Unidirectional microwave filter and preparation method thereof

Abstract

The invention discloses a unidirectional microwave filter and a preparation method, the filter comprises a substrate made of a ceramic dielectric, an input port, an output port and a plurality of dielectric resonators are sintered on the substrate by adopting a high-temperature silver sintering process, the substrate is also provided with ferrites, tantalum resistors and the like, and each functional port and device are connected through a sintered silver conduction band. The filter designed by the invention is processed and formed on the dielectric substrate, is compact in structure, has better reverse isolation performance and frequency selectivity, can protect a power source, effectively inhibits unnecessary signals, and meets the requirements of various communication standards.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave device design, and in particular relates to a unidirectional microwave filter and a preparation method thereof. Background Art

[0002] In communication and electronic systems, filters play a vital role, allowing specific frequency components in the signal to pass through while greatly attenuating other frequency components. The frequency selection function of the filter can be used to filter out interference noise or perform spectrum analysis. However, in the prior art, filters are indispensable in communication antenna feed systems. In order to prevent the power source from being damaged by the reflected power when the antenna is mismatched, an isolator needs to be connected to the antenna input. Since an external isolator is required, additional space is required in the overall layout, which increases the insertion loss of the entire machine. Therefore, it is necessary to improve the filter so that the filter can increase its isolator function.

[0003] Filters play an important role in communication systems. Their main function is to selectively allow electrical signals in a specific frequency range to pass through, while blocking signals in other frequency ranges from passing through. Their core functions include frequency selection, noise removal, signal enhancement, isolation, and protecting electronic equipment from interference. Since non-reciprocal microwave ferrite is used in the filter, it only allows electromagnetic waves to pass through in one direction. Electromagnetic waves transmitted in the opposite direction will produce a large attenuation, which can eliminate the effects of frequency drift caused by electromagnetic wave reflection, thereby preventing the power reflected by the antenna mismatch from damaging the power source and protecting the power source. Summary of the invention

[0004] Technical purpose: In view of the above technical problems, the present invention proposes a unidirectional microwave filter with higher selectivity, lower insertion loss and better isolation and protection function and a preparation method thereof.

[0005] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution:

[0006] A unidirectional microwave filter comprises a substrate made of ceramic dielectric, an input port and an output port are arranged on the substrate and are opposite to each other, and a plurality of dielectric resonators, ferrites, tantalum resistors and a plurality of silver conducting strips are arranged between the input port and the output port;

[0007] The dielectric resonators are arranged on the substrate at equal intervals, the outermost dielectric resonator at one end is connected to the input port through a first silver conduction band, the outermost dielectric resonator at the other end is connected to the ferrite through a second silver conduction band, and the ferrite is connected to the output port through a third silver conduction band;

[0008] The tantalum resistor is arranged outside the ferrite, and the ferrite is connected to the tantalum resistor through a fourth silver conduction band.

[0009] Preferably, the dielectric constant of the ceramic medium used to make the substrate is 45, and the size of the substrate is 28.5 mm*12 mm*5 mm.

[0010] Preferably, the input port and the output port are both silver conductive strips with a width of 0.86 mm, sintered on the substrate by a high-temperature silver sintering process, and the impedance of the output port is 50 ohms.

[0011] Preferably, the unidirectional microwave filter comprises three dielectric resonators, and an equally spaced resonant cavity is formed on the surface of a substrate by a high-temperature silver sintering process. In the signal transmission direction, the depths of the three dielectric resonators are 4.1 mm, 3.8 mm, and 4 mm, respectively, and the spacing between adjacent dielectric resonators is 2.4 mm.

[0012] Preferably, the ferrite is formed by stacking two upper and lower cylinders with a diameter of 2.6 mm and a thickness of 1.1 mm.

[0013] Preferably, the tantalum resistor is made of 50 ohm square resistance tantalum thin film material, and the tantalum resistor is bonded to the substrate with thermal conductive adhesive.

