CN109244608B - High-selectivity narrow-band reflection-free filter based on duplexer principle - Google Patents
High-selectivity narrow-band reflection-free filter based on duplexer principle Download PDFInfo
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- CN109244608B CN109244608B CN201811024166.1A CN201811024166A CN109244608B CN 109244608 B CN109244608 B CN 109244608B CN 201811024166 A CN201811024166 A CN 201811024166A CN 109244608 B CN109244608 B CN 109244608B
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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
- H01P1/20381—Special shape resonators
Abstract
The invention discloses a high-selectivity narrow-band reflection-free filter based on a duplexer principle, which comprises a single-passband band-pass filter, a double-passband band-pass filter, an input port of the reflection-free filter, a ground plane, a dielectric substrate, a metalized through hole, a chip resistor, an output port of the reflection-free filter and an output port of the double-passband band-pass filter; the reflection of the radio frequency signal of the filter is reduced as a design starting point, the duplexer is formed by utilizing a single-passband band-pass filter and a double-passband band-pass filter with continuous frequency bands according to the principle of the duplexer, and a 50 omega matching resistor is connected to an output port of the double-passband band-pass filter to realize the non-reflection filter. The invention has simple structure, easy processing, low cost and light weight, provides a new technical scheme for the design of the front end of a transceiver system of wireless communication, and expands the application of a microwave passive circuit.
Description
Technical Field
The invention relates to a non-reflection filter, in particular to a high-selectivity narrow-band non-reflection filter based on a duplexer principle.
Background
The filter is an essential microwave device in a wireless communication transceiving system. For a conventional band-pass filter, in order to achieve frequency selectivity, energy is reflected to different degrees, which brings a large number of unwanted nonlinear elements to the radio frequency front end, so that the amplifier operates in a nonlinear region, and intermodulation products in a conversion chain are increased. In order to reduce the reflection of the radio frequency signal, methods such as feedforward elimination, adding a passive circulator and an isolator can be used, but the size and the volume are sacrificed. Over the years, reflectionless filters are becoming a viable alternative.
The non-reflection filter is divided into two categories of band-stop and band-pass non-reflection filters, wherein the number of the non-reflection band-stop filters accounts for the vast majority, and the non-reflection band-stop filters can be divided into two forms of lumped elements and microstrip lines, so that the simple introduction is made: the lumped element type non-reflection band-stop filter is mainly formed by properly combining the acoustic wave resonators and the lumped elements, the reflection load is formed by N identical cascaded acoustic wave lumped element resonators and N static impedance inverters, and the band-stop bandwidth can be conveniently amplified by increasing the number of the acoustic wave lumped element resonators in the reflection load; a non-reflective band-stop filter in the form of a microstrip line utilizes the Kuroda rule, using open stubs of quarter and half wavelengths instead of lumped-element resonators. For the non-reflection band-pass filter, the implementation method is mainly divided into two categories: one approach is to implement a reflection-free bandpass filter from an all-pass network in a parallel cascade configuration, but requires that the transfer functions of two different all-pass filters remain symmetrical, and that a broadband coupler is used at the input to improve the stop-band bandwidth; another approach is based on the principle of transversal signal interference, however, the bandwidth of a non-reflective band-pass filter is constrained to a small range due to the limitations of the characteristic impedance design equation.
From the above, although the non-reflection band-pass filter has a good application prospect, no report about a high-selectivity narrow-band non-reflection filter is available.
Disclosure of Invention
The invention aims to provide a high-selectivity narrow-band reflection-free filter based on a duplexer principle, which can reduce the reflection of radio frequency signals in a certain frequency band.
