Magnetic loop antenna and method for adjusting frequency in magnetic loop antenna

Abstract

To provide a magnetic loop antenna capable of adjusting the resonant frequency and operating even in a high frequency band. [Solution] A substrate 2 has a circular large element 3 on one side thereof, a circular small element 4 on the other side thereof, and a fixed capacitor 6 having a fixed capacitance on the side of the substrate 2 on which the large element 3 is provided, and solder plating is applied onto the large element 3 to form a solder plating layer 5, 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 resonant frequency in a high frequency band. [Background technology]

[0002] Magnetic loop antennas (micro loop antennas) are used when performing wireless communication in environments where it is difficult to secure space to install an antenna. Various proposals have been made so far regarding magnetic loop antennas, and for example, Patent Document 1 discloses a magnetic field type loop antenna that can be directly powered and has a high Q. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-72612 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, a magnetic loop antenna is an antenna that uses LC resonance, and due to the constraints of the capacity of L (inductance) or C (capacitance), although it is theoretically possible, it is practically difficult to create an antenna that operates in high frequency bands (above 1 GHz).

[0005] Furthermore, even if it were possible to manufacture an antenna, the capacitance of L or C becomes so small at high frequencies (1 GHz or higher) that it is difficult to adjust the resonant frequency to an arbitrary value, making it difficult to operate at the desired frequency.

[0006] Therefore, the present invention has been made in consideration of the above-mentioned problems, and has an object to provide a magnetic loop antenna whose resonant frequency can be adjusted to operate even in high frequency bands. [Means for solving the problem]

[0007] In order to solve the above problems, the magnetic loop antenna of the present invention is characterized in that it comprises a circular large element and a circular small element on a substrate, solder plating is applied to the large element to form a solder plating layer, and the resonant frequency is adjusted by the thickness of the solder plating layer.

[0008] Here, it is preferable to provide large elements on one surface of the substrate and small elements on the other surface of the substrate.

[0009] Furthermore, it is preferable to provide a fixed capacitor having a fixed capacitance on the surface of the substrate on which the large element is provided.

[0010] The present invention can also be configured as a frequency adjustment method for a magnetic loop antenna, that is, a method for adjusting a frequency in a magnetic loop antenna, comprising providing a circular large element and a circular small element on a substrate, forming a solder plating layer on the large element by solder plating, and adjusting a resonant frequency by changing a thickness of the solder plating layer. Effect of the Invention

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

[0012] [Figure 1] FIG. 2 is a front view of the magnetic loop antenna. [Diagram 2] FIG. 2 is a rear view of the magnetic loop antenna. [Diagram 3] 2 is an enlarged front view showing an antenna portion of the magnetic loop antenna. FIG. [Figure 4] 2 is an enlarged side view showing an antenna portion of the magnetic loop antenna. FIG. [Diagram 5] 11 is a graph showing an example of a change in resonant frequency with respect to the amount of solder plating. [Figure 6] 1 is a graph showing an example of the VSWR of an antenna at resonance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

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

[0015] The magnetic loop antenna 1 according to this embodiment has a circular large element 3 on one side (front) of an end of a substrate 2, which is a glass cloth-based epoxy resin copper-clad laminate, and a circular small 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] FIG. 3 is an enlarged front view of the antenna portion of the magnetic loop antenna, and FIG. 4 is an enlarged side 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. The ends of the small element 4 other than the feed point are connected to the large element 3 using a transmission line, 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. However, metals other than copper foil may be used as long as they can be solder-plated.

[0019] A solder-plated layer 5, which is a layer that has been solder-plated, is laminated on the large element 3. The thickness of the solder-plated layer 5 is represented by "t". The solder-plated 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. In order to apply solder plating to the surface of the large element 3, it is preferable to remove the resist and expose the solder surface.

[0020] The fixed capacitor 6 is a capacitor having a certain capacitance. The fixed capacitor 6 is provided on the surface of the substrate 2 on which the large element 4 is provided, that is, on the same surface as the large element 3. This capacitor is selected to have an appropriate capacitance (for example, 0.3 pF to 0.4 pF) in order to form a resonant circuit with the large element 3. The large element 3 and the fixed capacitor 6 form an LC resonant circuit, with the L element corresponding to the large element 3 and the C element corresponding 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 the large element 3 has copper foil and solder plating, it also has a resistance component.

[0021] Generally, a high-voltage variable capacitor is used to adjust the frequency, and the resonant frequency is adjusted by changing the capacitance (C) of the capacitor. Since the capacitance of C becomes minute in the high-frequency band above 1 GHz, a variable capacitor with a small capacitance, small size, and high voltage resistance is required to adjust the resonant frequency in the high-frequency band in a magnetic loop antenna. However, such variable capacitors are rare and have the problem of being prone to failure because they include mechanical elements. Therefore, the higher the frequency, the more difficult it becomes to adjust the resonant frequency.

[0022] In contrast, the magnetic loop antenna 1 of this embodiment uses a fixed capacitor 6 having a fixed capacitance, and does not need to use a variable capacitor. This has the advantages of being 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 resonant frequency is adjusted by solder plating the large element 3 of the antenna. By solder plating the large element 3 and adding a conductor to the large element 3, the impedance of the large element 3 changes, and so does the resonant frequency. In this case, if the thickness of the solder plating on the large element 3 is increased, the resonant frequency becomes higher.

[0024] In this way, the magnetic loop antenna 1 does not adjust the C (capacitance) component, but adjusts the L (inductance) component of the large element 3, and by making the solder plating layer 5 thicker, L changes (the inductance component decreases), resulting in an increase in the resonant frequency. In other words, the magnetic loop antenna 1 adjusts the resonant frequency by changing the thickness of the solder plating layer 5 laminated on the large element 3. The resonant frequency can be adjusted to any desired value by adjusting the amount of solder plating.

