Filter circuits and communication devices

Abstract

To provide a filter circuit and communication device that can improve characteristics. [Solution] According to the embodiment, the filter circuit includes a first and second terminal and a filter element. The filter element includes a transmission line, a plurality of coupled transmission lines including a first and a second transmission line, and a plurality of resonant elements including a first and a second resonant element. The transmission line includes an input section, an output section, and an intermediate section. The first transmission line is coupled to a first connection point between the input section and the intermediate section. The second transmission line is coupled to a second connection point between the intermediate section and the output section. The first resonant element is coupled to the first transmission line. The second resonant element is coupled to the second transmission line. The first and second resonant elements resonate at the first and second frequencies, respectively. The sum of the electrical length of the intermediate section at a frequency of half the sum of the first and second frequencies, the electrical length of the first transmission line, and the electrical length of the second transmission line is (2n+1) × 90 degrees, where n is a non-negative integer.

Description

Technical Field

[0001] Embodiments of the present invention relate to a filter circuit and a communication device.

Background Art

[0002] For example, in a high-frequency circuit, a filter circuit is used. In the filter circuit, improvement in characteristics is required.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Embodiments of the present invention provide a filter circuit and a communication device capable of improving characteristics.

Means for Solving the Problems

[0005] According to embodiments of the present invention, the filter circuit includes a first terminal, a second terminal, and a filter element. The filter element includes a transmission line, a plurality of coupled transmission lines including a first transmission line and a second transmission line, and a plurality of resonant elements including a first resonant element and a second resonant element. The transmission line includes an input section configured to be coupled to the first terminal, an output section configured to be coupled to the second terminal, and an intermediate section between the input section and the output section. The first section of the first transmission line is configured to be coupled to a first connection point between the input section and the intermediate section. The second section of the second transmission line is configured to be coupled to a second connection point between the intermediate section and the output section. The first resonant element is configured to be coupled to a first other section of the first transmission line. The second resonant element is configured to be coupled to a second other section of the second transmission line. The first resonant element is configured to resonate at a first frequency. The second resonant element is configured to resonate at a second frequency. The intermediate section has a first intermediate section electrical length θc1 at a first center frequency which is half the sum of the first and second frequencies. The first transmission line has a first electrical length θ1 at the first center frequency. The second transmission line has a second electrical length θ2 at the first center frequency. The first sum of the first intermediate section electrical length θc1, the first electrical length θ1, and the second electrical length θ2 is substantially (2n+1) × 90 degrees, where n is a non-negative integer. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a schematic diagram illustrating a filter circuit according to the first embodiment. [Figure 2] Figure 2 is a schematic diagram illustrating an example filter circuit. [Figure 3] Figures 3(a) and 3(b) are graphs illustrating the characteristics of a sample filter circuit. [Figure 4] Figures 4(a) and 4(b) are graphs illustrating the characteristics of the filter circuit according to the first embodiment. [Figure 5] Figures 5(a) and 5(b) are schematic diagrams illustrating a filter circuit according to the first embodiment. [Figure 6] Figure 6 is a schematic plan view illustrating a filter circuit according to the first embodiment. [Figure 7] Figure 7 is a schematic plan view illustrating a filter circuit according to the first embodiment. [Figure 8] Figure 8 is a schematic plan view illustrating a filter circuit according to the first embodiment. [Figure 9] Figure 9 is a schematic plan view illustrating a filter circuit according to the first embodiment. [Figure 10] Figure 10 is a schematic diagram illustrating a filter circuit according to the first embodiment. [Figure 11] Figure 11 is a schematic plan view illustrating a filter circuit according to the first embodiment. [Figure 12] Figure 12 is a graph illustrating a filter circuit according to the first embodiment. [Figure 13] Figure 13 is a schematic diagram illustrating a filter circuit according to the first embodiment. [Figure 14] Figure 14 is a schematic diagram illustrating a filter circuit according to the first embodiment. [Figure 15] Figure 15 is a schematic diagram illustrating a filter circuit according to the first embodiment. [Figure 16] Figure 16 is a schematic diagram illustrating a filter circuit according to the first embodiment. [Figure 17] Figure 17 is a schematic diagram illustrating a filter circuit according to the first embodiment. [Figure 18] Figure 18 is a schematic diagram illustrating a filter circuit according to the first embodiment. [Figure 19] Figure 19 is a graph illustrating the characteristics of the filter according to the first embodiment. [Figure 20] Figure 20 is a schematic diagram illustrating a filter circuit according to the first embodiment. [Figure 21] Figure 21 is a schematic diagram illustrating a communication device according to the second embodiment. [Modes for carrying out the invention]

[0007] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between parts, etc. are not necessarily the same as the actual ones. Even when representing the same part, there are cases where the dimensions and ratios are represented differently in the drawings. In the specification of the present application and each figure, the same reference numerals are given to the same elements as those described above with respect to the previously shown figures, and the detailed description will be omitted as appropriate.

[0008] (First Embodiment) FIG. 1 is a schematic diagram illustrating a filter circuit according to the first embodiment. As shown in FIG. 1, the filter circuit 110 according to the embodiment includes a first terminal 11, a second terminal 12, and a filter element 60. For example, a signal is input to the first terminal 11. The first terminal 11 is configured to receive the input signal. The second terminal 12 is configured to output the signal. For example, the first terminal 11 is an input terminal. The second terminal 12 is an output terminal.

[0009] The filter element 60 includes a transmission line 20, a plurality of coupled transmission lines 20C, and a plurality of resonant elements 50. The plurality of coupled transmission lines 20C includes, for example, a first transmission line 21 and a second transmission line 22. The plurality of resonant elements 50 includes, for example, a first resonant element 51 and a second resonant element 52.

[0010] The transmission line 20 includes an input portion 20a, an output portion 20b, and an intermediate portion 20c. The input portion 20a is configured to be coupled to the first terminal 11. The output portion 20b is configured to be coupled to the second terminal 12. The intermediate portion 20c is between the input portion 20a and the output portion 20b.

[0011] The first part 21a of the first transmission line 21 is configured to couple with a first connection point Pa1 between the input section 20a and the intermediate section 20c. The second part 22a of the second transmission line 22 is configured to couple with a second connection point Pa2 between the intermediate section 20c and the output section 20b. The first transmission line 21 may be directly connected to the input section 20a and the intermediate section 20c at the first connection point Pa1. The second transmission line 22 may be directly connected to the output section 20b and the intermediate section 20c at the second connection point Pa2. The first resonant element 51 is configured to couple with a first other part 21b of the first transmission line 21. The second resonant element 52 is configured to couple with a second other part 22b of the second transmission line 22.

[0012] The first resonant element 51 is configured to resonate at a first frequency f1. The second resonant element 52 is configured to resonate at a second frequency f2. The first frequency f1 may be the same as the second frequency f2. The first frequency f1 may be different from the second frequency f2.

[0013] The intermediate section 20c has a first intermediate section electrical length θc1 at a first center frequency fc1 which is half the sum of the first frequency f1 and the second frequency f2. The first transmission line 21 has a first electrical length θ1 at the first center frequency fc1. The second transmission line 22 has a second electrical length θ2 at the first center frequency fc1.

[0014] In this embodiment, the sum of the first intermediate electrical length θc1, the first electrical length θ1, and the second electrical length θ2 (first sum) is substantially (2n+1) × 90 degrees, where "n" is a non-negative integer.

[0015] For example, the characteristics of the first resonant element 51 and the second resonant element 52 are combined via the first transmission line 21, the intermediate section 20c, and the second transmission line 22. The electrical length of the path between the first resonant element 51 and the second resonant element 52 is set to substantially an odd multiple of 90 degrees. This effectively provides good attenuation characteristics in the band including the first frequency f1 and the second frequency f2.

[0016] In this embodiment, the path between the two resonant elements 50 is separated into three parts (a first transmission path 21, an intermediate section 20c, and a second transmission path 22). The three parts can be easily configured independently of each other. Each of these parts can be configured, for example, to make the circuit size compact. Separation into three parts allows for greater flexibility in the placement of each of the multiple resonant elements 50, for example.

[0017] In the embodiment, for example, the first transmission line 21 and the second transmission line 22 can be designed to reduce the overall size of the circuit. For example, by providing the first transmission line 21 and the second transmission line 22, the electrical length of the intermediate section 20c can be shortened. This suppresses the loss in the intermediate section 20c for the passband signal passing through the input and output terminals. By shortening the electrical length of the intermediate section 20c, for example, the overall size of the circuit can be reduced. The desired filter characteristics can be obtained with a smaller size. For example, pass-through loss can be reduced with a smaller size. According to the embodiment, a filter circuit with improved characteristics can be provided.

[0018] For example, the deviation of the first sum from (2n+1) × 90 degrees can be, for example, ±20% or less. For example, the absolute value of the difference between the first sum and (2n+1) × 90 degrees can be 20 degrees or less.

[0019] The filter circuit 110 may have a target bandwidth. The target bandwidth may correspond to, for example, an attenuation bandwidth. The target bandwidth may correspond to, for example, a stopband. At least a portion of the bandwidth other than the target bandwidth corresponds to a passband. The filter circuit 110 is, for example, a band-stop filter.

[0020] The first frequency f1 and the second frequency f2 are above the lower limit frequency and below the upper limit frequency of the target bandwidth.

[0021] In the filter circuit 110, the input section 20a has an input electrical length θ01. The output section 20b has an output electrical length θ02. These electrical lengths may be set arbitrarily.

[0022] In the filter circuit 110, the first transmission line 21 has a first characteristic impedance Z1. The second transmission line 22 has a second characteristic impedance Z2. The intermediate section 20c has an intermediate characteristic impedance Zc. The input section 20a has an input impedance Z01. The output section 20b has an output impedance Z02. In this embodiment, these characteristic impedances may be set arbitrarily. The input impedance Z01 may be, for example, 50Ω. The output impedance Z02 may be, for example, 50Ω.

