KR100827842B1 - Notch coupling rf filter - Google Patents

Abstract

A notch coupling RF(Radio Frequency) filter is provided to improve a skirt characteristic by generating a lot of notches in comparison with a cross coupling method. A notch coupling RF filter includes a plurality of cavities, a plurality of resonators(310,312,314,316), at least one coupling bar(300,302), and a support member. The plurality of resonators are installed on the plurality of cavities respectively. The at least one coupling bar is installed on opened coupling window positions of the cavities to correspond to an RF signal progress direction. The support member supports the coupling bar. The support member is made of dielectric and extended from any one part of a housing. The number of the coupling bars corresponds to the number of notches.

Description

Notch Coupling RF Filter

1 is a view showing the structure of an RF filter using a conventional cross coupling.

      FIG. 2 shows an equivalent circuit for a notch RF filter using the conventional cross coupling shown in FIG. 1. FIG.

      3 is a cross-sectional plan view of a notched coupling RF filter in accordance with an embodiment of the present invention.

      4 is an exploded perspective view of a notch coupling filter in accordance with an embodiment of the present invention.

      5 illustrates a cross-sectional view of a notch coupling filter in accordance with one embodiment of the present invention.

      6 illustrates an equivalent circuit configuration of a notch coupling filter according to an embodiment of the present invention.

      7 is a diagram illustrating an output waveform of an RF filter to which a notch generation scheme is applied according to an embodiment of the present invention.

      8 shows an equivalent circuit configuration of an admittance inverter in a filter composed of a plurality of stages.

      TECHNICAL FIELD The present invention relates to an RF filter, and more particularly, to a notch coupling RF filter that generates a notch in a specific frequency band in order to improve a skirt characteristic of the filter.

       The RF filter is a device that passes only signals of a predetermined frequency band. The RF filter is classified into a low pass filter, a band pass filter, a high pass filter, and a band stop filter according to the frequency band to be filtered.

       Important characteristics of the filter include insertion loss and skirt characteristics. Insertion loss refers to the power dissipated as the signal passes through the filter, and the skirt characteristic refers to the steepness of the passband and stopband of the filter.

       The above insertion loss and skirt characteristics are traded off with each other according to the order of the filter. The higher the order of the filter, the better the skirt characteristics but the worse the insertion loss.

       A method of forming notches (damping poles) is mainly used to improve the skirt characteristics of the filter without raising the order of the filter. This is a method of enhancing the skirt characteristics of the filter without raising the order of the filter by forming a notch in a specific frequency band.

       The most common way to form a notch is the cross coupling method. Referring to FIGS. 1 and 2, notch formation using cross coupling is as follows.

       1 is a view showing the structure of an RF filter using a conventional cross coupling.

       Referring to FIG. 1, a conventional RF filter using cross coupling includes an input port 102, a cavity 104, an output port 108, a plurality of resonators 106-1,. Bar 112.

       In FIG. 1, filtering is performed while the RF signal applied to the input port 102 proceeds from the first resonator 106-1 to the second resonator 106-2 while being resonated by the resonators provided in the respective cavities.

       The RF signal proceeds while being coupled toward the open position in the cavity, where the order in which the RF signal proceeds is the same as the numbering order for the resonator.

       In a typical RF filter without cross coupling, coupling occurs adjacently in a known period, but when the coupling bar 112 is used as shown in FIG. 1, cross coupling rather than sequential resonance period coupling is performed. Occurs.

       Referring to FIG. 1, the coupling bar 112 penetrates an inner wall defining a cavity, and allows coupling to occur between the second resonator 106-2 and the fifth resonator 106-5.

       Since the coupling bar 112 is also made of metal and the inner wall defining the cavity is also made of metal, the outside of the coupling bar 112 is wrapped in a dielectric material such as Teflon to electrically isolate the coupling bar 112 from the inner wall. Combined.

       As shown in FIG. 1, when the coupling bar is installed on the inner wall defining the cavity, in addition to the coupling occurring sequentially, a cross coupling phenomenon occurs in the resonance period, and such cross coupling results in notches in a specific frequency band. This improves the skirt characteristics of the filter.

       FIG. 2 illustrates an equivalent circuit for a notch RF filter using the conventional cross coupling shown in FIG. 1.

       Referring to FIG. 2, a number of RLC combinations 201, 202, 204, 206, 208, 210, 212, 214, 216, 218 represent the resonators of FIG. 1.

