CN114156624A

CN114156624A - Millimeter-wave broadband low-loss directional coupler based on gap waveguide structure

Info

Publication number: CN114156624A
Application number: CN202111605582.2A
Authority: CN
Inventors: 冯文杰; 沈瑞亮; 施永荣; 倪啸宇; 史苏阳; 周新宇
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2021-12-25
Filing date: 2021-12-25
Publication date: 2022-03-08

Abstract

The invention discloses a millimeter wave broadband low-loss directional coupler based on a gap waveguide structure, which is realized by a machining technology and comprises three parts: the waveguide coupler comprises a metal bottom plate, a coupling plate and a metal cover plate, wherein the metal bottom plate is composed of two U-shaped metal grooves, square metal pins around the U-shaped metal grooves and a step transition conversion structure from a gap waveguide to a standard WR-28 waveguide; design cut angles are arranged at the corners of the two U-shaped metal grooves to change the propagation direction of an electric field; the coupling plate is inserted into the metal groove of the metal bottom plate, is directly connected with the metal cover plate, and is provided with five symmetrically distributed coupling gaps with the same size for realizing the coupling of energy from the main channel to the auxiliary channel; the metal cover plate is arranged at the top, and the whole structure is packaged. The directional coupler works in a millimeter wave frequency band and has the advantages of wide band, low loss, easiness in processing and the like.

Description

Millimeter wave broadband low-loss directional coupler based on gap waveguide structure

Technical Field

The invention belongs to the technical field of electromagnetic fields and microwaves, and particularly relates to a millimeter wave broadband low-loss directional coupler based on a gap waveguide structure.

Background

Modern wireless communication systems are moving towards high frequencies and high data transmission rates to accommodate future communication applications. The millimeter wave has the advantages of extremely wide bandwidth, narrow beam, high reliability, good directivity and the like, and is a main application frequency band of future passive devices.

Directional couplers are one of the most important passive devices in microwave and millimeter wave systems, and are widely used in microwave circuits such as balanced amplifiers, mixers, and feed networks of array antennas. Especially 0dB directional couplers, are widely used in measurement and isolation and shielding of signal sources, and 0dB couplers cannot be realized with backward wave coupling mechanism. In the millimeter wave band, some conventional transmission line technologies have drawbacks in performance, ease of integration, and manufacturing cost. In microwave-millimeter wave device design, the most common planar transmission lines are microstrip lines and striplines, which are often chosen for ease of integration with other active devices and for ease of fabrication. But as the working frequency increases, the loss of the working frequency is larger and larger, and the cavity resonance and other problems exist when the device is packaged. Cavity waveguides are generally suitable for high frequency and low loss applications, but they are difficult to integrate with active devices and have limitations due to high requirements on processing finesse. Therefore, the application of millimeter wave frequency band requires new technology to replace the conventional transmission line. In recent years, Substrate Integrated Waveguide (SIW) technology has been widely used in the millimeter wave band as a low loss transmission line. However, when designing microwave and millimeter wave passive devices, such as couplers, the low loss characteristics of the SIW are degraded, because bending, slotting or some other action can destroy the characteristics of the main mode of the SIW. In SIW, since electromagnetic waves propagate through a medium, the dielectric loss increases significantly as the frequency increases. The advent of Gap Waveguide (GWG) technology has been a good solution to the above problems.

The gap waveguide technology is a novel low-loss transmission line formed based on a parallel plate waveguide, one surface of the transmission line is an ideal electric conductor (PEC), the other surface of the transmission line is designed into a periodic surface, the periodic surface is an Electromagnetic Band Gap (EBG) structure and can be regarded as an ideal magnetic conductor, and the most typical electromagnetic band gap structure is a periodic metal pin and mushroom-shaped structure. When the distance between the two metal flat plates is less than or equal to 1/4 working wavelength, the gap becomes a high resistance region, which can prevent the transmission of electromagnetic wave in any direction in a certain frequency range to form an electromagnetic band gap. Unlike conventional waveguides, gap waveguides do not require two conductor sections to be closely connected to prevent leakage of electromagnetic waves. Therefore, the whole structure can be divided into a plurality of parts for processing, and finally, the assembling and the fixing are carried out, so that the processing difficulty is greatly reduced. Moreover, compared with the substrate integrated waveguide and the microstrip line, because the electromagnetic wave of the gap waveguide is propagated in the air, the dielectric loss and the conductor loss are greatly reduced, and the method is very suitable for the design of circuits and devices in millimeter wave bands.

