KR100858970B1 - Cpw low-pass filter with broad stop band - Google Patents

Abstract

A CPW(Coplanar Waveguide) low-pass filter with a broad stop band is provided to suppress a spurious response to less than a predetermined level by coupling a DGS(Detected Ground Structure) resonator. A first low-pass filter(40) is formed on a dielectric substrate and has a low-pass function with a first spurious response characteristic by including a first discontinuous pattern unit at a CPW transmission line. A second low-pass filter(50) is coupled to a rear end of the first low-pass filter on the dielectric substrate and has a low-pass function with a second spurious response characteristic by including a second discontinuous pattern unit at the CPW transmission line. A band stop filter(60) is coupled to a rear end of the second low-pass filter on the dielectric substrate and includes a pair of DGS resonators(54a,54b) having a stop characteristic of a third spurious response frequency band to remove a third spurious response generated in a coupling structure of the first and second low-pass filters.

Description

CPW Low-Pass Filter with Broad Stop Band

1A and 1B show the structure of the low pass filter 1 of the CPW type and the equivalent circuit thereof according to the first embodiment of the present invention,

2 is a T-shaped three-stage low pass circuit,

3 is a graph showing a simulation result of the CPW low pass filter 1 according to the first embodiment of the present invention;

4A and 4B show a structure of an CPW low pass filter 2 and an equivalent circuit thereof according to a first embodiment of the present invention, respectively.

5 is a graph showing a simulation result of CPW low pass filter 2 according to the first embodiment of the present invention;

6 is a structure in which CPW low pass filters 1 and 2 are combined according to a first embodiment of the present invention;

7 is an equivalent circuit of a structure in which CPW low pass filters 1 and 2 are combined according to a first embodiment of the present invention;

8 is a graph illustrating a simulation result of an equivalent circuit having a structure in which CPW low pass filters 1 and 2 are combined according to a first embodiment of the present invention;

9A and 9B show the structure of the DGS resonator and its equivalent circuit, respectively, according to the first embodiment of the present invention;

10 is a graph showing a simulation result for the DGS resonator according to the first embodiment of the present invention;

11 is a structure of a total filter in which CPW low pass filters 1 and 2 and a DGS resonator are combined according to a first embodiment of the present invention;

12 is a graph showing simulation results of a total filter combined with CPW low pass filters 1 and 2 and a DGS resonator according to a first embodiment of the present invention;

13 is a graph showing measurement results for an actual low pass filter designed according to a first embodiment of the present invention;

14A and 14B show the structure of the low pass filter 2 of CPW type and the equivalent circuit thereof according to the second embodiment of the present invention, respectively.

15 is a graph showing a simulation result of the CPW low pass filter 1 according to the second embodiment of the present invention;

16A and 16B show the structure of an CPW low pass filter 2 and an equivalent circuit thereof according to a second embodiment of the present invention, respectively.

17 is a graph showing a simulation result of CPW low pass filter 2 according to the second embodiment of the present invention;

18 is a graph for comparing simulation results of CPW low pass filters 1 and 2 according to the second embodiment of the present invention;

19 shows a structure in which CPW low pass filters 1 and 2 are combined according to a second embodiment of the present invention;

20 is a graph illustrating a simulation result of a structure in which CPW low pass filters 1 and 2 are combined according to a second embodiment of the present invention;

21 is a graph showing a simulation result for each case of combining the CPW low pass filter 1 and 2 according to the second embodiment of the present invention;

22 is a structure of a total filter in which CPW low pass filters 1 and 2 and a DGS resonator are coupled according to a second embodiment of the present invention;

23 is a graph showing the structure and simulation results of a DGS resonator according to a second embodiment of the present invention;

24 is a graph illustrating simulation results of a total low pass filter in which CPW low pass filters 1 and 2 and a DGS resonator are combined according to a second embodiment of the present invention;

25 is a graph showing measurement results of a pass band for an actual low pass filter designed according to a second embodiment of the present invention;

FIG. 26 is a graph showing a measurement result of broadband for an actual low pass filter designed according to a second embodiment of the present invention.

* Explanation of Signs of Major Parts of Drawings *

10,40; Low pass filter 1 20,50; Low Pass Filter 2

30,60; Band stop filter 24a, 24b, 54a, 54b; DGS resonator

100,200; Low pass filter

The present invention relates to a CPW low pass filter having a wide stop band, and more specifically, by combining two CPW low pass unit structures having different unwanted response characteristics, primarily suppressing harmonic components (undesired response), DGS By further coupling the resonator, the present invention relates to a CPW lowpass filter that can suppress the unwanted response to a certain level or less.

In general, the filter function to select only the desired frequency plays a very important role in the communication system. The filter is classified into four types according to the pass band: low pass filter, high pass filter, band pass filter, and band stop filter.

Among them, the bandpass filter that passes only a specific frequency band and the lowpass filter that passes only a specific frequency with a stopband frequency are most used. In particular, when the low pass filter is designed as a microstrip or a coplanar waveguide (CPW) structure, the harmonic components of the distributed integer elements, that is, the spurious in the stop band should be considered.

The Coplanar Waveguide (CPW) structure not only simplifies the circuit by using a conductor on one side of the substrate in designing a planar filter, but also eliminates via-holes and provides connectivity with active devices. It has excellent advantages.

Moreover, with the development of circuit fabrication technologies such as MMIC (Monolithic Microwave IC) and flip-chip, the application of CPW structures as transmission lines is increasing in the design and implementation of actual circuits. In addition, DGS (Defected Ground Structure) having an etched pattern on the ground plane of the transmission line has been proposed, and research on the application in the microwave band is being actively conducted. The DGS is similar to the photonic band-gap (PBG) structure in which the defects etched on the ground plane are periodically arranged. The periodic PBG structure exhibits propagation delay characteristics and stopband formation in a specific frequency band. Until now, most of these DGS structures have been applied to microstrip structures.

However, the CPW structure has the advantages of using a ground plane without via holes and an easier capacitive coupling between the signal line and the ground plane than the microstrip structure. From this point of view, the study of the filter in the CPW structure is in progress.

In addition, in designing the filter, it is necessary to suppress frequency components other than the frequencies desired in the communication system, that is, undesired response below a certain level. This is a major consideration in designing the filter because most filters have unwanted response caused by the distributed constant element.

In order to improve this, there has been a study of arranging five or more unit structures periodically. By simply increasing the number of array cycles of the unit structure, the attenuation (skirt) characteristics and unnecessary response characteristics can be improved. However, there is a problem in that the characteristics deteriorate due to an increase in return loss in the pass band when simply connected at a specific interval.

In addition, parasitic components may occur due to interaction between unit structures during coupling, and in order to reduce the coupling, when the coupling interval is set to 1/4 wavelength of the stopband center frequency, the size of the overall filter increases.

Moreover, in the microstrip structure, a filter having a filter and a stop band on the feed plane and the ground plane is designed to block each other's pass band, so that a study on the filter having the stop band of a wide band has been conducted. There are disadvantages that are difficult to apply to

Accordingly, the present invention has been made in view of the above problems of the prior art, and its object is primarily to suppress harmonic components (undesired response) by combining two CPW low pass unit structures having different unwanted response characteristics, and DGS The additional coupling of the resonator is to provide a CPW low pass filter that can secondarily suppress unwanted response below a certain level.

Another object of the present invention is to provide a CPW low pass filter capable of miniaturization and having a wide stop band.

Another object of the present invention is to provide a CPW low pass filter having a wide stop band having an excellent wideband stop characteristic of -20 dB or less and up to 7 times the cutoff frequency and having an excellent skirt characteristic.