[0023] In embodiments, “coupling” includes coupling by an electromagnetic field. “Coupling” may include coupling based on capacitance or inductance. “Coupling” may include, for example, coupling using a quarter-wavelength impedance converter.

[0024] Figure 2 is a schematic diagram illustrating an example filter circuit. As shown in Figure 2, in the example filter circuit 119, the first transmission line 21 and the second transmission line 22 are not provided. In the filter circuit 119, the first resonant element 51 is coupled to the first connection point Pa1 without going through the first transmission line 21. The second resonant element 52 is coupled to the second connection point Pa2 without going through the second transmission line 22.

[0025] In the filter circuit 119, the electrical length of the intermediate section 20c at the first center frequency fc1, which is half the sum of the first frequency f1 and the second frequency f2, is the electrical length θx1.

[0026] Figures 3(a) and 3(b) are graphs illustrating the characteristics of a sample filter circuit. The horizontal axis in these figures represents frequency. The vertical axis represents the transmission characteristic S(2,1). In Figure 3(a), the electrical length θx1 is 90 degrees. In Figure 3(b), the electrical length θx1 is 180 degrees. In these examples, the first frequency f1 is 1.01 GHz. The second frequency f2 is 0.99 GHz. The coupling degree between the first resonant element 51 and the first connection point Pa1, and the coupling degree between the second resonant element 52 and the second connection point Pa2 are both 30. This value is expressed as an external Q value.

[0027] As shown in Figure 3(a), when the electrical length θx1 is 90 degrees, a stopband with bandwidth is formed. This is due to the superposition of reflected waves from the two resonant elements 50. If the resonant frequencies of the two resonant elements 50 are the same, the stop attenuation increases. Thus, when multiple resonant elements 50 are connected with electrical lengths that are odd multiples of 90 degrees, the desired attenuation and bandwidth can be obtained.

[0028] As shown in Figure 3(b), when the electrical length θx1 is 180 degrees, the amount of signal transmitted is large and virtually no attenuation is obtained at the frequency midway between the resonant frequencies of the two resonant elements 50. In this case, two stopbands are independently formed by each of the two resonant elements 50. When obtaining a band-stop filter with multiple bands, the electrical length θx1 between the multiple resonant elements 50 may be set to an integer multiple of 180 degrees.

[0029] As explained with respect to Figures 3(a) and 3(b), different bandwidth characteristics can be obtained depending on the electrical length between the multiple resonators. When the electrical length between the multiple resonators is an odd multiple of 90 degrees, a single-bandband-stop filter is obtained. When the electrical length between the multiple resonators is an integer multiple of 180 degrees, a multi-bandband-stop filter can be obtained.

[0030] Figures 4(a) and 4(b) are graphs illustrating the characteristics of the filter circuit according to the first embodiment. The horizontal axis in these figures represents frequency. The vertical axis represents the pass-through characteristic S(2,1). In Figure 4(a), the above first sum is 90 degrees. In Figure 4(b), the above first sum is 180 degrees.

[0031] In the examples shown in Figures 4(a) and 4(b), the first frequency f1 is 0.992 GHz, and the second frequency f2 is 1.008 GHz. The degree of coupling between the two resonant elements 50 and the transmission line is 50. This value is expressed as an external Q value. The first characteristic impedance Z1, the second characteristic impedance Z2, the intermediate characteristic impedance Zc, the input impedance Z01, and the output impedance Z02 are all 50 Ω.

[0032] In Figure 4(a), the first intermediate electrical length θc1 is 70 degrees. The first electrical length θ1 and the second electrical length θ2 are each 10 degrees. As shown in Figure 4(a), one stopband is obtained. The passband transmission loss is affected by the intermediate section 20c. In the embodiment, when the first sum is an odd multiple of 90 degrees, the first intermediate electrical length θc1 is shorter than the electrical length θx1 in the above reference example. In the embodiment, passband loss can be reduced.

[0033] In Figure 4(b), the first intermediate electrical length θc1 is 160 degrees. The first electrical length θ1 and the second electrical length θ2 are each 10 degrees. As shown in Figure 4(b), two stopbands are obtained. The transmission loss in the passband is affected by the intermediate section 20c. Even when the first sum is an integer multiple of 180 degrees, in this embodiment, the first intermediate electrical length θc1 is shorter than the electrical length θx1 in the above reference example. In this embodiment, passband loss can be reduced.

[0034] Figures 5(a) and 5(b) are schematic diagrams illustrating a filter circuit according to the first embodiment. Figure 5(a) is a plan view. Figure 5(b) is a cross-sectional view. As illustrated in Figure 5(a), a microstrip line structure is applied in the filter circuit 110a according to the embodiment. In the filter circuit 110a, the first electrical length θ1 and the second electrical length θ2 are each 10 degrees. The first intermediate electrical length θc1 is 70 degrees.

[0035] As shown in Figure 5(b), a substrate 10s is provided between the second conductive layer 29L and the first conductive layer 28L. Depending on the pattern shape of the first conductive layer 28L, a transmission line 20, a plurality of coupled transmission lines 20C, and a plurality of resonant elements 50 are formed. The second conductive layer 29L corresponds to, for example, a ground layer.

[0036] The substrate 10s may be insulating. The substrate 10s may contain at least one of an inorganic material and an organic material. The substrate 10s may contain, for example, a material used in flexible substrates (e.g., polyimide or liquid crystal polymer material). The substrate 10s may contain, for example, a glass cloth substrate, a fluororesin substrate, or a ceramic substrate. The ceramic substrate may contain, for example, aluminum oxide.

[0037] The first conductive layer 28L and the second conductive layer 29L may contain a metal. The metal may include, for example, at least one selected from the group consisting of gold and copper. These conductive layers may contain, for example, at least one selected from the group consisting of aluminum, aluminum-containing alloys, niobium, niobium-containing alloys, tantalum, and tantalum-containing alloys. The niobium-containing alloy may include niobium titanium. These conductive layers may contain a superconducting material.

[0038] In the filter circuit 110a, the first resonant element 51 and the second resonant element 52 are quarter-wavelength resonators with one end grounded. The filter circuit 110a corresponds to a two-stage bandstop filter. One end of each of the first resonant element 51 and the second resonant element 52 is grounded. These ends are electrically connected to the second conductive layer 29L.

[0039] The relative permittivity of the substrate 10s is, for example, 3.4. The thickness of the substrate 10s is, for example, 0.5 mm. When the line width is 1.1 mm, the characteristic impedance is 50 Ω. If the resonant frequency of the resonant element 50 is 1 GHz, the length of the conductive layer corresponding to the resonant element 50 is set to a length that is 1 / 4 of the wavelength corresponding to the resonant frequency. For example, at a frequency of 1 GHz, the length of the conductive layer (line length) is 45.9 mm.

[0040] In this embodiment, the elements included in the filter circuit may be various structures other than a microstrip line structure, such as a coplanar structure, a waveguide, a stripline structure, or a coaxial structure.

[0041] In the example of filter circuit 110a, the distance between the first resonant element 51 and the first transmission line 21 is short. The distance between the second resonant element 52 and the second transmission line 22 is short. Capacitive coupling is applied.

[0042] Figure 6 is a schematic plan view illustrating a filter circuit according to the first embodiment. As illustrated in Figure 6, a microstrip line structure is applied in the filter circuit 110b according to the embodiment. In the filter circuit 110b, the first electrical length θ1 and the second electrical length θ2 are each 10 degrees. The first intermediate electrical length θc1 is 160 degrees. The filter circuit 110b provides a stop filter that includes two bandwidths.

[0043] Figure 7 is a schematic plan view illustrating a filter circuit according to the first embodiment. In the filter circuit 110c according to the embodiment illustrated in Figure 7, the first electrical length θ1 and the second electrical length θ2 are each 15 degrees. The first intermediate electrical length θc1 is 60 degrees. The filter circuit 110c is, for example, a two-stage bandstop filter.

[0044] In the filter circuit 110c, the first resonant element 51 and the second resonant element 52 are both open-ended resonators. A half-wavelength stepped impedance resonant element is applied to each of the first resonant element 51 and the second resonant element 52. In a stepped impedance resonant element, the line width of the conductive layer that forms the resonant element changes in a step-like manner. This makes it possible to shift the frequency of higher-order resonances to a higher frequency.

[0045] In this example, in the conductive layer that forms the resonant element, the width of each of the two ends is wider than the width of the intermediate portion between the two ends. The transmission line is bent so that the two ends are closer together. The parasitic capacitance between the two ends increases. This allows the resonant element to be made smaller. By increasing the impedance ratio between the thin and thick wire sections, higher-order resonances can be shifted to the higher frequency side. This makes it easier to obtain a wide passband. A wideband band-stop filter can be obtained.

[0046] Thus, at least one of the first resonant element 51 and the second resonant element 52 may include an open-ended resonator. The open-ended resonator includes a first conductive portion pL1, a second conductive portion pL2, and a third conductive portion pL3. The third conductive portion pL3 is located between the first conductive portion pL1 and the second conductive portion pL2. The third conductive portion line width wp3 of the third conductive portion pL3 is narrower than the first conductive portion line width wp1 of the first conductive portion pL1 and narrower than the second conductive portion line width wp2 of the second conductive portion pL2.

[0047] The distance between the first resonant element 51 and the first transmission line 21 is short. The distance between the second resonant element 52 and the second transmission line 22 is short. Capacitive coupling is applied.

[0048] Figure 8 is a schematic plan view illustrating a filter circuit according to the first embodiment. In the filter circuit 110d according to the embodiment illustrated in Figure 8, the first electrical length θ1 and the second electrical length θ2 are each 10 degrees. The first intermediate electrical length θc1 is 70 degrees. The filter circuit 110d is, for example, a two-stage bandstop filter.

