CN207719373U - Bicyclic mode filter is coupled based on the cascade all-wave length of parallel coupled line head and the tail - Google Patents

Abstract

The utility model discloses a full-wavelength coupled double-ring filter based on parallel coupling lines cascaded at the head and tail. The double-ring filter is composed of two ring resonators cascaded at the head and tail. Two pairs of 3/4 guided wavelength parallel coupled lines and a pair of 1/4 guided wavelength parallel coupled lines form two head-to-tail cascaded coupling rings, and the left and right pairs of parallel coupled lines are respectively cascaded head-to-tail to the middle pair of parallel coupled lines Both ends of the line, so as to ensure that both ring resonators meet the full wavelength coupling. This filter structure can theoretically generate 8 transmission zeros outside the passband. Since the input and output adopt the form of source-load cross-coupling, an additional transmission zero can be generated, so in fact the filter structure generates 9 outside the band. transmission zero, effectively achieving high stop-band rejection. The overall circuit structure can realize a bandwidth of 21.2% and a wide stop band, the structure is simple, only a single-layer structure, the volume is small, and it is easy to integrate and use with other planar circuits.

Description

Full-wavelength coupled double loop filter based on head-to-tail cascade of parallel coupled lines

technical field

The utility model belongs to a microwave and millimeter wave hybrid planar integrated circuit, in particular to a full-wavelength coupled double-ring filter based on head-to-tail cascading of parallel coupling lines.

Background technique

In modern radio and mobile communication systems, microwave circuits are developing towards complexity and integration. At the same time, filters play a very important and essential role in them. Because the filters of the planar structure can use printed circuits Technology is used to manufacture, and its compact structure, small size and low-cost manufacturing are more suitable for commercial applications, so filters with this type of structure are favored by a wide range of researchers. In addition, the filter designed with parallel coupled line structure has the characteristics of simple structure design, small circuit size and high performance, so it has aroused the interest of extensive researchers. In recent years, more and more researchers have devoted themselves to the filter research of high selectivity and high stop-band rejection. However, the shortcomings of the existing designed loop filter structure are: (1) Although the out-of-band suppression is good, But the performance in the band is poor, the edge of the passband drops slowly, and the selectivity in the band is poor; (2) the passband of the filter is narrow; (3) the whole circuit structure is complex, the size is large, the design is cumbersome, and the out-of-band The inhibition is poor and incomplete.

Utility model content

In view of this, the embodiment of the present invention provides a full-wavelength coupled double-loop filter based on parallel coupled lines cascaded head-to-tail, which has a simple structure and a small volume, and improves stop-band suppression.

The embodiment of the utility model provides a full-wavelength coupled double-loop filter based on parallel coupling lines head-to-tail cascaded, including:

The first port, the second port, the first parallel coupled line (3), the second parallel coupled line (4), and the third parallel coupled line (5);

The first parallel coupled lines (3) include a first coupled microstrip line and a second coupled microstrip line;

The second parallel coupled lines (4) include third coupled microstrip lines and fourth coupled microstrip lines;

The third parallel coupled lines (5) include fifth coupled microstrip lines and sixth coupled microstrip lines;

The first coupled microstrip line is connected to the first port;

The sixth coupled microstrip line is connected to the second port;

The second coupled microstrip line and the third coupled microstrip line form a first closed loop;

The fourth coupled microstrip line and the fifth coupled microstrip line form a second closed loop.

Further, the lengths of the first parallel coupled lines and the third parallel coupled lines are both 3/4 of the guided wavelength; the length of the second parallel coupled lines is 1/4 of the guided wavelength.

Further, the width of the second coupled microstrip line and the fifth coupled microstrip line is smaller than the width of the third coupled microstrip line and the fourth coupled microstrip line.

Further, the first port and the second port are located on the same side.

Further, it also includes: a first meandering microstrip line and a second meandering microstrip line; the first port is connected to one end of the first coupling microstrip line through the first meandering microstrip line; the first The second port is connected to one end of the third coupled microstrip line through the second meandering microstrip line.

Further, the filter has a left-right symmetrical structure, and the center line of symmetry is the center line of the second parallel coupled lines.

Further, the first parallel coupling line is in the shape of an anti-bow; the third parallel coupling line is in the shape of a bow.

Further, the coupling gaps of the first parallel coupled lines and the third parallel coupled lines are both 0.15 mm, and the coupling gaps of the second parallel coupled lines are 0.42 mm.

Further, the dielectric constant of the dielectric substrate is 2.65, and the height of the dielectric substrate is 1mm.

Further, the widths of the first coupled microstrip line, the second coupled microstrip line, the fifth coupled microstrip line and the sixth coupled microstrip line are all 0.54mm, and the third coupled microstrip line and the fourth coupled microstrip line The coupled microstrip line width is 1.05mm.