In order to achieve the above object, the present invention is a dielectric substrate; A first low pass filter formed on the dielectric substrate and having a low pass function having a first non-responsive characteristic by having a first discontinuous pattern portion on a coplanar waveguide (CPW) transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz; Coupled to the rear end of the first low pass filter on the dielectric substrate and having a second discontinuous pattern portion on the CPW transmission line, a 3-dB cutoff frequency is set equal to the first low pass filter and is a second unwanted response in the stop band. A second low pass filter having a low pass function set differently from the first unwanted response property; And a stop characteristic of a third unresponsive frequency band coupled to a rear end of the second low pass filter on the dielectric substrate to remove a third unresponsiveness occurring in a coupling structure of the first and second low pass filters. Provides a CPW low pass filter having a wide stop band, characterized in that it comprises a; band suppression filter having a pair of DGS (Defected Ground Structures) resonator having.

In this case, it is preferable to further include a first transmission line whose length is set to 1/4 wavelength of the stopband center frequency in order to minimize the parasitic unnecessary response between the first low pass filter and the second low pass filter.

In addition, the DGS resonator is formed on one side of the transmission line in a dumbbell shape of a single structure, characterized in that it is formed to have a characteristic of blocking the band (3 f _c ) three times the center frequency ( f _c ).

Setting of each cutoff frequency and stop band of the first low pass filter and the second low pass filter by adjusting the size of the slots of the signal lines and ground planes respectively constituting the first low pass filter and the second low pass filter Characterized in that made.

The first low pass filter and the second low pass filter are preferably coupled to each other at intervals where no further resonance occurs.

The present invention made as described above is made of a simpler structure, it is possible to ensure a wider and deeper stop band.

(Example)

Hereinafter, with reference to the accompanying drawings showing a preferred embodiment of the present invention described above in more detail.

The CPW low pass filter according to the present invention combines filters with differently designed unwanted response characteristics in order to secure a wider stopband, and reduces the unwanted response to less than a certain level. It is characterized by further design, and the present invention provides two embodiments for this purpose.

1. First embodiment

The low pass filters 1 and 2 constituting the low pass filter according to the first embodiment of the present invention are each formed of two unit structures and three unit structures.

1A and 1B are respectively a structure and an equivalent circuit of a low pass filter 1 of CPW type according to a first embodiment of the present invention, and FIG. 2 is a T-shaped three-stage low pass circuit.

Referring to FIG. 1A, the low pass filter 1 of the CPW type according to the first embodiment of the present invention has a discontinuous structure on a CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz ( w = 0.3 mm, s = 0.3 mm). By using the low pass filter 10 is designed.

For this purpose, the low pass filter 1 (10) of the CPW type has a first to fourth main slots 3a formed in a straight line parallel to the upper side and the lower side to form a CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz in the CPW structure. By forming 3b, 3c, and 3d, the first and second main signal lines 1a and 1b and the ground planes 2a and 2b are separated, respectively, and between the first and second main signal lines 1a and 1b. The discontinuous pattern part 4 which functions as the low pass filter 1 (10) is connected.

Main signal lines 1a and 1b using a change in the interval of the first to fourth main slots 3a-3d or the structure of the discontinuous pattern portion 4 between the main signal lines 1a and 1b and the ground planes 2a and 2b. A change in the width) changes the characteristic impedance ( Z ₀ ) and forms a resonance at a specific frequency, thereby forming the low pass filter 1 (10). Therefore, when an input signal is applied to the first main signal line 1a, the high pass signal is filtered by the low pass filter 1 10 of the CPW type, and then an output signal is obtained from the second main signal line 1b.

The discontinuous pattern portion 4 may include a pair of first and second parallel open lines 1c and 1d parallel to the main signal lines 1a and 1b on the ground planes 2a and 2b, respectively. The first slots 3a and 3c and the second and fourth main slots 3b and 3d each have a predetermined width f and vertically extend to the ground planes 2a and 2b, and are then interconnected while forming a rectangle. And second connection slots 5a and 5b.

The discontinuous pattern portion 4 is also arranged in parallel with the small signal line 1e and the small signal line 1e having a predetermined small width i for connecting the main signal lines 1a and 1b in series at a central portion thereof. The first and third main slots 3a and 3c and the first and third main opening lines 1f and 1g having a small width e are formed parallel to both sides of the small signal line 1e. The second and fourth main slots 3b and 3d each have a predetermined width f and are vertically extended inwardly of the main signal lines 1a and 1b, and are then bent at three right angles so that both ends of the first and third main slots ( First to fourth bent slots 4a-4d extending to have a width f equal to the width f between 3a, 3c and second and fourth main slots 3b, 3d.

As a result, vertical connecting lines vertically connecting the central portions of the first and second parallel opening lines 1c and 1d to the central portions of the small signal line 1e and the third and fourth parallel opening lines 1f and 1g, respectively. The furnace 1h is arrange | positioned so that it may cross | vertically perpendicularly. Accordingly, the vertical connecting line 1h has the same width f as the width f between the first and third main slots 3a and 3c and the second and fourth main slots 3b and 3d. .

The discontinuous pattern portion 4 forms a left / right, up / down symmetrical structure, and thus an equivalent circuit thereof also forms a symmetrical circuit structure. That is, the low pass filter 1 formed by the discontinuous pattern portion 4 includes first and third small signal lines 1e and third and fourth parallel opening lines 1f and 1g connected in series, as shown in FIG. Second inductors L _1a and L _1b are formed, and the small signal lines 1e and the vertical connection lines 1h perpendicular to the third and fourth parallel open lines 1f and 1g are first and second inductors. It may be equivalently represented as a series resonant circuit of the third inductor L ₂ and the capacitor C ₂ connected in parallel between the intermediate connection point ( L _1a , L _1b ) and ground.

In this case, the widths i and e of the small signal lines 1e connecting the main signal lines 1a and 1b in series and the third and fourth parallel open lines 1f and 1g become narrower and the length d becomes smaller. As it increases, the series inductance of the two first and second inductors L _1a and L _1b increases in the equivalent circuit, and the inductance value of the third inductor L ₂ connected in parallel increases in the vertical connection line 1h. The width f decreases and becomes larger as the length c increases. In addition, the parallel capacitor C ₂ , which varies depending on the width and length of the first and second connection slots 5a and 5b formed on the ground planes 2a and 2b, has the first and second parallel open lines 1c and 1d. It increases with the width (a) and the length (b), and increases as the distance (g) with the ground planes (2a, 2b) decreases.

That is, the low pass filter 1 (10) formed by the discontinuous pattern portion 4 forms the first to fourth bent slots 4a-4d in the main signal lines 1a and 1b connected in series, and thus the main signal line 1a. The series inductance increases as the width of the small signal line 1e between and 1b decreases, and when the first and second connection slots 5a and 5b are formed on the ground planes 2a and 2b, the first and second connected in parallel By changing the width and length of the second parallel open lines 1c and 1d, parallel inductance is formed, and the width and length of the first and second parallel open lines 1c and 1d and the main signal lines 1a and 1b. The parallel capacitance is formed according to the change in the distance between the ground planes 2a and 2b. That is, the slot sizes of the main signal lines 1a and 1b and the ground planes 2a and 2b are inductance values of the series first and second inductors L _1a and L _1b and the parallel third inductor L ₂ of the equivalent circuit. And a capacitance value of the parallel capacitor C ₂ .

The values of the series first and second inductors L _1a and L _1b and the parallel capacitor C ₂ formed at this time determine the cutoff frequency of the low pass filter 1 (10), and the parallel third inductor L ₂ . The values of and the parallel capacitor C ₂ are factors that determine the stop band attenuation poles.

