Antenna device and communication terminal device
By introducing a parallel resonant circuit into the antenna device, and utilizing the parallel resonant circuit composed of a second coil and a capacitor, the problem of current flow to unconnected radiating elements is solved, and wide bandwidth and multi-band support are achieved without degrading antenna characteristics.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- MURATA MFG CO LTD
- Filing Date
- 2024-10-07
- Publication Date
- 2026-06-19
Smart Images
Figure CN122249954A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the technology of an antenna device and a communication terminal device. Background Technology
[0002] In recent years, in communication terminal devices, antenna devices with two radiating elements that are directly or indirectly coupled have been used to increase the frequency band or to support multiple frequency bands. Specifically, Japanese Patent No. 6760545 (Patent Document 1) discloses an antenna device in which two radiating elements are used as transformer elements and the magnetic fields of the two radiating elements are coupled.
[0003] Existing technical documents
[0004] Patent documents
[0005] Patent Document 1: Japanese Patent No. 6760545 Summary of the Invention
[0006] The problem the invention aims to solve
[0007] In the antenna device shown in Patent Document 1, a transformer element is used to magnetically couple a first radiating element connected to the feed circuit with a second radiating element not connected to the feed circuit. However, in the antenna device shown in Patent Document 1, the current from the feed circuit flows not only to the first radiating element but sometimes also into the second radiating element via a ground electrode (grounding substrate). When current from the feed circuit flows into the second radiating element, the antenna characteristics (e.g., radiation efficiency) may be reduced.
[0008] This disclosure was made to solve such problems, and its purpose is to provide an antenna device and communication terminal device that can widen the frequency band or support multiple frequency bands without degrading antenna characteristics.
[0009] Solution for solving the problem
[0010] The antenna device according to this disclosure includes: a first radiating element connected to a feed circuit; a second radiating element; a first coil connected to the first radiating element; a second coil connected between the second radiating element and a ground electrode, and electromagnetically coupled to the first coil; and a capacitor circuit connected in parallel with the second coil, forming a parallel resonant circuit. The resonant frequency of the parallel resonant circuit is a frequency within the frequency band of the fundamental resonance or harmonic resonance of the first radiating element.
[0011] The communication terminal device according to this disclosure includes the antenna device and the power supply circuit described above.
[0012] The effects of the invention
[0013] In the antenna device based on this disclosure, a capacitor circuit is provided that forms a parallel resonant circuit with the second coil. The resonant frequency of the parallel resonant circuit is a frequency within the frequency band of the fundamental resonance or harmonic resonance of the first radiating element, thereby enabling the bandwidth to be widened or supporting multiple frequency bands without degrading the antenna characteristics. Attached Figure Description
[0014] Figure 1 This is a circuit diagram of the antenna device in Implementation Method 1.
[0015] Figure 2 This is a schematic diagram showing the communication terminal device in Embodiment 1.
[0016] Figure 3 This is a graph showing the frequency characteristics of the radiation efficiency of the antenna device in Embodiment 1.
[0017] Figure 4 This is a diagram used to illustrate the relationship between the polarity of transformer elements and the resonant frequency of an antenna device.
[0018] Figure 5 This is a diagram used to illustrate the relationship between the polarity of transformer elements and the resonant frequency of an antenna device.
[0019] Figure 6 This is a schematic diagram of the antenna device in Variation Example 1.
[0020] Figure 7 This is a schematic diagram of the antenna device in Variation Example 2.
[0021] Figure 8 This is a schematic diagram of the antenna device in Variation Example 3.
[0022] Figure 9 This is a schematic diagram of the antenna device in Variation Example 4.
[0023] Figure 10 This is a schematic diagram of the antenna device in Variation 5.
[0024] Figure 11 This is a circuit diagram of the antenna device in Implementation Method 2.
[0025] Figure 12 This is a circuit diagram of the antenna device in Implementation Method 3.
[0026] Figure 13 This is a circuit diagram of another antenna device in Implementation Method 3. Detailed Implementation
[0027] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings. Furthermore, the same or equivalent parts in the drawings will be labeled with the same reference numerals, and their descriptions will not be repeated.
[0028] [Implementation Method 1]
[0029] Figure 1 This is a circuit diagram of the antenna device 100 in Embodiment 1. The antenna device 100 includes a first antenna and a second antenna. The first antenna includes a first radiating element 11 and a first coil L1, wherein the first radiating element 11 is connected to a feed circuit 30, and the first coil L1 and the feed circuit 30 are connected in series between the first radiating element 11 and the ground electrode.
