2.5-D planar micro coaxial gap guided wave transmission line for high frequency

Abstract

The invention discloses a 2.5-D planar micro coaxial gap guided wave transmission line for high frequency. The 2.5-D planar micro coaxial gap guided wave transmission line comprises an upper metal plate, a dielectric substrate, a lower metal plate, a first half-height pin array and a second half-height pin array, the upper-layer metal plate and the lower-layer metal plate are oppositely arranged in parallel, and the dielectric substrate is horizontally arranged between the upper-layer metal plate and the lower-layer metal plate; the first half-height pin array is located on the bottom layer of the upper-layer metal plate, the second half-height pin array is located on the top layer of the lower-layer metal plate, a first air gap is formed between the bottom layer of the upper-layer metal plate and the top layer of the dielectric substrate, and a second air gap is formed between the top layer of the lower-layer metal plate and the bottom layer of the dielectric substrate; the dielectric substrate adopts a dielectric support strip line structure and transmits a TEM mode. According to the invention, the loss, the size, the integration degree, the cost, the weight and the like are obviously improved, and an efficient, economical and compact solution is provided for a millimeter wave system.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic field and microwave technology, and in particular to a 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency. Background Art

[0002] In millimeter-wave circuits and systems, transmission lines play a vital role, and their characteristics (such as loss, size, integration, cost, and weight) directly determine the overall performance. Traditional transmission lines include metal waveguides operating in transverse electric (TE) or transverse magnetic (TM) modes, and microstrip lines, striplines, and coplanar waveguides operating in quasi-transverse electromagnetic (TEM) modes. Metal waveguides are favored for their low loss, thermal stability, and high power handling capabilities, but their large size and complex assembly make them inflexible in millimeter-wave applications. In contrast, microstrip lines and substrate-integrated waveguides have certain advantages due to their thin profile, compact size, light weight, and cost-effectiveness. However, these types of transmission lines have significant dielectric losses in the millimeter-wave frequency band, limiting their scope of application. In order to overcome the above limitations, various millimeter-wave transmission line technologies and mode conversion structures have been widely studied to achieve a balance between compactness and low-loss performance. In addition, unlike TE / TM mode transmission lines, TEM mode transmission lines have the characteristics of no cutoff frequency, which can achieve broadband transmission and support more compact designs. In addition, TEM mode transmission lines have non-dispersive characteristics, their phase remains linear over the entire frequency range, and they have a fixed characteristic impedance, which is particularly beneficial for system design. Therefore, TEM mode transmission lines have attracted widespread attention from researchers around the world.

[0003] As an emerging transmission line technology, gap waveguide has significantly simplified the manufacturing process of millimeter wave devices with its unique non-contact design since its launch in 2009. By maintaining a tiny open gap between the perfect electric conductor (PEC) and the artificial magnetic conductor (AMC), the technology is able to confine the electromagnetic field inside the transmission line, effectively preventing energy leakage and exhibiting low-loss characteristics comparable to traditional waveguides.

[0004] The invention with publication number CN112259944B discloses a broadband transmission line and transmission system, including: a coplanar waveguide transmission line, a gap layer and a gap waveguide; the coplanar waveguide transmission line, the gap layer and the gap waveguide constitute the main part of the transmission line, wherein the inverted coplanar waveguide transmission line is located above the gap waveguide, and there is a gap layer between the upper surface of the gap waveguide and the coplanar waveguide transmission line. In this way, it is possible to achieve the problem of large losses at high frequencies while expanding the bandwidth coverage. However, the invention is based on coplanar waveguide technology, so that most of the electromagnetic field is concentrated inside the medium, and the loss is still large. In addition, its transmission mode is quasi-TEM, which still has certain limitations in terms of dispersion and bandwidth characteristics compared to the true TEM mode.

