Antenna device and electronic apparatus

Abstract

An antenna device (100) according to the present disclosure comprises: a radiation element (10); a variable reactance circuit (20) that is connected to the radiation element (10) and changes reactance; and a filter circuit (30) which is connected in parallel to the variable reactance circuit (20) and in which the resonance frequency is adjusted by the reactance of the variable reactance circuit (20). The filter circuit (30) is a parallel resonance circuit including at least two inductance elements (L1), (L2) that are magnetically coupled.

Description

Antenna device and electronic device

[0001] The present disclosure relates to an antenna device and an electronic device.

[0002] An antenna device provided with a filter circuit for broadening the usable frequency band is disclosed in International Publication No. 2023 / 120075 (Patent Document 1). The antenna device disclosed in Patent Document 1 is provided with a filter circuit between a radiating element and a ground, and a switch for switching the connection with a plurality of types of frequency adjustment elements is provided to adjust the resonance frequency of the filter circuit.

[0003] International Publication No. 2023 / 120075

[0004] Generally, an antenna device ensures the required radiation efficiency by matching the impedance of the radiating element at the frequencies in the passband. However, when a filter circuit is provided as in the antenna device disclosed in Patent Document 1 and the resonance frequency of the filter circuit is adjusted, the matching with the impedance of the radiating element is disrupted, the reactance in the passband fluctuates greatly, and the radiation efficiency of the antenna device deteriorates.

[0005] The present disclosure has been made to solve such problems, and an object thereof is to provide an antenna device that does not deteriorate the radiation efficiency even when the resonance frequency of a filter circuit is adjusted in an antenna device provided with the filter circuit.

[0006] An antenna device according to the present disclosure includes a radiating element, a variable reactance circuit connected to the radiating element and changing the reactance, and a filter circuit connected in parallel with the variable reactance circuit and having a resonance frequency adjusted by the reactance of the variable reactance circuit. The filter circuit is a parallel resonance circuit including at least two inductance elements magnetically coupled.

[0007] An antenna device according to this disclosure includes a filter circuit which is a parallel resonant circuit containing at least two magnetically coupled inductance elements. Therefore, even when the resonant frequency of the filter circuit is adjusted, fluctuations in reactance in the passband are suppressed, and the radiation efficiency of the antenna device is not deteriorated.

[0008] This is a diagram showing the configuration of the electronic device in Embodiment 1. This is a diagram showing the equivalent circuit of the filter circuit in Embodiment 1. This is a diagram showing the configuration of the electronic device in the comparative technology. This is a diagram showing the reactance before and after adjusting the resonant frequency of the filter circuit in Comparative Example 1. This is a diagram showing the reactance before and after adjusting the resonant frequency of the filter circuit in Embodiment 1. This is a diagram showing the reactance before and after adjusting the resonant frequency of the filter circuit in Comparative Example 2. This is a diagram showing the reactance before and after adjusting the resonant frequency of the filter circuit in Embodiment 2. This is a diagram showing the reactance before and after adjusting the resonant frequency of the filter circuit in Comparative Example 3. This is a diagram showing the reactance before and after adjusting the resonant frequency of the filter circuit in Embodiment 3. This is a diagram showing the configuration of the electronic device in Embodiment 2. This is a diagram showing the equivalent circuit of the filter circuit in Embodiment 2. This is a diagram showing the reactance before and after adjusting the resonant frequency of the filter circuit in the embodiment of Embodiment 2. This is a diagram showing the configuration of the electronic device in Modification 1 of Embodiment 1. This is a diagram showing the configuration of the electronic device in Modification 2 of Embodiment 1. This is a diagram showing the configuration of the electronic device in Modification 3 of Embodiment 1. This is a diagram showing the configuration of the electronic device in Modification 4 of Embodiment 1.

[0009] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0010] [Embodiment 1] Figure 1 shows the configuration of the electronic device 200 in Embodiment 1. The electronic device 200 includes an antenna device 100 and a power supply circuit 40 that supplies power to the radiating element 10. The electronic device 200 is, for example, a laptop computer, a mobile phone, a smartphone, or a tablet.

