CN112909461A

CN112909461A - Complementary duplex structure full-band absorption dual-frequency band-pass filter

Info

Publication number: CN112909461A
Application number: CN202110094584.3A
Authority: CN
Inventors: 吴永乐; 张一凡; 于会婷; 王卫民
Original assignee: Beijing University of Posts and Telecommunications
Current assignee: Beijing University of Posts and Telecommunications
Priority date: 2021-01-25
Filing date: 2021-01-25
Publication date: 2021-06-04
Anticipated expiration: 2041-01-25
Also published as: CN112909461B

Abstract

The invention discloses a full-band absorption dual-band pass filter with a complementary duplex structure, which belongs to the electrical field; the overall structure is composed of a dual-band pass filter structure and a left-right symmetrical complementary dual-band rejection absorption branch; the dual-band pass filter structure includes The coupling line c and the microstrip line s1 connected to it; the microstrip line s1 is respectively connected to the left and right complementary dual-band resistance and absorption branches, and is also connected to the input port and the output port; the complementary dual-band resistance absorption branch includes absorption branches and stepped impedances The open branch; the ladder impedance open branch includes the microstrip lines s3 and s4 in series; the absorption branch includes the microstrip line s5 in series and the grounding resistance R1; when the signal is input from the first port, the in-band signal is transmitted through a dual-band pass filter structure To the output port, the out-of-band signal is absorbed by the complementary dual-band resistance absorption branch, and the current is converted into energy dissipation through the resistance of the energy dissipation element. The present invention avoids the reflection of useless signals into the equipment connected with it, and causes interference to the performance of the communication system.

Description

Complementary duplex structure full-band absorption dual-frequency band-pass filter

Technical Field

The invention belongs to the field of electricity, relates to a passive radio frequency device, and particularly relates to a full-band absorption dual-band-pass filter with a complementary duplex structure.

Background

At present, with the rapid development of communication technology and the increasing diversification of the demand of people for communication functions, the demand for multiband and high-performance microwave devices that can be applied to various communication standards is increasing. With the development of 5G mobile communication systems, the entire mobile communication industry begins to explore brand new frequency bands.

At present, spectrum resources of sub-6GHz have been used for 5G communication in multiple countries around the world, and a filter is a key device in a radio frequency front end system and is widely applied to antenna feed networks of wireless communication, satellite navigation systems and the like, such as antenna arrays, power amplifiers, phase shifters and the like. The band-pass filter is a common frequency selective device, can transmit signals and energy in a specific frequency band, and can inhibit useless signals in a certain frequency band, namely all signals outside a pass band are reflected back to a port. In addition, in order to meet the requirements of high rate and large capacity of 5G communication, a filter is required to simultaneously support multiple frequency bands or cover as wide a frequency band range as possible in terms of frequency band support.

Bandpass filters are often connected to systems such as amplifiers and antenna arrays where a large number of nonlinear devices are present, and signals and power at the input port of the filter are reflected into the equipment connected to the filter and cause intermodulation interference with nonlinear components in these connected systems. The non-linear elements such as the amplifier have high sensitivity to noise and reflected signals, and the noise signals and the reflected signals have a large influence on the performance of the non-linear system, so that the sensitivity of the communication system is reduced, the signal-to-noise ratio is too low, and the performance of the communication system is seriously influenced.

Disclosure of Invention

Aiming at the problems, the invention provides a full-band absorption dual-band-pass filter with a complementary duplex structure, which not only can realize the broadband dual-band filtering performance and improve the performance of the band-pass filter, but also can absorb the full frequency of the reflected signal of an input port so as to prevent the signal from being reflected into a communication system and causing adverse effects on the communication system.

