KR102054503B1 - Band pass filter and design method thereof - Google Patents

Abstract

The present invention relates to a bandpass filter for improving the reliability of a circuit, and a design method thereof. The bandpass filter comprises a signal line formed on an upper surface of a dielectric and first and second stepped impedance coplanar waveguide transmission lines disposed to face each other in a direction of the signal line on a ground surface formed at a lower surface of the dielectric. The first and second stepped impedance coplanar waveguide transmission lines include multiple coplanar waveguide transmission lines with different impedance. The bandpass filter may be designed by using a coplanar waveguide transmission line structure with multi-step impedance on the ground surface in a structure using a defected ground structure.

Description

BAND PASS FILTER AND DESIGN METHOD THEREOF

The present invention relates to a bandpass filter, and more particularly, to a bandpass filter in which a coplanar waveguide having a multi-stage impedance is inserted into a ground plane of a microstrip transmission line and a design method thereof.

A typical transmission line structure that is widely used to implement circuits or components for radio frequency (RF) and microwave bands is a microstrip transmission line.

The microstrip transmission line, also called a microstrip line, refers to a distributed constant line composed of a set of conductive thin films on both sides with a dielectric substrate interposed therebetween.

The upper conductor of such a microstrip transmission line has a specified shape (strip shape), and the lower conductor (ground plane) is formed of a wide ground conductor, and has a vertically symmetrical structure in which a dielectric is placed on the upper conductor again.

As a filter using a stepped impedance resonators (SIR) according to the prior art, the flat type in the form of a printed circuit is dominant.

The SIR is a resonator which transmits a signal in a specific frequency region by the impedance ratio and length of a microstrip line which changes in stages, and blocks other frequency components.

The planar staged impedance resonator of the printed circuit is mainly in the form of a strip line, a microstrip line, and a coplanar waveguide (CPW) structure.

Among them, the filter using the strip line and the microstrip line combines the resonant period coupling structure by parallel coupling lines using three stages of SIR, and mainly results from a frequency band below 10 GHz.

The filter using the CPW combines the resonance period coupling structure using the gap and the ground structure by using the two-stage SIR, and has a result of a frequency band of 30 GHz or less.

Republic of Korea Patent Registration No. 10-0576773 (announced May 8, 2006) Republic of Korea Patent Registration No. 10-1144565 (announced May 11, 2012)

 "MODELING STEPPED U-SLOT DGS MICROSTRIP LINE", 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58: 583-587, 2016; View this article online at wileyonlinelibrary.com. DOI 10.1002 / mop.29626

On the other hand, the present inventor has proposed a new equivalent circuit model of a microstrip line having a stepped U-slot Defected Ground Structures (DGS) through the above Non-Patent Document 1.

Defected Ground Structures (DGS) etch certain shapes on the ground plane of a microstrip transmission line or CPW transmission line to provide additional inductance and capacitance components on the transmission line, exhibiting resonance characteristics at specific frequencies. Such resonator characteristics have been applied to the performance improvement of filter, oscillator and various microwave circuits.

In addition, the DGS is widely used for miniaturization of ultra-high frequency circuits by greatly improving the propagation delay effect of transmission lines, and with the exponential development of wireless communication systems, miniaturization, weight reduction, and multifunction of circuits operating in the microwave and millimeter wave bands. It has contributed greatly to the improvement of performance, etc., and active research is ongoing.

Non-Patent Document 1 describes a method of simply modeling a defect structure in the equivalent circuit model by a gap capacitor and a short-circuited stepwise impedance CPW.

In Non-Patent Document 1, the coupling between the etching pattern of the ground plane and the microstrip line occupied by DGS is modeled by an ideal transformer, and the normalized first simulated resonant frequency of 4 and 2 (η = f _s1 / f _r ). Two types of resonators were demonstrated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a bandpass filter and a design method in which a coplanar waveguide structure having a multi-level impedance is applied to a ground plane using a defect grounding structure. .

Another object of the present invention is to provide a bandpass filter and a method for designing the same, by adjusting the impedance of two coplanar waveguides inserted into the ground plane to adjust the ratio of the resonance frequency.

It is another object of the present invention to improve the reliability of the circuit by not passing important harmonic components, and to provide a band pass filter and a design method thereof, which enables the construction of other circuits on the plane where the signal line is located, thereby improving space efficiency. will be.

In order to achieve the object as described above, the bandpass filter according to the present invention symmetrically arranged a plurality of stepwise impedance coplanar waveguide transmission lines comprising a plurality of coplanar waveguide transmission lines having different impedances on the ground plane. Characterized in that the configuration.

