JP4629617B2 - High frequency coupled line and high frequency filter - Google Patents

Description

  The present invention relates to a high frequency coupling line and a high frequency filter used in a microwave band or a millimeter wave band.

  Microstrip line type coupled lines often used at high frequencies such as microwaves and millimeter waves include various types of coupled lines, but one of the main ones is two strip conductors with open ends on the top surface of a dielectric substrate. Some are arranged in parallel and in opposite directions. In this coupled line, the combination of the coupled line impedance (even mode impedance Ze and odd mode impedance Zo) is determined by appropriately selecting the dimensional parameters W and S of the width of the strip conductor and the distance between the strip conductors, and the strip conductors are parallel. A band-pass type frequency characteristic is exhibited centering on a frequency at which the length of the sections arranged in a line is approximately ¼ wavelength.

  For this reason, for example, a band pass filter can be realized by connecting a plurality of coupled lines in cascade. Since the band-pass filter having such a circuit configuration has a simple structure, it is very often used in a microwave or millimeter wave band (see, for example, Patent Document 1).

JP 2004-104588 A

  However, since the above-described coupled line has a simple configuration and can be easily manufactured, it is widely used in various circuits. However, when the dimension parameter h of the thickness of the dielectric substrate changes (dielectric substrate) If the thickness of the coupling line varies, the coupled line impedance changes, and the characteristics of the coupled line greatly vary. In the band pass filter as described in the above-mentioned patent document 1, the characteristic fluctuation is mainly caused such that the width of the pass band is widened or narrowed.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to realize a coupled line with little characteristic variation due to variations in the thickness of a dielectric substrate and to improve circuit yield.

  A high-frequency coupling line according to the present invention is formed on a dielectric substrate, a ground conductor provided on one main surface of the dielectric substrate, and the other main surface of the dielectric substrate, and is arranged substantially in parallel. A plurality of strip conductors that are electromagnetically coupled to each other, and a ground conductor formed by a connection conductor that is formed to be insulated from the surroundings by a cutout provided in the strip conductor and penetrates the dielectric substrate without electrical conduction with the strip conductor. And an input / output terminal provided at at least one end of each of the plurality of strip conductors.

  In addition, a high frequency coupling line according to another invention includes two dielectric substrates formed by lamination, two ground conductors respectively provided on one main surface of the two dielectric substrates, and the two dielectrics A plurality of strip conductors formed between the substrates, having cutouts and arranged substantially in parallel and electromagnetically coupled to each other, and through the cutouts and the two dielectric substrates without electrical continuity with the strip conductors The connection conductor for electrically connecting the two ground conductors, and the input / output terminals respectively provided at at least one end of the plurality of strip conductors.

  Furthermore, a high-frequency coupled line according to still another invention includes two dielectric substrates formed by lamination, two ground conductors respectively provided on one main surface of the two dielectric substrates, and the two dielectrics. A plurality of strip conductors formed between the body substrates and arranged in parallel to each other and electromagnetically coupled to each other, and formed by being insulated from the surroundings by cutouts provided in the strip conductors, and without electrical continuity with the strip conductors An internal strip conductor electrically connected to at least one of the two ground conductors by a connection conductor penetrating at least one of the dielectric plates, and an input / output terminal provided at at least one end of the plurality of strip conductors It is equipped with.

  The high frequency filter according to the present invention is configured using the high frequency coupling line described above.

  Furthermore, a high frequency filter according to another invention is formed by cascading a plurality of the high frequency coupling lines described above.

  According to the present invention, it is possible to obtain a high-frequency coupled line and a high-frequency filter that can realize a coupled line with little characteristic variation due to variations in the thickness of the dielectric substrate and can improve the yield of the circuit.

Embodiment 1 FIG.
1 is a perspective view showing a high-frequency coupling line according to Embodiment 1 of the present invention. 2 is a top view of FIG. 1 as viewed from above, and FIG. 3 is a cross-sectional view taken along line AA ′ of FIG. As shown in these drawings, a ground conductor 2 is provided on one main surface of a dielectric substrate 1, and a strip which is electromagnetically coupled by being arranged substantially parallel to each other and opposite to each other. Conductors 6a and 6b are formed. The strip conductors 6a and 6b have cutouts 5a and 5b, and are disposed inside the cutouts 5a and 5b with gaps 9a and 9b so as not to be short-circuited without electrical continuity with the strip conductors 6a and 6b. Internal strip conductors 8a and 8b electrically connected to the ground conductor 2 are formed at through-holes 7a-1, 7a-2, 7b-1, and 7b-2 as connecting conductors penetrating 1. Reference numerals 4a and 4b denote input / output terminals. 3, W1 and W2 are the widths of the strip conductors 6a and 6b, W is the width of the conventional strip conductor, S is the distance between the strip conductors 6a and 6b, and h is the thickness of the dielectric substrate 1.