The coupler designed by utilizing the gap waveguide technology generally has the characteristic of low loss of broadband, can be applied to a millimeter wave frequency band, and is easy to process. It is worth mentioning that the coupler designed based on the gap waveguide structure can be easily applied to other millimeter wave frequency bands, and only the size of the pin unit needs to be changed to generate a corresponding electromagnetic band gap. Therefore, the novel millimeter wave broadband coupler designed by utilizing the gap waveguide technology has a very good application prospect.

Disclosure of Invention

The invention aims to provide a millimeter wave broadband low-loss directional coupler based on a gap waveguide structure, which realizes 0dB coupling of a millimeter wave frequency band broadband, and the whole structure is manufactured by all metal processing, so that the dielectric loss is effectively reduced.

The technical scheme for realizing the purpose of the invention is as follows: a millimeter wave broadband low-loss directional coupler based on a gap waveguide structure adopts a transmission line structure of a slot gap waveguide technology, and the whole structure is manufactured by all-metal machining and comprises a metal bottom plate, a coupling plate and a metal cover plate;

the metal bottom plate consists of two U-shaped metal grooves, square metal pins around the U-shaped metal grooves and a step transition conversion structure from a gap waveguide to a standard WR-28 waveguide;

the coupling plate is inserted into the metal groove of the metal bottom plate, the top of the coupling plate is directly connected with the metal cover plate, and five symmetrically distributed coupling gaps with the same size are formed in the middle of the coupling plate and are used for realizing the coupling of energy from the main channel to the auxiliary channel;

the metal cover plate is positioned at the uppermost part of the coupler and encapsulates the whole structure.

Furthermore, two cutting angles are designed at the corners of the U-shaped metal groove and used for changing the propagation direction of the electric field.

Furthermore, the two U-shaped metal grooves are positioned in the metal bottom plate, and the middle of the two U-shaped metal grooves are separated by a coupling plate.

Further, there are at least 2 rows of periodic metal pins around the U-shaped metal slot.

Furthermore, the height of the grooves at the two sides of the U-shaped metal groove is not equal to that of the middle groove, and the stepped transition conversion structure is arranged at the corner of the U-shaped metal groove to realize impedance matching.

Furthermore, the four step transition conversion structures are respectively positioned in the U-shaped metal groove behind the corner cut.

Furthermore, the coupler also comprises 4 input/output ports which are respectively an input port, a through port, a coupling port and an isolation port, and the 4 input/output ports are directly connected with the U-shaped metal groove.

Further, the 4 input/output ports are standard WR-28 waveguide flange ports.

Furthermore, an air gap with a certain height is formed between the metal cover plate and the square metal pins on the metal bottom plate.

Further, the bottom of the coupling plate is flush with the U-shaped metal groove.

Compared with the prior art, the invention has the following remarkable advantages: (1) the directional coupler works in a millimeter wave frequency band of 30GHz, a novel gap waveguide technology is adopted, the processing difficulty is greatly reduced, the maximum insertion loss in a band is only 0.2dB, the relative working bandwidth is 14.7%, the return loss and the isolation in the band are both more than 10dB, and the broadband and the low loss are realized; (2) the invention also designs a broadband transition conversion structure from the slot gap waveguide to the standard WR-28 waveguide, which can be directly measured and used; (3) compared with other reported directional couplers, the directional coupler has the advantages of wider bandwidth, lower insertion loss, easier processing and manufacturing, simple assembly and the like.

