Broadband coaxial-to-microstrip line converter

Abstract

The broadband coaxial-to-microstrip line converter comprises a coaxial line, a gold strip and a substrate, the coaxial line comprises a coaxial outer conductor, a central medium and a coaxial inner conductor which are arranged from outside to inside, the coaxial inner conductor at one end of the coaxial line is shorter than the coaxial outer conductor, and a containing space for installing the gold strip and the substrate is formed. The substrate comprises a top-layer conduction band, a middle insulating layer and a bottom-layer conduction band, the top-layer conduction band comprises a top-layer gradual change area and a microstrip line which are located on the same center line with the coaxial inner conductor, and the bottom-layer conduction band is provided with a gradual change hollow area right below the top-layer gradual change area to jointly form a mode gradual change area. According to the utility model, the structure is exquisite, a TEM mode transmitted in a coaxial line can be smoothly transited to a quasi TEM mode transmitted by a microstrip line, the working bandwidth of the whole conversion circuit is effectively improved, the working frequency can reach up to 50GHz, and the return loss of each frequency point is less than-15dB.

Description

Technical Field

[0001] The utility model belongs to the technical field of radio frequency circuits, and in particular relates to a broadband coaxial to microstrip line converter. Background Art

[0002] In microwave circuit design, the transition from coaxial line to microstrip line is a key and common problem, which involves the sudden change of propagation mode from pure TEM mode to quasi-TEM mode. A common solution to this problem is impedance matching, that is, introducing appropriate inductance or capacitance at the discontinuity of the transition between the two according to the Smith chart theory, which is more suitable for the conversion of coaxial line to microstrip line in narrow band, or designing the conversion circuit of coaxial line and microstrip line, but it generally has problems such as large size and inconvenient connection. Utility Model Content

[0003] Technical purpose: In view of the above technical problems, the utility model proposes a broadband coaxial to microstrip line converter, which has a small size, a simple structure and a wide operating frequency band.

[0004] Technical solution: To achieve the above technical objectives, the utility model adopts the following technical solution:

[0005] A broadband coaxial to microstrip line converter, comprising a 50 ohm coaxial line, a gold strip and a substrate, wherein the coaxial line comprises a coaxial outer conductor, a center medium and a coaxial inner conductor arranged from outside to inside, wherein the coaxial inner conductor at one end of the coaxial line is shorter than the coaxial outer conductor, forming an accommodation space for installing the gold strip and the substrate;

[0006] The substrate comprises a top conductive strip, an intermediate insulating layer and a bottom conductive strip, wherein the top conductive strip comprises a top gradient region and a microstrip line located on the same center line as the coaxial inner conductor, wherein the top gradient region is a symmetrical conductor structure surrounded by a wide straight edge, a narrow straight edge and two top gradient lines, wherein one end of the wide straight edge of the top gradient region is overlapped with the coaxial inner conductor through a gold strip, and one end of the narrow straight edge is connected to the microstrip line; and a gradient hollow region is arranged in the bottom conductive strip directly below the top gradient region.

[0007] Preferably, the two top gradient lines are both fitting curves with a length of 0.75 mm, and the characteristic impedance of the top conductive strip remains unchanged at 50 ohm in the top gradient region; the width of the microstrip line 9 is 0.25 mm, and the characteristic impedance is 50 ohm.

[0008] Preferably, the area of ​​the gradient hollow region is larger than the top gradient region, and both sides of the bottom conductive strip overlap the coaxial outer conductor; the maximum width of the gradient hollow region 7 is 1.57 mm, and the maximum length is 1 mm.

[0009] Preferably, the width of the gold strip is between the diameter of the coaxial inner conductor and the diameter of the coaxial outer conductor, the height of the gold strip is equal to the thickness of the substrate, one end of the gold strip is overlapped with the top gradient area through a bonding process, and the other end is bent and tightly attached between the side of the substrate and the side of the coaxial inner conductor.

[0010] Preferably, the substrate is a sapphire substrate with a thickness of 0.254 mm and an axial dielectric constant of 11.5.

[0011] Preferably, the inner diameter of the coaxial outer conductor is 2.4 mm, the material of the central medium is air, and the outer diameter of the coaxial inner conductor is 1.04 mm, together forming a standard 2.4 mm, 50 ohm coaxial line.

[0012] Beneficial effects: Due to the adoption of the above technical solution, the utility model has the following beneficial effects:

[0013] The coaxial and microstrip line converter designed by the utility model has a sophisticated structure. By designing the mode gradient zone, the TEM mode transmitted in the coaxial line can be smoothly transitioned to the quasi-TEM mode transmitted in the microstrip line, effectively improving the working bandwidth of the entire conversion circuit. The working frequency can be as high as 50GHz, and the return loss at each frequency point is less than -15dB, which can meet the requirements of low loss and large bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a perspective view of a broadband coaxial to microstrip line converter;

[0015] Figure 2 yes Figure 1 Axial cross-section of a medium-bandwidth coaxial-to-microstrip line converter;

[0016] Figure 3 yes Figure 1 Return loss simulation curve of medium-bandwidth coaxial to microstrip line converter;

[0017] Among them, 1-coaxial outer conductor, 2-center medium, 3-coaxial inner conductor, 4-gold strip, 5-substrate, 6-top gradient line, 7-gradient hollow area, 8-bottom conductive strip, 9-microstrip line. DETAILED DESCRIPTION

[0018] The embodiments of the present utility model are described in detail below in conjunction with the accompanying drawings.

