JP2006186828A - Band pass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure of a filter for downsizing an apparatus by multilayering. <P>SOLUTION: An interdigital filter is constituted so that a plurality of resonators for folding line resonators, respectively, are arranged in parallel on a dielectric substrate of a strip line construction or a microstrip line construction, wherein broadside joint structures 1U and 1L having a plurality of conductors where both ends of the plurality of resonators are arranged on different surfaces across the dielectric bodies are formed, and edge joint structures 2 with a plurality of conductors where the other is arranged on the same plane is formed. In comparison with the case that all are edge joint structures, the thickness of the dielectric substrate can be reduced to one-third so as to laminate a plurality of filters. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a band-pass filter in a microwave band, and more particularly to a structure for miniaturization of a band-pass filter.

  In recent years, mobile communication has become widespread, and miniaturization of radio circuits is strongly demanded. A band-pass filter in the microwave band is an important circuit of a radio circuit, but generally occupies the largest area in the radio circuit, and particularly downsizing is important. Regarding the structure of the filter, there are many documents, but as a frequently used one, a filter using a half-wave resonator with open both ends, a short circuit with one side, and a quarter-wave resonator with one side open, There are interdigital type band-pass filters (Non-Patent Documents 1 to 3).

SEYMOUR B. COHN "Parallel-Coupled Transmission-Line-Resonator Filters" IRE Transactions ON Microwave Theory AND Techniques, pp.223-231 (1958) G. Matthaei, l.Young, E.M.T.Jones MICROWAVE FILTERS, Impedance-Matching Networks, AND Coupling Structures, Artech House (1985) Chi-Yang, Cheng-Chung Chen, AND Hong-Jie Huang "Folded quarter-wave resonator filters with Chebyshev, flat group delay, or quasi-elliptical function response" 2002 IEEE MTT-S pp.1609-1612

  Conventionally, the filter is wired on the same plane. Further, in terms of filter design, coupling at both ends is usually large, and an intermediate resonator needs to have small coupling, an interval between intermediate coupling lines is wide, and a line interval between coupling lines on both sides needs to be narrow. However, when producing a filter conductor on a printed board or a ceramic board, the limit of miniaturization is about 0.1 mm. If the line spacing is narrow and less than the production limit, it becomes impossible to produce. In such a case, it is necessary to widen the line spacing while maintaining the characteristics.

  In a circuit composed of a strip line or a strip-coupled line, when the dielectric thickness is multiplied by a, the same characteristics can be obtained by multiplying the line width and the line spacing by a. Therefore, the minimum line can be obtained by increasing the dielectric thickness. The design has been made so that the interval is about 0.1 mm or more. (In the microstrip structure, the equation is complicated, but qualitatively, by increasing the dielectric thickness, the same characteristics can be obtained by widening the line width and line interval.) This thickness is usually about 0.6 to 1 mm. However, since the apparatus is thin, the upper limit of the substrate thickness is often about 0.5 to 1 mm. Therefore, it has been difficult to reduce the area by multilayering the filter and arranging two filters on the upper and lower sides.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a filter structure that can be downsized by multilayering.

  The present invention provides an interdigital filter in which a plurality of resonators configured by bending line resonators on a dielectric substrate having a stripline structure or a microstripline structure are arranged in parallel, and at least at both ends of the plurality of resonators. The resonator has a broad side coupling structure having a plurality of conductors arranged on different surfaces across the dielectric, and the other resonator has an edge coupling structure having a plurality of conductors arranged in the same plane. Is.

  Preferably, the conductor having the edge coupling structure is disposed in the same plane as any one of the plurality of conductors according to the broad side coupling structure.

  The band-pass filter is, for example, a half-wavelength line resonator having both ends open on a dielectric substrate having a stripline structure or a microstripline structure bent into a hairpin shape. A line resonator having a length of 1/4 wavelength that is short-circuited is bent into a hairpin shape.

  The broadside coupling structure is one of the wiring configuration methods, and is a configuration method using two upper and lower layers of a multilayer substrate. An edge coupling line is also a wiring configuration method, in which two signal wirings are arranged side by side on the same wiring layer.

  In the present invention, a large coupling is realized by using a broadside coupling line in which the lines are arranged one above the other for coupling the coupling lines on both sides, while on the other hand, the edge coupling in which the lines are arranged on the same plane for the coupling of the intermediate coupling line A small coupling was realized by using a line. Such coupling is particularly required in a high-frequency bandpass filter. By using the structure of the present invention, the minimum line width and line interval can be made 0.1 mm or more, which is the manufacturing limit, while reducing the substrate thickness. Conventionally, if the minimum line width / line interval is set to 0.1 mm or more, the thickness of the substrate has to be increased. By making the substrate thin, it becomes possible to make a multilayer, and by making the multilayer, it is possible to reduce the size of the apparatus.

