Microstrip low-pass filter

Abstract

The application discloses a kind of microstrip low-pass filters, including dielectric substrate;Microstrip transmission line, microstrip transmission line is located on the first surface of dielectric substrate;Multiple resonance units, resonance unit is etched on the second surface of dielectric substrate, the second surface is opposite surface with the first surface, multiple resonance units are arranged in logarithmic periodic array on dielectric substrate, and a clamping angle is formed at the vertex of adjacent two resonance units in sawtooth shape.The present application adopts logarithmic periodic sawtooth-shaped defect ground structure, and is arranged as resonance unit on dielectric substrate to form microstrip low-pass filter, by setting the resonance unit of logarithmic periodic array arrangement in sawtooth shape, so that the insertion loss of filter in passband is low, and the filter has the characteristics of high performance, wide stopband, good return loss and low insertion loss, etc.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of microwave communication technology, and in particular to a microstrip low-pass filter. BACKGROUND

[0002] In today's increasingly connected world of wireless communication and the Internet of Things, microwave devices and other related components are indispensable in the present and future. This is because such filters can suppress wideband noise and spurious signals. Since microstrip filters are easy to make and low in cost, they can improve system performance while reducing costs. So far, many microstrip-based filters have been developed, but it is important that the performance of such filters needs to be further improved to meet all related applications. Therefore, the performance improvement of filters needs to be continuously carried out. Low-pass filters are important components widely used in noise and intermodulation signal suppression in today's wireless communication systems. In general, low-pass filters with ultra-wideband suppression and fast roll-off as well as low insertion loss in the passband are very desirable in many practical applications. The microstrip low-pass filter in the related art has a narrow stopband, poor return loss and high insertion loss, resulting in poor performance. SUMMARY

[0003] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a microstrip low-pass filter with high performance, wide stopband, good return loss and low insertion loss.

[0004] The microstrip low-pass filter according to the first aspect of the present application is characterized in that it comprises: a dielectric substrate; a microstrip transmission line provided on a first surface of the dielectric substrate; and a plurality of resonant units etched on a second surface of the dielectric substrate, the second surface being opposite to the first surface, the plurality of resonant units being arranged in a logarithmic periodic array on the dielectric substrate, and a vertex angle being formed at the vertex of two adjacent resonant units in a sawtooth shape.

[0005] The microstrip low-pass filter according to the present application has at least the following beneficial effects: the logarithmic periodic sawtooth-shaped defect ground structure is used as the resonant unit and arranged on the dielectric substrate to form the microstrip low-pass filter, the filter has low insertion loss in the passband, ultra-wideband suppression outside the passband and sharp transition characteristics from the passband to the stopband, and has high performance, wide stopband, good return loss and low insertion loss.

[0006] According to some embodiments of the present application, the microstrip transmission line is located in the middle of the resonant units, and the resonant units are periodically distributed on the microstrip transmission line.

[0007] According to some embodiments of the present application, the resonant units include a first resonant unit, a second resonant unit and a third resonant unit in sequence, the distance from the angle between two adjacent resonant units to the microstrip transmission line is a height, the distance from the first angle between the first resonant unit and the second resonant unit to the microstrip transmission line is a first height, the distance from the second angle between the second resonant unit and the third resonant unit to the microstrip transmission line is a second height, the ratio of the first height to the second height is a first scale factor value, and the height of two adjacent resonant units is proportionally increased according to the first scale factor value.

[0008] According to some embodiments of the present application, the distance between two vertices of the resonant unit is a spacing, the distance between two vertices of the first resonant unit is a first spacing, the distance between two vertices of the second resonant unit is a second spacing, the ratio between the first spacing and the second spacing is a second scale factor value, and the spacing of two adjacent resonant units is proportionally increased according to the second scale factor value.

[0009] According to some embodiments of the present application, the first scale factor value is equal to the second scale factor value.

[0010] According to some embodiments of the present application, the first scale factor value and the second scale factor value are between 0.7 and 0.9.

[0011] According to some embodiments of the present application, the input impedance of the microstrip transmission line is between 30 and 70 ohms.

[0012] According to some embodiments of the present application, there is a gap at the angle between two adjacent resonant units.