The technical solution for realizing the purpose of the invention is as follows: a high-selectivity narrow-band reflection-free filter based on a duplexer principle comprises a single-passband band-pass filter, a double-passband band-pass filter, an input port of the reflection-free filter, a ground plane, a dielectric substrate, a metalized through hole, a chip resistor, an output port of the reflection-free filter and an output port of the double-passband band-pass filter;
the upper surface of the dielectric substrate is printed with a single-passband band-pass filter, a double-passband band-pass filter, an input port of a non-reflection filter, an output port of the non-reflection filter and an output port of the double-passband band-pass filter, and the lower surface of the dielectric substrate is printed with a layer of metal copper sheet as a ground plane of the microstrip line; the single-passband band-pass filter consists of a short-circuit stub, an open-circuit coupling line and first microstrip transmission lines, wherein the short-circuit stub and the open-circuit stub are connected to adjacent ports of the open-circuit coupling line for transmitting energy, and the adjacent two ports are respectively connected with an input port of the non-reflection filter and an output port of the non-reflection filter through two first microstrip transmission lines; the dual-passband band-pass filter adopts a T-shaped structure, two paths are provided for signals transmitted by the dual-passband band-pass filter, for the first path, two open-circuit coupling lines are connected to the centers of two second microstrip transmission lines, and the open-circuit stub is positioned at the centers of the two open-circuit coupling lines; for the second path, a short-circuit stub is connected to the center of the third microstrip transmission line, the output port of the dual-passband bandpass filter is connected with the grounding metalized through hole on the dielectric substrate through a chip resistor, the chip resistor is arranged on the upper surface of the dielectric substrate, and the single-passband bandpass filter and the dual-passband bandpass filter are connected together through the input port of the nonreflection filter.
Furthermore, the single-passband bandpass filter and the dual-passband bandpass filter both comprise grounding metalized through holes, and the number of the grounding metalized through holes is different due to the difference of line widths, wherein the output port of the dual-passband bandpass filter is connected with 9 grounding metalized through holes on the dielectric substrate through a chip resistor, the short stub is connected with 4 grounding metalized through holes on the dielectric substrate, and the short stub is connected with 2 grounding metalized through holes on the dielectric substrate.
Furthermore, the diameter of the metalized through holes is 0.4mm-0.6mm, the distance between the metalized through holes is 0.3mm-0.5mm, and the distance between the metalized through holes and the edge is 0.1mm-0.2 mm.
Further, the characteristic impedance of the first microstrip transmission line is 65 Ω, the characteristic impedance of the second microstrip transmission line is 153 Ω, and the characteristic impedance of the third microstrip transmission line is 50 Ω.
The dielectric substrate has a dielectric constant of 2.2, 2.23, 2.55 or 2.65.
The thickness of the dielectric substrate is 0.5mm, 0.8mm, 1.0mm or 1.5 mm.
The medium substrate is made of domestic polytetrafluoroethylene, the dielectric constant of the medium substrate is 2.65, and the thickness of the medium substrate is 1.0mm
Compared with the prior art, the invention has the following remarkable advantages: (1) the design method of the high-selectivity narrow-band reflection-free filter based on the duplexer principle is simple and flexible; (2) the high-selectivity narrow-band reflection-free filter based on the duplexer principle can realize wide-range bandwidth change; (3) the high-selectivity narrow-band reflection-free filter based on the duplexer principle can increase the number of transmission zeros.
The present invention is described in further detail below with reference to the attached drawing figures.
Drawings
Fig. 1 is a schematic diagram of the operation of the high selectivity narrowband reflectionless filter based on the duplexer principle of the present invention.
Fig. 2 is a top view of a highly selective narrow band reflectionless filter based on the duplexer principle.
Fig. 3 is a bottom view of a highly selective narrow band reflectionless filter based on the duplexer principle.
Fig. 4 is a comparison graph of simulation and test S parameter characteristics of a high selectivity narrow band reflectionless filter based on the duplexer principle.
Fig. 5 is a comparison graph of simulated and tested group delay characteristics of a highly selective narrowband reflectionless filter based on the duplexer principle.
Detailed Description
The working principle of the high-selectivity narrow-band reflection-free filter based on the duplexer principle is shown in figure 1, and the high-selectivity narrow-band reflection-free filter comprises a single-passband band-pass filter 1, a double-passband band-pass filter 2, an input port 3 of the reflection-free filter, a ground plane 4, a dielectric substrate 5, a metalized through hole 6, a chip resistor 7, an output port 8 of the reflection-free filter and an output port 9 of the double-passband band-pass filter. The single-passband band-pass filter and the double-passband band-pass filter with continuous frequency bands are connected together through an input port 3 of the non-reflection filter, and when the single-passband band-pass filter works, the double-passband band-pass filter is positioned at a stop band; when the dual-passband band-pass filter works, the single-passband band-pass filter is positioned in a stop band, and a duplexer is formed. And the output port of the dual-passband band-pass filter is connected with a ground patch resistor of 50 omega, so that the energy transmitted to the dual-passband band-pass filter from the input port is absorbed by the ground patch resistor of 50 omega and cannot be reflected, and the dual-passband band-pass filter becomes a non-reflection filter. To design a high-selectivity non-reflection narrow-band-pass filter, a corresponding single-frequency-band high-selectivity narrow-band-pass filter is needed. Compared with other single-passband bandpass filters, the bandpass filter formed by the open/short circuit double resonators has the advantages of good selectivity and simple structure, so the single-passband bandpass filter is selected in the invention, and the short circuit stub, the open circuit stub and the open circuit coupling line in the open/short circuit double resonators can be properly folded in order to reduce the circuit area. The double-passband band-pass filter with the T-shaped structure is used, the passband bandwidth of the double-passband band-pass filter can be adjusted by the coupling coefficient of the open-circuit coupling line, and the double-passband band-pass filter and the single-passband band-pass filter can conveniently form a duplexer.