The filter provided by the above embodiment is only composed of three parallel coupled lines, which is simple in structure and smaller in size compared with the traditional side-coupled double-loop resonator; compared with the traditional side-coupled double-loop resonator structure, the full-wave coupled double-loop resonator can produce More transmission zeros greatly improve the stop band suppression; the bandwidth and the position of transmission zeros can be easily changed by adjusting the length, width and coupling spacing of parallel coupled lines.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention , for those of ordinary skill in the art, other drawings can also be obtained according to these drawings on the premise of not paying creative labor.

Fig. 1 is a top view of a filter according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an ideal circuit model of a filter according to an embodiment of the present invention.

Fig. 3 is an ideal circuit frequency response diagram of the filter of the embodiment of the present invention.

Fig. 4(a) is a frequency response diagram of the filter according to the embodiment of the present invention under the condition that the coupling coefficient k1 changes.

Fig. 4(b) is a frequency response diagram of the filter according to the embodiment of the present invention when the coupling coefficient k2 changes.

Fig. 5 is a simulation curve diagram of the filter of the embodiment of the present invention.

Fig. 6 is a frequency response diagram of the filter according to the embodiment of the present invention under the condition that the input-output coupling length changes.

FIG. 7 is a frequency response diagram of the filter according to the embodiment of the present invention when the width of the second and fifth coupled microstrip lines varies.

Detailed ways

In order to make the purpose, technical solutions and advantages of the utility model clearer, the utility model will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the utility model, not all of them. the embodiment. Based on the embodiments of the present utility model, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

Fig. 1 is a schematic structural diagram of a full-wavelength coupled double loop filter based on head-to-tail cascading of parallel coupled lines provided by an embodiment of the present invention. In this embodiment, the filter includes: a first parallel coupled line 3, a second parallel coupled line 4, and a third parallel coupled line 5; the lengths of the first parallel coupled line and the third parallel coupled line are both 3/4 guided wave wavelength; the length of the second parallel coupled line is 1/4 of the waveguide wavelength.

The first parallel coupled line 3 includes a first coupled microstrip line and a second coupled microstrip line; the second parallel coupled line 4 includes a third coupled microstrip line and a fourth coupled microstrip line; the third parallel coupled line 5 includes a first coupled microstrip line The fifth coupled microstrip line and the sixth coupled microstrip line. The second coupled microstrip line and the third coupled microstrip line form a first closed loop; the fourth coupled microstrip line and the fifth coupled microstrip line form a second closed loop. The width of the second coupled microstrip line and the fifth coupled microstrip line is smaller than the width of the third coupled microstrip line and the fourth coupled microstrip line. The first parallel coupling line is anti-bow; the third parallel coupling line is bow.

The first port and the second port are on the same side. The first coupled microstrip line is connected to the first port; the sixth coupled microstrip line is connected to the second port; the first port is connected to one end of the first coupled microstrip line through the first meandering microstrip line; The two ports are connected to one end of the third coupling microstrip line through the second meandering microstrip line.

In Figure 1, three pairs of parallel coupled lines are cascaded with each other to form two full-wave coupled closed loops. By adjusting the width of the parallel coupled lines, the coupling gap, etc., the coupling coefficient of the parallel coupled lines can be changed, and the zero point can be easily adjusted. Location. The whole circuit has a left-right symmetrical structure, and the center line of symmetry is the center line of the second parallel coupling line, its size is 38mm*26.44mm*1mm, the dielectric constant of the dielectric substrate is 2.65, and the thickness is 1mm. In Fig. 1, the length of the microstrip lines 1 and 2 is 18 mm, and the width is 2.7 mm. The first coupled microstrip line, the second coupled microstrip line, and the third parallel coupled line 5 included The fifth coupled microstrip line and the sixth coupled microstrip line have a width of 0.54 mm, a coupling pitch of 0.15 mm, and a length of 78.3 mm. The third coupled microstrip line and the fourth coupled microstrip line included in the second parallel coupled line 4 The width of the coupled microstrip line is 1.05 mm, the coupling pitch is 0.42 mm, and the average length is 25.6 mm.

Fig. 2 is the ideal circuit diagram of the full-wavelength coupled double ring filter of the parallel coupled lines cascaded head to tail, wherein, θ represents the electrical length of the second parallel coupled lines, and Z _0e2 and Z _0o2 represent the parity mode of the second parallel coupled lines The electrical lengths of the first parallel coupled line 3 and the third parallel coupled line 5 are 3θ, and their odd and even mode characteristic impedances are Z _0e1 and Z _0o1 respectively. Using the impedance network matrix method to analyze the circuit, we can obtain the voltage and current conditions of each port: V ₂ ＝V ₅ , I ₂ ＝-I ₅ , V ₃ ＝V ₈ , I ₃ ＝-I ₈ , V ₆ ＝V ₉ , I ₆ =-I ₉ , V ₇ =V ₁₂ , I ₇ =-I ₁₂ , and I ₄ =I ₁₁ =0, [Z] ^a represents the first parallel coupling line 3 and the third parallel coupling line 5 Impedance matrix, [Z] ^b is defined as the impedance matrix of the first parallel coupled line 2. From this, we can calculate the impedance matrix of the entire ideal circuit as:

in

According to the relationship between the impedance matrix and the S parameter, we can get the expression of the transmission coefficient _S21 :

