WO2021034177A1 - Low pass filter having transmission zero - Google Patents

Abstract

The present invention may provide a low pass filter comprising: a substrate having a ground electrode formed on at least one surface thereof; an input port; an output port; and a filter unit having a plurality of low impedance sections, comprising conductive lines having a line width equal to or greater than a first reference line width, and a plurality of high impedance sections, comprising conductive lines having a line width equal to or smaller than a second reference line width which is smaller than the first reference line width, alternately arranged between the input port and the output port of the substrate, and having a cross coupling formed by having at least a portion of at least two of the high impedance sections, among the plurality of high impedance sections, adjacently formed. Thus, by generating a transmission zero in a stopband, attenuation properties may be improved without increasing filter order and loss.

Description

Low pass filter with transmission zero

The present invention relates to a low pass filter, and relates to a step impedance type low pass filter having a transmission zero in a stopband.

A filter is a device that passes a signal of a predetermined specific frequency band from an RF signal, and is classified into a low pass filter, a band pass filter, a high pass filter, and a band stop filter according to the pass band.

The low pass filter is a component commonly used to remove the spurious mode characteristics of the band pass filter out of band (OOB). Microstrip, strip line, coaxial It can be implemented in the form of a coaxial line or the like.

In addition, when the low pass filter is implemented in a step impedance type, an improved attenuation characteristic can be obtained as the impedance difference between the low impedance section and the high impedance section increases. The coaxial line low-pass filter has advantages in that it is easy to implement low impedance and high impedance and can implement low loss, but has a disadvantage of being very large in size.

In the case of a ceramic waveguide band pass filter, which has recently emerged as a filter for 5G large-scale MIMO antenna systems, it is possible to implement a very small size, but due to the resonance characteristic of the waveguide cavity, unwanted waves are distributed close to the passband. It is essential to apply a low pass filter to suppress unwanted waves. In addition, it is difficult to apply a low-pass filter in the form of a coaxial line with a large size and limited interface to a ceramic waveguide band-pass filter implemented in a small size.

Accordingly, a step impedance type low pass filter implemented as a micro strip or strip line is mainly used as a ceramic waveguide band pass filter. The step-impedance type low-pass filter is implemented in a small size on a dielectric substrate such as a PCB and can be coupled to one side of a band-pass filter, and has an advantage in that it is easy to implement an interface with a ceramic waveguide band-pass filter.

1 and 2 show a cross-sectional view and a perspective view of a conventional step impedance type low pass filter, and as an example, show a step impedance type low pass filter implemented as a strip line.

1 and 2, the step impedance type low pass filter may include a substrate unit 110, an input port 121, an output port 122, and a filter unit 130.

The substrate portion 110 includes a substrate 111 and ground electrodes 112 and 113 formed on one or both surfaces of the substrate 111. In addition, the input port 121 receives a signal to be filtered and transmits it to the filter unit 130, and the output port 122 outputs the signal filtered by the filter unit 130 to the outside.

The filter unit 130 has a plurality of low impedance sections 131, 133, 135, 137 formed of conductive lines having a relatively wide line width and a relatively narrow line width between the input port 121 and the output port 122. A plurality of high- impedance sections 132, 134, and 136 formed of conductive lines having conductive lines are alternately arranged. Here, each of the plurality of low impedance sections 131, 133, 135, and 137 formed with a wide line width functions as a capacitor together with the ground electrodes 112 and 113 formed on one or both sides of the substrate. In addition, a plurality of high impedance sections 132, 134, and 136 formed with a narrow line width function as an inductor.

Here, since a plurality of low impedance sections 131, 133, 135, and 137 function as a capacitor together with the ground electrodes 112 and 113, the capacitor is in parallel with the inductor implemented as a plurality of high impedance sections 132, 134, and 136. It can be seen as being connected to. Accordingly, the low pass filter shown in FIGS. 1 and 2 can be regarded as a 7 order low pass filter implemented with four capacitors and three inductors.

