Resonator, filter device, and high frequency front end circuit

Abstract

A filter device (100) comprises a dielectric substrate (130), terminals (T1, T2) disposed on the dielectric substrate (130), resonators (RC1, RC4), and a ground electrode (GND1). The terminals (T1, T2) are terminals for connection to external devices. The resonator (RC1) is connected to the terminal (T1). The resonator (RC4) is connected to the terminal (T2). The ground electrode (GND1) is disposed on the dielectric substrate (130) so as to face the resonators (RC1, RC4). Each of the resonators (RC1, RC4) is a band-shaped flat plate electrode including a first end portion and a second end portion. A slit (SL1) is formed along a path from the first end portion to the second end portion in the resonator (RC1). The slit (SL1) is divided into at least two portions along the path.

Description

Resonator, filter device and high frequency front-end circuit

[0001] The present disclosure relates to a resonator, a filter device, and a high-frequency front-end circuit, and more particularly to a technique for improving the filter characteristics of a filter device including a plurality of resonators.

[0002] Japanese Patent Laid-Open Publication No. 7-94914 (Patent Document 1) discloses a strip line with slits formed in the length direction, which can also be used in resonators. By forming slits in the strip line as in Japanese Patent Laid-Open Publication No. 7-94914 (Patent Document 1), it is possible to reduce loss due to the so-called edge effect, in which current concentrates at the ends of the conductor, and improve the Q value.

[0003] Japanese Patent Application Publication No. 7-94914

[0004] When a stripline is used as a resonator, particularly a resonator with both ends open, it generally resonates in a resonance mode in which the entire length of the line is half the wavelength (λ / 2). If a slit is formed along the entire length of such a stripline as in JP-A-7-94914 (Patent Document 1), in addition to the resonance mode in which the entire length of the line is λ / 2 (hereinafter also referred to as the "first resonance mode"), a resonance mode (hereinafter also referred to as the "second resonance mode") caused by a current path circulating around the slit may occur.

[0005] This second resonance mode corresponds to a resonance mode in which the length around the slit is one wavelength (λ), but this resonance mode can cause an unnecessary attenuation pole, which can affect the attenuation characteristics of the filter device.

[0006] The present disclosure has been made to solve such problems, and its purpose is to improve the attenuation characteristics of a filter device that uses a resonator having a strip line with a slit formed therein.

[0007] A filter device according to an aspect of the present disclosure includes a substrate, a first terminal and a second terminal disposed on the substrate, a first resonator, a second resonator, and a ground electrode. The first terminal and the second terminal are terminals for connecting to an external device. The first resonator is connected to the first terminal. The second resonator is connected to the second terminal. The ground electrode is disposed on the substrate facing the first resonator and the second resonator. Each of the first resonator and the second resonator is a strip-shaped flat plate electrode having a first end and a second end. A first slit is formed along a first path extending from the first end to the second end of the first resonator. The first slit is divided into at least two portions along the first path.

[0008] A resonator according to another aspect of the present disclosure includes a substrate, a ground electrode disposed on the substrate, and a plate electrode. The plate electrode is a strip-shaped electrode disposed opposite the ground electrode and having a first end and a second end. A slit is formed in the plate electrode along a path from the first end to the second end. The slit is divided into at least two portions along the path from the first end to the second end.

[0009] In the filter device according to the present disclosure, a plate electrode (strip line) having a slit formed therein is used as a resonator, and the slit is divided along a path extending from a first end to a second end of the plate electrode. By changing the slit length, the resonant frequency of the second resonant mode can be adjusted to achieve desired attenuation characteristics. Therefore, the attenuation characteristics of a filter device using a resonator having a strip line having a slit formed therein can be improved.

[0010] 1 is a block diagram of a communication device having a high-frequency front-end circuit to which a filter device according to an embodiment is applied; FIG. 2 is a plan view of a filter device according to an embodiment; FIG. 3 is a side perspective view of the filter device of FIG. 2; FIG. 4 is a diagram for explaining a resonance mode of a resonator; FIG. 5 is a diagram for explaining a modified example of a resonator; FIG. 6 is a diagram for explaining the topology of the filter device; and FIG. 7 is a diagram for explaining the filter characteristics of the filter device; FIG. 8 is a plan view of a filter device according to a first modified example; FIG. 9 is a plan view of a filter device according to a second modified example; and FIG. 10 is a plan view of a filter device according to a third modified example.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0012] 1 is a block diagram of a communication device 10 having a high-frequency front-end circuit 20 to which a filter device according to an embodiment of the present invention is applied. The communication device 10 is, for example, a mobile terminal such as a smartphone, or a mobile phone base station.

