Strongly coupled stripline and microwave components containing same

Abstract

The invention provides a two-coupled stripline comprising: a first strip conductor disposed on a top surface of a dielectric substrate and a second strip conductor disposed on a bottom surface of the dielectric substrate, located at an opening in a conductive layer covering the bottom surface of the dielectric substrate, the conductive layer being separated from the second strip conductor by a gap, wherein at least a portion of the first strip conductor is disposed over a portion of the second strip conductor; at least one additional conductor disposed on the top surface of the dielectric substrate, separated from the first strip conductor by a gap, and connected to the conductive layer by a plated through hole in the dielectric substrate. The novel strongly coupled stripline provided by the invention is suitable for the manufacture of very simple microwave components comprising only printed circuit boards, overcomes the deficiencies of known coupled striplines, and provides a strongly coupled stripline formed on both surfaces of a single dielectric substrate by conventional printed circuit board technology.

Description

Technical Field

[0001] This invention relates to microwave transmission lines and microwave components manufactured using conventional printed circuit board technology.

[0002] Background Introduction

[0003] The modern mobile communications market demands sophisticated antennas that form narrow beams and operate across multiple frequency bands. Such antennas consist of radiating elements and beamforming networks containing numerous passive components, including directional couplers, differential phase shifters, and filters. Modern antennas for mobile communications must provide very low levels of passive intermodulation; therefore, the beamforming network components are interconnected via special coaxial cables soldered directly to the passive elements. The passive elements must be as small as possible to house them within a confined space inside the radome, protecting the antenna from harsh weather conditions.

[0004] Most broadband and compact directional couplers and phase shifters contain coupling striplines. Directional couplers with coupling levels between 30 dB and 10 dB contain two coupling lines positioned on the surface of a dielectric substrate and separated by a gap. However, this design cannot produce coupling between 10 dB and 2 dB because the gap between the striplines providing this level of coupling would have to be extremely narrow, which cannot be manufactured using industrial printed circuit board technology. Therefore, engineers use an alternative design to increase the coupled signal. Patent US 10833388 B2 describes a circuit that includes several couplers connected together via a power divider to increase the coupled signal. Four couplers connected together can provide coupling levels up to 3 dB, but such a circuit is too large and therefore expensive to manufacture.

[0005] As shown in CN 108110425 A, coupling striplines that generate coupling levels between 10dB and 2dB must be placed opposite each other on the surface of a thin dielectric substrate. Known circuits, including couplers and differential phase shifters, involve three dielectric substrates positioned between two metals and positioned above each other, making this design complex to manufacture. Furthermore, connecting coaxial transmission lines to metal plates can produce passive intermodulation products.

[0006] Other known couplers, such as the Lange, consist of several parallel thin striplines connected by bridges positioned above a dielectric substrate and soldered to the striplines. This design is complex for mass production and is typically used with striplines mounted on substrates made of expensive ceramic materials.

[0007] Another type of directional coupler includes a substrate consisting of two dielectric layers separated by a conductive layer. The conductive layer has windows, and two striplines are disposed on the top and bottom surfaces of the dielectric substrate. This design is also complex for mass production.

[0008] Because the modern communications industry uses a large number of microwave components, there is a need to simplify the design of coupling lines and provide coupling levels between 10dB and 2dB, suitable for manufacturing directional couplers and other microwave components that include strongly coupled striplines. Summary of the Invention

[0009] The purpose of this invention is to provide a novel strongly coupled stripline suitable for manufacturing very simple microwave components that consist only of a printed circuit board.

[0010] The first objective of this invention is to overcome the shortcomings of known coupled striplines and to provide strongly coupled striplines formed on the two surfaces of a single dielectric substrate using conventional printed circuit board technology.

[0011] A second objective of the present invention is to provide a simple microwave assembly comprising only a single dielectric substrate.

[0012] The coupling stripline intended to achieve the objectives of this invention includes a first strip conductor disposed on the top surface of a dielectric substrate, and a second strip conductor disposed along the first strip conductor in an opening located in a conductive layer covering the bottom surface of the dielectric substrate. The conductive layer covering the bottom surface of the dielectric substrate is separated from the second strip conductor by a gap. Two additional conductors disposed on the top surface of the dielectric substrate are separated from the first strip conductor by the gap and connected to the conductive layer through metal-plated vias in the dielectric substrate. At least a portion of the first strip conductor is disposed above a portion of the second strip conductor.