[0030] The second antenna includes a second radiating element 12, a second coil L2 connected in series with the second radiating element 12, and a capacitor C2 (capacitor circuit) connected in parallel with the second coil L2. The second coil L2 and the capacitor C2 constitute a parallel resonant circuit 25. Additionally, the first coil L1 and the second coil L2 are magnetically coupled. In the antenna device 100, the first antenna functions as a fed antenna powered by the feed circuit 30, and the second antenna functions as an unfed antenna not powered by the feed circuit 30.
[0031] The first coil L1 and the second coil L2 are mounted in the antenna device 100 as transformer elements 20, for example. The transformer element 20 is, for example, a cuboid-shaped chip component. The transformer element 20 is constructed by forming conductor patterns of a portion of the first coil L1 and the second coil L2 on each insulating substrate (e.g., liquid crystal polymer, low-temperature co-fired ceramic, etc.) and then stacking the respective insulating substrates. Furthermore, the transformer element 20 can be configured as a component different from the capacitor C2 that forms a parallel resonant circuit 25 with the second coil L2, or it can be configured as a single component including the capacitor C2.
[0032] In antenna devices installed in portable terminals such as smartphones, transformer elements are used to combine fed and unfed antennas to broaden the frequency band or support multiple frequency bands. In other words, the antenna device constitutes a multi-band communication antenna coupled by a transformer. However, in antenna devices where the first and second radiating elements are coupled via a transformer element, current from the feed circuit sometimes flows directly into the second radiating element via a ground electrode. If current from the feed circuit flows directly into the second radiating element, there is a concern that the current flowing to the first radiating element decreases, thereby reducing antenna characteristics (e.g., radiation efficiency).
[0033] Therefore, in the antenna device 100 according to this embodiment, capacitor C2 is connected in parallel with the second coil L2, thereby forming a parallel resonant circuit 25 by the second coil L2 and capacitor C2. This parallel resonant circuit 25 is configured with a resonant frequency within the frequency band of the fundamental or harmonic resonance of the first radiating element 11. By setting the parallel resonant frequency of the second coil L2 and capacitor C2 to a frequency within the frequency band of the fundamental or harmonic resonance of the first radiating element 11, the current at that frequency is blocked by the parallel resonant circuit 25, thereby suppressing the current flowing from the feed circuit 30 to the second radiating element 12, and allowing the current from the feed circuit 30 to flow efficiently to the first radiating element 11.
[0034] Specifically, the case where the antenna device 100 is installed on the communication terminal device will be described. Figure 2 This is a schematic diagram showing the communication terminal device 1000 in Embodiment 1. Figure 2 The communication terminal device 1000 shown is capable of communication, for example, in a frequency band including approximately 1.0 GHz and a frequency band including approximately 2.2 GHz. The communication terminal device 1000 is, for example, a smartphone, with a substrate 10 on which an antenna device 100 is mounted on a portion of the casing.
[0035] A first radiating element 11, a second radiating element 12, a transformer element 20, and a feed circuit 30 constituting an antenna device 100 are mounted on the substrate 10. For example... Figure 1 As shown, the first radiating element 11 and the second radiating element 12 are magnetically coupled through the transformer element 20. One end of the first radiating element 11 is connected to the ground electrode GND through the transformer element 20 and the power supply circuit 30. One end of the second radiating element 12 is connected to the ground electrode GND through the transformer element 20.
[0036] Transformer element 20, such as Figure 1 As shown, the parallel resonant circuit 25 is included, thus suppressing the current flowing from the feed circuit 30 to the second radiating element 12, thereby allowing the current from the feed circuit 30 to flow efficiently to the first radiating element 11. Therefore, the antenna device 100 can widen the frequency band or support multiple frequency bands without degrading the antenna characteristics.
[0037] Figure 3 This is a graph showing the frequency characteristics of the radiation efficiency of the antenna device 100 in Embodiment 1. Figure 3 In the diagram, the horizontal axis represents frequency, and the vertical axis represents radiation efficiency. Figure 3 The frequency characteristics of the radiation efficiency shown are in Figure 2The results were obtained by simulating the structure of the antenna device 100 shown. Specifically, the antenna device 100 was simulated with a first coil L1 = 1nH, a second coil L2 = 5nH, a coupling coefficient k = -0.5, and a capacitor C2 = 1.5pF. Furthermore, for the first antenna, the simulation was performed with an inductor (17nH) and a capacitor (2pF) connected in series with the first radiating element 11 independently of the first coil L1.