In order to achieve the object as described above, the band pass filter according to the present invention is a signal line formed on the upper surface of the dielectric and a first surface disposed to face each other in the direction of the signal line on the ground surface formed on the lower surface of the dielectric And a second staged impedance coplanar waveguide transmission line, wherein the first and second staged impedance coplanar waveguide transmission lines include a plurality of coplanar waveguide transmission lines having different impedances.

In addition, in order to achieve the object as described above, the bandpass filter design method according to the present invention includes a plurality of stepwise impedance coplanar waveguide transmission line including a plurality of coplanar waveguide transmission lines having different impedances on the ground plane. Are arranged symmetrically with each other to design a bandpass filter.

In addition, in order to achieve the above object, the method of designing a bandpass filter according to the present invention comprises the steps of (a) forming a signal line on the upper surface of the dielectric and (b) the signal line on the ground plane formed on the lower surface of the dielectric Arranging first and second stepped impedance coplanar waveguide transmission lines to face each other along a direction of the first and second stepped impedance coplanar waveguide transmission lines, wherein the first and second stepped impedance coplanar waveguide transmission lines have a plurality of coplanar waves having different impedances. And a waveguide transmission line.

As described above, according to the bandpass filter and the design method thereof according to the present invention, a bandpass filter can be designed by using a coplanar waveguide transmission line structure having a multi-stage impedance on the ground plane in a structure using a fault ground structure. Effect is obtained.

According to the present invention, there is provided a bandpass filter and a method of designing the same, by adjusting the impedance of two coplanar waveguides inserted into the ground plane to adjust the ratio of the resonance frequency.

That is, according to the present invention, by controlling the ratio of the first resonant frequency and the second resonant frequency by adjusting the CPW impedance of the multi-stage inserted into the ground plane, the second resonant frequency band than the first, second, third harmonics that become the noise of the circuit The effect is that it can be designed to occur in high bands.

In addition, according to the present invention, it is possible to improve the reliability of the circuit by not passing important harmonic components, and to enable the construction of other circuits on the plane where the signal line is located, thereby increasing the space efficiency.

1 and 2 is a view showing the structure of the coplanar waveguide transmission line,
3 and 4 are graphs measuring the characteristic impedance of the coplanar waveguide transmission line according to the width of the signal line and the distance between the signal line and the ground plane shown in FIGS.
5 to 7 are a plan view, a bottom view and a side view showing the CPW configuration respectively located on the ground plane;
8 is a view showing an equivalent circuit model of the CPW shown in FIGS.
9 is a graph measuring a simulation result of CPW shown in FIGS. 5 to 7;
10 and 11 are a plan view and a bottom view showing the configuration of the ground plane stepped impedance CPW, respectively;
12 is a view showing an equivalent circuit model of the CPW shown in FIGS. 10 and 11;
14 and 15 are a plan view and a bottom view of a bandpass filter according to a preferred embodiment of the present invention,
FIG. 16 is a diagram showing an equivalent circuit model of the bandpass filter shown in FIGS. 14 and 15;
17 and 18 are diagrams illustrating a simulation model of the bandpass filter shown in FIGS. 14 and 15;
19 is a graph of a characteristic measurement result using the simulation model illustrated in FIGS. 17 and 18.

Hereinafter, a bandpass filter and a design method thereof according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Hereinafter, terms indicating directions such as 'left', 'right', 'front', 'backward', 'upward' and 'downward' are defined as indicating respective directions based on the states shown in each drawing. do.

1 and 2 are views showing the structure of the coplanar waveguide transmission line, and FIGS. 3 and 4 are views of the coplanar waveguide transmission line according to the width of the signal line and the distance between the signal line and the ground plane shown in FIGS. 1 and 2. It is a graph measuring characteristic impedance.

FIG. 1 shows a side view of a dielectric to which a coplanar waveguide transmission line is applied, and FIG. 2 shows a plan view of the dielectric shown in FIG.

3 is a graph measuring characteristic impedance of a coplanar waveguide transmission line according to the width of the signal line in a state where the distance between the signal line and the ground plane is fixed, and FIG. 4 shows a signal line and a signal line in a state where the width of the signal line is fixed. A graph measuring the characteristic impedance of a coplanar waveguide transmission line with spacing between ground planes is shown.

The coplanar waveguide transmission line (hereinafter referred to as 'CPW') is a metal conductor layer 11 formed on the upper surface of the dielectric 10 as shown in FIGS. 1 and 2. The signal line 12 is etched and formed in the center portion, and a pair of ground planes 13 may be formed on both sides of the signal line 12, for example, in the upper and lower sides as shown in FIG. 2.

