CN109524749B - Double-passband filter with notch characteristic - Google Patents

Double-passband filter with notch characteristic Download PDF

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CN109524749B
CN109524749B CN201811405446.7A CN201811405446A CN109524749B CN 109524749 B CN109524749 B CN 109524749B CN 201811405446 A CN201811405446 A CN 201811405446A CN 109524749 B CN109524749 B CN 109524749B
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impedance
double
stepped
resonator
notch
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CN109524749A (en
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刘海文
刘天康
文品
任宝平
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Xian Jiaotong University
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01PWAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00Auxiliary devices
    • H01P1/20Frequency-selective devices, e.g. filters
    • H01P1/201Filters for transverse electromagnetic waves
    • H01P1/203Strip line filters
    • H01P1/20327Electromagnetic interstage coupling
    • H01P1/20336Comb or interdigital filters

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Abstract

The invention provides a dual-passband filter with a notch characteristic. The double-passband filter comprises a first double-stepped-impedance resonator and a second double-stepped-impedance resonator which are symmetrically arranged, a first notch unit and a second notch unit which are symmetrically arranged, and an input feeder structure and an output feeder structure which are symmetrically arranged. An input feed structure and an output feed structure are slot coupled to the first and second double stepped impedance resonators, respectively, to provide electromagnetic excitation. The first impedance double-step resonator is slot-coupled to the second impedance double-step resonator to produce a first pass band and a second pass band of the double-pass band filter under electromagnetic excitation. First and second notch units are slot coupled to the first and second double stepped impedance resonators, respectively, to produce a notch in the first pass band under electromagnetic excitation. The invention introduces a trap wave in one of the dual-pass bands, and effectively inhibits the interference frequency in the pass band.

Description

Double-passband filter with notch characteristic
Technical Field
The disclosed embodiments of the present invention relate to the field of radio frequency communication technologies, and more particularly, to a dual bandpass filter having a notch characteristic.
Background
With the rapid development of mobile communication, multiple mobile communication systems coexist, so that in practical applications, frequency signals of different mobile communication systems often appear in the same operating frequency band, and therefore, in a certain communication system, interference frequency signals of other communication systems need to be suppressed in the operating frequency band. At the same time, the system needs to receive signals of often several non-adjacent frequencies.
One of the main methods for suppressing the interference frequency in the passband is to integrate a band-stop filter in the bandpass filter, but the design method is complex, the specific implementation is difficult, the structure is complex, the circuit area is large, and the circuit integration is not easy. Meanwhile, if the system uses a conventional single-pass band filter, the communication device needs a radio frequency front-end device operating in multiple frequency bands, which undoubtedly increases the volume of the device. Furthermore, few studies and applications are currently available to combine high temperature superconducting technology with radio frequency interference suppression technology to design multi-passband high temperature superconducting filters with notch properties.
Disclosure of Invention
In view of the above, the present invention provides a dual-band filter with notch characteristics to solve the above problems.
The technical scheme adopted by the invention for solving the problems is to provide a dual-passband filter with a notch characteristic. The double-passband filter comprises a first double-stepped-impedance resonator and a second double-stepped-impedance resonator which are symmetrically arranged, a first notch unit and a second notch unit which are symmetrically arranged, and an input feeder structure and an output feeder structure which are symmetrically arranged. The symmetrically arranged input feeder structure and output feeder structure are respectively coupled with the first double-stepped-impedance resonator and the second double-stepped-impedance resonator in a slot mode so as to provide electromagnetic excitation for the double-passband filter. The first and second symmetrically arranged double stepped impedance resonators are slot-coupled to produce first and second passbands of the double pass band filter under electromagnetic excitation. First and second notch units are slot coupled to the first and second double stepped impedance resonators, respectively, to produce a notch in the first pass band under electromagnetic excitation.