[0038] Figure 3 The solid curve A represents the frequency response of the radiation efficiency of the antenna device 100, while the dashed curve B represents the frequency response of the radiation efficiency of the antenna device without the capacitor C2. Regarding curve B, the radiation efficiency in the approximately 2.4 GHz band decreases due to the influence of the current flowing from the feed circuit 30 to the second radiating element 12. On the other hand, regarding curve A, since the current flowing from the feed circuit 30 to the second radiating element 12 is suppressed by the parallel resonant circuit 25, the radiation efficiency in the approximately 2.4 GHz band does not decrease.
[0039] This is because, Figure 3 The fundamental resonant frequency of the first radiating element 11 shown is approximately 0.8 GHz, and the resonant frequency of the parallel resonant circuit 25 of the antenna device 100 is adjusted to approximately 2.4 GHz, which is the frequency of the third harmonic resonance of the first radiating element 11. By adjusting the resonant frequency of the parallel resonant circuit 25, which consists of the second coil L2 and the capacitor C2, to a frequency within the frequency band of the third harmonic resonance of the first radiating element 11, the radiation efficiency of the antenna device 100 will not be as... Figure 3 That way, even with a reduction in the frequency band of approximately 2.4 GHz, high radiation efficiency can be maintained.
[0040] Figure 3 The fundamental resonant frequency of the second radiating element 12 shown is adjusted to a frequency within the fundamental resonant frequency band of the first radiating element 11. Therefore, in Figure 3 As shown in curve A, the radiation efficiency increases in the band containing approximately 0.8 GHz. Furthermore, adjusting the fundamental resonant frequency of the second radiating element 12 to a frequency within the fundamental resonant frequency band of the first radiating element 11 is one example; different frequencies can also be used. Additionally, the resonant frequency of the parallel resonant circuit 25 is not limited to a frequency within the third harmonic resonant frequency band of the first radiating element 11; it can also be a frequency within the frequency bands of other harmonic resonants or the fundamental resonant frequency band.
[0041] In antenna device 100, to address the insufficient bandwidth of the first antenna, a second antenna is prepared, and the two antennas are coupled through transformer element 20 to achieve broadband operation. In actual use of antenna device 100, such as... Figure 2As shown, the area used to form the radiating elements is limited, and the first radiating element 11 and the second radiating element 12 are close to each other. Therefore, it is necessary to design the antenna so that its characteristics are not degraded by interference between the first and second antennas.
[0042] Specifically, in order to avoid interference between the first antenna and the second antenna, the polarity of the transformer element needs to be determined in such a way that the phase of the current flowing in the first coil L1 of the transformer element 20 is not opposite to the phase of the current flowing in the second coil L2. Figure 4 and Figure 5 This is a diagram used to illustrate the relationship between the polarity of transformer elements and the resonant frequency of an antenna device.
[0043] To simplify the explanation, Figure 4 and Figure 5 The antenna device shown does not include capacitor C2. The first radiating element 11 and the second radiating element 12 are coupled through transformer element 20. Furthermore, let the impedance of the first radiating element 11 be Z1, and the current flowing to the first radiating element 11 be I1. Let the voltage of the first coil L1 be V. 1、 The voltage of the power supply circuit 30 is V s Furthermore, let the impedance of the second radiating element 12 be Z2, and the current flowing to the second radiating element 12 be I2. Let the voltage of the second coil L2 be V2. Also, let the mutual inductance between the first coil L1 and the second coil L2 be M. When the polarity of the transformer element is decreasing, the mutual inductance between the first coil L1 and the second coil L2 is set to +M; when the polarity of the transformer element is increasing, the mutual inductance between the first coil L1 and the second coil L2 is set to -M.