[0049] In the filter circuit 110d, resonant elements are used for the first resonant element 51 and the second resonant element 52, each of which is fitted with a distributed constant transmission line and a variable capacitance element. For example, a variable capacitance element is connected to one end of a microstrip transmission line. The capacitance can be changed by changing the bias voltage applied to the variable capacitance element. The resonant frequency can be changed by changing the capacitance.

[0050] For example, the first resonant element 51 includes a first element line 51L and a first variable capacitance element Cv1. One end of the first element line 51L is coupled to the first transmission line 21. The other end of the first element line 51L is connected to one end of the first variable capacitance element Cv1. The other end of the first variable capacitance element Cv1 is grounded.

[0051] For example, the second resonant element 52 includes a second element line 52L and a second variable capacitance element Cv2. One end of the second element line 52L is coupled to the second transmission line 22. The other end of the second element line 52L is connected to one end of the second variable capacitance element Cv2. The other end of the second variable capacitance element Cv2 is grounded.

[0052] Thus, at least one of the first resonant element 51 and the second resonant element 52 may include a variable frequency resonator 50v. One end of the variable frequency resonator 50v is grounded. A variable capacitance element (such as the first variable capacitance element Cv1) is connected to the other end of the variable frequency resonator 50v. A bias circuit may be provided to apply a voltage to this variable capacitance element. The bias circuit may be included in the filter circuit 110d. The bias circuit may be provided separately from the filter circuit 110d.

[0053] Figure 9 is a schematic plan view illustrating a filter circuit according to the first embodiment. In the filter circuit 110e according to the embodiment illustrated in Figure 9, the first electrical length θ1 and the second electrical length θ2 are each 10 degrees. The first intermediate electrical length θc1 is 70 degrees. The filter circuit 110e is, for example, a two-stage bandstop filter.

[0054] A variable capacitance element may be used in the filter circuit 110e. This allows the resonant frequency to be changed.

[0055] For example, the first resonant element 51 includes a first inductor L1 and a first variable capacitance element Cv1. In this example, the first inductor L1 is connected in series with the first variable capacitance element Cv1. The first inductor L1 and the first variable capacitance element Cv1 correspond to an LC resonator. The first inductor L1 and the first variable capacitance element Cv1 may also be connected in parallel. The LC resonator including the first inductor L1 and the first variable capacitance element Cv1 may be coupled to the first transmission line 21 by a first coupling capacitance element Ck1.

[0056] For example, the second resonant element 52 includes a second inductor L2 and a second variable capacitance element Cv2. In this example, the second inductor L2 is connected in series with the second variable capacitance element Cv2. The second inductor L2 and the second variable capacitance element Cv2 correspond to an LC resonator. The second inductor L2 and the second variable capacitance element Cv2 may also be connected in parallel. The LC resonator including the second inductor L2 and the second variable capacitance element Cv2 may be coupled to the second transmission line 22 by a second coupling capacitance element Ck2.

[0057] Thus, at least one of the first resonant element 51 and the second resonant element 52 may include an LC resonator 50C. The LC resonator 50C includes a lumped element 50Ca. The lumped element 50Ca includes an inductive element 50Cb and a capacitive element 50Cc.

[0058] The first coupling capacitor element Ck1 and the second coupling capacitor element Ck2 may include, for example, a chip capacitor or a variable capacitance element. The first coupling capacitor element Ck1 and the second coupling capacitor element Ck2 may be, for example, capacitors including two parallel electrodes.

[0059] In the filter circuit 110e, the LC resonator may be coupled to the transmission line by inductive coupling using an inductor element.

[0060] Figure 10 is a schematic diagram illustrating a filter circuit according to the first embodiment. As shown in Figure 10, in the filter circuit 111 according to this embodiment, the intermediate section 20c includes a plurality of partial intermediate sections 20cx. The configuration of the filter circuit 111, excluding this, may be the same as that of the filter circuit 110.

[0061] In this example, the multiple partial intermediate sections 20cx include a first partial intermediate section 20cp, a second partial intermediate section 20cq, and a third partial intermediate section 20cr.

[0062] The first intermediate section 20cp has an electrical length θp1 at a first center frequency fc1. The second intermediate section 20cq has an electrical length θq1 at a first center frequency fc1. The third intermediate section 20cr has an electrical length θr1 at a third intermediate section at a first center frequency fc1.

[0063] The first intermediate section electrical length θc1 is the sum of the first partial intermediate section electrical length θp1, the second partial intermediate section electrical length θq1, and the third partial intermediate section electrical length θr1. Thus, the first intermediate section electrical length θc1 is the total electrical length of the multiple partial intermediate sections 20cx at the first center frequency fc1.

[0064] Figure 11 is a schematic plan view illustrating a filter circuit according to the first embodiment. As shown in Figure 11, in the filter circuit 111a according to the embodiment, the intermediate section 20c includes a plurality of partial intermediate sections 20cx. In this example, the plurality of partial intermediate sections 20cx include a first partial intermediate section 20cp, a second partial intermediate section 20cq, and a third partial intermediate section 20cr.

[0065] The second intermediate section 20cq is located between the first intermediate section 20cp and the third intermediate section 20cr. The second track width w2 of the second intermediate section 20cq is different from the first track width w1 of the first intermediate section 20cp. The second track width w2 is different from the third track width w3 of the third intermediate section 20cr. In this example, the second track width w2 is wider than the first track width w1 and wider than the third track width w3.

[0066] In these multiple intermediate sections 20cx, the line width changes discontinuously. This discontinuous change in line width causes a discontinuous change in characteristic impedance.

[0067] For example, the characteristic impedance of the first intermediate section 20cp is 50Ω. The characteristic impedance of the second intermediate section 20cq is 40Ω. The characteristic impedance of the third intermediate section 20cr is 50Ω. The discontinuous change in characteristic impedance can reduce losses, as will be explained later.

[0068] In the filter circuit 111a, the electrical length θp1 of the first intermediate section is 12.5 degrees. The electrical length θq1 of the second intermediate section is 45 degrees. The electrical length θr1 of the third intermediate section is 12.5 degrees. The electrical length θc1 of the first intermediate section is 70 degrees. The first electrical length θ1 and the second electrical length θ2 are each 10 degrees. The filter circuit 111a is, for example, a two-stage bandstop filter.

[0069] Figure 12 is a graph illustrating a filter circuit according to the first embodiment. The horizontal axis of Figure 12 represents frequency. The vertical axis represents the pass-through characteristic S(2,1) between the input and output terminals. Figure 12 illustrates the characteristics of the first configuration CC1 and the second configuration CC2. In the first configuration CC1, the characteristic impedances of the first intermediate section 20cp and the third intermediate section 20cr are 50Ω, and the characteristic impedance of the second intermediate section 20cq is 40Ω. In the second configuration CC2, the characteristic impedances of the first intermediate section 20cp, the second intermediate section 20cq, and the third intermediate section 20cr are 50Ω. The first frequency f1 is 0.992GHz, and the second frequency f2 is 1.008GHz.

[0070] As shown in Figure 12, in the first configuration CC1, compared to the second configuration CC2, the pass loss is improved outside the stopband, especially on the high-frequency side. In this way, the loss can be reduced by discontinuously changing the characteristic impedance.

[0071] In this embodiment, the second track width w2 may be narrower than the first track width w1 and narrower than the third track width w3. In this case as well, losses can be reduced.

[0072] Thus, in this embodiment, one first track width w1 of the multiple partial intermediate sections 20cx may be different from another second track width w2 of the multiple partial intermediate sections 20cx.

[0073] In one embodiment, the characteristic impedance of the second intermediate section 20cq may be lower than the characteristic impedance of the first intermediate section 20cp and lower than the characteristic impedance of the third intermediate section 20cr. In another embodiment, the characteristic impedance of the second intermediate section 20cq may be higher than the characteristic impedance of the first intermediate section 20cp and higher than the characteristic impedance of the third intermediate section 20cr. This can reduce losses.

[0074] Figure 13 is a schematic diagram illustrating a filter circuit according to the first embodiment. As illustrated in Figure 13, in the filter circuit 112 according to this embodiment, the first transmission line 21 includes multiple parts, and the second transmission line 22 also includes multiple parts. The configuration of the filter circuit 112, excluding these parts, may be the same as that of the filter circuit 110.

[0075] In the filter circuit 112, the first transmission line 21 includes a plurality of first partial transmission lines (such as transmission line 21p and transmission line 21q) configured to be coupled to one another. The second transmission line 22 includes a plurality of second partial transmission lines (such as transmission line 22p and transmission line 22q) configured to be coupled to one another.

[0076] The first electrical length θ1 is the total electrical length of multiple first partial transmission lines at the first center frequency fc1. The second electrical length θ2 is the total electrical length of multiple second partial transmission lines at the first center frequency fc1.

[0077] Figure 14 is a schematic diagram illustrating a filter circuit according to the first embodiment. As illustrated in Figure 14, in the filter circuit 113 according to this embodiment, the plurality of coupled transmission lines 20C further include a third transmission line 23 and a fourth transmission line 24. The plurality of resonant elements 50 further include a third resonant element 53 and a fourth resonant element 54. The configuration of the filter circuit 113, excluding these elements, may be the same as that of the filter circuit 110.

[0078] In the filter circuit 113, the third part 23a of the third transmission line 23 is configured to couple with the first connection point Pa1. The fourth part 24a of the fourth transmission line 24 is configured to couple with the second connection point Pa2. The third resonant element 53 is configured to couple with the third other part 23b of the third transmission line 23. The fourth resonant element 54 is configured to couple with the fourth other part 24b of the fourth transmission line 24.

[0079] The third resonant element 53 is configured to resonate at a third frequency f3. The fourth resonant element 54 is configured to resonate at a fourth frequency f4. The third frequency f3 and the fourth frequency f4 are above the lower limit frequency and below the upper limit frequency of the target band.

