CN116937093B - Broadband reflection-free band-pass filter - Google Patents

Abstract

The invention discloses a new type of broadband non-reflection bandpass filter, which belongs to the field of microwave technology. The filter includes a dielectric substrate, a metal floor provided on the lower layer of the dielectric substrate, a microstrip line structure provided on the upper layer of the dielectric substrate, and a metallized pass. holes and resistors. The upper microstrip line structure on the dielectric substrate includes two quarter-wavelength transmission lines as input and output terminals, a parallel coupling line between the input and output terminals as a bandpass branch, and two left and right structures connected to the input and output terminals. The same band-resistance branch includes a quarter-wavelength transmission line with an open-circuit parallel coupling line at the end of the parallel coupling line. The front end of the parallel coupling line is connected to a load resistor and is grounded through a metallized through hole. The invention realizes a broadband non-reflection bandpass filter with small return loss in the full passband, good absorption performance, large relative bandwidth, simple structure, easy implementation and low cost.

Description

A broadband non-reflection bandpass filter

Technical field

The invention belongs to the field of microwave technology, and in particular relates to a new type of broadband non-reflection bandpass filter.

Background technique

With the continuous development of wireless communication technology, mobile terminal equipment is improving towards the goals of miniaturization and high performance, and the microwave components that make up the terminal equipment require higher requirements. Filter is the basic component of RF microwave front-end part and one of the most important devices. Traditional filters reflect unwanted signals back to the input through the stopband. These signals reflected back to the input may adversely affect the performance of the entire system. Therefore, the non-reflection filter emerged as the times require. In the non-reflection filter, lossy filter components are used to absorb the stop-band signal and consume the stop-band signal inside the filter to avoid its impact on the system. However, the current reflection-free filter has a narrow bandwidth and low absorption of stop-band reflected signals, which cannot meet the rapid development of modern wireless communications.

Contents of the invention

The technical problem to be solved by the present invention is to propose a new type of broadband non-reflection bandpass filter, increase the bandwidth by cascading two bandstop branches and one bandpass branch, and add a metal floor to the bandstop branch structure. load resistor to absorb unwanted stopband signals. The non-reflection filter has a simple structure, a large working bandwidth, good absorption performance, and is easy to process. It has broad application prospects in radio frequency microwave systems.

The present invention adopts the following technical solutions to solve the above technical problems:

A new type of broadband non-reflection bandpass filter includes an upper microstrip line structure, a dielectric substrate and a lower metal floor arranged in sequence from top to bottom.

The microstrip line structure includes an input transmission line, an output transmission line, a first parallel coupling line, a second parallel coupling line, a third parallel coupling line, two quarter-wavelength transmission lines with open terminals, two load resistors, and two metallizations. through hole.

Further, the microstrip line structure includes a first band-resistance branch and a second band-resistance branch, and a third parallel coupling line serves as a band-pass branch of the filter and is provided between the input transmission line and the output transmission line to connect the input and output transmission lines. Two band-resistance branches with the same structure on the left and right.

The first band-resistance branch is a quarter-wavelength transmission line with an end of a first parallel coupling line connected to a first terminal open circuit, a starting end of a parallel line in the first parallel coupling line connected to one end of the input transmission line, and one of the first parallel coupling lines The starting end of the other parallel line is connected to one end of the first load resistor, and the other end of the first load resistor is connected to one end of the first metallized through hole. A cylinder is hollowed out in the middle of the first metallized through hole and surrounded by copper and metal. The floor is connected to the ground.

The second band-resistance branch is a quarter-wavelength transmission line with an end of a second parallel coupling line connected to an open circuit at the second terminal. The starting end of a parallel line in the second parallel coupling line is connected to one end of the output transmission line. The starting end of the other parallel line is connected to one end of the second load resistor, and the other end of the second load resistor is connected to one end of the second metallized through hole. A cylinder is hollowed out in the middle of the second metallized through hole and surrounded by copper and metal. The floor is connected to the ground.