[0013] This type of stripline has a larger wave impedance Ze in its even mode than that of a conventional stripline with the conductive layer opposite it, because the conductive layer is removed from the opening and is only disposed at the opposite edges of the strip conductors. The wide sides of the strip conductors are disposed opposite each other on the top and bottom surfaces of the dielectric substrate, therefore its odd mode wave impedance Zo is smaller than that of a conventional stripline, which contains strip conductors disposed on the top surface of the dielectric substrate and coupled only through their edges. Due to the coupling coefficient, this arrangement of the opening in the conductive layer and the strip conductors increases the coupling between the two striplines compared to conventional striplines formed on a single substrate.

[0014] An opening in the conductive layer and an additional conductor disposed on the top surface of the dielectric substrate provide electrical symmetry for the coupled stripline. The gap separating the stripline from the conductive layer and the additional conductor has a shape that provides equal electrical lengths for both modes; therefore, the stripline is preferred to provide directional coupling. The conductive layer and the two additional conductors providing the coupled stripline with a large coupling coefficient K include edge cutouts that are spaced apart from the edges of the first and second striplines by a gap to provide equal electrical lengths for both modes. Attached Figure Description

[0015] Some embodiments of the present invention are described with reference to the following drawings, wherein:

[0016] Figure 1a , 1b Figures 1 and 1c show the top and bottom surfaces and cross-section of a dielectric substrate containing the coupling strip of the present invention, forming a 3dB directional coupler operating in the 690-960MHz frequency band.

[0017] Figure 2a and 2b yes Figures 1a-1c The measured frequency characteristics of the fabricated sample of the directional coupler shown.

[0018] Figure 3 A perspective view of the bottom surface of a dielectric substrate and a metal plate disposed near the dielectric substrate is shown. The dielectric substrate contains the coupling strip of the present invention, forming a 3dB directional coupler operating in the 1600-2700MHz frequency band.

[0019] Figure 4a and 4b yes Figure 3 The measured frequency characteristics of the directional coupler sample are shown.

[0020] Figure 5a and 5b Top and bottom views of a dielectric substrate containing coupling striplines forming a phase shifter are shown, respectively.

[0021] Figure 6 Table 1 shows Figure 5a and 5b The simulated frequency characteristics of the phase shifter are shown. Detailed Implementation

[0022] It should be understood that the present invention is not limited to the specific forms disclosed in the above drawings. The present invention is intended to cover all modifications, equivalents, and substitutions falling within the spirit and scope of the invention as defined in the appended claims.

[0023] Coupled lines must meet the following conditions to match the four transmission lines connected to them and provide directional coupling. When the Z=50 Ohm of the four transmission lines, the impedances of the even and odd modes of the coupled line must satisfy the equation Ohm, and the electrical lengths Le and Lo of the even and odd modes must be equal. This means that when the four transmission lines have equal impedances, the two coupled lines must be electrically equal. Placing conventional coupled striplines on the same surface of the dielectric substrate can provide the above conditions and produce directional coupling, but it cannot provide strong coupling because conventional printed circuit board technology cannot make the edge gap less than 0.05 mm.

[0024] The strip conductors of the coupled stripline according to the invention provide a greater wave impedance Ze because the capacitance between the strip conductor and the conductive layer containing the openings disposed opposite to the strip conductor is less than the capacitance between the strip conductor and the unopened conductive layer of a conventional stripline. The strip conductors of the coupled stripline according to the invention are disposed opposite each other on the top and bottom surfaces of the dielectric substrate, providing a smaller odd-mode wave impedance than conventional coupled striplines disposed on one side of the dielectric substrate, because the capacitance between the stacked strip conductors is greater than the capacitance between conventional coupled striplines, which are located on the same surface and coupled only through their edges. Therefore, the coupled stripline of the present invention provides a larger coupling coefficient.

