CN111490321A - Broadband filter based on improved cross-shaped structure and design method - Google Patents

Broadband filter based on improved cross-shaped structure and design method Download PDF

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Publication number
CN111490321A
CN111490321A CN202010146263.9A CN202010146263A CN111490321A CN 111490321 A CN111490321 A CN 111490321A CN 202010146263 A CN202010146263 A CN 202010146263A CN 111490321 A CN111490321 A CN 111490321A
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coupling
filter
line
lines
transmission
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喇东升
关鑫
李钰莹
李弘诚
王梦宇
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Northeastern University Qinhuangdao Branch
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/203—Strip line filters
    • H01P1/20327—Electromagnetic interstage coupling
    • H01P1/20354—Non-comb or non-interdigital filters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P11/00—Apparatus or processes specially adapted for manufacturing waveguides or resonators, lines, or other devices of the waveguide type
    • H01P11/007—Manufacturing frequency-selective devices

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Abstract

The invention provides an improved cross-shaped structure-based broadband filter and a design method thereof, and relates to the technical field of microstrip filters. The broadband filter based on the improved cross structure comprises four coupling lines and two transmission lines; each coupling line is composed of two identical parallel microstrip lines, wherein two coupling lines are located at two ends of the filter structure and used as ports for feeding, the other two coupling lines are connected end to form an annular coupling line, one end of the transmission line is respectively connected with the coupling lines at the ports, and the other end of the transmission line is located in the middle of the annular coupling line to form a band-pass filter. By using a circuit analysis method of the odd-even mode, the filter is preliminarily analyzed and designed, five transmission poles and four transmission zeros are arranged, the passband frequency is 4.4GHz-9.6GHz, and the requirement of the current communication system on the ultra-wideband filter can be met.