The first double-stepped impedance resonator and the second double-stepped impedance resonator are symmetrical double-stepped impedance resonators; the double-impedance-step resonator comprises a first impedance step, a second impedance step and a stub, wherein two ends of the stub are respectively connected with the first impedance step and the second impedance step, and the first impedance step and the second impedance step are symmetrically arranged.
The first step impedance device and the second step impedance device are symmetrical step impedance devices; the impedance step comprises a first impedance part, a second impedance part and a third impedance part, wherein the first impedance part and the third impedance part are symmetrically arranged, and the equivalent impedance of the first impedance part or the third impedance part is smaller than that of the second impedance part.
Wherein, two ends of the stub are respectively connected with one end of the second impedance part of the first step impedance device and one end of the second impedance part of the second step impedance device.
The second impedance part is bent twice, so that the step impedance device is U-shaped.
Wherein the first notch unit and the second notch unit are symmetrically arranged about a first diagonal line; and the input and output feed line structures are symmetrically arranged about a second diagonal, wherein the first and second diagonals intersect.
Wherein the first notch unit extends from one end of the first double-stepped-impedance resonator along the first double-stepped-impedance resonator and is slot-coupled with the first double-stepped-impedance resonator; the second trap unit is extended from the other end of the second impedance-double-stepped resonator along the second impedance-double-stepped resonator and is slot-coupled with the second impedance-double-stepped resonator; one of the input feed line structure and the output feed line structure is slot coupled to the other end of the first double stepped impedance resonator and the other is slot coupled to one end of the second double stepped impedance resonator to provide electromagnetic excitation.
The input feeder structure comprises a first tapping part, a first feeder and a second feeder, wherein one end of the first feeder and one end of the second feeder are respectively connected with the first tapping part and are arranged at 90 degrees; the output feeder structure comprises a second tap part, a third feeder and a fourth feeder, wherein one end of the third feeder and one end of the fourth feeder are respectively connected with the second tap part and are arranged at 90 degrees.
Wherein the first feedline is coupled to the first double stepped impedance resonator slot along the first double stepped impedance resonator extension and the third feedline is coupled to the second double stepped impedance resonator slot along the second double stepped impedance resonator extension; the second feeder line is coupled with the first double-step impedance resonator and the second double-step impedance resonator respectively in partial gaps, and the fourth feeder line is coupled with the first double-step impedance resonator and the second double-step impedance resonator respectively in partial gaps; wherein the first or third feed line has a different resonant frequency than the second or fourth feed line.
The first feeder line and the third feeder line are respectively bent for three times, so that the first feeder line and the third feeder line are respectively coupled with the first double-step impedance resonator and the second double-step impedance resonator in a partial gap mode; and the second feeder line and the fourth feeder line are respectively bent twice so as to be in slot coupling with the second double step impedance resonator part.
The invention has the following beneficial effects: the first double-step impedance resonator and the second double-step impedance resonator are used for generating double pass bands, the first notch unit and the second notch unit are respectively in slot coupling with the first double-step impedance resonator and the second double-step impedance resonator, therefore, a notch is introduced into one of the double pass bands generated by the first double-step impedance resonator and the second double-step impedance resonator, the double pass band with notch characteristics is formed, a notch filter does not need to be additionally arranged in a system, the size of the system is reduced, and the interference frequency in the pass band is effectively restrained.
Drawings
FIG. 1 is a schematic diagram of a dual bandpass filter with notch characteristics according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a portion of the dual bandpass filter of FIG. 1 having a notch characteristic;
FIG. 3 is a graph of a frequency response of a dual bandpass filter with notch characteristics according to an embodiment of the invention;
fig. 4 is a graph of the frequency response of the notch portion of fig. 3 amplified.
Detailed Description
Certain terms are used throughout the description and claims to refer to particular components. As one skilled in the art can appreciate, electronic device manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following specification and claims, the word "comprise" is an open-ended term of art, and thus should be interpreted to mean "including, but not limited to …". Additionally, the term "coupled" is intended to mean either an indirect electrical connection or a direct electrical connection. Thus, when one device is coupled to another device, that connection may be through a direct electrical connection or through an indirect electrical connection via other devices and connections.