Further, the length of the dielectric substrate is in the range of 55-60 mm, the width is in the range of 40-45 mm, and the height is in the range of 0.5-1.0 mm.

Further, the length of the metal floor is in the range of 55-60 mm and the width is in the range of 40-45 mm.

Furthermore, the impedance of the input transmission line and the output transmission line are both 50Ω, and are used as the input and output terminals of the filter to connect the filter to the SMA female head to facilitate testing.

Further, the length of the third parallel coupling line is in the range of 25-35 mm, the width is in the range of 0.3-0.6 mm, and the gap is in the range of 0.12-0.22 mm.

Further, the length of the first parallel coupling line and the second parallel coupling line is in the range of 25-35 mm, the width is in the range of 0.3-0.6 mm, and the gap is in the range of 1.5-2.5 mm.

Further, the length of the two open-terminated quarter-wavelength transmission lines is in the range of 25-35 mm, and the width is in the range of 1.5-2.5 mm.

Furthermore, the two load resistors serve as the band-stop branches of the filter, and their resistance values are both 59Ω.

Further, the diameter of the two metallized through holes is 1 mm; the microstrip line structure is connected to the metal floor under the dielectric substrate through the first metallized through hole and the second metallized through hole.

Further, the first band-resistance branch is connected to the upper end of the third parallel coupling line, and the second band-resistance branch is connected to the lower end of the third parallel coupling line. There is a gap and line width. In order to facilitate the connection, the first band-resistance branch is connected to the lower end of the third parallel coupling line. It is 0.67 mm higher than the second band-resistance branch in the y-axis direction.

The present invention adopts the above technical solution, and compared with the existing technology, its significant technical effects are as follows:

The present invention proposes a new type of broadband non-reflection bandpass filter. The passband bandwidth is 1.21-2.99 GHz, the relative bandwidth is 71.2%, and the return loss passband 0-5 GHz is lower than -15 dB, which fully simplifies the filter. The structure and manufacturing process are simple, the cost is low, the working bandwidth is large, and the absorption performance is good, and it meets the application requirements of the new generation of broadband mobile communications.

Description of the drawings

Figure 1 is a schematic three-dimensional structural diagram of the non-reflection bandpass filter of the present invention.

Figure 2 is a schematic top view of the structure of the non-reflection bandpass filter of the present invention.

Figure 3 is a schematic diagram of the circuit structure of the non-reflection bandpass filter of the present invention.

Figure 4 is a graph showing the change curve of the bandpass branch input impedance Z _in1 of the non-reflection bandpass filter of the present invention under different coupling coefficients k ₁₂ .

Figure 5 is a graph showing the change curve of the input impedance Z _in2 of the band-stop branch of the band-pass branch of the non-reflection band-pass filter of the present invention under different Z ₅ conditions.

Figure 6 is a graph showing the change curve of the bandpass branch input impedance Z _in2 of the non-reflection bandpass filter of the present invention under different coupling coefficients k ₃₄ .

Figure 7 is a variation curve of the input impedance Z _in after matching of the non-reflection bandpass filter of the present invention.

Figure 8 is an S11 parameter diagram calculated using HFSS software for the non-reflection bandpass filter in the embodiment of the present invention.

Figure 9 is an S21 parameter diagram calculated using HFSS software for the non-reflection bandpass filter in the embodiment of the present invention.

Figure 10 is a comparison chart of the physical processing test of the non-reflective bandpass filter in the embodiment of the present invention and the S11 and S21 parameters calculated using HFSS software.

Implementation

The present invention will be further described below in conjunction with the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present invention, but cannot be used to limit the scope of the present invention.

It can be understood by one of ordinary skill in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms such as those defined in general dictionaries are to be understood to have meanings consistent with their meaning in the context of the prior art, and are not to be taken in an idealized or overly formal sense unless defined as herein. explain.

The invention provides a new type of broadband non-reflection bandpass filter, as shown in Figures 1 and 2, including a microstrip line structure 1, a dielectric substrate 2 and a metal floor 3 arranged in sequence from top to bottom.