[0025] The first embodiment of the invention is as follows: Figures 1a-1c As shown. A strip conductor and conductive layer are formed in a 3dB directional coupler operating in the 690-960MHz frequency band. The strip conductor and conductive layer are disposed on the surface of a dielectric substrate 1. The top surface of the dielectric substrate 1 includes a first strip conductor 2a and two additional conductors 3a and 3b, which are separated from the first strip conductor 2a by gaps 4a and 4b. The additional conductors 3a and 3b are connected to a conductive layer 5 disposed on the bottom surface of the dielectric substrate 1 through metal-plated holes 6. The edges of the additional conductors 3a and 3b include cutouts 7, which include a narrow portion 7a and a wide portion 7b. The end of the first strip conductor 2a is connected to strip conductors 8a and 8b.

[0026] The bottom surface of the dielectric substrate 1 includes a second strip conductor 2b and a conductive layer 5, which are separated from the second strip conductor 2b by a gap 11. The ends of the second strip conductor 2b are connected to the strip conductors 9a and 9b through metal plating holes 10a and 10b.

[0027] The conductive layer 5 includes a notch 12, which comprises a narrow portion 12a and a wide portion 12b. The cross-section AA of the dielectric substrate spanning the stripline and the conductive layer is shown below. Figure 1c As shown.

[0028] The other ends of the strip conductors 8a, 8b, 9a, and 9b are connected to the inner conductor of the coaxial cable (not shown). The outer conductor of the coaxial cable is connected to conductors 5a-5d located near the edge of the dielectric substrate 1 and is connected to the conductive layer 5 through the metal plating holes 6.

[0029] The odd-mode electromagnetic field of the coupled stripline is concentrated between the coupled lines on which the dielectric substrate is located; therefore, the dielectric substrate effectively delays the electromagnetic wave. The even-mode electromagnetic field of the coupled stripline is concentrated between the edge of the coupled line and the edges of the conductive layer and additional conductor; therefore, a portion of the electromagnetic wave propagates through the air region adjacent to the dielectric substrate, resulting in a smaller delay for the even mode than for the odd mode. The notch 12 significantly increases the even-mode impedance but has little effect on the odd-mode impedance. The notch 12 forms a periodic structure that connects multiple transmission lines with different impedances in series. This periodic structure increases the even-mode delay and allows the electrical lengths of the even and odd modes to be equal.

[0030] Therefore, the coupling line provides directional coupling and splits the electromagnetic wave that excites strip conductor 8a between strip conductors 8b and 9a. A small fraction of the electromagnetic wave that excites strip conductor 8a penetrates strip conductor 9b. Figures 2a and 2b illustrate the measured frequency characteristics of a fabricated sample of the directional coupler shown in Figures 1a-1c. Figure 1a In the middle section, strip conductor 8a corresponds to port 1, strip conductor 8b corresponds to port 2, strip conductor 9a corresponds to port 3, and strip conductor 9b corresponds to port 4. The directional coupler including the coupled strip lines according to the present invention provides S11 ≤ -31.7dB, S41 ≤ -31dB, and coupling of -3.4 ± 0.2dB in the 690-960 MHz frequency band.

[0031] Another embodiment of the present invention is a 3 dB directional coupler operating at frequencies above 1 GHz, such as... Figure 3 A perspective view of the bottom surface of the dielectric substrate 13 is shown. A metal plate 14, disposed opposite to the coupling line 15, is connected to the conductive layer 16 via bent portions 17a-17d. The metal plate 14 reduces radiation from the coupling line 15; therefore, the directional coupler including the metal plate 14 provides lower insertion loss than a directional coupler without the metal plate 14.

[0032] When the second metal plate is placed on the top surface of the dielectric substrate 13, the radiation from the coupling line will be reduced. Figure 4a and 4b Described as Figure 3 The measured frequency characteristics of the directional coupler fabrication sample are shown. The directional coupler, comprising a coupling stripline and a metal plate, provides S11 ≤ -28.3 dB, S41 ≤ -23.2 dB, and coupling of -3.6 ± 0.2 dB in the 1700–2800 MHz band.

[0033] Another embodiment of the present invention is a phase shifter. Figure 5a and 5b Top and bottom views of a dielectric substrate containing the coupling striplines forming the phase shifter are shown respectively.