Drawings

Fig. 1 is a three-dimensional schematic diagram of a millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to the present invention.

Fig. 2 is a schematic view of a millimeter-wave broadband low-loss directional coupler xoy based on a gap waveguide structure and its dimensions.

Fig. 3 is a plan view of a millimeter wave broadband low-loss directional coupler xoz based on a gap waveguide structure and a coupling plate structure and its dimensions.

Fig. 4 is an electric field distribution diagram of the millimeter wave broadband low-loss directional coupler based on the gap waveguide structure according to the present invention.

Fig. 5 is a simulation and measurement result of the performance of the millimeter wave broadband low-loss directional coupler based on the gap waveguide structure according to the present invention.

Detailed Description

The following describes an embodiment of a millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to the present invention with reference to the accompanying drawings:

as shown in fig. 1, the millimeter wave broadband low-loss directional coupler based on the gap waveguide structure includes: the waveguide coupler comprises a metal bottom plate 1, periodic square metal pins 2 distributed around a U-shaped metal groove 4, a chamfer 3 for changing the propagation direction of an electric field, a step transition conversion structure 5 from a groove gap waveguide to a standard WR-28 waveguide, a metal cover plate 6 (in the drawing, a part is removed for conveniently seeing the internal structure), a coupling plate 7 with five coupling gaps, and 4 input and output ports 8.

Two U-shaped metal grooves 4 are designed on the metal bottom plate 1, and two cutting angles 3 are designed at the corners of the U-shaped metal grooves 4 to change the direction of an electric field. Because the height of the grooves at two sides of the U-shaped metal groove 4 is not equal to that of the middle groove, a two-stage step transition conversion structure 5 is introduced at the corner to realize impedance matching, two rows of periodic square metal pins 2 are arranged around the U-shaped metal groove 4 to form an electromagnetic band gap, so that electromagnetic wave can be transmitted along the designed metal groove, transition conversion to a standard WR-28 waveguide is designed behind the two U-shaped metal grooves 4, and because the sizes of the grooves at two sides of the U-shaped metal groove 4 are matched with the size of the standard WR-28 waveguide through the chamfer 3 and the step transition conversion structure 5, the U-shaped metal groove can be directly connected with the standard WR-28 waveguide port without reflection. The coupling plate 7 is inserted into the metal bottom plate, the bottom of the coupling plate is flush with the U-shaped metal groove 4, the upper side of the coupling plate is directly connected with the metal cover plate 6, five coupling gaps which are the same in size and are symmetrically distributed are formed in the middle of the coupling plate and are used for realizing the coupling of energy from the main channel to the auxiliary channel, the size and the distance of the coupling gaps are reasonably designed, the energy can be coupled to the port 3, the metal cover plate 6 is arranged on the top of the coupling plate and is placed on the metal bottom plate, and a certain air gap is formed between the periodic metal pins on the metal bottom plate. The whole structure is packaged, 4 input and output ports 8 are provided, namely an input port 1, a through port 2, a coupling port 3 and an isolation port 4, and due to structural symmetry, the relative positions of the input and output ports can be changed in a corresponding sequence.

Examples

As shown in fig. 1, which is a three-dimensional schematic diagram of a millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to this embodiment, the directional coupler is manufactured by all-metal machining.