In this embodiment, the dielectric substrate 2 used is Rogers 5880, its dielectric constant is 2.2, the loss tangent is 0.0009, and the substrate thickness is 0.8 mm. The thickness of microstrip structure 1 and metal floor 3 is 0.0175 mm.

The microstrip line structure 1 includes an input transmission line 4, an output transmission line 4', a third parallel coupling line 5, a first parallel coupling line 6, a second parallel coupling line 6', a quarter-wavelength transmission line 7 with an open first terminal, The second open-ended quarter-wavelength transmission line 7', the first load resistor 8, the second load resistor 8', the first metallized through hole 9 and the second metallized through hole 9'.

The upper microstrip line structure 1 includes a first bandstop branch and a second bandstop branch. The third parallel coupling line 5 serves as the bandpass branch of the filter and is provided between the input transmission line 4 and the output transmission line 4'. The input and output transmission lines have two band-stop branches with the same structure on the left and right.

The first band-resistance branch is that the end of the first parallel coupling line 6 is connected to the quarter-wave transmission line 7 with an open first terminal, and the starting end of a parallel line in the first parallel coupling line 6 is connected to one end of the input transmission line 4. The first The starting end of another parallel line in the parallel coupling line 6 is connected to one end of the first load resistor 8, and the other end of the first load resistor 8 is connected to one end of the first metallized through hole 9. The first metallized through hole 9 is hollowed out in the middle. A cylinder is covered with copper on all sides and connected to the metal floor 3 for grounding.

The second band-resistance branch is that the end of the second parallel coupling line 6' is connected to the quarter-wavelength transmission line 7' with the second terminal open, and the starting end of a parallel line in the second parallel coupling line 6' is connected to the output transmission line 4'. One end, the starting end of the other parallel line in the second parallel coupling line 6' is connected to one end of the second load resistor 8', the other end of the second load resistor 8' is connected to one end of the second metallized through hole 9', the second metal The chemical through hole 9' is connected to the metal floor 3 by hollowing out a cylinder in the middle and surrounding it with copper for grounding.

The first band-resistance branch and the second band-resistance branch have the same structure but are asymmetrical. The first band-resistance branch is 0.67 mm higher than the second band-resistance branch in the y-axis direction.

The length of the input transmission line 4 and the output transmission line 4' are 27.3 mm, the width is 2.4 mm, and the impedance is 50Ω. They are used as the input and output terminals of the filter and are used to connect the filter to the SMA female head to facilitate testing.

The length of the third parallel coupling line 5 is in the range of 25-35 mm, the width is in the range of 0.3-0.6 mm, and the gap is 0.16 mm.

The length of the first parallel coupling line 6 and the second parallel coupling line 6' is in the range of 25-35 mm, the width is in the range of 0.3-0.6 mm, and the gap is 2.16 mm.

The first terminal open-circuited quarter-wavelength transmission line 7 and the second terminal open-circuited quarter-wavelength transmission line 7' have a length of 28.97 mm and a width of 1.53 mm.

The first load resistor 8 and the second load resistor 8' serve as the band-resistance branch of the filter, and their resistance values are both 59Ω.

The first metallized through hole 9 and the second metallized through hole 9' have a diameter of 1 mm; the microstrip line structure 1 is connected to the metal floor 3 through the first metallized through hole 9 and the second metallized through hole 9'.

As shown in the schematic diagram of the circuit structure in Figure 3, the port impedance Z ₀ =50Ω, and all electrical lengths θ =90°. The non-reflection bandpass filter can be divided into two parts, one is a bandpass branch composed of a section of parallel coupling transmission lines Z ₁ and Z ₂ , and the other is two left and right bandstop branches with identical structures. The band-resistance branch in Figure 3 is composed of a section of parallel coupling transmission lines Z ₃ and Z ₄ whose ends are connected in parallel to a quarter-wavelength transmission line Z ₅ with open terminals, and the other end is connected to an absorbing load resistor with an impedance of 59Ω that is grounded.