[0080] The intermediate section 20c has a second intermediate section electrical length θc2 at a second center frequency fc2 which is half the sum of the third frequency f3 and the fourth frequency f4. The third transmission line 23 has a third electrical length θ3 at the second center frequency fc2. The fourth transmission line 24 has a fourth electrical length θ4 at the second center frequency fc2.

[0081] In this embodiment, the second sum of the second intermediate electrical length θc2, the third electrical length θ3, and the fourth electrical length θ4 is (2m+1) × 90 degrees, where "m" is a non-negative integer.

[0082] In the bandwidth including the third frequency f3 and the fourth frequency f4, good attenuation characteristics can be effectively obtained. For example, the positions of the third resonant element 53 and the fourth resonant element 54 can be freely adjusted. The overall size of the circuit can be reduced. The electrical length of the intermediate section 20c can be shortened. For example, the pass loss can be reduced in a small size. A filter circuit with improved characteristics can be provided.

[0083] For example, a filter circuit is obtained that includes a first band containing a first frequency f1 and a second frequency f2, and a second band containing a third frequency f3 and a fourth frequency f4. The signal is attenuated in the first band and the second band. The filter circuit 113 attenuates the components of the first band and the components of the second band.

[0084] The third frequency f3 may be the same as the fourth frequency f4. The third frequency f3 may be different from the fourth frequency f4.

[0085] The third transmission line 23 has a third characteristic impedance Z3. The fourth transmission line 24 has a fourth characteristic impedance Z4. These characteristic impedances may be set arbitrarily.

[0086] Figure 15 is a schematic diagram illustrating a filter circuit according to the first embodiment. As illustrated in Figure 15, in the filter circuit 113a according to this embodiment, the third transmission line 23 includes multiple parts, and the fourth transmission line 24 also includes multiple parts. The configuration of the filter circuit 113a, excluding these parts, may be the same as that of the filter circuit 113.

[0087] In the filter circuit 113a, the third transmission line 23 includes a plurality of third sub-transmission lines (such as transmission line 23p and transmission line 23q) configured to be coupled to one another. The fourth transmission line 24 includes a plurality of fourth sub-transmission lines (such as transmission line 24p and transmission line 24q) configured to be coupled to one another. The third electrical length θ3 is the total electrical length of the plurality of third sub-transmission lines at the second center frequency fc2. The fourth electrical length θ4 is the total electrical length of the plurality of fourth sub-transmission lines at the second center frequency fc2.

[0088] Figure 16 is a schematic diagram illustrating a filter circuit according to the first embodiment. As illustrated in Figure 16, in the filter circuit 114 according to this embodiment, the plurality of coupled transmission lines 20C further include many transmission lines, and the plurality of resonant elements 50 further include many more resonant elements 50. The configuration of the filter circuit 114, excluding these, may be the same as, for example, the configuration of the filter circuit 110.

[0089] In the filter circuit 114, the plurality of coupled transmission lines 20C further include a third transmission line 23, a fourth transmission line 24, a fifth transmission line 25, a sixth transmission line 26, a seventh transmission line 27, and an eighth transmission line 28. The plurality of resonant elements 50 further include a third resonant element 53, a fourth resonant element 54, a fifth resonant element 55, and a sixth resonant element 56.

[0090] The third section 23a of the third transmission line 23 is configured to connect with the first connection point Pa1. The fifth section 25a of the fifth transmission line 25 is configured to connect with the third other section 23b of the third transmission line 23. The sixth section 26a of the sixth transmission line 26 is configured to connect with the third other section 23b.

[0091] The fourth section 24a of the fourth transmission line 24 is configured to connect with the second connection point Pa2. The seventh section 27a of the seventh transmission line 27 is configured to connect with the fourth other section 24b of the fourth transmission line 24. The eighth section 28a of the eighth transmission line 28 is configured to connect with the fourth other section 24b.

[0092] The third resonant element 53 is configured to couple with the fifth other part 25b of the fifth transmission line 25. The fifth resonant element 55 is configured to couple with the sixth other part 26b of the sixth transmission line 26. The fourth resonant element 54 is configured to couple with the seventh other part 27b of the seventh transmission line 27. The sixth resonant element 56 is configured to couple with the eighth other part 28b of the eighth transmission line 28.

[0093] The third resonant element 53 is configured to resonate at the third frequency f3. The fourth resonant element 54 is configured to resonate at the fourth frequency f4. The fifth resonant element 55 is configured to resonate at the fifth frequency f5. The sixth resonant element 56 is configured to resonate at the sixth frequency f6.

[0094] As already explained, the intermediate section 20c has a first intermediate section electrical length θc1 at a first center frequency fc1 which is half the sum of the first frequency f1 and the second frequency f2. The intermediate section 20c has a second intermediate section electrical length θc2 at a second center frequency fc2 which is half the sum of the third frequency f3 and the fourth frequency f4. The intermediate section 20c has a third intermediate section electrical length θc3 at a third center frequency fc3 which is half the sum of the fifth frequency f5 and the sixth frequency f6.

[0095] The third transmission line 23 has a third electrical length θ3 at the second center frequency fc2. The fourth transmission line 24 has a fourth electrical length θ4 at the second center frequency fc2. The fifth transmission line 25 has a fifth electrical length θ5 at the second center frequency fc2. The seventh transmission line 27 has a seventh electrical length θ7 at the second center frequency fc2.

[0096] The third transmission line 23 has a third electrical length θ3A at the third center frequency fc3. The fourth transmission line 24 has a fourth electrical length θ4A at the third center frequency fc3. The sixth transmission line 26 has a sixth electrical length θ6 at the third center frequency fc3. The eighth transmission line 28 has an eighth electrical length θ8 at the third center frequency fc3.

[0097] The second sum of the second intermediate electrical length θc2, the third electrical length θ3, the fifth electrical length θ5, the fourth electrical length θ4, and the seventh electrical length θ7 is (2m+1) × 90 degrees, where "m" is a non-negative integer.

[0098] The third sum of the third intermediate electrical length θc3, the third other electrical length θ3A, the sixth electrical length θ6, the fourth other electrical length θ4A, and the eighth electrical length θ8 is (2l+1) × 90 degrees, where "l" is a non-negative integer.

[0099] Because the second sum is an odd multiple of 90 degrees, good attenuation characteristics are obtained in the second band, which includes the third frequency f3 and the fourth frequency f4. Because the third sum is an odd multiple of 90 degrees, good attenuation characteristics are obtained in the third band, which includes the fifth frequency f5 and the sixth frequency f6.

[0100] The third frequency f3, the fourth frequency f4, the fifth frequency f5, and the sixth frequency f6 are above the lower limit frequency and below the upper limit frequency of the target bandwidth.

[0101] The third frequency f3 may be the same as the fourth frequency f4. The third frequency f3 may be different from the fourth frequency f4. The fifth frequency f5 may be the same as the sixth frequency f6. The fifth frequency f5 may be different from the sixth frequency f6.

[0102] The third transmission line 23 has a third characteristic impedance Z3. The fourth transmission line 24 has a fourth characteristic impedance Z4. The fifth transmission line 25 has a fifth characteristic impedance Z5. The sixth transmission line 26 has a sixth characteristic impedance Z6. The seventh transmission line 27 has a seventh characteristic impedance Z7. The eighth transmission line 28 has an eighth characteristic impedance Z8. These characteristic impedances may be set arbitrarily.

[0103] Figure 17 is a schematic diagram illustrating a filter circuit according to the first embodiment. As illustrated in Figure 17, the filter circuit 115 according to this embodiment is provided with a third connection point Pa3 and a fourth connection point Pa4. Except for these, the configuration of the filter circuit described above (such as filter circuit 110) can be applied to the filter circuit 115.

[0104] In the filter circuit 115, the transmission line 20 further includes another intermediate section 20cA between the intermediate section 20c and the output section 20b. The intermediate section 20c includes a first partial intermediate section 20cp and a second partial intermediate section 20cq.

[0105] The multiple coupled transmission lines 20C further include a third transmission line 23 and a fourth transmission line 24. The multiple resonant elements 50 further include a third resonant element 53 and a fourth resonant element 54.

[0106] The third section 23a of the third transmission line 23 is configured to couple with the third connection point Pa3 between the first intermediate section 20cp and the second intermediate section 20cq. The third resonant element 53 is configured to couple with the third other section 23b of the third transmission line 23. The third resonant element 53 is configured to resonate at a third frequency f3.

[0107] The fourth section 24a of the fourth transmission line 24 is configured to couple with the fourth connection point Pa4 between the intermediate section 20c and the other intermediate section 20cA. The fourth resonant element 54 is configured to couple with the fourth other section 24b of the fourth transmission line 24. The fourth resonant element 54 is configured to resonate at the fourth frequency f4.

[0108] The first intermediate section 20cp has an electrical length θp1 at a first center frequency fc1. The second intermediate section 20cq has an electrical length θq1 at a first center frequency fc1. The electrical length θc1 of the first intermediate section is the sum of the electrical length θp1 of the first intermediate section and the electrical length θq1 of the second intermediate section.

[0109] The other intermediate section 20cA has an electrical length θcA1 at the second center frequency fc2 between the third frequency f3 and the fourth frequency f4. The second intermediate section 20cq has a second electrical length θq2 at the second center frequency fc2.

[0110] The third transmission line 23 has a third electrical length θ3 at the second center frequency fc2. The fourth transmission line 24 has a fourth electrical length θ4 at the second center frequency fc2.

[0111] In the filter circuit 114, the fourth sum of the third electrical length θ3, the second intermediate electrical length θq2, the intermediate electrical length θcA1, and the fourth electrical length θ4 is (2q+1) × 90 degrees, where "q" is a non-negative integer.