By setting S ₂₁ =0, we can obtain the expressions of 8 transmission zeros as follows:

f _tz1 =0 (10)

f _tz8 = 2f ₀ (17)

in,

F＝4Z _0e1 Z _0e2 +2Z _0e1 Z _0o1 +4Z _0e1 Z _0o2 +4Z _0e2 Z _0o1 +4Z _0e2 Z _0o2 +4Z _0o1 Z _0o2 (18)

Figure 3 shows the ADS simulation results of the ideal circuit model (Figure 2). The filter has eight transmission zeros outside the passband to suppress the stopband, which is exactly in line with the theoretical calculation results. Four of the eight transmission zeros (f _tz1 , f _tz3 , f _tz6 , f _tz8 ) are fixed at 0, 2f ₀ /3, 4f ₀ /3, 2f ₀ positions, while the other four transmission zeros ( f _tz2 , f _tz4 , f _tz5 , f _tz7 ) are related to the characteristic impedance (Z _0e1 , Z _0o1 , Z _0e2 , Z _0o2 ) of the three parallel coupled lines, and the expressions of the eight transmission zeros are shown in formula (10)- (20). Generally, we use k to represent the coupling coefficient of a coupled line, and its definition is: k=(Z _0e -Z _0o )/(Z _0e +Z _0o ), and Figure 4(a)-(b) respectively depict S ₂₁ Simulation results and the coupling coefficient k ₁ of the first parallel coupled line and the third parallel coupled line (k ₁ =(Z _0e1 -Z _0o1 )/(Z _0e1 +Z _0o1 )) and the coupling coefficient k of the second parallel coupled line ₂ (k ₂ =(Z _0e2 -Z _0o2 )/(Z _0e2 +Z _0o2 )). By solving the formula and ADS simulation results (Figure 4), it can be obtained that f _tz2 , f _tz4 , f _tz5 , f _tz7 are related to Z _0e1 , Z _0o1 , Z _0e2 , Z _0o2 , that is, they are related to k ₁ and k ₂ , so as k ₁ and k ₂ change, f _tz2 , f _tz4 , f _tz5 , and f _tz7 will shift, and the theory and ADS simulation diagram just meet, indicating that these four transmission zeros are controllable, while f _tz1 , f _tz3 , f _tz6 , f _tz8 do not change with the change of k ₁ and k ₂ . This conclusion can also be drawn from formulas (10)-(20). It can also be concluded from Figure 4(a)-(b) that the bandwidth of the passband is mainly determined by the coupling coefficient k ₁ of the first parallel coupled line and the third parallel coupled line, the larger the k ₁ , the wider the bandwidth; and the second The coupling coefficient k ₂ of the two parallel coupled lines mainly controls the suppression range of the transmission zero point, the smaller the k ₂ is, the higher the out-of-band suppression range is. Fig. 1 is the actual circuit diagram of the full-wavelength coupled double-loop filter cascaded at the head and tail of the parallel coupled lines. The source-load cross-coupling form is adopted at the input and output ends, which can generate an additional transmission zero point, so in fact the The filter structure can generate 9 transmission zeros outside the band, as shown in Figure 5, the actual circuit simulation curve of the full-wavelength coupled double-ring filter based on the parallel coupling line cascaded head-to-tail, the designed filter center frequency is 2.08GHz . Nine transmission zeros can be clearly seen in the figure, which verifies our theory, and this conclusion can also be reached if filters with other center frequencies are designed.

In Fig. 6, as a preferred embodiment provided by the utility model, when the electrical lengths of the first coupled microstrip line and the sixth coupled microstrip line of the filter are 3/4 waveguide wavelength, that is, the input and output ends When both are three-quarter wavelength coupled, there are as many as 9 out-of-band transmission zeros, which effectively improves the out-of-band suppression capability of the filter. And when the electrical lengths of the first coupled microstrip line and the sixth coupled microstrip line of the filter are both 1/4 waveguide wavelength, that is, when the input and output ends are both coupled with a quarter wavelength, the out-of-band transmission zero point will be significantly reduced, resulting in a significant deterioration of the out-of-band rejection of the filter. Obviously, the preferred embodiment provided by the utility model adopts two pairs of 3/4 waveguide wavelength parallel coupling lines and a pair of 1/4 waveguide wavelength parallel coupling lines to form a cascade ring, because the whole ring structure is composed of parallel coupling line stages The two loops meet the full-wave coupling, and the input and output terminals adopt the form of source-load cross-coupling, so some unnecessary resonance modes can be suppressed, and nine transmission zeros are generated, which greatly improves the impedance. with suppression.

