High rectangular coefficient filter and design method

Abstract

The application relates to the technical field of filters, in particular to a high-rectangular-coefficient filter and a design method. The filter comprises resonant structures T1 / T2, input / output feeding structures and open-circuit branches arranged on a dielectric substrate; the two open-circuit branches are distributed in left-right axis symmetry, the open-circuit branches are connected with the input / output feeding structures, the input / output feeding structures are connected with the first resonant unit and the fourth resonant unit respectively; and the open-circuit branches are in L-shaped bending state, and a coupling relationship is formed between the open-circuit branches and the resonant structures T1 / T2. The application aims to improve the out-of-band suppression of the filter under the condition that the filter order and the size are unchanged.

Description

Technical Field

[0001] This invention relates to the field of filter technology, and in particular to a high rectangular coefficient filter and its design method. Background Technology

[0002] Filters are primarily used in microwave and radio frequency communication fields to select frequencies, allowing signals in specific frequency bands to pass while suppressing unwanted signals. Due to continuous technological advancements, spectrum resources are becoming increasingly scarce, channel spacing is shrinking, and signal interference is intensifying. Filters, through their frequency selectivity, isolate signals, reduce interference, and improve signal quality. Simultaneously, the increasing integration and miniaturization of electronic products necessitates filters that are also miniaturized, easily integrated, and possess better selectivity. This represents a current and future challenge for filters. While miniaturization is required, higher out-of-band rejection is also needed. Traditional filters can incorporate transmission zeros, but this is complex, especially when multiple transmission zeros are required. Traditional microstrip filters have poor frequency selectivity; improving suppression necessitates increasing the filter order, leading to higher losses and increased design and simulation complexity.

[0003] Existing filters of this type require additional coupling structures between resonant units to have multiple transmission zeros. Adding these coupling structures causes the frequency of the original resonant units to change, increasing the design difficulty. This means that the size of the resonant units and the size of the coupling structures must be adjusted repeatedly. Furthermore, due to the transmission characteristics of microstrip lines, the introduction of coupling structures leads to more parasitic coupling and increases the strength of the original parasitic coupling, further increasing the design difficulty. Summary of the Invention

[0004] The purpose of this invention is to provide a high rectangular coefficient filter and its design method. In order to improve the out-of-band rejection of the filter while keeping the filter order and size unchanged, the size of the filter can be reduced in a way, thereby achieving the goal of miniaturization and high performance.

[0005] To address the aforementioned technical problems, this invention provides a high rectangular coefficient filter, comprising: a filter disposed on a dielectric substrate.

[0006] The resonant structures T1 / T2 are symmetrically distributed along the left and right axes. The resonant structure T1 is composed of a first resonant unit, a second resonant unit, and a third resonant unit; the resonant structure T2 is composed of a fourth resonant unit, a fifth resonant unit, and a sixth resonant unit.

[0007] The first resonant unit and the second resonant unit are arranged horizontally from left to right, and the angle between their openings is 90°; the second resonant unit and the third resonant unit are arranged vertically from top to bottom, and the angle between their openings is 180°.

[0008] Input / output power supply structure;

[0009] Open-circuit stubs; the two open-circuit stubs are symmetrically distributed along the left and right axes, and the open-circuit stubs are connected to the input / output feed structure, which is connected to the first resonant unit and the fourth resonant unit respectively;

[0010] Furthermore, the open-circuit stub is in an L-shaped bend, and the open-circuit stub is coupled to the resonant structure T1 / T2.

[0011] Preferably, the dielectric substrate is a ceramic substrate with a dielectric constant of 9.8 and a thickness of 0.254 mm.

[0012] Preferably, the opening of the first resonant unit faces vertically upward, the opening of the second resonant unit faces horizontally to the right, and the opening of the third resonant unit faces horizontally to the left.

[0013] Preferably, the input / output power supply structure includes, but is not limited to, a left-right axis symmetrical distribution.

[0014] Preferably, the filter generates five transmission zeros on the same plane. The resonant positions of the five transmission zeros can be freely controlled, and four of the transmission zeros are approximately symmetrically distributed. The fifth transmission zero is located in the highest segment, and its position is directly controlled by the open stub.

[0015] Preferably, the size of the filter is less than 4.8mm*2.8mm.

[0016] Preferably, the filter is a microstrip filter, an LTCC filter, or an MMIC filter.

[0017] This invention also provides a design method for a high rectangular coefficient filter, comprising the following steps:

[0018] Step 1: Conduct a comprehensive evaluation based on the filter specifications to determine the location of the filter's transmission zero and the operating frequency of the resonant unit;

[0019] Step 2: Calculate the initial size of the resonant unit based on its operating frequency and half-wavelength theory, and then arrange the filter space according to the layout of the filter described above.

[0020] Step 3: Simulation Optimization Design

[0021] First, tune the resonant frequency to the center frequency, and then adjust the spacing between the resonant elements so that the coupling can operate at the combined coupling bandwidth.