Fig. 1 is a schematic structural diagram of a dual-bandpass filter with notch characteristics according to an embodiment of the present invention. The dual bandpass filter 100 includes a first dual stepped impedance resonator 130 and a second dual stepped impedance resonator 140 that are symmetrically disposed, a first notch unit 150 and a second notch unit 160 that are symmetrically disposed, and an input feed line structure 110 and an output feed line structure 120 that are symmetrically disposed.
The symmetrical arrangement of the first and second double- stepped impedance resonators 130 and 140, the first and second notch units 150 and 160, and the input and output feedline structures 110 and 120 may be arranged in accordance with practical circuit design considerations. In the present embodiment, the first dual stepped-impedance resonator 130 and the second dual stepped-impedance resonator 140 are horizontally and vertically symmetrically disposed. In other embodiments, the first dual-stepped impedance resonator 130 and the second dual-stepped impedance resonator 140 may be disposed vertically and laterally symmetrically, or disposed symmetrically with respect to a tilted line.
Symmetrically disposed input feed structure 110 and output feed structure 120 slot-couple with first dual-stepped impedance resonator 130 and second dual-stepped impedance resonator 140, respectively, to provide electromagnetic excitation to dual-bandpass filter 100.
The first double stepped impedance resonator 130 and the second double stepped impedance resonator 140, which are symmetrically disposed, are slot-coupled to produce a first pass band 310 and a second pass band 320 of the dual pass band filter 100 under electromagnetic excitation. Wherein the center resonant frequency of the second channel 320 is greater than the center resonant frequency of the first channel 310.
The first notch unit 150 and the second notch unit 160 are slot-coupled to the first dual-stepped-impedance resonator 130 and the second dual-stepped-impedance resonator 140, respectively, to create a notch 330 within the first pass band 310 under electromagnetic excitation.
In this embodiment, a dual passband is generated by the first double stepped-impedance resonator 130 and the second double stepped-impedance resonator 140, and a notch is introduced into one of the dual passbands generated by the first double stepped-impedance resonator 130 and the second double stepped-impedance resonator 140 by the first notch unit 150 and the second notch unit 160, so as to form the dual passband having a notch characteristic, without additionally adding a notch filter in the system, thereby reducing the volume of the system and effectively suppressing the interference frequency in the passband.
The respective portions of the dual band pass filter 100 having notch characteristics are described in detail below with reference to fig. 2 to 4. In fig. 3, the solid line is a reflection response curve S11, the dotted line is a transmission response curve S21, Frequency represents Frequency, and Magnitude represents amplitude.
The first and second double- stepped impedance resonators 130 and 140 are slot-coupled to produce first and second pass bands 310 and 320. In one embodiment, the first dual stepped-impedance resonator 130 and the second dual stepped-impedance resonator 140 are both symmetric dual stepped-impedance resonators 200. Fig. 2 is a schematic structural diagram of the first dual stepped-impedance resonator 130 or the second dual stepped-impedance resonator 140 in fig. 1. Specifically, the dual stepped impedance resonator 200 includes a first stepped impedance device 210, a second stepped impedance device 230, and a stub 220, wherein both ends of the stub 220 are connected to the first stepped impedance device 210 and the second stepped impedance device 230, respectively, and the first stepped impedance device 210 and the second stepped impedance device 230 are symmetrically disposed. Further, the first and second stepped impedances 210 and 230 are disposed left-right symmetrically with respect to the stub 220.