       In FIG. 2, the coupling bar is represented by C 242 coupled to the second RLC combination 202 and the fifth RLC combination 206.

       That is, a capacitance is formed between the second resonator and the fifth resonator by the coupling bar, which causes a coupling phenomenon between the second resonator and the fifth resonator.

       The notch forming method by cross coupling using the coupling bars shown in FIGS. 1 and 2 has the following problems.

       First, there is a problem that cross coupling cannot be performed in a filter in which a coupling bar cannot be inserted like a lined filter. As shown in FIG. 1, a two-column filter may be cross-coupled in a direction different from a traveling direction, but in the case of a single-line filter, cross-coupling in the form of FIG. 1 may not be possible. That is, whether or not cross coupling is possible has a problem depending on the structure of the filter.

       Second, notch formation by cross coupling using a conventional coupling bar has a problem that a sufficient number of notches cannot be generated. In the filter having the structure shown in FIG. 1, a combination capable of cross coupling (for example, between the second and fifth resonators and between the sixth and ninth resonators) is determined, and for other combinations, cross coupling is performed. There is a problem that is difficult to implement.

In order to solve the problems of the prior art as described above, the present invention proposes an RF filter capable of generating notches without being dependent on the structure of the filter.

      Another object of the present invention is to propose an RF filter which can improve skirt characteristics by generating a larger number of notches than a conventional notch generating method such as cross coupling.

      Other objects of the present invention will be understood by those skilled in the art through the following examples.

      In order to achieve the object as described above, according to a preferred embodiment of the present invention, a plurality of cavities; A plurality of resonators installed in each of the plurality of cavities; At least one coupling bar installed at a coupling window position open to the cavity corresponding to an advancing direction of an RF signal; And a support member for supporting the coupling bar.

       The support member is a dielectric material and extends from any part of the housing to support the coupling bar.

       The number of coupling bars can be set corresponding to the number of notches to be produced.

       The coupling bar is made of metal and may be cylindrical or disc shaped.

      The male member is formed on the support member and the female thread is formed on the coupling bar so that the coupling bar is coupled to the support member in the form of a screw connection and the height thereof is adjusted by rotation.

       According to another aspect of the present invention, a plurality of resonating elements configured to resonate an RF signal in a specific frequency band; A coupling element for coupling an RF signal from one resonant element to another, wherein at least one of said coupling elements is inductive coupling means for inductive coupling and capacitive for capacitive coupling; A notched coupling RF filter is provided that includes all of the coupling means.

       Hereinafter, with reference to the accompanying drawings, a preferred embodiment of the notch coupling RF filter according to the present invention will be described in detail.

       3 is a cross-sectional plan view of a notched coupling RF filter according to an embodiment of the present invention.

       Referring to FIG. 3, a notch coupling RF filter according to an embodiment of the present invention may include coupling bars 300 and 302, a plurality of resonators 310, 312, 314, and 316, an input connector 320, and an output connector. 322 may be included.

       3 is a diagram illustrating an example of a filter structure to which the idea of the present invention is applied, and a filter in a line is illustrated, but it will be apparent to those skilled in the art that the idea of the present invention can be applied to RF filters having various structures. .

       The notch forming method by the conventional cross coupling is not applicable to a filter having a single line as shown in FIG. 3, but the notch forming method according to the preferred embodiment of the present invention may be applied to a filter having a single line as shown in FIG. 3. have.

       In addition, FIG. 3 illustrates an RF cavity filter in which a plurality of cavities are provided with a resonator having a cylindrical or similar shape, but the notch forming method according to the preferred embodiment of the present invention may include various types of RF as well as an RF cavity filter. Applicability to the filter will be understood by those skilled in the art through the following embodiments.

       In FIG. 3, each cavity is provided with resonators 310, 312, 314, and 316, and a coupling window is formed on one surface of the cavity to open an RF signal. The resonator is coupled to the bottom of the filter, a dielectric resonator may be used for TE and TM mode resonances, and a metal resonator may be used for TEM mode resonances.

       The RF signal to be filtered is input to the input port 320, and the input RF signal is resonated by the first resonator 310, and then the second resonator may be formed by inductive coupling through an open coupling window of the cavity. 312).

       The number of resonators is related to the order of the filters, and FIG. 3 shows a fourth order RF filter with four resonators.