  Before describing the high-frequency coupling line according to the first embodiment, first, the relationship between the coupling line impedance and the thickness of the dielectric substrate in the conventional high-frequency coupling line will be described. Here, as a conventional coupled line, a coupled line having a symmetrical structure in which two strip conductors arranged in parallel on a dielectric substrate have the same width is considered. In a coupled line having a symmetric structure, it is assumed that a magnetic wall or an electrical wall is used as the structural symmetry plane, and the coupled line impedance is obtained by calculating the capacitance between one strip conductor and the ground conductor (or ground conductor and electrical wall). Is estimated.

  The coupled line impedance includes an even mode impedance and an odd mode impedance. In particular, when the thickness h of the dielectric substrate 1 changes, the even-mode impedance varies greatly. This is because the even mode impedance is determined only by the capacitance Cg generated between the strip conductor and the ground conductor facing each other through the dielectric substrate. On the other hand, the odd mode impedance includes an electrostatic capacity Cg generated between the strip conductor 6 and the ground conductor 2 and an electrostatic capacity Cw generated between the strip conductor and the electric wall, and the sum of the two contributes to the impedance. . Since the capacitance Cw generated between the strip conductor and the electric wall is not greatly changed by the change of the substrate thickness h, the total capacitance change rate is higher than that of the even mode impedance. It becomes smaller. Since this relationship always holds, a coupled line with a small rate of change in even-mode impedance due to the substrate thickness has a small characteristic variation as a coupled line.

  Next, regarding the first embodiment, the relationship between the coupled line impedance and the thickness of the dielectric substrate 1 will be described as in the conventional coupled line. 4 shows the capacitance related to the even mode impedance of the high-frequency coupling line according to the first embodiment, and FIG. 5 shows the capacitance related to the odd mode impedance. In FIG. W. Is a magnetic wall, E. in FIG. W. Indicates an electrical wall. In this high-frequency coupled line, the internal strip conductor 8 and the through hole 7 arranged in the cutout 5 of the strip conductor 6 have substantially the same potential as that of the ground conductor 2, and thus play the same role as the ground conductor 2. For this reason, the electrostatic capacity related to the even mode impedance includes the electrostatic capacity Cg between the strip conductor 6 and the ground conductor 2 and the electrostatic capacity Cp between the strip conductor 6 and the inner strip conductor 8 (and the through hole 7). There are two types.

  On the other hand, the capacitance related to the odd mode impedance includes the strip conductor 6 and the electric wall E.P. in addition to the capacitances Cg and Cp. W. The capacitance Cw between the two is added, so that there are three types. When a coupled line having the same characteristics as a conventional coupled line is realized on the same dielectric substrate, the dimensions of each of the even and odd impedances are set so that the sum of the related capacitances roughly matches that of the conventional coupled line. Will be selected. At this time, the electrostatic capacitance between the strip conductor 6 and the ground conductor 2 in the high-frequency coupling line according to the first embodiment is always greater than that of the conventional coupling line due to the presence of the internal strip conductor 8 and the through hole 7. Since it becomes small, it turns out that the ratio occupied with respect to a total electrostatic capacitance becomes small. Further, the electrostatic capacitance between the strip conductor 6 and the inner strip conductor 8 (and the through hole 7) does not change greatly with respect to the change in the thickness of the dielectric substrate 1. Therefore, in the high-frequency coupling line according to the first embodiment, the fluctuation of the coupling line impedance due to the change in the thickness of the dielectric substrate 1 is smaller than that of the conventional coupling line.

  In addition, as a supplement, actually, the through hole 7 connecting the internal strip conductor 8 and the ground conductor 2 has an inductance, and the electrical length of the through hole 7 is changed due to the change in the thickness of the dielectric substrate 1. Changes. For this reason, the contribution that the internal strip conductor 8 (and the through hole 7) gives to the strip conductor 6 is the negative of the sum of the reactance given by the capacitance between the two and the reactance given by the inductance of the through hole 7 described above. Expressed from reactance. For this reason, when the thickness of the dielectric substrate 1 is increased, the negative reactance approaches 0 due to an increase in the inductance of the through hole 7, so that the gap between the internal strip conductor 8 and the strip conductor 6 is increased. This is equivalent to a slight increase in capacitance. That is, it is added that the electrostatic capacitance between the inner strip conductor 8 (and the through hole 7) and the strip conductor 6 acts in a direction to cancel the change in the electrostatic capacitance between the strip conductor 6 and the ground conductor 2. .