In one embodiment, since the first impedance step 210 and the second impedance step 230 are symmetrically disposed, the first impedance step 210 and the second impedance step 230 are both symmetrical impedance steps. The step impedance device is a half-wavelength step impedance device and is made of a half-wavelength microstrip line. Specifically, the step resistor includes a first resistance portion 211, a second resistance portion 212, and a third resistance portion 213, wherein the first resistance portion 211 and the third resistance portion 213 are symmetrically disposed. In the present embodiment, the equivalent impedance of the first impedance portion 211 or the third impedance portion 213 is smaller than the equivalent impedance of the second impedance portion 212, and the equivalent electrical length of the first impedance portion 211 or the third impedance portion 213 is equal to the equivalent electrical length of the second impedance portion 212. In other embodiments, the equivalent impedance of the first impedance portion 211 or the third impedance portion 213 may be greater than the equivalent impedance of the second impedance portion 212. In order to adjust the center frequencies of the first and second pass bands 310 and 320, the ratio of the equivalent electrical lengths of the first or third impedance portion 211 or 213 to the second impedance portion 212 may be adjusted. It should be noted that the first stepped resistor 210 and the second stepped resistor 230 are the same stepped resistor, and therefore, for simplicity, only the first stepped resistor 210 is labeled in fig. 2, but it is understood that the same labeling for the first stepped resistor 210 is also applicable to the second stepped resistor 230.
In one embodiment, two ends of the stub 220 are connected to one end of the second impedance portion 212 of the first stepped impedance device 210 and one end of the second impedance portion 212 of the second stepped impedance device 230, respectively, so that the third impedance portion 213 of the first stepped impedance device 210 is disposed adjacent to the first impedance portion 211 of the second stepped impedance device 230 and is disposed in parallel along a long side thereof. In one embodiment, the equivalent impedance of the stub 220 is the same as the equivalent impedance of the second impedance part 212.
In one embodiment, the second impedance portion 212 is bent twice, so that the impedance step is U-shaped. After the second impedance portion 212 of each of the first and second stepped impedance devices 210 and 230 is bent twice, the first and second double stepped impedance resonators 130 and 140 symmetrically disposed occupy a substantially rectangular region as shown in fig. 1.
The first notch unit 150 and the second notch unit 160 are slot-coupled to the first dual-stepped-impedance resonator 130 and the second dual-stepped-impedance resonator 140, respectively, to create a notch 330 within the first pass band 310. In one embodiment, first notch unit 150 and second notch unit 160 are symmetrically disposed about a first diagonal. The input feed line structure 110 and the output feed line structure 120 are symmetrically arranged about a second diagonal, wherein the first diagonal and the second diagonal intersect. It should be noted that the first diagonal line and the second diagonal line may be regarded as two diagonal lines of a rectangle occupied by the first double stepped impedance resonator 130 and the second double stepped impedance resonator 140 which are symmetrically disposed.
First notch cell 150 and second notch cell 160 are identical half-wavelength uniform impedance resonators. Wherein the first notch unit 150 extends from one end of the first double stepped impedance resonator 130 along the first double stepped impedance resonator 130 to be slot-coupled with the first double stepped impedance resonator 130. The first notch unit 150 is partially slot-coupled to the first stepped impedance device 210 of the first double stepped impedance resonator 130 and is fully slot-coupled to the second stepped impedance device 230. Further, the first notch unit 150 is slot-coupled to the second impedance section 212 and the third impedance section 213 of the first stepped resistor 210.
The second notch unit 160 extends from the other end of the second double stepped impedance resonator 140 along the second double stepped impedance resonator 140 to be slot-coupled to the second double stepped impedance resonator 140. The second notch unit 160 is slot-coupled to the entire first impedance step 210 and a portion of the second impedance step 230 of the second double stepped impedance resonator 140. Further, second notch section 160 is slot-coupled to first impedance section 211 and second impedance section 212 of second impedance step 230.