With reference to fig. 2 and fig. 3, the high-selectivity narrow-band reflectionless filter based on the duplexer principle of the present invention includes a single-passband bandpass filter 1, a dual-passband bandpass filter 2, an input port 3 of the reflectionless filter, a ground plane 4, a dielectric substrate 5, a metalized through hole 6, a chip resistor 7, an output port 8 of the reflectionless filter, and an output port 9 of the dual-passband bandpass filter.
The upper surface of a dielectric substrate 5 is printed with a single-passband band-pass filter 1, a double-passband band-pass filter 2, an input port 3 without a reflection filter, an output port 8 without a reflection filter and an output port 9 without a double-passband band-pass filter, the lower surface of the dielectric substrate is printed with a layer of metal copper sheet as a ground plane 4 of a microstrip line, the single-passband band-pass filter 1 consists of a short-circuit stub 1-1, an open-circuit stub 1-2, an open-circuit coupling line 1-3 and a first microstrip transmission line 1-4 with characteristic impedance of 65 omega, the short-circuit stub 1-1 and the open-circuit stub 1-2 are connected with adjacent ports of the open-circuit coupling line 1-3 for transmitting energy, and the adjacent ports are respectively connected with the input port 3 without a reflection filter through the two first microstrip transmission lines 1-4 with characteristic impedance of, The output port 8 of the non-reflection filter is connected; the dual-passband band-pass filter 2 adopts a T-shaped structure, two paths are provided for signals when the dual-passband band-pass filter 2 transmits, for the first path, two open-circuit coupled lines 2-1 are connected at the centers of two second microstrip transmission lines 2-4 having characteristic impedance of 153 Ω, an open-circuit stub 2-2 is located at the center of the two open-circuit coupled lines 2-1, for the second path, a short stub 2-3 is connected in the center of a third microstrip transmission line 2-5 having a characteristic impedance of 50 Ω, the output port 9 of the dual bandpass filter is connected to a ground metallized via 6 on a dielectric substrate 5 through a chip resistor 7, the chip resistor 7 is also arranged on the upper surface of the dielectric substrate 5, and the single-passband band-pass filter 1 and the double-passband band-pass filter 2 are connected together through the input port 3 of the nonreflective filter.
The single-passband band-pass filter and the double-passband band-pass filter both comprise grounding metallized through holes, the number of the grounding metallized through holes is different due to the difference of line widths, the diameter of each metallized through hole is 0.4mm-0.6mm, the distance between every two metallized through holes is 0.3mm-0.5mm, and the distance between every two metallized through holes and the side is 0.1mm-0.2 mm.
The dielectric substrate has a dielectric constant of 2.2, 2.23, 2.55 or 2.65. The thickness of the dielectric substrate is 0.5mm, 0.8mm, 1.0mm or 1.5 mm.
Preferably, the dielectric substrate is made of domestic polytetrafluoroethylene, the dielectric constant of the dielectric substrate is 2.65, and the thickness of the dielectric substrate is 1.0 mm.
Specifically, the invention is a single-layer PCB structure, the upper and lower surfaces of the dielectric substrate 5 are metal copper sheets, wherein the upper surface is a microstrip line structure, and the lower surface is a metal ground. The single-passband band-pass filter 1 and the dual-passband band-pass filter 2 are connected through an input port 3 of a non-reflection filter, short circuit stubs 1-1 in the single-passband band-pass filter 1 are provided with 2 metalized through holes, short circuit stubs 2-3 in the dual-passband band-pass filter 2 are provided with 4 metalized through holes, 9 metalized through holes are connected with a chip resistor 7 in a grounding mode, and 15 metalized through holes 6 are used for connecting an upper copper sheet and a lower copper sheet. The output port 9 of the dual-passband band-pass filter is loaded with a chip resistor 7, and the other end of the chip resistor 7 is grounded.