  As a design example, FIG. 6 shows the calculated value of the pass characteristic of the conventional coupled line, and FIG. 7 shows the calculated value of the pass characteristic of the high-frequency coupled line according to the first embodiment. The frequency freq on the horizontal axis indicates the frequency, and S21 on the vertical axis indicates the S parameter of the two-terminal circuit. The port 1 to port 2 when the input / output terminal 4a and the input / output terminal 4b of FIG. The transmission pass characteristic to is shown. Both are configured using the same dielectric substrate 1 having a relative dielectric constant er = 3.4, and the frequency characteristics obtained using the electromagnetic simulator are overwritten with the thickness h of the dielectric substrate 1 as a parameter. It is a thing. The characteristic calculation was performed around 14 GHz where the electrical length of the coupled line was 90 degrees. As can be seen from these figures, the coupling line according to the present embodiment has a small characteristic variation due to the thickness of the dielectric substrate.

  As described above, according to the high-frequency coupled line according to the first embodiment, since a coupled line with less characteristic variation due to variation in the thickness h of the dielectric substrate 1 can be obtained, the circuit yield is improved and the yield is improved. There is an effect that the cost reduction by is achieved. In particular, due to recent progress in material technology, low-cost resin-based dielectric substrates have come to be used in microwave millimeter-wave circuits instead of ceramic-based substrates. There is a problem that the thickness of the dielectric substrate is slightly larger than that of the ceramic substrate, and the conventional coupled line has a large variation in characteristics. The coupled line of the present embodiment has an effect that a microwave millimeter wave circuit having stable characteristics can be obtained even with a resin-based dielectric substrate having a relatively large thickness error of the dielectric substrate. There is.

  In the first embodiment, a coupled line having a microstrip line structure is shown as an example. Needless to say, the same effect can be expected with other planar circuit lines including a triplate line structure.

  In the first embodiment, the coupled line is described in which two strip conductors 6a and 6b are arranged in parallel and in opposite directions on the upper surface of the dielectric substrate 1, but the two strip conductors are the same. It goes without saying that the same effect can be obtained even if the orientation is adjusted.

  Further, in the first embodiment, the structure in which one of the cutouts 5a and 5b is provided in the strip conductors 6a and 6b has been described. However, even if there are two or more cutouts, the basic effect remains unchanged.

  Furthermore, in the first embodiment, for the sake of simplicity, the description has been given by taking the example of the structure in which the cross-sectional structure of the coupled line is bilaterally symmetric. However, the same effect can be obtained even if the structure is bilaterally asymmetric. Needless to say.

Embodiment 2. FIG.
FIG. 8 is a perspective view showing a microstrip line type bandpass filter according to Embodiment 2 of the present invention. FIG. 9 is a top view of FIG. 8 viewed from above. The microstrip line type bandpass filter according to the second embodiment is configured by cascading three coupled lines having basically the same structure as the coupled line shown in the first embodiment. Reference numerals 1 to 9 indicate the same as those in the first embodiment.

  As shown in the first embodiment, the high-frequency coupled line used in the bandpass filter according to the second embodiment has a small change in the coupled line impedance due to the variation in the thickness of the dielectric substrate 1. That is, the change in the coupling coefficient of the high-frequency coupling line is small. In the band pass filter of the second embodiment, the bandwidth is expressed as a function of the coupling coefficient. For this reason, the band pass filter according to the second embodiment has a small variation in bandwidth.

  That is, according to the bandpass filter of the second embodiment, even if the thickness of the dielectric substrate 1 varies, there is an effect that a bandpass filter with small characteristic fluctuation, in particular, with little fluctuation in bandwidth can be obtained. is there.

  In the second embodiment, the band-pass filter having the circuit configuration shown in FIG. 8 has been described as an example. However, the effect of reducing the characteristic variation due to the variation in the thickness of the dielectric substrate is limited to the circuit type. However, it goes without saying that the effect can be expected with filters of various circuit types, directional couplers, etc. using coupled lines.

  In the second embodiment, three coupled lines having basically the same structure as the coupled line shown in the first embodiment are cascade-connected, but all three coupled lines are not necessarily implemented. The coupled line having the same structure as the coupled line of the first embodiment may not be used. For example, of the three coupled lines, only one of the central portions may be a coupled line having the same structure as that of the first embodiment, and the remaining two may be conventional coupled lines.