[0112] In the filter circuit 114, good attenuation characteristics are obtained in the first band including the first frequency f1 and the second frequency f2, and in the second band including the third frequency f3 and the fourth frequency f4.

[0113] In the filter circuit 114, the third frequency f3 may be the same as the fourth frequency f4. The third frequency f3 may also be different from the fourth frequency f4.

[0114] In the filter circuit 115, the electrical length θp1 of the first intermediate section may be an integer multiple of 180 degrees. The electrical length θcA1 of the other intermediate section may also be an integer multiple of 180 degrees. For example, both the electrical length θp1 of the first intermediate section and the electrical length θcA1 of the other intermediate section may be substantially 0 degrees. For example, a first band of attenuation and a second band of attenuation can be obtained separately.

[0115] In this embodiment, multiple transmission lines may be coupled to a single connection point. For example, multiple first transmission lines 21 and multiple third transmission lines 23 may be coupled to a first connection point Pa1. Multiple first transmission lines 21 may each be coupled to a first resonant element 51. Multiple third transmission lines 23 may each be coupled to a third resonant element 53. Multiple second transmission lines 22 and multiple fourth transmission lines 24 may be coupled to a second connection point Pa2. Multiple second transmission lines 22 may each be coupled to a second resonant element 52. Multiple fourth transmission lines 24 may each be coupled to a fourth resonant element 54.

[0116] Figure 18 is a schematic diagram illustrating a filter circuit according to the first embodiment. As illustrated in Figure 18, in the filter circuit 116 according to this embodiment, the plurality of coupled transmission lines 20C further include a fifth transmission line 25 and a sixth transmission line 26. The plurality of resonant elements 50 further include a fifth resonant element 55 and a sixth resonant element 56. The configuration of the filter circuit 116, excluding these elements, may be the same as that of the filter circuit 110.

[0117] In the filter circuit 116, the fifth part 25a of the fifth transmission line 25 is configured to couple with the first connection point Pa1. The sixth part 26a of the sixth transmission line 26 is configured to couple with the second connection point Pa2. The fifth resonant element 55 is configured to couple with the fifth other part 25b of the fifth transmission line 25. The sixth resonant element 56 is configured to couple with the sixth other part 26b of the sixth transmission line 26.

[0118] The fifth resonant element 55 is configured to resonate at the fifth frequency f5. The sixth resonant element 56 is configured to resonate at the sixth frequency f6. The fifth frequency f5 and the sixth frequency f6 are above the lower limit frequency and below the upper limit frequency of the target band.

[0119] The intermediate section 20c has a third intermediate section electrical length θc3 at a third center frequency fc3 which is half the sum of the fifth frequency f5 and the sixth frequency f6. The fifth transmission line 25 has a fifth electrical length θ5 at the third center frequency fc3. The sixth transmission line 26 has a sixth electrical length θ6 at the third center frequency fc3.

[0120] In this embodiment, the third sum of the third intermediate electrical length θc3, the fifth electrical length θ5, and the sixth electrical length θ6 is (2l+1) × 90 degrees, where "l" is a non-negative integer.

[0121] In the bandwidth including the fifth frequency f5 and the sixth frequency f6, good attenuation characteristics can be effectively obtained. For example, the positions of the fifth resonant element 55 and the sixth resonant element 56 can be freely adjusted. The overall size of the circuit can be reduced. The electrical length of the intermediate section 20c can be shortened. For example, the pass loss can be reduced in a small size. A filter circuit with improved characteristics can be provided.

[0122] For example, a filter circuit is obtained that includes a first band containing a first frequency f1 and a second frequency f2, and a third band containing a fifth frequency f5 and a sixth frequency f6. The signal is attenuated in the first band and the third band. The filter circuit 116 attenuates the components of the first band and the components of the third band.

[0123] The fifth frequency f5 may be the same as the sixth frequency f6. The fifth frequency f5 may be different from the sixth frequency f6.

[0124] The fifth transmission line 25 has a fifth characteristic impedance Z5. The sixth transmission line 26 has a sixth characteristic impedance Z6. These characteristic impedances may be set arbitrarily.

[0125] In the filter circuit 116, the plurality of coupled transmission lines 20C may further include a seventh transmission line 27 and an eighth transmission line 28. The plurality of resonant elements 50 may further include a seventh resonant element 57 and an eighth resonant element 58.

[0126] The seventh section 27a of the seventh transmission line 27 is configured to couple with the first connection point Pa1. The eighth section 28a of the eighth transmission line 28 is configured to couple with the second connection point Pa2. The seventh resonant element 57 is configured to couple with the seventh other section 27b of the seventh transmission line 27. The eighth resonant element 58 is configured to couple with the eighth other section 28b of the eighth transmission line 28.

[0127] The seventh resonant element 57 is configured to resonate at the seventh frequency f7. The eighth resonant element 58 is configured to resonate at the eighth frequency f8. The seventh frequency f7 and the eighth frequency f8 are above the lower limit frequency and below the upper limit frequency of the target band.

[0128] The intermediate section 20c has a fourth intermediate section electrical length θc4 at a fourth center frequency fc4 which is half the sum of the seventh frequency f7 and the eighth frequency f8. The seventh transmission line 27 has a seventh electrical length θ7 at the fourth center frequency fc4. The eighth transmission line 28 has an eighth electrical length θ8 at the fourth center frequency fc4.

[0129] In this embodiment, the fourth sum of the fourth intermediate electrical length θc4, the seventh electrical length θ7, and the eighth electrical length θ8 is (2q+1) × 90 degrees, where "q" is a non-negative integer.

[0130] In the bandwidth including the 7th frequency f7 and the 8th frequency f8, good attenuation characteristics can be effectively obtained. For example, there is a high degree of freedom in the position of the 7th resonant element 57 and the 8th resonant element 58. The overall size of the circuit can be reduced. The electrical length of the intermediate section 20c can be shortened. For example, the pass loss can be reduced in a small size. A filter circuit with improved characteristics can be provided.

[0131] For example, a filter circuit is obtained that includes a third band containing the third frequency f3 and the fourth frequency f4, and a fourth band containing the seventh frequency f7 and the eighth frequency f8. The signal is attenuated in the first and third bands. The filter circuit 116 attenuates the components of the second band and the components of the fourth band.

[0132] The 7th frequency f7 may be the same as the 8th frequency f8. The 7th frequency f7 may be different from the 8th frequency f8.

[0133] The seventh transmission line 27 has a seventh characteristic impedance Z7. The eighth transmission line 28 has an eighth characteristic impedance Z8. These characteristic impedances may be set arbitrarily.

[0134] Figure 19 is a graph illustrating the characteristics of the filter according to the first embodiment. Figure 19 illustrates the simulation results of the characteristics of the filter circuit 110 illustrated in Figure 1 when the first sum (the sum of the first intermediate electrical length θc1, the first electrical length θ1, and the second electrical length θ2) is changed. In Figure 19, the horizontal axis is the electrical length difference Δθ. The electrical length difference Δθ corresponds to the difference between the first sum and 90 degrees. The vertical axis is the attenuation P1. As shown in Figure 19, as the absolute value of the electrical length difference Δθ increases, the attenuation P1 decreases. The absolute value of the electrical length difference Δθ can be 20 degrees or less. A good attenuation P1 is obtained. The absolute value of the electrical length difference Δθ can be 10 degrees or less. An even better characteristic can be obtained.

[0135] The characteristics illustrated in Figure 19 can also be applied when the electrical length difference Δθ is the difference between the first sum and (2n+1) × 90 degrees. In the embodiment, the first absolute value of the difference between the first sum and (2n+1) × 90 degrees may be 20 degrees or less. Preferably, the first absolute value is 10 degrees or less. More preferably, the first absolute value is 5 degrees or less.

[0136] For example, in this embodiment, the second absolute value of the difference between the second sum and (2m+1) × 90 degrees may be 20 degrees or less. Preferably, the second absolute value is 10 degrees or less. More preferably, the second absolute value is 5 degrees or less. The third absolute value of the difference between the third sum and (2l+1) × 90 degrees may be 20 degrees or less. Preferably, the third absolute value is 10 degrees or less. More preferably, the third absolute value is 5 degrees or less.

[0137] Figure 20 is a schematic diagram illustrating a filter circuit according to the first embodiment. In the filter circuit 120 illustrated in Figure 20, the first sum is an integer multiple of 180 degrees. Aside from this, the configuration of the filter circuit described above (such as filter circuit 110) can be applied to filter circuit 116.

[0138] Thus, the filter circuit 120 includes a first terminal 11, a second terminal 12, and a filter element 60. The filter element 60 includes a transmission line 20, a plurality of coupled transmission lines 20C including a first transmission line 21 and a second transmission line 22, and a plurality of resonant elements 50 including a first resonant element 51 and a second resonant element 52.

[0139] The transmission line 20 includes an input section 20a configured to be coupled to a first terminal 11, an output section 20b configured to be coupled to a second terminal 12, and an intermediate section 20c between the input section 20a and the output section 20b. The first section 21a of the first transmission line 21 is configured to be coupled to a first connection point Pa1 between the input section 20a and the intermediate section 20c. The second section 22a of the second transmission line 22 is configured to be coupled to a second connection point Pa2 between the intermediate section 20c and the output section 20b.

[0140] The first resonant element 51 is configured to be coupled with the first other part 21b of the first transmission line 21. The second resonant element 52 is configured to be coupled with the second other part 22b of the second transmission line 22. The first resonant element 51 is configured to resonate at a first frequency f1. The second resonant element 52 is configured to resonate at a second frequency f2.

[0141] The intermediate section 20c has a first intermediate section electrical length θc1 at a first center frequency fc1 which is half the sum of the first frequency f1 and the second frequency f2. The first transmission line 21 has a first electrical length θ1 at the first center frequency fc1. The second transmission line 22 has a second electrical length θ2 at the first center frequency fc1. In the filter circuit 120, the first intermediate section electrical length θc1, the first sum of the first electrical length θ1 and the second electrical length θ2 is substantially n × 180 degrees, where "n" is an integer greater than or equal to 1.