A dielectric constant ε of the dielectric substrate 5r2.65, and 1mm in thickness. The dielectric constant can be selected from the range of 2.2-2.65, and the thickness can be selected from the range of 0.5mm-1.5 mm.
The high-selectivity narrow-band non-reflection filter based on the duplexer principle keeps a distance of 10mm from the upper side to the lower side, and the input end and the output end of the high-selectivity narrow-band non-reflection filter are 50 omega microstrip lines.
The present invention will be described in detail with reference to examples.
Examples
The size of the complete circuit board is 92.62mm multiplied by 60.02 mm; the line width of the 50 omega microstrip line of the input end and the output end is 2.72mm, the input end and the output end are welded SMA joints, and the line length of the 50 omega microstrip line is 10 mm. In order to avoid coupling between the single-passband bandpass filter and the dual-passband bandpass filter as much as possible, the distance between the upper and lower sides of the two-passband bandpass filter is 4.09 mm. The discontinuity of the microstrip line can be caused by the bending of the microstrip line, in order to reduce the parallel capacitance effect of the corner, the corner cut processing is adopted, the corner cut is an isosceles right triangle, and the length of the right-angle side of the triangle is consistent with the line width of the microstrip line where the corner cut is located. The microstrip line and the coupling line in the single-passband bandpass filter are not chamfered, wherein the line width of the open-circuit stub is 1.78mm, the length of the transverse microstrip line after bending is 16.58mm, the length of the longitudinal microstrip line is 6.34mm, the line width of the short-circuit stub is also 1.78mm, the length of the bus is 44.1mm, the line width of the open-circuit coupling line is 0.44mm, the gap is 0.35mm, and the length of the bus is 32.4 mm. The corner of a microstrip transmission line with the line widths of 2.72mm and 3.53mm in the dual-passband bandpass filter is subjected to corner cutting treatment, the line width of an open-circuit coupling line in the dual-passband bandpass filter is 0.67mm, a gap is 0.21mm, the microstrip transmission line is in a range which can be processed by a processing technology, the line length of the open-circuit coupling line is 25.75mm, in order to achieve the characteristic of no reflection, a chip resistor is loaded on an output port of the dual-passband bandpass filter, the packaging type is 0402, and the resistance is 49.9 omega. Fifteen metallized through holes have a radius of 0.3mm and a height of 1 mm.
The bandwidth of the filter of the embodiment meets the design requirement, and the bending of the plate in the test process can cause that the matching of partial frequency points is not good. As shown in fig. 4, the center frequency of the pass band in the test results was slightly shifted to a higher frequency than the simulation results, within an acceptable range. The additional pass band group delay tested is shown in fig. 5, although again somewhat shifted in frequency, but the test is very close to the simulation results.
The following describes the preparation process of the high-selectivity narrow-band reflectionless filter based on the duplexer principle of the present invention in detail.
(1) First, the center frequency of the reflectionless filter and the parameters of the dielectric substrate, mainly the dielectric constant and the thickness, are determined. The thickness is typically selected to be between 0.5mm and 1.6mm based on considerations of the size and overall weight of the PCB board.
(2) The center frequency and bandwidth are determined by the index of the reflection-free band-pass filter.
(3) The single-passband band-pass filter and the double-passband band-pass filter are placed at a proper distance, when the distance between the two filters is reduced, unnecessary coupling can be generated, and continuous debugging is needed in the simulation process.
(4) And (4) selecting the length of the bent microstrip transmission line from the input port to the dual-channel band-pass filter to be a proper value according to the requirement of keeping a proper distance between the two filters in the step (3).
(5) The distance between the output port of the dual-channel band-pass filter and the grounding metalized through hole has great influence on the reflection-free band-pass filter, and the size of the actually processed chip resistor is also required to be considered so as to facilitate welding.
(6) The duplexer can be designed in the design process, the output port of the dual-passband band-pass filter is connected with a ground patch resistor of 50 omega according to the parameters of the duplexer, and then the determined circuit parameters are finely adjusted to obtain the optimal reflection-free filtering effect.
Based on the duplexer principle, the output port of the dual-passband band-pass filter is connected with a ground patch resistor of 50 omega, so that energy transmitted to the dual-passband band-pass filter is absorbed by the ground patch resistor and is not reflected any more, and no reflected signal can be generated in a certain frequency band to cause adverse effects on other devices in the wireless communication transceiving system. The insertion loss of the non-reflection band-pass filter at the central frequency of 2GHz is 1.43dB, the relative bandwidth of the passband is 8.5%, and S11 is lower than-10 dB in the frequency band range of 1.33GHz-2.81GHz, so that the non-reflection band-pass filter has good non-reflection filtering characteristics.