[0011] <Basic Configuration of Antenna Device> The antenna device 100 includes a radiating element 10, a variable reactance circuit 20, and a filter circuit 30. The variable reactance circuit 20 and the filter circuit 30 are connected between the radiating element 10 and the feed circuit 40. The antenna device 100 is, for example, an inverted F antenna.

[0012] The variable reactance circuit 20 is connected to the radiating element 10. The variable reactance circuit 20 includes at least one reactance element 21 and a switch 22 that switches the electrical connection with the reactance element 21. When the switch 22 is switched, the reactance of the variable reactance circuit 20 changes.

[0013] The filter circuit 30 is connected in parallel to the variable reactance circuit 20. The filter circuit 30 includes paths T1 (first path) and T2 (second path) provided in parallel, and a path T3 (third path) connected in series to paths T1 and T2. Path T1 constitutes a series resonant circuit 32 in which an inductance element L1 (first inductance element) and a capacitance element C1 are connected in series. Path T3 has an inductance element L2 (second inductance element).

[0014] The inductance elements L1 and L2 of the filter circuit 30 are magnetically coupled. Figure 2 shows the equivalent circuit 31 of the filter circuit 30 in Embodiment 1. Let L1 be the inductance of inductance element L1, and L2 be the inductance of inductance element L2. Let k be the coupling coefficient of the magnetic field coupling between inductance element L1 and inductance element L2, and let M be the mutual inductance. As shown in Figure 2, the mutual inductance M occurs on path T2, inductance element L1 is replaced by L1-M, and inductance element L2 is replaced by L2-M. Also, let C1 be the capacitance of capacitance element C1. Since path T1 has inductance elements L1-M and capacitance element C1, and path T2 has mutual inductance M, the circuit consisting of path T1 and path T2 constitutes a parallel resonant circuit 33.

[0015] Although not shown in the diagram, the filter circuit 30 is, for example, a rectangular parallelepiped chip component. The filter circuit 30 is constructed by forming conductive patterns of inductance elements L1, L2, and capacitance elements C1 on each insulating substrate (for example, liquid crystal polymer, low-temperature co-fired ceramics, etc.) and stacking the respective insulating substrates. The filter circuit 30 is not limited to chip components, and each or some of the elements may be composed of different components.

[0016] <Reducing Reactance Fluctuations> In the antenna device 100, a filter circuit 30 is used to block radio waves flowing in from outside the antenna device 100 in a frequency band that includes the resonant frequency. The filter circuit 30 can block radio waves in a predetermined frequency band centered on the resonant frequency from flowing into the antenna device 100 from the outside. Here, the filter circuit 30 has a variable reactance circuit 20 connected in parallel, and the resonant frequency of the filter circuit 30 can be adjusted by changing the reactance of the variable reactance circuit 20. As a result, the antenna device 100 can adjust the frequency band to be blocked by adjusting the resonant frequency of the filter circuit 30. However, when a filter circuit of the comparative technology described below is used in an antenna device, changing the reactance of the variable reactance circuit causes a large fluctuation in the reactance at the frequency that the antenna device wants to pass through (passband). As a result, the radiation efficiency deteriorates in an antenna device using a filter circuit of the comparative technology.

[0017] <Mode of Comparative Technology> Specifically, the filter circuit of the mode of comparative technology will be described. Figure 3 is a diagram showing the configuration of the electronic device 200b in the mode of comparative technology. The electronic device 200b includes an antenna device 100b and a power supply circuit 40 that supplies power to the radiating element 10. The antenna device 100b includes a radiating element 10, a variable reactance circuit 20 and a filter circuit 30b. The only difference between the electronic device 200b in the mode of comparative technology and the electronic device 200 in Embodiment 1 is the difference between the filter circuit 30b and the filter circuit 30. The filter circuit 30b constitutes a parallel resonant circuit in which an inductance element L2b and a capacitance element C2b are connected in parallel. In other words, the filter circuit 30b does not include two inductance elements that are magnetically coupled like the filter circuit 30. The variable reactance circuit 20 includes at least one reactance element 21 and a switch 22 that switches the electrical connection with the reactance element 21.