Description

Broadband filter based on improved cross-shaped structure and design method
Technical Field
The invention relates to the technical field of microstrip filters, in particular to a broadband filter based on an improved cross-shaped structure and a design method.
Background
The broadband and UWB Band-pass Filter is one of the key Components of the radio frequency front end of the high data Transmission rate communication system, has been the research focus of radio frequency devices since 2002, has been the Simple and Compact Transmission line of micro-Band-pass filters, such as pass Band, pass.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a broadband filter based on an improved cross-shaped structure and a design method.
The technical scheme adopted by the invention is as follows:
on one hand, the invention provides a broadband filter based on an improved cross-shaped structure, which comprises four coupling lines and two transmission lines; the two coupling lines are positioned at two ends of the filter structure and used as ports for feeding, the coupling line at the feeding end is composed of two identical parallel microstrip lines, and the length and the width of each microstrip line are equal and the same; the other two coupling lines are composed of four microstrip lines, the length and the width of the four microstrip lines are the same, the four microstrip lines are connected end to form an annular coupling line, one end of the transmission line is connected with the coupling line at the feed port respectively, and the other end of the transmission line is positioned in the middle of the annular coupling line to form a band-pass filter.
On the other hand, the invention provides a design method of a broadband filter based on an improved cross-shaped structure, which comprises the following steps:
step 1: designing an improved broadband filter circuit with a cross structure, and calculating to obtain a transmission zero pole formula of the filter according to a micro-strip transmission line theory and an odd-even mode circuit analysis method;
step 2: analyzing the parameter value range influencing the change of the zero pole, determining the value of the parameter, and utilizing Z in the expression of the odd-even mode impedance of the coupling line of the load end1Parameter Z in the expression for the odd-even mode impedance of the loop-coupled line2Impedance of transmission line Z3Coupling coefficient k of circuit coupling line of feed terminal1Coupling coefficient k of the loop-coupled line2Adjusting the positions of a transmission zero point and a transmission pole to determine a final parameter value;
and step 3: for the band-pass filter adopting the coupling line structure, the distance between the coupling lines and the width of the coupling lines are calculated through simulation software, and the maximum coupling is realized on the basis of an actual manufacturing process;
and 4, step 4: and drawing the initial size of the obtained filter in three-dimensional full-wave electromagnetic simulation software to obtain a simulation result of the filter.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:
a formula of a pole-zero is obtained through an odd-even mode circuit and a transmission line theory, the position of the pole-zero is adjusted by adjusting impedance parameters and coupling coefficients in the circuit, a microstrip filter with low insertion loss, low return loss and good edge roll-off characteristics is obtained, and the pole-zero of a pass band can be adjusted according to actual requirements and the relation of parameters.
Drawings
FIG. 1 is a schematic diagram of a filter circuit according to an embodiment of the present invention;
wherein figure (a) -filter circuit schematic; FIG. (b) -even mode circuit of the cross-coupled structure; FIG. (c) -odd mode circuit of cross-coupled configuration;
FIG. 2 is a diagram illustrating a distribution of poles-zero of a filter circuit according to an embodiment of the present invention;
FIG. 3 shows a parameter z according to an embodiment of the present invention1,z2,z3The influence of the change on the transmission pole of the filter is shown in a diagram;
FIG. 4 shows a parameter k according to an embodiment of the present invention1And k2Schematic of the effect on the filter;
wherein diagrams (a) -k1The effect of the variation on the filter parameters; graphs (b) -k2The effect of the variation of (b) on the filter parameters;
FIG. 5 is a diagram illustrating the dimensions of a filter according to an embodiment of the present invention;
FIG. 6 is a diagram illustrating a simulation result of a band-pass filter test according to an embodiment of the present invention;
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings.
In one aspect, the present invention provides a wideband filter based on an improved cross-shaped structure,
on one hand, the invention provides a broadband filter based on an improved cross-shaped structure, which comprises four coupling lines and two transmission lines; the two coupling lines are positioned at two ends of the filter structure and used as ports for feeding, the coupling line at the feeding end is composed of two identical parallel microstrip lines, and the length and the width of each microstrip line are equal and the same; the other two coupling lines are composed of four microstrip lines, the length and the width of the four microstrip lines are the same, the four microstrip lines are connected end to form an annular coupling line, one end of the transmission line is connected with the coupling line at the feed port respectively, and the other end of the transmission line is positioned in the middle of the annular coupling line to form a band-pass filter.
On the other hand, the invention provides a design method of a broadband filter based on an improved cross-shaped structure, which comprises the following steps:
step 1: designing an improved broadband filter circuit with a cross structure, and calculating to obtain a transmission zero pole formula of the filter according to a micro-strip transmission line theory and an odd-even mode circuit analysis method;
step 2: analyzing the parameter value range influencing the change of the zero pole, determining the value of the parameter, and utilizing Z in the expression of the odd-even mode impedance of the coupling line of the load end1Of odd-even mode impedance of loop-coupled lineParameter Z in the expression2Impedance of transmission line Z3Coupling coefficient k of circuit coupling line of feed terminal1Coupling coefficient k of the loop-coupled line2Adjusting the positions of a transmission zero point and a transmission pole to determine a final parameter value;
step 3, calculating the distance between the coupled lines and the width of the coupled lines by using ADS L ineclean software in the embodiment through simulation software for the band-pass filter adopting the coupled line structure, and realizing maximum coupling on the basis of an actual manufacturing process;
and 4, step 4: and drawing the initial size of the obtained filter in three-dimensional full-wave electromagnetic simulation software to obtain a simulation result of the filter.