The slot sizes of the main signal lines 1a and 1b of FIG. 1A form inductance values of the first and second inductors L _1a and L _1b constituting the equivalent circuit, and the sizes of the slots of the ground planes 2a and 2b. Determines inductance and capacitance values of the third inductor L ₂ and the capacitor C ₂ .

Therefore, the device value of the equivalent circuit extracts the corresponding L and C values to match the return loss, the cutoff frequency and the attenuation pole of the EM simulation result, and optimizes the L and C values to satisfy the desired filter characteristics. The filter can be designed by reflecting the result back to the CPW structure.

The equivalent circuit extraction process equalizes the respective L and C values to match the return loss, cutoff frequency, and attenuation poles of the EM simulation results, and approximates the device values of the low pass filter prototype. The filter can be optimized so as to extract the equivalent circuit parameter to reflect the result back to the CPW structure to implement the filter.

Equivalent circuit L and C parameters corresponding to the EM simulation results can be obtained using Equation 1 below. That is, the value of the third inductor L ₂ and the capacitor C ₂ related to the attenuation electrode may be obtained by using Equation 1.

Here, ω _n is the stop band center angular frequency, and the obtained L ₂ value and C ₂ value can be represented by the capacitance value as shown in FIG. Therefore, the values of the series first and second inductors L _1a and L _1b can be obtained from Equation 2 using a 3-dB cutoff frequency.

Where ω _c is the 3-dB blocking angular frequency. Therefore, parameters corresponding to the cutoff frequency and the attenuation pole of the EM simulation result can be obtained using Equations 1 and 2, and the return loss characteristics are the values of the parallel third inductor L ₂ and the parallel capacitor C of FIG. ₂ ) Since it can be adjusted according to the ratio of values, the equivalent circuit can be implemented by extracting the device value matching the EM simulation result.

The low pass filter 1 (10) used an FR-4 epoxy substrate having a dielectric constant ( ε _r ) of 4.4 and the cutoff frequency ( f _c ) was set to 6 GHz. The corresponding parameters of CPW low pass filter 1 (10) are shown in Table 1 below, and the parameters of the LC equivalent circuit are shown in Table 2. 3 shows that the results of the EM simulation (HFSS) of the CPW unit structure and the simulation (ADS) of the LC equivalent circuit are in good agreement with each other.

Simulation Results The LC equivalent circuit does not exhibit an unwanted response at 3 f _c (18 GHz) by the lumped element, but the EM simulation result of CPW structure has an unwanted response at 3 f _c by the distributed integer device.

a 3.4 mm b 0.7 mm c 1.6 mm d 1.35 mm e 0.3 mm f 0.3 mm g 0.2 mm h 0.3 mm i 0.4 mm s 0.3 mm w 3 mm －

L _1a , L _1b L ₂ C ₂ nH 1.37 0.34 － pF － 0.69

This unwanted response can be primarily suppressed by designing and combining filters with another unwanted response characteristic.

In other words, since the unwanted response varies slightly depending on the structure and attenuation characteristics of the filter, the suppression effect obtained by combining with the filter of another structure is more efficient than the coupling through the arrangement of the unit structure having the same unwanted response characteristic. That is, unnecessary responses having different positions and sizes cancel each other, so that an overall suppression effect of the unwanted responses can be expected. Therefore, in order to combine with the low pass filter 1 designed before, the CPW low pass filter 2 having the different slot shape of FIG. 4a is designed.

4A and 4B respectively show a structure of CPW low pass filter 2 and an equivalent circuit thereof according to the first embodiment of the present invention, and FIG. 5 shows a simulation result of CPW low pass filter 2 according to the first embodiment of the present invention. It is a graph.

CPW low pass filter 2 (20) generates the respective slots in the ground plane (12a, 12b) and the main signal lines (11a, 11b) in the same manner as the design method of CPW low pass filter 1 (10) in series first and second An inductor L _11a , L _11b , a parallel third inductor L ₁₂ , and a capacitor C ₁₂ were implemented. That is, the low pass filter 2 (20) is designed by using a discontinuous structure in the CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 kHz.

For this purpose, the low pass filter 2 (20) of the CPW type has a first to fourth main slots 13a- parallel formed on the upper side and the lower side so as to form a CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz in the CPW structure. 13d) separates the first and second main signal lines 11a and 11b and the ground planes 12a and 12b, respectively, and the low pass filter 2 between the first and second main signal lines 11a and 11b. (20) The discontinuous pattern part 14 which functions is connected. Therefore, when an input signal is applied to the first main signal line 11a, the high pass signal is filtered by the low pass filter 2 20 of the CPW type, and then an output signal is obtained from the second main signal line 11b.

The discontinuous pattern portion 14 has first and third main slots 13a and 13c to form a small signal line 11g having a predetermined small width f for connecting the main signal lines 11a and 11b in series at a central portion thereof. ) And the second and fourth main slots 13b and 13d respectively include first to fourth bent slots 14a to 14d extending after being vertically bent at one step and vertically extending inwardly.

In addition, the discontinuous pattern portion 14 is disposed in parallel with the small signal line 11g, and has a wide width over each of the two sides of the main signal lines 11a and 11b and the ground planes 12a and 12b, respectively. The pair of first and second parallel open lines 11c and 11d and the third and fourth parallel open lines 11e and 11f are formed parallel to both sides of the small signal line 11g at intervals i. After the first and third main slots 13a and 13c and the second and fourth main slots 13b and 13d extend vertically to the ground planes 12a and 12b, respectively, the first to fourth bent slots 14a-14d. ) And the first and second connection slots 15a and 15b and the third and fourth connection slots 15c and 15d which are interconnected in a rectangular shape.

As a result, the first and second vertical connecting lines 11h and 11i vertically connecting the central portions of the first and second parallel opening lines 11c and 11d and the third and fourth parallel opening lines 11e and 11f. Is arranged perpendicular to the small signal line 11g.

The discontinuous pattern portion 14 forms a left / right, up / down symmetrical structure, and thus an equivalent circuit thereof forms a symmetrical circuit structure as shown in FIG. 4B.

The series first and second inductors L _11a , L _11b , and L ₁₃ formed therein become larger as the width f of the small signal line 11g decreases and the length h increases, and the parallel third inductor L ₁₂ ) value increases as the width d of the first and second vertical connecting lines 11h and 11i decreases and the lengths e and b increase. In addition, the value of the parallel capacitor C ₁₂ is increased as the width a and length b of the first and second parallel open lines 11c and 11d and the third and fourth parallel open lines 11e and 11f increase. As the distance g from the ground planes 12a and 12b decreases, it becomes larger.

Here, the low pass filter 2 (20) is designed to combine the two basic unit structures in order to improve the attenuation characteristics and unnecessary response characteristics. At this time, an additional capacitance component is formed according to the coupling interval i of the unit structure, thereby coupling between the resonators. The capacitance value of the added capacitor C ₁₁ becomes larger as the coupling interval i decreases, which affects the formation of additional attenuation poles in the stopband.

The low pass filter 2 (20) is designed to combine two basic unit structures in order to improve the attenuation and unnecessary response characteristics, and has the same dielectric constant (4.4) to combine with the low pass filter 1 (10). The substrate was used and designed to have the same 3-dB cutoff frequency ( f _c = 6 GHz).

The parameters of the low pass filter 2 (20) are shown in Table 3 below, and the LC equivalent circuit can extract respective L and C values from the basic unit structure, as in the low pass filter 1 (10) designed above, and 2 Considering the capacitance coupling value and the additional inductance value between the resonators generated when the two unit structures are combined, the equivalent circuit is represented as shown in FIG. 4B, and the parameters of the extracted equivalent circuit are shown in Table 4 below.

a 4mm b 2.4mm c 8.8mm d 0.4mm e 0.4mm f 0.4mm g 0.2mm h 4.8mm i 0.8mm s 0.3mm w 3.0mm -

L _11a , L _11b L ₁₂ L ₁₃ C ₁₁ C ₁₂ nH 1.25 0.52 3.02 － pF － 0.008 0.52

Figure 5 shows the EM simulation (HFSS) results of the low pass filter 2 and the simulation (ADS) results of the LC equivalent circuit.

