JP4236667B2 - filter - Google Patents

Description

  The present invention relates to a filter having a balanced terminal.

As a filter having a balanced terminal, for example, an unbalanced input-balanced output type bandpass filter is known. One such filter uses a balun. The balun mutually converts an unbalanced signal (unbalanced signal) and a balanced signal (balanced signal). In wireless communication devices such as cellular phones, there is a demand for a reduction in size and thickness as a filter.
Note that in a line that transmits an unbalanced signal, a signal is transmitted by the potential of one signal line with respect to the ground potential. In a line that transmits a balanced signal, a signal is transmitted by a potential difference between a pair of signal lines. A balanced signal can generally be said to be in a state of excellent balance characteristics if the phase of each signal transmitted between a pair of signal lines is 180 ° different from each other and the amplitudes are approximately equal.

  FIG. 21 shows the general structure of a balun. This balun includes a ½ wavelength (λ / 2) resonator 101 and first and second ¼ wavelength resonators 102 and 103. The half-wave resonator 101 has both ends open (open), and an unbalanced input terminal 111 is connected to one open end. The short-circuit ends of the first and second quarter-wave resonators 102 and 103 face the half-wave resonator 101 so that the open ends of the half-wave resonator 101 face each other. Are arranged. The balanced output terminals 112 and 113 are connected to the open ends of the first and second quarter-wave resonators 102 and 103, respectively, and a pair of balanced output terminals is formed.

As a balun having this structure, there are stacked balun transformers described in Patent Document 1 and Patent Document 2. In Patent Document 1 and Patent Document 2, each resonator is formed by a spiral conductor line pattern, and the conductor line pattern is formed on a plurality of dielectric substrates to form a laminated structure, thereby reducing the size. I am trying. Patent Documents 3 and 4 describe a multilayer bandpass filter using a half-wave resonator as a balanced output type bandpass filter.
JP 2002-190413 A JP 2003-007537 A JP 2005-045447 A JP-A-2005-080248

However, in the multilayer balun transformer described in Patent Document 1 and Patent Document 2, the overall size is limited by the size of the 1/2 wavelength resonator (the size of 1/2 wavelength of the operating frequency), Miniaturization is difficult. Patent Documents 1 and 2 also disclose that each resonator has a spiral structure, but in that case, unnecessary coupling between lines and the balance of physical arrangement are lost from the ideal state. For this reason, there is a problem that the amplitude balance and the phase balance are lost when balanced output is performed, and desired characteristics cannot be obtained. Similarly, the multilayer bandpass filters described in Patent Document 3 and Patent Document 4 basically use a ½ wavelength resonator, so that the overall size depends on the size of the ½ wavelength resonator. It is limited and it is difficult to reduce the size.
Also, in order to cope with UWB (Ultra Wide Band) using a broadband frequency, a broadband balanced signal is required. However, in the conventional structure, coupling between an input-side resonator and an output-side resonator is required. Since it cannot be removed strongly, it is difficult to increase the bandwidth.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a filter that is easy to reduce in size, particularly in area, and can transmit a balanced signal in a wide band with excellent balance characteristics. It is to provide.

The filter according to the present invention includes a plurality of pairs of quarter-wave resonators that are interdigitally coupled so as to face each other and each quarter-wave resonator is laminated in the same direction, and at least one pair of quarter-wave resonators. A pair of quarter-wave resonators having one terminal connected to one of the pair of quarter-wave resonators and the other terminal connected to the other of the pair of quarter-wave resonators And a balanced terminal.
In the filter according to the present invention, “a pair of interdigitally coupled quarter-wave resonators” means an open end of one quarter-wave resonator and a short-circuited end of the other quarter-wave resonator. Are arranged so that the short-circuited end of one quarter-wave resonator and the open end of the other quarter-wave resonator are opposed to each other. Say.

Here, in the filter according to the present invention, each pair of quarter wavelength resonators is a single unit when the resonance frequency of each of the quarter wavelength resonators when not interdigitally coupled is f _0. A first resonance mode that resonates at a _first resonance frequency f ₁ that is higher than the resonance frequency f _{0 of} the first resonance mode, and a second resonance mode that resonates at a _second resonance frequency f ₂ that is lower than the single resonance frequency f _0. And a pair of adjacent quarter wavelength resonators are electromagnetically coupled at the second resonance frequency f ₂ . Each pair of quarter-wave resonators are excited in opposite phases in the second resonance mode.