As shown in FIGS. 1 and 2, the step-impedance type low-pass filter has the advantage of being able to be implemented in a small size on the substrate, but in order to suppress unwanted waves that exist close to the upper frequency band of 2 GHz from the pass band, A low pass filter is required, and there is a problem in that loss increases due to this.

An object of the present invention is to provide a low-pass filter capable of improving attenuation characteristics without increasing filter order and loss by implementing a zero transmission point in a stopband.

A low pass filter according to an embodiment of the present invention for achieving the above object comprises: a substrate having a ground electrode formed on at least one surface thereof; Input port; Output port; And a plurality of low impedance sections formed of conductive lines having a line width greater than or equal to a first reference line width between the input port and the output port of the substrate and a conductive line having a line width less than or equal to a second reference line width less than the first reference line width. A plurality of high-impedance sections formed by are alternately arranged, and at least two high-impedance sections of the plurality of high-impedance sections are formed to be adjacent to each other and include a filter unit for cross-coupling.

The filter unit may set an interval and a length between two high impedance sections in which cross-coupling is performed such that a transmission zero point is generated in the stop band of the low pass filter.

The filter unit may be divided into a plurality of sub-filter units each including at least one low impedance section and at least one high impedance section based on at least one high impedance section designated as a reference impedance section among the plurality of high impedance sections. .

The plurality of sub-filter units may be formed parallel to each other on both sides of the reference impedance section.

The plurality of sub-filter units may be formed so that at least some regions of at least one high-impedance section corresponding to each other in each of a pair of sub-filter units formed in parallel on both sides of the reference impedance section protrude to be adjacent to each other.

The filter unit may include the plurality of low impedance sections and the plurality of high impedance sections as one of a microstrip or a strip line.

The low pass filter further includes a plurality of vias formed through the input port, the output port, and the substrate at a predetermined interval along the outer periphery of the filter unit, and electrically connected to a ground electrode formed on at least one surface of the substrate. Can include.

The input port and the output port may each be formed of a conductive line having a predetermined line width, and at least a portion may be formed adjacent to each other so as to achieve cross coupling.

A low pass filter according to another embodiment of the present invention for achieving the above object includes: a substrate having a ground electrode formed on at least one surface thereof; An input port formed of a conductive line having a predetermined line width on the substrate; An output port formed of a conductive line having a predetermined line width on the substrate, and at least partially adjacent to the input port so as to cross-couple the input port; And a plurality of low impedance sections formed of conductive lines having a line width greater than or equal to a first reference line width between the input port and the output port of the substrate and a conductive line having a line width less than or equal to a second reference line width less than the first reference line width. And a filter unit in which a plurality of high-impedance sections formed of are alternately disposed.

Accordingly, the low pass filter according to an embodiment of the present invention can improve attenuation characteristics without increasing the filter order and loss by implementing a transmission zero point in a stopband.

1 and 2 show a cross-sectional view and a perspective view of a conventional step impedance type low pass filter.

3 and 4 are cross-sectional views and perspective views of a step impedance type low pass filter according to an embodiment of the present invention.

5 shows a result of simulation of the characteristics of the step impedance type low pass filter according to the present embodiment.

6 is a cross-sectional view of a step impedance type low pass filter according to another embodiment of the present invention.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the implementation of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, the present invention will be described in detail by describing a preferred embodiment of the present invention with reference to the accompanying drawings. However, the present invention may be implemented in various different forms, and is not limited to the described embodiments. In addition, in order to clearly describe the present invention, parts irrelevant to the description are omitted, and the same reference numerals in the drawings indicate the same members.

Throughout the specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components unless specifically stated to the contrary. In addition, terms such as "... unit", "... group", "module", and "block" described in the specification mean units that process at least one function or operation, which is hardware, software, or hardware. And software.