As a result of the simulation, the LC equivalent circuit shows no unwanted response at 3 f _c , but the EM simulation results of the CPW low pass filter 2 (20) show an unwanted response at 3 f _c . However, by forming two attenuation poles by the coupling between the resonators, the attenuation characteristics are sharper than those of the low pass filter 1 (10) described above, and the unwanted response characteristics are also different.

Therefore, by combining these two low pass filters 1 and 2 (10, 20), better attenuation characteristics and unnecessary response characteristics can be obtained.

Figure 6 shows a low pass filter combining two of the low pass filters 1 and 2 (10, 20). Each parameter of the low pass filters 1 and 2 (10, 20) is the same as the previously presented parameter. However, an additional resonance occurs according to the coupling interval g1 of the low pass filters 1 and 2 (10,20), which creates another unwanted response, so an appropriate coupling interval g1 is required.

FIG. 7 shows an equivalent circuit of the low pass filter 1 and 2 (10, 20) in which the transmission line 16 having the characteristic impedance of 50 Ω is combined with the two equivalent circuits previously extracted. At this time, the length of the transmission line 16 was set to 1/4 wavelength of the stopband center frequency (10.8 GHz) to minimize parasitic unnecessary response due to the transmission line 16.

Therefore, the coupling interval g1 was set to 1.8 mm to match the simulation result of the equivalent circuit. As a result, FIG. 8 shows the simulation result of the coupling structure, and the 3-dB cutoff frequency is about 5.5 GHz. This is the result of a slight decrease in the 3-dB cutoff frequency as a result of combining two lowpass filters 1 and 2 (10,20) with a cutoff frequency of 6GHz. In addition, the unwanted response at 3 f _c is suppressed below -15dB, and the combined lowpass filter exhibits a seventh-order sharp attenuation overall.

On the other hand, although the unwanted response is reduced by the combination of the low pass filter 1 and 2 (10,20), it is necessary to further suppress the unnecessary response of 3 f _c to a predetermined level or less. In order to prevent propagation of a specific frequency band, the present invention attempts to suppress unwanted response by adding a DGS (Defected Ground Structure) resonator. That is, a single DGS resonator of CPW structure is designed as follows to stop propagation in 18GHz band where unwanted response occurs.

9A and 9B show a shape and an equivalent circuit of a band stop filter using a DGS resonator having a pattern etched in the ground plane of a CPW structure. The equivalent circuit and simulation results of the bandstop filter using the proposed DGS resonator are shown in FIG. 10.

In general, DGS (Defected Ground Structure) is a periodic structure having the characteristic of preventing the progress of the electromagnetic wave for a specific frequency band through the periodic change of the wave impedance. Filters with a periodic DGS structure show wider band-stopping characteristics than stubs, and are suitable for removing broadband harmonics. In the present invention, a bandstop filter 30 using a dumbbell-shaped DGS resonator is proposed as a method of extending the stopband of the low pass filter 1 (10).

FIG. 9A illustrates a structure of the bandstop filter 30 including the dumbbell-type DGS resonators 24a and 24b having an etched pattern on the ground plane of the CPW structure. Dumbbell-type DGS resonators 24a and 24b of the CPW type are designed using a DGS structure in a CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz.

The band stop filter 30 of the present invention includes first and second main slots 23a and 23B formed in a straight line parallel to the upper side and the lower side to form a CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz in the CPW structure. The main signal line 21 and the first and second ground planes 22a and 22b are separated from each other, and the CPW-type dumbbell-type DGS resonators 24a and 24b are formed so as to have a blocking characteristic for a specific frequency band. First and second etch grounds connected in the first and second ground planes 22a and 22b from the first and second main slots 23a and 23B through the first and second gaps 25a and 25b. Defected Ground Structure (DGS).

The CPW-type DGS resonators 24a and 24b change the impedance of the main signal line 21 due to an increase in inductance due to an additional magnetic flux passing through the etched square plane and an increase in capacitance in the first and second gaps 25a and 25b. It acts to block the propagation of specific frequency band.

That is, the DGS structure may be represented by a parallel LC equivalent circuit as shown in FIG. 9B. In order to model the equivalent circuit for the DGS structure, the parameters for the DGS structure and the LC equivalent circuit must first be extracted. The dumbbell-type DGS unit structure as shown in FIG. 9A has a cutoff frequency and a resonance point at a specific frequency for a unit area.

In order to investigate the frequency characteristics of this DGS structure, the Electro-Magnetic (EM) simulator uses Ansoft's High Frequency Structure Simulator (HFSS) based on the finite element method (FEM), and the LC equivalent circuit is Agilent's circuit simulator. ADS (Advanced Design System) was used.

Here, w and s are the width of the main signal line 21 having a characteristic impedance of 50 Hz, and the distance between the main signal line 21 and the ground planes 22a and 22b, that is, the first and second main slots 23a and 23b, respectively. Where a and b are the grating sizes of the DGS resonator and c and d are the width and length of the gap of the DGS resonator.

The equivalent circuit and simulation results of the proposed DGS resonator are shown in FIG. 10. The simulation used an epoxy substrate with a dielectric constant of 4.4 and each parameter of the DGS resonator was a = 2mm, b = 1.3mm, c = d = 0.4mm. The distance between the width of the transmission line and the ground plane was set to w = 3mm and s = 0.3mm to have a characteristic impedance of 50Ω.

The L and C parameters of the DGS equivalent circuit can be obtained from Equation 3 using the EM simulation results for the DGS structure.

Where w ₀ is the LC resonant angular frequency, w _c is the 3-dB blocking angular frequency, and g ₁ is the device value of the first stage Butterworth low pass filter. As shown in Fig. 8, the resonant frequency is 18.4 GHz, the cutoff frequency is 12.2 GHz, and g ₁ is 2.0, and the parameters of the parallel LC equivalent circuit are C = 0.100pF and L = 0.737nH. Matches. Therefore, by combining the low pass filter 1 and 2 (10, 20) and the band stop filter 30 using the DGS resonators 24a and 24b, the unwanted response can be further suppressed.

Meanwhile, referring to FIG. 10, the simulation result shows that the center frequency f ₀ of the stop band is 18.6 GHz, indicating an attenuation of -18 dB. The characteristics of the wide and deep stopbands are the main aspects of the DGS structure. That is, it is preferable that the attenuation occurs sufficiently at the center frequency of the stop band, and the Q value of the resonator is relatively small. To satisfy this condition, the effective inductance component may be increased, and the effective inductance component increases with the size of the rectangular area etched in the ground planes 22a and 22b.

As an effect of the etched square grid size, the effective series inductance increases as the size of the etched square area increases. This effective series inductance generates a cutoff frequency at a specific frequency. Therefore, it can be seen that the size of the square unit grid increases the effective series inductance and accordingly, the cutoff frequency is lowered.

Here, the attenuation pole is changed according to the parallel capacitance along with the series inductance. This capacitance depends on the size of the gaps 25a and 25b, ie the width d, etched in the ground planes 22a and 22b. The position of the attenuation pole corresponds to the resonance frequency of the parallel LC equivalent circuit. In order to confirm this, look at the frequency characteristics according to the size of the gap (25a, 25b), the size of the gap (25a, 25b) does not affect the series inductance only affects the parallel capacitance. In other words, when the size of the gaps 25a and 25b increases, the effective capacitance decreases and the position of the attenuation electrode moves to a high frequency. Parallel capacitance, together with series inductance, provides an attenuation pole at the parallel LC resonant frequency position.