[0014] Preferably, the width of the first silver conductive strip is 0.21 mm, and the widths of the second silver conductive strip, the third silver conductive strip and the fourth silver conductive strip are all 0.86 mm.

[0015] A method for preparing a unidirectional microwave filter comprises the following steps:

[0016] Select materials, including substrate, dielectric resonator, ferrite and tantalum resistor, according to the requirements of the filter to be designed;

[0017] The input port and the output port are sintered on the substrate using a high-temperature silver sintering process;

[0018] A plurality of dielectric resonators are arranged at equal intervals at the input port on the surface of the substrate by using a high temperature silver burning process;

[0019] The ferrite and tantalum resistors are bonded to the substrate using thermally conductive adhesive;

[0020] A high-temperature silver sintering process is used to sinter a first silver conductive strip, a second silver conductive strip, a third silver conductive strip and a fourth silver conductive strip at corresponding positions on the substrate.

[0021] Beneficial effects: Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0022] The filter designed in the present invention is processed on a dielectric substrate, has a simple and compact structure, has better reverse isolation performance and frequency selectivity, can protect the power source, effectively suppress unnecessary signals, and also has lower insertion loss and working bandwidth, reduces signal loss during transmission, and meets the requirements of various communication standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of the structure of the filter designed for the present invention;

[0024] Figure 2 A simulation diagram for calculating the depth of a resonator when designing a filter for the present invention;

[0025] Figure 3 A simulation diagram for calculating the spacing between adjacent resonators when designing a filter for the present invention;

[0026] Figure 4 A simulation diagram of the filtering performance of the filter designed for the present invention. DETAILED DESCRIPTION

[0027] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0028] Embodiment 1

[0029] like Figure 1 As shown, this embodiment provides a filter, including an input port 1 , an output port 4 , a dielectric resonator 2 , a ferrite 3 and a tantalum resistor 5 .

[0030] Microwave signals can only be input from input port 1 and output from output port 4. When the impedance of the antenna connected to output port 4 changes, the output energy will be reflected back. Since the filter designed by the present invention is unidirectional, the signal can only be transmitted from input port 1 to output port 4. When the output port 4 has radiated energy, the input port 1 will not have energy output, thereby protecting the power source from damage caused by reflected power.

[0031] The filter designed by the present invention is made of ceramic medium as the substrate material. The dielectric constant of the ceramic medium used is 45, and it has the characteristics of low loss and good temperature stability. The substrate is a rectangular parallelepiped with a size of 28.5*12*5mm. The input port 1 and the output port 4 are both made of high-temperature silver burning processes to directly leave a 0.86mm wide conduction band on the substrate, so that the port impedance is 50 ohms. In use, it can be matched and connected with the antenna and the power amplifier to reduce its reflection loss.

[0032] The dielectric resonator 2 is formed directly on the surface of the dielectric using high dielectric constant ceramic materials and high-temperature silver sintering and other processes. It can be regarded as a dielectric waveguide with one end open, and the oscillation mode corresponds to the mode in the dielectric waveguide. The interface between the dielectric and the air is in a short-circuit state. When electromagnetic waves propagate in materials with high dielectric constants, they are repeatedly totally reflected inside the dielectric, and their wavelength can be shortened to form a microwave resonator. High dielectric constant media can ensure that most of the field is within the resonator and is not easy to radiate or leak. The resonant frequency is determined by factors such as the oscillation mode, the material used for the resonator, and the size. The number of resonators can be calculated based on the depth required for the resonant frequency through software simulation, such as Figure 2 The number of resonators can be obtained through software simulation according to the requirement of 30dB suppression at 500MHz out of band, and the spacing between adjacent resonators can be determined by simulating the dual-cavity model to calculate its resonant frequency and coupling coefficient, as shown in Figure 3 shown.

[0033] The input port 1 and the dielectric resonator 2 are directly connected by a silver conduction band, and the width of the silver conduction band at the connection is 0.21 mm. This embodiment uses three dielectric resonators 2, and spatial coupling is used between the dielectric resonators 2. The distance between the dielectric resonators 2 is 2.4 mm. The resonant frequency of the resonator can be adjusted by adjusting the depth of the resonator 2. The depths of the resonators designed in this embodiment are 4.1 mm, 3.8 mm, and 4 mm respectively.