3 and 4 are cross-sectional views and perspective views of a step impedance type low pass filter according to an embodiment of the present invention, and as in FIGS. 1 and 2, a step impedance type low pass filter implemented as a strip line as an example is shown. I did.

3 and 4, the step impedance type low pass filter according to the present embodiment may include a substrate unit 210, an input port 221, an output port 222, and a filter unit 230.

The substrate portion 210 may include a substrate 211 and ground electrodes 212 and 213 formed on one or both surfaces of the substrate 211. Here, the substrate 211 may be implemented as a dielectric substrate such as a PCB.

In addition, the ground electrodes 212 and 213 are formed on one side or both sides of the substrate 211 depending on whether the filter unit 230 formed in the form of a step impedance is implemented as a microstrip or a strip line. For example, when the filter unit 230 is implemented as a microstrip, the ground electrode 213 is formed only on one surface of the substrate 211, and the input port 221, the output port 222, and the other surface of the substrate 211 The filter unit 230 may be formed in a conductive line shape. On the other hand, when the filter unit 230 is implemented as a strip line, ground electrodes 212 and 213 are formed on both sides of the laminated substrate 211, and the input port 221, the output between the laminated substrates 211 The port 222 and the filter unit 230 may be formed in a conductive line shape.

Hereinafter, as shown in FIG. 4, assuming that the filter unit 230 is implemented as a strip line, ground electrodes 212 and 213 are formed on both sides of the substrate 211, and the input port 221, The output port 222 and the filter unit 230 will be described as being formed between the stacked substrates 211.

The input port 221 receives a signal to be low-pass filtered from the outside and transmits it to the filter unit 130. The input port 221 may receive a signal output from the ceramic waveguide band pass filter and transmit it to the filter unit 230, for example. In addition, the output port 222 receives the filtered signal from the filter unit 230 and outputs it to the outside. For example, the output port 222 may transmit the filtered signal to an A/D converter or the like.

Meanwhile, the filter unit 230 is disposed between the input port 221 and the output port 222 to perform low-pass filtering of the signal applied through the input port 221 and transmits it to the output port 222.

The filter unit 230 includes a plurality of low impedance sections 231, 233, 235, 237 formed of conductive lines having a relatively wide line width, and a plurality of high impedance sections 232 formed of a conductive line having a relatively narrow line width. , 234, 236, and a plurality of low impedance sections 231, 233, 235, 237 and a plurality of high impedance sections 232, 234, 236 are alternately arranged with each other.

1 and 2, each of the plurality of low impedance sections 231, 233, 235, and 237 formed with a wide line width in the filter unit 230 is formed on one or both sides of the substrate. Together with the ground electrodes 212 and 213, they function as capacitors, and a plurality of high impedance sections 232, 234, and 236 formed with narrow line widths function as inductors. Here, each of the plurality of low impedance sections 231, 233, 235, and 237 may have a line width greater than or equal to a predetermined first reference line width, and the plurality of low impedance sections 231, 233, 235, 237 are less than the first reference line width. It may have a line width less than or equal to a small predetermined second reference line width.

Accordingly, like the low pass filter shown in FIGS. 1 and 2, the low pass filter according to the present embodiment shown in FIGS. 3 and 4 may also be viewed as a 7th order low pass filter implemented with four capacitors and three inductors. .

Here, the length and line width of each of the plurality of low impedance sections 231, 233, 235, and 237 and each of the plurality of high impedance sections 232, 234, and 236 may be determined in consideration of the stopband and loss characteristics of the low pass filter. . That is, the size of each of the plurality of low impedance sections 231, 233, 235, 237 and each of the plurality of high impedance sections 232, 234, 236 is the impedance required for each step (or order) in the step impedance type low pass filter. It can be adjusted in various ways according to.