Embodiment 3 FIG.
FIG. 10 is a perspective view showing a microstrip line type coupled line according to Embodiment 3 of the present invention. Although it has basically the same structure as the coupled line shown in the first embodiment, in the coupled line of the third embodiment, two strip conductors having open ends are arranged in the same direction.

  The relationship between the thickness of the dielectric substrate 1 and the coupled line impedance described with reference to FIGS. 4 and 5 is determined by the cross-sectional structure of the two strip conductors 6 and does not depend on the orientation of the two strip conductors 6. For this reason, also in the coupled line of the third embodiment, similarly to the coupled line of the first embodiment, a coupled line with small characteristic variation can be obtained even if the thickness of the dielectric substrate 1 varies.

Embodiment 4 FIG.
FIG. 11 is a perspective view showing a microstrip line type coupled line according to Embodiment 4 of the present invention. The strip conductor constituting the coupled line of the fourth embodiment is provided with input / output terminals at both ends, and is a four-terminal coupled line.

  The relationship between the thickness of the dielectric substrate 1 and the coupled line impedance described with reference to FIGS. 4 and 5 is determined by the cross-sectional structure of the two strip conductors 6 and does not depend on the presence or absence of an open end or a short-circuit end. For this reason, also in the coupled line of the fourth embodiment, similarly to the coupled lines described in the other embodiments, a coupled line with small characteristic variation can be obtained even if the thickness of the dielectric substrate varies.

Embodiment 5. FIG.
FIG. 12 is a perspective view showing a triplate line type coupled line according to Embodiment 5 of the present invention. FIG. 13 is a cross-sectional view taken along line AA ′ in FIG. Cutouts 5a and 5b are provided in the two strip conductors 6a and 6b, and through holes 7a-1 and 7a- are used as connection conductors that penetrate the cutouts 5a and 5b and electrically connect the upper and lower ground conductors 2a and 2b. 2, 7b-1, 7b-2 are provided.

  The coupled line of the fifth embodiment exhibits the same operations and effects as the coupled line described in the first embodiment. Further, the structure of the fifth embodiment can form a through-hole by laminating two dielectric plates 1a and 1b and then forming a through-hole for plating and plating. Does not require strip conductors. For this reason, there exists an effect that a coupling line with a small width can be constituted. 4 and 5, the capacitance Cp between the inner strip conductor and the strip conductor corresponds to the capacitance between the through-hole and the strip conductor, and is substantially the same as that of the coupled line of the other embodiments. There is no difference in the functions, and the obtained effects are the same.

  In the fifth embodiment, the triplate line structure has been described as an example, but it goes without saying that the same effect can be obtained even when realized by another similar line structure such as a suspended line.

  In the fifth embodiment, through holes 7a-1, 7a-2, 7b-1, 7b-2 are used as connecting conductors that penetrate the cutouts 5a, 5b and electrically connect the upper and lower ground conductors 2a, 2b. In place of this, instead of this, as in the first embodiment, a connection is provided inside the cutout with a gap without electrical continuity with the strip conductor and penetrating at least one of the dielectric plates. An internal strip conductor electrically connected to at least one of the two ground conductors by a conductor may be provided.

  As described above, according to the present invention, in a coupled line composed of a planar circuit type line structure such as a microstrip line or a triplate line, a strip conductor is provided with a cutout, and a ground conductor is provided by a connecting conductor inside the strip conductor. And an internal conductor electrically connected to each other. For this reason, the ratio of the capacitance generated between the strip conductor and the ground conductor is reduced in the total capacitance generated by the strip conductor, so that the fluctuation of the coupled line impedance due to the variation in the thickness of the dielectric substrate is reduced. Thus, there is an effect that a coupled line with small characteristic fluctuation can be obtained. In addition, the reduction in characteristic variation has the effect of improving yield and reducing manufacturing costs.

  Further, in a coupled line composed of a planar circuit type line such as a triplate line provided with ground conductors on both of the two main surfaces of the dielectric substrate, a cut is provided in the strip conductor, and 2 passes through the inside thereof. A connection conductor for electrically connecting two ground conductors was provided. Since the cutout has no internal strip conductor, the width of the coupled line can be reduced, and the circuit can be reduced in size.

  In addition, in a coupled line formed by arranging two strip conductors having one end as an open end or a short-circuited end and an input / output terminal at the other end in parallel, the coupled line has less characteristic fluctuation due to variations in the thickness of the dielectric substrate. There is an effect that can be obtained.