In FIG. 7 , the widths of the second coupled microstrip line and the fifth coupled microstrip line are always kept equal, represented by W ₁ . When W ₁ is smaller than the width of the third coupled microstrip line and the fourth coupled microstrip line, as a preferred embodiment provided by the present invention, preferably, W ₁ =0.54mm, at the center frequency of 2.08GHz, through The band width is about 21.2%, and the filter square coefficient is good. And when W ₁ is greater than or equal to the width of the third coupled microstrip line and the fourth coupled microstrip line, for example, when W ₁ =1.05mm or 1.56mm, the bandwidth and squareness factor of the filter will deteriorate significantly, and even a notch will appear Case. Obviously, the preferred embodiment provided by the utility model adopts the stepped impedance design for the first closed loop and the second closed loop, which improves the passband characteristics of the filter and expands the bandwidth of the filter.

The above is the design method and specific example design of the full-wavelength coupled double loop filter cascaded head-to-tail with the parallel coupled lines, two pairs of 3/4 guided wavelength parallel coupled lines and a pair of 1/4 guided wavelength parallel coupled lines form Cascaded rings, since the entire ring structure is formed by cascading parallel coupled lines, both rings satisfy full-wave coupling, and the input and output terminals adopt the form of source-load cross-coupling, so some unwanted resonance modes can be Suppressed, resulting in 9 transmission zeros, greatly improving the stopband rejection. The 3dB bandwidth of the entire frequency band is about 21.2%, the suppression range of the upper stop band is better than 30dB, and the suppression range of the lower stop band is better than 20dB, which has very good stop band suppression. And the structure design of the entire working circuit is simple and more practical. Figure 5 shows the circuit simulation curve of the filter model at a center frequency of 2.08GHz. The circuit is shown in Figure 1, and its size is 38mm*26.44mm* 1mm, light weight.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present utility model, and are not intended to limit it; although the present utility model has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand : It can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements to some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the embodiments of the present utility model Scope of technical solutions.

Claims (10)

1. A full-wavelength coupled double-loop filter based on parallel coupled lines head-to-tail cascaded, comprising: a first port, a second port, a first parallel coupled line (3), a second parallel coupled line (4), a third Parallel coupled lines (5); The first parallel coupled lines (3) include a first coupled microstrip line and a second coupled microstrip line; The second parallel coupled lines (4) include third coupled microstrip lines and fourth coupled microstrip lines; The third parallel coupled lines (5) include fifth coupled microstrip lines and sixth coupled microstrip lines; The first coupled microstrip line is connected to the first port; The sixth coupled microstrip line is connected to the second port; It is characterized by: The second coupled microstrip line and the third coupled microstrip line form a first closed loop; The fourth coupled microstrip line and the fifth coupled microstrip line form a second closed loop. 2. The filter according to claim 1, characterized in that, the lengths of the first parallel coupling line (3) and the third parallel coupling line (5) are 3/4 waveguide wavelength; The length of the second parallel coupled line (4) is 1/4 of the waveguide wavelength. 3. The filter according to claim 1, wherein the width of the second coupled microstrip line and the fifth coupled microstrip line is smaller than that of the third coupled microstrip line and the fourth coupled microstrip line. The width of the microstrip line. 4. The filter according to claim 2, wherein the first port and the second port are located on the same side. 5. The filter according to claim 4, further comprising: a first meandering microstrip line (1), a second meandering microstrip line (2); The first port is connected to one end of the first coupling microstrip line through the first meandering microstrip line (1); The second port is connected to one end of the third coupling microstrip line through the second meandering microstrip line (2). 6. The filter according to any one of claims 1-5, characterized in that, the filter is a left-right symmetrical structure, and the center line of symmetry is the center line of the second parallel coupling line (4). 7. The filter according to claim 6, characterized in that, the first parallel coupling line (3) is in the shape of a reverse bow; the third parallel coupling line (5) is in the shape of a bow. 8. The filter according to claim 6, characterized in that, the coupling gaps of the first parallel coupling line (3) and the third parallel coupling line (5) are the same as 0.15mm, and the second The coupling gap of the parallel coupled lines (4) is 0.42 mm. 9. The filter according to claim 6, wherein the dielectric constant of the dielectric substrate is 2.65, and the height of the dielectric substrate is 1 mm. 10. The filter according to claim 6, wherein the widths of the first coupled microstrip line, the second coupled microstrip line, the fifth coupled microstrip line and the sixth coupled microstrip line are all 0.54 mm, the width of the third coupled microstrip line and the fourth coupled microstrip line is 1.05 mm.