[0013] 1 , a communication device 10 includes an antenna 12, a high-frequency front-end circuit 20, a mixer 30, a local oscillator 32, a D / A converter (DAC) 40, and an RF circuit 50. The high-frequency front-end circuit 20 also includes band-pass filters 22 and 28, an amplifier 24, and an attenuator 26. Although the description of FIG. 1 illustrates a case in which the high-frequency front-end circuit 20 includes a transmission circuit that transmits a high-frequency signal from the antenna 12, the high-frequency front-end circuit 20 may also include a reception circuit that receives a high-frequency signal via the antenna 12.

[0014] The communication device 10 upconverts a transmission signal transmitted from the RF circuit 50 to a high-frequency signal and radiates it from the antenna 12. The modulated digital signal output from the RF circuit 50 is converted to an analog signal by the D / A converter 40. The mixer 30 upconverts the transmission signal, converted from digital to analog by the D / A converter 40, to a high-frequency signal by mixing it with an oscillation signal from the local oscillator 32. The bandpass filter 28 removes unwanted waves generated by the upconversion and extracts only the transmission signal in the desired frequency band. The attenuator 26 adjusts the intensity of the transmission signal. The amplifier 24 power-amplifies the transmission signal that has passed through the attenuator 26 to a predetermined level. The bandpass filter 22 removes unwanted waves generated during the amplification process and passes only signal components in the frequency band specified by the communication standard. The transmission signal that has passed through the bandpass filter 22 is radiated from the antenna 12.

[0015] A filter device according to the present disclosure can be employed as the bandpass filters 22, 28 in the communication device 10 described above.

[0016] [Configuration of Filter Device] Next, a detailed configuration of the filter device according to the embodiment will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a plan view of the filter device 100 according to the embodiment. Fig. 3 is a side perspective view of the filter device 100.

[0017] 2 and 3, the device includes a dielectric substrate 130 having a plurality of dielectric layers stacked thereon, plate electrodes PL1 to PL3, a terminal T1 (input terminal), a terminal T2 (output terminal), a ground terminal GND, ground electrodes GND1 and GND2, and vias V1, V2, VG1, and VG2.

[0018] The dielectric substrate 130 is a rectangular parallelepiped having a substantially rectangular main surface when viewed from above in the stacking direction of the dielectric layers. In the following description, the stacking direction of the dielectric layers (the normal direction to the main surface) is referred to as the Z-axis direction, the direction along the long side of the main surface is referred to as the X-axis, and the direction along the short side of the main surface is referred to as the Y-axis. The positive direction of the Z-axis may be referred to as the upward direction, and the negative direction as the downward direction.

[0019] The dielectric substrate 130 may be, for example, a low temperature co-fired ceramics (LTCC) multilayer substrate, a multilayer resin substrate formed by laminating multiple resin layers made of resins such as epoxy or polyimide, a multilayer resin substrate formed by laminating multiple resin layers made of liquid crystal polymer (LCP) having a lower dielectric constant, a multilayer resin substrate formed by laminating multiple resin layers made of fluorine-based resin, a multilayer resin substrate formed by laminating multiple resin layers made of PET (Polyethylene Terephthalate), or a ceramic multilayer substrate other than LTCC. Note that the dielectric substrate 130 does not necessarily have a multilayer structure and may be a single-layer substrate.

[0020] A flat-plate-shaped ground electrode GND1 is arranged over the entire surface of the upper surface 131 of the dielectric substrate 130 or a dielectric layer close to the upper surface 131. Similarly, a flat-plate-shaped ground electrode GND2 is arranged on the dielectric layer close to the lower surface 132 of the dielectric substrate 130.

[0021] With regard to the ground electrode GND2, when the dielectric substrate 130 is viewed in a plane from the stacking direction, an opening is formed near the center of the dielectric substrate 130 (inside the area OP1 enclosed by the dashed line in FIG. 2), and an electrode is disposed only in a portion corresponding to the outer periphery of the dielectric substrate 130. Note that the ground electrode GND2 is not an essential component, and it is sufficient that at least the ground electrode GND1 is disposed.

[0022] The ground electrodes GND1 and GND2 are electrically connected by a plurality of vias VG2 arranged along the outer periphery of the dielectric substrate 130. The vias VG2 function as connection electrodes for connecting the ground electrodes GND1 and GND2, and also function as a shield for blocking noise from outside the dielectric substrate 130.