In the filter according to the present invention, each pair of quarter-wave resonators is configured to be interdigitally coupled, thereby facilitating downsizing. In particular, since the quarter wavelength resonators of the plurality of pairs of quarter wavelength resonators are all stacked in the same direction, the area can be easily reduced. In addition, a pair of balanced terminals are connected to at least one pair of quarter-wave resonators, and each quarter-wave resonator is laminated in the same direction, so that a pair of quarter-wave resonators. It is easy to strengthen the coupling between them, and a broadband balanced signal is transmitted with excellent balance characteristics.
Here, when the pair of quarter-wave resonators is interdigital type and strongly coupled, the resonance frequency f ₀ determined by the length of the physical quarter-wavelength (one each when the interdigital coupling is not performed). The first resonance mode that resonates at a _first resonance frequency f ₁ that is higher than the resonance frequency f ₁ , and the second resonance frequency f ₂ that is lower than the resonance frequency f _0. Two modes, the second resonance mode, appear and the resonance frequency is separated into two. In this case, by setting the second resonance frequency f ₂ having a frequency lower than the resonance frequency f ₀ corresponding to the physical length to the pass frequency (operating frequency) as the filter, the pass frequency as the filter Can be made smaller than when the resonance frequency is set to the resonance frequency f ₀ . For example, when designing a filter having a pass frequency in the 2.4 GHz band, a quarter wavelength resonator having a physical length corresponding to, for example, 8 GHz can be used. This is smaller than the case of a quarter wavelength resonator whose physical length corresponds to the 2.4 GHz band. Further, the second resonance mode resonating at the second resonance frequency f ₂ having a low frequency is an excitation mode in which the pair of quarter-wave resonators are in opposite phases to each other, and thus has excellent balance characteristics.

The filter according to the present invention may further include a plurality of ground layers. The plurality of ground layers may be formed at positions that sandwich at least a pair of quarter-wave resonators provided with a pair of balanced terminals. The pair of quarter-wave resonators provided with a pair of balanced terminals has a rotationally symmetric axis and has a rotationally symmetric structure as a whole, and the plurality of ground layers are rotationally symmetric with respect to the rotationally symmetric axis. It may be formed so as to sandwich the pair of quarter-wave resonators at the positions. Further, a ground layer may be provided between a pair of adjacent quarter wavelength resonators, and a coupling window for coupling a pair of adjacent quarter wavelength resonators to the ground layer may be provided. .
In the case of this configuration, a pair of adjacent quarter-wave resonators is partitioned by a ground layer, and each portion provided with each pair of quarter-wave resonators can easily have a rotationally symmetric structure. . As a result, a balanced signal is transmitted with a better balance characteristic. Further, since the coupling window is provided, it is easy to perform coupling adjustment between a pair of adjacent quarter wavelength resonators.

In the filter according to the present invention, the pair of quarter-wave resonators has a rotationally symmetric axis and has a rotationally symmetric structure as a whole, and the pair of balanced terminals are rotationally symmetric with respect to the rotationally symmetric axis. It is preferable to be connected to a pair of quarter-wave resonators at the position.
In the case of this configuration, a balanced signal is transmitted with a better balance characteristic.

  Further, the filter according to the present invention further includes an unbalanced terminal provided in another pair of quarter-wave resonators not provided with a pair of balanced terminals, and as a whole unbalanced input-balanced output type or balanced input. -An unbalanced output type filter may be configured.

  Further, in the filter according to the present invention, two pairs of balanced terminals are provided, and a pair of balanced terminals are provided in each of the two pairs of quarter-wave resonators. As a whole, a balanced input-balanced output type filter May be configured.

  According to the filter of the present invention, each pair of quarter-wave resonators is interdigitally coupled, and all the quarter-wave resonators are all stacked in the same direction, thereby reducing size and area. Becomes easy. In addition, since a pair of balanced terminals are connected to at least one pair of quarter-wave resonators, a balanced signal can be transmitted. At this time, all the quarter-wave resonators are all stacked in the same direction, so that the coupling between the pair of quarter-wave resonators can be easily strengthened, and a balanced signal over a wide band has excellent balance characteristics. Can be transmitted. As a result, it is possible to reduce the size, particularly to reduce the area, and to transmit a balanced signal in a wide band with excellent balance characteristics.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]

  First, the filter according to the first embodiment of the present invention will be described. In this embodiment, an unbalanced input-balanced output type or balanced input-unbalanced output type filter having a balanced terminal only on one of the input end side or the output end side and an unbalanced terminal on the other side is taken as an example. Explained.

  1, 2 </ b> A, and 2 </ b> B show a configuration example of the filter according to this embodiment. 2A shows the structure viewed from the side surface (YZ plane) in the A direction in FIG. 1, and FIG. 2B shows the structure viewed from the side surface in the B direction (YX plane) in FIG. Yes. FIG. 3 schematically shows the structure of interdigital coupling in this filter. This filter includes a first resonator 1, a second resonator 2, an unbalanced terminal 3 connected to the first resonator 1, and a pair of balanced terminals connected to the second resonator 2. 4A, 4B. For example, this filter has an unbalanced input-balanced output type filter as a whole by using the unbalanced terminal 3 as an input terminal and a pair of balanced terminals 4A and 4B as output terminals. Alternatively, a balanced input-unbalanced output type filter may be configured as a whole by using the unbalanced terminal 3 as an output terminal and the pair of balanced terminals 4A and 4B as input terminals.

  As schematically shown in FIG. 3, the first resonator 1 includes a pair of quarter-wave resonators 11 and 12 that are interdigitally coupled to each other. Each of the pair of quarter-wave resonators 11 and 12 has a short-circuit end at one end and an open end at the other end. The unbalanced terminal 3 is connected to one quarter wavelength resonator 11 of the pair of quarter wavelength resonators 11 and 12. The pair of quarter-wave resonators 11 and 12 has a rotationally symmetric axis 6 and has a rotationally symmetric structure as a whole. The unbalanced terminal 3 may be provided not on one quarter wavelength resonator 11 (lower layer side) but on the other quarter wavelength resonator 12 (upper layer side).