[0044] exist Figure 4 and Figure 5 In the antenna device shown, the polarity of the transformer element is subtractive because the conductors of the first coil L1 and the second coil L2 are wound such that the direction of the magnetic flux generated in the first coil L1 when current flows from the first radiating element 11 towards the feed circuit 30 is opposite to the direction of the magnetic flux generated in the second coil L2 when current flows from the second radiating element 12 towards the ground electrode. Conversely, the polarity of the transformer element is additive because the conductors of the first coil L1 and the second coil L2 are wound such that the direction of the magnetic flux generated in the first coil L1 when current flows from the first radiating element 11 towards the feed circuit 30 is the same as the direction of the magnetic flux generated in the second coil L2 when current flows from the second radiating element 12 towards the ground electrode.
[0045] In the case defined as above, according to Equation (1), the relationship between the current I1 of the first radiation element 11 and the current I2 of the second radiation element 12 is determined by the polarity of the transformer element and the impedance of the second coil L2.
[0046] [Number 1]
[0047]
[0048] The impedance Z2 of the second radiation element 12 as a non-fed antenna at the resonant frequency of the first radiation element 11 as a fed antenna has a capacitive property when the resonant frequency f2 of the second radiation element 12 is greater than the resonant frequency f1 of the first radiation element 11 (f1 < f2). Therefore, the impedance Z2 can be expressed as Equation (2). Here, C in Equation (2) is the capacitance component in the equivalent circuit of the second antenna as a non-fed antenna. In addition, the resistance component of this equivalent circuit is ignored.
[0049] [Number 2]
[0050]
[0051] By applying Equation (2) to Equation (1), the relationship between the current I1 of the first radiation element 11 and the current I2 of the second radiation element 12 can be expressed as Equation (3).
[0052] [Number 3]
[0053]
[0054] According to Equation (3), the phase θ of the current I1 of the first radiation element 11 with respect to the current I2 of the second radiation element 12 is 0° in the case of subtractive polarity and 180° in the case of additive polarity as shown in Equation (4). Therefore, when the resonant frequency f2 of the second radiation element 12 is greater than the resonant frequency f1 of the first radiation element 11 (f1 < f2), the antenna device 100 preferably uses a transformer element 20 with subtractive polarity that results in the same phase to avoid interference between the first antenna and the second antenna. In addition, in Figure 4 summarizes and graphically shows the polarity of the transformer element 20 when the resonant frequency f2 of the second radiation element 12 is greater than the resonant frequency f1 of the first radiation element 11 (f1 < f2).
[0055] [Number 4]
[0056]
[0057] On the other hand, the impedance Z2 of the second radiating element 12 at the resonant frequency of the first radiating element 11 is inductive when the resonant frequency f2 of the second radiating element 12 is smaller than the resonant frequency f1 of the first radiating element 11 (f1>f2). Therefore, the impedance Z2 can be expressed as in equation (5). Here, L in equation (5) is the inductive component in the equivalent circuit of the second antenna as an unfed antenna. Furthermore, the resistive component of this equivalent circuit is ignored.
[0058] [Number 5]
[0059]
[0060] By applying equation (5) to equation (1), the relationship between the current I1 of the first radiating element 11 and the current I2 of the second radiating element 12 can be expressed as equation (6).
[0061] [Number 6]
[0062]
[0063] According to equation (6), the phase θ of the current I1 of the first radiating element 11 relative to the current I2 of the second radiating element 12 is 180° in the case of subtractive polarity and 0° in the case of additive polarity, as shown in equation (7). Therefore, when the resonant frequency f2 of the second radiating element 12 is smaller than the resonant frequency f1 of the first radiating element 11 (f1>f2), the antenna device 100 preferably uses an additive polarity transformer element 20 with the same phase to avoid interference between the first antenna and the second antenna. Furthermore, in Figure 5 The diagram illustrates the polarity of transformer element 20 when the resonant frequency f2 of the second radiating element 12 is smaller than the resonant frequency f1 of the first radiating element 11 (f1>f2).
[0064] [Number 7]
[0065]
[0066] In the above, assuming that the first antenna and the second antenna are completely independent, the relationship between the current I1 of the first radiating element 11 and the current I2 of the second radiating element 12 was obtained. However, when the first antenna and the second antenna are not completely independent and there is coupling between the antennas, the relationship between the current I1 of the first radiating element 11 and the current I2 of the second radiating element 12 can be obtained by coinciding the phase relationship derived above with the phase relationship generated by the coupling between the antennas.
[0067] (Modified Example)
[0068] In the above description, the types of the first and second antennas of the antenna device 100 are not particularly limited. Below, a modified example in which the types of the first and second antennas are limited in the antenna device will be described. Furthermore, the limitation on the types of the first and second antennas described below can also be applied to other embodiments.