[0005] The invention with the publication number CN117748079A discloses a broadband conversion structure from a Ka-band ridge gap waveguide to a microstrip line, including a metal upper cover, a metal base, a microstrip circuit and a metal lower cover. The metal upper cover, the metal base and the metal lower cover are realized by mechanical processing technology, and the microstrip circuit is a double-sided copper-clad plate, which is realized by printed circuit board processing technology; the electromagnetic wave in the ridge gap waveguide is transmitted to a resonant cavity through a three-step impedance transformation structure, and the impedance matching is improved by a tuning plate; in the resonant cavity, the electromagnetic wave is converted into a TE101 mode and coupled to a broadband monopole conversion probe, and the probe can convert the working mode of the electromagnetic wave into a quasi-TEM mode of the microstrip line; the microstrip line is a standard 50Ω transmission line, which can be easily interconnected with other circuits or systems; the structure can work at all frequency points of the Ka band, and has the characteristics of broadband, compact and simple structure, easy processing and assembly, and low loss. However, the invention is only for realizing the connection between the waveguide and the microstrip line, and does not involve the problem of assembly gap. Summary of the invention

[0006] The purpose of the present invention is to provide a 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency, which sandwiches a dielectric substrate between two upper and lower metal plates composed of an electromagnetic bandgap structure formed by periodic vertical stacking, and a strip line is arranged on the dielectric substrate to form a TEM mode to guide the propagation of electromagnetic waves. Compared with the prior art, the transmission line structure of the present invention is a substrate integration solution for traditional slot gap waveguides, which has achieved significant improvements in loss, size, integration, cost and weight, and provides an efficient, economical and compact solution for millimeter wave systems, which can be applied to active chips such as front-end transceivers of embedded wafer-level packaging to build a fully dielectric integrated front-end system.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0008] A 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency, the transmission line comprising an upper metal plate, a dielectric substrate, a lower metal plate, a first half-height pin array, and a second half-height pin array;

[0009] The upper metal plate and the lower metal plate are arranged relatively parallel, and the dielectric substrate is arranged horizontally between the upper metal plate and the lower metal plate; the first half-height pin array is located on the bottom layer of the upper metal plate, and the second half-height pin array is located on the top layer of the lower metal plate, a first air gap is arranged between the bottom layer of the upper metal plate and the top layer of the dielectric substrate, and a second air gap is arranged between the top layer of the lower metal plate and the bottom layer of the dielectric substrate;

[0010] The dielectric substrate adopts a dielectric support strip line structure to transmit the TEM mode.

[0011] Furthermore, the operating frequency of the electromagnetic wave is in the millimeter wave band.

[0012] Furthermore, the first half-height pin array and the second half-height pin array are arranged opposite to each other, and the array period p is less than half of the wavelength of the electromagnetic wave.

[0013] Furthermore, a microstrip line is provided on the top layer of the dielectric substrate, and electromagnetic waves propagate along the microstrip line located on the top layer of the dielectric substrate. The electromagnetic wave transmission path includes a first air gap, a second air gap, an upper metal plate and a lower metal plate.

[0014] Furthermore, microstrip lines are provided on the top layer and the bottom layer of the dielectric substrate, and the two microstrip lines are connected through metallized vias.

[0015] Furthermore, the first half-height pin array and the second half-height pin array each include two groups of pin units, and the two groups of pin units are symmetrical about the center of the microstrip line.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] First, the 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency of the present invention uses two upper and lower pin metal plates composed of an electromagnetic band gap structure formed by periodic vertical stacking to sandwich the dielectric substrate in the middle. It should be pointed out that the transmission structure is designed with full consideration of the error problems that may exist in the actual processing process. Specifically, there is no need to achieve a completely tight fit between the upper and lower metal plates and the dielectric substrate, and a certain assembly gap is allowed. This design tolerance not only reduces the processing accuracy requirements, but also improves the practicality of the structure. In the presence of an air gap, due to the unique electromagnetic characteristics of the electromagnetic band gap structure, the leakage of electromagnetic waves can be effectively suppressed, ensuring that the electromagnetic energy maintains a high degree of integrity during the transmission process, thereby achieving stable signal transmission performance.

