Composite substrate for terahertz waveguide difference phase shift circulator and preparation method thereof

Abstract

The invention discloses a composite substrate for a terahertz waveguide difference phase shift circulator and a preparation method of the composite substrate, and belongs to the technical field of electromagnetism and microwaves, the composite substrate is composed of an upper substrate layer and a lower substrate layer, the thickness of the substrate layer is 0.20-0.24 mm, the thickness of the substrate layer is 0.08-0.12 mm, and the thickness of the substrate layer is 0.20-0.24 mm. The thickness of a welding layer between the base plate layer and the substrate layer is 0.01-0.03 mm, and the total thickness of the composite substrate is 0.32-0.36 mm; the preparation of the composite substrate comprises the steps of welding, grinding and polishing, cutting and the like; according to the composite substrate, the problem that an existing substrate is prone to cracking is solved, the reliability of the differential phase shift type circulator is improved, and the precision of the composite substrate is improved in a tool clamp auxiliary welding mode.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic and microwave technologies, and particularly to a composite substrate for a terahertz waveguide differential phase shift type circulator and a preparation method thereof. Background Art

[0002] Terahertz includes electromagnetic waves with frequencies ranging from 0.1 to 10 THz, which is between millimeter waves and infrared rays. Compared with electromagnetic waves in other frequency bands, terahertz waves have good penetrability, low energy, and broadband characteristics, and have broad application prospects in fields such as high-speed space communication, medical detection, and national defense security. Since the transmission loss of terahertz waves in free space is very large, functional devices based on waveguides have become the key to the wide application of terahertz waves.

[0003] The function of a waveguide circulator in an electromagnetic wave system is to control the signal transmission direction, which can realize duplex transmission to share an antenna; it can be combined with a filter to achieve frequency sorting; it can be combined with a load to achieve unidirectional signal transmission, reduce the influence of reflected power on the previous stage, stabilize the output of the power source, and prevent the power source from being burned by excessive reflected power from the subsequent stage.

[0004] In a radar system, the circulator has a wide and important role, playing the role of standing wave matching, protecting the previous stage, and realizing duplex transmission. Common transmission lines include various forms such as microstrip, strip line, and waveguide. In high-power radar transceiver systems, the waveguide form is mostly used. Common circulators include three-port waveguide junction type and four-port waveguide differential phase shift type. Among them, the four-port waveguide differential phase shift type circulator has the advantage of large power capacity and is one of the key components in high-power radar transceiver systems.

[0005] The differential phase shift type waveguide circulator usually consists of a magic T part 1, a 90° phase shift section part 2, and a 3dB bridge part 3. The magic T mainly realizes the equal-amplitude and in-phase distribution of the input signal. The phase shift section consists of two groups of non-reciprocal phase shifters. Double sheets of transversely magnetized ferrite are symmetrically loaded in two waveguide cavities. The traveling waves propagating in the positive and negative z directions have different propagation constants β and different phase constants, realizing the differential phase shift function. The bridge mainly realizes the synthesis and decomposition of signals. The schematic diagram is as Figure 1 shown: When a signal with an amplitude of W and a phase of φ is input at port 1, after passing through the magic T part 1, it is split into two signals with an amplitude of W / and a phase of φ. After passing through the phase shift section part 2, the two signals respectively become signals with an amplitude of W / and a phase of φ - φ1 and an amplitude of W / , two signals with a phase of φ - φ2 (at this time, φ2 - φ1 = 90°). After passing through the 3dB bridge section 3, two signals with an amplitude of W / 2 and phases of φ - φ1 and φ - φ2 + 90° are formed at port 2. At this time, the energies are equal and the phases are the same, and they are combined and output. At port 3, two signals with an amplitude of W / 2 and phases of φ - φ1 + 90° and φ - φ2 are formed. At this time, the energies are equal and the phases are opposite, and they cancel each other out, and there is no signal output, realizing the isolation function.

