JP4770793B2 - Antenna device - Google Patents

Description

  The present invention relates to an antenna device including a minute loop antenna used in a wireless communication device.

  For example, a micro loop antenna as shown in Non-Patent Document 1 has a total length of the loop antenna reduced to about 1/10 or less of the transmission wavelength, and has a feature that is stronger against a noise electric field than a micro dipole antenna. . Therefore, it has been widely used for portable wireless communication devices and the like.

  In an antenna device using a micro loop antenna, in order to achieve matching with the output impedance of the radio circuit at the desired communication frequency, a capacitance is inserted in series at one point on the conductor constituting the micro loop. Another point on the conductor constituting the loop is grounded to the ground of the radio circuit section. By the way, if the loop area of a micro loop antenna is reduced in response to a request for downsizing a portable radio communication device or the like, there is a problem that the antenna gain is remarkably lowered.

Patent Document 1 discloses the use of a capacitor and grounding the minute loop antenna in order to suppress a decrease in antenna gain of the open loop minute loop antenna.
The Institute of Electronics, Information and Communication Engineers “Antenna Engineering Handbook” PP.62-63 Ohmsha 1st edition issued on October 30, 1980 Japanese Patent No. 3735635

  The present invention has been made in order to solve the above-described problems of the conventional example, and even when the loop area of the minute loop antenna is small, an antenna device that can obtain a higher antenna gain than the conventional one. Is to provide.

In order to solve the above problems, the invention of claim 1
A small loop antenna is formed to be substantially perpendicular to the mounting surface of the circuit board, it is formed on the mounting surface of the front SL circuit board, and the ground pattern which functions as a dipole antenna, which is mounted on the circuit board An antenna device including a wireless circuit unit ,
The minute loop antenna is mounted on the circuit board 2 and the first conductor pattern and the second conductor pattern formed on the circuit board, the capacitor inserted between the first conductor pattern and the second conductor pattern. It consists of an approximately U-shaped antenna element,
The feeding point to the minute loop antenna and the ground point of the minute loop antenna are both connected to the first conductor pattern .

The invention of claim 2 is the antenna device according to claim 1,
One end of the capacitor is connected to a ground point of the minute loop antenna.

The invention of claim 3 is the antenna device according to claim 1 or 2,
A feeding position changing means capable of changing a feeding position to the minute loop antenna;
In the test mode, when a test signal is output from the radio circuit unit to the micro loop antenna, the magnitude of the reflected wave generated due to mismatch between the output impedance of the radio circuit unit and the input impedance of the micro loop antenna is measured. Reflected wave measuring means to
In the test mode, the power supply position changing means sets at least two power supply positions, measures the magnitude of the reflected wave at each power supply position, and supplies power so that the magnitude of the reflected wave is minimized. The power supply position determining means for determining the position is further provided.

The invention of claim 4 is the antenna device according to claim 1 or 2,
A grounding position changing means capable of changing the grounding position of the minute loop antenna;
In the test mode, when a test signal is output from the radio circuit unit to the micro loop antenna, the magnitude of the reflected wave generated due to mismatch between the output impedance of the radio circuit unit and the input impedance of the micro loop antenna is measured. Reflected wave measuring means to
In the test mode, the grounding position changing means sets at least two grounding positions, measures the magnitude of the reflected wave at each grounding position, and minimizes the magnitude of the reflected wave. It further comprises a ground contact position determining means for determining the ground contact position.

  According to the invention of claim 1, by destroying the symmetry of the minute loop antenna, the ratio of the dipole mode current flowing in the ground pattern functioning as the dipole antenna to the minute loop mode current flowing in the minute loop antenna is increased. Accordingly, the intensity of the radio wave radiated from the dipole antenna increases. Therefore, even if the loop area of the micro loop antenna is small and the intensity of the radio wave radiated from the micro loop antenna is low, it is supplemented by the radio wave radiated from the dipole antenna, and the antenna gain of the entire antenna device can be increased. . As a result, even if the loop area of the minute loop antenna is reduced, that is, the antenna device is downsized, the antenna gain is not significantly reduced, and the communicable distance of the antenna device can be maintained.