For the bandpass branch part, the input impedance Zin1 is determined by the coupling coefficient k ₁₂ between parallel coupling lines. Figure 4 shows the relationship between the coupling coefficient k ₁₂ of the parallel coupling lines and the input impedance Zin1 as the frequency changes. When When the coupling coefficient k ₁₂ is greater than -6.6 or less than -6.6, the out-of-band matching changes very little but the in-band matching becomes worse. Finally, the coupling coefficient k ₁₂ of the parallel coupling line is selected to be -6.6.

For the band-resistance branch part, the input impedance Zin2 is determined by the coupling coefficient k ₃₄ and the impedance Z ₅ between parallel coupling lines. Figure 5 shows the relationship between different impedances Z ₅ and the input impedance Zin2 as the frequency changes. It can be It can be seen that when Z ₅ is greater than 50Ω, the out-of-band matching becomes better but the in-band bandwidth becomes narrower. On the contrary, when Z ₅ is less than 50Ω, the out-of-band matching becomes worse but the bandwidth becomes wider. This determines the quarter wavelength of the terminal open circuit. The impedance Z ₅ of the transmission line is 50Ω. Under the condition of determining the impedance Z ₅ of the transmission line, Figure 6 shows the relationship between the coupling coefficient k ₃₄ of different parallel coupling lines and the input impedance Zin2 as a function of frequency. When the coupling coefficient k ₃₄ is greater than - When 21.5 or less than -21.5, the out-of-band matching changes very little but the in-band matching becomes worse. The coupling coefficient k ₃₄ of the parallel coupling line is finally selected to be -21.5.

Figure 7 shows the relationship between the overall input impedance Z _in and frequency changes after the band-pass branch and the band-resistance branch are connected in parallel. It can be seen that the input impedance Z _in fluctuates around 50Ω as the frequency changes, and the impedance matching is good.

Figure 8 is the return loss S11 of the non-reflection bandpass filter of this embodiment calculated using HFSS software. From the figure, it can be seen that the S11 passband of the present invention from 0 to 5 GHz is lower than -15 dB, and the passband bandwidth It is wider and the return loss within the band can be smaller, and the absorption performance is good, which meets the purpose of no reflection.

Figure 9 is the insertion loss S21 of the reflection-free bandpass filter of this embodiment calculated using HFSS software. It can be seen from the figure that the -3 dB passband bandwidth of the present invention is 1.21-2.99 GHz, and the relative bandwidth FBW=71.2% , which has a relatively large bandwidth and meets the design requirements of the filter.

Figure 10 shows the return loss and insertion loss of the non-reflective bandpass filter measured by a vector network analyzer after processing the actual object, and compared with the data calculated by the HFSS software. The -3 dB passband bandwidth of the actual object is 1.24-2.93 GHz, relative bandwidth FBW=67.6%, return loss S11 is lower than -11 dB in the pass frequency 0-5 GHz. It can be seen that the physical and simulation results are consistent. The error lies in processing loss and measurement error. Moreover, the vacuum medium is used in the simulation, but the air medium is actually used, which is within the error range.

To sum up, the new broadband non-reflection bandpass filter proposed by the present invention has simple manufacturing process, low cost, large operating bandwidth and good absorption performance, and can meet the application requirements of the new generation of broadband mobile communications.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above-mentioned embodiments are illustrative and should not be construed as limitations of the present invention. Those of ordinary skill in the art can carry out the above-mentioned implementations within the scope of the present invention. Examples include changes, modifications, substitutions and variations. Any other corresponding changes and modifications made based on the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (10)