As shown in fig. 1, fig. 1(a) shows an integral BPF, and the characteristic impedances of the microstrip lines of the input/output ports of the present embodiment are all 50 Ω, and each microstrip line includes four coupled lines and two transmission lines; the two coupling lines are positioned at two ends of the filter structure and used as ports for feeding, the coupling line at the feeding end is composed of two identical parallel microstrip lines, and the length and the width of each microstrip line are equal and the same; the other two coupling lines are composed of four microstrip lines, the length and the width of the four microstrip lines are the same, the four microstrip lines are connected end to form an annular coupling line, one end of the transmission line is connected with the coupling line at the feed port respectively, and the other end of the transmission line is positioned in the middle of the annular coupling line to form a band-pass filter. The impedance of the circuit coupling line at the feed end is
Figure BDA0002400837420000041
Electrical length theta, coupling coefficient k1The other two coupled lines have an even mode impedance of
Figure BDA0002400837420000042
Odd mode impedance
Figure BDA0002400837420000043
Electrical length of theta and coupling coefficient of k2。
Design of Filter the even-mode circuit and the odd-mode circuit of the cross-coupling structure shown in FIGS. 1(b) and (c) were first analyzed for the filterThe design is analyzed, and the input impedance of the coupled line structure of fig. 1(a) is calculated to obtain the input impedance of the circuit as shown in formula (1). The odd-even mode structure of the circuit is shown in fig. 1(b) and (c), the load impedance of the odd-even mode circuit can be obtained according to the odd-even mode circuit, the load impedance is brought into (1) as shown in formulas (2) and (3), and the input impedance Z of the odd-even mode is obtainedine,Zino。
Figure BDA0002400837420000044
Figure BDA0002400837420000045
Figure BDA0002400837420000046
Wherein Zine(o)For odd-even mode input impedance, Z, of the circuitLeIs the load of the even-mode circuit, ZLoIs a load of an odd-mode circuit, wherein Z1、Z2Is the odd-even mode impedance parameter of the parallel coupled lines,
Figure BDA0002400837420000047
Z3θ is the transmission line impedance and the transmission line length.
The transmission zero of the structure is calculated. Let Zine＝ZinoI.e. ZLe＝ZLoAnd obtaining formula (4), and expressing complex formula by a, b and c, wherein the specific expression is shown as formula (5a) (5b) (5c), and the zero point position of the filter structure can be obtained.
atan4(θ)+btan2(θ)+c＝0 (4)
Figure BDA0002400837420000051
Figure BDA0002400837420000052
Figure BDA0002400837420000053
Obviously a>0、c>0 always holds (coupling coefficient k)1，k2Greater than zero and less than one), the value of b can be determined according to the value of the parameter, and the parameter b appears in the form of square in the discriminant. If the formula (4) is regarded as
Figure BDA0002400837420000054
A function of (b), wherein fpIs the transmission zero pole of the band-pass filter; f. of0The center frequency of the filter is, then, its root decision △ ═ b24ac will determine the number of solutions in equation (4). Assuming that the filter design parameters satisfy Δ>0, the structure has two pairs of adjustable transmission zeros with frequency positions of
Figure BDA0002400837420000055
Figure BDA0002400837420000056
Wherein f isz11、fz12、fz21、fz22Are the four transmission zeros of the filter.
The transmission poles of the structure are calculated. The on-mode input impedance is obtained by the formulas (1), (2) and (3), and the even-mode resonance condition is ZineInfinity, odd mode resonance condition is ZinoInfinity, two even mode resonance poles and two odd mode resonance poles can be obtained from equations (7) and (8);
Figure BDA0002400837420000057
Figure BDA0002400837420000058
Figure BDA0002400837420000059
Figure BDA00024008374200000510
wherein
Figure BDA00024008374200000511
Thus, the filter has a pair of f0Symmetrical even mode transmission poles and a pair about f0Symmetric odd-mode transmission poles with frequency positions (10a), (10b), (10c) and (10 d);
Figure BDA0002400837420000061
Figure BDA0002400837420000062
Figure BDA0002400837420000063
Figure BDA0002400837420000064
wherein f ispe1、fpe2Is a pair of0Symmetric even mode transmission pole frequency position, fpo1、fpo2Is a pair of0Symmetric odd-mode transmission pole frequency positions;
the pole-zero of the ideal circuit of the filter is shown in figure 2.
The structure of the filter is characterised entirely by Z1,Z2,Z3,k1,k2These five parameters are determined. By properly setting the values, five transmission poles of the filter structure can form a transmission passband, and two transmission zeros close to the transmission passband can improve the selectivity of the passband. In this embodiment, a structure transmission line model shown in fig. 1(a) is established in ADS software, and parameters are performedAnd optimizing and selecting proper design parameters of the band-pass filter. For a band-pass filter adopting a coupling line structure, stronger coupling of the coupling line is often required to obtain a wide passband characteristic, and under such a requirement, the final microstrip line width is determined by combining an actual engineering situation. During the optimization process, the positions of the transmission zeros and transmission poles are adjusted with changes in several parameters. In addition, the processability of the PCB microstrip circuit is also considered in the optimization process, and design parameters convenient for processing are selected.
In the aspect of parameter selection, as can be seen from fig. 3 and 4, Z in this embodiment1,Z2,Z3Is 0.7, 1.1, 1.7, k1,k2A value of 0.7, wherein z1,z2,z3Is Z1,Z2And Z3Normalized impedance z of1＝Z1/Z,z2＝Z2/Z，z3＝Z3Z, Z are characteristic impedances of the microstrip lines of the input/output port in this embodiment each of which is 50 Ω. On the basis, considering the actual processing capacity of the PCB, further optimization adjustment is performed in simulation software, and finally an ultra-wideband filter is obtained, and the specific size is shown in fig. 5, where a is 1.54 mm; b is 15.5 mm; c is 14.9 mm; d is 0.2 mm; e 1.2 mm; f is 31 mm; g is 2.3 mm; h is 0.2 mm; l is 4 mm; k is 1.1 mm.
The bandpass filter in this example is designed in Rogers RT5880(m 0.508mm, m being the thickness of the dielectric slab,re＝2.2,reis dielectric constant, tan 0.0009, tan is dielectric loss tangent) on a microwave dielectric slab the initial dimensions of the filter were calculated by ADS L inecac tool, and the filter was then optimized in three-dimensional full-wave electromagnetic simulation software HFSS.
The simulation results of the HFSS of the bandpass filter are shown in fig. 6, with an absolute bandwidth of 3dB for HFSS simulation of 4.4-9.6 GHz; the return loss simulation results are better than 10dB over the entire passband.
The relative bandwidth FBW measured by the band-pass filter is 74%, and the return loss measured in the whole pass band is better than 10 dB. In addition, the stop band rejection of the filter is better than 10dB within the frequency range of 3-4.4 GHz; within the frequency range of 9.6-11 GHz, the stop band rejection is better than 12 dB.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions and scope of the present invention as defined in the appended claims.