Due to the coupling characteristics of the first notch unit 150 and the first double-stepped-impedance resonator 130 and the coupling characteristics of the second notch unit 160 and the second double-stepped-impedance resonator 140, and the coupling characteristics of the first double-stepped-impedance resonator 130 and the second double-stepped-impedance resonator 140, a transmission zero is generated in the notch 330 formed by the first notch unit 150 and the second notch unit 160, respectively, as shown in fig. 4, that is, the transmission zero 331 and the transmission zero 332, and the frequency in the notch 330 in the first pass band 310 can be well suppressed. Meanwhile, due to the first and second double-stepped- impedance resonators 130 and 140 and the first and second notch units 150 and 160, two transmission poles are respectively generated at both sides of the notch 330, as shown in fig. 4, that is, a transmission pole 341 and a transmission pole 342, thereby improving the selectivity of the notch 330 and further suppressing the frequency within the first pass band 310. In addition, due to the resonance characteristics of the first notch unit 150 and the second notch unit 160 themselves, a transmission zero is generated at the upper band of the second pass band 320, as shown in fig. 3, that is, a transmission zero 303 and a transmission zero 304, respectively.
The input feed line structure 110 and the output feed line structure 120 are symmetrically arranged about a second diagonal. In one embodiment, one of the input feed line structure 110 and the output feed line structure 120 is slot coupled to the other end of the first double stepped impedance resonator 130 and the other is slot coupled to one end of the second double stepped impedance resonator 140 to provide electromagnetic excitation. In addition, since the input feeder structure 110 and the output feeder structure 120 are symmetrically disposed about the second diagonal line, and the input feeder structure 110 and the output feeder structure 120 are structured themselves, a transmission zero is generated between the first pass band 310 and the second pass band 320, as shown in fig. 3 and 4, i.e., the transmission zero 308, improving the isolation characteristic between the double pass bands.
It should be noted that, since the first stepped impedance resonator 130 and the second stepped impedance resonator 140 are symmetrically disposed, one end of the first double stepped impedance resonator 130 is opposite to the other end of the second stepped impedance resonator 140, that is, the other end of the first stepped impedance resonator 130 is the same as the other end of the second stepped impedance resonator 140. Also, one end of the first stepped impedance resonator 130 is the same end as one end of the second stepped impedance resonator 140.
Specifically, the input feed line structure 110 includes a first tap portion 111, a first feed line 112, and a second feed line 113, wherein one end of the first feed line 112 and one end of the second feed line 113 are connected to the first tap portion 111, respectively, and are disposed at 90 degrees. The output feed line structure 120 includes a second tap portion 121, a third feed line 122, and a fourth feed line 123, wherein one end of the third feed line 122 and one end of the fourth feed line 123 are respectively connected to the second tap portion 121 and are disposed at 90 degrees. The end surface of the first tap section 111 serves as an input point Pin to which an electromagnetic signal is fed, and the end surface of the second tap section 121 serves as an output point Pout to which an electromagnetic signal is fed. Note that Pin and Pout are merely illustrative, and in other embodiments, the end face of the first tap portion 111 may be referred to as Pout, while the end face of the second tap portion 121 is referred to as Pin.
The first feedline 112 extends along the first dual stepped-impedance resonator 130 to slot couple with the first dual stepped-impedance resonator 130 and the third feedline 122 extends along the second dual stepped-impedance resonator 140 to slot couple with the second dual stepped-impedance resonator 140.
The second feed line 113 is partially slot-coupled to the first and second double-stepped impedance resonators 130 and 140, respectively, and the fourth feed line 123 is partially slot-coupled to the first and second double-stepped impedance resonators 130 and 140, respectively.
The first feed line 112 or the third feed line 122 has a different resonant frequency from the second feed line 113 or the fourth feed line 123.
