Antenna device and electronic apparatus

Abstract

The present invention provides an antenna device and an electronic apparatus that make it possible to achieve a small size and a wide bandwidth. An antenna device (100) according to the present disclosure comprises: a first radiation element (11) to which a power supply circuit (30) is connected; a second radiation element (12) at least one end of which is open; and a filter circuit (20) which is provided at an intermediate portion of the second radiation element (12). The first radiation element (11) and the second radiation element (12) are electromagnetically coupled. The filter circuit (20) includes a plurality of inductance elements, at least two of which are magnetically coupled to constitute a parallel resonance circuit.

Description

Antenna device and electronic device

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

[0002] In recent years, in electronic devices, an antenna device including a dipole element and two parasitic elements has been used to widen the frequency band or support multiple frequency bands. Specifically, an antenna device including a dipole element and two parasitic elements is disclosed in Japanese Patent Application Laid-Open No. 2015-162888 (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2015-162888

[0004] In the antenna device disclosed in Patent Document 1, broadbanding is achieved by including a dipole element connected to a power feeding circuit and two parasitic elements spaced apart from the dipole element and having bent portions. However, the antenna device disclosed in Patent Document 1 needs to use two large-area parasitic elements to achieve broadbanding, and the device itself becomes large.

[0005] The present disclosure has been made to solve such problems, and an object thereof is to provide an antenna device and an electronic device that can achieve broadbanding in a small size.

[0006] An antenna device according to the present disclosure includes a first radiating element to which a power feeding circuit is connected, a second radiating element having at least one open end, and a filter circuit provided in an intermediate portion of the second radiating element. The first radiating element and the second radiating element are electromagnetically coupled. The filter circuit includes a plurality of inductance elements, and at least two inductance elements are magnetically coupled to form a parallel resonance circuit.

[0007] An electronic device according to the present disclosure includes the above antenna device and a power feeding circuit.

[0008] In the antenna device according to the present disclosure, since the filter circuit provided in the intermediate portion of the second radiating element forms a parallel resonance circuit with at least two inductance elements magnetically coupled, broadbanding can be achieved while reducing the size of the device itself.

[0009] This is a circuit diagram of the antenna device in Embodiment 1. This is a diagram illustrating the equivalent circuit of the filter circuit in Embodiment 1. This is a schematic diagram showing the electronic equipment in Embodiment 1. This is a diagram showing the frequency characteristics of the reflection loss of the antenna device in Embodiment 1. This is a diagram showing the frequency characteristics of the radiation efficiency of the antenna device in Embodiment 1. This is a circuit diagram of the antenna device in Embodiment 2. This is a circuit diagram of the antenna device in a modified example of Embodiment 2. This is a diagram illustrating a modified example of the filter circuit.

[0010] 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.

[0011] [Embodiment 1] Figure 1 is a circuit diagram of the antenna device 100 in Embodiment 1. The antenna device 100 comprises a first antenna and a second antenna. The first antenna includes a first radiating element 11 to which a power supply circuit 30 is connected.

[0012] The second antenna includes a second radiating element 12 and a filter circuit 20 provided in the middle of the second radiating element 12. The second antenna is an open-ended antenna and is electromagnetically coupled to the first antenna. In other words, the antenna device 100 functions as a fed antenna, where the first antenna is fed by the feeding circuit 30, and the second antenna functions as an unfed antenna, where it is not fed by the feeding circuit 30.

[0013] The second radiating element 12 is divided into radiating element 12a and radiating element 12b, separated by a filter circuit 20, and is electromagnetically coupled to the first antenna on the side of radiating element 12a. The filter circuit 20 includes a first path 21 having a series resonant circuit in which a first coil L1 (first inductance element) and a capacitor C1 (capacitor element) are connected in series, and a second path 22 provided in parallel with the first path 21. Furthermore, the filter circuit 20 includes a third path 23 having a second coil L2 (second inductance element) and connected in series with the first path 21 and the second path 22.