The complementary duplex structure full-band absorption dual-frequency band-pass filter is constructed on a single-layer circuit board and consists of a dual-frequency band-pass filter structure and complementary dual-frequency band-stop absorption branches which are bilaterally symmetrical;

the dual-frequency band-pass filtering structure is a symmetrical structure and comprises a coupling line group c with two ports and an open-ended terminal and a microstrip line s1 vertically connected with the coupling line group c; the lower end of the left line of the coupling line c is open-circuited, the upper end of the left line is connected with the right end of a left microstrip line s1, the left end of a microstrip line s1 is connected with a left complementary double-frequency band-stop absorption branch, and meanwhile, the left end of the microstrip line s1 is directly connected with an input port, namely a first port;

symmetrically, the lower end of the right line of the coupling line c is open-circuited, and the upper end of the right line is connected with the left end of the right microstrip line s 1; the right end of the microstrip line s1 is connected with the complementary double-frequency band elimination absorption branch on the right side, and is also directly connected with an output port, namely a second port;

the complementary double-frequency band-stop absorption branch circuits are connected in parallel at two ports and comprise absorption branch nodes and step impedance open-circuit branch nodes;

the stepped impedance open-circuit branch comprises microstrip lines s3 and s4 which are connected in series; the absorption branch knot comprises a microstrip line s5 and a grounding resistor R1 which are connected in series;

microstrip lines s1 connected to the two ports are connected to the upper ends of left and right microstrip lines s2, respectively, the lower ends of microstrip lines s2 are connected to microstrip lines s3 in left and right stepped impedance open-circuit stubs, and microstrip lines s5 of absorbing stubs are connected in parallel between microstrip lines s2 and s 3.

The microstrip line s1, the microstrip line s2, the microstrip line s3, the microstrip line s4 and the microstrip line s5 have different line widths and lengths, and are specifically determined by two electrical characteristic parameters, namely the electrical length and the characteristic impedance of the microstrip line.

The input port and the output port are both SMA connectors.

The full-band absorption dual-frequency band-pass filter with the complementary duplex structure has the working principle as follows:

when signals are input from the first port, in-band signals are transmitted to the output port through the dual-band-pass filtering structure, out-band signals are absorbed through the complementary dual-band-stop absorption branch circuit, and current is converted into energy through the energy loss element resistor to be dissipated.

1) The transmission of the in-band signal is specifically as follows:

first, two operating frequency components of the filter are definedIs otherwise f₁And f₂(f₁<f₂) The line lengths of the corresponding microstrip lines at the frequency are respectively theta₁And theta₂。

Then, the impedance of the filter input port is calculated: z_in＝Z_{BPF_in}//Z_{BSF_in}；

Z_{BPF_in}Input impedance, Z, for a dual-band bandpass filtering structure_{BSF_in}The input impedance of the complementary double-frequency band-stop absorption branch circuit;

finally, the input impedance Z in the filter at two operating frequencies_inAnd the input impedance Z of the dual-frequency band-pass filtering structure_{BPF_in}Are all equal to the resistance Z at the port₀Namely: z_in(θ₁)＝Z_in(θ₂)＝Z₀，Z_{BPF_in}(θ₁)＝Z_{BPF_in}(θ₂)＝Z₀(ii) a Port impedance matching may be achieved.

At the same time, the input impedance Z of the complementary double-frequency band-stop absorption branch_{BSF_in}Is ∞: z_{BSF_in}(θ₁)＝Z_{BSF_in}(θ₂) Infinity; the band-stop branch section is equivalent to an open circuit, and effective transmission of the dual-frequency band-pass filtering structure to signals is realized.

2) The absorption process of the out-of-band signal is as follows:

first, the filter has f-2 nf at dc and even harmonics₀(n-0, 1,2, …), equivalent to a ground resistance R₁Connected to the port, the reflection coefficient of the circuit is as follows:

by adjusting the resistance R₁The resistance value of the power supply further adjusts the absorption level of the reflected energy at the direct current and even harmonic; when R1 is 50 Ω, | S₁₁The dual-band filter achieves ideal absorption at both the direct and even harmonics.

The filter then becomes (2n +1) f at the center frequency and odd harmonics₀(n-0, 1,2, …), dual band bandpass filtering architectureThe step impedance open circuit branch is equivalent to an open circuit; the filter is overall equivalent to a characteristic impedance of Z₂A half-wavelength microstrip line s2 with characteristic impedance Z₅The quarter-wave microstrip line s5 and the grounding resistor R₁In series with the port, the reflection coefficient of the circuit is as follows:

when the resistance R is₁After the resistance value is determined, by adjusting the impedance value Z₅Adjusting the absorption level of the reflected energy at the central frequency and the odd harmonics; when R1 is 50 omega and Z is₅At 50 Ω, the dual-frequency filter achieves ideal absorption at the center frequency and odd harmonics.