  By using the structure according to the present invention, the thickness of the substrate can be reduced while keeping the minimum dimension large. As a result, the number of substrates can be increased, and the occupied area can be significantly reduced.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the structure of a bandpass filter according to an embodiment of the present invention. 1A is a top view of the bandpass filter, FIG. 1B is a cross-sectional view of the filter taken along the line aa ′, and FIG. 1C is a cross-sectional view of the filter taken along the line bb ′. Show. In these figures, 1 is a broad-side coupled line, 2 is an edge-coupled line, 3 is an input / output terminal, and 4 is a ground electrode. 1L is a lower layer electrode having a broadside bond structure, and 1U is an upper layer electrode. A dielectric D is filled between the coupled lines 1L and 1U and the ground electrode 4, between the coupled line 2 and between the coupled line 2 and the ground electrode 4. For ease of viewing, the display of the ground electrode 4 and the dielectric D is omitted in FIG.

FIG. 2 is a perspective view of the band-pass filter of FIG. For ease of viewing, the display of the ground electrode 4 and the display of the dielectric are omitted in FIG.
As can be easily seen from these drawings, the coupled lines on both sides of the bandpass filter according to the embodiment of the present invention are composed of broad-side coupled lines, and the intermediate coupled line is composed of edge-coupled coupled lines. A coupling line 1U is provided on the coupling line 1L so as to overlap with a predetermined interval (the dielectric D exists in this gap). Since the length of the coupled line 1U is slightly longer than that of the coupled line 1L, the end thereof does not overlap the coupled line 1L. An input / output terminal 3 is provided at the end thereof.

  As shown in FIG. 1 (b), the coupled lines 1L and 1U at both ends constitute broadside coupled lines arranged above and below, and the coupled lines 2 and 2 are on the same plane as shown in FIG. 1 (c). The edge-coupled coupling line arranged in the above is configured. As shown in FIGS. 1B and 1C, ground electrodes 4 are disposed on both sides (up and down). As shown in FIG. 1B, in the broadside coupling structure, the distance between the upper ground electrode 4 and the coupled line 1U, the coupled lines 1U and 1L, and the coupled line 1L and the lower ground electrode 4 is the same. (Reference t). As shown in FIG. 1C, in the edge coupling structure according to the embodiment of the present invention, the distance (2t) between the upper ground electrode 4 and the coupling line 2 is the same as that between the coupling line 2 and the lower installation electrode 4. It is twice the interval (t). This is because the line 1 at both ends has a broad side coupling structure, and edge coupling is formed in the same plane as one of the conductors.

  In the band-pass filter according to the embodiment of the invention, the coupled lines at both ends, which normally require large coupling, are constituted by broad-side coupled lines that are inherently coupled. When the left side of FIG. 1 is used as an input, the signal input from the end 3 of the upper line moves from the upper layer electrode 1U related to the broadside coupled line to the lower layer electrode 1L. By adjusting the length to ¼ of the wavelength at the center frequency, only the signal of that frequency is transmitted to the lower electrode. Next, the signal transmitted to the lower layer propagates only at the desired frequency on the edge-coupled coupling lines 2 and 2, and the frequency is selected in the same manner on the right coupled lines 1 L and 1 U. Only the band signal is extracted.

  By using the structure according to the embodiment of the invention, it is possible to reduce the thickness of the substrate while keeping the minimum dimension large, and it is possible to greatly reduce the occupied area by multilayering. The reason for this is explained in detail in the description of the embodiment below. In short, a large coupling is realized by using a broadside coupling line in which the lines are arranged one above the other for coupling the coupling lines on both sides, while the middle This is because small coupling is realized by using an edge coupling line in which the lines are arranged on the same plane, and the line width and the line spacing can be made below the production limit for all parts of the filter.

