CN106785258B - A kind of Wide stop bands microstrip line low-pass filter and design method - Google Patents

Abstract

The invention relates to the field of electronic technology, and provides a wide stopband microstrip line low-pass filter and a design method. The invention arranges the inductance line segments of the folded stepped impedance low-pass filter according to certain shapes, so that the zero point in the stop band of the folded stepped impedance low-pass filter is moved to the same or near the position as the parasitic passband pole, so as to produce a canceling effect, thereby The original parasitic passband is turned into a stopband to achieve the purpose of expanding the filter stopband bandwidth. Appropriate shape arrangement will achieve the effect of reducing the volume at the same time. In the invention, the microstrip line is bent at a right angle to form a low-pass filter of the wide stop-band microstrip line; at least one of the first inductance unit to the nth inductance unit is set to keep the inductance offset of the out-of-band zero point and the pole point of the microstrip line. The inductance cancellation structure is formed by folding the inductance unit; the four sides of the inductance cancellation structure are parallel to the x-axis and the y-axis at the same time.

Description

A kind of wide stopband microstrip line low-pass filter and design method

technical field

The invention relates to the field of electronic technology, in particular to a wide stopband microstrip line low-pass filter and a design method.

Background technique

Electronic countermeasures and other broadband microwave communication fields require microwave low-pass filters with wide stopbands to remove high-frequency clutter signals. Microstrip lines are the most widely used due to their relatively small size and ease of integration with other microwave devices. At present, there are four main types of low-pass filters for common microstrip lines: (1) As shown in Figure 1a, the stepped impedance line The low-pass filter, that is, the equivalent parallel capacitance of the line with a wider line width, and the series inductance of the line with a narrow line width are used to simulate the series inductance. This filter is easy to design and manufacture, and can generally achieve a stopband width of 3 times the frequency, but The volume is large, and the near-end out-of-band suppression is not good; (2) the open-circuit branch line low-pass filter, this form uses the open-circuit branch line to realize the parallel capacitor, the overall volume is slightly smaller, and the stopband width of 3 times the frequency can be realized, and the close The out-of-band suppression at the end is also not good; (3) As shown in Figure 1b, a semi-lumped low-pass filter, this low-pass filter uses a stepped impedance line to directly realize a parallel capacitor, which is smaller in size and has a better near-end Out-of-band suppression, but the stop-band width is only about 2 times the frequency; (4) As shown in Figure 1c, the folded ladder impedance line low-pass filter is to bend the inductance of the traditional ladder impedance low-pass filter to make the parallel connection The capacitors are close together and are strongly coupled to each other. This structure is very compact and has good near-end out-of-band suppression, but the stopband width is usually only about 2 times the frequency. It is often used in practical projects, but due to the resistance The tape width is relatively narrow, limiting its application range.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a wide stopband microstrip line low-pass filter and a design method for the problems existing in the prior art. The invention arranges the inductance line segments of the folded stepped impedance low-pass filter according to certain shapes, so that the zero point in the stop band of the folded stepped impedance low-pass filter is moved to the same or near the position as the parasitic passband pole, so as to produce a canceling effect, thereby The original parasitic passband is turned into a stopband to achieve the purpose of expanding the filter stopband bandwidth. Appropriate shape arrangement will achieve the effect of reducing the volume at the same time.

The technical scheme adopted in the present invention is as follows:

A design method of a wide-stop-band microstrip line low-pass filter includes:

Step 1: Equivalent parallel capacitance at the wider part of the microstrip line to form a capacitor unit; use the narrower part of the microstrip line to simulate the series inductance to form an inductance unit; input and output ports of the low-pass filter of the wide stopband microstrip line All are realized by the inductance unit; the capacitance unit and the inductance unit are arranged at intervals; the first capacitance unit is arranged between the first inductance unit and the second inductance unit; the nth capacitance unit is arranged between the m-1th inductance unit and the mth inductance unit; m=n+1, n>1; initial value of inductance unit length Initial value of capacitor unit length in is the phase constant, R ₀ is the characteristic impedance, Z _l and Z _h correspond to the impedance of the inductor unit and the impedance of the capacitor unit respectively, C and L are the normalized component values of the corresponding order low-pass filter prototype, μ is the magnetic permeability, ∈ is the dielectric constant; if the volume and process allow, the ratio of the line width of the capacitor unit to the line width of the inductor unit is as large as possible, and the initial value of the length of the inductor unit and the initial value of the capacitor unit are fine-tuned, and the response after fine-tuning meets the wide stopband micrometer. Indicators for return loss design of stripline low-pass filters;