Claims (8)
1. A high-selectivity narrow-band reflection-free filter based on a duplexer principle is characterized by comprising a single-passband band-pass filter (1), a double-passband band-pass filter (2), an input port (3) of the reflection-free filter, a ground plane (4), a dielectric substrate (5), a metalized through hole (6), a chip resistor (7), an output port (8) of the reflection-free filter and an output port (9) of the double-passband band-pass filter;
the upper surface of a dielectric substrate (5) is printed with a single-passband band-pass filter (1), a double-passband band-pass filter (2), an input port (3) of a non-reflection filter, an output port (8) of the non-reflection filter and an output port (9) of the double-passband band-pass filter, and the lower surface of the dielectric substrate is printed with a layer of metal copper sheet as a ground plane (4) of a microstrip line; the single-passband bandpass filter (1) consists of a short-circuit stub (1-1), an open-circuit stub (1-2), an open-circuit coupling line (1-3) and a first microstrip transmission line (1-4), wherein the short-circuit stub (1-1) and the open-circuit stub (1-2) are connected to adjacent ports of the open-circuit coupling line (1-3) for transmitting energy, and two adjacent ports of the open-circuit coupling line (1-3) are respectively connected with an input port (3) of a non-reflective filter and an output port (8) of the non-reflective filter through the two first microstrip transmission lines (1-4); the dual-passband band-pass filter (2) adopts a T-shaped structure, two paths are provided for signals transmitted by the dual-passband band-pass filter (2), for the first path, two open-circuit coupling lines (2-1) are connected to the tail ends of two second microstrip transmission lines (2-4), and the open-circuit stub (2-2) is positioned at the center of the two open-circuit coupling lines (2-1); for the second path, a short-circuit stub (2-3) is connected to the center of the third microstrip transmission line (2-5), an output port (9) of the dual-passband band-pass filter is connected with a grounding metalized through hole (6) on the dielectric substrate (5) through a patch resistor (7), the patch resistor (7) is arranged on the upper surface of the dielectric substrate (5), and the single-passband band-pass filter (1) and the dual-passband band-pass filter (2) are connected together through an input port (3) of the nonreflecting filter.
2. The high selectivity narrow band reflectionless filter based on duplexer principle as claimed in claim 1, wherein the single-bandpass filter (1) and the dual-bandpass filter (2) each contain a ground-metalized via, and the number of the ground-metalized vias is different due to the difference of the line widths, wherein the output port (9) of the dual-bandpass filter is connected to 9 ground-metalized vias on the dielectric substrate (5) through a chip resistor (7), the short stub (2-3) is connected to 4 ground-metalized vias on the dielectric substrate (5), and the short stub (1-1) is connected to 2 ground-metalized vias on the dielectric substrate (5).
3. A highly selective narrow band reflectionless filter according to the duplexer principle, according to claim 2, wherein the diameter of the metallized through holes (6) is 0.4mm-0.6mm, the pitch of the metallized through holes (6) is 0.3mm-0.5mm, and the distance of the metallized through holes (6) from the sides is 0.1mm-0.2 mm.
4. A highly selective narrow-band reflectionless filter according to the duplexer principle, according to claim 1, wherein the first microstrip transmission line (1-4) has a characteristic impedance of 65 Ω.
5. A highly selective narrow-band reflectionless filter according to the duplexer principle, according to claim 1, wherein the characteristic impedance of the second microstrip transmission line (2-4) is 153 Ω.
6. A highly selective narrow-band reflectionless filter according to the duplexer principle, according to claim 1, wherein the third microstrip transmission line (2-5) has a characteristic impedance of 50 Ω.
7. A highly selective narrow band reflectionless filter according to the duplexer principle, according to claim 1, 2 or 3, wherein the dielectric substrate (5) has a dielectric constant of 2.2, 2.23, 2.55 or 2.65.
8. A highly selective narrow band reflectionless filter according to the duplexer principle, according to claim 7, wherein the dielectric substrate (5) has a thickness of 0.5mm, 0.8mm, 1.0mm or 1.5 mm.
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| CN103928732A (en) * | 2014-05-07 | 2014-07-16 | 电子科技大学 | Micro-strip line absorption band-pass filter |
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