Next, specific examples and characteristic examples of the structure according to the embodiment of the invention will be described. For convenience of explanation, description will be added in the order of an edge coupling structure (comparative example), a broadside coupling structure (comparative example), and a combination of both.
(1) When configuring a filter using only an edge coupling structure (comparative example)
Consider a case in which a filter is formed on a dielectric having a thickness of 0.4 mm. For example, a printed circuit board for a mobile phone is manufactured with a dielectric thickness of about 0.8 mm. If a filter can be formed in a 0.4 mm dielectric, the top and bottom are divided into 0.4 mm, and a filter is provided for each. Since it can be manufactured, it takes half the area compared to the case of manufacturing on the same surface. When a filter is manufactured by edge coupling, the electrodes are arranged in the center, so that the dielectric thickness is arranged 0.2 mm above and below the line conductor. When a filter of 10% bandwidth, ripple 0.1 dB, and three stages, which is often used now, is manufactured in accordance with the aforementioned Non-Patent Document 1, the values of the even mode impedance Ze and odd mode impedance Zo of the first coupled line Becomes Ze = 77Ω and Zo = 38Ω. In the second coupled line, Ze = 58Ω and Zo = 44Ω. The third coupled line has the same impedance as the second coupled line, and the fourth coupled line has the same impedance as the first coupled line. The coupling coefficient C is obtained by C = (Ze−Zo) / (Ze + Zo), the coupling coefficient of the first and fourth coupling lines at both ends is 0.34, and the coupling coefficient of the middle second and third coupling lines Is 0.14 and the coupling coefficient at both ends is overwhelmingly large. When the coupling coefficient is large, the interval between the coupled lines needs to be narrowed.

  Normally, the metal thickness of the electrode is very thin, so if the metal thickness is approximated to infinity, the line width and line spacing to achieve the desired Ze and Zo with the above substrate thickness are unique if the dielectric constant of the dielectric is specified. Determined. For example, when the dielectric constant is 3.7 (relative dielectric constant of a commercially available low-loss substrate material), the electrode width of the coupled line in the case of a resin substrate is 0.15 mm and the line interval is 0.033 mm, and the line interval is smaller than 0.1 mm. Therefore, it is necessary to triple the thickness of the substrate so that the distance is 0.1 mm, so that the line interval is 0.1 mm. The substrate thickness is 1.2 mm at this time, and 2.4 mm when the filters are stacked on the upper and lower sides. Such a thick substrate cannot be used normally because the apparatus becomes large. On the other hand, the line width of the intermediate coupled line is 0.204 mm, the line interval is 0.118 mm, and this can be realized with a minimum dimension of 0.1 mm.

  FIG. 3A shows an example of characteristics when a filter is configured using only the edge coupling structure. FIG. 3A shows a band-pass filter manufactured by edge coupling and having a dielectric substrate of 0.4 mm and 1.2 mm. The line length of 0.4 mm is 15.9 mm, the line width and line interval are the dimensions shown in the examples. As described above, in the bandpass filter configured only by edge coupling, the same characteristic can be obtained with the minimum line width of 0.099 mm and the minimum dimension of approximately 0.1 mm by triple the dielectric thickness. However, in order to make the minimum dimension 0.1 mm or more, it is necessary to increase the dielectric thickness. When the dielectric thickness is 1.2 mm, the line length is 15.9 mm and the dielectric thickness is tripled, so the line width and line spacing are tripled. As can be seen from the figure, the two characteristics are exactly the same. However, if the filters are stacked at 1.2 mm with the dielectric thickness tripled, the thickness becomes 2.4 mm and cannot be mounted on a mobile phone or the like.

(2) When configuring a filter using only the broadside coupling structure (comparative example)
Next, a dimension is calculated | required about the case where a broad side coupling | bonding is used. Since the dielectric is divided into three layers in the broadside coupled line, the dimensions are obtained when the overall thickness is set to 0.39 mm as a dielectric thickness of 0.13 mm / 0.13 mm / 0.13 mm, for example. At this time, when the same dielectric constant is 3.7 and the line width is 0.144 mm, Ze = 77Ω and Zo = 38Ω are obtained, and desired Ze and Zo can be realized with a minimum dimension of 0.1 mm or more. In the broad-side coupled line, with the above substrate configuration, Ze and Zo of the intermediate coupled line cannot be realized because the coupling is too small.

(3) Combination of broad side coupling structure and edge coupling structure (embodiment of the invention)
As described above, when a broadside coupling structure is applied to the coupled lines at both ends, Ze = 77Ω and Zo = 38Ω are obtained when the line width is 0.144 mm, and desired Ze and Zo are obtained with a minimum dimension of 0.1 mm or more. Can be realized. If the edge coupling structure is applied to the intermediate coupling line, the line width is 0.204 mm, the line interval is 0.118 mm, and the minimum dimension is 0.1 mm. Therefore, the combination of the broad side coupling structure and the edge coupling structure can reduce the minimum line width and line spacing to 0.1 mm or more of the manufacturing limit while reducing the substrate thickness (0.4 mm). With this thickness, even when two filters are stacked, the dielectric thickness of the printed circuit board (0.8 mm) can be suppressed, and the filter can be mounted on a mobile phone or the like.