  According to the invention of claim 2, the symmetry of the micro loop antenna can be maximized by connecting one end of the capacitance component to the ground point of the micro loop antenna. As a result, the dipole mode current flowing through the dipole antenna can be maximized, and the antenna gain of the entire antenna device can be maximized.

  According to the invention of claim 3, since the adjustment of the correction capacitance amount that has been manually performed in the shipping inspection process of the antenna device can be automated, the manufacturing cost of the antenna device can be reduced. Further, by periodically executing the test mode in the actual use state, it is possible to periodically correct the deviation of the resonance frequency due to the installation environment, and to reduce the decrease in the antenna gain at the desired transmission frequency.

  According to the invention of claim 4, in the shipping inspection process of the antenna device, it is possible to suppress a variation in input impedance caused by a performance variation, a dimensional error, a mounting position error, etc. of each component constituting the antenna device, and a desired transmission frequency Thus, variation in antenna gain can be suppressed. Further, by periodically executing the test mode in the actual use state, it is possible to periodically correct the deviation of the resonance frequency due to the installation environment, and to reduce the decrease in the antenna gain at the desired transmission frequency.

(First embodiment)
A first embodiment of an antenna device according to the present invention will be described. FIG. 1 shows a basic configuration of an antenna device 1A using a minute loop antenna according to the first embodiment. The antenna device 1A includes a circuit board 2, a first conductor pattern 3 and a second conductor pattern 4 formed on the circuit board 2, and a capacitor (capacitor) inserted between the first conductor pattern 3 and the second conductor pattern 4. ) 5 and a micro loop antenna 11 composed of a substantially U-shaped antenna element 10 mounted on the circuit board 2, a radio circuit section 12 and a control circuit section 13 mounted on the circuit board 2, etc. Has been. On the circuit board 2, a ground pattern 6, a ground line 7 for connecting the first conductor pattern 3 and the ground pattern 6, a feed line 8 for supplying a signal to the minute loop antenna 11, and the like are provided.

When the frequency of the radio communication with the f _0, from the radio circuit portion 12 outputs a signal of frequency f ₀ is small loop antenna 11, as the overall length of one turn loop is 1/10 of the transmission wavelength lambda _0, The width and height are designed, and the impedance is adjusted so that the loss is minimized (the decrease in antenna gain is reduced) at the frequency f ₀ (= 2π / λ ₀ ). Specifically, the resonance frequency of the minute loop antenna 11 is adjusted by appropriately selecting the capacitance of the capacitor 5. Further, assuming that the resonance frequency of the antenna is a desired frequency, the distance X from the connection point P1 between the feeder line 8 and the first conductor pattern 3 to the connection point P2 between the ground line 7 and the first conductor pattern 3 by changing, it is possible to adjust the antenna input impedance S _11.

When a high frequency signal is output from the radio circuit unit 12, a high frequency current is excited in the antenna device 1A. As shown in FIG. 2, this high-frequency current flows along the conductive path constituting the micro loop antenna 11 and contributes to the radiation as the micro loop antenna 11 (micro loop mode current) I _1, and the circuit board 2 It can be considered that the current (dipole mode current) I ₂ flows in the longitudinal direction and contributes to radiation as a dipole antenna in the longitudinal direction of the circuit board 2. The minute loop mode current I ₁ excites a polarized wave (horizontal polarization component) parallel to the minute loop surface in a direction parallel to the rectangle formed by the minute loop antenna 11. On the other hand, the dipole mode current I ₂ excites a polarized wave (vertical polarization component) parallel to the longitudinal direction of the ground pattern 6 in a direction perpendicular to the longitudinal direction of the ground pattern 6.