Step 2: Bend the microstrip line at a right angle; set at least one of the second inductance unit to the n-1th inductance unit to maintain an inductance cancellation structure that cancels the out-of-band zero point of the microstrip line and the parasitic passband pole. The inductance cancellation structure is The inductance unit is folded; the four sides of the inductance cancellation structure are parallel to the x-axis or the y-axis, wherein the x-axis is perpendicular to the y-axis.

Further, the design process of the inductance cancellation structure in the step 2 specifically includes:

Step 21: On the basis of step 1, the microstrip line is bent at a right angle; the equivalent parallel capacitor is formed at the wider part of the microstrip line to form a capacitor unit, and a folded stepped impedance low-pass filter is formed;

Step 22: Perform electromagnetic three-dimensional simulation on the folded ladder impedance low-pass filter formed in step 21 and the wide-stop-band microstrip line low-pass filter in step 1 respectively;

Step 23: Compare the simulation results. Under the condition that the cut-off frequency of the low-pass filter is the same as the cut-off frequency of the folded stepped impedance line, if the selected inductance cancellation structure makes the parasitic passband of the wide-stop-band microstrip line low-pass filter If the out-of-band rejection of all or part of the frequencies increases, the inductance cancellation structure is an inductance cancellation structure when the zero point of the low-pass filter of the wide stopband microstrip line and the parasitic passband pole are cancelled.

Further, the first inductance unit and the nth inductance unit are provided with right-angle bending parts, that is, the microstrip line of the first inductance unit and the nth inductance unit is parallel to the y-axis, and the rest of the first inductance unit and the nth inductance unit. The microstrip lines are parallel to the x-axis.

Further, when n is an even number, the first capacitor unit in the capacitor unit has the same area as the nth capacitor unit; the second capacitor unit in the capacitor unit has the same area as the n-1th capacitor unit; the n/2th capacitor has the same area. The area of the unit is the same as that of the n/2+1th capacitor unit; m is an odd number, the line width and line length of the first inductance unit in the inductance unit and the mth inductance unit are correspondingly equal; the second inductance unit in the inductance unit is equal to the mth The line width and line length of -1 inductance unit are correspondingly equal; the line width and line length of the (m-1)/2th capacitor unit and the (m+3)/2th capacitor unit are correspondingly equal;

When n is an odd number, the area of the first capacitor unit in the capacitor unit is equal to that of the nth capacitor unit; the area of the second capacitor unit in the capacitor unit is equal to the area of the n-1th capacitor unit; (n-1)/2 The area of the capacitor unit is equal to that of the (n+3)/2th capacitor unit.

Further, the line width of the microstrip line is more than 5 times larger than the width of the narrow line width; the difference between the inductance length after bending and the inductance length before bending is plus or minus 10%.

A wide-stop-band microstrip line low-pass filter includes:

Folded ladder impedance low-pass filter is used for the equivalent parallel capacitor in the wide part of the microstrip line to form a capacitor unit; the narrow part of the microstrip line is used to simulate the series inductance to form an inductance unit; wide stop-band microstrip The input and output ports of the line low-pass filter are realized by the inductance unit; the capacitance unit and the inductance unit are arranged at intervals; the first capacitance unit is arranged between the first inductance unit and the second inductance unit; the m-1th inductance unit and the mth inductance unit are arranged The nth capacitor unit is set between; m=n+1, n>1; the initial value of the length of the inductor unit Initial value of capacitor unit length in is the phase constant, R ₀ is the characteristic impedance, Z _l and Z _h correspond to the impedance of the inductor unit and the impedance of the capacitor unit respectively, C and L are the normalized component values of the corresponding order low-pass filter prototype, μ is the magnetic permeability, ∈ is the dielectric constant; if the volume and process allow, the ratio of the line width of the capacitor unit to the line width of the inductor unit is as large as possible, and the initial value of the length of the inductor unit and the initial value of the capacitor unit are fine-tuned, and the response after fine-tuning meets the wide stopband micrometer. Indicators for return loss design of stripline low-pass filters;