[0014] In the filter circuit 20, the first coil L1 and the second coil L2 are magnetically coupled, generating a mutual inductance M. The coupling coefficient between the first coil L1 and the second coil L2 is denoted as k. Figure 2 is a diagram illustrating the equivalent circuit of the filter circuit 20 in Embodiment 1. In the filter circuit 20, the magnetic field coupling of the first coil L1 and the second coil L2 generates a negative mutual inductance -M in the first coil L1 and the second coil L2, and a positive mutual inductance +M in the second path 22. Therefore, the filter circuit 20 functions as a parallel resonant circuit as shown in the equivalent circuit in Figure 2.

[0015] The filter circuit 20, although not shown in the diagram, is, for example, a rectangular parallelepiped chip component. The filter circuit 20 is constructed by forming conductor patterns for the first coil L1, the second coil L2, and the capacitor C1 on each insulating substrate (for example, liquid crystal polymer, low-temperature co-fired ceramics, etc.) and then stacking the insulating substrates. Note that the filter circuit 20 is not limited to chip components, and each element or some of the elements may be composed of different components.

[0016] Antenna devices implemented in mobile devices such as smartphones use electromagnetic field coupling of a fed antenna and a parasitic antenna to broaden the frequency bandwidth or to support multiple frequency bands. Furthermore, to broaden the frequency bandwidth or support multiple frequency bands, it is necessary to add parasitic antennas that are electromagnetically coupled to the fed antenna, for example, according to the number of additional frequency bands. However, simply adding parasitic antennas according to the number of additional frequency bands would increase the size of the antenna device itself.

[0017] Therefore, in the antenna device 100 of this embodiment, a filter circuit 20 is provided in the middle of the second radiating element 12, so that the second radiating element 12, which is a parasitic antenna, functions as an antenna with two resonant frequencies. The filter circuit 20 is a parallel resonant circuit formed by the magnetic field coupling of the first coil L1 and the second coil L2. Specifically, as shown in Figure 1, by providing the filter circuit 20, the second radiating element 12 has a fundamental wave F1 where the length of the radiating element 12a + radiating element 12b is half a wavelength (λ / 2), and a wavelength F2 due to double resonance where the length of the radiating element 12a is half a wavelength (λ / 2).

[0018] This is thought to be because, in the passband of the filter circuit 20, the entire second radiating element 12 of the antenna device 100 functions as a passive antenna, and in the stopband (attenuation band) of the filter circuit 20, a part of the second radiating element 12 functions as a passive antenna. For this reason, it is preferable that the frequency due to the double resonance of the second radiating element 12 (= propagation speed / wavelength F2) is included in the attenuation band of the filter circuit.

[0019] Since the antenna device 100 functions as an antenna with two resonant frequencies using one second radiating element 12, it can broaden the frequency bandwidth or support multiple frequency bands without adding a parasitic antenna to match the number of additional frequency bands. Therefore, the antenna device 100 can broaden the frequency bandwidth or support multiple frequency bands without increasing the size of the device, and can be made smaller compared to antenna devices that can support the same frequency band.

[0020] Specifically, we will describe the case where the antenna device 100 is mounted on an electronic device and a simulation is performed. Figure 3 is a schematic diagram showing the electronic device 200 in Embodiment 1. The electronic device 200 shown in Figure 3 is capable of communication in a band including approximately 3.0 GHz, and further capable of communication in a band including approximately 4.8 GHz. The electronic device 200 is, for example, a smartphone, and a circuit board 40 with the antenna device 100 mounted on it is mounted on a part of the housing.

[0021] The circuit board 40 is mounted with a first radiating element 11, a second radiating element 12, a filter circuit 20, and a power supply circuit 30, which constitute the antenna device 100. The second radiating element 12 is divided into a radiating element 12a and a radiating element 12b, separated by the filter circuit 20. One end of the first radiating element 11 is grounded to the ground electrode GND via the power supply circuit 30. Both ends of the second radiating element 12 are open ends.