Conventionally, in an antenna device using a minute loop antenna, attention is paid only to the horizontal polarization component excited by the minute loop mode current I ₁ flowing through the minute loop antenna, and the amplitude of the horizontal polarization component is minimized. impedance adjustment of the loop antenna has been performed, the vertical polarization component which is excited by the dipole mode current I ₂ is ignored, or has been adjusted as much as possible reduced.

In the antenna device 1A according to the first embodiment shown in FIG. 1, the current flows small loop mode current I ₁ and the dipole mode current I ₂ as described above is synthesized, the dipole mode current I ₂ is small loop The ratio increases as the symmetry of the antenna 11 is lost. Therefore, one end of the capacitor 5 is connected to the connection point P <b> 2 between the first conductor pattern 3 and the ground line 7.

  Next, specific dimensions are set as shown in FIG. 3 for the antenna device 1A shown in FIG. 1, and numerical calculation of the radiation pattern of the yz plane (plane including the loop plane) is performed by the finite element method. . FIG. 4 is a graph showing a radiation pattern on the yz plane calculated by the finite element method.

The antenna element 10 is made of copper (conductivity 5.8 × 10 ⁷ Simens / m) having a height of 10 mm, a width of 23 mm, and a cross section of 1 mm × 1 mm. The circuit board 2 has a longitudinal direction of 120 mm, a width of 25 mm, a thickness of 0.8 mm, and a material of FR-4 (relative dielectric constant 4.4, dielectric loss tangent 0.02). The ground pattern 6 is a copper foil pattern on the circuit board 2 and has a longitudinal direction of 113 mm and a width of 23 mm. The power supply line 8, the ground line 7, the first conductor pattern 3, and the second conductor pattern 4 are copper foil patterns on the circuit board 2, similarly to the ground pattern 6. The distance from the connection point P1 between the feeder 8 and the first conductor pattern 3 to the connection point P2 between the ground line 7 and the first conductor pattern 3 is 2.5 mm. The capacitance of the capacitor 5 is 4.0 pF.

As can be seen from FIG. 4, the horizontal polarization component parallel to the loop surface and the vertical polarization component perpendicular to the loop surface are both almost omnidirectional, and the average gain of the horizontal polarization component is −15.7 dBi. The average gain of the vertical polarization component is -8.2 dBi. As described above, the horizontal polarization component is a radio wave excited by the minute loop mode current I ₁ , and the gain of the horizontal polarization component is the gain of the minute loop antenna 11 of the antenna device 1A. In contrast, the vertically polarized wave component is a current excited by the dipole mode current I _2, the gain of the vertically polarized wave component is gain achieved by the effect of the present invention.

FIG. 5 is a flowchart for designing the antenna device 1A. By designing according to this flowchart, it is possible to design the antenna device having a size different from that shown in FIG. 3 so that the dipole mode current I ₂ is maximized.

First, the position and dimensions of each part such as the circuit board 2, the ground pattern 6, and the antenna element 10 are determined, and the position of the feeder 8 is determined (# 1). Next, the position of the ground line 7 is provisionally determined, and the capacitor 5 is arranged so that the connection point P2 between the ground line 7 and the first conductor pattern 3 and one end of the capacitor 5 coincide (# 2). Next, the capacitance of the capacitor 5 is provisionally determined (# 3). In this way, the input impedance of the antenna apparatus 1A temporarily assembled is measured (# 4). Then, the measured input impedance value is plotted on the Smith chart, and it is determined whether or not the impedance locus passes through the center of the Smith chart (# 5). When the impedance locus does not pass through the center of the Smith chart (NO in # 5), the position of the ground line 7 and the position of the capacitor 5 are changed (# 6), and the above steps are repeated. When the impedance trajectory passes through the center of the Smith chart (YES in # 5), next, the desired transmission frequency is the resonance frequency of the antenna of the antenna device 1A (the minute loop antenna 11 and the ground pattern 6 functioning as the dipole antenna). determines whether or not coincident with the f ₀ (# 7). When the resonance frequency of the small loop antenna 11 is not matched to the transmission frequency f ₀ to a desired, change the capacitance of the capacitor 5 (# 8), and repeats the above steps. According to the antenna device 1A according to the first embodiment configured as described above, since the dipole mode current is configured to be the maximum, even when the loop area of the minute loop antenna is small, A high antenna gain can be obtained compared to the conventional one.