[0013] According to some embodiments of the present application, the two ends of the dielectric substrate are respectively provided with SMA connectors.

[0014] According to some embodiments of the present application, the dielectric constant of the dielectric substrate is between 9 and 10, the loss tangent value is between 0.002 and 0.004, and the thickness is between 0.7 and 0.9 millimeters.

[0015] Additional aspects and advantages of the present application will be given in part in the following description, will become apparent in part from the following description, or will be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0016] The present application will be further described below in conjunction with the drawings and embodiments, wherein:

[0017] Figure 1 A schematic diagram of a microstrip low-pass filter provided by some embodiments of the present application is shown;

[0018] Figure 2 A microstrip low pass filter schematic diagram provided for another embodiment of the present application;

[0019] Figure 3 A resonant unit layout schematic diagram provided for another embodiment of the present application;

[0020] Figure 4 A band in response test schematic diagram of the microstrip low pass filter provided for another embodiment of the present application;

[0021] Figure 5 A wideband rejection response test schematic diagram of the microstrip low pass filter provided for another embodiment of the present application. DETAILED DESCRIPTION

[0022] The embodiments of the present application are described in detail below with reference to the accompanying drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, only for explaining the present application, and cannot be understood as a limitation of the present application.

[0023] In the description of the present application, it is understood that the orientation description, such as the orientation or position relationship indicated by the upper, lower, front, rear, left, right, etc. is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as a limitation of the present application.

[0024] In the description of the present application, if the meaning of several is more than one, the meaning of multiple is more than two, greater than, less than, more than, etc. is understood as not including the number, above, below, etc. is understood as including the number. If it is described as first, second, only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the order of indicated technical features.

[0025] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be understood in a broad sense, and the person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0026] In the description of the application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the description, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0027] Referring to Figures 1 to 3 As shown in the drawings, the embodiment of the application provides a microstrip low-pass filter, which comprises a dielectric substrate 110, a microstrip transmission line 120 and a resonant unit 130. The microstrip transmission line 120 is arranged on the first surface of the dielectric substrate 110, and the resonant unit 130 is formed by etching a groove on the second surface of the dielectric substrate 110. The second surface of the dielectric substrate 110 is a ground surface, and the first surface and the second surface are opposite surfaces. A plurality of resonant units 130 are arranged in a logarithmic periodic array on the dielectric substrate 110, and a notch angle is formed at the vertex of the adjacent two resonant units 130 in a zigzag shape, thereby forming a groove array with a certain periodicity. The embodiment of the application adopts a logarithmic periodic zigzag defect ground structure, and sets the resonant unit 130 on the dielectric substrate 110 to form a microstrip low-pass filter. By arranging the resonant unit 130 in a zigzag shape and arranged in a logarithmic periodic array, the filter has low insertion loss in the passband, has super-wide band suppression and sharp transition characteristics from the passband to the stopband, and has high performance, wide stopband, good return loss and low insertion loss and the like.

[0028] Referring to Figure 3 As shown in the drawings, in some embodiments of the application, the microstrip transmission line 120 is located in the middle of the resonant unit 130, and the resonant unit 130 is periodically distributed on the microstrip transmission line 120. A plurality of resonant units are periodically distributed around the two ends of the microstrip transmission line 120.

[0029] Referring to Figure 3As shown, in some embodiments of the present application, the resonant unit 130 includes a first resonant unit 131, a second resonant unit 132 and a third resonant unit 133, the first resonant unit 131, the second resonant unit 132 and the third resonant unit 133 are three adjacent resonant units 130, the length of the slot formed by the three resonant units 130 increases in turn, the first resonant unit 131, the second resonant unit 132 and the third resonant unit 133 can be any three adjacent resonant units 130, the distance from the included angle between the adjacent resonant units 130 to the microstrip transmission line 120 is the height, the distance from the first included angle 134 formed by the first resonant unit 131 and the second resonant unit 132 to the microstrip transmission line 120 is the first height, the distance from the second included angle 135 formed by the second resonant unit 132 and the third resonant unit 133 to the microstrip transmission line 120 is the second height, the ratio of the first height to the second height is the first scale factor value, the first scale factor value is a predetermined value, in an embodiment, the first height divided by the second height is equal to the first scale factor, the value of the first scale factor is taken as the first scale factor value, so the ratio of the first height to the second height is the first scale factor value, in an embodiment, the first scale factor value is less than 1, so the slot height of the first resonant unit 131, the second resonant unit 132 and the third resonant unit 133 increases in proportion, in an embodiment, the first resonant unit 131, the second resonant unit 132 and the third resonant unit 133 are arranged from left to right on the dielectric substrate 110, under the premise of meeting the requirements of the embodiments of the present application, the first resonant unit 131, the second resonant unit 132 and the third resonant unit 133 can also be arranged in other directions on the dielectric substrate 110, which is not specifically limited by the present application.