The invention has the advantages that:

1) a full-band absorption dual-band-pass filter with a complementary duplex structure has a novel structure and comprises a dual-band-pass filter structure and a complementary dual-band absorption band-stop branch.

2) A complementary duplex structure full-band absorption dual-frequency band-pass filter is characterized in that the dual-frequency band-pass filter structure is based on branch nodes of a terminal open-circuit coupling line, so that the dual-frequency filter can effectively transmit dual-frequency signals within two pass-band ranges, and has good filtering performance.

3) A complementary duplex structure full-band absorption dual-frequency band-pass filter adds complementary dual-frequency band-stop absorption branch circuits at two ports of a dual-frequency band-pass filter structure, wherein the absorption branch circuits are formed by connecting resistors and short-circuited quarter-wavelength branch circuits in series, the complementary dual-frequency band-stop branch circuits are equivalent to open circuits within a pass band range, the influence on the filtering performance of the filter is small, the dual-frequency filter can effectively absorb reflection noise outside the pass band range, and a ground resistor is used as an energy loss element and can convert the current of an input port into heat for dissipation so as to avoid the interference of useless signals to the performance of a communication system.

4) The utility model provides a complementary duplex structure full frequency channel absorbs dual-frenquency band-pass filter, the circuit structure size is very little, and simple structure, consequently easily processing is integrated, and the circuit structure is complanate, can adopt single-deck circuit board processing, can the wide application in the radio frequency circuit that has the dual-frenquency filtering demand.

Drawings

FIG. 1 is a structural diagram of a full-band absorption dual-band bandpass filter of a complementary duplex structure according to the present invention;

fig. 2 is a schematic diagram of a microstrip line of a full-band absorption dual-band bandpass filter with a complementary duplex structure according to the present invention;

FIG. 3 is a schematic diagram of the full band absorption dual band bandpass filter of the complementary duplex structure incorporating input impedance according to the present invention;

FIG. 4 is a schematic diagram of a circuit structure in an embodiment of the present invention with a center operating frequency of 1.80 GHz;

FIG. 5 shows S under excitation in an embodiment of the present invention₂₁，S₁₁And S₂₂And (5) parameter simulation result schematic diagram.

Detailed Description

The present invention will be described in further detail and with reference to the accompanying drawings so that those skilled in the art can understand and practice the invention.

The invention relates to a full-band absorption dual-frequency band-pass filter with a complementary duplex structure, which consists of a dual-frequency band-pass filtering structure based on an open-circuit coupling line stub and a complementary dual-frequency band-stop absorption branch with an absorption stub. By adding complementary double-frequency band-stop absorption branches at the two ports, a double-port reflection noise full-frequency absorption function can be realized. In addition, the integral double-frequency filter has small size and wide bandwidth, and meets the miniaturization trend of a communication system and the requirement on the bandwidth. And the whole double-frequency filter is a simple plane structure, has easy realizability, can realize the absorption of out-of-band noise, effectively improves the performance of a radio frequency system, reduces the influence of reflected noise on the system, reduces the complexity of a microwave system and obviously improves the performance of the system.

The dual-frequency band-pass filter is realized by a single-layer printed circuit board as shown in fig. 1, wherein the top layer of the circuit board is a circuit of the dual-frequency band-pass filter based on a coupling line and having full-frequency absorption performance, and the bottom layer is a metal grounding surface; the design method of the single-layer printed circuit board is utilized for realizing the design, the whole structure is simple, the processing and the integration are easy, and the design idea is novel.