[0006] Similarly, as Figure 2 shown, when a signal is input at port 2, after passing through the bridge, the 90° phase shift section, and the magic T, a signal is output at Port4, and signal isolation is achieved at Port1.

[0007] Generally speaking, the signal transmission direction is Port1 → Port2 → Port4 → Port3.

[0008] According to this principle, a differential phase shift type waveguide circulator structure is established, as Figures 3 to 5 shown: The magic T section 1, the 90° phase shift section 2, and the 3dB bridge section 3 are all processed with upper and lower cavities. Stainless steel screws are used to connect the upper and lower cavities and the parts. The gyromagnetic substrate 4, the absorber 5, and the matching ceramic are bonded to the cavity, and the permanent magnet is bonded to the magnetic circuit. The magnetic circuit and the magic T load are fastened to the cavity with screws.

[0009] The size of the terahertz waveguide circulator is relatively small, and the inner cavity size is 1.09mm × 0.55mm. For waveguide devices, the higher the frequency, the shorter the wavelength of the electromagnetic wave, and the thickness of the ferrite substrate needs to be thinned to match the working wavelength to achieve better standing wave matching. An overly thick substrate may cause edge field leakage or mode distortion, increasing the transmission loss, that is, the problem cannot be simply solved by increasing the thickness of the substrate.

[0010] In the existing technical solution, through HFSS simulation, the size of the ferrite substrate corresponding to the terahertz waveguide circulator with good electrical performance matching is 20mm × 0.25mm × 0.1mm. During the processing and assembly process, it is easy to break due to its thin thickness. The existing technical solution generally avoids the phenomenon of substrate breakage by cutting the substrate in the length direction into several small pieces and then bonding the small pieces with silicone rubber. However, in terahertz band devices, adopting this solution requires cutting the substrate into 10 small pieces and then bonding them. Because the number of intermediate glue layers is relatively large, the finally bonded substrate has a large difference from the simulated size. And the terahertz band has high requirements for size accuracy, resulting in large electrical performance deviations of the device during testing. Summary of the Invention

[0011] One of the objectives of the present invention is to provide a composite substrate for a terahertz waveguide differential phase shift circulator to solve the above problems.

[0012] To achieve the above objective, the technical solution adopted by the present invention is as follows: A composite substrate for a terahertz waveguide differential phase shift circulator, the composite substrate is composed of a substrate layer located above and a substrate layer located below. Among them, the thickness of the substrate layer is 0.20 - 0.24 mm, the thickness of the substrate layer is 0.08 - 0.12 mm, the thickness of the welding layer between the substrate layer and the substrate layer is 0.01 - 0.03 mm, and the total thickness of the composite substrate is 0.32 - 0.36 mm.

[0013] As a preferred technical solution, the substrate layer is ferrite, and the substrate layer is ceramic or metal; the thermal expansion coefficient of the substrate layer material is the same as or close to that of the substrate layer; the surface of the substrate layer is metallized.

[0014] In the present invention, the substrate and the substrate are compounded and processed by welding to increase the thickness of the composite substrate, avoid cracking during processing and when joining the cavity, and at the same time solve the problem that the size gap between the substrate and the simulation size is large, resulting in a large deviation in the electrical performance of the device during testing. The substrate can be selected from ceramics or metals, and the metals can include aluminum alloy and brass. Materials with a thermal expansion coefficient close to that of the ferrite substrate are selected to improve the reliability of the combination of the substrate and the substrate; the substrate needs to reflect microwave signals, so surface metallization treatment is required, such as silver plating, gold plating, etc.

[0015] The second objective of the present invention is to provide a preparation method for a composite substrate for a terahertz waveguide differential phase shift circulator. The technical solution adopted is as follows: The method includes the following steps: (1) First, weld the substrate blank and the substrate after surface metallization treatment. (2) After welding, grind and polish the upper and lower surfaces to obtain a composite substrate blank. (3) Process grooves in the composite substrate blank, and then cut it to obtain the finished product.