[0030] Referring to Figure 3 As shown, in some embodiments of the present application, a plurality of resonant units 130 form a slot array, each slot is long strip-shaped and has two vertices, two adjacent slots are connected together through one vertex each, the distance between the two vertices of the resonant unit 130 is the interval, the distance between the two vertices of the first resonant unit 131 is the first interval, the distance between the two vertices of the second resonant unit 132 is the second interval, the ratio between the first interval and the second interval is the second scale factor value, the second scale factor value is a predetermined value, in an embodiment, the first interval divided by the second interval is equal to the second scale factor, the value of the second scale factor is taken as the second scale factor value, so the ratio of the first interval to the second interval is the second scale factor value, in an embodiment, the second scale factor value is less than 1, so the slot width of the first resonant unit 131, the second resonant unit 132 and the third resonant unit 133 increases in proportion. It should be noted that in some embodiments of the present application, the height and the interval jointly determine the length of the slot.

[0031] In some embodiments of the present application, in order to simplify the design, the first scale factor value is equal to the second scale factor value, so that the groove array with a certain periodicity is formed.

[0032] In some embodiments of the present application, the first scale factor value and the second scale factor value are between 0.7 and 0.9, the first scale factor and the second scale factor are determined by the sweep parameter, the sweep parameter range is from 0.7 to 0.9, the shortest groove has the highest suppression frequency, and the scale factor, the initial height and the initial periodicity, and the specific periodicity number are used to determine the microstrip low-pass filter of the embodiments of the present application, which can be developed by using a full-wave electromagnetic simulator. In an embodiment, the first scale factor value and the second scale factor value are 0.8352, and the microstrip low-pass filter of the embodiments of the present application has the highest performance, wide stopband, good return loss and low insertion loss.

[0033] In some embodiments of the present application, the input impedance of the microstrip transmission line 120 is between 30 and 70 ohms, and in an embodiment, the input impedance of the microstrip transmission line 120 is 50 ohms. When the input impedance is about 70 ohms, the transmission loss is the smallest, and when the input impedance is about 30 ohms, the power is the largest. The standard microstrip transmission line 120 with an input impedance of 50 ohms can simultaneously consider both performances, and simultaneously consider the transmission loss and the power, so that the microstrip low-pass filter in the embodiments of the present application has the optimal performance.

[0034] In some embodiments of the present application, the gap is provided at the included angle between the two adjacent resonant units 130. As shown in Figure 3 In order to separate the grooves between the two adjacent vertices of the sawtooth shape, a small gap is introduced at the top end of each vertex. In the limit, when the period of the resonant unit 130 approaches negative infinity, the groove array converges to the leftmost side of the dielectric substrate 110. When the period of the resonant unit 130 approaches positive infinity, the groove array becomes an infinite array. In an embodiment, the size of the gap is determined by the height and the pitch.

[0035] As shown in Figure 2 In some embodiments of the present application, the dielectric substrate 110 is provided with an SMA connector 140 at each end, and the microstrip transmission line 120 is matched with the SMA connector 140 coaxial connector. The SMA connector 140 is a small-sized threaded coaxial connector widely used in the microwave field with a frequency range of direct current to 26.5 GHz. The SMA connector 140 has the characteristics of wide frequency band, good performance, reliable life and long service life. By providing the SMA connector 140, the characteristics of wide frequency band, good performance, reliable life and long service life are suitable for connecting the microstrip transmission line 120.