  In FIG. 1, the ground line 7 is disposed between the power supply line 8 and the capacitor 5. However, the positions of the power supply line 8 and the ground line 7 are switched, and the power supply line 8 is disposed between the ground line 7 and the capacitor 5. May be. A trimmer capacitor may be inserted in parallel with the capacitor 5. In that case, a shift in resonance frequency caused by variations in component performance, component dimensional errors, mounting position errors, and the like can be corrected by adjusting the capacitance of the trimmer capacitor.

(Second Embodiment)
A second embodiment of the antenna device of the present invention will be described. FIG. 6 shows a schematic configuration of an antenna device 1B according to the second embodiment. In the antenna device 1B according to the second embodiment, the variable capacitor 14 is connected in parallel to the capacitor 5 inserted in series in the loop of the minute loop antenna 11, and the temperature sensor 15 is mounted on the circuit board 2. is there.

  In advance, a data table of the correction capacitance amount corresponding to the ambient temperature is stored in the memory of the control circuit unit 13 based on the temperature characteristics of the capacitor 5, and the data table according to the temperature measurement value by the temperature sensor 15. The amount of correction capacitance of the variable capacitor 14 is controlled with reference to FIG. According to such a configuration, the change in the resonance frequency of the antenna device 1B can be reduced regardless of the change in the ambient temperature, and the decrease in the antenna gain can be further reduced at the desired transmission frequency.

(Third embodiment)
A third embodiment of the antenna device of the present invention will be described. FIG. 7 shows a schematic configuration of an antenna apparatus 1C according to the third embodiment. In the antenna device 1C according to the third embodiment, the variable capacitor 14 is connected in parallel to the capacitor 5 inserted in series in the loop of the minute loop antenna 11, and the reflected wave of the signal output from the radio circuit unit 12 is A detection circuit 16 for measuring the size is provided.

  In the shipping inspection process of the antenna device, the control circuit unit 13 is set to the test mode, and the test signal is output from the radio circuit unit 12 in a state where the correction capacitance amount of the variable capacitor 14 is set to a predetermined value. At this time, a reflected wave is generated due to the matching state of the output impedance of the radio circuit unit 12 and the input impedance of the minute loop antenna 11. The magnitude of this reflected wave is measured by the detection circuit 16 in the radio circuit unit 12. Next, the correction capacitance amount of the variable capacitor 14 is set to another value by the control signal from the control circuit unit 13, and the magnitude of the reflected wave is similarly measured. In this way, the magnitude of the reflected wave is measured for each of the plurality of corrected capacitance amounts, and the corrected capacitance amount with the smallest reflected wave is obtained.

  According to such a configuration, in the shipping inspection process of the antenna device, the adjustment of the correction capacitance amount that has been performed manually in the past can be automated, so that the manufacturing cost of the antenna device can be reduced. Further, by periodically executing the test mode in the actual use state, it is possible to periodically correct the deviation of the resonance frequency due to the installation environment, and to reduce the decrease in the antenna gain at the desired transmission frequency. In the test mode, since it is necessary to output a test signal from the wireless circuit unit 12, it is not possible to execute the originally performed communication and the test mode simultaneously. In a wireless device that performs intermittent communication, there is a time during which communication is not performed immediately after one communication sequence is completed. By executing the test mode using the time during which this communication is not performed, the test mode can be surely executed without hindering the communication that should be performed.

(Fourth embodiment)
A fourth embodiment of the antenna device of the present invention will be described. FIG. 8 shows a schematic configuration of an antenna device 1D according to the fourth embodiment. In the antenna device 1D according to the fourth embodiment, the detection circuit 16 that measures the magnitude of the reflected wave of the signal output from the wireless circuit unit 12, and the path of the feed line 8 are switched to feed the feed line 8 and the first conductor pattern. 3 is provided with a change-over switch 17 that can change the position of the connection point P1 with the switch 3.