[0018] <Comparative Example 1> In the comparative technology, the filter circuit 30b has a resonant frequency of 3 GHz before adjustment and is set to block a predetermined frequency band from 2 GHz to 4 GHz. The passband of the antenna device 100b is set to the 2 GHz band or the 4 GHz band. In this case, as Comparative Example 1, in the filter circuit 30b of Figure 3, the inductance of the inductance element L2b is set to 1.5 nH, and the capacitance of the capacitance element C2b is set to 1.88 pF. The reactance element 21a is a capacitance element having 0.82 pF. In this case, when the switch 22 is switched from the open state to the state connected to the reactance element 21b, the resonant frequency of the filter circuit 30b is adjusted from 3 GHz to 2.5 GHz.

[0019] Figure 4 shows the reactance of the filter circuit 30b of Comparative Example 1 before and after adjusting the resonant frequency F1. The resonant frequency F1 of the filter circuit 30b is 3 GHz, and the reactance is maximum at 3 GHz, blocking a predetermined frequency band from 2 GHz to 4 GHz. When the resonant frequency F1 is adjusted to 2.5 GHz by switching the switch 22 from the open state to the state connected to the reactance element 21b, the reactance is maximum at 2.5 GHz, but the reactance at the pass frequency F2 of 2 GHz fluctuates significantly. Focusing on the reactance X at the pass frequency F2 (2 GHz) in Figure 4, the reactance X before adjustment is 33.7 Ω, but the reactance X after adjustment is 50.8 Ω, showing a large fluctuation. That is, the amount of change in reactance X is 17.1 Ω.

[0020] Thus, when adjusting the resonant frequency F1 of the filter circuit 30b in Comparative Example 1, the reactance at the pass frequency F2 fluctuates significantly. As a result, the radiation efficiency of the antenna device 100b deteriorates.

[0021] <Example 1> In Embodiment 1, the filter circuit 30, similar to the comparative technology, has a resonant frequency of 3 GHz before adjustment and is set to block a predetermined frequency band from 2 GHz to 4 GHz. The passband of the antenna device 100 is set in the 2 GHz band or the 4 GHz band. In this Example 1, in the equivalent circuit 31 of Figure 2, the inductance element L1 is set to 1.5 nH, the inductance element L2 is set to 0.5 nH, and the coupling coefficient k between the inductance element L1 and the inductance element L2 is set to 0.6. The capacitance element C1 is set to 1.88 pF. The reactance element 21a is a capacitance element having 4.45 pF. In this case, when the switch 22 is switched from the open state to the connected state to the reactance element 21a, the resonant frequency of the filter circuit 30 is adjusted from 3 GHz to 2.5 GHz, similar to Comparative Example 1.

[0022] Figure 5 shows the reactance of the filter circuit 30 in Example 1 before and after adjusting the resonant frequency F1. The resonant frequency F1 of the filter circuit 30 is 3 GHz, and the reactance is maximum at 3 GHz, blocking a predetermined frequency band from 2 GHz to 4 GHz. When the resonant frequency F1 is adjusted to 2.5 GHz by switching the switch 22 from the open state to the state connected to the reactance element 21a, the reactance is maximum at 2.5 GHz, but the fluctuation of the reactance at the pass frequency F2 of 2 GHz is smaller than that in Comparative Example 1. In Figure 5, as in Comparative Example 1, if we focus on the reactance X at the pass frequency F2 (2 GHz), the reactance X before adjustment is 8.1 Ω, but the reactance X after adjustment has changed to 14.7 Ω. That is, the amount of fluctuation of reactance X is 6.6 Ω, which is smaller than the amount of fluctuation of reactance X of 17.1 Ω in Comparative Example 1.

[0023] Thus, in the filter circuit 30 of Example 1, by magnetically coupling inductance elements L1 and L2 to generate mutual inductance M, the fluctuation of reactance at the pass frequency F2 can be kept small even when the resonant frequency F1 of the filter circuit 30 is adjusted. As a result, the radiation efficiency of the antenna device 100 can be prevented from deteriorating.