As shown in fig. 2 and fig. 3, the millimeter wave broadband low-loss directional coupler based on the gap waveguide structure is labeled in size. The length of the metal bottom plate is 80mm, the width of the metal bottom plate is 60mm, the height of the metal bottom plate is 11.4mm, the width of the periodic square metal pins is 2.5mm, the space between the pins is 1.5mm, the height of the pins is 1mm, the air gap is 0.4mm, and the thickness h of the coupling plate_mIs 0.5mm, the length and the width of the coupling gap on the coupling plate are respectively 8mm and 1mm, the gap distance is 3.5mm, the width of two sides of the U-shaped metal groove 4 is 3.556mm, the width of the middle part is 2.4mm, the height is 7mm, the side length of two sides of the cut angle is respectively 3.8mm and 1.8mm, the length and the height of the first stage of step transition conversion are respectively 6mm and 0.85mm, the length and the height of the second stage are respectively 4mm and 1.8mm1 mm. The length and width of the standard WR-28 waveguide port are 7.112mm and 3.556mm, respectively. The specific structure size is as follows: l₁＝6mm,l₂＝4mm,a₁＝3.8mm,a₂＝1.8mm,h_m＝0.5mm,W₁＝2.4mm,W₂＝3.556mm,p＝4mm,d＝2.5mm,h₁＝2mm,h₂＝0.4mm,h₃＝0.85mm,h₄＝1mm,h₅＝7.112mm,h_g＝7mm,l_s＝8mm,W_s＝1mm,p₁＝3.5mm。

Fig. 4 is an electric field distribution diagram of a millimeter wave broadband low-loss directional coupler based on a gap waveguide structure according to the present invention, and it can be seen that energy is substantially completely coupled from an input port 1 to a port 3.

Fig. 5 is a graph of simulation results of the present invention, and it can be observed that the maximum insertion loss measured in the frequency band range from 27.1GHz to 31.5GHz is about 0.2dB, the average insertion loss in the band is less than 0.4dB, and the in-band input return loss is better than 10dB with isolation.

Claims

1. A millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure is characterized in that, this directional coupler adopts the transmission line structure of slot gap waveguide technology, and the whole structure is manufactured by all-metal machining, including a metal base plate ( 1), coupling plate (7) and metal cover plate (6);

The metal base plate (1) consists of two U-shaped metal grooves (4), square metal pins (2) around them, and a stepped transition transition structure (5) from a gap waveguide to a standard WR-28 waveguide;

The coupling plate (7) is inserted into the U-shaped metal groove (4) of the metal base plate (1), the top is directly connected to the metal cover plate (6), and five coupling slots of the same size and symmetrically distributed are opened in the middle. To realize the coupling of energy from the main channel to the secondary channel;

The metal cover plate (6) is located at the top of the coupler and encapsulates the entire structure.

2. The millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to claim 1, characterized in that, two chamfers (3) are designed at the corners of the U-shaped metal groove (4), with to change the direction of electric field propagation.

3. The millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to claim 2, wherein the two U-shaped metal grooves (4) are located in the metal base plate (1), and the two U-shaped metal grooves (4) are located in the metal base plate (1). The middle of the slot (4) is separated by a coupling plate (7).

The millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to claim 2, characterized in that, there are at least two rows of periodic square metal pins (2) around the U-shaped metal groove (4). .

5. The millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to claim 2, wherein the heights of the grooves on both sides of the U-shaped metal groove (4) are not equal to the heights of the middle grooves, and the step transition transition structure (5) It is arranged at the corner of the U-shaped metal groove (4) to realize impedance matching.

6 . The millimeter-wave broadband low-loss directional coupler based on the gap waveguide structure according to claim 5 , wherein the four stepped transition transition structures ( 5 ) are respectively located in the U-shaped metal grooves ( 4) in.

7. The millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to claim 1, wherein the coupler further comprises 4 input and output ports (8), which are an input port, a straight-through port, Coupling ports and isolation ports, four input and output ports (8) are directly connected to the U-shaped metal groove (4).

8. The millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to claim 7, wherein the four input and output ports (8) are standard WR-28 waveguide flange ports.

9 . The millimeter-wave broadband low-loss directional coupler based on a gap waveguide structure according to claim 1 , wherein the metal cover plate ( 6 ) and the square metal pins ( 2 ) on the metal base plate ( 1 ) There is an air gap of a certain height between them.

10 . The millimeter-wave broadband low-loss directional coupler based on the gap waveguide structure according to claim 1 , wherein the bottom of the coupling plate ( 7 ) is flush with the U-shaped metal groove ( 4 ). 11 .