In particular, in the filter unit 230 of the low-pass filter according to the present embodiment, at least two of the high- impedance sections 232, 234, and 236 are adjacent to each other so that cross-coupling is achieved Is formed. When at least two high- impedance sections 232 and 236 are formed adjacent to each other and cross-coupling is performed, a transmission-zero is generated, thereby improving attenuation characteristics of the ceramic waveguide filter.

In addition, the low-pass filter of the present embodiment is different from the conventional low-pass filter in which a plurality of low impedance sections 231, 233, 235, 237 and a plurality of high impedance sections 232, 234, 236 are arranged in a straight line, FIG. 3 And as shown in FIG. 4, a plurality of low- impedance sections 231, 233, 235, 237 and a plurality of high- impedance sections 232, 234, 236 alternately arranged are centered on the high-impedance section 234. By being arranged in parallel in a U shape on both sides, at least two high impedance sections 232 and 236 can be easily arranged adjacent to each other.

Here, since the 7th low pass filter is illustrated as an example, the high impedance section 234 located at the center of the filter unit 230 is designated as the reference impedance section, and the remaining low impedance sections 231 and 233 are on both sides of the reference impedance section. , 235 and 237 and the high impedance sections 232 and 236 are shown to be arranged in parallel. In this case, the combination of the low impedance section 231, 233 and the high impedance section 232 disposed on one side of the reference impedance section and the combination of the low impedance section 235, 237 and the high impedance section 236 disposed on the other side Each can be viewed as a sub filter unit.

That is, in the present embodiment shown in FIGS. 3 and 4, it is seen that the filter unit 230 forms a U-shaped structure by arranging two sub-filter units in parallel on both sides around the high impedance section 234 which is the reference impedance section. I can. In this way, when the filter unit 230 has a U-shaped structure, at least two high impedance sections 232 and 236 can be disposed adjacent to each other, and the size of the filter unit 230 can be reduced. .

However, when the filter unit 230 is formed in a U-shaped structure so that cross-coupling between the two high- impedance periods 232 and 236 is formed, the high- impedance periods 232 and 236 to be cross-coupled Cross-coupling may also be performed between the low impedance sections 231 and 237 and 233 and 235 at the corresponding positions or between the high impedance sections. Accordingly, in this embodiment, the filter unit 230 is formed in a U-shaped structure, but is spaced apart so that cross coupling is not performed between the low impedance sections (231, 237), (233, 235) at positions corresponding to each other. The two high impedance sections 232 and 236 are formed so that at least some regions protrude in a direction adjacent to each other, so that cross-coupling can be easily achieved.

3 and 4 show the 7th order low-pass filter as an example only, and thus the filter unit 230 is shown to be formed in a U-shaped structure. However, if the filter unit 230 is implemented as a high-order low-pass filter of 7th order or higher, at least A plurality of sub-filters including one low impedance section and at least one high impedance section may be formed to be arranged in a zigzag pattern such as an S or W shape.

Meanwhile, the lengths and intervals of regions protruding between the two high impedance sections 232 and 236 in which cross-coupling is performed and adjacent to each other may be set such that a transmission zero point is generated in the stop band of the low pass filter. This is to enable the low-pass filter according to the present embodiment to precisely suppress unwanted waves in a stop band and improve attenuation characteristics without increasing harvest or loss.

A magnetic field is coupled between the two high- impedance sections 232 and 236 to couple with a part of the signal applied to the filter unit 230. However, in the pass band of the low pass filter, the magnitude of the signal coupled between the high impedance sections 232 and 236 is much smaller than that of the signal traveling through the filter unit 230. Therefore, the effect on the signal of the passband is very slight and does not affect the passband characteristics. On the other hand, the signal in the stopband becomes similar to the magnitude of the signal coupled between the two high impedance sections 232 and 236, thereby affecting each other. Accordingly, a transmission zero point can be generated in the stop band of the low pass filter by adjusting the length and spacing of regions adjacent to each other between the two high impedance sections 232 and 236.

