Magnetic loop antenna and method for frequency tuning in a magnetic loop antenna

Abstract

This invention provides a magnetic loop antenna that can be operated by adjusting the resonant frequency even in high-frequency bands. [Solution] The substrate 2 is provided with a large annular element 3 on one side and a small annular element 4 on the other side of the substrate 2, a fixed capacitor 6 having a fixed capacitance is provided on the side of the substrate 2 on which the large element 3 is provided, a solder plating layer 5 is formed by applying solder plating to the large element 3, and the resonant frequency is adjusted by the thickness t of the solder plating layer 5.

Description

Technical Field

[0001] The present invention relates to a magnetic loop antenna for wireless communication, and more particularly to a magnetic loop antenna capable of setting a resonance frequency in a high frequency band.

Background Art

[0002] A magnetic loop antenna (miniature loop antenna) is used when performing wireless communication in an environment where it is difficult to secure space for installing an antenna. Various proposals have been made for magnetic loop antennas so far. For example, Patent Document 1 discloses a magnetic field type loop antenna that enables direct power supply and has a high Q.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, a magnetic loop antenna is an antenna using LC resonance, and there is a problem that although it is theoretically possible to manufacture an antenna operating in a high frequency band (1 GHz or higher), it is actually difficult due to limitations in the capacitance of L (inductance) or C (capacitance).

[0005] Also, even if an antenna could be manufactured, it would be difficult to adjust to an arbitrary resonance frequency because L or C becomes a minute capacitance in a high frequency band (1 GHz or higher), and it is difficult to operate at the target frequency.

[0006] Therefore, the present invention has been made in view of the above-mentioned problems, and aims to provide a magnetic loop antenna that can be operated by adjusting the resonant frequency even in the high-frequency band. [Means for solving the problem]

[0007] To solve the above problems, the magnetic loop antenna according to the present invention comprises a large annular element and a small annular element on a substrate, a solder plating layer is formed on the large element by applying solder plating, and the resonant frequency is adjusted by the thickness of the solder plating layer.

[0008] In this case, it is preferable to provide a large element on one side of the substrate and a small element on the other side of the substrate.

[0009] Furthermore, it is preferable to provide a fixed capacitor having a fixed capacitance on the substrate surface on the side where the large element is located.

[0010] Furthermore, the present invention can also be configured as a frequency adjustment method for a magnetic loop antenna. That is, a magnetic loop antenna may be constructed by providing a large annular element and a small annular element on a substrate, forming a solder plating layer on the large element, and adjusting the resonant frequency by changing the thickness of the solder plating layer. [Effects of the Invention]

[0011] According to the magnetic loop antenna of the present invention, large and small loop elements are arranged on a substrate, and solder plating is applied to the larger loop element. The resonant frequency is adjusted by the thickness of the solder plating, thereby realizing a magnetic loop antenna that can operate by adjusting the resonant frequency even in the high frequency range. [Brief explanation of the drawing]

[0012] [Figure 1] This is a front view of a magnetic loop antenna. [Figure 2] This is a rear view of the magnetic loop antenna. [Figure 3] This is a front view showing a magnified view of the antenna portion of a magnetic loop antenna. [Figure 4] This is a side view showing a magnified view of the antenna portion of a magnetic loop antenna. [Figure 5] This graph shows an example of how the resonant frequency changes with respect to the amount of solder plating. [Figure 6] This graph shows an example of the VSWR of an antenna at resonance. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below with reference to the drawings.

[0014] Figure 1 is a front view showing the magnetic loop antenna, and Figure 2 is a rear view.

[0015] The magnetic loop antenna 1 according to this embodiment has a large annular element 3 on one side (front) of the end of a substrate 2 which is a glass cloth-based epoxy resin copper-clad laminate, and a small annular element 4 on the other side (back) of the substrate 2, with a solder plating layer 5 formed on the large element 3. A coaxial connector 10 is soldered to the other end of the substrate 2, and power is supplied to the small element 4 via a grounded coplanar line 11 which is a transmission line.

[0016] Figure 3 is a front view showing an enlarged view of the antenna portion of the magnetic loop antenna, and Figure 4 is a side view showing an enlarged view of the antenna portion of the magnetic loop antenna.

[0017] A large element 3 is provided on one surface of the substrate 2, and a small element 4 is provided on the other surface. Ends of the small element 4 other than the power supply point are connected to the large element 3 using transmission lines, and a dielectric is provided between the large element 3 and the small element 4.

[0018] Both the large element 3 and the small element 4 are made of copper foil. Note that metals other than copper foil may be used if solder plating is possible.