FIG. 11 shows the structure of the low pass filter 100 according to the first embodiment of the present invention in which a CPW low pass filter 1 and 2 and a band stop filter using a DGS resonator for suppressing unwanted response are combined.

In consideration of the size of the filter, the band-stop filter 30 using the DGS resonators 24a and 24b having a single structure is combined, and the coupling interval g2 between the low pass filter 2 20 and the DGS resonators 24a and 24b is 0.4 mm was set. 12 shows that as a result of the EM simulation, the unwanted response of 3 f _c , which occurred before adding the DGS resonators 24a and 24b, was suppressed to −25 dB or less. Based on the simulation results, the measurement results of the actual low pass filter 100, which is sampled, show that the reflection loss in the pass band is 10 dB or less, the insertion loss is 0.5 dB or less, and the stop band is 20 GHz, as shown in FIG. Maintain -25dB or less and agree well with simulation result.

Therefore, the first embodiment of the present invention has the same cutoff frequency of 6 GHz, and the unwanted response characteristic is one of the unwanted responses generated by designing and combining two different low pass filters 1 and 2 (10, 20). A single DGS resonator (24a, 24b) that suppresses -15dB differentially and at the same time achieves improved attenuation, and also blocks certain frequency bands (3 f _{c of the} filter) to achieve lower levels of unwanted response (-25dB). ), And by combining with the filter, the secondary response suppression effect can be obtained.

In other words, through the simulation and measurement results, it was confirmed that the unwanted response was kept below -25dB up to 3 f _c , and the sudden attenuation characteristic of the 7th order was confirmed, the return loss was less than 10dB, and the insertion loss was less than 0.5dB. . In addition, the overall size of the filter is 17.2mm (l1) x 6.8mm (w1) has the advantage of having a small size. Therefore, the low pass filter 100 according to the first embodiment of the present invention can be applied to the MIC / MMIC field that requires a wide stop band.

2. Second Embodiment

As shown in FIG. 22, the low pass filters 1 and 2 constituting the low pass filter according to the second embodiment of the present invention have different characteristics and are formed in two unit structures.

First, Fig. 14A is a block diagram of a low pass filter 1 according to a second embodiment of the present invention, and Fig. 14B is an equivalent circuit thereof.

Referring to FIG. 14A, the low pass filter 1 40 of the CPW type according to the second embodiment of the present invention has a characteristic impedance Z ₀ similar to the low pass filter 1 of the CPW type according to the first embodiment. The low pass filter 40 is designed using a discontinuous structure in a CPW transmission line having a 50 kHz ( w = 5.00 mm, s = 0.25 mm). However, in the low pass filter 1 (40) of the second embodiment, a large transmission line can be designed to set a 3-dB cutoff frequency ( f _c ) to 3 GHz by implementing a large value of inductance and capacitance, and has a low dielectric loss. Teflon substrates ( ε _r = 3.48, h = 0.762 mm) were used.

CPW low pass filter 1 (40) of the second embodiment includes first to fourth main slots (33a-) formed in a straight line parallel to the upper side and the lower side to form a CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz in the CPW structure. 33d) separates the first and second main signal lines 31a and 31b and the ground planes 32a and 32b, respectively, and the low pass filter 1 between the first and second main signal lines 31a and 31b. The discontinuous pattern part 34 which functions as 40 is connected.

Since the low pass filter 1 (40) of the second embodiment has a lower cutoff frequency (3 GHz) than the low pass filter 1 (10) of the first embodiment, it is necessary to form a parallel capacitance with a large value equivalently.

To this end, the discontinuous pattern portion 34 may include a pair of first and second parallel open lines 31c and 31d parallel to the main signal lines 31a and 31b on the ground planes 32a and 32b, respectively. The third main slots 33a and 33c and the second and fourth main slots 33b and 33d each have a predetermined width f, extend vertically to the ground planes 32a and 32b, and are interconnected while forming a rectangle. First and second connection slots 35a and 35b are included.

The discontinuous pattern portion 34 also forms a small signal line 31e having a predetermined small width i for connecting the main signal lines 31a and 31b in series at the center thereof, and at the same time from the main signal lines 31a and 31b. A pair of extensions having a predetermined width (f) equal to the gap between the first and second connection slots (35a, 35b) and formed separately, parallel to both sides of the small signal line (31e), and having a predetermined small width (e) First to fourth bent slots 34a to 34d are formed to form third and fourth parallel open lines 31f and 31g.

That is, in the first to fourth bent slots 34a to 34d, the first and third main slots 33a and 33c and the second and fourth main slots 33b and 33d each have a predetermined width a. After extending vertically to the inside of the main signal lines (31a, 31b) is bent in three stages at right angles, both ends extend in opposite directions.

As a result, the vertical connection lines 31h for vertically connecting the central portions of the first and second parallel open lines 31c and 31d are vertically arranged at the center portion of the small signal line 31e. Accordingly, the vertical connection line 31h has a predetermined width f that is equal to the gap between the first and second connection slots 35a and 35b.

The discontinuous pattern portion 34 forms a left / right, up / down symmetrical structure, and therefore, an equivalent circuit thereof also forms a symmetrical circuit structure. That is, the low pass filter 1 40 formed by the discontinuous pattern portion 34 has a small signal line 31e and third and fourth parallel opening lines 31f and 31g connected in series as shown in FIG. 14B. First and second inductors L _21a and L _21b are formed, and the small signal line 31e and the vertical connection line 31h perpendicular to the third and fourth parallel open lines 31f and 31g are respectively formed in the first and second inductors L _21a and L _21b . It may be connected in parallel between the intermediate connection point between the second inductors L _21a and L _21b and the ground, and may be equivalently represented as a series resonant circuit of the third inductor L ₂₂ and the capacitor C ₂₂ .

In this case, the widths i and e of the small signal lines 31e connecting the main signal lines 31a and 31b in series and the third and fourth parallel open lines 31f and 31g become narrower and the length d becomes smaller. As it increases, the series inductance of the two first and second inductors L _21a and L _21b increases in the equivalent circuit, and the inductance value of the third inductor L ₂₂ connected in parallel increases in the vertical connection line 31h. The width f decreases and becomes larger as the length c increases. In addition, the parallel capacitor C ₂₂ increases with the width (a, f) and the length (b, c) of the first and second parallel open line (31c, 31d), and the ground plane (32a, 32b) It increases as the interval g decreases.

That is, the low pass filter 1 40 formed by the discontinuous pattern portion 34 forms the first to fourth bent slots 34a to 34d in the main signal lines 31a and 31b connected in series, and thus the main signal line 31a. The series inductance increases as the width of the small signal line 31e between, 1b decreases, and when the first and second connection slots 35a and 35b are formed on the ground planes 32a and 32b, the first and second connected in parallel By changing the width and length of the second parallel open lines 31c and 31d, parallel inductance is formed, and the width and length of the first and second parallel open lines 31c and 31d, and the main signal lines 31a and 31b and ground. Parallel capacitance is formed in accordance with the change of the space | interval with the surface 32a, 32b.

That is, the slot sizes of the main signal lines 31a and 31b and the ground planes 32a and 32b are inductances of the serial first and second inductors L _21a and L _21b and the parallel third inductor L ₂₂ of the equivalent circuit. Value and the capacitance value of the parallel capacitor C ₂₂ . That is, in the second embodiment, the capacitance value of the parallel capacitor C ₂₂ is increased according to the signal lines close to the ground planes 32a and 32b, that is, the widths of the first and second parallel open lines 31c and 31d. Larger capacitance than the parallel capacitance of the first embodiment can be realized.