[0024] The following sections present comparative examples and examples of adjusting the resonant frequency of the filter circuit to various other frequencies.

[0025] <Comparative Example 2> As a second comparative example, in the filter circuit 30b of Figure 3, the inductance of the inductance element L2b is set to 1.5 nH, and the capacitance of the capacitance element C2b is set to 1.88 pF. The reactance element 21b is an inductance element having 4.1 nH. In this case, when the switch 22 is switched from the open state to the state connected to the reactance element 21b, the resonant frequency of the filter circuit 30b is adjusted from 3 GHz to 3.5 GHz.

[0026] Figure 6 shows the reactance of the filter circuit 30b of Comparative Example 2 before and after adjusting the resonant frequency F1. The resonant frequency F1 of the filter circuit 30b is 3 GHz, and the reactance is maximum at 3 GHz, blocking a predetermined frequency band from 2 GHz to 4 GHz. When the resonant frequency F1 is adjusted to 3.5 GHz by switching the switch 22 from the open state to the state connected to the reactance element 21b, the reactance is maximum at 3.5 GHz, but the reactance at the pass frequency F2 of 4 GHz fluctuates significantly. Focusing on the reactance X at the pass frequency F2 (4 GHz) in Figure 6, the reactance X before adjustment is -48.2 Ω, but the reactance X after adjustment is -89.3 Ω, showing a large fluctuation. That is, the amount of change in reactance X is 41.1 Ω.

[0027] Thus, when adjusting the resonant frequency F1 of the filter circuit 30b in Comparative Example 2, the reactance at the pass frequency F2 fluctuates significantly. As a result, the radiation efficiency of the antenna device 100b deteriorates.

[0028] <Example 2> In Example 2, in the equivalent circuit 31 of Figure 2, the inductance element L1 is set to 1.5 nH, the inductance element L2 is set to 1.0 nH, and the coupling coefficient k between the inductance elements L1 and L2 is set to 0.7. The capacitance element C1 is set to 1.88 pF. The reactance element 21b is set to an inductance element having 0.85 nH. In this case, when the switch 22 is switched from the open state to the state connected to the reactance element 21b, the resonant frequency of the filter circuit 30 is adjusted from 3 GHz to 3.5 GHz, similar to Comparative Example 2.

[0029] Figure 7 shows the reactance of the filter circuit 30 in Example 2 before and after adjusting the resonant frequency F1. The resonant frequency F1 of the filter circuit 30 is 3 GHz, and the reactance is maximum at 3 GHz, blocking a predetermined frequency band from 2 GHz to 4 GHz. When the resonant frequency F1 is adjusted to 3.5 GHz by switching the switch 22 from the open state to the state connected to the reactance element 21b, the reactance is maximum at 3.5 GHz, but the fluctuation of the reactance at the pass frequency F2 of 4 GHz is smaller than that of Comparative Example 2. In Figure 7, similar to Comparative Example 2, if we focus on the reactance X at the pass frequency F2 (4 GHz), the reactance X before adjustment is -2.8 Ω, but the reactance X after adjustment has changed to -2.4 Ω. That is, the amount of fluctuation of reactance X is 0.4 Ω, which is smaller than the amount of fluctuation of reactance X of 41.1 Ω in Comparative Example 2.

[0030] Thus, in the filter circuit 30 of Example 2, by magnetically coupling inductance elements L1 and L2 to generate mutual inductance M, the fluctuation of reactance at the pass frequency F2 can be kept small even when the resonant frequency F1 of the filter circuit 30 is adjusted. As a result, the radiation efficiency of the antenna device 100 can be prevented from deteriorating.

[0031] <Comparative Example 3> As a third comparative example, in the filter circuit 30b of Figure 3, the inductance of the inductance element L2b is set to 1.5 nH, and the capacitance of the capacitance element C2b is set to 1.88 pF. The reactance element 21a is a capacitance element having 5.6 pF. In this case, when the switch 22 is switched from the open state to the state connected to the reactance element 21a, the resonant frequency of the filter circuit 30b is adjusted from 3 GHz to 1.5 GHz.