[0142] In the filter circuit 120, the component of the first frequency f1 and the component of the second frequency f2 are attenuated. In the filter circuit 120, the path between the two resonant elements 50 is separated into three parts (first transmission path 21, intermediate section 20c, and second transmission path 22). For example, there is a high degree of freedom in the position of each of the multiple resonant elements 50. For example, it is easy to design the first transmission path 21 and the second transmission path 22 so that the overall size of the circuit is small. For example, the electrical length of the intermediate section 20c can be shortened. Losses in the intermediate section 20c can be suppressed. The desired filter characteristics can be obtained with a small size. For example, the pass loss can be reduced with a small size. According to the embodiment, a filter circuit that can improve characteristics can be provided.

[0143] In the filter circuit 120, the first frequency f1 is different from the second frequency f2.

[0144] (Second Embodiment) Figure 21 is a schematic diagram illustrating a communication device according to the second embodiment. As shown in Figure 21, the communication device 210 according to the embodiment includes a filter circuit according to the first embodiment (e.g., filter circuit 110). In this example, the communication device 210 includes an antenna 81, a transmitting / receiving circuit 82, a converter 83, and a processor 84.

[0145] If the communication device 210 is a receiving device, the communication signal received by the antenna 81 is supplied to the filter circuit 110. In the filter circuit 110, signals of the target frequency band are attenuated, and signals of other passbands are allowed to pass through. The passed signals may be processed by the transmitting / receiving circuit 82, such as detection and amplification. The output of the transmitting / receiving circuit 82 is, for example, converted by AD in the converter 83. The converted signal is processed in the processor 84 to obtain the desired signal (or information).

[0146] If the communication device 210 is a transmitting device, the communication signal from the transmitting / receiving circuit 82 is supplied to the antenna 81 via the filter circuit 110. In the filter circuit 110, signals of the target frequency band are attenuated, while signals of other passbands are allowed to pass through.

[0147] Thus, the communication device 210 according to the embodiment may include a filter circuit (e.g., filter circuit 110, etc.) according to the first embodiment and a transmitting / receiving circuit 82. The transmitting / receiving circuit 82 is configured to receive or transmit a communication signal via the filter circuit (e.g., filter circuit 110, etc.). The filter circuit (e.g., filter circuit 110, etc.) is configured to attenuate the frequency components of the target band of the communication signal.

[0148] The filter circuit according to the embodiment may include various circuit structures. For example, the filter circuit according to the embodiment may include circuit structures such as a coplanar structure, a stripline, a coaxial cable, or a waveguide.

[0149] For example, filter circuits are used in high-frequency devices such as transmitters or receivers. For instance, one method involves providing a transmission line with an electrical length of 90 degrees between multiple reflective resonators. This increases the attenuation of the stopband of the band-stop filter. On the other hand, when combining multiple band-stop filters, there is a method of connecting the multiple band-stop filters via a transmission line with an electrical length of 180 degrees. This reduces interference. When multiple resonators or filters are connected via a transmission line, the substrate size increases, and the transmission loss increases. According to this embodiment, the size can be reduced and the transmission loss can be reduced.

[0150] In this specification, "electrical length" may include not only the exact length but also variations in the manufacturing process, for example. "Electrical length" may be substantially represented by the example values.

[0151] The embodiments may include the following technical proposals. (Technical proposal 1) First terminal and, The second terminal and Filter element, Equipped with, The aforementioned filter element is Transmission line and Multiple coupled transmission lines including a first transmission line and a second transmission line, A plurality of resonant elements, including a first resonant element and a second resonant element, Includes, The aforementioned transmission line is An input section configured to be coupled to the first terminal, An output section configured to be coupled to the second terminal, An intermediate section between the input section and the output section, Includes, The first part of the first transmission line is configured to be coupled to a first connection point between the input section and the intermediate section. The second part of the second transmission line is configured to be coupled to a second connection point between the intermediate part and the output part. The first resonant element is configured to be coupled to the first other part of the first transmission line. The second resonant element is configured to be coupled to the second other part of the second transmission line. The first resonant element is configured to resonate at a first frequency, The second resonant element is configured to resonate at a second frequency, The aforementioned intermediate portion has a first intermediate portion electrical length θc1 at a first center frequency which is half the sum of the first frequency and the second frequency. The first transmission line has a first electrical length θ1 at the first center frequency, The second transmission line has a second electrical length θ2 at the first center frequency, The first intermediate electrical length θc1, the first electrical length θ1, and the first sum of the second electrical length θ2 are substantially (2n+1) × 90 degrees. A filter circuit in which n is a non-negative integer.

[0152] (Technical proposal 2) The filter circuit according to claim 1, wherein the absolute value of the difference between the first sum and (2n+1) × 90 degrees is 20 degrees or less.

[0153] (Technical proposal 3) The first transmission line includes a plurality of first partial transmission lines configured to be coupled to one another. The second transmission line includes a plurality of second partial transmission lines configured to be coupled to one another. The first electrical length θ1 is the total electrical length of the plurality of first partial transmission lines at the first center frequency. The filter circuit according to claim 1, wherein the second electrical length θ2 is the total electrical length of the plurality of second partial transmission lines at the first center frequency.

[0154] (Technical proposal 4) The aforementioned intermediate portion includes a plurality of partial intermediate portions configured to be joined together, The filter circuit according to claim 1, wherein the first intermediate electrical length θc1 is the total electrical length of the plurality of partial intermediates at the first center frequency.

[0155] (Technical proposal 5) The filter circuit according to claim 4, wherein one first line width of the plurality of intermediate sections is different from another second line width of the plurality of intermediate sections.

[0156] (Technical proposal 6) The aforementioned plurality of coupled transmission lines further include a third transmission line and a fourth transmission line, The plurality of resonant elements further include a third resonant element and a fourth resonant element, The third part of the third transmission line is configured to be coupled with the first connection point. The fourth part of the fourth transmission line is configured to be coupled to the second connection point. The third resonant element is configured to be coupled to the third other part of the third transmission line. The fourth resonant element is configured to be coupled to the fourth other part of the fourth transmission line. The third resonant element is configured to resonate at a third frequency, The fourth resonant element is configured to resonate at a fourth frequency, The aforementioned intermediate portion has a second intermediate portion electrical length θc2 at a second center frequency which is half the sum of the third and fourth frequencies. The third transmission line has a third electrical length θ3 at the second center frequency, The fourth transmission line has a fourth electrical length θ4 at the second center frequency, The second sum of the second intermediate electrical length θc2, the third electrical length θ3, and the fourth electrical length θ4 is (2m+1) × 90 degrees. The filter circuit according to claim 1, wherein m is an integer greater than or equal to 0.

[0157] (Technical proposal 7) The third transmission line includes a plurality of third sub-transmission lines configured to be coupled to one another. The fourth transmission line includes a plurality of fourth sub-transmission lines configured to be coupled to one another. The third electrical length θ3 is the total electrical length of the plurality of third partial transmission lines at the second center frequency. The filter circuit according to claim 6, wherein the fourth electrical length θ4 is the total electrical length of the plurality of fourth partial transmission lines at the second center frequency.

[0158] (Technical proposal 8) The aforementioned plurality of coupled transmission lines further include a third transmission line, a fourth transmission line, a fifth transmission line, a sixth transmission line, a seventh transmission line, and an eighth transmission line. The plurality of resonant elements further include a third resonant element, a fourth resonant element, a fifth resonant element, and a sixth resonant element. The third part of the third transmission line is configured to be coupled with the first connection point. The fifth part of the fifth transmission line is configured to be coupled with the third other part of the third transmission line. The sixth part of the sixth transmission line is configured to be coupled with the third other part, The fourth part of the fourth transmission line is configured to be coupled to the second connection point. The seventh part of the seventh transmission line is configured to be coupled with the fourth other part of the fourth transmission line. The eighth part of the eighth transmission line is configured to be coupled with the fourth other part, The third resonant element is configured to be coupled to the fifth other part of the fifth transmission line. The fifth resonant element is configured to be coupled with the sixth other part of the sixth transmission line. The fourth resonant element is configured to be coupled with the seventh other part of the seventh transmission line. The sixth resonant element is configured to be coupled to the eighth other part of the eighth transmission line. The third resonant element is configured to resonate at a third frequency, The fourth resonant element is configured to resonate at a fourth frequency, The fifth resonant element is configured to resonate at a fifth frequency, The sixth resonant element is configured to resonate at the sixth frequency, The aforementioned intermediate portion has a second intermediate portion electrical length θc2 at a second center frequency which is half the sum of the third and fourth frequencies. The aforementioned intermediate portion has a third intermediate portion electrical length θc3 at a third center frequency which is half the sum of the fifth and sixth frequencies. The third transmission line has a third electrical length θ3 at the second center frequency, The fourth transmission line has a fourth electrical length θ4 at the second center frequency, The fifth transmission line has a fifth electrical length θ5 at the second center frequency, The seventh transmission line has a seventh electrical length θ7 at the second center frequency, The third transmission line has a third electrical length θ3A at the third center frequency, The fourth transmission line has a fourth electrical length θ4A at the third center frequency, The sixth transmission line has a sixth electrical length θ6 at the third center frequency, The eighth transmission line has an eighth electrical length θ8 at the third center frequency, The second sum of the second intermediate electrical length θc2, the third electrical length θ3, the fifth electrical length θ5, the fourth electrical length θ4, and the seventh electrical length θ7 is (2m+1) × 90 degrees. Prem is a non-negative integer, The third sum of the third intermediate electrical length θc3, the third other electrical length θ3A, the sixth electrical length θ6, the fourth other electrical length θ4A, and the eighth electrical length θ8 is (2l+1) × 90 degrees. The filter circuit according to claim 1, wherein l is an integer greater than or equal to 0.