Wide stopband microstrip line low-pass filter, used for folded ladder impedance low-pass filter, the microstrip line is bent at a right angle, and at least one of the second inductance unit to the n-1th inductance unit is set as Maintain the inductance cancellation structure in which the out-of-band zero point of the microstrip line and the parasitic passband pole are cancelled. The inductance cancellation structure is formed by folding the inductance unit;

Further, the design process of the inductance cancellation structure specifically includes:

On the basis of the folded ladder impedance low-pass filter, the microstrip line is bent at a right angle, and the wider part of the microstrip line is equivalent to a parallel capacitor to form a capacitor unit and form a folded ladder impedance low-pass filter;

The electromagnetic three-dimensional simulation of the folded ladder impedance low-pass filter and the wide-stop-band microstrip line low-pass filter was carried out respectively;

Comparing the simulation results, when the cut-off frequency of the low-pass filter is the same as that of the folded ladder impedance, if the selected inductance cancellation structure makes all or part of the frequencies at the parasitic pass-band of the wide-stop-band microstrip line low-pass filter When the out-of-band suppression increases, the inductance cancellation structure is a kind of inductance cancellation structure when the zero and pole of the low-pass filter of the wide stopband microstrip line are cancelled.

Further, the first inductance unit and the nth inductance unit are provided with right-angle bending parts, that is, the microstrip line of the first inductance unit and the nth inductance unit is parallel to the y-axis, and the rest of the first inductance unit and the nth inductance unit. The microstrip lines are parallel to the x-axis.

Further, when n is an even number, the first capacitor unit in the capacitor unit has the same area as the nth capacitor unit; the second capacitor unit in the capacitor unit has the same area as the n-1th capacitor unit; the n/2th capacitor has the same area. The area of the unit is the same as that of the n/2+1th capacitor unit; m is an odd number, the line width and line length of the first inductance unit in the inductance unit and the mth inductance unit are correspondingly equal; the second inductance unit in the inductance unit is equal to the mth The line width and line length of -1 inductance unit are correspondingly equal; the line width and line length of the (m-1)/2th capacitor unit and the (m+3)/2th capacitor unit are correspondingly equal;

When n is an odd number, the area of the first capacitor unit in the capacitor unit is equal to that of the nth capacitor unit; the area of the second capacitor unit in the capacitor unit is equal to the area of the n-1th capacitor unit; (n-1)/2 The area of the capacitor unit is equal to that of the (n+3)/2th capacitor unit.

Further, the line width of the microstrip line is more than 5 times larger than the width of the narrow line width; the difference between the inductance length after bending and the inductance length before bending is plus or minus 10%.

To sum up, due to the adoption of the above-mentioned technical solutions, the beneficial effects of the present invention are:

Find the inductance cancellation structure when the zero-pole cancellation of the wide-stop-band microstrip low-pass filter is equal to the cut-off frequency of the folded ladder-impedance low-pass filter, so that the output frequency of the wide-stop microstrip low-pass filter can reach 4 times or more.

The wide stopband low-pass filter is manufactured by the thin film process. The thin film process has high line width and line accuracy, and the error is within ±2um. Therefore, the inductance shape error caused by the process error is very small, and the yield can approach 100% in most cases. . In addition, the film technology has the advantages of low plate-making cost, short processing cycle and reliable quality.

Description of drawings

1a is a schematic diagram of a stepped impedance line in the prior art.

Fig. 1b is a schematic diagram of a semi-lumped low-pass filter in the prior art.

Figure 1c is a schematic diagram of a folded ladder impedance low-pass filter.

Figure 2a is a structural diagram of an implementation of the present invention.

FIG. 2b is a diagram of the selection signal of the inductor unit in the present invention.

Fig. 3a is another implementation structure diagram of the present invention.

Figure 3b is the effect diagram of the wide stop-band microstrip low-pass filter.

FIG. 4 is a third implementation structure diagram of the present invention.

Detailed ways

All features disclosed in this specification, or all disclosed steps in a method or process, may be combined in any way except mutually exclusive features and/or steps.