[0023] The plate electrodes PL1 to PL3 are disposed on a dielectric layer between the ground electrode GND1 and the ground electrode GND2 within the dielectric substrate 130. Each of the plate electrodes PL1 to PL3 is a strip-shaped electrode and is disposed opposite at least the ground electrode GND1. That is, the plate electrodes PL1 to PL3, together with the ground electrode GND1, form a strip line and function as a distributed constant type resonator.

[0024] Each of the plate electrodes PL1 to PL3 has a substantially C-shape when viewed from above in the stacking direction of the dielectric substrate 130. The plate electrodes PL1, PL2, and PL3 are arranged on the dielectric substrate 130 in this order from the negative direction to the positive direction of the X-axis, with a gap between them.

[0025] The shape of each of the plate electrodes PL1 to PL3 does not necessarily have to be C-shaped, and may be, for example, a linear electrode. By using a C-shape like the filter device 100 of the embodiment, the filter device 100 can be made smaller.

[0026] The plate electrode PL1 is arranged so that the opening of the C faces the negative direction of the X-axis. The plate electrode PL1 is connected to the terminal T1 through a via V1 midway along the path from the end E1 to the end E2. Since the ends E1 and E2 of the plate electrode PL1 are open ends, the plate electrode PL1 operates as a 1 / 2 wavelength (λ / 2) resonator (resonator RC1).

[0027] The plate electrode PL3 is arranged so that the opening of the C faces the positive direction of the X-axis. The plate electrode PL3 is connected to the terminal T2 through a via V2 midway along the path from the end E5 to the end E6. Since the ends E5 and E6 of the plate electrode PL3 are open ends, the plate electrode PL3 operates as a half-wave resonator (resonator RC4).

[0028] The plate electrode PL2 is disposed between the plate electrodes PL1 and PL3 with the opening of the C facing in the negative direction of the Y axis. The plate electrode PL2 is connected to the ground terminal GND through a via VG1 at the midpoint or approximately the midpoint of the path from the end E3 to the end E4.

[0029] A quarter-wave (λ / 4) resonator (resonator RC2) is formed by the portion of plate electrode PL2 from the connection point of via VG1 to end E3, which is the open end on the plate electrode PL1 side. Similarly, a quarter-wave resonator (resonator RC3) is formed by the portion of plate electrode PL2 from the connection point of via VG1 to end E4, which is the open end on the plate electrode PL3 side.

[0030] The resonators RC1 to RC4 are electromagnetically coupled to one another. That is, the filter device 100 is a four-stage bandpass filter in which four resonators are arranged between terminals T1 and T2. When a high-frequency signal is input to terminal T1, the high-frequency signal in a specific frequency band determined by the resonators RC1 to RC4 is filtered and output from terminal T2.

[0031] In the filter device 100 of this embodiment, slits SL1 and SL3 are formed in the plate electrodes PL1 and PL3 constituting each resonator along a path from one end (first end) to the other end (second end). The slits are divided into multiple sections in the plate electrodes PL1 and PL3. While a slit is also formed in the plate electrode PL2 in this embodiment, the slit does not necessarily have to be formed in the plate electrode PL2. When a plate electrode PL2 without a slit is used, the loss in the plate electrode PL2 can be reduced and the Q value can be improved.

[0032] In the plate electrode PL1, the slit SL1 is divided into three portions: a slit SL11 (first portion) formed in a region RG1 including the end E1, a slit SL12 (second portion) formed in a region RG2 including the end E2, and a slit SL13 (third portion) formed between the slits SL11 and SL12 along the line.

[0033] In addition, in the plate electrode PL3, the slit SL3 is divided into three portions: a slit SL21 (fourth portion) formed in a region RG3 including the end E5, a slit SL22 (fifth portion) formed in a region RG4 including the end E6, and a slit SL23 (sixth portion) formed between the slits SL21 and SL22 along the line.

[0034] The slit width of slit SL13 may be the same as or different from the slit widths of slits SL11 and SL12. The slit length of slit SL11 may be the same as or different from the slit length of slit SL12. Similarly, the slit width of slit SL23 may be the same as or different from the slit widths of slits SL21 and SL22. The slit length of slit SL21 may be the same as or different from the slit length of slit SL22.