[0032] Figure 8 shows the reactance of the filter circuit 30b of Comparative Example 3 before and after adjusting the resonant frequency F1. The resonant frequency F1 of the filter circuit 30b is 3 GHz, and the reactance is maximum at 3 GHz, blocking a predetermined frequency band from 2 GHz to 4 GHz. When the resonant frequency F1 is adjusted to 1.5 GHz by switching the switch 22 from the open state to the state connected to the reactance element 21a, the reactance is maximum at 1.5 GHz, but the reactance at the pass frequency F2 of 2 GHz fluctuates significantly. Focusing on the reactance X at the pass frequency F2 (2 GHz) in Figure 8, the reactance X before adjustment is 33.7 Ω, but the reactance X after adjustment is 24.0 Ω, showing a large fluctuation. That is, the amount of change in reactance X is 9.7 Ω.

[0033] Thus, when adjusting the resonant frequency F1 of the filter circuit 30b in Comparative Example 3, the reactance at the pass frequency F2 fluctuates significantly. As a result, the radiation efficiency of the antenna device 100b deteriorates.

[0034] <Example 3> In Example 3, in the equivalent circuit 31 of Figure 1, the inductance element L1 is set to 1.5 nH, the inductance element L2 is set to 0.5 nH, and the coupling coefficient k between the inductance elements L1 and L2 is set to 0.6. The capacitance element C1 is set to 1.88 pF. The reactance element 21a is set to a capacitance element having 20 pF. In this case, when the switch 22 is switched from the open state to the state connected to the reactance element 21a, the resonant frequency of the filter circuit 30 is adjusted from 3 GHz to 1.5 GHz, similar to Comparative Example 3.

[0035] Figure 9 shows the reactance of the filter circuit 30 in Example 3 before and after adjusting the resonant frequency F1. The resonant frequency F1 of the filter circuit 30 is 3 GHz, and the reactance is maximum at 3 GHz, blocking a predetermined frequency band from 2 GHz to 4 GHz. When the resonant frequency F1 is adjusted to 1.5 GHz by switching the switch 22 from the open state to the state connected to the reactance element 21a, the reactance is maximum at 1.5 GHz, but the fluctuation of the reactance at the pass frequency F2 of 2 GHz is smaller than that in Comparative Example 3. In Figure 9, as in Comparative Example 3, if we focus on the reactance X at the pass frequency F2 (2 GHz), the reactance X before adjustment is 8.1 Ω, but the reactance X after adjustment has changed to 7.8 Ω. That is, the amount of fluctuation of reactance X is 0.3 Ω, which is smaller than the amount of fluctuation of reactance X of 9.7 Ω in Comparative Example 3.

[0036] Thus, in the filter circuit 30 of Example 3, by magnetically coupling inductance elements L1 and L2 to generate mutual inductance M, the fluctuation of reactance at the pass frequency F2 can be kept small even when the resonant frequency F1 of the filter circuit 30 is adjusted. As a result, the radiation efficiency of the antenna device 100 can be prevented from deteriorating.

[0037] [Embodiment 2] Figure 10 shows the configuration of the electronic device 200c in Embodiment 2. The electronic device 200c includes an antenna device 100c and a power supply circuit 40 that supplies power to the radiating element 10. The electronic device 200c is, for example, a laptop computer, a mobile phone, a smartphone, or a tablet.

[0038] <Basic Configuration of Antenna Device> The antenna device 100c includes a radiating element 10, a variable reactance circuit 20, and a filter circuit 30c. The variable reactance circuit 20 and the filter circuit 30c are connected between the radiating element 10 and the feed circuit 40. The antenna device 100c is, for example, an inverted F antenna.

[0039] The variable reactance circuit 20 is connected to the radiating element 10. The variable reactance circuit 20 includes at least one reactance element 21 and a switch 22 that switches the electrical connection with the reactance element 21. When the switch 22 is switched, the reactance of the variable reactance circuit 20 changes.

