth is comparable to that of the short-circuit type two-wire balun. Its advantage is simple structure and easy integration, but it also has the defect of serious radiation leakage.

[0005] (3) The parallel cavity balun is a broadband balun formed by exchanging the positive and negative poles of the unbalanced transmission line and then using a half-wavelength short-circuit cavity to control radio frequency radiation. Its advantage is that the low-frequency cut-off is relatively slow, and the theoretical bandwidth can reach 36:1. The actual bandwidth in engineering is generally between 10:1 and 15:1, and it is mostly used in the feeding of broadband conical spirals. The disadvantage is that the structure is relatively complex and the transverse size is relatively large, which is not conducive to the miniaturization of the directly-fed broadband spiral-like antennas.

[0006] (4) The series cavity balun, also known as the Machand balun, has a bandwidth generally around 10:1. Through parameter compromise processing in engineering, the bandwidth can reach 15:1, and it is mostly used in the feeding of broadband planar spirals. However, the structure is complex and the transverse size is relatively large, which is not conducive to the miniaturization of the directly-fed broadband spiral-like antennas.

[0007] (5) There are many types of planar integrated broadband baluns, which are mainly used in broadband radio frequency circuits. Its biggest disadvantage is large transmission loss and low power capacity, and it is not widely used in the feeding of antennas.

[0008] For commercial direct-feed broadband spiral antennas, the commonly used microstrip-planar line balun or coaxial cable cutting balun (with a bandwidth of up to 100:1), known as the "broadband balun", actually does not solve the fundamental problem of poor differential balance, resulting in the problems of beam tilting and distortion at some frequency points of such feed antennas not being fundamentally solved. Summary of the Invention

[0009] To solve the above problems, the present invention proposes a broadband balun, which combines the advantages of a short-circuit type differential balun and a series cavity balun, can solve the balanced feeding of antenna forms such as direct-feed broadband planar spiral, conical spiral, and dipole-excited back cavity antennas, realizes the compression of the transverse size, eliminates problems such as beam tilting and pattern distortion, improves the producibility of products, and reduces production costs.

[0010] The technical solution adopted by the present invention is as follows:

[0011] A broadband balun, comprising:

[0012] A printed short-circuit type differential balun, which is provided with three layers of circuits. The middle layer circuit includes a first impedance compensation transformation section and a low-impedance open-circuit coupling section that are electrically connected. The two side circuits include a short-circuit double line section, a second impedance compensation transformation section, and a differential output section that are sequentially electrically connected. The short-circuit double line section corresponds to the middle layer circuit;

[0013] A shielding cavity, which is set as a 1 / 4 wavelength short-circuit-open cavity. The short-circuit double line section is arranged in the shielding cavity, and the symmetry line coincides with the axis of the shielding cavity. The short-circuit position of the printed short-circuit type differential balun is connected to the short-circuit position of the shielding cavity.

[0014] Further, the middle layer circuit further includes an input matching section, and the input matching section, the first impedance compensation transformation section, and the low-impedance open-circuit coupling section are sequentially electrically connected.

[0015] Further, the input matching section, the first impedance compensation transformation section, and the low-impedance open-circuit coupling section are sequentially connected to form a U-shaped structure.

[0016] Further, the shielding cavity and the short-circuit double line section form a high-impedance 1 / 4 wavelength suppression cavity to suppress differential radiation.

[0017] Further, the shielding cavity is set as a hollow cylindrical structure.

[0018] Further, the short-circuit double line sections on both sides of the middle layer circuit are connected through metallized vias.

[0019] Further, the short-circuit double line sections on both sides of the middle layer circuit are connected through short-circuit lines.

[0020] Further, the intermediate layer circuit and the two side circuits are disposed on a dielectric substrate layer.

[0021] The beneficial effects of the present invention are as follows:

[0022] (1) The broadband balun of the present invention combines the advantages of a short-circuit type two-wire balun and a series cavity type balun, can solve the balanced feeding of antenna forms such as direct-feed broadband planar spiral type, conical spiral type, and dipole-excited back cavity type, etc., realizes the compression of the lateral dimension, eliminates problems such as beam tilt and pattern distortion, improves the producibility of the product, and reduces the production cost.

[0023] (2) The printed short-circuit type two-wire balun of the present invention adopts a three-layer printing technology, has a simple structure, can solve the consistency problem of mass-produced products and reduce the cost.

[0024] (3) The bandwidth of the broadband balun of the present invention can be controlled within the range of 4:1 to 10:1 (within the X-band), which is equivalent to that of a fourth-order Machand balun.

[0025] (4) The insertion loss of the broadband balun of the present invention can be controlled within 1 dB (including the loss introduced by port reflection, dielectric loss, metal loss, radiation loss, etc.). Description of the Drawings

[0026] Figure 1 is a schematic structural diagram of the broadband balun according to an embodiment of the present invention.

[0027] Figure 2 is a schematic diagram of the outer circuit of the printed short-circuit type two-wire balun according to an embodiment of the present invention.

[0028] Figure 3 is a schematic diagram of the intermediate layer circuit of the printed short-circuit type two-wire balun according to an embodiment of the present invention.

[0029] Figure 4 is a schematic diagram of the S parameters of a width balun according to an embodiment of the present invention.