Furthermore, the values of the series first and second inductors L _21a and L _21b and the parallel capacitor C ₂₂ formed at this time determine the cutoff frequency of the low pass filter 1 40, and form a series resonance. The values of the third inductor L ₂₂ and the parallel capacitor C ₂₂ are factors determining the attenuation pole of the stop band. Therefore, the cutoff frequency and the stopband can be easily adjusted by adjusting the size of the slot of the signal line and the ground plane.

The device value of the equivalent circuit is extracted in the same way as the low pass filter 1 of the first embodiment to extract the respective L and C values corresponding to the return loss, the cutoff frequency and the attenuation pole of the EM simulation result and satisfy the desired filter characteristics. The filter can be designed by optimizing the values of L and C so that they are reflected and reflecting the results back to the CPW structure.

As described above, the low pass filter 1 (40) was designed using a Teflon substrate ( ε _r = 3.48, h = 0.762 mm), and the 3-dB cutoff frequency f _c was aimed at 3 GHz. The design parameters of the low pass filter 1 (40) are shown in Table 5, and the parameters of the LC equivalent circuit are shown in Table 6.

a 5.20 mm b 1.60 mm c 1.30 mm d 2.60 mm e 0.50 mm f 0.80 mm g 0.20 mm h 0.50 mm i 0.20mm j 0.40 mm s  0.25 mm w 5.00 mm

L _One L ₂ C ₂ nH 3.38 0.23 － pF － 1.50

Fig. 15 shows the results of the EM simulation (HFSS) of the low pass filter 40 and the simulation (ADS) of the LC equivalent circuit. The 3-dB cut-off frequency f _c is 3 GHz and forms an attenuation pole at 7.5 GHz. . In the EM simulation results, an unresponsive phenomenon occurred at 10.5 GHz by the distributed integer device.

In order to improve such unwanted response characteristics, another filter having the same cutoff frequency and having different unwanted response characteristics as in the first embodiment is required. Therefore, in order to combine with the low pass filter 1 (40), a low pass filter 2 (50) of CPW type having another slot shape of FIG. 16A is designed.

16A and 16B respectively show a structure of CPW low pass filter 2 and an equivalent circuit thereof according to the second embodiment of the present invention, and FIG. 17 shows a simulation result of CPW low pass filter 2 according to the second embodiment of the present invention. It is a graph.

CPW low pass filter 2 (50) generates the respective slots in the ground plane (42a, 42b) and the main signal line (41a, 41b), similar to the design method of CPW low pass filter 1 (10) in series first and second Inductors L _31a and L _31b , a third inductor L ₃₂ , and a capacitor C ₃₂ were implemented. That is, the low pass filter 2 (50) is designed by using a discontinuous structure in the CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz.

To this end, the low pass filter 2 (50) of the CPW type first to fourth main slots (43a-) formed in a straight line parallel to the upper side and the lower side to form a CPW transmission line having a characteristic impedance ( Z ₀ ) 50 에서 in the CPW structure. 43d) separates the first and second main signal lines 41a and 41b and the ground planes 42a and 42b, respectively, and the low pass filter 2 between the first and second main signal lines 41a and 41b. The discontinuous pattern part 44 which functions as 50 is connected.

The discontinuous pattern portion 44 has first and third main slots 43a and 43c to form a small signal line 41g having a predetermined small width j for connecting the main signal lines 41a and 41b in series at a central portion thereof. ) And the second and fourth main slots 43b and 43d respectively include first to fourth bent slots 44a to 44d extending vertically after being vertically extended inward.

In addition, the discontinuous pattern portion 44 is disposed in parallel with the small signal line 41g and has a wide width each half of each of the main signal lines 41a and 41b and the ground planes 42a and 42b, respectively. The first and third main slots 13a and 13c and the second and fourth main slots (A) to form a pair of first and second parallel open lines 41c and 41d in parallel to both sides of the small signal line 41g. 43b and 43d extend vertically to the ground planes 42a and 42b, respectively, and then the first and second connection slots 45a, which are interconnected in a substantially rectangular shape with the first to fourth bent slots 44a to 44d, 45b).

Further, in the first and second connection slots 45a and 45b of the discontinuous pattern portion 44, the first and second parallel opening lines 41c and 41d in the center portion to form a larger parallel capacitance value C ₃₂ . Square groove slots (45c, 45d) protruding into the inner).

As a result, the first and second vertical connecting lines 41e and 41f which vertically connect the center portions of the first and second parallel open lines 41c and 41d are arranged so as to vertically intersect the small signal lines 41g. .

The discontinuous pattern portion 44 forms a left / right, up / down symmetrical structure, and therefore, an equivalent circuit thereof forms a symmetrical circuit structure as shown in FIG. 16B.

In the equivalent circuit of FIG. 16B, the values of the series first and second inductors L _31a and L _31b increase as the width j of the small signal line 41g decreases and the length k increases, and the parallel third inductor L _The value ₃₂ increases as the width e of the vertical connecting lines 41e and 41f decreases and the length f and i increases. In addition, the value of the parallel capacitor C ₃₂ is the distance between the ground planes 42a and 42b as the widths a and c and the lengths b and d of the first and second parallel open lines 41c and 41d increase. It becomes larger as (g) decreases.

Here, the low pass filter 2 (50) increases the area adjacent to the ground plane (42a, 42b) by adding the rectangular groove slots (45c, 45d) to the first and second parallel open line (41c, 41d) As a result, larger parallel capacitor ( C ₃₂ ) values can be achieved.

The low pass filter 2 (60) has slots in the ground plane and signal line of a CPW transmission line (w = 5.00 mm, s = 0.25 mm) structure having a characteristic impedance of 50 Ω, similar to the design of the low pass filter 1 (50). The same Teflon substrate was used to combine with the low pass filter 1 and designed to have the same 3-dB cutoff frequency ( f _c = 3 GHz). The physical parameters of low pass filter 2 are shown in Table 7, and the parameters of the LC equivalent circuit are shown in Table 8.

a 3.10 mm b 2.25 mm c 2.00 mm d 1.60 mm e 0.90 mm f 1.10 mm g 0.20 mm h 0.40 mm i 3.60mm j 0.60 mm s 0.25 mm w 5.00 mm

L _One L ₂ C ₂ nH 3.30 0.36 － pF － 1.40

FIG. 17 has a 3-dB cutoff frequency f _c at 3 GHz as an EM simulation result of the low pass filter 2 (50) and a simulation result of the LC equivalent circuit. However, unlike the low pass filter 1 (40), the attenuation pole is formed at 6.8 GHz, and it can be seen that the unresponsive characteristic appears at 12.5 GHz.

18 shows the same characteristics in the passband as simulation results of the low pass filters 1 and 2 (40, 50), but shows that the response characteristics in the stopband are different from each other. Thus, by combining the low pass filters 1 and 2 (40, 50), better attenuation and unresponsiveness can be obtained.

19 shows the structure of a low pass filter combining low pass filters 1 and 2 (40, 50). The parameters of the low pass filters 40 and 50, respectively, are the same as the design parameters presented above. However, an additional resonance occurs according to the spacing g11 between the bonds, creating another unwanted response, so an appropriate spacing g11 is necessary.

In the present invention, the coupling interval g11 is set to 0.8 mm in order to minimize additional unnecessary response, and the EM simulation result of the coupling structure is shown in FIG. 20.

Simulation results show that the combined lowpass filter cancels the unresponsiveness of 10.5 GHz and 12.5 GHz, which occurred in the monolithic structures of the low pass filters 1 and 2 (40, 50), respectively, resulting in a wide rejection of less than -20 dB down to 15 GHz overall. It can be seen that it has a band, and exhibits 5th abrupt attenuation characteristic.