  As schematically shown in FIG. 3, the second resonator 2 is also composed of another pair of quarter-wave resonators 21 and 22 that are interdigitally coupled to each other. Of the pair of quarter-wave resonators 21 and 22, one balanced terminal 4 </ b> A is connected to one quarter-wave resonator 21, and the other balanced terminal 4 </ b> B is connected to the other quarter-wave resonator 22. Is connected. Each of the pair of quarter-wave resonators 21 and 22 has a short-circuit end at one end and an open end at the other end. The pair of quarter-wave resonators 21 and 22 has a rotationally symmetric axis 5 and has a rotationally symmetric structure as a whole. The pair of balanced terminals 4A and 4B are preferably connected to the pair of quarter-wave resonators 21 and 22 at positions that are rotationally symmetric with respect to the rotational symmetry axis 5. Thereby, it can be set as the state excellent in the balance characteristic.

  Here, as shown in FIG. 1, the first resonator 1 and the second resonator 2 are stacked and arranged adjacent to each other in the vertical direction at a predetermined interval. More specifically, the pair of quarter-wave resonators 11 and 12 in the first resonator 1 and the other pair of quarter-wave resonators 21 and 22 in the second resonator 2 are all the same. Laminated and arranged at predetermined intervals in the direction (vertical direction).

As will be described later, the pair of quarter-wave resonators 11 and 12 are strongly interdigitally coupled, so that the first resonance mode and the first resonance frequency that resonate at the first resonance frequency f ₁ are used. and a second resonance mode that resonates at a _second resonance frequency f ₂ lower than f ₁ . More specifically, the first resonant frequency higher than the single resonance frequency f ₀ when the single resonance frequency of each of the quarter-wave resonators 11 and 12 when not interdigitally coupled is f _0. It has a first resonance mode that resonates at f ₁ and a second resonance mode that resonates at a _second resonance frequency f ₂ that is lower than the single resonance frequency f ₀ . Similarly, the other pair of quarter wavelength resonators 21 and 22 has two resonance modes. This filter is configured such that the first resonator 1 and the second resonator ₂ resonate at a _second resonance frequency f ₂ having a low frequency and are electromagnetically coupled. As a result, an unbalanced input-balanced output type or balanced input-unbalanced output type bandpass filter having the second resonance frequency f ₂ as a pass band is configured.

  The main components of the filter described above are constituted by TEM lines. The TEM line can be composed of a conductor pattern such as a strip line or a through conductor formed inside the dielectric substrate. The TEM line is a transmission line that transmits an electromagnetic wave (TEM wave) in which both an electric field and a magnetic field exist only in a cross section perpendicular to the traveling direction of the electromagnetic wave.

  More specifically, as shown in FIG. 1, this filter includes a dielectric substrate 61 made of a dielectric material, and the dielectric substrate 61 has a multi-layer structure. . A conductor line pattern (strip line) is formed inside the dielectric substrate 61, and the first resonator 1, the second resonator 2, the unbalanced terminal 3, A pair of balanced terminals 4A and 4B is formed. In such a structure, for example, a plurality of sheet-like dielectric substrates are prepared, each resonator and each terminal portion are formed on the sheet-like dielectric substrate with a conductor line pattern, and the sheet-like dielectric substrate is formed. This can be realized by a laminated structure in which body substrates are stacked. The pair of quarter-wave resonators 21 and 22 has a rotationally symmetric axis 5 and has a rotationally symmetric structure as a whole. The pair of balanced terminals 4 </ b> A and 4 </ b> B are connected to positions that are rotationally symmetric with respect to the rotationally symmetric axis 5.

  Although not shown, the dielectric substrate 61 is provided with a ground layer for grounding each short-circuited end of the pair of quarter-wave resonators 11 and 12 and the pair of quarter-wave resonators 21 and 22. . The ground layer can be provided, for example, on the upper surface or the bottom surface of the dielectric substrate 61 or inside. In this case, for example, a connection conductor pattern for connecting each quarter wavelength resonator to the ground layer is provided on both side surfaces facing in the longitudinal direction, and each quarter wavelength resonator is connected via the connection conductor pattern. For example, each short-circuit end may be connected to the ground layer. Further, a through hole may be formed between each short-circuited end of each quarter-wave resonator and the ground layer, and the two may be conducted through the through hole.

  In the configuration example shown in FIG. 1, the unbalanced terminal 3 is connected to the open end side end of one quarter wavelength resonator 11, but as in the other configuration example shown in FIG. In addition, instead of the end portion, it may be connected in the middle of one quarter wavelength resonator 11 (between the open end and the short-circuit end). Similarly, the pair of balanced terminals 4 </ b> A and 4 </ b> B may be connected in the middle of the pair of quarter-wave resonators 21 and 22 instead of the open ends.