[0069] Figure 6 This is a schematic diagram of the antenna device 100a in Modified Example 1. Furthermore, for Figure 6 The antenna device 100a shown, and Figure 1 The antenna device 100 shown has the same structure and is labeled with the same reference numerals, so detailed descriptions will not be repeated. In antenna device 100a, the first radiating element 11a constitutes a monopole antenna, and the second radiating element 12a also constitutes a monopole antenna. Antenna device 100a is a basic antenna structure, and by coupling two monopole antennas with wide bandwidths, the bandwidth can be further widened. Furthermore, the resonant frequency of the parallel resonant circuit 25, which consists of the second coil L2 and the capacitor C2, is within the bandwidth of the feed circuit 30 that supplies current to the first radiating element 11a (the fundamental resonant frequency of the first radiating element 11a).
[0070] Figure 7 This is a schematic diagram of the antenna device 100b in Variation Example 2. For Figure 7 The antenna device 100b shown is in the form of... Figure 1 The antenna device 100 shown has the same structure and is labeled with the same reference numerals, so detailed descriptions will not be repeated. In the antenna device 100b, the first radiating element 11b constitutes an inverted-F antenna (IFA), and the second radiating element 12b constitutes a monopole antenna. Since the first radiating element 11b is an inverted-F antenna, the design freedom of the antenna device 100b is increased. In addition, the first radiating element 11b has a path to the ground electrode midway from the end of the feed circuit 30 to the end of the first radiating element 11b, thus suppressing the influence of external factors such as the human body. Furthermore, the resonant frequency of the parallel resonant circuit 25 composed of the second coil L2 and the capacitor C2 is within the frequency band of the feed circuit 30 that supplies current to the first radiating element 11b (the fundamental resonant frequency of the first radiating element 11b).
[0071] Figure 8 This is a schematic diagram of the antenna device 100c in Variation Example 3. For Figure 8 The antenna device 100c shown is in the form of... Figure 1 The antenna device 100c shown has the same structure and is labeled with the same reference numerals, so detailed descriptions will not be repeated. In the antenna device 100c, the first radiating element 11c constitutes an inverted-F antenna, and the second radiating element 12c constitutes a monopole antenna. The first radiating element 11c and... Figure 7 Unlike the first radiating element 11b of the inverted-F antenna shown, the first coil L1 is connected in a path that is not connected to the feed circuit 30. That is, the first coil L1 and the feed circuit 30 are connected in parallel between the first radiating element 11c and the ground electrode. Therefore, the first coil L1 is not present in the path connecting the first radiating element 11c to the feed circuit 30, thus reducing the power loss caused by the first coil L1.
[0072] Since the first radiating element 11c is an inverted-F antenna, the design freedom of the antenna device 100c is increased. Furthermore, the first radiating element 11c has a path to the ground electrode that is independent of the path from the feed circuit 30 to the end of the first radiating element 11c, thus suppressing external influences such as those from the human body. In addition, the resonant frequency of the parallel resonant circuit 25, composed of the second coil L2 and the capacitor C2, is within the frequency band of the feed circuit 30 that supplies current to the first radiating element 11c (the fundamental resonant frequency of the first radiating element 11c).
[0073] Figure 9 This is a schematic diagram of the antenna device 100d in Variation Example 4. For Figure 9 The antenna device 100d shown is in the form of... Figure 1 The antenna device 100 shown has the same structure and is labeled with the same reference numerals, so detailed descriptions will not be repeated. In the antenna device 100d, the first radiating element 11d constitutes a monopole antenna, and the second radiating element 12d constitutes an inverted-F antenna. Since the second radiating element 12d is an inverted-F antenna, the design freedom of the antenna device 100d is increased. In particular, inductors and capacitors are provided in the path from the feed circuit 30 to the ground electrode midway from the end of the first radiating element 11b, thereby allowing adjustment of the phase relationship between the current of the first radiating element 11d and the current of the second radiating element 12d.
[0074] Furthermore, the first radiating element 11d has a path to the ground electrode midway from the end of the feed circuit 30 to the end of the first radiating element 11d, thus suppressing external influences such as those from the human body. In addition, the resonant frequency of the parallel resonant circuit 25, composed of the second coil L2 and the capacitor C2, is within the frequency band of the feed circuit 30 that supplies current to the first radiating element 11d (the fundamental resonant frequency of the first radiating element 11b).