[0022] The first radiating element 11 has a length of 3 mm in the X direction, a length of 8 mm in the Y direction, and a line width of 1 mm, as shown in Figure 1. The second radiating element 12 has a length of 30 mm in the X direction and a line width of 1 mm. The radiating element 12a has a length of 21 mm in the X direction. The filter circuit 20 has a first coil L1 = 1 nH, a second coil L2 = 3 nH, a capacitor C1 = 1 pF, and a coupling coefficient k = 0.7. Under these conditions, a simulation of the antenna device 100 was performed.

[0023] Figure 4 shows the frequency characteristics of the reflection loss of the antenna device 100 in Embodiment 1. In Figure 4, the horizontal axis represents frequency and the vertical axis represents reflection loss. Figure 5 shows the frequency characteristics of the radiation efficiency of the antenna device 100 in Embodiment 1. In Figure 5, the horizontal axis represents frequency and the vertical axis represents radiation efficiency. The frequency characteristics of the reflection loss shown in Figure 4 and the frequency characteristics of the radiation efficiency shown in Figure 5 are the results of simulations performed with the antenna device 100 configuration shown in Figure 3.

[0024] Figure 4 shows the frequency characteristics of the reflection loss of the antenna device 100 as shown by the solid line graph A, and the frequency characteristics of the reflection loss of the antenna device without the filter circuit 20 as shown by the dashed line graph B. Graph B shows that there is an attenuation pole around 3.1 GHz, but no attenuation poles at frequencies above 4 GHz. On the other hand, graph A shows that there is an attenuation pole around 2.9 GHz, and another attenuation pole around 4.8 GHz.

[0025] Figure 5 shows the frequency characteristics of the radiation efficiency of antenna device 100 (solid line graph A) and the frequency characteristics of the radiation efficiency of antenna device without capacitor C2 (dashed line graph B). Graph B shows that the radiation efficiency is high around 3.1 GHz, but low at frequencies between approximately 4 GHz and 5 GHz. On the other hand, graph A shows that the radiation efficiency is high around 2.9 GHz, and also high around 4.8 GHz.

[0026] From the frequency characteristics of reflection loss shown in Figure 4 and the frequency characteristics of radiation efficiency shown in Figure 5, it can be seen that the electronic device 200 on which the antenna device 100 is mounted is capable of communication not only in the band including approximately 3.0 GHz, but also in the band including approximately 4.8 GHz.

[0027] The second radiating element 12 functions as an antenna with two resonant frequencies by providing a filter circuit 20 in its middle section because a portion of the second radiating element 12 functions as a passive antenna within the stopband (attenuation band) of the filter circuit 20. The stopband (attenuation band) of the filter circuit 20 is equal to the resonant frequency (= 1 / (2π(L1 × C1)) １／２ This can be determined by the following: In the simulation of the antenna device 100, the first coil L1 = 1 nH and the capacitor C1 = 1 pF, so the resonant frequency of the filter circuit 20 can be determined to be approximately 5.0 GHz. Therefore, in graph A shown in Figure 5, the frequency band where the radiation efficiency is high around 4.8 GHz coincides with the stopband (attenuation band) of the filter circuit 20, and is the frequency due to the double resonance of the second radiating element 12.

[0028] Furthermore, the fundamental wave F1 of the second radiating element 12 is predominantly transmitted through the second path 22 from the equivalent circuit of the filter circuit 20 shown in Figure 2, and is therefore affected by the mutual inductance M (coupling coefficient k). Specifically, the radiation efficiency of the fundamental wave F1 of the second radiating element 12 decreases as the mutual inductance M (coupling coefficient k) increases, and increases as the mutual inductance M (coupling coefficient k) decreases.

[0029] On the other hand, in the filter circuit 20, the attenuation rate increases as the mutual inductance M (coupling coefficient k) increases. Therefore, the wavelength F2 due to the double resonance of the second radiating element 12 has a higher radiation efficiency when the mutual inductance M (coupling coefficient k) increases, and a lower radiation efficiency when the mutual inductance M (coupling coefficient k) decreases. In other words, there is a trade-off relationship between the fundamental wave F1 of the second radiating element 12 and the wavelength F2 due to the double resonance with respect to the mutual inductance M (coupling coefficient k).