Therefore, it is possible to improve the attenuation characteristics by effectively suppressing the unwanted waves existing in the high frequency band without causing an increase in loss by maintaining the passband characteristics as much as possible without increasing the order of the low pass filter.

In addition, as shown in FIGS. 3 and 4, the low-pass filter according to the present embodiment wraps the input port 221, the output port 222, and the filter unit 230 along the outer periphery of the substrate at predetermined intervals. A plurality of vias 240 formed through 211 may be further included. The plurality of vias 240 are electrically connected to ground electrodes 212 and 213 formed on one or both sides of the substrate 211, so that a signal applied from the substrate 211 to the input port 221 is a low pass filter. Blocks so as not to leak outside the implemented area.

5 shows a result of simulation of the characteristics of the step impedance type low pass filter according to the present embodiment.

In FIG. 5, in order to analyze the characteristics of the step-impedance type low-pass filter of the present embodiment shown in FIGS. 3 and 4, insertion loss of the conventional low-pass filter of the same order shown in FIGS. 1 and 2 And return loss characteristics were simulated together.

As shown in Fig. 5, the step impedance type low pass filter of this embodiment appears almost similar to the conventional low pass filter in terms of return loss characteristics. In addition, the insertion loss also has a 3dB cutoff frequency of 4.7 GHz, showing the same characteristics within the passband.

However, in the low-pass filter of this embodiment, as cross-coupling is performed in at least two high-impedance intervals, a transmission zero point is generated around 8.9 GHz in the stop band. In addition, it can be seen that the attenuation characteristic is improved by more than 10 dB in the range of 6 to 8 GHz and more than 30 dB in the range of 8 to 10 GHz by the generated transmission zero point.

That is, it can be seen that the attenuation characteristic is greatly improved while maintaining the loss in the low pass filter of the same order.

6 is a cross-sectional view of a step impedance type low pass filter according to another embodiment of the present invention.

The low pass filter of FIG. 6 also includes a substrate 310 including a substrate 311 and ground electrodes 312 and 313 formed on one or both surfaces of the substrate 311 like the low pass filter illustrated in FIGS. 3 and 4. ) And an input port 321, an output port 322, and a filter unit 330 formed as conductive line lines on the substrate 311. In addition, the filter unit 330 may be formed by alternately disposing a plurality of low impedance sections 331, 333, 335, and 337 and a plurality of high impedance sections 332, 334, and 336.

Although in FIG. 6, for example, a plurality of low impedance sections 331, 333, 335, and 337 of the filter unit 330 and a plurality of high impedance sections 332, 334, 336 are shown in the filter unit 230 of FIGS. 3 and 4. Similar to ), the high impedance section 334 is used as the reference impedance section and is shown to be formed parallel to each other in a U shape. However, in the low pass filter of FIG. 6, since cross coupling is not performed between the high impedance sections 332, 334, and 336 of the filter unit 330, no protruding regions are formed in the high impedance sections 332 and 336.

3 and 4, the filter unit 230 has a U-shaped arrangement of a plurality of impedance sections 231 to 237 in a structure designed to facilitate cross-coupling between the high impedance sections 232 and 236. Therefore, in the low pass filter of FIG. 6, the plurality of impedance sections 231 to 237 of the filter unit 330 may be formed in a straight line as shown in FIGS. 1 and 2, or may be formed in a different form. have.

However, in the low-pass filter of FIG. 6, some regions of the input port 321 and the output port 322 protrude and are formed adjacent to each other, thereby cross-coupling between the input port 321 and the output port 322. Lose. As cross coupling between the input port 321 and the output port 322 is made, a transmission zero point may be generated similar to the low pass filter of FIGS. 3 and 4. That is, even if the high impedance sections 332 and 336 are not disposed adjacent to each other, the input port 321 and the output port 322 are disposed adjacent to each other to generate a transmission zero point.