[0034] The ferrite 3 is an upper and lower cylinder with a diameter of 2.6 mm and a thickness of 1.1 mm. The ferrite 3 is composed of two upper and lower ferrites, which can enhance the isolation effect of the signal and ensure that the signal will not be interfered during the transmission process, thereby improving the stability and reliability of the system. It can also expand its bandwidth so that it can process signals in a wider frequency range, and reduce the insertion loss during signal transmission, ensuring that the signal loss is small during transmission and maintaining a high signal strength. The ferrite 3 and the dielectric resonator 2 are connected by a silver conductive tape with a width of 0.86 mm, which is directly sintered on the substrate. The ferrite 3 and the output port 4 are connected by a silver conductive tape with a width of 0.86 mm, which is directly sintered on the substrate, so that the impedance of the output port 4 is 50 ohms. The ferrite 3 and the tantalum resistor 5 are connected by a silver conductive tape with a width of 0.86 mm, which is directly sintered on the substrate. The ferrite 3 and the tantalum resistor 5 are bonded to the substrate with thermal conductive adhesive.

[0035] Ferrite 3 is a microwave device made by utilizing the gyromagnetic effect of ferrite materials. The gyromagnetic effect of ferrite comes from the spin motion of electrons. An electron with a negative charge must have angular momentum and magnetic moment at the same time when performing spin motion. Under the action of the spin magnetic moment, the electrons precess in the right-handed direction around the magnetic lines of force. If a high-frequency alternating magnetic field is added in a direction perpendicular to the magnetic lines of force, the energy loss of the precession can be compensated, so that the precession of the electrons can be maintained. When the frequency of the alternating magnetic field is equal to the precession frequency of the electrons, the amplitude of the precession reaches a maximum. This is the ferromagnetic resonance phenomenon. At this time, the frequency of the high-frequency alternating magnetic field is called the ferromagnetic resonance frequency. The present invention utilizes this characteristic of ferrite to select an appropriate size so that it resonates at the desired frequency. Because the direction of the electron movement is fixed, the present invention can ensure the unidirectional transmission performance of its filter.

[0036] Tantalum resistor 5 is made of 50 ohm square resistance tantalum film material to form a load resistor that can absorb the energy transmitted by the antenna. Tantalum film is usually prepared by reactive sputtering and co-sputtering methods, and is also prepared by cathode sputtering using a sintered alloy as a target. Since tantalum silicon film can be deposited by a general sputtering process, the basic process equipment in the factory that produces the film can continue to be used, as long as the raw materials and manufacturing process are changed. Tantalum film is deposited directly on a microcrystalline glass substrate. After the tantalum film is prepared, it is heat treated in a vacuum. A resistor is formed on its surface, and then this value is multiplied by its film thickness to obtain the resistivity of the tantalum film. Its resistance stability is high, which can produce high-precision and high-stability precision resistors.

[0037] like Figure 4 As shown, Goals represents the red square area, which represents the passband area, and is the operating frequency area of ​​the filter that needs to be designed.

[0038] The blue line S21 indicates the transmission characteristics of the filter, which represents the attenuation characteristics of signals of different frequencies from input port 1 through the filter to output port 4. From the simulation diagram, it can be seen that the attenuation in the required passband of 15000-15200MHz is very small, and the attenuation outside 500MHz is greater than 30dB.

[0039] The red line S11 represents the echo reflection of input port 1. It can be seen that the reflection of the signal at input port 1 changes with frequency. The echo in the passband of 15000~15200MHz is greater than 20dB.

[0040] The green line tGd represents the transmission delay, which is the time required for the signal to transmit from input port 1 through the filter to output port 4 at different frequencies, which is required to be less than 10ns.