[0030] As described above, the antenna device 100 includes a first radiating element 11 to which the power supply circuit 30 is connected, a second radiating element 12 with open ends at both ends, and a filter circuit 20 provided in the middle of the second radiating element 12. The first radiating element 11 and the second radiating element 12 are electromagnetically coupled. The filter circuit 20 includes a plurality of inductance elements (first coil L1 and second coil L2), and the first coil L1 and the second coil L2 are magnetically coupled to form a parallel resonant circuit.

[0031] The filter circuit 20 includes a first path 21 and a second path 22 arranged in parallel, and a third path 23 connected in series to the first path 21 and the second path 22. The first path 21 has a series resonant circuit including a first coil L1 and a capacitor C1. The third path 23 has a second coil L2 that is magnetically coupled to the first coil L1.

[0032] Therefore, the antenna device 100 can be miniaturized while achieving a wide bandwidth. Preferably, the frequency due to the double resonance of the second radiating element 12 is included in the attenuation band of the filter circuit 20. Furthermore, the electronic device 200, which includes the antenna device 100 and the power supply circuit 30 that supplies current to the first radiating element 11, can communicate over a wide bandwidth even if it is small in size.

[0033] [Embodiment 2] In the above-described embodiment, it was explained that both ends of the second radiating element 12 are open ends. However, the configuration is not limited to both ends of the second radiating element 12 being open ends; it is sufficient if at least one end is open. Figure 6 is a circuit diagram of the antenna device 100a in Embodiment 2. In the antenna device 100a shown in Figure 6, the same reference numerals are used for components that are the same as those in the antenna device 100 shown in Figure 1, and detailed explanations are not repeated.

[0034] The antenna device 100a comprises a first antenna and a second antenna. The first antenna includes a first radiating element 11 to which a feed circuit 30 is connected. The second antenna includes a second radiating element 12 and a filter circuit 20 provided in the middle of the second radiating element 12. The second antenna is a monopole antenna with one end open and the other end grounded to the ground electrode GND, and is electromagnetically coupled to the first antenna.

[0035] The second radiating element 12 is divided into radiating element 12a and radiating element 12b, separated by a filter circuit 20, and is electromagnetically coupled to the first antenna on the side of radiating element 12a. One end of radiating element 12a is connected to the filter circuit 20, and the other end is grounded to the ground electrode GND.

[0036] In the antenna device 100a, a filter circuit 20 is provided in the middle of the second radiating element 12, which functions as a monopole antenna. The filter circuit 20 forms a parallel resonant circuit by magnetically coupling the first coil L1 and the second coil L2. Therefore, as shown in Figure 6, the second radiating element 12 has a fundamental wave F3 where the length of the radiating element 12a + radiating element 12b is one-quarter of the wavelength (λ / 4), and a wavelength F4 due to double resonance where the length of the radiating element 12a is one-quarter of the wavelength (λ / 4). In other words, the second radiating element 12 functions as an antenna with two resonant frequencies by providing the filter circuit 20 in the middle.

[0037] Since the antenna device 100a functions as an antenna with two resonant frequencies using one second radiating element 12, it can broaden the frequency bandwidth or support multiple frequency bands without adding a parasitic antenna to match the number of additional frequency bands. Therefore, the antenna device 100a can broaden the frequency bandwidth or support multiple frequency bands without increasing the size of the device, and can be made smaller compared to antenna devices that can support the same frequency band.

[0038] (Modification) In the antenna device 100a, it was explained that the first antenna is electromagnetically coupled to the radiating element 12a, but the first antenna may be electromagnetically coupled to the radiating element 12b. Figure 7 is a circuit diagram of the antenna device 100b in a modified example of Embodiment 2. In the antenna device 100b shown in Figure 7, the same reference numerals are used for components that are the same as those in the antenna device 100 shown in Figure 1, and detailed explanations are not repeated.