The whole double-frequency filter can realize full-frequency band absorption, is of a complementary duplex structure and consists of a double-frequency band-pass filtering structure and complementary double-frequency band-stop absorption branches which are bilaterally symmetrical;

as shown in fig. 2, the dual-band bandpass filtering structure is a symmetrical structure based on the coupled line open-circuit minor matters; the microstrip line comprises a coupling line group c with an open terminal and a microstrip line s1 vertically connected with the coupling line group c; the lower end of the left line of the coupling line c is open-circuited, the upper end of the left line is connected with the right end of a left microstrip line s1, the left end of a microstrip line s1 is connected with a left complementary double-frequency band-stop absorption branch, and meanwhile, the left end of the microstrip line s1 is directly connected with an input port, namely a first port;

the stepped impedance open-circuit branch comprises microstrip lines s3 and s4 which are connected in series; the absorption branch knot comprises a quarter-wavelength microstrip line s5 and a grounding resistor R1 which are connected in series;

In this embodiment, the even-mode impedance of the coupling line c is Z_eOdd mode impedance of Z_oThe electrical length is 90 °. Microstrip line s1, microstrip line s2, microstrip line s3, microstrip line s4 and microstripCharacteristic impedances of the strip line s5 are Z₁、Z₂、Z₃、Z₄And Z₅The electrical length of all microstrip lines is 90 °.

The input port and the output port are both SMA connectors.

The complementary duplex structure full-band absorption dual-frequency band-pass filter can have broadband filtering performance, complementary dual-frequency band-stop absorption branch circuits are added at the two ports, when signals are input from the first port, in-band signals are transmitted to the output port through the dual-frequency band-pass filter structure, out-of-band signals are absorbed through the complementary dual-frequency band-stop absorption branch circuits, and the current is converted into energy to be dissipated through the grounding resistance of an energy dissipation element. In addition, the absorption level of the reflected energy of the port at the positions of direct current and even harmonic is adjusted by adjusting the resistance value of the resistor, and the absorption level of the reflected energy of the port at the positions of central frequency and odd harmonic is adjusted by adjusting the impedance value of the quarter microstrip line of the absorption branch. The specific working principle is as follows:

1) the transmission of the in-band signal is specifically as follows:

firstly, two working frequencies of the filter are defined as f₁And f₂(f₁<f₂) The line lengths of the corresponding microstrip lines at two working frequencies are respectively theta₁And theta₂Resistance Z at the port₀Is 50 omega.

Then, the input impedance Z of the dual-frequency band-pass filtering structure is utilized_{BPF_in}And the input impedance Z of the complementary dual-band bandstop absorption branch_{BSF_in}In parallel, the impedance of the input port of the filter is calculated: z_in＝Z_{BPF_in}//Z_{BSF_in}；

Finally, the total input impedance Z in the filter at both operating frequencies_inAnd the input impedance Z of the dual-frequency band-pass filtering structure_{BPF_in}Are all equal to the resistance at the port 50 Ω, i.e.: z_in(θ₁)＝Z_in(θ₂)＝Z₀，Z_{BPF_in}(θ₁)＝Z_{BPF_in}(θ₂)＝Z₀(ii) a Port impedance matching can be achieved so that signals can be transmitted well in both pass band ranges.

At the same time, the input impedance Z of the complementary double-frequency band-stop absorption branch_{BSF_in}Is ∞: z_{BSF_in}(θ₁)＝Z_{BSF_in}(θ₂) Infinity; meaning that the band-stop stubs in the two pass-band ranges are equivalent to open circuits, and the resistors and the band-stop stubs do not function. Therefore, in the two pass band ranges, the filter can realize effective transmission of signals, and the influence of the band-stop branch section and the absorption resistor on the signals can be ignored.

2) The absorption process of the out-of-band signal is as follows:

the absorption properties can be defined as the reflection coefficient | S₁₁|<10dB, and in the stop band range, the complementary band-stop absorption branch can effectively absorb the out-of-band signal reflected by the filter.

First, the filter has f-2 nf at dc and even harmonics₀(n is 0,1,2, …), as shown in fig. 3a, the circuit is equivalent to a ground resistance R₁Connected to the port, the reflection coefficient of the circuit is as follows:

The filter then becomes (2n +1) f at the center frequency and odd harmonics₀(n-0, 1,2, …), as shown in fig. 3b, due to the input impedance Z of the dual-band bandpass filtering structure_{BPF_in}Infinity, equivalent to open circuit, and stepped impedance open circuit branch equivalent to open circuit; the filter is overall equivalent to a characteristic impedance of Z₂A half-wavelength microstrip line s2 with characteristic impedance Z₅The quarter-wave microstrip line s5 and the grounding resistor R₁In series with the port, the reflection coefficient of the circuit is as follows:

at the resistance R₁After the resistance value is determined, by adjusting the impedance Z₅Adjusting the absorption level of the reflected energy at the central frequency and the odd harmonics; when R is₁50 Ω and Z₅At 50 Ω, the dual-frequency filter achieves ideal absorption at the center frequency and odd harmonics.