21 is a comparison result of EM simulation according to the combination of the same low pass filter and the low pass filter having different characteristics according to the present invention (FIG. 19).

Case 1 (Case1) of Figure 21 is the result of combining the two low pass filter 1 (40), case 2 (Case2) is the result of combining the two low pass filter 2 (50), Case 3 ( Case 3) is the result of combining the low pass filters 1 and 2 (40, 50).

Looking at the frequency characteristics of each structure, the combination of different structures (case 3) shows wider stopband characteristics than the combination of the same structure (cases 1 and 2). In other words, different unwanted responses cancel each other out, resulting in a wider stopband. Therefore, it can be seen that the combination of different structures is more advantageous than the combination of the same structure in order to obtain the broadband blocking characteristics.

On the other hand, although the stopband can be extended by combining the low pass filters 1 and 2 (40, 50) as described above, an unwanted response near 20 GHz occurs. Therefore, in the present invention, in order to eliminate the unnecessary response near 20 GHz generated in the coupling structure of the low pass filters 1 and 2, a single DGS resonator having a CPW structure formed in a dumbbell shape having a stop characteristic of the 20 GHz frequency band is further deepened and expanded. Implemented stopband characteristics.

22 shows a structure in which the low pass filters 1 and 2 are combined with a band stop filter using a DGS resonator. The band stop filter 60 using the DGS resonator added to FIG. 22 is a dumbbell-type DGS resonator 54a having a pattern etched on the ground plane of the CPW structure in the same manner as the band stop filter 30 shown in FIG. 9A. , 54b). Dumbbell-type DGS resonators 54a and 54b of the CPW type are designed using a DGS structure in a CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz. Since the design principle of the DGS resonators 54a and 54b is the same as that of the bandstop filter 30 of the first embodiment, detailed description thereof will be omitted.

The bandstop filter 60 of the second embodiment is designed to have a stop characteristic of the 20 GHz frequency band in order to remove the unwanted response near 20 GHz, and the DGS resonators 54a and 54b are first used for the low pass filters 1 and 2 (40,). The same Teflon substrate ( ε _r = 3.48, h = 0.762mm) was used to bind to 50).

The design parameters of the DGS resonators 54a and 54b are a = 2.0 mm, b = 1.3 mm, c = 0.4 mm, d = 0.4 mm, w = 5.0 mm, s = 0.25 mm, and the extracted parameters of the LC equivalent circuit are L = 0.91 nH, C = 0.07 pF. Fig. 23 shows simulation results of the designed DGS resonator. As a result of the simulation, it can be seen that an attenuation pole of -18 dB or less is formed at 20 GHz.

The coupling interval g21 between the DGS resonators 54a and 54b and the low pass filter 2 (50) was set to 0.4 mm. The combined low pass filter 200 has a size of 18.2 mm x 11 mm.

24 shows the results of the EM simulation for the overall low pass filter 200 coupling structure. Simulation results show that the unwanted response near 20 GHz that occurred before combining DGS is suppressed below -20 dB due to the coupling of the DGS resonator, thus securing a wide stopband of -20 dB below 20 GHz (7 f _c ). .

25 and 26 show the frequency characteristics of the measured results and EM simulation results for the actually produced filter (combined low pass filters 1 and 2 and DGS in the same manner as the above method).

In the passband characteristics shown in FIG. 25, the 3-dB cutoff frequency is about 3 GHz which is the same as the EM simulation result, and the reflection loss in the passband is 10 dB or less and the insertion loss is 0.5 dB or less. As shown in FIG. 26, the stop band exhibits excellent broadband stop characteristic of -20 dB or less up to 20 GHz, which is about 7 times the cutoff frequency, and agrees well with the simulation result.

The low pass filters 100 and 200 according to the first and second embodiments of the present invention have a discrete structure in which slots are formed in the main signal line and the ground plane with a CPW transmission line having a characteristic impedance of 50Ω. Designed by using the same cutoff frequency, the harmonic components, i.e. the unwanted response characteristics, are designed to combine two different low-pass unit structures to improve not only the skirt characteristics but also the unwanted response characteristics. Can be.

This is because the conventional techniques mostly combine five or more identical unit structures periodically to improve the response characteristics. The present invention provides a wider and deeper stopband by combining two low pass filters with different characteristics and a DGS resonator. Characteristics can be obtained.

The low pass filter 200 of the first embodiment of the present invention has a cutoff frequency of 6 GHz and a stop band (up to -20 dB) of up to 20 GHz which is about three times the cutoff frequency. The cutoff frequency is 3GHz, and the stop band (below -20dB) has characteristics up to 20GHz, which is about 7 times the cutoff frequency.

Further, the second embodiment is formed more compact than the cutoff frequency.

In addition, compared to the first embodiment in which the unit structures constituting the low pass filters 1 and 2 are the same, the second embodiment has a different stop structure by forming different unit structures of the low pass filters 1 and 2. great.

According to the present invention, the low pass filter having wider and deeper stop band characteristics is realized in a compact structure by combining two low pass filters having different structures and a DGS resonator having a band blocking function.

Therefore, the low pass filter of the present invention having the above characteristics can be applied to various high frequency circuit design fields such as MIC / MMIC and RFIC that require a wide stopband.

In the above, the present invention has been illustrated and described with reference to specific preferred embodiments, but the present invention is not limited to the above-described embodiments and the general knowledge in the technical field to which the present invention pertains without departing from the spirit of the present invention. Various changes and modifications will be made by those who possess.

Claims (16)