[0040] The filter circuit 30c is connected in parallel to the variable reactance circuit 20. The filter circuit 30c includes parallel paths T1c and T2c, and a path T3c connected in series to paths T1c and T2c. Path T1c constitutes a series resonant circuit 32c in which an inductance element L1c and a capacitance element C1c are connected in series. Path T2c has an inductance element L2c.

[0041] The inductance elements L1c and L2c of the filter circuit 30c are magnetically coupled. Figure 11 shows the equivalent circuit 31c of the filter circuit 30c in Embodiment 2. The inductance of inductance element L1c is L1c, and the inductance of inductance element L2c is L2c. The coupling coefficient of the magnetic field coupling between inductance element L1c and inductance element L2c is k, and the mutual inductance is -M. As shown in Figure 11, the mutual inductance -M occurs on path T3c, inductance element L1 is replaced by L1c+M, and inductance element L2 is replaced by L2c+M. Also, the capacitance of capacitance element C1c is C1c. Since path T1c has inductance element L1c+M and capacitance element C1c, and path T2c has inductance element L2c+M, the circuit consisting of path T1 and path T2 constitutes a parallel resonant circuit 33c.

[0042] Note that although not shown in the figure, the filter circuit 30c is, for example, a rectangular parallelepiped chip component. The filter circuit 30c is configured by forming conductor patterns of an inductance element L1c, an inductance element L2c, and a capacitance element C1c on respective insulating substrates (for example, liquid crystal polymer, low-temperature co-fired ceramics, etc.) and laminating the respective insulating substrates. Note that the filter circuit 30c is not limited to a chip component, and each element or some of the elements may be configured by different components.

[0043] <Reduction of Reactance Variation> In the antenna device 100c, the filter circuit 30c is used to block radio waves flowing in from outside the antenna device 100c in a frequency band including the resonance frequency. The filter circuit 30c can block radio waves in a predetermined frequency band centered on the resonance frequency from flowing into the antenna device 100c from the outside. Here, the filter circuit 30c is connected in parallel with the variable reactance circuit 20, and the resonance frequency of the filter circuit 30c can be adjusted by changing the reactance of the variable reactance circuit 20. Thereby, the antenna device 100c can adjust the resonance frequency of the filter circuit 30c to adjust the frequency band to be blocked.

[0044] The difference between the electronic device 200c in the second embodiment and the electronic device 200 in the first embodiment is only the difference in the configuration between the filter circuit 30c and the filter circuit 30. Therefore, when the filter circuit of the comparative technical form described above is used in the antenna device, when the reactance of the variable reactance circuit is changed, the reactance in the frequency (pass band) to be passed through in the antenna device varies greatly. As a result, in the antenna device using the filter circuit of the comparative technical form, the radiation efficiency deteriorates. The specific filter circuit of the comparative technical form is as shown in Comparative Examples 1-3.

[0045] <Example of Embodiment 2> In Embodiment 2, the filter circuit 30c, similar to the embodiments of Embodiment 1 and the comparative technology, has a resonant frequency of 3 GHz before adjustment and is set to block a predetermined frequency band from 2 GHz to 4 GHz. The passband of the antenna device 100c is set in the 2 GHz band or the 4 GHz band. In this embodiment of Embodiment 2, in the equivalent circuit 31c of Figure 11, the inductance element L1c is set to 3.05 nH, the inductance element L2c is set to 1.5 nH, and the coupling coefficient k between the inductance element L1c and the inductance element L2c is set to 0.4. The capacitance element C1c is set to 0.45 pF. The reactance element 21a is a capacitance element having 20 pF. In this case, when the switch 22 is switched from the open state to the connected state to the reactance element 21a, the resonant frequency of the filter circuit 30c is adjusted from 3 GHz to 3.5 GHz, similar to Comparative Example 2.