  In the antenna device shipment inspection process, the control circuit unit 13 is set to the test mode, and the wireless circuit unit is set in a state where the connection point P1 between the feeder 8 and the first conductor pattern 3 is set to a predetermined position by the changeover switch 17 12 outputs a test signal. At this time, a reflected wave is generated due to the matching state of the output impedance of the radio circuit unit 12 and the input impedance of the minute loop antenna 11. The magnitude of this reflected wave is measured by the detection circuit 16 in the radio circuit unit 12. Next, the changeover switch 17 is switched by a control signal from the control circuit unit 13, and the magnitude of the reflected wave is similarly measured. In this way, a plurality of paths of the feeder line 8 are set, the magnitude of the reflected wave with respect to each path is measured, and the path with the smallest reflected wave is obtained. The changeover switch 17 may be one that mechanically switches the path, or may be one that electrically switches the path, such as a diode switch.

  According to such a configuration, in the shipping inspection process of the antenna device, it is possible to suppress variations in input impedance due to performance variations, dimensional errors, mounting position errors, etc. of each component constituting the antenna device, and at a desired transmission frequency. Variations in antenna gain can be suppressed. Further, by periodically executing the test mode in the actual use state, it is possible to periodically correct the deviation of the resonance frequency due to the installation environment, and to reduce the decrease in the antenna gain at the desired transmission frequency. In the test mode, since it is necessary to output a test signal from the radio circuit unit 12, it is not possible to execute the originally performed communication and the test mode at the same time. In a wireless device that performs intermittent communication, there is a time during which communication is not performed immediately after one communication sequence is completed. By executing the test mode using the time during which this communication is not performed, the test mode can be surely executed without hindering the communication that should be performed.

(Fifth embodiment)
A fifth embodiment of the antenna device of the present invention will be described. FIG. 9 shows a schematic configuration of an antenna apparatus 1E according to the fifth embodiment. In the antenna device 1E according to the fifth embodiment, the detection circuit 16 that measures the magnitude of the reflected wave of the signal output from the radio circuit unit 12, and the ground line 7 and the first conductor pattern by switching the path of the ground line 7 are switched. 3 is provided with a changeover switch 18 that can change the position of the connection point P2 with the switch 3.

  In the shipping inspection process of the antenna device, the control circuit unit 13 is set to the test mode, and the connection point P2 between the ground line 7 and the first conductor pattern 3 is set to a predetermined position by the changeover switch 18, and the radio circuit unit 12 outputs a test signal. At this time, a reflected wave is generated due to the matching state of the output impedance of the radio circuit unit 12 and the input impedance of the minute loop antenna 11. The magnitude of this reflected wave is measured by the detection circuit 16 in the radio circuit unit 12. Next, the changeover switch 18 is switched by a control signal from the control circuit unit 13, and the magnitude of the reflected wave is similarly measured. In this way, a plurality of paths of the ground line 7 are set, the magnitude of the reflected wave with respect to each path is measured, and the path with the smallest reflected wave is obtained. The changeover switch 18 may be one that mechanically switches the path, or may be one that electrically switches the path, such as a diode switch.

  According to such a configuration, in the shipping inspection process of the antenna device, it is possible to suppress variations in input impedance due to performance variations, dimensional errors, mounting position errors, etc. of each component constituting the antenna device, and at a desired transmission frequency. Variations in antenna gain can be suppressed. Further, by periodically executing the test mode in the actual use state, it is possible to periodically correct the deviation of the resonance frequency due to the installation environment, and to reduce the decrease in the antenna gain at the desired transmission frequency. In the test mode, since it is necessary to output a test signal from the radio circuit unit 12, it is not possible to execute the originally performed communication and the test mode at the same time. In a wireless device that performs intermittent communication, there is a time during which communication is not performed immediately after one communication sequence is completed. By executing the test mode using the time during which this communication is not performed, the test mode can be surely executed without hindering the communication that should be performed.