Here, the length and spacing of regions formed adjacent to the input port 321 and the output port 322 may be set such that a transmission zero point is generated in the stop band of the low pass filter. Accordingly, it is possible to suppress an unwanted wave in a stop band and improve attenuation characteristics without increasing the order and loss of the filter unit 330.

In addition, although not shown, in the low pass filter illustrated in FIGS. 3 and 4, a partial region may be formed adjacent to each other so that cross coupling between the input port 221 and the output port 222 is performed as in FIG. 6. . In this case, since cross-coupling is performed between the high- impedance periods 232 and 236 and between the input port 221 and the output port 222, the frequency band in which the transmission zero point is generated can be more accurately adjusted.

The present invention has been described with reference to the embodiments shown in the drawings, but these are merely exemplary, and those of ordinary skill in the art will appreciate that various modifications and other equivalent embodiments are possible therefrom.

Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

Claims (11)

1. A substrate having a ground electrode formed on at least one surface;

   Input port;

   Output port; And

   A plurality of low impedance sections formed of conductive lines having a line width greater than or equal to a first reference line width between the input port and the output port of the substrate and a conductive line having a line width less than or equal to a second reference line width less than the first reference line width. A low pass filter comprising a filter unit in which a plurality of high impedance sections are alternately arranged, and at least two high impedance sections of the plurality of high impedance sections are formed to be adjacent to each other to perform cross coupling.
2. The method of claim 1, wherein the filter unit

   A low pass filter in which an interval and a length between two high impedance sections in which cross-coupling is performed are set such that a transmission zero point is generated in the stop band of the low pass filter.
3. The method of claim 1, wherein the filter unit

   It is divided into a plurality of sub-filter units each including at least one low impedance section and at least one high impedance section based on at least one high impedance section designated as a reference impedance section among the plurality of high impedance sections,

   The plurality of sub-filter units

   Low pass filters formed parallel to each other on both sides of the reference impedance section.
4. The method of claim 3, wherein the plurality of sub-filter units

   A low pass filter in which at least some regions of at least one high impedance section corresponding to each other in each of a pair of sub-filter units formed in parallel on both sides of the reference impedance section protrude to be adjacent to each other.
5. The method of claim 1, wherein the filter unit

   A low pass filter in which the plurality of low impedance sections and the plurality of high impedance sections are formed as one of a microstrip or a strip line.
6. The method of claim 5, wherein the low pass filter is

   The low-pass filter further comprises a plurality of vias formed through the substrate at predetermined intervals along the periphery of the input port, the output port, and the filter unit, and electrically connected to a ground electrode formed on at least one surface of the substrate. .
7. The method of claim 1, wherein the input port and the output port are

   A low-pass filter formed of conductive lines each having a predetermined line width, and at least partially adjacent to each other so as to achieve cross coupling.
8. A substrate having a ground electrode formed on at least one surface;

   An input port formed of a conductive line having a predetermined line width on the substrate;

   An output port formed of a conductive line having a predetermined line width on the substrate, and at least partially adjacent to the input port so as to cross-couple the input port; And

   A plurality of low impedance sections formed of conductive lines having a line width greater than or equal to a first reference line width between the input port and the output port of the substrate and a conductive line having a line width less than or equal to a second reference line width less than the first reference line width. A low pass filter including a filter unit in which a plurality of high impedance sections to be formed are alternately arranged.
9. The method of claim 8, wherein the input port and the output port are

   A low pass filter in which an interval and length at which cross-coupling is performed are set such that a transmission zero point is generated in the stop band of the low pass filter.
10. The method of claim 8, wherein the input port, the output port, and the filter unit

    Low pass filter formed by either microstrips or strip lines.
11. The method of claim 10, wherein the low pass filter is

    The low-pass filter further comprises a plurality of vias formed through the substrate at predetermined intervals along the periphery of the input port, the output port, and the filter unit, and electrically connected to a ground electrode formed on at least one surface of the substrate. .

Images