[0036] In some embodiments of the present application, the dielectric constant of the dielectric substrate 110 is between 9 and 10, the loss tangent is between 0.002 and 0.004, and the thickness is between 0.7 and 0.9 mm. In one embodiment, the dielectric constant of the dielectric substrate 110 is 9.6, the loss tangent is 0.003, and the thickness is 0.8 mm. The use of a dielectric substrate 110 with a high dielectric constant can strictly control the size of the circuit design, the insertion loss is low in the entire passband, two transmission zeros are generated in the high frequency band, which effectively ensures good out-of-band characteristics, the filter notch depth is large enough, and meets the requirements of narrowband notching. At the same time, the microstrip low-pass filter of the embodiment of the present application has small overall storage, adjustable notching, compact structure, easy processing, and easy integration with other circuits.

[0037] It should be noted that in some embodiments of the present application, the microstrip low-pass filter of the embodiment of the present application uses a dielectric substrate 110 with a relative dielectric constant of 9.6, a loss tangent of 0.003, and a thickness of 0.8 mm, so that the cutoff frequency of the microstrip low-pass filter is fc, fc is 2 GHz, and the expected suppression band is 24 GHz, i.e. 12fc, thus having a high-bandwidth suppression effect. On the above substrate, when the slot is used as a half-wavelength resonator at fc, the length of the longest slot is about 24 mm.

[0038] It should be noted that in some embodiments of the present application, the first slot is used as a half-wave resonator with a basic resonant frequency of 2 GHz, the initial height is 16 mm, and the first scale factor value and the second scale factor value are 0.7 to 0.9. The initial spacing is set to 8 mm, and the scanning range is from 7 mm to 9 mm. Based on these initial values, the microstrip low-pass filter in the embodiment of the present application can be developed using a full-wave electromagnetic simulator.

[0039] It should be noted that in some embodiments of the present application, after comprehensive parameter scanning research and full-wave electromagnetic optimization, the suppression band suppression level of the microstrip low-pass filter in the embodiment of the present application is 20 dB, and the in-band return loss is 10 dB. In one embodiment, a total of 10 slot line resonators (i.e. the number of periods is 10) are used. Therefore, the longest slot has a height of 16 mm and a scale factor of 0.8352. Thus, the first slot has a height of 3.164 mm, the first slot has a spacing of 1.999 mm, the slot gap width is 1.213 mm, and the gap between the two slot gap vertices is fixed at 0.45 mm. Therefore, the size of the dielectric substrate 110 is 40.65 x 29.546 square millimeters.

[0040] Reference Figure 4 and Figure 5It is shown that the cut-off frequency of the microstrip low-pass filter in the embodiment of the present application is about 1.96GHz, which is found by testing, and the simulation response is given for comparison, the simulation cut-off frequency is about 2.14GHz, and the in-band response is as shown in Figure 4 It is shown that the insertion loss is better than 1dB from DC to about 1.85GHz, and the insertion loss is less than 0.7dB from DC to 1.54GHz. It is noted that the loss includes the conductor loss of the microstrip transmission line 120 and the conductor loss of the two SMA connectors 140 at both ends, and the transition between the connecting end and the microstrip transmission line 120. Overall, the measured in-band group delay is 0.4ns, and at the same time, the simulation and measurement results show that the microstrip low-pass filter in the embodiment of the present application has a sharp transition from the passband to the stopband, and the wideband suppression response is as shown in Figure 5 The microstrip low-pass filter in the embodiment of the present application has a high suppression characteristic in a wide frequency band, and the out-of-band suppression level reaches 20dB from 2.6GHz to more than 26.5GHz.

[0041] The above describes the embodiments of the present application in combination with the drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge range of ordinary skilled in the art without departing from the purpose of the present application. In addition, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A microstrip low-pass filter, characterized by, The utility model relates to a microstrip transmission line, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, a plurality of resonant units, ​ ​ ​ ​ ​ ​ 2. The microstrip lowpass filter of claim 1, wherein, ​ 3. The microstrip lowpass filter of claim 1, wherein, ​ 4. The microstrip lowpass filter of claim 1, wherein, ​ 5. The microstrip lowpass filter of claim 1, wherein, ​ 6. The microstrip lowpass filter of claim 1, wherein, ​

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