[0046] Figure 12 shows the reactance before and after adjusting the resonant frequency F1 of the filter circuit 30c in the embodiment of the second embodiment. The resonant frequency F1 of the filter circuit 30c is 3 GHz, and the reactance is maximum at 3 GHz, blocking a predetermined frequency band from 2 GHz to 4 GHz. When the resonant frequency F1 is adjusted to 3.5 GHz by switching the switch 22 from the open state to the state connected to the reactance element 21a, the reactance is maximum at 3.5 GHz, but the fluctuation of the reactance at the pass frequency F2 of 4 GHz is smaller than that of Comparative Example 2. In Figure 12, similar to Comparative Example 2, if we focus on the reactance X at the pass frequency F2 (4 GHz), the reactance X before adjustment is 13.1 Ω, but the reactance X after adjustment has changed to 17.9 Ω. That is, the amount of fluctuation of reactance X is 4.8 Ω, which is smaller than the amount of fluctuation of reactance X of 41.1 Ω in Comparative Example 2.

[0047] Thus, in the filter circuit 30c of the embodiment 2 example, by causing the inductance element L1c and the inductance element L2c to be magnetically coupled to generate the mutual inductance M, even if the resonance frequency F1 of the filter circuit 30c is adjusted, the variation in reactance at the passing frequency F2 can be suppressed to a small level. As a result, the radiation efficiency of the antenna device 100c can be prevented from deteriorating.

[0048] [Modification Example of Antenna Device] In the first embodiment, although the variable reactance circuit 20 and the filter circuit 30 have been described as being connected between the radiating element 10 and the power feeding circuit 40, the present invention is not limited to this.

[0049] <Modification Example 1> FIG. 13 is a diagram showing the configuration of an electronic device 200d in Modification Example 1 of the first embodiment. As shown in FIG. 13, the variable reactance circuit 20 and the filter circuit 30 may be connected between the radiating element 10 and the ground electrode 50 and may be electrically connected to the wiring connecting the radiating element 10 and the power feeding circuit 40.

[0050] Also in Modification Example 1, when adjusting the resonance frequency of the filter circuit 30, the variation in reactance in the passing band can be suppressed. As a result, the radiation efficiency of the antenna device 100d can be prevented from deteriorating.

[0051] <Modification Example 2> FIG. 14 is a diagram showing the configuration of an electronic device 200e in Modification Example 2 of the first embodiment. As shown in FIG. 14, the variable reactance circuit 20 and the filter circuit 30 may be connected between the radiating element 10 and the ground electrode 50 and may be directly and electrically connected to the radiating element 10.

[0052] Also in Modification Example 2, when adjusting the resonance frequency of the filter circuit 30, the variation in reactance in the passing band can be suppressed. As a result, the radiation efficiency of the antenna device 100e can be prevented from deteriorating.

[0053] Further, in the first embodiment, although the variable reactance circuit 20 has been described as including at least one reactance element 21 and a switch 22 for switching the electrical connection with the reactance element 21, the present invention is not limited to this.

[0054] <Modification 3> Figure 15 shows the configuration of the electronic device 200f in Modification 3 of Embodiment 1. The variable reactance circuit 20f includes a reactance element 21g and a Pin diode 60 connected in series with the reactance element 21g. The antenna device 100f also includes an inductance element L3a and an inductance element L3b for switching the voltage applied to the reactance element 21g and the Pin diode 60.

[0055] One end of the inductance element L3a is connected to the path connecting the radiating element 10 and the power supply circuit 40, and the other end is grounded. One end of the inductance element L3b is connected to the path connecting the radiating element 10 and the power supply circuit 40, and a predetermined voltage can be applied to the other end. When no predetermined voltage is applied to the other end of the inductance element L3b (voltage OFF), no voltage is applied to the reactance element 21g and the Pin diode 60, so only the filter circuit 30 conducts with the radiating element 10. On the other hand, when a predetermined voltage is applied to the other end of the inductance element L3b (voltage ON), voltage is applied to the reactance element 21g and the Pin diode 60, so the filter circuit 30 and the reactance element 21g conduct with the radiating element 10.