       Although not shown in FIG. 3, a tuning bolt for tuning the resonant frequency of the filter corresponding to each resonator may be installed through the RF filter housing, and the capacitance of each cavity may correspond to the distance between the resonator and the tuning bolt. By changing, the resonance frequency can be tuned.

       In the conventional case, it is not easy to form notches by cross coupling in filters arranged in a line as shown in FIG. 3. In order to achieve the cross coupling, the coupling phenomenon may be induced between the first resonator 310 and the third resonator 314, or the coupling phenomenon may be induced between the first resonator 310 and the fourth resonator 316. 3, the coupling bar may not be provided between the first resonator 310 and the third resonator 314, which may be the first resonator 310 and the fourth resonator 316. The same is true.

       Therefore, in the filter of the structure as shown in FIG.

       The present invention proposes a new notch forming method for forming a notch by installing a coupling bar between sequential resonators according to the RF propagation direction. For example, a coupling bar may be provided at a coupling window position between a second resonator 312 and a third resonator 314 and between adjacent resonators such as between the third resonator 314 and the fourth resonator 316. To form a notch.

       8 is a diagram showing an equivalent circuit configuration of an admittance inverter in a filter composed of a plurality of stages.

       An equivalent circuit is implemented between the resonator and the resonator by an admittance inverter. Referring to FIG. 8, as shown in (a) and (b), the admittance inverter is composed of a capacitor (a) and an inductor (b). ) Is implemented as an inductor.

       In FIG. 8, (c) is the structure which the inverter of (a) and (b) combined.

       In the equivalent circuit of the filter, negative components L and C are absorbed by the positive L and C components implemented by the resonator, and the positive and negative components L and C resonate when all of the following Equation 1 is satisfied.

       In Equation 1 above, J is a characteristic admittance of the interleaver.

       The inventors of the present invention devised a method of generating a notch by using the self-resonance phenomenon of the inverter using the circuit of FIG. Referring to FIG. 2, although the resonators adjacent to each other are inductively coupled through a coupling window (L coupling is shown), a method of generating a notch by generating capacitive coupling together is provided in the present invention. Is suggested by.

       That is, capacitive coupling occurs with inductive coupling typically occurring through the coupling window, thereby generating notches at the resonant frequencies of the L and C components.

       According to a preferred embodiment of the present invention, coupling bars (300, 302) are provided in the coupling window rather than the cavity inner wall, such as the conventional cross coupling, so that the coupling bar as well as the inductive coupling by the coupling window ( Capacitive coupling by 300, 302 occurs together.

       That is, in contrast to the conventional cross-coupling generated coupling between non-adjacent resonators in the advancing direction of the RF signal, the present invention includes a coupling bar between adjacent resonators in the RF signal advancing direction. Generating capacitive coupling.

       By providing coupling bars between adjacent resonators, inductive coupling and capacitive coupling occur simultaneously, with notches occurring in the frequency bands corresponding to the resonant frequencies of the L and C components.

       4 and 5, the filter structure for forming the notch according to the preferred embodiment of the present invention will be described in more detail.

       4 is an exploded perspective view of a notch coupling filter according to an exemplary embodiment of the present invention, and FIG. 5 is a cross-sectional view of the notched coupling filter according to an exemplary embodiment of the present invention.

       Conventional cross-coupling is to insert the coupling bar into the inner wall, the coupling bar is fixed by the inner wall, there is no need for a separate support component.

       However, in the embodiment of the present invention, since the coupling bar must be provided in the middle of the coupling window, a component for supporting the coupling bar without affecting the filter characteristics is required.

       4 and 5 illustrate an example for supporting the coupling bar so that the coupling bar may be provided in the coupling window.

       4 and 5, a bar 400 extending from the upper housing of the RF filter is formed, and the coupling bar is coupled to the bar to support the coupling bar on the coupling window. At this time, the bar extending from the upper housing of the RF filter is preferably a dielectric material such as Teflon so as not to affect the filter characteristics.

       That is, the coupling bar is fixedly provided at the coupling window position by coupling the coupling bar to one end of the dielectric bar 400.

       As shown in FIG. 5, a capacitance is formed between the coupling bar and the two resonators 302 and 304 by the coupling bar provided in the coupling window, which causes a capacitive coupling phenomenon.