[0075] Figure 10 This is a schematic diagram of the antenna device 100e in Variation Example 5. Furthermore, for Figure 10 The antenna device 100e shown is in the form of... Figure 1The antenna device 100e shown has the same structure and is labeled with the same reference numerals, so detailed descriptions will not be repeated. In the antenna device 100e, the first radiating element 11e constitutes a monopole antenna, and the second radiating element 12e also constitutes a monopole antenna. By setting up a parallel resonant circuit 25 composed of the second coil L2 and the capacitor C2, the antenna device 100e can suppress the influence of the second radiating element 12e on the first radiating element 11e, and can achieve... Figure 10 The second radiating element 12e is thus positioned close to the first radiating element 11e. Furthermore, the resonant frequency of the parallel resonant circuit 25, which consists of the second coil L2 and the capacitor C2, is within the frequency band of the feed circuit 30 that supplies current to the first radiating element 11d (the fundamental resonant frequency of the first radiating element 11d).
[0076] [Implementation Method 2]
[0077] In the above embodiment, the following structure is described: the first radiating element 11 is connected to the ground electrode via the first coil L1 and the feed circuit 30, and the second radiating element 12 is connected to the ground electrode via the second coil L2. However, in order to match the impedance of the first antenna including the first radiating element with the impedance of the second antenna including the second radiating element, a matching circuit may be provided in one or both. Figure 11 This is a circuit diagram of the antenna device 200 in Embodiment 2. Furthermore, for Figure 11 The antenna device 200 shown, and Figure 1 The antenna device 100 shown has the same structure and is labeled with the same reference numerals, so detailed descriptions will not be repeated.
[0078] The antenna device 200 includes a first antenna and a second antenna. The first antenna includes a first radiating element 11 connected to the feed circuit 30, and a first coil L1 and a matching circuit 41 (first matching circuit) connected in series between the first radiating element 11 and the feed circuit 30.
[0079] The second antenna includes: a second radiating element 12, a second coil L2 connected in series with the second radiating element 12 and a matching circuit 42 (second matching circuit), and a capacitor C2 (capacitor circuit) connected in parallel with the second coil L2. The second coil L2 and the capacitor C2 constitute a parallel resonant circuit 25. In addition, the first coil L1 and the second coil L2 are magnetically coupled.
[0080] In the antenna device 200, the first antenna functions as a fed antenna powered by the feeding circuit 30, and the second antenna functions as an unfed antenna not powered by the feeding circuit 30. Furthermore, matching circuits 41 and 42 are used to match the impedance of the first antenna with that of the second antenna. Additionally, the matching circuits 41 and 42 consist of inductors, capacitors, and circuitry including them.
[0081] By matching the impedance of the first antenna to the impedance of the second antenna, the antenna device 200 can optimize the isolation between the first radiating element 11 and the second radiating element 12. Furthermore, the antenna device 200 can appropriately employ the structure described in Embodiment 1.
[0082] [Implementation Method 3]
[0083] In the above embodiment, the electrostatic capacitance of the capacitor C2 connected in parallel with the second coil L2 is described as a fixed value. However, a capacitor circuit that allows the electrostatic capacitance to be variable can be used instead of capacitor C2. Figure 12 This is a circuit diagram of the antenna device 300 in Embodiment 3. Furthermore, for Figure 12 The antenna device 300 shown, and Figure 1 The antenna device 100 shown has the same structure and is labeled with the same reference numerals, so detailed descriptions will not be repeated.
[0084] The antenna device 300 includes a first antenna and a second antenna. The first antenna includes a first radiating element 11 connected to the feed circuit 30, and a first coil L1 connected in series between the first radiating element 11 and the feed circuit 30.
[0085] The second antenna includes: a second radiating element 12, a second coil L2 connected in series with the second radiating element 12, and a variable capacitor element Ca (capacitor circuit) connected in parallel with the second coil L2. The second coil L2 and the variable capacitor element Ca constitute a parallel resonant circuit 25. In addition, the first coil L1 and the second coil L2 are magnetically coupled.
[0086] In antenna device 300, the first antenna functions as a fed antenna powered by feed circuit 30, and the second antenna functions as an unfed antenna not powered by feed circuit 30. The variable capacitor element Ca allows for variable electrostatic capacitance, thus enabling adjustment of the resonant frequency of parallel resonant circuit 25. By adjusting the resonant frequency of parallel resonant circuit 25, antenna device 300 can block current flowing from feed circuit 30 to second radiating element 12 over a wider bandwidth, thereby achieving a wider bandwidth.