[0034] The top surface of the dielectric substrate 18 includes a first strip conductor 19a and an additional conductor 20 separated from the first strip conductor 19a by a gap 21. The additional conductor 20 is connected to the conductive layer 22 through a metallized hole 23. The edge of the additional conductor 20, which is disposed opposite to the first strip conductor 19a, includes a cutout 24. The left end of the first strip conductor 19a is connected to a strip conductor 25 to form a transmission line connected to the phase shifter input port.

[0035] The bottom surface of the dielectric substrate 18 includes a conductive layer 22 and a second strip conductor 19b disposed in the opening 30. The left end of the second strip conductor 19b is connected to a strip conductor 26 through a metallized hole 27. The strip conductor 26 forms a transmission line connected to the output port of the phase shifter. The right ends of the first strip conductor 19a and the second strip conductor 19b are connected together by metallized holes 28a and 28b. The edge of the conductive layer 22, which is disposed opposite to the second strip conductor 19b, includes a notch 29.

[0036] The dimensions of the first strip conductor 19a, the second strip conductor 19b, the additional conductor 20, the gap 21, and the opening 30 are calculated to provide a coupling line that matches the transmission lines of strip conductors 25 and 26. Figure 6 shows the simulated S11 of the phase shifter shown in Figures 5a and 5b. Table 1 shows the simulated phase of the phase shifter shown in Figures 5a and 5b. Compared to a transmission line with an electrical length of 3 / 4 wavelength at the intermediate frequency of the 1710-2690MHz operating band, the phase shifter provides S11 = -30.76dB and a phase shift of 90 + / - 2.5 degrees.

[0037] Table 1

[0038]

Claims

1. Two coupled striplines comprising: a first stripline conductor disposed on a top surface of a dielectric substrate and a second stripline conductor disposed on a bottom surface of the dielectric substrate, the second stripline conductor being located at an opening of a conductive layer covering the bottom surface of the dielectric substrate, the conductive layer being separated from the second stripline conductor by a gap, wherein at least a portion of the first stripline conductor is disposed over a portion of the second stripline conductor; at least one additional conductor disposed on the top surface of the dielectric substrate, separated from the first stripline conductor by a gap, and connected to the conductive layer through a plated via in the dielectric substrate; the conductive layer and the two additional conductors include a cutout in an edge separated from an edge of the first stripline conductor and the second stripline conductor by a gap, the cutout forming a periodic structure, the periodic structure formed by the cutout capable of increasing the delay of the even mode and allowing the electrical lengths of the even mode and the odd mode to be equal.

2. The two coupled striplines as defined in claim 1, wherein, At least one cutout has a narrow portion and a wide portion.

3. The two coupled striplines according to any one of claims 1-2, characterized in that, A metal plate is disposed below the dielectric substrate and connected to the conductive layer through a metal strap.

4. A directional coupler comprising two coupled striplines according to any of claims 1-2, characterized in that, Four stripline transmission lines are connected to the ends of the first stripline conductor and the second stripline conductor.

5. A directional coupler comprising two coupled striplines according to any of claims 1-2, characterized in that, A third stripline conductor and a fourth stripline conductor are disposed on the top surface of the dielectric substrate, their ends connected to the ends of the second stripline conductor through plated vias in the dielectric substrate, their other ends connected to a coaxial cable or a coaxial connector.

6. A differential phase shifter comprising two coupled striplines according to any of claims 1-2, characterized in that, The first end of the first stripline conductor and the first end of the second stripline conductor are connected to a coaxial cable or a coaxial connector, the other ends of the first stripline conductor and the second stripline conductor are connected together through plated vias in the dielectric substrate.

7. A differential phase shifter comprising two coupled striplines according to any of claims 1-2, characterized in that, A third stripline conductor is disposed on the top surface of the dielectric substrate, its first end connected to the first end of the second stripline conductor through a plated via in the dielectric substrate, its other end connected to a coaxial cable or a coaxial connector.

8. A beamforming network comprising two coupled striplines according to any of claims 1-2 forming a directional coupler and a differential phase shifter.

9. The beamforming network of claim 8, wherein, comprising a 3 dB directional coupler and a 90 degree phase shifter forming a 0 / 180 degree directional coupler.

10. The beamforming network of claim 8, wherein, comprising a 3db directional coupler and a 90 degree phase shifter, connected by striplines, distributing an RF signal from either of two inputs to three outputs.

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