[0018] Second, the 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency of the present invention has a strip line on the dielectric substrate to form a TEM mode to guide the propagation of electromagnetic waves. This transmission line is significantly different from the traditional microstrip line structure. Specifically, the traditional microstrip line usually adopts a standard configuration in which the signal line is laid on the upper layer of the dielectric substrate and the reference ground is set on the lower layer, while the transmission line structure proposed by the present invention has higher design flexibility: the signal line can be laid separately on the upper or lower layer of the dielectric substrate, or double-layer wiring can be achieved. More importantly, this structure breaks through the limitation that the traditional microstrip line must set a reference ground, and effective signal transmission can be achieved without setting a reference ground on the dielectric substrate. This feature provides new possibilities for RF circuit design. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of a 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency of the present invention.

[0020] Figure 2 It is a three-dimensional schematic diagram of the non-etched single-strip planar coaxial gap waveguide transmission line of the present invention.

[0021] Figure 3 It is a three-dimensional schematic diagram of the etched single-strip planar coaxial gap waveguide transmission line of the present invention.

[0022] Figure 4 It is a three-dimensional schematic diagram of the non-etched dual-strip planar coaxial gap waveguide transmission line of the present invention.

[0023] Figure 5 It is a three-dimensional schematic diagram of the etched dual-strip planar coaxial gap waveguide transmission line of the present invention.

[0024] Figure 6 This is a transmission performance diagram of the non-etched single-strip planar coaxial gap waveguide transmission line of the present invention.

[0025] Figure 7 This is a transmission performance diagram of the etched single-strip planar coaxial gap waveguide transmission line of the present invention.

[0026] Figure 8 This is a transmission performance diagram of the non-etched dual-band planar coaxial gap waveguide transmission line of the present invention.

[0027] Fig. 9 This is a transmission performance diagram of the etched dual-band planar coaxial gap waveguide transmission line of the present invention. DETAILED DESCRIPTION

[0028] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0029] See also Figure 1 , the present invention discloses a 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency, the transmission line comprising an upper metal plate 3, a dielectric substrate 9, a lower metal plate 4, a first half-height pin array and a second half-height pin array;

[0030] The upper metal plate 3 and the lower metal plate 4 are arranged relatively parallel, and the dielectric substrate 9 is horizontally arranged between the upper metal plate 3 and the lower metal plate 4; the first half-height pin array is located on the bottom layer of the upper metal plate 3, and the second half-height pin array is located on the top layer of the lower metal plate 4. A first air gap 5 is arranged between the bottom layer of the upper metal plate 3 and the top layer of the dielectric substrate 9, and a second air gap 6 is arranged between the top layer of the lower metal plate 4 and the bottom layer of the dielectric substrate 9.

[0031] The present invention introduces gap waveguide technology, which is an open structure, and the middle layer adopts a dielectric support stripline structure to transmit TEM mode. The working frequency of the electromagnetic wave can be designed in the millimeter wave frequency band, and can be very conveniently combined with the embedded wafer-level packaged millimeter wave and terahertz active chips to form a fully dielectric integrated front-end transceiver system.

[0032] The present invention is divided into single-strip planar coaxial gap waveguide transmission line and double-strip planar coaxial gap waveguide transmission line according to the number of strip lines on the dielectric substrate; it is divided into non-etched planar coaxial gap waveguide transmission line and etched planar coaxial gap waveguide transmission line according to whether the dielectric substrate is etched. It should be noted that the transmission line structure of the invention is not limited to the above four types. Figure 1 Taking the non-etched single-strip planar coaxial gap waveguide transmission line as an example, the electromagnetic wave propagates along the microstrip line 7 on the upper surface of the dielectric substrate 9, and the electromagnetic wave transmission path 1 includes the first air gap layer 5, the first air gap layer 6, the upper metal plate 3 and the lower metal plate 4. The dielectric substrate 9 can select the same or different types of substrate materials.