  As can be seen from the above discussion, a band-pass filter having the same desired characteristics can be formed even on a thin substrate by using broad-side coupling for the coupling lines on both sides and using edge coupling for the intermediate coupling lines. In this case, as shown in FIG. 1C, the edge-coupled coupled line is an asymmetric coupled line in which the distance to one ground electrode 4 is 0.13 mm and the distance to the other ground electrode 4 is 0.26 mm. However, Ze = 58Ω and Zo = 44Ω, which are the impedances of the intermediate coupling line, can be realized with a line width of 0.155 mm and a line interval of 0.13 mm, which can also be realized with a line width of 0.1 mm or more and a line interval.

  FIG. 3B shows an example of a change in characteristics due to the structure of the present invention. FIG. 3 (b) shows the characteristics (reference E) of a bandpass filter made of all edge-coupled coupled lines, and the bandpass structure of the present invention composed of broadside coupled on both sides and edge-coupled coupled lines on the middle. This is a comparison of filter characteristics (symbol B + E). The dielectric thickness of all edge-coupled filters is 1.2 mm, whereas the dielectric thickness of the structure according to the embodiment of the present invention is 0.39 mm. As can be seen from the figure, the two characteristics are almost the same. The characteristic of the embodiment of the present invention is almost the same as that of only edge coupling, but the thickness of the dielectric is only about 1/3 that of edge coupling.

  As specifically described above, by using the structure of the present invention, the minimum line width is smaller than the limit of miniaturization (for example, 0.1 mm) when a filter conductor is formed on a printed board or a ceramic board. The substrate thickness can be reduced while keeping it large. Since a thinner substrate can be used, the substrate can be multilayered, and the occupied area can be greatly reduced.

  4A is a plan view of the structure of the first embodiment of the invention applied to an interdigital filter having a quarter wavelength line, and FIG. 4B is a cross-sectional view taken along the line cc ′. is there. 11L is a broad-side coupled line (lower layer electrode), 11U is a broad-side coupled line (upper layer electrode), and 12 is an edge-coupled coupled line (upper layer electrode). Reference numeral 13 denotes a lower electrode ground, 14 an upper electrode ground, 15 an input / output terminal, and 16 an impedance matching stub.

As shown in FIG. 4, it is possible to reduce the thickness of a resonator having a quarter wavelength of one-side short as well.
Needless to say, a filter having a microstrip line structure can also be made thin.

  The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

It is a figure which shows the structure of the bandpass filter using (wavelength) / 2 line | wire based on embodiment of invention, FIG. 1 (a) is the top view, FIG.1 (b) is the aa 'sectional drawing. FIG. 1C is a sectional view taken along the line bb ′. It is a perspective view of the bandpass filter of FIG. FIG. 3 (a) shows a comparison of characteristics of a conventional bandpass filter having a dielectric thickness of 0.4 mm and 1.2 mm fabricated with edge-coupled coupled lines, and FIG. 3 (b) is fabricated with edge-coupled coupled lines. A characteristic comparison between a conventional band-pass filter having a dielectric thickness of 1.2 mm and a band-pass filter having a dielectric thickness of 0.39 mm having a structure according to an embodiment of the present invention is shown. It is a figure which shows the structure of the bandpass filter using (wavelength) / 4 line concerning embodiment of invention, and Fig.4 (a) is the top view, FIG.4 (b) is the cc 'sectional drawing. It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Broadside coupling coupling line 1L Lower layer electrode 1U Upper layer electrode 2 Edge coupling coupling line 3 Input / output terminal 4 Ground electrode 11L Broadside coupling coupling line (lower layer electrode)
11U Broadside coupled line (upper layer electrode)
12 Edge-coupled coupling line (upper layer electrode)
13 Grounding of lower layer electrode 14 Grounding of upper layer electrode 15 Input / output terminal 16 Stub for impedance matching

Claims (2)

  In an interdigital filter in which a plurality of resonators each formed by bending a line resonator on a dielectric substrate having a stripline structure or a microstripline structure are arranged in parallel, the resonators at least at both ends of the plurality of resonators, It has a broad side coupling structure having a plurality of conductors arranged on different surfaces across a dielectric, and the other resonator has an edge coupling structure having a plurality of conductors arranged in the same plane. Bandpass filter to be used. The band-pass filter according to claim 1, wherein the edge coupling structure is disposed in the same plane as any one of the plurality of conductors according to the broadside coupling structure.

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