In this CPW structure, when the width s of the signal line 12 is adjusted in a state where the interval s of the gap between the signal line 12 and the ground plane 13 is fixed at 0.6 mm, as shown in FIG. 3. As the width w of the signal line 12 increases, the characteristic impedance of the CPW decreases.

On the other hand, when the distance s between the signal line 12 and the ground plane 13 is adjusted in a state where the width w of the signal line 12 is fixed to 0.6 mm, the signal line 12 and It can be seen that the characteristic impedance of the CPW increases as the spacing between the ground planes 13 increases.

Next, the CPW configuration located on the ground plane will be described with reference to FIGS. 5 to 9.

5 to 7 are a plan view, a bottom view and a side view showing a CPW configuration respectively located on the ground plane. 8 is a diagram illustrating an equivalent circuit model of the CPW illustrated in FIGS. 5 to 7, and FIG. 9 is a graph measuring simulation results of the CPW illustrated in FIGS. 5 to 7.

As shown in FIGS. 5 to 7, the CPW 20 etches the ground plane 13 provided on the bottom surface of the dielectric 10 in a state where the signal line 11 is formed on the top surface of the dielectric 10. It may be formed in a 'U' shape along the direction.

That is, the CPW 20 may include a pair of straight portions parallel to each other and a connection portion connecting one end of the pair of straight portions.

As such the equivalent circuit model of a CPW (20) are shown in Figure 8, the characteristic impedance of the capacitor _{(C gap), CPW (20} ) corresponding to the gap capacitance (gap_cpw) to the function of the link portion and the length (θ _cpw CPW 20 with = βl), and a transformer 21 representing the coupling of circuitry and signal lines 11 configured at ground plane 13.

Here, the dielectric constant ε _r of the dielectric 10 may be about 10.2, and the thickness of the dielectric 10 may be set to about 1.27 mm.

In the CPW 20 having such a configuration, the distance s between grounds is set to 0.2 mm, the width w of the line is set to 1.2 mm, and the length l of the line is set to 12 mm to simulate. One result is shown in FIG.

In FIG. 9, it can be seen that the first resonance frequency f ₀ is about 2.5 Hz, and the second resonance frequency f _s1 is 7.5 Hz, which is three times the first resonance frequency f ₀ .

Next, the ground plane stepped impedance CPW configuration will be described in detail with reference to FIGS. 10 to 12.

10 and 11 are a plan view and a bottom view of the ground plane stepped impedance CPW, respectively, and FIG. 12 is a view showing an equivalent circuit model of the CPW shown in FIGS. 10 and 11.

As shown in FIGS. 10 and 11, the signal line 12 is etched on the upper surface of the dielectric 10, and the traveling direction of the signal line 12 is provided on the ground surface 13 provided on the lower surface of the dielectric 10. Accordingly, the stepwise impedance coplanar waveguide transmission line 30 to which two CPWs cpw1 and cpw2 having different impedances are applied is formed by etching.

As shown in FIGS. 11 and 12, the equivalent circuit model of the stepped impedance CPW 30 includes the capacitor C _gap corresponding to the gap capacitance gap_cpw, the characteristic impedance and the length of each CPW (cpw1, cpw2). _{cpw1 θ,,} θ _cpw2) having a first and a 2 CPW (31,32), and may include a transformer (transformer), (33) represents a combination of circuit and signal line 11 are configured on the ground plane 13, the have.

The admittance Y _in of the equivalent circuit may be defined as in Equation 1 below.

[Equation 1]

Since the resonance condition is admittance (Y _in ) = 0, it can be summarized as in Equation 2 below.

[Equation 2]

Where c is the speed of light, ε _e1 and ε _e2 are the effective dielectric constants of the first and second _CPWs , respectively, and Z _cpw1 and Z _cpw2 represent the characteristic impedances of the first and second _CPWs , respectively.

The above ε _e1 , ε _e2 , Z _cpw1 , Z _cpw2 , C _gap values are 'Gupta, KC, R. Garg, IJ Bahl, and P. Bhartia, Microstrip Lines and Slotline, 2nd ed. Obtained by Artech House, 1996.

In addition, if the equation 2 is numerically calculated, a higher-order resonant frequency f _s1 different from the first resonant frequency f ₀ may be calculated.

For example, FIG. 13 is a graph showing results obtained when the impedances of the first and second CPWs are set differently from each other, and Table 1 is a result table shown in FIG. 13.