[0035] In the case of a λ / 2 resonator, the voltage is generally maximum at the open end of the line, and the current is maximum at the center of the line. By making the slits at both ends of each resonator RC1 and RC4 the same length, the current and voltage distributions in the line are reduced and symmetrical, thereby reducing the variation in the resonator characteristics. Furthermore, by adjusting the slit width, the resonant frequency can be fine-tuned.

[0036] In open-ended λ / 2 resonators such as resonator RC1 formed with plate electrode PL1 and resonator RC4 formed with plate electrode PL3, by forming slits along the lines, a resonant mode (first resonant mode) in which the entire length of the line is half the wavelength (λ / 2) can be generated, as well as a resonant mode (second resonant mode) in which the current path circulating around the slit connected to the signal input / output point (input / output terminal) is one wavelength (λ). In other words, resonators RC1 and RC4 operate as so-called dual-mode resonators.

[0037] As a result, each of the resonators RC1 and RC4 apparently functions as two resonators. Therefore, the filter device 100 can be considered to be a six-stage filter device including six resonators. As will be described later, this additional resonator creates a new attenuation pole in the frequency region higher than the pass band of the filter device 100, thereby improving the attenuation characteristics on the high frequency side without increasing the size compared to a typical four-stage filter device.

[0038] Furthermore, in the filter device 100 according to the embodiment, the slits formed in the plate electrodes PL1, PL3 are divided along the line direction, which allows the resonant frequency of the second resonant mode to be set higher than when the slits are not divided. Therefore, by appropriately changing the dividing positions of the slits, the attenuation characteristics on the high frequency side above the pass band can be adjusted to desired characteristics.

[0039] Fig. 4 is a diagram for explaining the resonance modes of the resonators RC1 and RC4 of the filter device 100. For ease of explanation, Fig. 4 will be described using the resonator RC1 as an example.

[0040] 4, the upper part shows the case of the resonator RC1 according to the embodiment, and the lower part shows the case of the resonator of Comparative Example 1. Each of the upper and lower examples shows the structure of the plate electrodes and the current flowing through the plate electrodes in each of the first resonance mode (mode I) and the second resonance mode (mode II).

[0041] 4, in the plate electrode PL1 of the first embodiment, as described above, the slit SL1 is divided into three portions, namely, slits SL11, SL12, and SL13. On the other hand, in the plate electrode PL1X of the first comparative example, one slit SL1X is formed over the entire length of the line.

[0042] In the first resonance mode, in both the plate electrode PL1 of the first embodiment and the plate electrode PL1X of the first comparative example, a current flowing from one end to the other end causes a resonance in which the total length of the line is ½ wavelength (arrows AR1 and AR3 in FIG. 4). Therefore, in both the plate electrode PL1 of the first embodiment and the plate electrode PL1X of the first comparative example, when the line length of the electrode is λ １ Resonance occurs in a high frequency signal with a frequency of 1 / 2.

[0043] In the second resonance mode, a current circulating through a slit formed in the portion of the plate electrode to which the terminal T1 is connected causes resonance with the circumferential length being one wavelength. That is, in the plate electrode PL1 of the embodiment, resonance occurs due to a current path circulating through the slit SL13 as indicated by the arrow AR2 in Fig. 4. Note that no current flows through the regions RG1 and RG2 where the slits SL11 and SL12 are formed (the portions indicated by the dashed lines in Fig. 4).

[0044] On the other hand, in the plate electrode PL1X of Comparative Example 1, resonance occurs due to a current path that circles around the slit SL1X as indicated by the arrow AR4 in Fig. 4. In the plate electrode PL1X of Comparative Example 1, the slit SL1X is formed over the entire length of the line, so the frequency of the second resonance mode is λ １ The frequency corresponds to

[0045] In the plate electrode PL1 of the embodiment, the length of the slit SL13 along the line is shorter than the length of the slit SL1X along the line, so the frequency of the second resonance mode is λ ２ The frequency corresponds to (λ １ >λ ２ ).

[0046] In other words, the resonant frequency of the second resonant mode in the plate electrode PL1 of the embodiment is higher than the resonant frequency of the second resonant mode in the plate electrode PL1X of Comparative Example 1. That is, by changing the dividing position of the slit, it is possible to adjust the frequency of the attenuation pole on the higher frequency side than the pass band.

[0047] In the second resonance mode of the plate electrode PL1 of the embodiment, it is sufficient that a closed loop of the current path is formed circling the slit SL13, and no current flows through the regions RG1 and RG2. Therefore, as in the modified plate electrode PL1A shown in Figure 5, the ends E1 and E2 of the plate electrode PL1A may be open in the slits SL11A and SL12A formed in the regions RG1 and RG2, respectively.