[0033] The present invention designs a new type of 2.5D planar coaxial gap waveguide transmission line structure for high frequency, that is, a non-etched single-strip planar coaxial gap waveguide transmission line such as Figure 2 As shown, it is composed of two metal plates, upper and lower, vertically installed by half-height pins 2, which are respectively welded to the bottom layer of the upper metal plate 3 and the top layer of the lower metal plate 4, and then the dielectric substrate 9 is installed on the top of the lower pins and the bottom of the upper pins. The air gap is formed by the half-height pins between the bottom layer of the upper metal plate 3 and the top layer of the dielectric substrate 9 and the top layer of the lower metal plate 4 and the bottom layer of the dielectric substrate 9.

[0034] like Figure 3 As shown in FIG. 1 , the non-etched dual-strip planar coaxial gap waveguide transmission line is based on the single-strip planar coaxial gap waveguide transmission line, in which a strip line is added to the bottom of the dielectric substrate 9, and the upper and lower strip lines are connected by metallized vias, thereby realizing a stable TEM mode. By etching the dielectric substrate, an etched single-strip planar coaxial gap waveguide transmission line and an etched dual-strip planar coaxial gap waveguide transmission line are obtained, respectively, as shown in FIG. Figure 4 and 5 As shown. The metal through hole 10 can effectively suppress the TE mode and ensure that the mode is a stable TEM mode. The half-height pin arrays on both sides of the electromagnetic wave propagation path 1 can effectively suppress the leakage of electromagnetic waves.

[0035] Examples

[0036] In this example, the heights of the upper and lower metal plates, the half-height pins, and the dielectric substrate are h 1 、h 2 and h 3The width and length of the 2.5D planar coaxial gap waveguide transmission line structure are w = 15.3 mm and l = 30 mm respectively; the distance between the half-height pin arrays is g = 5 mm, its period is p = 3 mm, and the pin height h 2 =1mm, air gap height h 4 =0.123mm. In addition, the dielectric substrate is Arlon CLTE-XT, and the other parameters are: ε r =2.94,tanδ=0.0012,h 3 =0.254mm. The height of the upper and lower metal plates is set to h 1 =0.3mm, microstrip line width w 1 =1mm. Metallized vias used to connect the upper and lower microstrip lines in dual-strip planar coaxial gap waveguide transmission lines 1 The diameter is set to 0.4 mm, and the width of the etched groove 1 is w 2 Both are set to 1.75mm, length l 1 and l 2 The values ​​are set to 9mm and 10mm respectively, and the etching groove 1 is symmetrical about the center of the microstrip line. The above parameters are only examples and are not limited to this value. The impedance matching of the port is achieved through the microstrip line structure. By optimizing the width of the microstrip line, not only can the transmission loss be significantly reduced, but also good impedance matching characteristics can be achieved. In this example, the optimal value range of the microstrip line width is 0.8-1mm (0.09λ 0 -0.12λ 0 , where λ 0 is the wavelength corresponding to the center frequency), and 1mm is used as the optimal value. The stopband characteristics of the gap waveguide are mainly controlled by the following parameters: pin height, air gap, array unit period and pin side length. Among them, the ratio of the pin side length to the array unit period has a significant impact on the performance. In the example, its optimal value range is 0.4-0.6, and 0.5 is used as the optimal value. The pin height has an important influence on the stopband range. With the increase of the pin height, the upper and lower cutoff frequencies of the stopband show a downward trend. After optimization analysis, the optimal value range of the pin height is 0.8-1.2mm (corresponding to 0.09λ 0 -0.14λ 0 ), when it is 1mm, it can effectively cover the working frequency band of 25-45GHz. The size of the air gap is inversely proportional to the relative bandwidth, and theoretically should be minimized as much as possible. However, considering the actual existence of the dielectric substrate and the limitations of the processing technology, the minimum value of the air gap should be equivalent to the thickness of the dielectric substrate, and can be appropriately increased to leave a margin. Therefore, in this example, the optimal value range of the air gap is determined to be 0.254-0.5mm (corresponding to 0.03λ 0 -0.06λ 0), and finally 0.5mm was adopted as the optimal value.