[0025] Here, one possible method for adjusting the L component of the element is to change the shape of the element, for example by cutting off part of the element loop or deforming the loop into an ellipse. However, changing the shape of the element has the problem that it cannot be corrected, and it can cause a disturbance in the antenna radiation pattern.

[0026] In this regard, the magnetic loop antenna 1 can be modified many times without changing the shape of the large element 3 by adjusting the thickness of the solder plating layer 5 formed on the large element 3. In addition, since solder is used, there is an advantage that no machine tool is required and the amount can be easily adjusted. Furthermore, changes in frequency have little effect on changes in the radiation pattern, allowing ideal frequency adjustment.

[0027] In addition, 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 the solder plating layer 5 laminated thereon, from the small element 4, which is not solder plated, a structure is achieved in which unnecessary portions are not plated.

[0028] The large element 3 and the small element 4 may be arranged on the same surface of the substrate 2. When the large element 3 and the small element 4 are arranged on the same surface of the substrate 2, the small element 4 is covered with a resist so that the small element 4 is not affected by the solder applied to the large element 3. When the large element 3 and the small element 4 are arranged on the same surface of the substrate 2, one end of the small element 4 needs to be connected to the large element 3, and the other end needs to be connected to the coaxial connector 10 via a transmission line that straddles the large element 3. If such a transmission line is configured to straddle the large element 3, it may be a factor in degrading the antenna characteristics. In this regard, if the large element 3 and the small element 4 are arranged separately on both sides of the substrate 2, the small element 4 can be connected without the transmission line straddling the large element 3, so there is no risk of degrading the antenna characteristics. Therefore, it can be said that it is preferable to arrange the large element 3 and the small element 4 separately on both 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 the resonant frequency with respect to the amount of solder plating was determined by simulating an antenna model to see how the resonant frequency changes with the amount of solder plating. FIG. 5 is a graph showing an example of the change in the resonant frequency with respect to the amount of solder plating. As shown in FIG. 5, by increasing the value of the thickness t of the solder plating layer 5 by 1 mm, the resonant frequency changes by about 80 MHz. It has been shown 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 VSWR (Voltage Standing Wave Ratio) of the magnetic loop antenna 1 produced for verification is about 1.05 around the set center frequency (1.3 GHz), which is a value of 2.0 or less, which is said to ensure practical use as an antenna, and its practical use is sufficiently ensured. In addition, four magnetic loop antennas 1 were prototyped and verification was carried out to see if the resonant frequency of all antennas could be adjusted to the specified target frequency. It was found that the characteristics of all four prototype antennas could be adjusted by solder plating, and the characteristics after adjustment were almost the same. It can be said that it is possible to mass-produce antennas with any resonant frequency by frequency adjustment by solder plating.

[0031] Although the resonant frequency is set to about 1.3 GHz here, the magnetic loop antenna 1 can also be operated at a resonant frequency exceeding this.

[0032] In this way, in the magnetic loop antenna of this embodiment, a large loop element is provided on one side of the substrate and a small loop element is provided on the other side, and solder plating is applied to the large loop element. The resonant frequency is adjusted by the thickness of the solder plating, thereby obtaining a magnetic loop antenna that can operate in high frequency bands of 1 GHz or more.

[0033] In addition, since solder plating is used to adjust the resonant frequency, the frequency can be repeatedly adjusted, and the resonant frequency can be adjusted by adjusting the amount of solder on the board, which simplifies the antenna manufacturing process.

[0034] Furthermore, since the resonant frequency is adjusted by changing the thickness of the loop element of the antenna, there is little change in the radiation pattern in response to changes in frequency, making it possible to perform ideal frequency adjustment.

[0035] The magnetic loop antenna according to the present invention has been described above based on an embodiment, but the present invention is not limited to this. Various design modifications are possible as long as the object of the present invention can be achieved and the gist of the invention is not deviated from, and all of these are included within the scope of the present invention.

[0036] For example, while the above embodiment has been 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 circular large element on one side of a substrate in the magnetic loop antenna, providing a circular small element on the other side of the substrate, and solder plating is applied to the large element to form a solder plating layer, and the thickness of the solder plating layer is changed to adjust the resonant frequency. [Industrial Applicability]

[0037] The magnetic loop antenna according to the present invention can be used as an antenna for communication devices that require a small antenna, and is particularly suitable as a communication antenna in a narrow frequency band where many other communications are conducted. [Explanation of symbols]

[0038] 1 Magnetic loop antenna 2. Board 3 Major Elements 4. Small Elements 5 Solder plating layer 6 Fixed Capacitors 10 Coaxial Connector 11 Grounded coplanar line

Claims

1. A substrate is provided with a large annular element and a small annular element, Solder plating is applied on the large element to form a solder plating layer, The thickness of the solder plating layer is used to adjust the resonance frequency. The magnetic loop antenna is characterized by the above.

2. A large element is provided on one side of the substrate; The other side of the substrate is provided with small elements.

2. The magnetic loop antenna according to claim 1, wherein the magnetic loop antenna is a magnetic loop antenna.

3. Furthermore, a fixed capacitor having a fixed capacitance is provided on the substrate surface on which the large element is provided.

3. The magnetic loop antenna according to claim 1, wherein the magnetic loop antenna is a magnetic loop antenna.

4. providing a circular large element and a circular small element on a substrate; A solder plating layer is formed on the large element to form a magnetic loop antenna; The thickness of the solder plating layer is changed to adjust the resonance frequency. A method for adjusting a frequency in a magnetic loop antenna, comprising:

Images