[0019] A solder plating layer 5, which is a layer subjected to solder plating, is laminated on the large element 3. The thickness of the solder plating layer 5 is represented by “t”. The solder plating layer 5 is laminated only on the large element 3, which is the larger loop element, and the small element 4, which is the smaller loop element, remains as copper foil. Note that it is preferable to remove the resist to expose the solder surface on the surface of the large element 3 in order to perform solder plating.

[0020] The fixed capacitor 6 is a capacitor having a constant capacitance. The fixed capacitor 6 is provided on the surface of the substrate 2 on the side where the large element 4 is provided, that is, on the same surface as the large element 3. Since this capacitor forms a resonance circuit with the large element 3, one having an appropriate capacitance (for example, 0.3 pF to 0.4 pF) is selected. Note that the large element 3 and the fixed capacitor 6 form an LC resonance circuit, where the L element corresponds to the large element 3 and the C element corresponds to the fixed capacitor 6. However, since the frequency is higher than the element shape, the large element 3 also has a C element component, and since it has copper foil and solder plating, the large element 3 also has a resistance component.

[0021] Generally, a variable capacitor with high withstand voltage is used for frequency adjustment, and the resonance frequency is adjusted by changing the capacitance C (capacitance) of the capacitor. In a high-frequency band of 1 GHz or higher, since the capacitance of C becomes very small, if one attempts to adjust the resonance frequency in a high-frequency band in a magnetic loop antenna, a variable capacitor with a very small capacitance, small size, and high withstand voltage is required. However, such variable capacitors are rare and contain mechanical elements, so there is a problem that they are prone to failure. Therefore, as the frequency increases, it becomes more difficult to adjust the resonance frequency.

[0022] In contrast, in the magnetic loop antenna 1 of the present embodiment, a fixed capacitor 6 having a fixed capacitance is used, and there is no need to use a variable capacitor. Therefore, it has the advantage of being highly resistant to mechanical failures and enabling high-power transmission because there is no need to consider the withstand voltage of the variable capacitor.

[0023] In the magnetic loop antenna 1, the resonance frequency is adjusted by applying solder plating to the large element 3 of the antenna. By applying solder plating to the large element 3 and adding a conductor to the large element 3, the impedance of the large element 3 changes and the resonance frequency also changes. At this time, if the thickness of the solder plating of the large element 3 is increased, the resonance frequency will increase.

[0024] In this way, the magnetic loop antenna 1 adjusts not by the component of C (capacitance), but by the component of L (inductance) of the large element 3. When the solder plating layer 5 is thickened, L changes (the inductance component decreases), and as a result, the resonance frequency increases. That is, the magnetic loop antenna 1 adjusts the resonance frequency by changing the thickness of the solder plating layer 5 laminated on the large element 3. And by adjusting the amount of solder plating, it can be adjusted to an arbitrary resonance frequency.

[0025] One way to adjust the L component of the element is to change its shape, for example, by cutting off part of the loop or deforming the loop into an ellipse. However, changing the shape of the element has the problem of being irreparable and can disrupt the antenna's radiation pattern.

[0026] In this respect, the magnetic loop antenna 1 allows for repeated modifications because the thickness of the solder plating layer 5 formed on the large element 3 is adjusted, without requiring any changes to the shape of the large element 3. Furthermore, because solder is used, it has the advantage of easily adjusting the amount without the need for machine tools. In addition, it minimizes the impact of frequency changes on the radiation pattern, enabling ideal frequency adjustment.

[0027] Furthermore, in the magnetic loop antenna 1, the substrate 2 is interposed between the large element 3 and the small element 4, so the small element 4 is not affected by the solder on the large element 3. In other words, by separating the large element 3, which has a solder plating layer 5, from the small element 4, which is not solder plated, the structure is such that plating is not applied to unnecessary parts.

[0028] The large element 3 and the small element 4 may be placed on the same surface of the substrate 2. When the large element 3 and the small element 4 are placed on the same surface of the substrate 2, the small element 4 is covered with resist so that it is not affected by the solder applied to the large element 3. When the large element 3 and the small element 4 are provided on the same surface of the substrate 2, one end of the small element 4 must be connected to the large element 3, and the other end must be connected to the coaxial connector 10 via a transmission line that crosses over the large element 3. Such a configuration where the transmission line crosses over the large element 3 can be a cause of degrading the antenna's characteristics. In this respect, if the large element 3 and the small element 4 are placed on opposite sides of the substrate 2, the small element 4 can be connected without the transmission line crossing over the large element 3, thus eliminating the risk of degrading the antenna's characteristics. For this reason, it is preferable to place the large element 3 and the small element 4 on opposite sides of the substrate 2.