Any feature disclosed in this specification, unless expressly stated otherwise, may be replaced by other equivalent or alternative features serving a similar purpose. That is, unless expressly stated otherwise, each feature is but one example of a series of equivalent or similar features.

Description of the present invention:

When extending from the midpoint to both ends of the microstrip line, the lengths of the inductor unit and the capacitor unit gradually decrease, which is the same as the normalized component value trend of the low-pass prototype.

The inductance unit with line adopts the microstrip printed board technology; the inductance unit of the microstrip line adopts the thin film technology.

The main reasons why this structure can achieve wide stopband characteristics are as follows:

1) Selection of processing technology

Since the change of the line segment of the inductance will cause the position of the stop-band resonance zero point, the error introduced by the processing technology will cause the resonance zero point to deviate from the set position, resulting in a poor stop-band suppression effect of the actual product. Therefore, it should be evaluated according to the actual indicators before design, and a high-precision process implementation method, such as thin film process, should be adopted as far as possible.

2) The selection method of the shape of the inductance line segment

First, the basic folded ladder impedance low-pass filter model in Fig. 1c is established, and the electromagnetic 3D simulation is carried out. Then replace one or some inductance coils in the basic model with other shapes, and then conduct three-dimensional electromagnetic simulation, compare the simulation results, and find the out-of-band zeros and parasitic pass-band poles while keeping the cutoff frequency basically unchanged. The shape of the offset inductance line segment (as shown in FIG. 2b ), then FIG. 2a is a specific implementation method of the present invention.

Embodiment 1: As shown in Fig. 3a, using the low-pass filter formed by the shape of the inductance line segment as shown in Fig. 3a can achieve a stopband bandwidth of 4 times or even wider in a very compact volume. Fig. 3b is the simulation effect of the structure of Fig. 3a.

Embodiment 2: A method for designing a wide-stop-band microstrip line low-pass filter includes:

Step 1: Equivalent parallel capacitance at the wider part of the microstrip line to form a capacitor unit; use the narrower part of the microstrip line to simulate the series inductance to form an inductance unit; input and output ports of the low-pass filter of the wide stopband microstrip line All are realized by the inductance unit; the capacitance unit and the inductance unit are arranged at intervals; the first capacitance unit is arranged between the first inductance unit and the second inductance unit; the nth capacitance unit is arranged between the m-1th inductance unit and the mth inductance unit; m=n+1, n>1;

Step 2: Bend the microstrip line at a right angle, and set at least one of the second inductance unit to the n-1th inductance unit to maintain an inductance cancellation structure that cancels the zero and pole outside the microstrip line. The inductance cancellation structure is a folding inductance unit. The four sides of the inductance cancellation structure are respectively parallel to the x-axis and the y-axis, wherein the x-axis and the y-axis are perpendicular.

The design process of the inductance cancellation structure in the step 2 specifically includes:

Step 21: On the basis of step 1, a capacitor unit is directly realized with a stepped impedance line to form a folded stepped impedance low-pass filter;

Step 22: Perform electromagnetic three-dimensional simulation on the folded ladder impedance low-pass filter formed in step 21 and the wide-stop-band microstrip line low-pass filter obtained in step 1;

Step 23: Compare the simulation results. Under the condition that the cut-off frequency of the low-pass filter is the same as that of the folded ladder impedance, if the selected inductance cancellation structure makes the parasitic passband of the wide-stop-band microstrip line low-pass filter all or When the out-of-band suppression of a part of the frequency is increased, the inductance cancellation structure is an inductance cancellation structure when the zero point of the low-pass filter of the wide stopband microstrip line and the parasitic passband pole are cancelled.

The first inductance unit and the nth inductance unit are provided with right-angle bending parts, that is, the microstrip line of the first inductance unit and the nth inductance unit is parallel to the y-axis, and the microstrip line of the first inductance unit and the rest of the nth inductance unit is parallel to the y-axis. Lines are parallel to the x-axis.