[0022] Adjust the position of the transmission zero point according to the current waveform;

[0023] The transmission zeros are divided into two pairs, each with a variable control. The spacing between the second resonant unit and the fifth resonant unit controls the transmission zeros closer to the passband. The smaller the spacing, the closer the transmission zeros are to the passband.

[0024] The length of the open stub and the spacing between the open stub and the resonant unit control the position of another pair of transmission zeros. The smaller the spacing, the stronger the coupling and the closer it is to the passband.

[0025] After several iterations in the third step, the performance requirements can be met.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] Compared to traditional filters, this invention generates transmission zeros through a rationally arranged array of resonant units. Open-circuit stubs are introduced at the ports to alter the distribution of transmission zeros, reducing parasitic effects and making the transmission zero distribution easier to control. The symmetry of the transmission zero distribution is more pronounced. Furthermore, new transmission zeros are introduced. This invention consists of six resonant units and two open-circuit stubs, achieving five transmission zeros. Four transmission zeros are approximately symmetrically distributed at the high and low ends of the passband, with an additional transmission zero located at the high end, far from the symmetrical zeros. The position of the transmission zeros can be easily controlled by changing the values ​​of independent variables. The filter of this invention is smaller, has higher out-of-band suppression, and a better rectangular coefficient. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structural layout of the filter of the present invention.

[0029] Figure 2 This is a schematic diagram of the simulation result response curve of an embodiment of the filter of the present invention.

[0030] Figure 3 This is a schematic diagram of the response curve of the filter structure of the present invention after removing open-circuit stubs.

[0031] In the figure: 1-Dielectric substrate, 2-First resonant unit, 3-Second resonant unit, 4-Third resonant unit, 5-Fourth resonant unit, 6-Fifth resonant unit, 7-Sixth resonant unit, 8-Input feeding structure, 9-Output feeding structure, 10-Open circuit stub. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0033] like Figure 1 As shown, the filter consists of at least 6 resonant units, a dielectric substrate 1, an input feed structure 8, an output feed structure 9, and an open-circuit stub 10. This filter is symmetrically distributed along the left and right axes. The resonant units are the first resonant unit 2, the second resonant unit 3, the third resonant unit 4, the fourth resonant unit 5, the fifth resonant unit 6, and the sixth resonant unit 7. There are two open-circuit stubs 10, the input feed structure 8, and the output feed structure 9. The feed structures do not have to be symmetrically distributed along the left and right axes and can be adjusted according to the actual use. Symmetrical distribution can reduce the amount of simulation. The input feed structure 21 is connected to the first resonant unit 2 and the first open-circuit stub 10 on the left. The output feed structure 9 is connected to the fourth resonant unit 5 and the second open-circuit stub 10 on the right. The second resonant unit 3 is on the same horizontal line as the first resonant unit 2. The second resonant unit 3 has an additional bend in its opening direction to enhance coupling and miniaturization. The opening direction of the second resonant unit 3 is 90° clockwise from the opening direction of the first resonant unit 2. The third resonant unit 4 is on the same vertical line as the second resonant unit 3, distributed vertically, with its opening direction at 180°. Furthermore, the sixth resonant unit 7 is symmetrically distributed with the third resonant unit 4, the fifth resonant unit 6 with the second resonant unit 3, and the third resonant unit 4 with the first resonant unit 2. The open-circuit stub 10 has an L-shaped bend, mainly to increase its coupling with the resonant units and reduce spatial coupling. At the same time, the two L-shaped open-circuit stubs 10 are more conducive to mutual coupling to form new transmission zeros, improving the rectangularity coefficient of the transmitted signal.

[0034] like Figure 2The simulation results shown have an operating center frequency of 22 GHz, a substrate dielectric constant of 9.8, and a thickness of 0.254 mm. The final size of the entire filter is less than 4.8 mm * 2.8 mm. The results show two transmission zeros each at the high and low ends, exhibiting an approximately symmetrical distribution. The control of the transmission zeros is determined by the distance between the second resonant unit 3 and the fifth resonant unit 6, and the size of the open-circuit stub 10 and its distance from the third resonant unit 4 and the sixth resonant unit 7. Specifically, the distance between the second resonant unit 3 and the third resonant unit 4 controls the two transmission zeros closer to the passband; the size of the open-circuit stub 10 and its distance from the third resonant unit 4 and the sixth resonant unit 7 control the two transmission zeros farther from the passband. Simultaneously, the two open-circuit stubs 10 together generate a fifth transmission zero at the high end. In this embodiment, the distance between the open-circuit stub 10 and the input feed structure 8 is 1.8 mm, the distance between the end of the open-circuit stub 10 and the third resonant unit 4 is 0.3 mm, and the distance between the second resonant unit 3 and the fifth resonant unit 6 is 0.44 mm. The size of the resonant unit can be obtained through simulation in this mode. At the same time, the style of the resonant unit can be diverse. The core lies in the opening direction and placement of the resonant unit.