[0037] Figures 6 to 9 They are transmission performance diagrams of the non-etched single-band planar coaxial gap waveguide transmission line, the etched single-band planar coaxial gap waveguide transmission line, the non-etched dual-band planar coaxial gap waveguide transmission line, and the etched dual-band planar coaxial gap waveguide transmission line according to the present invention, in which S11 and S21 represent the reflection coefficient and the transmission coefficient respectively, the horizontal axis Frequency represents the frequency, and the vertical axis Magnitude represents the logarithmic amplitude-frequency characteristic. The former represents the ratio of the signal reflected from port 1 to the input signal, and the latter represents the ratio of the signal transmitted from port 1 to port 2 to the input signal. Figures 6 to 9 It can be seen that the passband frequency range of the 2.5D planar coaxial gap waveguide transmission line structure is 25-45GHz, within which the normal transmission of electromagnetic waves can be achieved.

[0038] The 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency of the present invention utilizes two upper and lower metal plates composed of an electromagnetic bandgap structure formed by periodic vertical stacking to sandwich a dielectric substrate in the middle, and strip lines are arranged on the dielectric substrate to form a TEM mode to guide the propagation of electromagnetic waves. According to the number of strip lines on the dielectric substrate, it is divided into a single-strip planar coaxial gap waveguide transmission line and a double-strip planar coaxial gap waveguide transmission line; according to whether the dielectric substrate is etched, it is divided into a non-etched planar coaxial gap waveguide transmission line and an etched planar coaxial gap waveguide transmission line. The key feature of this planar coaxial design is its open structure, especially that even if there is no electrical contact between the layers, wave propagation can be achieved without causing leakage or unexpected resonance. Compared with the existing transmission TE 10 The present invention is a waveguide structure with a mode, which has the advantages of wide bandwidth, low profile, compact structure, high integration, high flexibility, and easy processing. Compared with the existing microstrip structure based on a dielectric substrate, the present invention has the advantages of low loss. The above characteristics enable the technology to be widely used in millimeter wave frequency band circuit design and antenna fields. With the front-end transceiver chip of wafer-level embedded packaging, the present invention can provide a dielectric integration solution for the front-end system of the millimeter wave frequency band.

[0039] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0040] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency, characterized in that: The transmission line comprises an upper pin metal plate, a dielectric substrate and a lower pin metal plate; the upper pin metal plate and the lower pin metal plate are arranged relatively parallel, the dielectric substrate is horizontally placed between the two, and supports the strip line structure thereon for electromagnetic wave propagation in TEM mode The upper pin metal plate comprises an upper metal plate and a first half-height pin array located on a bottom layer of the upper metal plate, and the lower pin metal plate comprises a lower metal plate and a second half-height pin array located on a top layer of the lower metal plate; A first air gap is provided between the bottom layer of the upper metal plate and the top layer of the dielectric substrate, and a second air gap is provided between the top layer of the lower metal plate and the bottom layer of the dielectric substrate.

2. The 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency according to claim 1, characterized in that: The operating frequency of the electromagnetic wave is in the millimeter wave band.

3. The 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency according to claim 1, characterized in that: The first half-height pin array and the second half-height pin array are arranged opposite to each other, and the array period p is smaller than half of the wavelength of the electromagnetic wave.

4. The 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency according to claim 1, characterized in that: A microstrip line is arranged on the top layer of the dielectric substrate, and electromagnetic waves propagate along the microstrip line located on the top layer of the dielectric substrate. The electromagnetic wave transmission path includes a first air gap, a second air gap, an upper metal plate and a lower metal plate.

5. The 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency according to claim 1, characterized in that: Microstrip lines are arranged on the top layer and the bottom layer of the dielectric substrate, and the two microstrip lines are connected through metallized vias.

6. The 2.5-D planar micro-coaxial gap waveguide transmission line for high frequency according to claim 1, characterized in that: The first half-height pin array and the second half-height pin array each include two groups of pin units, and the two groups of pin units are symmetrical about the center of the microstrip line.

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