[0019] Example

[0020] This embodiment provides a coaxial to microstrip line conversion circuit with an operating frequency of up to 50 GHz. Figure 1As shown, the coaxial line is connected, and the coaxial line includes a coaxial outer conductor 1, a central medium 2 and a coaxial inner conductor 3. The inner diameter of the coaxial outer conductor 1 is 2.4 mm, the material of the central medium 2 is air, and the outer diameter of the coaxial inner conductor 3 is 1.04 mm. The coaxial outer conductor 1, the central medium 2 and the coaxial inner conductor 3 together constitute a standard 2.4 mm coaxial line.

[0021] The coaxial inner conductor at one end of the coaxial line is shorter than the coaxial outer conductor, forming a housing space for mounting the gold belt and the substrate. The housing space is provided with a gold belt 4 and a substrate 5. The substrate 5 is a sapphire substrate with a thickness of 0.254 mm, an axial dielectric constant of 11.5, and extremely low dielectric loss. The width of the gold belt 4 is 1 mm, and its height is equal to the thickness of the substrate 5.

[0022] like Figure 2 As shown, the substrate 5 includes a top conductive strip, an intermediate insulating layer and a bottom conductive strip. The top conductive strip includes a top gradient region and a microstrip line 9 located on the same center line as the coaxial inner conductor 3. The top gradient region is a symmetrical conductor structure surrounded by a wide straight edge, a narrow straight edge and two top gradient lines 6. The top gradient line 6 of the substrate 5 is a fitting curve with a length of 0.75 mm, and its characteristic impedance remains unchanged at 50 ohms in the gradient region. The bottom conductive strip of the substrate 5 is provided with a gradient hollowing region 7 facing the top gradient region. The maximum width of the gradient hollowing region 7 is 1.57 mm and the maximum length is 1 mm. The width of the microstrip line 9 of the substrate 5 is 0.25 mm, and the characteristic impedance is 50 ohms. The bottom conductive strip 8 of the substrate 5 provides a reference ground for the microstrip line 9 of the substrate 5. The coaxial inner conductor 3 and the top conductive strip of the substrate serve as the transmission signal line, and the coaxial outer conductor 1 and the bottom conductive strip 8 of the substrate together constitute the reference ground of the transmission signal line. In the utility model, a width gradient line segment of a specific length is designed on the top conductive strip of the substrate, and a width gradient hollow region is designed on the corresponding bottom conductive strip of the substrate, the two are collectively referred to as a mode gradient zone, and the mode gradient zone can smoothly transition the TEM mode transmitted in the coaxial line to the quasi-TEM mode transmitted in the microstrip line, effectively improving the working bandwidth of the entire conversion circuit.

[0023] By using simulation software to model and simulate this embodiment, a specific S parameter simulation curve is obtained, such as Figure 3 As shown by Figure 3 It can be seen from the return loss simulation curve that the operating frequency of this embodiment is as high as 50GHz, and the return loss is less than -15dB. The substrate is processed by thin film circuit technology, which is mature and has low production cost, high production efficiency, and small finished product volume. By innovating on the traditional transmission line structure, it makes up for the limitation that the common impedance matching method is only applicable to the conversion of coaxial to microstrip lines in narrow bands, and can be effectively applied to the design of ultra-wideband microwave devices.

[0024] The above shows and describes the basic principle, main features and advantages of the utility model. Those skilled in the art should understand that the above embodiments do not limit the utility model in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the utility model.

Claims

1. A broadband coaxial to microstrip line converter, characterized in that: It includes a coaxial line, a gold strip and a substrate. The coaxial line includes a coaxial outer conductor, a center medium and a coaxial inner conductor arranged from outside to inside. The coaxial inner conductor at one end of the coaxial line is shorter than the coaxial outer conductor, forming an accommodation space for installing the gold strip and the substrate. The substrate comprises a top conductive strip, an intermediate insulating layer and a bottom conductive strip, wherein the top conductive strip comprises a top gradient region and a microstrip line located on the same center line as the coaxial inner conductor, wherein the top gradient region is a symmetrical conductor structure surrounded by a wide straight edge, a narrow straight edge and two top gradient lines, wherein one end of the wide straight edge of the top gradient region is overlapped with the coaxial inner conductor through a gold strip, and one end of the narrow straight edge is connected to the microstrip line; and a gradient hollow region is arranged in the bottom conductive strip directly below the top gradient region.

2. The broadband coaxial to microstrip line converter according to claim 1, characterized in that: The two top-layer gradient lines are both fitting curves with a length of 0.75 mm, and the characteristic impedance of the top-layer conduction strip remains unchanged at 50 ohm in the top-layer gradient region; the width of the microstrip line (9) is 0.25 mm, and the characteristic impedance is 50 ohm.

3. The broadband coaxial to microstrip line converter according to claim 1, characterized in that: The area of ​​the gradient hollowed-out region is larger than that of the top gradient region, and both sides of the bottom conductive strip overlap the coaxial outer conductor; the maximum width of the gradient hollowed-out region (7) is 1.57 mm, and the maximum length is 1 mm.

4. The broadband coaxial to microstrip line converter according to claim 1, characterized in that: The width of the gold strip is between the diameter of the coaxial inner conductor and the diameter of the coaxial outer conductor, the height of the gold strip is equal to the thickness of the substrate, one end of the gold strip is overlapped with the top gradient area through a bonding process, and the other end is bent and tightly attached between the side of the substrate and the side of the coaxial inner conductor.

5. The broadband coaxial to microstrip line converter according to claim 1, characterized in that: The substrate is a sapphire substrate with a thickness of 0.254 mm and an axial dielectric constant of 11.

5.

6. The broadband coaxial to microstrip line converter according to claim 1, characterized in that: The inner diameter of the coaxial outer conductor is 2.4 mm, the material of the central medium is air, and the outer diameter of the coaxial inner conductor is 1.04 mm, which together constitute a standard 2.4 mm, 50 ohm coaxial line.

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