Next, the operation of the filter according to the present embodiment will be described.
In this filter, the unbalanced signal input from the unbalanced terminal 3 is filtered with the second resonance frequency f ₂ as a passband by the action of each resonator between the input end and the output end, and as a balanced signal. Output from the pair of balanced terminals 4A and 4B. Or, a pair of balanced terminals 4A, the balanced signal input from 4B, is filtered as the passband of the second resonant frequency f ₂ by the action of each resonator is outputted from the unbalanced terminal 3 as an unbalanced signal. Here, in this filter, the first resonator 1 and the second resonator 2 are stacked adjacent to each other in the vertical direction, and each quarter wavelength resonator is stacked in the same direction (vertical direction). By being arranged, the coupling between the first resonator 1 and the second resonator 2 can be easily strengthened, and the area can be saved. FIG. 22 shows a filter structure of a comparative example. In FIG. 22, parts corresponding to the constituent parts of the filter shown in FIG. The filter of the comparative example shown in FIG. 22 is obtained by arranging the first resonator 1 and the second resonator 2 in parallel in the plane direction. Compared to the filter structure of the comparative example shown in FIG. 22, the filter structure according to the present embodiment is downsized in the planar direction.

Further, in this filter, the second resonant frequency f ₂ having a low frequency in the pair of interdigitally coupled quarter-wave resonators is used as a pass band, so that the size of the filter can be easily reduced compared with the conventional filter. Signals can be transmitted with excellent balance characteristics. Next, functions and effects obtained by this interdigital combination will be described.

  As a method for coupling two resonators composed of TEM lines, there are generally two types of combline coupling and interdigital coupling. Of these, interdigital coupling is known to provide very strong coupling. Interdigital coupling means two resonances such that the open end of one resonator faces the short-circuited end of the other resonator, and the short-circuited end of one resonator faces the open-end of the other resonator. This is a coupling method that results in a structure in which containers are arranged opposite to each other.

  In the pair of interdigitally coupled quarter-wave resonators 11 and 12 (and the other pair of quarter-wave resonators 21 and 22), the resonance state can be divided into two unique resonance modes. FIG. 5 shows a first resonance mode in the pair of quarter-wave resonators 11 and 12 (or another pair of quarter-wave resonators 21 and 22), and FIG. 6 shows the second resonance mode. Is shown. In FIGS. 5 and 6, the curve indicated by the broken line indicates the distribution of the electric field E in each resonator. In the following, the pair of quarter-wave resonators 11 and 12 will be described, but the same applies to the other pair of quarter-wave resonators 21 and 22.

  In the first resonance mode, in each of the pair of quarter-wave resonators 11 and 12, current i flows from the open end side to the short-circuit end side, and the direction of the current i flowing in each direction is opposite. In the first resonance mode, electromagnetic waves are excited in phase by the pair of quarter-wave resonators 11 and 12.

  On the other hand, in the second resonance mode, the current i flows from the open end side to the short-circuit end side in one quarter-wave resonator 11 and the other quarter-wave resonator 12 from the short-circuit end side to the open end side. The current i flows through each of them, and the direction of the current i flowing through each of them is the same direction. That is, in this second resonance mode, as can be seen from the distribution of the electric field E, the pair of quarter-wave resonators 11 and 12 excites electromagnetic waves in opposite phases. In this second resonance mode, the phase of the electric field E is 180 ° different at positions that are rotationally symmetric with respect to the physical rotational symmetry axis 6 of the entire pair of quarter-wave resonators 11 and 12.

Here, in the case of the rotationally symmetric structure, the resonance frequency of the first resonance mode is represented by f ₁ in the following equation (1A), and the resonance frequency of the second resonance mode is expressed by the following equation (1B). F ₂ . In equations (1A) and (1B), c is the speed of light, ε _r is the effective relative permittivity, and l is the length of the resonator.

Z _e represents the characteristic impedance of the even mode, and Z _O represents the characteristic impedance of the odd mode. In a symmetric coupling transmission line, the transmission mode propagating to the transmission line is decomposed into two independent modes (not interfering with each other) of an even mode and an odd mode.

  FIG. 7A shows the distribution of the electric field E in the odd mode of the coupling transmission line, and FIG. 7B shows the distribution of the electric field E in the even mode. 7A and 7B, a ground layer 50 is formed at the outer peripheral portion, and symmetrical conductor lines 51 and 52 are formed inside. 7A and 7B show the electric field distribution in a cross section orthogonal to the transmission direction of the coupling transmission line, and the signal transmission direction is a direction orthogonal to the paper surface.

As shown in FIG. 7A, in the odd mode, the electric field intersects perpendicularly with respect to the symmetry plane of the conductor lines 51 and 52, and the symmetry plane becomes a virtual electric wall 53E. FIG. 8A shows a transmission line equivalent to FIG. As shown in FIG. 8A, by replacing the symmetry plane with an actual electrical wall 53E (zero potential wall, ground), a structure equivalent to a line with only one conductor line 51 can be obtained. The characteristic impedance of the line shown in FIG. 8A becomes the odd-mode characteristic impedance Z _{O in} the above equations (1A) and (1B).