At this time, at the center frequency, the half wavelength is 180 °, and since the input impedances at two points apart by the half wavelength on the transmission line are equal, the impedance Z is₂Here cancelled, impedance Z₂The effect of (c) is negligible.

In the invention, in order to realize the absorption of the reflection noise of the two ports of the dual-frequency band-pass filter, complementary dual-frequency band-stop absorption branches are added to the two ports of the dual-frequency band-pass filter, so that the absorption of the reflection noise outside the band can be realized, and the resistance can convert the reflection energy into heat for dissipation, thereby realizing the full-frequency absorption function.

In order to facilitate the display and adapt to the current communication frequency band requirement, the invention shows the embodiment with the center frequency of 1.8 GHz. In this example, the dielectric substrate was selected to be Rogers R4360B, with a dielectric constant of 6.15, a thickness of 1.524mm, and a dielectric loss of 0.0035. The lower surface of the dielectric substrate is covered with metal to serve as a ground.

Fig. 4 is a schematic diagram of a circuit structure with a center operating frequency of 1.8GHz, where fig. 4a is a schematic diagram of the whole circuit structure, and fig. 4b is a schematic diagram of a connection portion between a ground resistor R1 and a microstrip line s 5.

In this embodiment, the characteristic impedance of both ports is 50 ohms, and the width w of both ports_pIs 2.2mm, length l_p19.8 mm; c line width w of coupled line_e0.2mm, coupling gap s_e0.2mm, length l_e17.4 mm; microstrip line s1 line width w connected between coupling line c and input/output port_s1Is 0.1mm, length l_s1Is 22 mm; line width w of microstrip line s2_s2Is 4.0mm, length l_s2Is 18.2 mm; microstrip line s3 line width w of stepped impedance open-circuit branch_s3Is 1.1mm, length l_s3Is 19mm, and the microstrip line s4 line width w_s4Is 3.3mm, length l_s4Is 17 mm; microstrip line s5 of stub connected between microstrip lines s2 and s3, having line width w_s5Is 0.6mm, length l_s520mm, ground resistance R₁＝72Ω。

When the input port is excited, the reflection coefficient of the input port and the transmission coefficient of the output port (center frequency is 1.8GHz) are simulated, as shown in fig. 5, the operating frequencies of the dual-band bandpass filter are 0.8GHz and 3.04GHz, and the insertion loss of the filter is 0.7dB and 1.35dB at the two operating frequencies, respectively. Meanwhile, the double-frequency filter can absorb the full frequency of two-port reflected signals and return loss S in a pass band₁₁Less than-10 dB, outside the pass band range, the double-frequency band-pass filter can realize the absorption of two-port reflected signals, and the minimum absorption amplitude is-11 dB.

The size of the whole circuit is 72mm multiplied by 38mm, and the dual-frequency band-pass filter has the characteristics of miniaturization and easy integration, so that the dual-frequency band-pass filter with the full-frequency absorption function can be widely applied to various microwave systems, accords with the trend of miniaturization of systems and devices, can help to reduce the interference to the systems, and has a very wide application prospect.

Claims

1. a complementary duplex structure full-band absorption dual-band-pass filter, it is characterized in that, described filter is constructed on single-layer circuit board, by dual-band-pass filter structure and left-right symmetrical complementary dual-band resistance absorption branch road composition;

The dual-band-pass filter structure is a symmetrical structure, including a coupling line group c with an open terminal and a microstrip line s1 vertically connected to it; the lower end of the left line of the coupling line c is open, and the upper end is connected to the right end of the left microstrip line s1. The left end of s1 is connected to the complementary dual-band blocking and absorbing branch on the left, and is also directly connected to the input port, that is, the first port;