[0029] As described above, in the magnetic loop antenna 1, the resonant frequency is adjusted by the thickness of the solder plating layer 5 applied to the large element 3. Specifically, the change in resonant frequency with respect to the amount of solder plating was determined by simulating the antenna model. Figure 5 is a graph showing an example of the change in resonant frequency with respect to the amount of solder plating. As shown in Figure 5, increasing the thickness t of the solder plating layer 5 by 1 mm changes the resonant frequency by approximately 80 MHz. This demonstrates that the resonant frequency can be adjusted even in the high-frequency range by adjusting the thickness of the solder plating layer 5.

[0030] Figure 6 is a graph showing an example of the VSWR of an antenna at resonance. As shown in Figure 6, the magnetic loop antenna 1, which was fabricated for verification, has a VSWR (Voltage Standing Wave Ratio) of approximately 1.05 around the set center frequency (1.3 GHz), which is below 2.0, indicating that it is practical as an antenna and its practicality is well ensured. Furthermore, four prototype magnetic loop antennas 1 were fabricated, and it was verified whether the resonant frequency of all antennas could be adjusted to a predetermined target frequency. The characteristics of all four prototype antennas could be adjusted by solder plating, and the characteristics after adjustment were almost identical. This demonstrates that it is possible to mass-produce antennas with arbitrary resonant frequencies by frequency adjustment using solder plating.

[0031] Although the resonant frequency was set to around 1.3 GHz here, the magnetic loop antenna 1 can also operate at resonant frequencies exceeding this.

[0032] In this embodiment, the magnetic loop antenna is provided with a large loop element on one side of the substrate and a small loop element on the other side. Solder plating is applied to the large loop element, and the resonant frequency is adjusted by the thickness of the solder plating. This makes it possible to obtain a magnetic loop antenna that can operate even in high frequency bands of 1 GHz or higher.

[0033] Furthermore, since solder plating is used for resonant frequency adjustment, the frequency can be repeatedly adjusted, and the resonant frequency can be set by adjusting the amount of solder on the circuit board, thus simplifying the antenna manufacturing process.

[0034] Furthermore, by adjusting the thickness of the antenna's loop element, the resonant frequency is controlled, resulting in minimal change in the radiation pattern in response to frequency changes, thus enabling ideal frequency tuning.

[0035] The magnetic loop antenna according to the present invention has been described above based on embodiments. However, the present invention is not limited thereto, and various design modifications are possible as long as they achieve the objectives of the present invention and do not depart from the gist of the invention, and all of these are also included within the scope of the present invention.

[0036] For example, although the above embodiment was described as a magnetic loop antenna, the present invention can also be configured as a frequency adjustment method in which a magnetic loop antenna is constructed by providing a large annular element on one side of a substrate and a small annular element on the other side of the substrate, forming a solder plating layer by applying solder plating on the large element, and adjusting the resonant frequency by changing the thickness of the solder plating layer. [Industrial applicability]

[0037] The magnetic loop antenna according to the present invention can be used as an antenna for communication equipment that requires a small antenna, and is particularly suitable as a communication antenna in a frequency band with a narrow bandwidth where many other communications are taking place. [Explanation of Symbols]

[0038] 1. Magnetic Loop Antenna 2 circuit boards 3 Major Elements 4 small elements 5. Solder plating layer 6 Fixed Capacitors 10 Coaxial connectors 11 Coplanar track with ground

Claims

1. The substrate comprises a large annular element and a small annular element. A solder plating layer is formed on top of the large element. The resonant frequency is adjusted by the thickness of the solder plating layer. A magnetic loop antenna characterized by the following features.

2. A large element is provided on one side of the substrate. The substrate has small elements on the other side. The magnetic loop antenna according to claim 1, characterized in that it is a magnetic loop antenna as described in claim 1.

3. Furthermore, a fixed capacitor with a fixed capacitance is provided on the substrate surface on the side where the large element is located. A magnetic loop antenna according to claim 1 or 2, characterized in that it is a magnetic loop antenna according to claim 1 or 2.

4. A large annular element and a small annular element are provided on the substrate. A magnetic loop antenna is constructed by applying solder plating to the large element to form a solder plating layer. The resonant frequency is adjusted by changing the thickness of the aforementioned solder plating layer. A method for adjusting the frequency of a magnetic loop antenna, characterized by the following:

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