On the other hand, in the even mode, as shown in FIG. 7B, the electric field is balanced with respect to the symmetry plane of the conductor lines 51 and 52, and the magnetic field intersects perpendicularly with respect to the symmetry plane. In the even mode, the plane of symmetry is a virtual magnetic wall 53H. FIG. 8B shows a transmission line equivalent to FIG. As shown in FIG. 8B, by replacing the symmetry plane with an actual magnetic wall 53H (an infinite impedance wall), a structure equivalent to a line with only one conductor line 51 can be obtained. The characteristic impedance of the line shown in FIG. 8B becomes the characteristic impedance Z _e of the even mode in the above formulas (1A) and (1B).

Here, the characteristic impedance Z of the transmission line is generally expressed as a ratio of the capacitance C to the ground per unit length of the signal line and the inductance component L per unit length of the signal line. That is,
Z = √ (L / C) (2)
In addition, √ indicates that the square root of the whole (L / C) is taken.

The characteristic impedance Z _O in the odd mode, the line structure of FIG. 8 (A), since the plane of symmetry capacitance C is increased with respect to the ground (electric wall 53E) becomes ground, (2) from the equation the value of Z _O Get smaller. On the other hand, the characteristic impedance Z _e of the even mode, the line structure of FIG. 8 (B), since the symmetrical plane becomes a magnetic wall 53H capacitance C is reduced from (2), the value of Z _e is increased .

Based on this, the equations (1A) and (1B), which are resonance frequencies of the resonance modes of the pair of quarter-wave resonators 11 and 12 that are interdigitally coupled, will be examined. Since the arctangent function is a monotonically increasing function, the resonance frequency increases as the portion related to tan ⁻¹ in formulas (1A) and (1B) increases, and the resonance frequency decreases as it decreases. That is, as the value of the characteristic impedance Z _O in the odd mode decreases, the value of the characteristic impedance Z _e in the even mode increases, and the difference between them increases, the first resonance mode from the equation (1A) The resonance frequency f ₁ of the second resonance mode increases, and the resonance frequency f ₂ of the second resonance mode decreases from the equation (1B).

Therefore, if the ratio of the symmetry planes of the coupled transmission lines is increased, the first resonance frequency f ₁ and the second resonance frequency f ₂ are separated from each other as shown in FIG. FIG. 9 shows a distribution state of resonance frequencies in the pair of quarter-wave resonators 11 and 12 that are interdigitally coupled. The resonance frequency f ₀ intermediate between the first resonance frequency f ₁ and the second resonance frequency f ₂ is a frequency when resonance occurs at a quarter wavelength determined by the physical length of the line (no interdigital coupling). Resonance frequency of each quarter wavelength resonator alone). Here, increasing the ratio of the symmetry plane of the transmission path corresponds to increasing the capacity C in the odd mode from the equation (2). Increasing the capacitance C corresponds to increasing the degree of coupling of the lines. Accordingly, in the pair of quarter-wave resonators 11 and 12 that are interdigitally coupled, the stronger the coupling between the resonators, the larger the first resonance frequency f ₁ and the second resonance frequency f ₂ are. Will be separated.

The following advantages can be obtained by strongly coupling the pair of quarter-wave resonators 11 and 12 to the interdigital type. By strong coupling, the resonance frequency f ₀ determined by the length of the physical quarter wavelength is separated into two. That is, between the first resonance mode that resonates at first resonant frequency f ₁ is higher than the resonance frequency f _0, and a second resonance mode that resonates at the resonance frequency f ₀ the second resonance frequency f ₂ lower than Two modes appear.
In this case, by setting the second resonance frequency f ₂ having a low frequency as a pass frequency (operating frequency) as a filter, as a first advantage, the pass frequency as a filter is first set to the resonance frequency f ₀ . It can be made smaller than the case. For example, when designing a filter having a pass frequency in the 2.4 GHz band, a quarter wavelength resonator having a physical length corresponding to, for example, 8 GHz can be used. This is smaller than the case of a quarter wavelength resonator whose physical length corresponds to the 2.4 GHz band.

As a second advantage, excellent balance characteristics can be obtained when balanced terminals are coupled (in this embodiment, a pair of balanced terminals 4A and 4B are connected to another pair of quarter-wave resonators 21 and 22). Is connected). As described with reference to FIGS. 5 and 6, the pair of quarter-wave resonators 11 and 12 that are interdigitally coupled are excited in phase in the first resonance mode and reversed in the second resonance mode. Excited by the phase. Accordingly, the pair of quarter-wave resonators 11 and 12 are strongly coupled to the interdigital type so that the first resonance frequency f ₁ is set sufficiently high and sufficiently separated from the second resonance frequency f _2. Thus, the in-phase component can be made only to the anti-phase component without exciting the in-phase component with respect to the filter passing frequency (= second resonance frequency f ₂ ). Thereby, the balance characteristic can be made favorable. From this viewpoint, it is preferable that the first resonance frequency f ₁ is sufficiently higher than the frequency band of the input signal. For example, it is preferable that the first resonance frequency f ₁ is more than three times the _second resonance frequency f ₂ . That is,
f ₁ > 3f ₂
It is preferable to satisfy the following condition.
When the second resonance frequency f ₂ having a low frequency is set as a pass frequency as a filter, the frequency characteristics deteriorate when the frequency band of the input signal overlaps the first resonance frequency f ₁ . This is prevented by setting the first resonance frequency f ₁ higher than the frequency band of the input signal.