[0087] Furthermore, if a control circuit can be provided to adjust the electrostatic capacitance of the variable capacitor element Ca, the resonant frequency of the parallel resonant circuit 25 can be actively adjusted. For example, the antenna device 300 can adjust the electrostatic capacitance of the variable capacitor element Ca in time by the control circuit, thereby adjusting the frequency band that prevents current from flowing to the second radiating element 12.
[0088] A capacitor circuit that can make the electrostatic capacitance variable is not limited to a variable capacitor element Ca; it can also be a capacitor circuit that uses a switching element to switch multiple capacitors with different electrostatic capacitances. Figure 13 This is a circuit diagram of another antenna device 300a in Embodiment 3. Furthermore, for Figure 13 The antenna device 300a shown is in the form of... Figure 1 The antenna device 100 shown has the same structure and is labeled with the same reference numerals, so detailed descriptions will not be repeated.
[0089] Antenna device 300a includes a first antenna and a second antenna. The first antenna includes a first radiating element 11 connected to a feed circuit 30, and a first coil L1 connected in series between the first radiating element 11 and the feed circuit 30.
[0090] The second antenna includes: a second radiating element 12, a second coil L2 connected in series with the second radiating element 12, and a capacitor circuit Cb connected in parallel with the second coil L2. The second coil L2 and the capacitor circuit Cb constitute a parallel resonant circuit 25. In addition, the first coil L1 and the second coil L2 are magnetically coupled.
[0091] In antenna device 300a, the first antenna functions as a fed antenna powered by feed circuit 30, and the second antenna functions as an unfed antenna not powered by feed circuit 30. Capacitor circuit Cb includes multiple capacitors Cb1 with different electrostatic capacitances, and a switching element Cb2 electrically connected to one of the capacitors Cb1. Capacitor circuit Cb can make the electrostatic capacitance variable by switching the capacitor Cb1 electrically connected to switching element Cb2. By making the electrostatic capacitance variable, capacitor circuit Cb can adjust the resonant frequency of parallel resonant circuit 25. By adjusting the resonant frequency of parallel resonant circuit 25, antenna device 300a can block current flowing from feed circuit 30 to second radiating element 12 over a wider bandwidth, thus achieving a wider bandwidth.
[0092] Furthermore, if a control circuit can be provided for adjusting the electrostatic capacitance of the capacitor circuit Cb, the resonant frequency of the parallel resonant circuit 25 can be actively adjusted. For example, the antenna device 300 can adjust the electrostatic capacitance of the capacitor circuit Cb by switching the capacitor Cb1 electrically connected to the switching element Cb2 in time via the control circuit, thereby adjusting the frequency band that prevents current from flowing to the second radiating element 12.
[0093] Furthermore, the antenna devices 300 and 300a can be appropriately adopted using the structures described in Embodiment 1 and Embodiment 2.
[0094] (Way)
[0095] (1) The antenna device involved in this disclosure has the following features:
[0096] The first radiating element is connected to the feed circuit;
[0097] Second radiating element;
[0098] A first coil, which is connected to a first radiating element;
[0099] A second coil, connected between the second radiating element and the ground electrode, and electromagnetically coupled to the first coil; and
[0100] The capacitor circuit is connected in parallel with the second coil, forming a parallel resonant circuit.
[0101] The resonant frequency of the parallel resonant circuit is the frequency within the frequency band of the fundamental or harmonic resonance of the first radiating element.
[0102] (2) In the antenna device described in (1), the resonant frequency of the parallel resonant circuit is the frequency within the frequency band of the third harmonic resonance of the first radiating element.
[0103] (3) In the antenna device described in (1) or (2), the fundamental frequency of the second radiating element is the frequency within the frequency band of the fundamental frequency resonance of the first radiating element.
[0104] (4) In any one of (1) to (3) of the antenna device, the conductors of the first coil and the second coil are wound such that the direction of the magnetic flux generated in the first coil when the current flows from the first radiating element toward the feed circuit is opposite to the direction of the magnetic flux generated in the second coil when the current flows from the second radiating element toward the ground electrode.