Claims (2)

1. The utility model provides a broadband filter based on improved generation cruciform structure which characterized in that: comprises four coupling lines and two transmission lines; each coupling line is composed of two identical parallel microstrip lines, wherein two coupling lines are located at two ends of the filter structure and used as ports for feeding, the other two coupling lines are connected end to form an annular coupling line, one end of the transmission line is respectively connected with the coupling lines at the ports, and the other end of the transmission line is located in the middle of the annular coupling line to form a band-pass filter.
2. A design method of a broadband filter based on an improved cross-shaped structure is characterized by comprising the following steps:
step 1: designing an improved broadband filter circuit with a cross structure, and calculating to obtain a transmission zero pole formula of the filter according to a micro-strip transmission line theory and an odd-even mode circuit analysis method;
step 2: analyzing the parameter value range influencing the change of the zero pole, determining the value of the parameter, and utilizing Z in the expression of the odd-even mode impedance of the coupling line of the load end1Parameter Z in the expression for the odd-even mode impedance of the loop-coupled line2Impedance of transmission line Z3Coupling coefficient k of circuit coupling line of feed terminal1Coupling coefficient k of the loop-coupled line2Adjusting the positions of a transmission zero point and a transmission pole to determine a final parameter value;
and step 3: for the band-pass filter adopting the coupling line structure, the distance between the coupling lines and the width of the coupling lines are calculated through simulation software, and the maximum coupling is realized on the basis of an actual manufacturing process;
and 4, step 4: and drawing the initial size of the obtained filter in three-dimensional full-wave electromagnetic simulation software to obtain a simulation result of the filter.
CN202010146263.9A 2020-03-05 2020-03-05 Broadband filter based on improved cross-shaped structure and design method Pending CN111490321A (en)

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Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20010094509A (en) * 2000-03-31 2001-11-01 김남영 The Microstrip Ring Bandpass Filter with Interdigital Side-Coupling and Its Manufacturing Method
CN203760600U (en) * 2013-11-27 2014-08-06 哈尔滨飞羽科技有限公司 Ultra-wideband filter possessing compact structure and resisting WLAN interference
CN104779424A (en) * 2015-04-13 2015-07-15 南京邮电大学 Microstrip dual-passband coupling filter
CN106257744A (en) * 2016-07-27 2016-12-28 南京理工大学 The BREATHABLE BANDWIDTH ultra wide band bandpass filter loaded based on parallel coupled line
CN106876847A (en) * 2017-01-18 2017-06-20 南京邮电大学 Broadband band-pass filter based on interdigital coupled resonators
CN107093785A (en) * 2017-03-28 2017-08-25 中国科学院微电子研究所 Multimode resonator and its wave filter
CN107394321A (en) * 2017-06-23 2017-11-24 深圳市景程信息科技有限公司 Load the broadband band-pass filter of three minor matters coupled microstrip lines
CN107895829A (en) * 2017-12-07 2018-04-10 电子科技大学 A kind of microstrip filter with the accurate oval bandpass response of three ranks
CN109411862A (en) * 2018-10-25 2019-03-01 成都会讯科技有限公司 The double detail parallel resonators of asymmetry open circuit and bandpass filter and design method

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20010094509A (en) * 2000-03-31 2001-11-01 김남영 The Microstrip Ring Bandpass Filter with Interdigital Side-Coupling and Its Manufacturing Method
CN203760600U (en) * 2013-11-27 2014-08-06 哈尔滨飞羽科技有限公司 Ultra-wideband filter possessing compact structure and resisting WLAN interference
CN104779424A (en) * 2015-04-13 2015-07-15 南京邮电大学 Microstrip dual-passband coupling filter
CN106257744A (en) * 2016-07-27 2016-12-28 南京理工大学 The BREATHABLE BANDWIDTH ultra wide band bandpass filter loaded based on parallel coupled line
CN106876847A (en) * 2017-01-18 2017-06-20 南京邮电大学 Broadband band-pass filter based on interdigital coupled resonators
CN107093785A (en) * 2017-03-28 2017-08-25 中国科学院微电子研究所 Multimode resonator and its wave filter
CN107394321A (en) * 2017-06-23 2017-11-24 深圳市景程信息科技有限公司 Load the broadband band-pass filter of three minor matters coupled microstrip lines
CN107895829A (en) * 2017-12-07 2018-04-10 电子科技大学 A kind of microstrip filter with the accurate oval bandpass response of three ranks
CN109411862A (en) * 2018-10-25 2019-03-01 成都会讯科技有限公司 The double detail parallel resonators of asymmetry open circuit and bandpass filter and design method

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