[0056] In this way, the voltage applied to the reactance element 21g and the Pin diode 60 is switched, thereby changing the connection state of the reactance element 21g to the filter circuit 30. As a result, the reactance of the variable reactance circuit 20f changes, and the resonant frequency of the filter circuit 30 is adjusted.

[0057] In the third modified example, when adjusting the resonant frequency of the filter circuit 30, fluctuations in the reactance in the passband can be suppressed. As a result, the radiation efficiency of the antenna device 100f can be avoided.

[0058] <Modification 4> Figure 16 shows the configuration of the electronic device 200g in Modification 4 of Embodiment 1. The variable reactance circuit 20g is a variable reactance element 21h.

[0059] The resonant frequency of the filter circuit 30 is adjusted by changing the reactance of the variable reactance element 21h.

[0060] In the modified example 4, when adjusting the resonant frequency of the filter circuit 30, fluctuations in the reactance in the passband can be suppressed. As a result, the radiation efficiency of the antenna device 100g can be avoided.

[0061] Although modifications 1-4 of Embodiment 1 have been described, similar modifications may be made to Embodiment 2 as well.

[0062] Furthermore, although the antenna device described in each embodiment is an inverted F-type antenna, the antenna device may be other antennas such as a monopole antenna.

[0063] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope of the claims are intended to be included.

[0064] 10 Radiating element, 20, 20f, 20g Variable reactance circuit, 21, 21a, 21b, 21g Reactance element, 21h Variable reactance element, 22 Switch, 30, 30b, 30c Filter circuit, 31, 31c Equivalent circuit, 32, 32c Series resonant circuit, 33, 33c Parallel resonant circuit, 40 Feed circuit, 50 Ground electrode, 60 Pin diode, 100, 100b, 100c, 100d, 100e, 100f, 100g Antenna device, 200, 200b, 200c, 200d, 200e, 200f, 200g Electronic equipment, C1c, C1, C2b Capacitance element, F1 Resonant frequency, F2 Pass frequency, L1, L1c, L2c, L2, L2b, L3a, L3b; Inductance element, M, -M; Mutual inductance, T1c, T1, T2, T2c, T3, T3c; Path, X; Reactance, k; Coupling coefficient.

Claims

1. An antenna device comprising: a radiating element; a variable reactance circuit connected to the radiating element for changing its reactance; and a filter circuit connected in parallel to the variable reactance circuit, the filter circuit being a parallel resonant circuit including at least two magnetically coupled inductance elements.

2. The antenna device according to claim 1, wherein the filter circuit includes a first path and a second path provided in parallel, and a third path connected in series with respect to the first path and the second path, the first path having a series resonant circuit including a first inductance element, and either the second path or the third path having a second inductance element that is magnetically coupled with the first inductance element.

3. The antenna device according to claim 2, wherein the first path has a series resonant circuit in which the first inductance element and the capacitance element are connected in series, and the third path has the second inductance element.

4. The antenna device according to claim 2, wherein the first path has a series resonant circuit in which the first inductance element and the capacitance element are connected in series, and the second path has the second inductance element.

5. The antenna device according to any one of claims 1 to 4, wherein the variable reactance circuit and the filter circuit are connected between the radiating element and the power supply circuit.

6. The antenna device according to any one of claims 1 to 4, wherein the variable reactance circuit and the filter circuit are connected between the radiating element and the ground electrode.

7. The antenna device according to claim 6, wherein the variable reactance circuit and the filter circuit are electrically connected to the wiring connecting the radiating element and the power supply circuit.

8. The antenna device according to any one of claims 1 to 7, wherein the variable reactance circuit includes at least one reactance element and a switch for switching the electrical connection with the reactance element.

9. The antenna device according to any one of claims 1 to 7, wherein the variable reactance circuit includes a reactance element and a Pin diode connected in series with the reactance element, and the voltage applied to the reactance element and the Pin diode is switched to switch the connection state of the reactance element to the filter circuit.

10. The antenna device according to any one of claims 1 to 7, wherein the variable reactance circuit is a variable reactance element.

11. An electronic device comprising the antenna device according to any one of claims 1 to 10, and a power supply circuit for supplying power to the radiating element.

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