[0035] like Figure 3 As shown Figure 1 The response curve of the structure after removing open branches, from Figure 3 As can be seen, there are only 4 transmission zeros, and the zero distribution is severely asymmetrical, whereas theoretically, this structure should exhibit a symmetrical zero distribution. This invention solves the asymmetrical zero distribution problem by adding open-circuit stubs within a limited space, while simultaneously introducing a new transmission zero, improving out-of-band rejection, especially in the high-frequency band, and increasing the rectangular coefficient of the filter.

[0036] Step 1: Conduct a comprehensive evaluation based on the filter specifications to determine the location of the filter's transmission zero and the operating frequency of the resonant unit.

[0037] Step 2: Calculate the initial dimensions of the resonant unit based on its operating frequency and half-wavelength theory, and then... Figure 1 The filter layout method involves spatial arrangement of the filter.

[0038] Step 3: Simulation Optimization Design. First, tune the resonant frequency to the center frequency. Then, adjust the spacing between the resonant elements to ensure the coupling operates within the overall coupling bandwidth. Based on the current waveform, adjust the position of the transmission zeros. There are two pairs of transmission zeros, each controlled by a variable. The spacing between the second resonant element 3 and the fifth resonant element 6 controls the transmission zeros closer to the passband; the smaller the spacing, the closer the zeros are to the passband. The length of the open stub and the spacing between the open stub and the resonant element control the position of the second pair of transmission zeros; the smaller the distance, the stronger the coupling and the closer to the passband. After several iterations in Step 3, the performance requirements can be met.

[0039] The core of this invention lies in the placement of the resonant units, including the orientation of their openings, the introduction of open-circuit stubs, the shape of the open-circuit stubs, and the control method of the transmission zeros. This invention generates transmission zeros simply by rationally arranging the resonant units, introducing open-circuit stub lines at the ports to alter the zero distribution, and reducing parasitic effects. This makes the transmission zero distribution of the filter easier to control and closer to the theoretical distribution, i.e., the zeros are symmetrically distributed at both ends of the passband, thus improving filter performance and simplifying design. All transmission zeros in this invention are controllable, unlike transmission zeros generated by parasitic coupling, which can be adjusted by modifying their dimensions. Furthermore, this invention can be used not only for microstrip filters but also for multilayer substrate filters, such as LTCC and MMIC filters.

[0040] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A high rectangular coefficient filter, characterized in that, Including those disposed on the dielectric substrate: The resonant structures T1 / T2 are symmetrically distributed along the left and right axes. The resonant structure T1 is composed of a first resonant unit, a second resonant unit, and a third resonant unit; the resonant structure T2 is composed of a fourth resonant unit, a fifth resonant unit, and a sixth resonant unit. The first resonant unit and the second resonant unit are arranged horizontally from left to right, and the angle between their openings is 90°; the second resonant unit and the third resonant unit are arranged vertically from top to bottom, and the angle between their openings is 180°. Input / output power supply structure; Open-circuit stubs; the two open-circuit stubs are symmetrically distributed along the left and right axes, and the open-circuit stubs are connected to the input / output feed structure, which is connected to the first resonant unit and the fourth resonant unit respectively; the open-circuit stubs are in an L-shaped bend, and the open-circuit stubs are coupled to the resonant structures T1 / T2; The filter generates five transmission zeros on the same plane. The resonant positions of the five transmission zeros can be freely controlled. Four of the transmission zeros are approximately symmetrically distributed, and the fifth transmission zero is located in the highest segment, its position being directly controlled by the open-circuit stub.

2. A high rectangular coefficient filter as described in claim 1, characterized in that, The opening of the first resonant unit faces vertically upward, the opening of the second resonant unit faces horizontally to the right, and the opening of the third resonant unit faces horizontally to the left.

3. A high rectangular coefficient filter as described in claim 1, characterized in that, The input / output power supply structure is symmetrically distributed along the left and right axes.

4. A high rectangular coefficient filter as described in claim 1, characterized in that, The filter is a microstrip filter, an LTCC filter, or an MMIC filter.

5. A design method for a high rectangular coefficient filter as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Conduct a comprehensive evaluation based on the filter specifications to determine the location of the filter's transmission zero and the operating frequency of the resonant unit; Step 2: Calculate the initial size of the resonant unit based on its operating frequency and half-wavelength theory, and then arrange the filter space according to the layout of the filter described above. Step 3: Simulation Optimization Design First, tune the resonant frequency to the center frequency, and then adjust the spacing between the resonant elements so that the coupling can operate at the combined coupling bandwidth. Adjust the position of the transmission zero point according to the current waveform; The transmission zeros are divided into two pairs, each with a variable control. The spacing between the second resonant unit and the fifth resonant unit controls the transmission zeros closer to the passband. The smaller the spacing, the closer the transmission zeros are to the passband. The length of the open stub and the spacing between the open stub and the resonant unit control the position of another pair of transmission zeros. The smaller the spacing, the stronger the coupling and the closer it is to the passband. After several iterations in the third step, the performance requirements can be met.

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