[0105] (5) In any one of (1) to (3) of the antenna device, the conductors of the first coil and the second coil are wound such that the direction of the magnetic flux generated in the first coil when the current flows from the first radiating element toward the feed circuit is the same as the direction of the magnetic flux generated in the second coil when the current flows from the second radiating element toward the ground electrode.
[0106] (6) In any one of (1) to (5), the antenna device further comprises a first matching circuit, which is connected between the first coil and the feed circuit.
[0107] (7) In any one of (1) to (6), the antenna device further comprises a second matching circuit, which is connected between the second coil and the ground electrode and is connected in series with the second coil and the capacitor circuit.
[0108] (8) In any of the antenna devices described in (1) to (7), the capacitor circuit is a variable capacitor element.
[0109] (9) In any one of (1) to (7) the antenna device,
[0110] The capacitor circuit includes:
[0111] Multiple capacitors with different electrostatic capacitances; and
[0112] A switching element that is electrically connected to one of a plurality of capacitors.
[0113] (10) In any one of (1) to (9) of the antenna device,
[0114] The first coil and the feed circuit are connected in series between the first radiating element and the ground electrode.
[0115] (11) In any one of (1) to (9) the antenna device,
[0116] The first coil and the feed circuit are connected in parallel between the first radiating element and the ground electrode.
[0117] (12) The communication terminal device involved in this disclosure has the following features:
[0118] The antenna device according to any one of (1) to (11); and the feeding circuit that supplies current to the first radiating element.
[0119] The embodiments disclosed herein should be considered illustrative rather than restrictive in all respects. The scope of the 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.
[0120] Explanation of reference numerals in the attached figures
[0121] 10: Substrate; 11, 11a~11e: First radiating element; 12, 12a~12e: Second radiating element; 20: Transformer element; 30: Feeding circuit; 100, 100a~100e, 200, 300, 300a: Antenna device; 1000: Communication terminal device.
Claims
1. An antenna device comprising: The first radiating element is connected to the feed circuit; Second radiating element; A first coil, which is connected to the first radiating element; The second coil is connected between the second radiating element and the ground electrode, and is electromagnetically coupled to the first coil; as well as A capacitor circuit is connected in parallel with the second coil, forming a parallel resonant circuit with the second coil. The resonant frequency of the parallel resonant circuit is the frequency within the frequency band of the fundamental resonance or harmonic resonance of the first radiating element.
2. The antenna device according to claim 1, wherein, The resonant frequency of the parallel resonant circuit is the frequency within the frequency band of the third harmonic resonance of the first radiating element.
3. The antenna device according to claim 1 or 2, wherein, The fundamental frequency of the second radiating element is the frequency within the fundamental frequency band of the first radiating element.
4. The antenna device according to any one of claims 1 to 3, wherein, The conductors of the first coil and the second coil are wound such that the direction of the magnetic flux generated in the first coil when current flows from the first radiating element toward the feed circuit is opposite to the direction of the magnetic flux generated in the second coil when current flows from the second radiating element toward the ground electrode.
5. The antenna device according to any one of claims 1 to 3, wherein, The conductors of the first coil and the second coil are wound such that the direction of the magnetic flux generated in the first coil when current flows from the first radiating element toward the feed circuit is the same as the direction of the magnetic flux generated in the second coil when current flows from the second radiating element toward the ground electrode.
6. The antenna device according to any one of claims 1 to 5, wherein, It also includes a first matching circuit, which is connected between the first coil and the power supply circuit.
7. The antenna device according to any one of claims 1 to 6, wherein, It also includes a second matching circuit, which is connected between the second coil and the ground electrode, and is connected in series with the second coil and the capacitor circuit.
8. The antenna device according to any one of claims 1 to 7, wherein, The capacitor circuit is a variable capacitor element.
9. The antenna device according to any one of claims 1 to 7, wherein, The capacitor circuit includes: Multiple capacitors with different electrostatic capacitances; and A switching element that is electrically connected to one of the plurality of capacitors.
10. The antenna device according to any one of claims 1 to 9, wherein, The first coil and the feeding circuit are connected in series between the first radiating element and the ground electrode.
11. The antenna device according to any one of claims 1 to 9, wherein, The first coil and the feeding circuit are connected in parallel between the first radiating element and the ground electrode.
12. A communication terminal device, comprising: The antenna device according to any one of claims 1 to 11; and The power supply circuit supplies current to the first radiating element.