[0048] Next, the topology of the filter device 100 according to the embodiment will be described in comparison with a filter device (Comparative Example 2) in which no slits are formed in the plate electrodes, using Fig. 6. In Fig. 6, the topology of the filter device 100 is shown in the upper part, and the topology of the filter device of Comparative Example 2 is shown in the lower part.

[0049] Note that the numbers at each node in the topology of FIG. 6 correspond to "virtual" resonators. That is, each of the resonators RC1 and RC4 in the filter device 100 includes two nodes because it operates as a dual-mode resonator. The numbers at the nodes indicate the order of the main signal transmission path (hereinafter also referred to as the "main path") from terminal T1 to terminal T2. In the following description, the numbers at each node may be used to refer to the "first-stage resonator" and the "second-stage resonator," for example.

[0050] In the filter device 100 of the embodiment, as described above, each of the resonators RC1 and RC4 operates as a dual-mode resonator, and therefore the number of nodes is six. The resonator RC1 includes a first-stage resonator and a second-stage resonator. The resonator RC2 includes a third-stage resonator, and the resonator RC3 includes a fourth-stage resonator. The resonator RC4 includes a fifth-stage resonator and a sixth-stage resonator. On the other hand, in the filter device 100A of the second comparative example, each of the resonators RC1 to RC4 includes one resonator.

[0051] In both the filter device 100 of the embodiment and the filter device of Comparative Example 2, in addition to the main path indicated by the solid line, there is a sub-path in which two resonators are coupled so as to bypass the series path of the main path.

[0052] In the filter device 100 of the embodiment, the sub-paths are the coupling between the terminal T1 and the second-stage resonator, the coupling between the second-stage resonator and the fourth-stage resonator, the coupling between the third-stage resonator and the fifth-stage resonator, and the coupling between the fifth-stage resonator and the terminal T2. In the filter device of the comparative example 2, the sub-paths are the coupling between the first-stage resonator and the third-stage resonator, and the coupling between the second-stage resonator and the fourth-stage resonator.

[0053] Coupling through such a sub-path is generally called a “cross-coupling.” It is known that forming a “cross-coupling” can add an attenuation pole to a filter device.

[0054] In FIG. 6, couplings marked with "+" indicate couplings where magnetic coupling is dominant, and couplings marked with "-" indicate couplings where electric field coupling is dominant. The position of the generated attenuation pole differs depending on the sign of the cross-coupling. Specifically, when the sign of the cross-coupling is "+", an attenuation pole is generated in a non-pass band on the higher frequency side than the pass band. When the sign of the cross-coupling is "-", an attenuation pole is generated in a non-pass band on the lower frequency side than the pass band.

[0055] That is, in the case of the filter device of Comparative Example 2, two attenuation poles are generated in the non-pass band on the lower frequency side than the pass band, whereas in the case of the filter device 100 of the embodiment, two attenuation poles are generated in the non-pass band on the lower frequency side than the pass band, and further two attenuation poles are generated in the non-pass band on the higher frequency side than the pass band.

[0056] Therefore, as in the filter device 100 of the embodiment, by forming a slit in the flat electrode that constitutes the resonator and dividing the slit along the line, it is possible to adjust the frequency of the attenuation pole on the higher frequency side than the pass band.

[0057] The frequency of the second resonant mode generated in the current path circulating around the slit varies depending on the length of the slit along the line (specifically, slit SL13 in FIG. 4 ), with the shorter the slit, the higher the frequency. In other words, if the slit is too short, an attenuation pole occurs at a frequency much higher than the passband. As a result, the contribution of this attenuation pole to the attenuation characteristics near the passband decreases. Therefore, the length of the path surrounding the slit SL13 is preferably set to a value between 1.5 and 2.0 times the line length from end E1 to end E2 of the plate electrode PL1.

[0058] 7 is a diagram illustrating the filter characteristics of the filter device 100 of the embodiment and the filter device of Comparative Example 2, which are described in FIG. 6. In FIG. 7, a solid line LN10 indicates the insertion loss of the filter device 100, and a dashed line LN11 indicates the insertion loss of the filter device of Comparative Example 2.

[0059] As shown in FIG. 7, in the filter device 100, attenuation poles occur near 35 GHz and 37 GHz near the high frequency side of the pass band, thereby improving the attenuation and steepness near the pass band compared to Comparative Example 2.