In this embodiment, the input feeder structure 110 and the output feeder structure 120 also generate transmission zeros under their own electromagnetic excitation, thereby suppressing harmonics of the upper band of the dual passband formed by the first dual-stepped impedance resonator 130 and the second dual-stepped impedance resonator 140. Specifically, the first feed line 112 and the third feed line 122 are coupled to each other by the electromagnetic excitation, and generate a transmission zero in the upper band of the second pass band 320, as shown in fig. 3, i.e., the transmission zero 301 and the transmission zero 302, respectively. Due to the symmetrical arrangement of the input and output feed line structures 110, 120 about the second diagonal, and the structures of the input and output feed line structures 110, 120 themselves, the input and output feed line structures 110, 120 generate a transmission zero in the upper band of the second passband 320, as shown in fig. 3, i.e. transmission zero 305. The first tap section 111 and the second tap section 121 are coupled to each other by the electromagnetic excitation to generate a transmission zero in the upper band of the second pass band 320, as shown in fig. 3, i.e., the transmission zero 306 and the transmission zero 307, respectively.
As shown in fig. 3, the transmission zeroes 301, 302, 305, 306, 307 generated by the input feed line structure 110 and the output feed line structure 120, and the transmission zeroes 303, 304 generated by the first notch unit 150 and the second notch unit 160, together enable the harmonic rejection of the dual bandpass filter 100 to reach above 7GHz, and thus the dual bandpass filter 100 has wider stop band characteristics.
The first and third feeding lines 112 and 122 are bent three times to be partially slot-coupled to the first and second double stepped- impedance resonators 130 and 140, respectively. Further, the first feed line 112 is slot-coupled to the first impedance portion 211 of the first stepped impedance resonator 210 of the first double stepped impedance resonator 130, and the third feed line 122 is slot-coupled to the third impedance portion 213 of the second stepped impedance resonator 230 of the second double stepped impedance resonator 140.
The second feeding line 113 and the fourth feeding line 123 are bent twice, respectively, so as to be partially slot-coupled to the second double stepped impedance resonator 140. Further, the second feed line 113 is slot-coupled to the first impedance portion 211 of the first stepped impedance resonator 210 of the first double stepped impedance resonator 130 and the first impedance portion 211 of the first stepped impedance resonator 210 of the second double stepped impedance resonator 140. The fourth feed line 123 is slot-coupled to the third impedance part 213 of the second stepped impedance 230 of the first double stepped impedance resonator 130 and the third impedance part 213 of the second stepped impedance 230 of the second double stepped impedance resonator 140.
Further, in one embodiment, the dual band-pass filter 100 further comprises a high temperature superconducting dielectric substrate (not shown), the first and second symmetrically arranged double step- impedance resonators 130 and 140, the first and second symmetrically arranged notch units 150 and 160, and the input and output feed line structures 110 and 120. That is to say, adopt high temperature superconducting medium base plate to make this dual passband filter, this high temperature superconducting medium base plate's dielectric constant is 9.78, and thickness is 0.5mm, and then, this dual passband filter's loss is little, and the quality factor is high, and at this moment, it is better to be applied to special application systems such as radio astronomy observation in the effect, uses stably, and the live time is of a specified duration. The high-temperature superconducting medium substrate is made of magnesium oxide, and the upper surface and the lower surface of the high-temperature superconducting medium substrate are made of yttrium barium copper oxide superconducting films. Of course, in other embodiments, the bandpass filter can be made by using dielectric substrates with other parameters within the understanding range of those skilled in the art, and the disclosure is not limited thereto.
It will be apparent to those skilled in the art that many modifications and variations can be made in the apparatus and method while maintaining the teachings of the present disclosure. Accordingly, the above disclosure should be considered limited only by the scope of the following claims.