[0016] As a preferred technical solution, in step (1), a gold-tin solder sheet is used as the solder during welding.

[0017] As a preferred technical solution, in step (1), a fixture is used for welding. The fixture sequentially includes a first-layer groove for placing the substrate blank and the solder, a second-layer groove for placing the substrate, and a pressing block from bottom to top.

[0018] First, weld the substrate blank and the substrate after surface metallization treatment through the fixture. The fixture of the present invention can avoid the influence of welding errors on the electrical performance.

[0019] As a further preferred technical solution, before welding, the substrate blank is first placed in the first layer groove, and then the solder of the same size as the substrate blank is placed, and then the metallized substrate is placed in the second layer groove, and then the pressing block is pressed on the upper surface of the substrate and fixed with screws so that the thickness of the welding layer after welding is controlled at 0.01 to 0.03 mm; finally, the clamped fixture is placed in the soldering station for welding.

[0020] As a further preferred technical solution, the thickness of the substrate blank and the base plate are both 0.8-1.2 mm, the welding temperature is 280-320° C., and the welding time is 20-30 min.

[0021] As a preferred technical solution, in step (2), after grinding and polishing, the thickness of the substrate layer is controlled to 0.08-0.12 mm, and the thickness of the base plate layer is controlled to 0.20-0.24 mm.

[0022] As a preferred technical solution, in step (3), the length of the substrate is controlled to be 8.6 mm and the width is controlled to be 0.546 mm during cutting. These are the dimensions of the preferred technical solution obtained through HFSS simulation.

[0023] Compared with the prior art, the advantages of the present invention are: the present invention uses the substrate and the base plate to be composited by welding, thereby increasing the thickness of the composite substrate, so that the composite substrate is not easy to break during the processing and assembly process; at the same time, combined with the auxiliary processing of the tooling fixture, it solves the problem of a large gap between the substrate and the simulation size, low dimensional accuracy of the composite substrate, and large deviation in the electrical performance of the device during testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the input schematic diagram of port 1 of the differential phase-shifted waveguide circulator; Figure 2 This is the 2-port input schematic diagram of the differential phase-shifted waveguide circulator; Figure 3 This is a structural diagram of a differential phase-shift waveguide circulator in the prior art; Figure 4 for Figure 3 Middle AA section view; Figure 5 for Figure 3 Middle BB cross-section; Figure 6 is a structural diagram of the clamp of the present invention; Figure 7 This is a processing diagram of the composite substrate blank; Figure 8 It is a schematic diagram of cutting the composite substrate blank in the length direction; Figure 9 Schematic diagram of cutting the composite substrate blank in the width direction.

[0025] In the figure: 1. Magic-T part; 2. 90° phase shift section part; 3. 3dB bridge part; 4. Gyromagnetic substrate; 5. Absorber; 6. Substrate layer; 7. Substrate layer; 8. Gold-tin solder sheet; 9. Polytetrafluoroethylene pressing block; 10. Groove. Specific implementation mode

[0026] The present invention will be further described below in conjunction with embodiments.

[0027] Embodiment 1: Refer to Figure 6 , a composite substrate for a terahertz waveguide differential phase shift type circulator, the composite substrate is composed of a substrate layer 6 located above and a substrate layer 7 located below, wherein the thickness of the substrate layer is 0.22 mm, the thickness of the substrate layer is 0.1 mm, the thickness of the welding layer is 0.02 mm, and the total thickness of the composite substrate is 0.34 mm.