[0060] In this way, in a filter device using a strip line with a slit as a resonator, the frequency of the attenuation pole on the higher frequency side than the pass band can be adjusted by dividing the slit along the line and adjusting the slit length, thereby achieving the desired attenuation characteristics.

[0061] The "resonator RC1," "resonator RC4," "resonator RC2," and "resonator RC3" in the embodiments are examples of the "first resonator" to "fourth resonator" in the present disclosure. The "terminal T1" and "terminal T2" in the embodiments are examples of the "first terminal" and "second terminal" in the present disclosure. The "slit SL1" and "slit SL2" in the embodiments are examples of the "first slit" and "second slit" in the present disclosure. The "end E1" and "end E5" in the embodiments are examples of the "first end" in the present disclosure. The "end E2" and "end E6" in the embodiments are examples of the "second end" in the present disclosure. The "ground electrode GND1" in the embodiments is an example of the "ground electrode" in the present disclosure.

[0062] [Modifications] (Modification 1) In Modification 1, a configuration will be described in which a slit is formed in the resonator on the input terminal side, and a slit is not formed in the resonator on the output terminal side.

[0063] Fig. 8 is a plan view of a filter device 100A according to Modification 1. In filter device 100A, the plate electrode PL3 connected to terminal T2 in filter device 100 shown in Fig. 2 is replaced with a plate electrode PL3A. The other configuration of filter device 100A is the same as that of filter device 100, and therefore description of overlapping elements will not be repeated.

[0064] The plate electrode PL3A has the same external shape as the plate electrode PL3, but does not have slits formed in the electrode, so that the plate electrode PL3A resonates only in the first resonance mode.

[0065] On the other hand, a slit SL1 is formed in the plate electrode PL1 connected to the terminal T1. Therefore, the plate electrode PL1 operates as a dual-mode resonator. As a result, one attenuation pole is generated in the non-pass band, which is higher in frequency than the pass band, due to cross-coupling in the resonator RC1.

[0066] Even with this configuration, the attenuation characteristics at frequencies higher than the passband can be improved compared to when no slits are formed in the plate electrodes on either the input or output terminal sides, as in Comparative Example 2 described in Fig. 6. Furthermore, by configuring the resonator RC4 without slits, the Q value can be improved compared to the filter device 100.

[0067] (Modification 2) In Modification 2, a configuration will be described in which a slit is formed in the resonator on the output terminal side, and a slit is not formed in the resonator on the input terminal side.

[0068] Fig. 9 is a plan view of a filter device 100B according to Modification 2. In filter device 100B, the plate electrode PL1 connected to terminal T1 in filter device 100 shown in Fig. 2 is replaced with a plate electrode PL1B. The other configuration of filter device 100B is the same as that of filter device 100, and therefore description of overlapping elements will not be repeated.

[0069] The plate electrode PL1B has the same external shape as the plate electrode PL1, but does not have a slit formed in the electrode, so that the plate electrode PL1B resonates only in the first resonance mode.

[0070] On the other hand, a slit SL2 is formed in the plate electrode PL3 connected to the terminal T2. Therefore, the plate electrode PL3 operates as a dual-mode resonator. As a result, a single attenuation pole is generated in the non-pass band, which is higher in frequency than the pass band, due to cross-coupling in the resonator RC4.

[0071] Even with this configuration, the attenuation characteristics at frequencies higher than the passband can be improved compared to when no slits are formed in the plate electrodes on either the input terminal side or the output terminal side, as in Comparative Example 2 described in Fig. 6. Furthermore, by configuring the resonator RC1 without slits, the Q value can be improved compared to the filter device 100.

[0072] (Modification 3) In Modification 3, a configuration in which the intermediate stage resonator is a λ / 2 resonator will be described.

[0073] Fig. 10 is a plan view of a filter device 100C according to Modification 3. In filter device 100C, the plate electrode PL2 in filter device 100 shown in Fig. 2 is replaced with two electrodes, plate electrodes PL2A and PL2B. The other configuration of filter device 100C is the same as that of filter device 100, and therefore description of overlapping elements will not be repeated.

[0074] Each of the plate electrodes PL2A and PL2B is a strip-shaped electrode having a substantially C-shape, and has the same outer shape and line length as the plate electrodes PL1 and PL3. Note that no slits are formed in the plate electrodes PL2A and PL2B.