  Furthermore, as a third advantage, conductor loss can be reduced. FIGS. 10A and 10B schematically show the distribution of the magnetic field H in the pair of quarter-wave resonators 11 and 12 that are interdigitally coupled. 10A and 10B, in the cross section orthogonal to the direction in which the current i flows in the second resonance mode in the pair of quarter-wave resonators 11 and 12 shown in FIG. The magnetic field distribution is shown. The direction in which the current i flows is a direction orthogonal to the paper surface. In the second resonance mode, as shown in FIG. 10A, the magnetic field H is distributed in the same direction within the cross section (for example, counterclockwise) in the pair of quarter-wave resonators 11 and 12. . In this case, when strongly interdigitally coupled (when the resonators are brought close to each other), as shown in FIG. 10B, the pair of quarter-wave resonators 11 and 12 are virtually regarded as one conductor. Magnetic field distribution equivalent to the state. That is, since the conductor thickness is virtually increased, the conductor loss is reduced.

  As described above, according to the filter according to the present embodiment, the pair of quarter-wave resonators 11 and 12 and the other pair of quarter-wave resonators 21 and 22 are interdigitally coupled. Therefore, downsizing becomes easy. In addition, since the pair of balanced terminals 4A and 4B are connected to the other pair of quarter-wave resonators 21 and 22, the balanced signal can be transmitted with excellent balance characteristics. Further, the first resonator 1 and the second resonator 2 are stacked adjacent to each other, and all the quarter wavelength resonators are stacked in the same direction (vertical direction). The coupling between the first resonator 1 and the second resonator 2 is easily strengthened, and a broadband balanced signal can be transmitted, and the area can be easily reduced. As a result, it is possible to reduce the size, particularly to reduce the area, and to transmit a balanced signal in a wide band with excellent balance characteristics. Furthermore, signal transmission with less conductor loss can be performed.

  FIG. 11 shows loss characteristics (S parameter characteristics) of the filter shown in FIG. A curve denoted by reference numeral S21 represents a passage loss characteristic of a signal output from one balanced terminal 4A, and a curve denoted by reference numeral S31 represents a passage loss characteristic of a signal output from the other balanced terminal 4B. A curve denoted by reference numeral S11 indicates a reflection loss characteristic viewed from the unbalanced terminal 3. As shown in the figure, this filter realizes a good bandpass filter having a pass band in the vicinity of the 4 GHz to 7 GHz band. In particular, the band-pass filter excellent in amplitude balance can be realized because the attenuation loss characteristics of the pair of balanced terminals 4A and 4B are substantially equal to each other.

FIG. 12 shows the phase balance characteristics of the balanced signal of the filter shown in FIG. FIG. 13 shows the amplitude balance characteristic of the balanced signal. As can be seen from FIG. 12, in this filter, the phases of the balanced output signals differ from each other by approximately 180 ° in the pass band, and the phase balance is excellent. As can be seen from FIG. 13, the amplitude balance is also excellent.
[Second Embodiment]

  Next, a filter according to a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the component substantially the same as the filter which concerns on the said 1st Embodiment, and description is abbreviate | omitted suitably. 14 and 15 show a configuration example of the filter according to the present embodiment. In the filter according to the present embodiment, ground layers 70 and 71 are formed at positions that sandwich the first resonator 1 provided with a pair of balanced terminals 4A and 4B. The ground layer 70 is provided on the upper layer side with respect to the first resonator 1. The ground layer 71 is disposed between the first resonator 1 and the second resonator 2, that is, a pair of quarter-wave resonators 11 and 12 and another pair of quarter-wave resonators 21 and 22. It is arranged between. The filter is structurally similar to the filter according to the first embodiment except that the ground layers 70 and 71 are provided. A ground layer may also be provided on the lower layer side of the second resonator 2.

  A coupling window (opening) 71A is provided in a part of the ground layer 71 in the intermediate layer, for example, in the center. The position in the plane of the coupling window 71A is preferably a position corresponding to the position where the upper and lower adjacent quarter-wave resonators 12 and 21 are provided. In addition, the position of the ground layer 71 in the vertical direction (stacking direction) is the distance d1 between the ¼ wavelength resonator 21 and the ground layer 71, the other ¼ wavelength resonator 22, and the ground layer on the upper layer side. It is preferable that the distance d2 between 70 is provided at the same position (d1 = d2). As a result, between the ground layer 70 on the upper layer side and the intermediate ground layer 71, the pair of quarter-wave resonators 21 and 22 are close to an ideal rotationally symmetric structure including dielectric portions between the layers. Become. By connecting the pair of balanced terminals 4A and 4B to the pair of quarter-wave resonators 21 and 22 having a physically rotationally symmetric structure in this way, a filter with better balance characteristics can be realized. .