1. A broadband non-reflection bandpass filter, including a microstrip line structure (1), a dielectric substrate (2) and a metal floor (3). The microstrip line structure (1) is located on the upper layer of the dielectric substrate (2). The floor (3) is provided on the lower layer of the dielectric substrate (2), and is characterized in that the microstrip line structure (1) includes an input transmission line (4), an output transmission line (4'), a third parallel coupling line (5), a first parallel Coupling line (6), second parallel coupling line (6'), first terminal open-circuited quarter-wavelength transmission line (7), second terminal open-circuited quarter-wavelength transmission line (7'), first load Resistor (8), second load resistor (8'), first metallized through hole (9) and second metallized through hole (9'); Among them, the microstrip line structure (1) includes a first band-stop branch and a second band-stop branch, and the third parallel coupling line (5) serves as the band-pass branch of the filter and is located on the input transmission line (4) and the output Between the transmission lines (4'), connect the two band-resistance branches with the same structure on the left and right of the input and output transmission lines; The first band-resistance branch is the end of the first parallel coupling line (6) connected to the quarter-wavelength transmission line (7) with the first terminal open circuit, and the starting end of a parallel line in the first parallel coupling line (6) is connected to the input One end of the transmission line (4) and the starting end of another parallel line in the first parallel coupling line (6) are connected to one end of the first load resistor (8), and the other end of the first load resistor (8) is connected to the first metallized through hole. At one end of (9), the first metallized through hole (9) is connected to the metal floor (3) by hollowing out a cylinder in the middle and surrounding it with copper for grounding; The second band-resistance branch is the end of the second parallel coupling line (6') connected to the quarter-wavelength transmission line (7') with the second terminal open circuit, and the starting end of a parallel line in the second parallel coupling line (6') Connect one end of the output transmission line (4'), the starting end of the other parallel line in the second parallel coupling line (6') is connected to one end of the second load resistor (8'), and the other end of the second load resistor (8') is connected One end of the second metallized through hole (9') is connected to the metal floor (3) by hollowing out a cylinder in the middle and surrounding it with copper for grounding. 2. The broadband non-reflection bandpass filter according to claim 1, characterized in that the first band-stop branch and the second band-stop branch have the same structure but are asymmetrical, and the first band-stop branch is in the y-axis direction. is 0.67 mm higher than the second band-resistance branch. 3. The broadband non-reflection bandpass filter according to claim 1, characterized in that the length of the dielectric substrate (2) is in the range of 55-60 mm, the width is in the range of 40-45 mm, and the height is in the range of 0.5-1.0 mm. within the range. 4. The broadband non-reflection bandpass filter according to claim 1, characterized in that the length of the metal floor (3) is in the range of 55-60 mm, and the width is in the range of 40-45 mm. 5. The broadband non-reflection bandpass filter according to claim 1, characterized in that both the input transmission line (4) and the output transmission line (4’) have an impedance of 50Ω. 6. The broadband non-reflection bandpass filter according to claim 1, characterized in that the length of the third parallel coupling line (5) is in the range of 25-35 mm, the width is in the range of 0.3-0.6 mm, and the gap is in the range of 0.12 -0.22 mm range. 7. The broadband non-reflection bandpass filter according to claim 1, characterized in that the length of the first parallel coupling line (6) and the second parallel coupling line (6') is in the range of 25-35 mm, and the width is in the range of 25-35 mm. Within the range of 0.3-0.6 mm, the gap is within the range of 1.5-2.5 mm. 8. The broadband non-reflection bandpass filter according to claim 1, characterized in that the quarter-wavelength transmission line (7) with an open circuit at the first terminal and the quarter-wavelength transmission line (7' with an open circuit at the second terminal) ) Length ranges from 25-35 mm, width ranges from 1.5-2.5 mm. 9. The broadband non-reflection bandpass filter according to claim 1, characterized in that the first load resistor (8) and the second load resistor (8') serve as the band-rejection branch of the filter, and their resistance values are equal. is 59Ω. 10. The broadband non-reflection bandpass filter according to claim 1, characterized in that the diameter of the first metallized through hole (9) and the second metallized through hole (9') is 1 mm; microstrip line structure (1) Connect to the metal floor (3) through the first metallized through hole (9) and the second metallized through hole (9').