[0075] The plate electrodes PL1, PL2A, PL2B, and PL3 are arranged in this order from the negative to the positive direction of the X-axis on the dielectric substrate 130. That is, the plate electrode PL2A is disposed between the plate electrodes PL1 and PL3, and the plate electrode PL2B is disposed between the plate electrodes PL2A and PL3.

[0076] The plate electrodes PL2A and PL2B are not connected to the ground terminal GND, and therefore each of the plate electrodes PL2A and PL2B operates as a λ / 2 resonator.

[0077] Even when the intermediate stage resonator is configured as a λ / 2 resonator in this way, by forming slits in the resonators on the input terminal side and the output terminal side and adjusting the length of the slits, the attenuation characteristics can be improved at frequencies higher than the passband.

[0078] In the above description, the filter device has four resonators RC1 to RC4, but any filter device having at least resonators RC1 and RC4 may be used, and the number of resonators in the intermediate stage may be any number.

[0079] Aspects It will be understood by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0080] (Item 1) A filter device according to one aspect includes a substrate, a first terminal and a second terminal disposed on the substrate, a first resonator, a second resonator, and a ground electrode. The first terminal and the second terminal are terminals for connecting to an external device. The first resonator is connected to the first terminal. The second resonator is connected to the second terminal. The ground electrode is disposed on the substrate facing the first resonator and the second resonator. Each of the first resonator and the second resonator is a strip-shaped flat plate electrode having a first end and a second end. A first slit is formed along a first path extending from the first end to the second end of the first resonator. The first slit is divided into at least two portions along the first path.

[0081] (Item 2) In the filter device described in Item 1, the first slit includes first to third portions. The first portion is formed on a first end side of the plate electrode. The second portion is formed on a second end side of the plate electrode. The third portion is formed between the first and second portions along the first path.

[0082] (Item 3) In the filter device described in item 2, the length of the path surrounding the third portion in the first resonator is 1.5 times or more and less than 2 times the line length from the first end to the second end in the first resonator.

[0083] (4) In the filter device according to the second or third aspect, the slit length of the first portion is the same as the slit length of the second portion.

[0084] (Item 5) In the filter device according to any one of items 2 to 4, the slit width of the third portion is different from the slit widths of the first and second portions.

[0085] (Item 6) In the filter device according to any one of items 1 to 5, a second slit is formed along a second path extending from the first end to the second end of the second resonator. The second slit is divided into at least two portions along the second path.

[0086] (Item 7) In the filter device described in Item 6, the second slit includes fourth to sixth portions. The fourth portion is formed on the first end side of the plate electrode. The fifth portion is formed on the second end side of the plate electrode. The sixth portion is formed between the fourth and fifth portions along the second path.

[0087] (Item 8) In the filter device described in item 7, the length of the path surrounding the sixth portion in the second resonator is 1.5 times or more and less than 2 times the line length from the first end to the second end in the second resonator.

[0088] (Item 9) In the filter device according to item 7 or 8, the slit length of the fourth portion is the same as the slit length of the fifth portion.

[0089] (10) In the filter device according to any one of the seventh to ninth aspects, the slit width of the sixth portion is different from the slit widths of the fourth and fifth portions.

[0090] (Item 11) The filter device described in any one of items 1 to 10 further comprises a third resonator disposed on the substrate between the first resonator and the second resonator and electromagnetically coupled to the first resonator.

[0091] (Item 12) In the filter device according to item 11, the third resonator is a strip-shaped flat plate electrode with both ends open. The line length of the third resonator is the same as the line length of the first resonator.

[0092] (Item 13) In the filter device according to item 11, the third resonator is a strip-shaped flat electrode having one end connected to the ground electrode. The line length of the third resonator is half the line length of the first resonator.

[0093] (Item 14) The filter device according to item 13 further includes a fourth resonator disposed on the substrate between the second resonator and the third resonator and electromagnetically coupled to the second resonator.

[0094] (Item 15) In the filter device according to item 14, the fourth resonator is a strip-shaped flat plate electrode with both ends open. The line length of the fourth resonator is the same as the line length of the second resonator.

[0095] (Item 16) In the filter device according to item 14, the fourth resonator is a strip-shaped flat plate electrode having one end connected to the ground electrode. The line length of the fourth resonator is half the line length of the second resonator.

[0096] (17th Item) A high-frequency front-end circuit according to one aspect includes the filter device according to any one of the first to sixteenth items.