Further, by changing the position, size and shape of the coupling window 71A in the intermediate ground layer 71, the degree of coupling between the first resonator 1 and the second resonator 2 is changed, and the resonator Coordination adjustments can be made. For example, the larger the size of the coupling window 71A, the stronger the degree of coupling. The shape of the coupling window 71A is not limited to the illustrated rectangular shape, and may be a polygonal shape or a curved shape such as an ellipse. The point is that a region where the intermediate ground layer 71 is not formed may be formed so that the first resonator 1 and the second resonator 2 can be coupled. The shapes of the ground layers 70 and 71 are not limited to the illustrated rectangular shape, and may be a polygonal shape or a curved shape such as an ellipse. Further, as shown in the drawing, the ground layers 70 and 71 need not be provided entirely in the plane, and may be partially formed in the plane. In short, the ground layers 70 and 71 may be formed in a rotationally symmetric structure with respect to the rotational symmetry axis 5 of the pair of quarter-wave resonators 21 and 22 to which the pair of balanced terminals 4A and 4B are connected. .
[Third Embodiment]

  Next, a filter according to a third embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the component same as the filter which concerns on the said 1st and 2nd embodiment, and description is abbreviate | omitted suitably. In the first and second embodiments, two pairs of quarter-wave resonators, ie, a pair of quarter-wave resonators 11 and 12 and another pair of quarter-wave resonators 21 and 22. However, a configuration in which three or more pairs of quarter-wave resonators are stacked and arranged is also possible. As the number of the pair of quarter wavelength resonators to be stacked increases, the physical length of each quarter wavelength resonator can be designed to be shorter, and the size can be further reduced.

FIG. 16 shows a first configuration example of the filter according to the present embodiment. In contrast to the configuration of the filter according to the first embodiment, an intermediate stage resonator 30 is provided between the first resonator 1 and the second resonator 2 with a predetermined interval. is there. Similarly to the first resonator 1 and the second resonator 2, the intermediate-stage resonator 30 also includes a pair of quarter-wave resonators 31 and 32 that are interdigitally coupled to each other. The first resonator 1 and the second resonator 2 including the intermediate-stage resonator 30 resonate at the second resonance frequency f ₂ and are electromagnetically coupled to each other. In this filter, three pairs of a pair of quarter-wave resonators 11 and 12, a pair of quarter-wave resonators 31 and 32, and a pair of quarter-wave resonators 21 and 22 are sequentially arranged from the lower layer side. The quarter-wave resonators are all stacked in the same direction (vertical direction) with a predetermined interval, so that compared to a configuration in which two pairs of quarter-wave resonators are stacked, Further downsizing is possible.

17 and 18 show a second configuration example of the filter according to the present embodiment. This second configuration example has a structure in which the first configuration example shown in FIG. 16 is combined with the configuration of the second embodiment. This second configuration example is the same as the first configuration example shown in FIG. 16 except that ground layers 70, 71, and 72 are added. The ground layer 70 is provided on the upper layer side with respect to the first resonator 1. In FIG. 18, the upper ground layer 70 is not shown. The ground layers 71 and 72 are provided in the intermediate layer. That is, the ground layer 72 is provided between the first resonator 1 and the intermediate-stage resonator 30 (between the pair of quarter-wave resonators 11 and 12 and the pair of quarter-wave resonators 31 and 32). Between the resonator 30 in the intermediate stage and the second resonator 2 (between the pair of quarter-wave resonators 31 and 32 and the pair of quarter-wave resonators 21 and 22). A ground layer 71 is disposed on the surface. The ground layers 71 and 72 are provided with coupling windows (openings) 71A and 72A. As in the second embodiment, the coupling between adjacent resonators can be adjusted by changing the position, size and shape of the coupling windows 71A and 72A in the ground layers 71 and 72. The shape of the coupling windows 71A and 72A is not limited to the rectangular shape shown in the figure, and may be a polygonal shape or a curved shape such as an ellipse.
[Other embodiments]

  The present invention is not limited to the above embodiments, and various modifications can be made. For example, in each of the above embodiments, an unbalanced input-balanced output type or balanced input-unbalanced output type filter has been described as an example. However, the present invention includes a balanced terminal at at least one of the input end and the output end. Applicable to other filters. That is, the present invention can be applied to a balanced input-balanced output type filter in which both input and output terminals are balanced terminals.

  19 and 20 show configuration examples of balanced input-balanced output type filters. FIG. 19 schematically shows the structure of interdigital coupling in this filter. The balanced input-balanced output type filter includes a first resonator 1, a second resonator 2, a pair of balanced terminals 3A and 3B connected to the first resonator 1, and a second resonator. 2 and a pair of balanced terminals 4A and 4B. This filter has the same configuration as the filter according to the first embodiment shown in FIG. 1 except that a pair of balanced terminals 3A and 3B are connected to the first resonator 1. Yes.

Similarly to the filter according to the first embodiment, this filter also has a second resonance frequency f _{2 having} a low frequency in a resonator in which the first resonator 1 and the second resonator 2 are interdigitally coupled. And is configured to be electromagnetically coupled. As a result, a balanced input-balanced output type band-pass filter having the second resonance frequency f ₂ as a pass band is configured. The balanced input-balanced output type filter also has the same configuration as that of the second embodiment, that is, a pair of quarter-wave resonators 11 and 12 and another pair of quarter-wave resonators. A configuration in which a ground layer 71 is provided between the two layers 21 and 22 is also possible. Further, similarly to the third embodiment, it is possible to adopt a configuration in which three or more pairs of quarter-wave resonators are stacked.