Claims (8)

1. A dual bandpass filter having a notch characteristic, comprising:
the dual-stage feed line structure comprises a first dual-step impedance resonator, a second dual-step impedance resonator, a first trap unit, a second trap unit, an input feed line structure and an output feed line structure, wherein the first dual-step impedance resonator and the second dual-step impedance resonator are symmetrically arranged;
an input feeder structure and an output feeder structure which are symmetrically arranged are respectively coupled with the first double-stepped-impedance resonator and the second double-stepped-impedance resonator in a slot mode so as to provide electromagnetic excitation for the double-passband filter;
the first double-stepped impedance resonator and the second double-stepped impedance resonator which are symmetrically arranged are in slot coupling so as to generate a first passband and a second passband of the double-passband filter under the action of electromagnetic excitation;
the first notch unit and the second notch unit are respectively coupled with the first double-step impedance resonator and the second double-step impedance resonator so as to generate a notch in the first pass band under the action of electromagnetic excitation;
the first double-stepped impedance resonator and the second double-stepped impedance resonator are both symmetrical double-stepped impedance resonators;
the double-impedance-step resonator comprises a first impedance step, a second impedance step and a stub, wherein two ends of the stub are respectively connected with the first impedance step and the second impedance step, and the first impedance step and the second impedance step are symmetrically arranged; the first step impeder and the second step impeder are both symmetrical step impeders;
the impedance step comprises a first impedance part, a second impedance part and a third impedance part, wherein the first impedance part and the third impedance part are symmetrically arranged, and the equivalent impedance of the first impedance part or the third impedance part is smaller than that of the second impedance part.
2. The dual bandpass filter with notch characteristics as claimed in claim 1, wherein both ends of said stub are connected to one end of said second impedance portion of said first stepped impedance device and one end of said second impedance portion of said second stepped impedance device, respectively.
3. The double bandpass filter with notch characteristics as claimed in claim 2, wherein said second impedance portion is bent twice so that said stepped impedance device has a U-shape.
4. The dual bandpass filter with notch characteristics as recited in claim 1, wherein said first notch unit and said second notch unit are symmetrically disposed about a first diagonal; and the input and output feed line structures are symmetrically arranged about a second diagonal, wherein the first and second diagonals intersect.
5. The dual bandpass filter with notch characteristics as claimed in claim 4, wherein said first notch unit is slot-coupled to said first double stepped-impedance resonator extending from one end of said first double stepped-impedance resonator along said first double stepped-impedance resonator;
the second notch unit extends from the other end of the second impedance double-stepped resonator along the second impedance double-stepped resonator and is slot-coupled to the second impedance double-stepped resonator;
one of the input feed line structure and the output feed line structure is slot coupled to the other end of the first double stepped impedance resonator and the other is slot coupled to one end of the second double stepped impedance resonator to provide electromagnetic excitation.
6. The dual bandpass filter with notch characteristics according to claim 5 wherein said input feed line structure comprises a first tap section, a first feed line and a second feed line, wherein one end of said first feed line and one end of said second feed line are connected to said first tap section, respectively, and are disposed at 90 degrees;
the output feeder structure comprises a second tap part, a third feeder and a fourth feeder, wherein one end of the third feeder and one end of the fourth feeder are respectively connected with the second tap part and are arranged at 90 degrees.
7. The dual bandpass filter with notch characteristics as recited in claim 6, wherein said first feedline extends along said first impedance double stepped resonator to couple with said first impedance double stepped resonator slot, and said third feedline extends along said second impedance double stepped resonator to couple with said second impedance double stepped resonator slot;
the second feeder line is partially slot-coupled to the first double-stepped impedance resonator and the second double-stepped impedance resonator, respectively, and the fourth feeder line is partially slot-coupled to the first double-stepped impedance resonator and the second double-stepped impedance resonator, respectively;
wherein the resonant frequency of the first or third feed line is different from the resonant frequency of the second or fourth feed line.
8. The dual band-pass filter having a notch characteristic as claimed in claim 7, wherein said first feed line and said third feed line are respectively subjected to bending processing three times so as to be partially slot-coupled with said first double stepped impedance resonator and said second double stepped impedance resonator, respectively;
and the second feeder line and the fourth feeder line are respectively bent twice so as to be in slot coupling with the second double step impedance resonator part.
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