Z ₀ (Ω) f ₀ f _s1 f _s1 / f ₀ First CPW 2nd CPW 78 103 2.23 7.7 3.45 78 158 1.95 7.96 4.08 78 235 1.63 8.27 5.07

13 and Table 1, as the impedance Z _cpw2 of the second CPW 32 becomes larger than the impedance Z _cpw1 of the first CPW cpw1, the first resonance frequency f ₀ and the second resonance frequency f _s1. It can be seen that the ratio f _s1 / f ₀ increases.

Thus, the present invention can adjust the ratio of the first resonance frequency and the second resonance frequency by adjusting the two CPW impedance inserted into the ground plane.

Accordingly, the present invention is designed so that the ratio of the first resonant frequency to the second resonant frequency is increased so that the second resonant frequency band occurs in a band higher than the first, second, and third harmonics, which are noises in the circuit.

As described above, the present invention can design a bandpass filter using a coplanar waveguide transmission line structure having multiple stage impedances in the ground plane in a structure using a fault ground structure.

Next, the configuration of the bandpass filter according to the preferred embodiment of the present invention will be described in detail with reference to FIGS. 14 to 16.

14 and 15 are plan and bottom views of a bandpass filter according to an exemplary embodiment of the present invention, and FIG. 16 is a diagram illustrating an equivalent circuit model of the bandpass filter illustrated in FIGS. 14 and 15.

The bandpass filter according to the present invention is configured by symmetrically arranging a plurality of stepwise impedance coplanar waveguide transmission lines including a plurality of coplanar waveguide transmission lines having different impedances on the ground plane.

In detail, the bandpass filter 40 according to the preferred embodiment of the present invention implements a gap capacitance in the signal line 12 formed on the upper surface of the dielectric 10, as shown in FIGS. 14 and 15. In the ground plane 13 formed on the bottom surface of the dielectric 10, the first and second stepped impedance CPWs 50 and 60 having multiple stage impedances along the direction of the signal line 12 are arranged to face each other.

The first stepped impedance CPW 50 includes first and second CPWs 51 and 52 having different impedances, and the second stepped impedance CPW 60 includes third and fourth CPWs having different impedances ( 61,62).

At the mutually adjacent ends of the first and second stepped impedance CPWs 50 and 60, the outer side of the dielectric 10 to enhance magnetic coupling between the first and second stepped impedance CPWs 50 and 60 structures. A pair of first and second slot lines 53 and 63 may be inserted toward the end.

The band pass filter 40 configured as described above has a gap between the signal line gap capacitor Cgap_line and the first and second stepped impedance CPWs 50 and 60 corresponding to the gap capacitance of the signal line 12 as shown in FIG. 16. A pair of capacitors corresponding to the capacitance (gap_cwp), the first to fourth CPWs (51, 52, 61, 62) having a characteristic impedance and a length (θ _cpw ) of each CPW (51, 52, 61, 62), And it can be modeled as an equivalent circuit including a transformer (transformer) representing the coupling of the circuit and the signal line 11 configured on the ground plane (13).

Here, the signal line gap capacitor Cgap_line may be disposed at the center portion between the first port Port1 and the second port Port2, and the pair of transformers may be disposed at both sides of the signal line gap capacitor Cgap_line, respectively.

The first and second CPWs 51 and 52 and the third and fourth CPWs 61 and 62 may be disposed adjacent to positions corresponding to each other.

The pair of first and second slot lines 53 and 63 formed at the ends of the first to fourth CPWs 51, 52, 61, and 62 respectively have a base and a first and second CPWs 51, 52. It may be disposed on a branch line between the potential line GND and between the third and fourth CPWs 61 and 62 and the base potential line GND, respectively.

For example, FIGS. 17 and 18 are diagrams illustrating simulation models of the bandpass filter shown in FIGS. 14 and 15, and FIG. 19 is a graph of a characteristic measurement result using the simulation models illustrated in FIGS. 17 and 18.

In the simulation model, as shown in FIG. 17, the width of the signal line 12 is set to 1.2 mm, and the gap capacitance of 0.2 mm is set in the signal line 12.

As shown in FIG. 18, the line width of the first CPW 51 and the fourth CPW 62 is set to 1.2 mm, the distance between the grounds is set to 0.2 mm, and the line length l ₁ is 6.0 mm. Is set, and the gap capacitance is set to 0.2 mm.

The line widths of the second CPW 52 and the third CPW 61 are set to 0.2 mm, the distance between the grounds is set to 1.7 mm, and the line length l ₂ is set to 6.0 mm.