[0159] (Technical proposal 9) The transmission line further includes another intermediate section between the intermediate section and the output section, The aforementioned intermediate portion includes a first partial intermediate portion and a second partial intermediate portion. The aforementioned plurality of coupled transmission lines further include a third transmission line and a fourth transmission line, The plurality of resonant elements further include a third resonant element and a fourth resonant element, The third portion of the third transmission line is configured to be coupled to a third connection point between the first intermediate portion and the second intermediate portion. The third resonant element is configured to be coupled to the third other part of the third transmission line. The third resonant element is configured to resonate at a third frequency, The fourth part of the fourth transmission line is configured to connect to the fourth connection point between the intermediate part and the other intermediate part. The fourth resonant element is configured to be coupled to the fourth other part of the fourth transmission line. The fourth resonant element is configured to resonate at a fourth frequency, The first intermediate portion has an electrical length θp1 of the first intermediate portion at the first center frequency. The second intermediate portion has an electrical length θq1 of the second intermediate portion at the first center frequency. The first intermediate electrical length θc1 is the sum of the first partial intermediate electrical length θp1 and the second partial intermediate electrical length θq1. The aforementioned other intermediate portion has an electrical length θcA1 of the other intermediate portion at a second center frequency between the third frequency and the fourth frequency. The second intermediate portion has the second intermediate portion electrical length θq2 at the second center frequency, The third transmission line has a third electrical length θ3 at the second center frequency, The fourth transmission line has a fourth electrical length θ4 at the second center frequency, The fourth sum of the third electrical length θ3, the second intermediate electrical length θq2, the other intermediate electrical length θcA1, and the fourth electrical length θ4 is (2q+1) × 90 degrees. The filter circuit according to claim 1, wherein q is an integer greater than or equal to 0.

[0160] (Technical proposal 10) The first frequency is the same as the second frequency, The filter circuit according to any one of claims 1 to 9, wherein the second electrical length θ2 is different from the first electrical length θ1.

[0161] (Technical proposal 11) The first frequency differs from the second frequency, The filter circuit according to any one of claims 1 to 9, wherein the second electrical length θ2 is the same as the first electrical length θ1.

[0162] (Technical proposal 12) At least one of the first resonant element and the second resonant element includes a first conductive portion, a second conductive portion, and a third conductive portion between the first conductive portion and the second conductive portion. The filter circuit according to any one of claims 1 to 11, wherein the line width of the third conductive portion of the third conductive portion is narrower than the line width of the first conductive portion of the first conductive portion and narrower than the line width of the second conductive portion of the second conductive portion.

[0163] (Technical proposal 13) At least one end of the first resonant element and the second resonant element is open, The filter circuit according to any one of claims 1 to 11, wherein at least one other end of the first resonant element and the second resonant element is grounded.

[0164] (Technical proposal 14) At least one of the first resonant element and the second resonant element includes a frequency-variable resonator, One end of the aforementioned variable frequency resonator is grounded, The filter circuit according to any one of claims 1 to 11, wherein a variable capacitance element is connected to another end of the frequency-variable resonator.

[0165] (Technical proposal 15) At least one of the first resonant element and the second resonant element includes an LC resonator, The LC resonator includes lumped element elements, The filter circuit according to any one of claims 1 to 11, wherein the lumped element includes an inductive element and a capacitive element.

[0166] (Technical proposal 16) The filter comprises a plurality of the aforementioned filter elements, The filter circuit according to claim 1, wherein two of the plurality of filter elements are configured to be coupled to one another.

[0167] (Technical proposal 17) The first frequency of the first resonant element included in one of the plurality of filter elements is different from the first frequency of the first resonant element included in another of the plurality of filter elements. The filter circuit according to claim 15, wherein the second frequency of the second resonant element included in one of the plurality of filter elements is different from the second frequency of the second resonant element included in another of the plurality of filter elements.

[0168] (Technical proposal 18) First terminal and, The second terminal and Filter element, Equipped with, The aforementioned filter element is Transmission line and Multiple coupled transmission lines including a first transmission line and a second transmission line, A plurality of resonant elements, including a first resonant element and a second resonant element, Includes, The aforementioned transmission line is An input section configured to be coupled to the first terminal, An output section configured to be coupled to the second terminal, The intermediate section between the input section and the output section, Includes, The first part of the first transmission line is configured to be coupled to a first connection point between the input section and the intermediate section. The second part of the second transmission line is configured to be coupled to a second connection point between the intermediate part and the output part. The first resonant element is configured to be coupled to the first other part of the first transmission line. The second resonant element is configured to be coupled to the second other part of the second transmission line. The first resonant element is configured to resonate at a first frequency, The second resonant element is configured to resonate at a second frequency, The aforementioned intermediate portion has a first intermediate portion electrical length θc1 at a first center frequency which is half the sum of the first frequency and the second frequency. The first transmission line has a first electrical length θ1 at the first center frequency, The second transmission line has a second electrical length θ2 at the first center frequency, The first intermediate electrical length θc1, the first electrical length θ1, and the first electrical length θ2 are substantially n × 180 degrees. A filter circuit in which n is an integer greater than or equal to 1.

[0169] (Technical proposal 19) The filter circuit according to claim 18, wherein the first frequency is different from the second frequency.

[0170] (Technical proposal 20) A filter circuit according to any one of claims 1 to 19, A receiving / transmitting circuit configured to receive or transmit a communication signal via the aforementioned filter circuit, Equipped with, A communication device wherein the filter circuit is configured to attenuate frequency components in a target band including the first frequency and the second frequency that are included in the communication signal.

[0171] According to the embodiment, a filter circuit and a communication device capable of improving characteristics are provided.

[0172] Embodiments of the present invention have been described above with reference to examples. However, the present invention is not limited to these examples. For example, the specific configuration of each element included in the filter circuit, such as terminals, transmission lines, resonant elements, and conductive layers, is included within the scope of the present invention as long as those skilled in the art can appropriately select from the known range to implement the present invention and obtain similar effects.

[0173] Combinations of two or more elements from each example, to the extent technically feasible, are also included within the scope of the present invention, insofar as they encompass the gist of the invention.

[0174] All filter circuits and communication devices that can be implemented by those skilled in the art by appropriately modifying the design based on the filter circuit and communication device described above as embodiments of the present invention also fall within the scope of the present invention, insofar as they encompass the gist of the present invention.

[0175] Within the scope of the concept of this invention, a person skilled in the art would be able to conceive of various modifications and alterations, and it is understood that such modifications and alterations also fall within the scope of this invention.

[0176] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0177] 10s: Base, 11, 12: 1st, 2nd terminals, 20: Transmission line, 20C: Coupling transmission line, 20a: Input section, 20b: Output section, 20c: Intermediate section, 20cA: Other intermediate section, 20cp~20cr: 1st~3rd partial intermediate section, 20cx: Partial intermediate section, 21~28: 1st~8th transmission lines, 21a~28a: 1st~8th section, 21b~28b: 1st~8th other section, 21p~24p, 21q~24q: Transmission lines, 28L: 1st conductive layer, 29L: 2nd conductive layer, 50: Resonant element, 50C: LC resonator, 50Ca: Lumped element, 50Cb: Inductive element, 50Cc: Capacitive element, 50v: Variable frequency resonator 51-58: 1st-8th resonant elements, 51L, 52L: 1st and 2nd element lines, 60: filter element, 81: antenna, 82: transmitting / receiving circuit, 83: converter, 84: processor, 110, 110a-110e, 111-116, 111a, 113a, 119, 120: filter circuits, 210: communication device, CC1, CC2: 1st and 2nd configurations, Ck1, Ck2: 1st and 2nd coupled capacitance elements, Cv1, Cv2: 1st and 2nd variable capacitance elements, L1, L2: 1st and 2nd inductors, P1: attenuation, Pa1-Pa4: 1st-4th connection points, pL1-pL3: 1st-3rd conductive parts, w1-w3: 1st-3rd line widths, wp1~wp3: First to third conductive section line widths, Δθ: Electrical length difference

Claims

1. First terminal and, The second terminal and, Filter element, Equipped with, The aforementioned filter element is Transmission line and A plurality of coupled transmission lines including a first transmission line and a second transmission line, A plurality of resonant elements including a first resonant element and a second resonant element, Includes, The aforementioned transmission line is An input section configured to be coupled to the first terminal, An output section configured to be coupled to the second terminal, The intermediate section between the input section and the output section, Includes, The first part of the first transmission line is configured to be coupled to a first connection point between the input section and the intermediate section. The second part of the second transmission line is configured to be coupled to a second connection point between the intermediate part and the output part. The first resonant element is configured to be coupled to the first other part of the first transmission line. The second resonant element is configured to be coupled to the second other part of the second transmission line. The first resonant element is configured to resonate at a first frequency, The second resonant element is configured to resonate at a second frequency, The aforementioned intermediate portion has a first intermediate portion electrical length θc1 at a first center frequency which is half the sum of the first frequency and the second frequency. The first transmission line has a first electrical length θ1 at the first center frequency, The second transmission line has a second electrical length θ2 at the first center frequency, The first intermediate electrical length θc1, the first electrical length θ1, and the first sum of the second electrical length θ2 are substantially (2n+1) × 90 degrees. A filter circuit in which n is a non-negative integer.

2. The filter circuit according to claim 1, wherein the absolute value of the difference between the first sum and (2n+1) × 90 degrees is 20 degrees or less.

3. The first transmission line includes a plurality of first partial transmission lines configured to be coupled to one another. The second transmission line includes a plurality of second partial transmission lines configured to be coupled to one another. The first electrical length θ1 is the total electrical length of the plurality of first partial transmission lines at the first center frequency. The filter circuit according to claim 1, wherein the second electrical length θ2 is the total electrical length of the plurality of second partial transmission lines at the first center frequency.