Dielectric substrates; A first low pass filter formed on the dielectric substrate and having a low pass function having a first non-responsive characteristic by having a first discontinuous pattern portion on a coplanar waveguide (CPW) transmission line having a characteristic impedance ( Z ₀ ) of 50 Hz; Coupled to the rear end of the first low pass filter on the dielectric substrate and having a second discontinuous pattern portion on the CPW transmission line, a 3-dB cutoff frequency is set equal to the first low pass filter and is a second unwanted response in the stop band. A second low pass filter having a low pass function set differently from the first unwanted response property; And It is coupled to the rear end of the second low pass filter on the dielectric substrate, and has a stop characteristic of the third unresponsive frequency band to remove the third unwanted response generated in the coupling structure of the first and second low pass filter A band blocking filter having a pair of DGS (Defected Ground Structures) resonators; CPW low pass filter having a wide stop band, characterized in that it comprises a. 2. The apparatus of claim 1, further comprising a first transmission line whose length is set to a quarter wavelength of a stopband center frequency to minimize parasitic unnecessary response between the first low pass filter and the second low pass filter. CPW lowpass filter with wide stopband. The method of claim 1, wherein the first and second low pass filters are respectively The CPW transmission line is formed between the first and fourth main slots formed in a straight line parallel to the upper side and the lower side and separated at predetermined intervals in the center to form a CPW transmission line having a characteristic impedance ( Z ₀ ) of 50 kHz. First and second main signal lines applied to obtain output transmission signals, respectively; A ground plane disposed above and below the first to fourth main slots and grounded; And The characteristic impedance Z ₀ is changed by changing the width of the first and second main signal lines disposed between the first and second main signal lines and using a change structure of the first to fourth main slots or a setting structure of a discontinuous pattern. CPW low pass filter having a wide stop band, characterized in that it comprises a discontinuous pattern portion to form a resonance at a specific frequency by acting as a low pass. The method of claim 3, wherein the discontinuous pattern portion of the first low pass filter After the first and third main slots and the second and fourth main slots each have a predetermined width and vertically extend to the ground plane, the first and third main slots respectively extend parallel to the first and second main signal lines to form a rectangular interconnect. First and second connection slots forming a pair of first and second parallel open lines; And The first and the second signal lines for connecting the first and second main signal lines in series to the central portion and a pair of third and fourth parallel open lines arranged in parallel with the small signal lines to be parallel to both sides of the small signal lines; After the third main slot and the second and fourth main slots are vertically extended to the inside of the first and second main signal lines, respectively, the three main slots and the second and fourth main slots are bent at three right angles, respectively, so that both ends of the third and fourth main slots A first to fourth bent slots extending to have a width equal to the width therebetween, Wide stop bands are arranged in the center of the small signal line and the third and fourth parallel open line to vertically cross the vertical connection line that vertically connects the center of the first and second parallel open line, respectively. CPW low pass filter. The equivalent circuit of claim 4, wherein the equivalent circuit of the first low pass filter is First and second inductors connected in series with the small signal lines and the third and fourth parallel open lines; A series resonant circuit of a third inductor and a first capacitor connected in parallel between an intermediate connection point between first and second inductors and a ground in correspondence to a vertical connection line orthogonal to the small signal line and the third and fourth parallel open lines CPW low pass filter having a wide stop band, characterized in that consisting of. The method of claim 5, As the widths of the small signal lines and the third and fourth parallel open lines decrease and the length increases, the series inductances of the first and second inductors increase, and the inductance values of the third inductors connected in parallel increase in the vertical connection lines. The width decreases, increases as the length increases, and the parallel capacitor increases with the width and length of the first and second parallel open lines, and increases with decreasing distance from the ground plane. CPW low pass filter with band. 7. The method of claim 6, wherein the second low pass filter has a value of series first and second inductors and a parallel capacitor to determine a cutoff frequency of the first low pass filter, and a value of the parallel third inductor and a parallel capacitor to a stopband. CPW low pass filter having a wide stop band, characterized in that for determining the attenuation poles. 4. The discontinuous pattern portion of the second low pass filter of claim 3, wherein The first and third main slots and the second and fourth main slots are respectively vertically extended inward to form small signal lines connecting the first and second main signal lines in series to the central portion thereof, and are then bent at a right angle and extended. 1 to 4 bent slots; And A pair of first and second parallel open lines and third and fourth parallel open lines disposed in parallel with the small signal lines and disposed on both sides of the first and second main signal lines and the ground plane, respectively; After the first and third main slots and the second and fourth main slots respectively extend vertically to the ground plane so as to be formed parallel to both sides of the small signal line with a first coupling interval, together with the first to fourth bent slots. Comprising two rectangular and interconnected first and second connecting slots and third and fourth connecting slots, A wide stop band, characterized in that the first and second vertical connecting lines vertically connecting the central portions of the first and second parallel opening lines and the third and fourth parallel opening lines are perpendicular to the small signal lines. CPW low pass filter. The method of claim 1, wherein the DGS resonator is made of an etch pattern consisting of a single dumbbell shape on the upper and lower sides of the transmission line, And the DGS resonator is set to block three times the band (3 f _c ) of the filter center frequency ( f _c ). The method of claim 3, wherein the discontinuous pattern portion of the first low pass filter The first and third main slots and the second and fourth main slots extend vertically to the ground plane, respectively, to form a pair of first and second parallel open lines parallel to the first and second main signal lines on the ground plane, respectively. First and second connecting slots connected to each other in a rectangular shape; And The first and third main slots and the first main slots and the first main slots are formed to form a small signal line connecting the first and second main signal lines in series at the center and a pair of third and fourth parallel open lines parallel to both sides of the small signal lines. A second and fourth main slots each extending perpendicularly to the inner side of the main signal line and then bent at three right angles to include first to fourth bent slots having opposite ends extending in opposite directions; CPW low pass filter having a wide stop band, characterized in that the vertical connection line that vertically connects the center portion of the first and second parallel open line vertically intersecting the small signal line. 11. The circuit of claim 10 wherein the equivalent circuit of the first low pass filter is First and second inductors connected in series with the small signal lines and the third and fourth parallel open lines; A series resonant circuit of a third inductor and a first capacitor connected in parallel between an intermediate connection point between first and second inductors and a ground in correspondence to a vertical connection line orthogonal to the small signal line and the third and fourth parallel open lines It consists of As the widths of the small signal lines and the third and fourth parallel open lines decrease and the length increases, the series inductances of the first and second inductors increase, and the inductance values of the third inductors connected in parallel increase in the vertical connection line. The width decreases, increases as the length increases, and the parallel capacitor increases with the width and length of the first and second parallel open lines, and increases with decreasing distance from the ground plane. CPW low pass filter with band. 12. The method of claim 11, wherein the values of the series first and second inductors and the parallel capacitor determine the cutoff frequency of the first low pass filter, and the values of the parallel third inductor and the parallel capacitor determine the stop band attenuation poles. , CPW low pass filter having a wide stop band characterized in that the cutoff frequency is lowered as the value of the parallel capacitor increases. The method of claim 3, wherein the discontinuous pattern portion of the second low pass filter The first and third main slots and the second and fourth main slots are respectively vertically extended inward to form small signal lines connecting the first and second main signal lines in series to the central portion thereof, and are then bent at a right angle and extended. 1 to 4 bent slots; A first and a second pair of first and second parallel open lines disposed in parallel with the small signal lines and disposed on both sides of the main signal line and the ground plane, respectively, in parallel to both sides of the small signal line; First and second connection slots each having a third main slot and a second and fourth main slots vertically extended to the ground plane, and interconnected in a rectangle with the first to fourth bent slots; And CPW having a wide stop band, characterized in that it comprises a rectangular groove slot protruding into the interior of the first and second parallel open line at the center of the first and second connection slots to form a large parallel capacitance value. Low pass filter. 14. The circuit of claim 13 wherein the equivalent circuit of the second low pass filter First and second inductors connected in series corresponding to the small signal lines; A series resonant circuit of a third inductor and a first capacitor connected in parallel between an intermediate connection point between first and second inductors and a ground in correspondence to a vertical connection line orthogonal to the small signal line and the first and second parallel open lines It consists of The series first and second inductor values increase as the width of the small signal line decreases and as the length increases, and the parallel third inductor value increases as the width of the vertical connecting line decreases and the length increases, and the parallel capacitor value becomes zero. As the width and length of the first and second parallel open lines increase, as the distance from the ground plane decreases, the parallel capacitor value increases as the area adjacent to the ground plane increases by adding the groove slot. CPW lowpass filter with wide stopband. Dielectric substrates; Disposed between the first and second main slots formed in a straight line parallel to the upper side and the lower side to form a CPW (Coplanar Waveguide) transmission line having a characteristic impedance ( Z ₀ ) of 50 kHz. First and second main signal lines respectively obtained; A ground plane disposed above and below the first and second main slots and grounded; A first low pass filter formed on the dielectric substrate and having a low pass function having a first non-responsive characteristic by having a first discontinuous pattern portion on the coplanar waveguide (CPW) transmission line; Coupled to the rear end of the first low pass filter on the dielectric substrate and having a second discontinuous pattern portion on the CPW transmission line, a 3-dB cutoff frequency is set equal to the first low pass filter and is a second unwanted response in the stop band. A second low pass filter having a low pass function set differently from the first unwanted response property; And It is coupled to the rear end of the second low pass filter on the dielectric substrate, and has a stop characteristic of the third unresponsive frequency band to remove the third unwanted response generated in the coupling structure of the first and second low pass filter A band blocking filter having a pair of DGS (Defected Ground Structures) resonators; CPW low pass filter having a wide stop band, characterized in that it comprises a. 16. The transmission line and ground plane of claim 15, wherein each of the cutoff frequencies and the stopbands of the first low pass filter and the second low pass filter is configured for each of the first low pass filter and the second low pass filter. CPW low pass filter having a wide stop band, characterized in that by adjusting the size of the slot.

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