[0028] In this embodiment, the substrate layer is ferrite, and the thermal expansion coefficient is 4e -6 / k, the substrate layer is ceramic, and the thermal expansion coefficient is 6e -6 / k; the surface of the substrate layer 6 is metallized, such as by using conventional silver plating or gold plating, etc.; Its preparation method is: First, the substrate blank and the surface-metallized substrate are welded by a fixture, and the fixture can avoid the influence of welding errors on the electrical performance. The specific clamping method is; First, the substrate blank is placed in the first-layer groove, then the equal-sized gold-tin solder sheet 8 is placed, and then the metallized substrate is placed in the second-layer groove. At this time, by controlling the depth dimension of the groove for placing the substrate to be a negative tolerance, the gold-tin solder sheet and the metallized substrate are closely attached to avoid a large void ratio during subsequent welding. Then, the polytetrafluoroethylene pressing block 9 is pressed on it, and the polytetrafluoroethylene cushion block is fixed with screws, so that the welding layer after welding is controlled at 0.02 mm to avoid deviating from the design value. At this time, the thicknesses of both the substrate blank and the substrate are 1 mm, and the thickness of the blank is increased to avoid cracking of the substrate blank and the substrate when pressure is applied; finally, the whole is placed on a soldering table at 300 °C and kept for 25 min; After the substrate blank and the surface-metallized ceramic are welded by the fixture, first, the upper and lower surfaces of the composite substrate blank are ground and polished to control the thickness of the substrate layer to 0.1 mm and the thickness of the substrate layer to 0.24 mm. Then, the composite substrate blank is processed, and grooves 10 are processed in the large sheet. The processing schematic diagram is as Figure 7 shown; Finally, cutting is performed to control the length direction of the composite substrate to be 8.6 mm and the length in the width direction to be 0.546 mm, as Figure 8 and Figure 9as shown

[0029] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A composite substrate for a terahertz waveguide differential phase shift type circulator, characterized in that, The composite substrate is composed of a substrate layer located above and a wafer layer located below. Among them, the thickness of the substrate layer is 0.20 - 0.24 mm, the thickness of the wafer layer is 0.08 - 0.12 mm, the thickness of the welding layer between the substrate layer and the wafer layer is 0.01 - 0.03 mm, and the total thickness of the composite substrate is 0.32 - 0.36 mm.

2. The composite substrate for the terahertz waveguide differential phase shift type circulator according to claim 1, characterized in that, The wafer layer is ferrite, and the substrate layer is ceramic or metal; the thermal expansion coefficient of the substrate layer material is the same as or close to that of the wafer layer; the surface of the substrate layer is metallized.

3. The preparation method of the composite substrate for the terahertz waveguide differential phase shift type circulator according to claim 1 or 2, characterized in that, It includes the following steps: (1) First, weld the wafer blank and the substrate after surface metallization treatment. (2) After welding, grind and polish the upper and lower surfaces to obtain a composite substrate blank. (3) Process grooves in the composite substrate blank and then perform cutting to obtain the finished product.

4. The method according to claim 3, wherein In step (1), a gold-tin solder sheet is used as the solder during welding.

5. The method according to claim 3, characterized in that, In step (1), a fixture is used for welding. The fixture sequentially includes a first-layer groove for placing the wafer blank and the solder, a second-layer groove for placing the substrate, and a pressing block from bottom to top.

6. The method according to claim 5, wherein Before welding, first place the wafer blank in the first-layer groove, then place a solder of the same size as the wafer blank, then place the metallized substrate in the second-layer groove, then press the pressing block on the upper surface of the substrate, and use screws to fix the pressing block to control the thickness of the welding layer after welding to be 0.01 - 0.03 mm; finally, place the clamped fixture on the soldering station for welding.

7. The method according to claim 6, wherein The thicknesses of both the wafer blank and the substrate are 0.8 - 1.2 mm. The welding temperature is 280 - 320 °C, and the time is 20 - 30 min.

8. The method according to claim 3, wherein In step (2), after grinding and polishing, control the thickness of the wafer layer to 0.08 - 0.12 mm and the thickness of the substrate layer to 0.20 - 0.24 mm.

9. The method according to claim 3, wherein In step (3), control the length of the wafer to be 8.6 mm and the width to be 0.546 mm during cutting.

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