The perspective view which shows the structure of 1st Embodiment of the antenna device which concerns on this invention. The perspective view which shows the direction of the minute loop mode electric current and dipole mode electric current in the antenna device which concerns on this invention, and the relationship between the horizontal deflection | deviation component by these antennas, and a vertical deflection | deviation component. The perspective view which shows the example of the concrete design dimension in 1st Embodiment. The graph which shows the radiation pattern on yz surface calculated by the finite element method. The flowchart for designing the antenna apparatus in 1st Embodiment. The perspective view which shows the structure of 2nd Embodiment of the antenna apparatus which concerns on this invention. The perspective view which shows the structure of 3rd Embodiment of the antenna apparatus which concerns on this invention. The perspective view which shows the structure of 4th Embodiment of the antenna apparatus which concerns on this invention. The perspective view which shows the structure of 5th Embodiment of the antenna apparatus which concerns on this invention.

Explanation of symbols

1A, 1B, 1C, 1D, 1E Antenna device 2 Circuit board 3 First conductor pattern 4 Second conductor pattern 5 Capacitor 6 Ground pattern 7 Ground line 8 Feed line 10 Antenna element 11 Micro loop antenna 12 Radio circuit unit 13 Control circuit unit (Power supply position determining means, grounding position determining means)
14 variable capacitor 15 temperature sensor 16 detection circuit (reflected wave measuring means)
17 changeover switch (power supply position change means)
18 changeover switch (grounding position changing means)
Connection point (feeding point) between the P1 feeding line 8 and the first conductor pattern 3
Connection point (grounding point) between P2 grounding wire 7 and first conductor pattern 3
X Distance from connection point P1 to connection point P1 I ₁ Small loop mode current I ₂ Dipole mode current S ₁₁ Antenna input impedance f ₀ Transmission frequency

Claims (4)

A small loop antenna is formed to be substantially perpendicular to the mounting surface of the circuit board, it is formed on the mounting surface of the front SL circuit board, and the ground pattern which functions as a dipole antenna, which is mounted on the circuit board An antenna device including a wireless circuit unit ,
The minute loop antenna is mounted on the circuit board 2 and the first conductor pattern and the second conductor pattern formed on the circuit board, the capacitor inserted between the first conductor pattern and the second conductor pattern. It consists of an approximately U-shaped antenna element,
An antenna device, wherein a feeding point to the minute loop antenna and a grounding point of the minute loop antenna are both connected to the first conductor pattern . The antenna device according to claim 1, wherein one end of the capacitor is connected to a ground point of the minute loop antenna. A feeding position changing means capable of changing a feeding position to the minute loop antenna;
In the test mode, when a test signal is output from the radio circuit unit to the micro loop antenna, the magnitude of the reflected wave generated due to mismatch between the output impedance of the radio circuit unit and the input impedance of the micro loop antenna is measured. Reflected wave measuring means to
In the test mode, the power supply position changing means sets at least two power supply positions, measures the magnitude of the reflected wave at each power supply position, and supplies power so that the magnitude of the reflected wave is minimized. The antenna apparatus according to claim 1, further comprising a feeding position determining unit that determines a position. A grounding position changing means capable of changing the grounding position of the minute loop antenna;
In the test mode, when a test signal is output from the radio circuit unit to the micro loop antenna, the magnitude of the reflected wave generated due to mismatch between the output impedance of the radio circuit unit and the input impedance of the micro loop antenna is measured. Reflected wave measuring means to
In the test mode, the grounding position changing means sets at least two grounding positions, measures the magnitude of the reflected wave at each grounding position, and minimizes the magnitude of the reflected wave. The antenna apparatus according to claim 1, further comprising a grounding position determining unit that determines a grounding position.

Images