       4 and 5 illustrate a structure in which the dielectric bar extends from the upper housing of the RF filter to support the coupling bar, but the dielectric bar may extend from any part of the RF filter to support the coupling bar. For example, it will be apparent to those skilled in the art that an extension from the bottom of the RF filter may support the coupling bar, and an extension from the side of the RF filter may support the coupling bar.

       According to an embodiment of the present invention, a male thread is formed on the dielectric bar and a female thread is formed on the coupling bar so that the dielectric bar and the coupling bar are coupled by screwing, and the height may be adjusted by rotating the coupling bar. There will be.

       In addition, the shape of the coupling bar is not limited to the cylindrical shape as shown in Figs. 4 and 5, a disk-shaped coupling bar may be used, and the change of the shape of the coupling bar is a matter of the idea of the present invention. It will be apparent to those skilled in the art that they fall within the scope.

       The capacitance formed between the coupling bar and the resonators adjacent to the coupling bar is determined by the distance between the coupling bar and the resonator and the cross-sectional area of the coupling bar, and as described above, the notch is formed by the capacitance value and the inductance value. The frequency is determined.

       3 to 5, according to a preferred embodiment of the present invention, by forming a coupling bar at a position on the coupling window, a notch for improving skirt characteristics is formed.

       Notch formation according to a preferred embodiment of the present invention as described above has a number of advantages over the conventional cross coupling.

       First, there is an advantage that the notch can be formed regardless of the structure of the filter. In the conventional cross-coupling method, notches are not formed because the inner wall in which the coupling bar can be installed does not exist in the filters formed in a line as shown in FIG. 3.

       However, according to the preferred embodiment of the present invention, since the coupling bar is provided at the coupling window position, the notch can be formed without being limited by the structure of the filter regardless of whether the filter is in a row or not.

       In addition, more notches can be formed in the same filter order (number of resonators) than in the conventional cross coupling method.

       6 illustrates an equivalent circuit configuration of a notch coupling filter according to an embodiment of the present invention.

       Referring to FIG. 6, inductor and capacitor combinations L1C1, L2C2, L3C3, and L4C4 corresponding to each resonator are connected in a cascade manner. Unlike FIG. 2, the cascaded inductor and capacitor combinations are coupled by inductors and capacitors L20C20 and L21C21.

       That is, the circuit of FIG. 6 has a form in which a band pass filter and a band stop filter are combined.

       In the circuit of Figure 6, two notches occur, and the frequency at which the notches occur is determined by L20 and C20 and L21 and C21.

       7 is a diagram illustrating an output waveform of an RF filter to which a notch generation method is applied according to an embodiment of the present invention.

       7 shows the output waveform of a filter with one coupling bar for notch formation. Referring to FIG. 7, it can be seen that one notch is formed at 2.3 GHz, and the skirt characteristic of the left stop band is improved compared to the right stop band due to the formed notch.

       Preferred embodiments of the present invention described above are disclosed for purposes of illustration, and those skilled in the art will be able to make various modifications, changes, and additions within the spirit and scope of the present invention. Additions should be considered to be within the scope of the following claims.

 As described above, according to one embodiment of the present invention, there is an advantage that a notch can be generated without being dependent on the structure of the filter.

 In addition, according to an embodiment of the present invention, there is an advantage that can improve the skirt characteristics by generating a larger number of notches than the notch generation method such as cross coupling.

Claims (7)

       Multiple cavities;        A plurality of resonators installed in each of the plurality of cavities;        At least one coupling bar installed at a coupling window position open to the cavity corresponding to an advancing direction of an RF signal; And        And a support member for supporting the coupling bar.        The method of claim 1,        And the support member is a dielectric material and extends from any part of the housing to support the coupling bar.        The method of claim 1,        And the number of coupling bars is set corresponding to the number of notches to be produced.        The method of claim 1,       The coupling bar is a metal material, notch coupling RF filter, characterized in that the cylindrical or disk shape.        The method of claim 1,       The male member is formed on the support member and the female thread is formed on the coupling bar so that the coupling bar is coupled to the support member in the form of a screw connection and the height thereof is adjusted by rotation.        A plurality of resonant elements configured to resonate an RF signal in a specific frequency band;       A coupling element for coupling an RF signal from one resonance element to another;       At least one of the coupling elements comprises both inductive coupling means for inductive coupling and capacitive coupling means for capacitive coupling.        The method of claim 6,       Wherein the inductive coupling means is an inductor, the capacitive coupling means is a capacitor, and a notch is formed corresponding to the inductor value and the capacitor value.

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