[0030] Reference numerals: 1 - shielding cavity, 2 - printed short-circuit type two-wire balun, 3 - short-circuit double wire segment, 4 - second impedance compensation transformation segment, 5 - two-wire output segment, 6 - dielectric substrate layer, 7 - metallized via or short circuit line, 8 - low impedance open circuit coupling section, 9 - first impedance compensation transformation segment, 10 - input matching section. Detailed Embodiments

[0031] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific implementation manners of the present invention will now be described. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0032] This embodiment provides a broadband balun, as Figure 1 shown, including a printed short-circuit type two-wire balun 2 and a shielding cavity 1, wherein the printed short-circuit type two-wire balun 2 is provided with three layers of circuits. As Figure 2 shown, the two side circuits include a short-circuit double-line segment 3, a second impedance compensation transformation segment 4, and a two-wire output segment 5 that are electrically connected in sequence. As Figure 3 shown, the middle layer circuit includes an input matching segment 10, a first impedance compensation transformation segment 9, and a low-impedance open-circuit coupling section 8 that are electrically connected in sequence. The middle layer circuit corresponds to the short-circuit double-line segment 3 of the two side circuits.

[0033] As Figure 1 shown, the shielding cavity 1 is set as a 1 / 4 wavelength short-circuit - open-circuit cavity. The short-circuit double-line segment 3 is arranged in the shielding cavity 1, and the symmetry line coincides with the axis of the shielding cavity 1. The short-circuit position of the printed short-circuit type two-wire balun 2 is connected to the short-circuit position of the shielding cavity 1. The shielding cavity 1 and the short-circuit double-line segment 3 form a high-impedance 1 / 4 wavelength suppression cavity, thereby suppressing two-wire radiation.

[0034] Preferably, as Figure 2 shown, the short-circuit double-line segments 3 on both sides of the middle layer circuit are connected by metallized vias or short-circuit lines 7.

[0035] Preferably, as Figure 2 shown, both the middle layer circuit and the two side circuits are arranged on the dielectric substrate layer 6.

[0036] Preferably, as Figure 3 shown, the input matching segment 10, the first impedance compensation transformation segment 9, and the low-impedance open-circuit coupling section 8 are connected in sequence to form a U-shaped structure.

[0037] Preferably, as Figure 1 shown, the shielding cavity 1 is set as a hollow columnar structure.

[0038] Specifically, as Figure 4 shown is the S-parameter schematic diagram of a 425 MHz - 2250 MHz broadband balun provided by this embodiment. The insertion loss of this broadband balun is controlled within 0.5 dB, and the port standing wave ratio in the full frequency band is not greater than 2.

[0039] Specifically, the printed short-circuit type two-wire balun 2 and the shielding cavity 1 of this embodiment can be adjusted according to specific frequency band ranges and specific usage requirements. From a principle perspective, the broadband balun of this embodiment can be regarded as a folded variant of a fourth-order Machand balun, and its original electrical parameters can be optimized according to the analytical model of the conventional Machand balun, and then optimized and adjusted according to the requirements that can be achieved in engineering. For example, the adverse effects brought by the distributed inductance and distributed capacitance introduced by the printed processing are mainly reduced. Given that the radiation of this balun is extremely small, it can be embedded inside a symmetric antenna for feeding, thereby compressing the longitudinal and transverse dimensions of the antenna.

[0040] The above are only the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications, and environments, and can be changed within the scope of the concept described herein through the above teachings or the technology or knowledge in related fields. Any changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A broadband balun, characterized in that, Comprising: A printed short - circuit type two - wire balun, which is provided with three - layer circuits. The middle - layer circuit includes an electrically connected first impedance compensation transformation section and a low - impedance open - circuit coupling section. The two - side circuits include a short - circuit double - line section, a second impedance compensation transformation section, and a two - wire output section that are sequentially electrically connected. The short - circuit double - line section corresponds to the middle - layer circuit; A shielding cavity, which is set as a 1 / 4 - wavelength short - circuit - open - circuit cavity. The short - circuit double - line section is arranged in the shielding cavity, and the symmetry line coincides with the axis of the shielding cavity. The short - circuit position of the printed short - circuit type two - wire balun is connected to the short - circuit position of the shielding cavity; The middle - layer circuit further includes an input matching section, and the input matching section, the first impedance compensation transformation section, and the low - impedance open - circuit coupling section are sequentially electrically connected; The input matching section, the first impedance compensation transformation section, and the low - impedance open - circuit coupling section are sequentially connected to form a U - shaped structure; The shielding cavity and the short - circuit double - line section form a high - impedance 1 / 4 - wavelength suppression cavity to suppress two - wire radiation.

2. The broadband balun according to claim 1, characterized in that, The shielding cavity is set as a hollow columnar structure.

3. The broadband balun according to claim 1 or 2, characterized in that, The short - circuit double - line sections on both sides of the middle - layer circuit are connected through metallized vias.

4. The broadband balun according to claim 1 or 2, characterized in that, The short - circuit double - line sections on both sides of the middle - layer circuit are connected through short - circuit lines.

5. The broadband balun according to claim 1 or 2, characterized in that, The middle - layer circuit and the two - side circuits are arranged on a dielectric substrate layer.

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