[0041] It can be seen that the filter designed by the present invention has higher selectivity, lower insertion loss and better isolation protection. The unidirectional filter designed by the present invention is applied to microwave circuits, can protect the receiving end from interference from the transmitting end, improve the integration of the communication system, reduce the volume and cost, and ensure the stability and efficiency of communication.

[0042] Embodiment 2

[0043] The filter of the present invention can be implemented by the following steps:

[0044] According to the design requirements, select the appropriate dielectric material and size;

[0045] The various components of the filter are made using high-temperature silver-sintering and other precision manufacturing processes;

[0046] The use of thin film resistors makes its structure compact;

[0047] Assemble and test to ensure product performance meets expected targets.

[0048] The filter of the present invention is innovative in technology and has broad market prospects in application. Its excellent performance and reliability have been proved through actual tests.

[0049] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A unidirectional microwave filter, characterized in that: The invention comprises a substrate made of ceramic dielectric, wherein an input port (1) and an output port (4) are arranged on the substrate and are located opposite to each other, and a plurality of dielectric resonators (2), ferrites (3), tantalum resistors (5) and a plurality of silver conducting strips are arranged between the input port (1) and the output port (4); The dielectric resonators (2) are arranged on the substrate at equal intervals, the outermost dielectric resonator (2) at one end is connected to the input port (1) via a first silver conduction band, the outermost dielectric resonator (2) at the other end is connected to the ferrite (3) via a second silver conduction band, and the ferrite (3) is connected to the output port (4) via a third silver conduction band; The tantalum resistor (5) is arranged outside the ferrite (3), and the ferrite (3) is connected to the tantalum resistor (5) via a fourth silver conductive band.

2. A unidirectional microwave filter according to claim 1, characterized in that: The dielectric constant of the ceramic medium used to make the substrate is 45, and the size of the substrate is 28.5 mm*12 mm*5 mm.

3. A unidirectional microwave filter according to claim 1, characterized in that: The input port (1) and the output port (4) are both silver conductive strips with a width of 0.86 mm, sintered on a substrate using a high-temperature silver sintering process, and the impedance of the output port (4) is 50 ohms.

4. A unidirectional microwave filter according to claim 1, characterized in that: The unidirectional microwave filter comprises three dielectric resonators (2), and resonant cavities with equal spacing are formed on the surface of a substrate by a high-temperature silver sintering process. In the signal transmission direction, the depths of the three dielectric resonators (2) are 4.1 mm, 3.8 mm, and 4 mm respectively, and the spacing between adjacent dielectric resonators (2) is 2.4 mm.

5. The unidirectional microwave filter according to claim 1, characterized in that: The ferrite (3) is composed of two stacked cylinders, an upper cylinder and a lower cylinder, each with a diameter of 2.6 mm and a thickness of 1.1 mm.

6. The unidirectional microwave filter according to claim 1, characterized in that: The tantalum resistor (5) is made of a 50 ohm square resistance tantalum thin film material, and the tantalum resistor (5) is bonded to the substrate using a heat-conducting adhesive.

7. The unidirectional microwave filter according to claim 1, characterized in that: The width of the first silver conductive strip is 0.21 mm, and the widths of the second silver conductive strip, the third silver conductive strip, and the fourth silver conductive strip are all 0.86 mm.

8. The method for preparing a unidirectional microwave filter according to any one of claims 1 to 7, characterized in that: Includes steps: Selecting materials including a substrate, a dielectric resonator (2), a ferrite (3) and a tantalum resistor (5) according to the requirements of the filter to be designed; An input port (1) and an output port (4) are sintered on the substrate using a high-temperature silver sintering process; A plurality of dielectric resonators (2) are arranged at equal intervals at the input port on the surface of the substrate by using a high-temperature silver sintering process; The ferrite (3) and the tantalum resistor (5) are bonded to the substrate using a thermally conductive adhesive; A high-temperature silver sintering process is used to sinter a first silver conductive strip, a second silver conductive strip, a third silver conductive strip and a fourth silver conductive strip at corresponding positions on the substrate.

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