The present invention is not limited to the foregoing specific embodiments. The present invention extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims (10)

1. a wide stopband microstrip line low-pass filter design method is characterized in that comprising: Step 1: Equivalent parallel capacitance at the wider part of the microstrip line to form a capacitor unit; use the narrower part of the microstrip line to simulate the series inductance to form an inductance unit; input and output ports of the low-pass filter of the wide stopband microstrip line All are realized by the inductance unit; the capacitance unit and the inductance unit are arranged at intervals; the first capacitance unit is arranged between the first inductance unit and the second inductance unit; the nth capacitance unit is arranged between the m-1th inductance unit and the mth inductance unit; m=n+1, n>1; initial value of inductance unit length Initial value of capacitor unit length in is the phase constant, R ₀ is the characteristic impedance, Z _l and Z _h correspond to the impedance of the inductor unit and the impedance of the capacitor unit respectively, C and L are the normalized component values of the corresponding order low-pass filter prototype, μ is the magnetic permeability, ∈ is the dielectric constant, ω is the angular frequency; if the volume and process allow, the ratio of the line width of the capacitor unit to the line width of the inductor unit is as large as possible, and the initial value of the length of the inductor unit and the initial value of the capacitor unit are fine-tuned, and the response after fine-tuning Meet the index of return loss design of wide stopband microstrip line low-pass filter; Step 2: Bend the microstrip line at a right angle; set at least one of the second inductance unit to the n-1 th inductance unit to maintain an inductance cancellation structure in which the out-of-band zero point of the microstrip line and the parasitic pass-band pole are cancelled. The inductance cancellation structure The inductance unit is folded; the four sides of the inductance cancellation structure are parallel to the x-axis or the y-axis, wherein the x-axis is perpendicular to the y-axis. 2. the design method of a kind of wide stopband microstrip line low-pass filter according to claim 1, is characterized in that the design process of inductance cancellation structure in described step 2 specifically comprises: Step 21: On the basis of step 1, the microstrip line is bent at a right angle; the equivalent parallel capacitor is formed at the wider part of the microstrip line to form a capacitor unit, and a folded stepped impedance low-pass filter is formed; Step 22: Perform electromagnetic three-dimensional simulation on the folded ladder impedance low-pass filter formed in step 21 and the wide-stop-band microstrip line low-pass filter in step 1 respectively; Step 23: Compare the simulation results. Under the condition that the cut-off frequency of the low-pass filter is the same as the cut-off frequency of the folded stepped impedance line, if the selected inductance cancellation structure makes the parasitic passband of the wide-stop-band microstrip line low-pass filter If the out-of-band rejection of all or part of the frequencies increases, the inductance cancellation structure is an inductance cancellation structure when the zero point of the low-pass filter of the wide stopband microstrip line and the parasitic passband pole are cancelled. 3 . The design method of a wide-stop-band microstrip line low-pass filter according to claim 1 , wherein the first inductance unit and the n-th inductance unit are provided with right-angle bending parts, that is, the first inductance unit. 4 . And the microstrip line of the nth inductance unit is parallel to the y-axis, and the first inductance unit and the rest of the nth inductance unit are parallel to the x-axis of the microstrip line. 4. the design method of a kind of wide stopband microstrip line low-pass filter according to claim 1, is characterized in that, When n is an even number, the area of the first capacitor unit and the nth capacitor unit in the capacitor unit are equal; the area of the second capacitor unit and the n-1th capacitor unit in the capacitor unit are equal; the area of the n/2th capacitor unit and the nth capacitor unit are equal. n/2+1 capacitor units have the same area; m is an odd number, the line width and line length of the first inductance unit in the inductance unit and the mth inductance unit correspond to the same; the second inductance unit in the inductance unit is equal to the m-1th The line width and line length of the inductor unit are correspondingly equal; the line width and line length of the (m-1)/2th capacitor unit and the (m+3)/2th capacitor unit are correspondingly equal; When n is an odd number, the area of the first capacitor unit in the capacitor unit is equal to that of the nth capacitor unit; the area of the second capacitor unit in the capacitor unit is equal to the area of the n-1th capacitor unit; (n-1)/2 The area of the capacitor unit is equal to that of the (n+3)/2th capacitor unit. 5. the design method of a kind of wide stopband microstrip line low-pass filter according to claim 1, it is characterized in that the line width of described microstrip line is more than 5 times larger than the narrower width of line width; The error between the length of the inductor after bending and the length of the inductor before bending is plus or minus 10%. 