It is a perspective view showing an example of 1 composition of a filter concerning a 1st embodiment of the present invention. It is the 1st side view (A) and the 2nd side view (B) which show the example of 1 composition of the filter concerning a 1st embodiment of the present invention. It is explanatory drawing which shows typically the structure of the interdigital coupling in the filter which concerns on the 1st Embodiment of this invention. It is a perspective view which shows the other structural example of the filter which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the 1st resonance mode of a pair of 1/4 wavelength resonator by which the interdigital coupling was carried out. It is explanatory drawing which shows the 2nd resonance mode of a pair of 1/4 wavelength resonator by which the interdigital coupling was carried out. It is explanatory drawing about the transmission mode of a left-right symmetric coupling transmission line, (A) shows the electric field distribution in odd mode, (B) is explanatory drawing which shows the electric field distribution in even mode. It is explanatory drawing about the structure of a transmission line equivalent to a left-right symmetric coupling transmission line, (A) shows the odd mode in the equivalent transmission line, (B) is explanatory drawing which shows the even mode. It is explanatory drawing which shows the distribution state of the resonant frequency in a pair of 1/4 wavelength resonator by which the interdigital coupling was carried out. It is the 1st explanatory view (A) and the 2nd explanatory view (B) which show magnetic field distribution in a pair of quarter wavelength resonators by which interdigital combination was carried out. It is a characteristic view which shows the loss characteristic of the filter which concerns on the 1st Embodiment of this invention. It is a characteristic view which shows the phase characteristic of the filter which concerns on the 1st Embodiment of this invention. It is a characteristic view which shows the amplitude characteristic of the filter which concerns on the 1st Embodiment of this invention. It is a side view showing an example of 1 composition of a filter concerning a 2nd embodiment of the present invention. It is a disassembled perspective view which shows the example of 1 structure of the filter which concerns on the 2nd Embodiment of this invention. It is a side view which shows the 1st structural example of the filter which concerns on the 3rd Embodiment of this invention. It is a side view which shows the 2nd structural example of the filter which concerns on the 3rd Embodiment of this invention. It is a disassembled perspective view of the filter which concerns on the 2nd structural example shown in FIG. It is explanatory drawing which shows typically the structure of the interdigital coupling in the filter which concerns on other embodiment of this invention. It is a perspective view which shows one structural example of the filter which concerns on other embodiment of this invention. It is explanatory drawing which shows the basic structure of the conventional balun. It is a perspective view which shows the structure of the comparative example with respect to the filter which concerns on the 1st Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... 1st resonator, 2 ... 2nd resonator, 3 ... Unbalanced terminal, 3A, 3B, 4A, 4B ... Balanced terminal, 5, 6 ... Axis of rotation, 11, 12, 21, 22, ... 1 / 4 wavelength resonator, 71, 72 ... ground layer, 71A, 72A ... coupling window.

Claims (7)

A plurality of pairs of quarter-wave resonators that are interdigitally coupled so as to face each other and each quarter-wave resonator is laminated in the same direction;
Provided in at least one pair of quarter-wave resonators, one terminal is connected to one of the pair of quarter-wave resonators, and the other to the other of the pair of quarter-wave resonators And a pair of balanced terminals connected to
Each pair of quarter-wave resonator, when the resonance frequency of the alone of each quarter-wave resonators when no interdigital coupling as f _0, than the resonance frequency f ₀ in the single A first resonance mode that resonates at a higher first resonance frequency f ₁ and a second resonance mode that resonates at a _second resonance frequency f ₂ lower than the resonance frequency f ₀ of the single unit,
And each pair of adjacent quarter-wave resonators is electromagnetically coupled at the _second resonance frequency f ₂ ,
The filter, wherein each of the pair of quarter-wave resonators is excited in mutually opposite phases in the second resonance mode . A plurality of ground layers;
2. The filter according to claim 1, wherein the plurality of ground layers are formed at positions that sandwich at least the pair of quarter-wave resonators provided with the pair of balanced terminals. The pair of quarter-wave resonators provided with the pair of balanced terminals has a rotationally symmetric axis, and has a rotationally symmetric structure as a whole.
3. The filter according to claim 2, wherein the plurality of ground layers are formed so as to sandwich the pair of quarter-wave resonators at positions that are rotationally symmetric with respect to the rotational symmetry axis. . The ground layer is provided between the pair of adjacent quarter wavelength resonators, and a coupling window for coupling the pair of adjacent quarter wavelength resonators to each other is provided in the ground layer. The filter according to claim 2 or 3, wherein The pair of quarter-wave resonators has a rotationally symmetric axis and a rotationally symmetric structure as a whole.
The pair of balanced terminals are connected to the pair of quarter-wave resonators at positions that are rotationally symmetric with respect to the rotational symmetry axis. The filter described in. The filter further comprises an unbalanced terminal provided in another pair of quarter-wave resonators not provided with the pair of balanced terminals, and is an unbalanced input-balanced output type or balanced input-unbalanced output type filter as a whole. The filter according to any one of claims 1 to 5, wherein the filter is configured. Two pairs of balanced terminals are provided, and the pair of balanced terminals are provided in each of the two pairs of quarter-wave resonators, and a balanced input-balanced output type filter is configured as a whole. The filter according to any one of claims 1 to 5, wherein:

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