  Furthermore, in the most versatile coupled line, which is composed of two strip conductors with one open end and one input / output terminal at the other end, parallel to each other, the fluctuations in characteristics due to variations in the thickness of the dielectric substrate There is an effect that a coupled line with a small number of lines can be obtained.

  In addition, since the high-frequency filter is configured using a coupled line having a small characteristic variation due to variations in the thickness of the dielectric substrate, there is an effect that a filter having a small characteristic variation can be obtained.

  Further, the coupled line that is a component of the most widely used bandpass filter is a coupled line that has a small characteristic variation due to variations in the thickness of the dielectric substrate. Since the bandwidth of the present bandpass filter is a function of the coupling coefficient of the coupled line, there is an effect that a bandpass filter having a small variation in bandwidth due to variations in the thickness of the dielectric substrate can be obtained.

It is a perspective view of the coupling line used as Embodiment 1 of this invention. It is a top view of the coupled line which concerns on Embodiment 1 of this invention. FIG. 3 is a cross-sectional view taken along the line AA ′ in FIG. 2 and main dimensional parameters. It is the figure which showed the electrostatic capacitance in connection with the even mode impedance of the coupling line which concerns on Embodiment 1 of this invention. It is the figure which showed the electrostatic capacitance in connection with the odd mode impedance of the coupling line which concerns on Embodiment 1 of this invention. It is a figure which shows the passage characteristic of the conventional coupling line for comparing with the coupling line which concerns on Embodiment 1 of this invention. It is a figure which shows the passage characteristic of the coupling line which concerns on Embodiment 1 of this invention. It is a perspective view of the bandpass filter used as Embodiment 2 of this invention. It is a top view of the band pass filter used as Embodiment 2 of this invention. It is a perspective view of the coupling line used as Embodiment 3 of this invention. It is a perspective view of the coupling line used as Embodiment 4 of this invention. It is a perspective view of the coupling line used as Embodiment 5 of this invention. It is a figure which shows sectional drawing in the AA 'cross section in FIG.

Explanation of symbols

  1 dielectric substrate, 2 ground conductor, 3 open end, 4 input / output terminal, 5 cutout, 6 signal conductor (strip conductor), 7 connection conductor, 8 internal signal conductor (internal strip conductor), 9 gap.

Claims (9)

A dielectric substrate;
A ground conductor provided on one main surface of the dielectric substrate;
A plurality of strip conductors formed on the other main surface of the dielectric substrate and arranged in substantially parallel to each other and electromagnetically coupled to each other;
An internal strip conductor that is formed to be insulated from the surroundings by a cutout provided in the strip conductor, and is electrically connected to the ground conductor by a connection conductor that penetrates the dielectric substrate without electrical continuity with the strip conductor;
A high-frequency coupled line comprising: an input / output terminal provided at at least one end of each of the plurality of strip conductors. Two dielectric substrates formed by lamination;
Two ground conductors respectively provided on one main surface of the two dielectric substrates;
A plurality of strip conductors formed between the two dielectric substrates, having cutouts and arranged in parallel and electromagnetically coupled to each other;
A connection conductor that passes through the cutout and the two dielectric substrates without electrical continuity with the strip conductor and electrically connects the two ground conductors;
A high-frequency coupled line comprising: an input / output terminal provided at at least one end of each of the plurality of strip conductors. Two dielectric substrates formed by lamination;
Two ground conductors respectively provided on one main surface of the two dielectric substrates;
A plurality of strip conductors formed between the two dielectric substrates and arranged substantially in parallel and electromagnetically coupled to each other;
A connection conductor that is formed to be insulated from the surroundings by a cutout provided in the strip conductor and penetrates at least one of the dielectric plates without electrical continuity with the strip conductor, and is electrically connected to at least one of the two ground conductors. Connected internal strip conductors;
A high-frequency coupled line comprising: an input / output terminal provided at at least one end of each of the plurality of strip conductors. In the high frequency coupling line according to any one of claims 1 to 3,
The plurality of strip conductors include two strip conductors each having an open end or a short-circuit end at one end and an input / output terminal at the other end. In the high frequency coupling line according to any one of claims 1 to 3,
The plurality of strip conductors include two strip conductors having input / output terminals at both ends. In the high frequency coupling line according to claim 4,
The two strip conductors are substantially parallel and have open ends arranged in opposite directions to each other. In the high frequency coupling line according to claim 4,
The two strip conductors are substantially parallel and have open ends arranged in the same direction as each other.   The high frequency filter comprised using at least 1 the high frequency coupling line of any one of Claim 1-7.   A high frequency filter formed by cascading a plurality of high frequency coupling lines according to claim 6 or 7.

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