[0039] In the antenna device 100b, a filter circuit 20 is provided in the middle of the second radiating element 12, which functions as a monopole antenna. The filter circuit 20 forms a parallel resonant circuit by magnetically coupling the first coil L1 and the second coil L2. Therefore, as shown in Figure 7, the second radiating element 12 has a fundamental wave F3 whose length is one-quarter of the wavelength (λ / 4) of the length of the radiating element 12a + radiating element 12b.

[0040] However, the radiating element 12b that electromagnetically couples with the first antenna has one open end and the other end connected to the filter circuit 20. Therefore, the radiating element 12b can be considered to have open ends at both ends, and has a wavelength F5 due to double resonance where the length of the radiating element 12b is half a wavelength (λ / 2). In other words, the second radiating element 12 functions as an antenna with two resonant frequencies by providing the filter circuit 20 in the middle.

[0041] Although it was explained that in the antenna device 100 shown in Figure 1, the first antenna is electromagnetically coupled to the radiating element 12a, the first antenna may be electromagnetically coupled to the radiating element 12b, similar to the antenna device 100b shown in Figure 7.

[0042] [Other Modification Examples] In the above-described embodiments, the filter circuit 20 has been described as having the circuit configuration shown in FIG. 2. However, the circuit configuration of the filter circuit 20 is not limited to the circuit configuration shown in FIG. 2. FIG. 8 is a diagram for explaining a modification example of the filter circuit. The filter circuit 20a shown in FIG. 8 includes a first path 21 having a series resonance circuit in which a first coil L1 (first inductance element) and a capacitor C1 (capacitor element) are connected in series, and a second path 22 provided in parallel with the first path 21. Further, the filter circuit 20a has a second coil L2 (second inductance element) in the second path 22. Therefore, the filter circuit 20a does not have an inductance element in the third path 23 connected in series to the first path 21 and the second path 22.

[0043] In the filter circuit 20a, the first coil L1 and the second coil L2 are magnetically coupled, so that a positive mutual inductance +M is generated in the first coil L1 and the second coil L2, and a negative mutual inductance -M is generated in the third path 23. Therefore, the filter circuit 20a functions as a parallel resonance circuit as shown in the equivalent circuit of FIG. 8.

[0044] The filter circuit 20a can be used in place of the filter circuit 20 of the antenna device 100 in Embodiment 1 and the antenna devices 100a and 100b in Embodiment 2, and the same effects can be obtained.

[0045] Further, the first antenna including the first radiating element 11 is not limited to the monopole antenna shown in FIG. 1 or the like, and may be a loop antenna or an inverted-F antenna as long as it is a feeding antenna.

[0046] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above embodiments but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0047] 11 First radiating element, 12 Second radiating element, 12a, 12b Radiating elements, 20, 20a Filter circuit, 21 First path, 22 Second path, 23 Third path, 30 Power supply circuit, 40 Circuit board, 100, 100a, 100b Antenna device, 200 Electronic equipment.

Claims

1. An antenna device comprising: a first radiating element to which a power supply circuit is connected; a second radiating element having at least one open end; and a filter circuit provided in the middle of the second radiating element, wherein the first radiating element and the second radiating element are electromagnetically coupled, and the filter circuit includes a plurality of inductance elements, with at least two inductance elements being magnetically coupled to form a parallel resonant circuit.

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 capacitor 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 capacitor 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 second radiating element has open ends at both ends.

6. The antenna device according to any one of claims 1 to 4, wherein the second radiating element has one end open and the other end grounded to a ground electrode.

7. The antenna device according to any one of claims 1 to 6, wherein the frequency due to the double resonance of the second radiating element is included in the attenuation band of the filter circuit.

8. An electronic device comprising the antenna device according to any one of claims 1 to 7, and a power supply circuit for supplying current to the first radiating element.

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