[0097] (Item 18) A resonator according to one aspect includes a substrate, a ground electrode disposed on the substrate, and a plate electrode. The plate electrode is a strip-shaped electrode disposed opposite the ground electrode and having a first end and a second end. A slit is formed in the plate electrode along a path from the first end to the second end. The slit is divided into at least two portions along the path from the first end to the second end.

[0098] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0099] 10 Communication device, 12 Antenna, 20 High frequency front end circuit, 22, 28 Band pass filter, 24 Amplifier, 26 Attenuator, 30 Mixer, 32 Local oscillator, 40 D / A converter, 50 RF circuit, 100, 100A to 100C Filter device, 130 Dielectric substrate, 131 Upper surface, 132 Lower surface, E1 to E6 End, GND Ground terminal, GND1, GND2 Ground electrode, OP1, RG1 to RG4 Area, PL1 to PL3, PL1A, PL1B, PL1X, PL2A, PL2B, PL3A Plate electrode, RC1 to RC4 Resonator, SL1 to SL3, SL11 to SL13, SL1X, SL11A, SL12A, SL21 to SL23 slits, T1, T2 terminals, V1, V2, VG1, VG2 vias.

Claims

1. A filter device comprising: a substrate; a first terminal and a second terminal disposed on the substrate for connecting to an external device; a first resonator connected to the first terminal; a second resonator connected to the second terminal; and a ground electrode disposed on the substrate opposite to the first and second resonators, wherein each of the first and second resonators is a strip-shaped flat electrode having a first end and a second end; a first slit is formed along a first path from the first end to the second end of the first resonator; and the first slit is divided into at least two parts along the first path.

2. A filter device as described in claim 1, wherein the first slit includes: a first portion formed on the first end side of the plate electrode; a second portion formed on the second end side of the plate electrode; and a third portion formed along the first path between the first portion and the second portion.

3. A filter device according to claim 2, wherein the length of the path surrounding the third portion in the first resonator is 1.5 times or more and less than twice the line length from the first end to the second end in the first resonator.

4. A filter device according to claim 2 or 3, wherein the slit length of the first portion is the same as the slit length of the second portion.

5. A filter device according to any one of claims 2 to 4, wherein the slit width of the third portion is different from the slit widths of the first portion and the second portion.

6. A filter device according to any one of claims 1 to 5, wherein a second slit is formed along a second path extending from the first end to the second end of the second resonator, and the second slit is divided into at least two portions along the second path.

7. A filter device as described in claim 6, wherein the second slit includes a fourth portion formed on the first end side of the plate electrode, a fifth portion formed on the second end side of the plate electrode, and a sixth portion formed along the second path between the fourth portion and the fifth portion.

8. The filter device according to claim 7, wherein the length of the path surrounding the sixth portion in the second resonator is 1.5 times or more and less than twice the line length from the first end to the second end in the second resonator.

9. The filter device according to claim 7 or claim 8, wherein the slit length of the fourth portion is the same as the slit length of the fifth portion.

10. The filter device according to any one of claims 7 to 9, wherein the slit width of the sixth portion is different from the slit widths of the fourth and fifth portions.

11. The filter device according to any one of claims 1 to 10, further comprising a third resonator disposed between the first resonator and the second resonator on the substrate and electromagnetically coupled with the first resonator.

12. The filter device according to claim 11, wherein the third resonator is a strip-shaped flat plate electrode with open ends, and the line length of the third resonator is the same as the line length of the first resonator.

13. The filter device according to claim 11, wherein the third resonator is a strip-shaped flat electrode with one end connected to the ground electrode, and the line length of the third resonator is half the line length of the first resonator.

14. The filter device according to claim 13, further comprising a fourth resonator disposed between the second resonator and the third resonator on the substrate and electromagnetically coupled with the second resonator.

15. The filter device according to claim 14, wherein the fourth resonator is a strip-shaped flat plate electrode with both ends open, and the line length of the fourth resonator is the same as the line length of the second resonator.

16. The filter device according to claim 14, wherein the fourth resonator is a strip-shaped flat electrode with one end connected to the ground electrode, and the line length of the fourth resonator is half the line length of the second resonator.

17. A high-frequency front-end circuit equipped with the filter device described in any one of claims 1 to 16.

18. A resonator comprising a substrate, a ground electrode disposed on the substrate, and a strip-shaped flat electrode disposed opposite the ground electrode and having a first end and a second end, wherein a slit is formed in the flat electrode along a path from the first end to the second end, and the slit is divided into at least two parts along the path from the first end to the second end.

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