6. A wide stopband microstrip line low-pass filter is characterized in that comprising: Folded ladder impedance low-pass filter is used for the equivalent parallel capacitor in the wide part of the microstrip line to form a capacitor unit; the narrow part of the microstrip line is used to simulate the series inductance to form an inductance unit; wide stop-band microstrip The input and output ports of the line low-pass filter are realized by the inductance unit; the capacitance unit and the inductance unit are arranged at intervals; the first capacitance unit is arranged between the first inductance unit and the second inductance unit; the m-1th inductance unit and the mth inductance unit are arranged The nth capacitor unit is set between; m=n+1, n>1; the initial value of the length of the inductor unit Initial value of capacitor unit length in is the phase constant, R ₀ is the characteristic impedance, Z _l and Z _h correspond to the impedance of the inductor unit and the impedance of the capacitor unit respectively, C and L are the normalized component values of the corresponding order low-pass filter prototype, μ is the magnetic permeability, ∈ is the dielectric constant, ω is the angular frequency; if the volume and process allow, the ratio of the line width of the capacitor unit to the line width of the inductor unit should be as large as possible, and the initial value of the length of the inductor unit and the initial value of the capacitor unit should be fine-tuned. Meet the index of return loss design of wide stopband microstrip line low-pass filter; Wide stopband microstrip line low-pass filter, used for folded ladder impedance low-pass filter, the microstrip line is bent at a right angle, and at least one of the second inductance unit to the n-1th inductance unit is set as Maintain the inductance cancellation structure in which the out-of-band zero point of the microstrip line and the parasitic passband pole are cancelled. The inductance cancellation structure is formed by folding the inductance unit; 7. The wide stop-band microstrip line low-pass filter according to claim 6, wherein the design process of the inductance cancellation structure specifically comprises: On the basis of the folded ladder impedance low-pass filter, the microstrip line is bent at a right angle, and the wider part of the microstrip line is equivalent to a parallel capacitor to form a capacitor unit and form a folded ladder impedance low-pass filter; The electromagnetic three-dimensional simulation of the folded ladder impedance low-pass filter and the wide-stop-band microstrip line low-pass filter was carried out respectively; Comparing the simulation results, when the cut-off frequency of the low-pass filter is the same as that of the folded ladder impedance, if the selected inductance cancellation structure makes all or part of the frequencies at the parasitic pass-band of the wide-stop-band microstrip line low-pass filter When the out-of-band suppression increases, the inductance cancellation structure is an inductance cancellation structure when the zero point of the low-pass filter of the wide stopband microstrip line and the parasitic passband pole are cancelled. 8 . The wide stop-band microstrip line low-pass filter according to claim 6 , wherein the first inductance unit and the n-th inductance unit are provided with right-angle bending parts, that is, the first inductance unit and the Part of the microstrip line of the nth inductance unit is parallel to the y-axis, and the first inductance unit and the rest of the microstrip line of the nth inductance unit are parallel to the x-axis of the microstrip line. 9. A wide stopband microstrip line low-pass filter according to claim 6, characterized in that when n is an even number, the area of the first capacitor unit and the nth capacitor unit in the capacitor unit are equal; The area of the second capacitor unit is equal to that of the n-1th capacitor unit; the area of the n/2th capacitor unit and the n/2+1th capacitor unit is equal; m is an odd number, and the first inductor unit in the inductor unit has the same area as the mth capacitor unit. The line width and line length of each inductance unit are correspondingly equal; the line width and line length of the second inductance unit in the inductance unit are correspondingly equal to the m-1th inductance unit; the (m-1)/2th capacitor unit is equal to the (m+ 3)/2 The line width and line length of the capacitor unit are correspondingly equal; When n is an odd number, the area of the first capacitor unit in the capacitor unit is equal to that of the nth capacitor unit; the area of the second capacitor unit in the capacitor unit is equal to the area of the n-1th capacitor unit; (n-1)/2 The area of the capacitor unit is equal to that of the (n+3)/2th capacitor unit. 10. The wide stop-band microstrip line low-pass filter according to claim 6, wherein the line width of the microstrip line is more than 5 times larger than the width of the narrow line width; The error between the inductor length and the inductor length before bending is plus or minus 10%.