Symmetrically, the lower end of the right line of the coupling line c is open, and the upper end is connected to the left end of the microstrip line s1 on the right; directly connected;

The complementary dual-band resistance and absorption branch is connected in parallel at two ports, and includes an absorption branch and a stepped impedance open branch;

The step impedance open branch includes microstrip lines s3 and s4 connected in series; the absorption branch includes microstrip line s5 connected in series and grounding resistance R1;

The microstrip lines s1 connected to the two ports are respectively connected to the upper ends of the left and right microstrip lines s2, and the lower ends of the microstrip lines s2 are both connected to the microstrip line s3 in the left and right stepped impedance open branches. In addition, in the microstrip line s2 The microstrip line s5 that absorbs the branch in parallel with s3;

When the signal is input from the first port, the in-band signal is transmitted to the output port through the dual-band-pass filter structure, and the out-band signal is absorbed by the complementary dual-band blocking absorption branch, and the current is converted into energy dissipation through the resistance of the energy loss element.

2. a kind of complementary duplex structure full-band absorption dual-band pass filter as claimed in claim 1, is characterized in that, described microstrip line s1, microstrip line s2, microstrip line s3, microstrip line s4 , the line width and length of the microstrip line s5 are different, which are specifically determined by two electrical characteristic parameters, the electrical length and the characteristic impedance of the microstrip line.

3 . The full-band absorption dual-band pass filter of a complementary duplex structure according to claim 1 , wherein the input port and the output port are both SMA connectors. 4 .

4. a kind of complementary duplex structure full-band absorption dual-band pass filter as claimed in claim 1, is characterized in that, the transmission of described in-band signal is specifically:

First, define the two operating frequencies of the filter as f ₁ and f ₂ (f ₁ <f ₂ ), and the corresponding electrical lengths of the microstrip lines at the frequencies are θ ₁ and θ ₂ ;

Then, calculate the impedance of the input port of the filter: Z _in =Z _{BPF_in} //Z _{BSF_in} ;

Z _{BPF_in} is the input impedance of the dual-band pass filter structure, and Z _{BSF_in} is the input impedance of the complementary dual-band blocking absorption branch;

Finally, at the two operating frequencies, the input impedance Z _in the filter and the input impedance Z _{BPF_in} of the dual-bandpass filter structure are both equal to the resistance Z ₀ at the port, namely: Z _in (θ ₁ )=Z _in (θ ₂ )=Z ₀ , Z _{BPF_in} (θ ₁ )=Z _{BPF_in} (θ ₂ )=Z ₀ ; port impedance matching can be realized;

At the same time, the input impedance Z _{BSF_in} of the complementary dual-band blocking and absorbing branch is ∞: Z _{BSF_in} (θ ₁ )=Z _{BSF_in} (θ ₂ )=∞; effective transmission.

5. a kind of complementary duplex structure full-band absorption dual-band pass filter as claimed in claim 1, is characterized in that, the absorption process of described out-of-band signal is as follows:

First of all, the filter is at DC and even harmonics f=2nf ₀ (n=0,1,2,...), which is equivalent to grounding resistance R ₁ connected to the port, and the reflection coefficient of the circuit is as follows:

The absorption level of reflected energy at DC and even harmonics can be adjusted by adjusting the resistance value of resistor R ₁ ; when R1=50Ω, |S ₁₁ |=-∞, the dual-frequency filter is at DC and even harmonics. achieve ideal absorption;

Then, the filter is f=(2n+1)f ₀ (n=0, 1, 2, ...) at the center frequency and odd harmonics, and the dual-band-pass filter structure is equivalent to an open circuit, a step impedance open circuit branch, etc. The effect is an open circuit; the overall equivalent of the filter is a half _- wavelength microstrip line s2 whose characteristic impedance is Z2, _a quarter _- wavelength microstrip line s5 whose characteristic impedance is Z5, and grounding resistance R1 in series with the port, The reflection coefficient of the circuit is as follows:

When the resistance value _of the resistor R1 is determined, the absorption level of the reflected energy at the center frequency and odd harmonics is adjusted by adjusting the impedance value Z5 _; when R1=50Ω and Z5=50Ω, the dual _- frequency filter is at the center frequency and ideal absorption at odd harmonics.