4. The aforementioned intermediate portion includes a plurality of partial intermediate portions configured to be joined together, The filter circuit according to claim 1, wherein the first intermediate electrical length θc1 is the total electrical length of the plurality of partial intermediates at the first center frequency.

5. The filter circuit according to claim 4, wherein the first line width of one of the plurality of intermediate sections is different from the second line width of another of the plurality of intermediate sections.

6. The plurality of coupled transmission lines further include a third transmission line and a fourth transmission line, The plurality of resonant elements further include a third resonant element and a fourth resonant element, The third part of the third transmission line is configured to be coupled to the first connection point. The fourth part of the fourth transmission line is configured to be coupled to the second connection point. The third resonant element is configured to be coupled to the third other part of the third transmission line. The fourth resonant element is configured to be coupled to the fourth other part of the fourth transmission line. The third resonant element is configured to resonate at a third frequency, The fourth resonant element is configured to resonate at a fourth frequency, The aforementioned intermediate portion has a second intermediate portion electrical length θc2 at a second center frequency which is half the sum of the third frequency and the fourth frequency. The third transmission line has a third electrical length θ3 at the second center frequency, The fourth transmission line has a fourth electrical length θ4 at the second center frequency, The second sum of the second intermediate electrical length θc2, the third electrical length θ3, and the fourth electrical length θ4 is (2m + 1) × 90 degrees. The filter circuit according to claim 1, wherein m is an integer greater than or equal to 0.

7. The third transmission line includes a plurality of third sub-transmission lines configured to be coupled to one another. The fourth transmission line includes a plurality of fourth sub-transmission lines configured to be coupled to one another. The third electrical length θ3 is the total electrical length of the plurality of third partial transmission lines at the second center frequency. The filter circuit according to claim 6, wherein the fourth electrical length θ4 is the total electrical length of the plurality of fourth partial transmission lines at the second center frequency.

8. The aforementioned plurality of coupled transmission lines further include a third transmission line, a fourth transmission line, a fifth transmission line, a sixth transmission line, a seventh transmission line, and an eighth transmission line. The plurality of resonant elements further include a third resonant element, a fourth resonant element, a fifth resonant element, and a sixth resonant element. The third part of the third transmission line is configured to be coupled to the first connection point. The fifth part of the fifth transmission line is configured to be coupled with the third other part of the third transmission line. The sixth part of the sixth transmission line is configured to be coupled with the third other part, The fourth part of the fourth transmission line is configured to be coupled to the second connection point. The seventh part of the seventh transmission line is configured to be coupled with the fourth other part of the fourth transmission line. The eighth part of the eighth transmission line is configured to be coupled with the fourth other part, The third resonant element is configured to be coupled with the fifth other part of the fifth transmission line. The fifth resonant element is configured to be coupled with the sixth other part of the sixth transmission line. The fourth resonant element is configured to be coupled with the seventh other part of the seventh transmission line. The sixth resonant element is configured to be coupled with the eighth other part of the eighth transmission line. The third resonant element is configured to resonate at a third frequency, The fourth resonant element is configured to resonate at a fourth frequency, The fifth resonant element is configured to resonate at a fifth frequency, The sixth resonant element is configured to resonate at a sixth frequency, The aforementioned intermediate portion has a second intermediate portion electrical length θc2 at a second center frequency which is half the sum of the third frequency and the fourth frequency. The aforementioned intermediate portion has a third intermediate portion electrical length θc3 at a third center frequency which is half the sum of the fifth and sixth frequencies. The third transmission line has a third electrical length θ3 at the second center frequency, The fourth transmission line has a fourth electrical length θ4 at the second center frequency, The fifth transmission line has a fifth electrical length θ5 at the second center frequency, The seventh transmission line has a seventh electrical length θ7 at the second center frequency, The third transmission line has a third electrical length θ3A at the third center frequency, The fourth transmission line has a fourth electrical length θ4A at the third center frequency, The sixth transmission line has a sixth electrical length θ6 at the third center frequency, The eighth transmission line has an eighth electrical length θ8 at the third center frequency, The second sum of the second intermediate electrical length θc2, the third electrical length θ3, the fifth electrical length θ5, the fourth electrical length θ4, and the seventh electrical length θ7 is (2m + 1) × 90 degrees. The aforementioned m is a non-negative integer, The third sum of the third intermediate electrical length θc3, the third other electrical length θ3A, the sixth electrical length θ6, the fourth other electrical length θ4A, and the eighth electrical length θ8 is (2l + 1) × 90 degrees. The filter circuit according to claim 1, wherein l is an integer greater than or equal to 0.

9. The transmission line further includes another intermediate section between the intermediate section and the output section, The aforementioned intermediate portion includes a first partial intermediate portion and a second partial intermediate portion. The plurality of coupled transmission lines further include a third transmission line and a fourth transmission line, The plurality of resonant elements further include a third resonant element and a fourth resonant element, The third portion of the third transmission line is configured to connect to a third connection point between the first intermediate portion and the second intermediate portion. The third resonant element is configured to be coupled to the third other part of the third transmission line. The third resonant element is configured to resonate at a third frequency, The fourth part of the fourth transmission line is configured to be coupled to a fourth connection point between the intermediate part and the other intermediate part. The fourth resonant element is configured to be coupled to the fourth other part of the fourth transmission line. The fourth resonant element is configured to resonate at a fourth frequency, The first intermediate portion has an electrical length θp1 of the first intermediate portion at the first center frequency. The second intermediate portion has an electrical length θq1 of the second intermediate portion at the first center frequency. The first intermediate electrical length θc1 is the sum of the first partial intermediate electrical length θp1 and the second partial intermediate electrical length θq1. The aforementioned other intermediate portion has an electrical length θcA1 of the other intermediate portion at a second center frequency between the third frequency and the fourth frequency. The second intermediate portion has the second intermediate portion electrical length θq2 at the second center frequency, The third transmission line has a third electrical length θ3 at the second center frequency, The fourth transmission line has a fourth electrical length θ4 at the second center frequency, The fourth sum of the third electrical length θ3, the second intermediate electrical length θq2, the other intermediate electrical length θcA1, and the fourth electrical length θ4 is (2q + 1) × 90 degrees. The filter circuit according to claim 1, wherein q is an integer greater than or equal to 0.

10. The first frequency is the same as the second frequency, The filter circuit according to any one of claims 1 to 9, wherein the second electrical length θ2 is different from the first electrical length θ1.

11. The first frequency differs from the second frequency, The filter circuit according to any one of claims 1 to 9, wherein the second electrical length θ2 is the same as the first electrical length θ1.

12. At least one of the first resonant element and the second resonant element includes a first conductive portion, a second conductive portion, and a third conductive portion between the first conductive portion and the second conductive portion. The filter circuit according to any one of claims 1 to 9, wherein the line width of the third conductive portion of the third conductive portion is narrower than the line width of the first conductive portion of the first conductive portion and narrower than the line width of the second conductive portion of the second conductive portion.

13. At least one end of the first resonant element and the second resonant element is open, The filter circuit according to any one of claims 1 to 9, wherein at least one other end of the first resonant element and the second resonant element is grounded.

14. At least one of the first resonant element and the second resonant element includes a frequency-variable resonator, One end of the aforementioned variable frequency resonator is grounded, The filter circuit according to any one of claims 1 to 9, wherein a variable capacitance element is connected to another end of the frequency-variable resonator.

15. At least one of the first resonant element and the second resonant element includes an LC resonator, The LC resonator includes lumped element elements, The filter circuit according to any one of claims 1 to 9, wherein the lumped element includes an inductive element and a capacitive element.

16. The filter comprises a plurality of the aforementioned filter elements, The filter circuit according to claim 1, wherein two of the plurality of filter elements are configured to be coupled to one another.

17. The first frequency of the first resonant element included in one of the plurality of filter elements is different from the first frequency of the first resonant element included in another of the plurality of filter elements. The filter circuit according to claim 15, wherein the second frequency of the second resonant element included in one of the plurality of filter elements is different from the second frequency of the second resonant element included in another of the plurality of filter elements.

18. First terminal and, The second terminal and, Filter element, Equipped with, The aforementioned filter element is Transmission line and A plurality of coupled transmission lines including a first transmission line and a second transmission line, A plurality of resonant elements including a first resonant element and a second resonant element, Includes, The aforementioned transmission line is An input section configured to be coupled to the first terminal, An output section configured to be coupled to the second terminal, The intermediate section between the input section and the output section, Includes, The first part of the first transmission line is configured to be coupled to a first connection point between the input section and the intermediate section. The second part of the second transmission line is configured to be coupled to a second connection point between the intermediate part and the output part. The first resonant element is configured to be coupled to the first other part of the first transmission line. The second resonant element is configured to be coupled to the second other part of the second transmission line. The first resonant element is configured to resonate at a first frequency, The second resonant element is configured to resonate at a second frequency, The aforementioned intermediate portion has a first intermediate portion electrical length θc1 at a first center frequency which is half the sum of the first frequency and the second frequency. The first transmission line has a first electrical length θ1 at the first center frequency, The second transmission line has a second electrical length θ2 at the first center frequency, The first intermediate electrical length θc1, the first electrical length θ1, and the first sum of the second electrical length θ2 are substantially n × 180 degrees. A filter circuit in which n is an integer greater than or equal to 1.

19. The filter circuit according to claim 18, wherein the first frequency is different from the second frequency.

20. A filter circuit according to any one of claims 1 to 9, A receiving / transmitting circuit configured to receive or transmit a communication signal via the aforementioned filter circuit, Equipped with, A communication device wherein the filter circuit is configured to attenuate frequency components of a target band including the first frequency and the second frequency included in the communication signal.

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