The length l _slot of the first and second slot lines 53 and 63 is set to 3 mm, and the distance between the first and second stepped impedance CPWs 50 and 60 is set to 0.25 mm.

As a result of measuring the simulation characteristics of the bandpass filter modeled as described above, as shown in FIG. 19, the center frequency f ₀ is 1.5 Hz, the bandwidth is 0.32 Hz, and the second passband characteristic corresponds to 4.7 times the center frequency. It can be seen that more than 7㎓.

Therefore, the present invention adjusts the ratio of the first resonant frequency and the second resonant frequency by adjusting the CPW impedance of the multi-stage inserted into the ground plane, so that the second resonant frequency band is higher than the first, second, and third harmonics that become the noise of the circuit. Can be designed to occur.

That is, the present invention can design a bandpass filter using a coplanar waveguide transmission line structure having a multi-stage impedance on the ground plane in a structure using a fault ground structure.

As mentioned above, although the invention made by the present inventor was demonstrated concretely according to the said Example, this invention is not limited to the said Example and can be variously changed in the range which does not deviate from the summary.

That is, in the above embodiment, two coplanar waveguide transmission lines are provided in the first and second stepped impedance coplanar waveguide transmission lines, respectively, but the present invention is not limited thereto.

For example, the present invention may be modified so that three or more coplanar waveguide transmission lines of multiple stages are provided in each staged coplanar waveguide transmission line.

The present invention is applied to a bandpass filter using a coplanar waveguide transmission line structure having a multi-stage impedance on the ground plane and a design method thereof.

10: dielectric
11: metal conductor layer
12: signal line
13: ground plane
20: coplanar waveguide transmission line
21: transformer
30: Stepped impedance coplanar waveguide transmission line
31, 32: first and second waveguide transmission line
33: transformer
40: bandpass filter
50 and 60: first and second stepped impedance coplanar waveguide transmission lines
51, 52, 61, 62: first to fourth waveguide transmission lines
53, 63: first and second slot lines

Claims (10)

delete A signal line formed on an upper surface of the dielectric,
A first and second stepped coplanar waveguide transmission lines disposed to face each other in the direction of the signal line on a ground plane formed on a bottom surface of the dielectric,
The first and second staged impedance coplanar waveguide transmission lines are provided with a plurality of coplanar waveguides equivalent to the transmission line.
It is possible to adjust the ratio of the resonance frequency by adjusting the line width of each coplanar waveguide transmission line so that each coplanar waveguide has a different impedance.
Among the plurality of coplanar waveguide transmission lines, a coplanar waveguide transmission line disposed outside the dielectric such that an impedance of a first plane frequency and a second resonance frequency of the coplanar waveguide transmission line disposed at the center side of the dielectric increases. Is set greater than the impedance of
And said second resonant frequency band is designed to occur in a band higher than the first, second, and third harmonics of the circuit noise. The method of claim 2,
At a pair of adjacent ends of the first and second stepped coplanar waveguide transmission lines, a pair of first ends toward the outside of the dielectric to enhance magnetic coupling between the first and second stepped coplanar waveguide transmission line structures. Bandpass filter, characterized in that the first and second slot line is inserted. delete The method of claim 2,
Band pass filter, characterized in that the gap capacitance is implemented in the center portion of the signal line. delete In the method for designing a bandpass filter according to any one of claims 2, 3, and 5,
(a) forming a signal line on the top surface of the dielectric;
(b) disposing first and second stepped coplanar waveguide transmission lines facing each other along the direction of the signal line on a ground plane formed on the bottom surface of the dielectric;
The first and second staged impedance coplanar waveguide transmission lines are provided with a plurality of coplanar waveguides equivalent to the transmission line.
It is possible to adjust the ratio of the resonance frequency by adjusting the line width of each coplanar waveguide transmission line so that each coplanar waveguide has a different impedance.
Among the plurality of coplanar waveguide transmission lines, a coplanar waveguide transmission line disposed outside the dielectric such that an impedance of a first plane frequency and a second resonance frequency of the coplanar waveguide transmission line disposed at the center side of the dielectric increases. Is set greater than the impedance of
And the second resonant frequency band is designed to occur in a band higher than the first, second, and third harmonics of the circuit noise. The method of claim 7, wherein
(c) facing outward of the dielectric to enhance magnetic coupling between the first and second stepped impedance coplanar waveguide transmission line structures at adjacent ends of the first and second stepped impedance coplanar waveguide transmission lines. And inserting the first and second slot lines of the pair. delete The method of claim 7, wherein
The method of designing a bandpass filter, characterized in that the gap capacitance is implemented in the center portion of the signal line in step (a).

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