JP6080928B1 - Antenna device - Google Patents

Abstract

In a portable device antenna device such as a remote keyless entry system, a minute loop antenna is used. However, a radiated radio wave is weak and needs to be improved. When a holding unit of a device in which an antenna device is incorporated and a feeding circuit of the antenna device are arranged close to each other and a user holds the device, the human body is coupled in a high frequency and effectively dipole mode current The radiated radio wave of the antenna was reinforced. [Selection] Figure 2

Description

  The present invention relates to an antenna device suitable for use as a transmission antenna mounted on a portable device that transmits a lock / unlock signal such as a remote keyless entry system for a vehicle.

  The remote keyless entry system performs radio communication by radio waves between a portable device possessed by a user and an in-vehicle device mounted on the vehicle. In a typical one-way communication system, the portable device includes a vehicle. An antenna device that emits a radio wave that instructs to lock or unlock the door is provided, and when the user operates the portable device, a radio wave that instructs to lock or unlock the door of the vehicle is radiated from the portable device. The antenna device of the vehicle-mounted device receives the radiated radio wave and is configured to lock or unlock the door.

When an antenna device is provided in a portable device, the antenna efficiency is often not sufficient due to the size restriction of the portable device case. In particular, as a portable device antenna device, a minute loop antenna having a conductor formed in a loop shape is used. However, in a portable device operated by a user when power is supplied to the minute loop antenna when radio waves are radiated. The problem that the radiated radio wave is weakened due to the influence of the human body has been pointed out.
In other words, the human body is a medium that is very lossy with respect to high frequencies, and the radio wave emission from the human body is small. Therefore, if the circuit board that radiates radio waves is covered with the user's hand, the radio wave emission is weakened Is.
For this reason, in order to reduce the influence of the human body, for example, in the antenna device disclosed in Patent Document 1, a part of the outer box of the case is formed of a conductor, and the conductor is used as a ground circuit of the feeder circuit. By adopting a connection structure, it is proposed that the ground potential side of the power feeding circuit and the termination circuit side of the antenna device be grounded to the ground through the human body when in use, so that sufficient performance can be demonstrated for antenna gain during communication. ing.

JP-A-9-199920

In the antenna device of Patent Document 1, a part of a case generally made of a dielectric is used as a conductor, and the user connects the portable device to the ground circuit of the power feeding circuit by connecting the conductor to the ground circuit. When grasped, it is devised so that the antenna performance is not reduced by connecting the conductor part of the case and the substrate ground through the human body. However, the structure in which a part of the case is a conductor in order to connect the substrate ground to the case has a problem of high cost and a large number of manufacturing steps.
An object of the present invention is to provide a device having a sufficient function as an antenna without greatly changing the manufacturing process as an antenna device used in a portable device.

The antenna device of the present invention is disposed on the circuit board in the vicinity of the circuit board housed in the case of the portable device, the minute loop antenna attached to the circuit board, the holding portion of the case of the portable device, and the minute device A feeding circuit that is connected to a loop antenna and feeds power to the minute loop antenna, a termination circuit that adjusts the minute loop antenna to a desired frequency band, and an antenna area provided with the minute loop antenna on the circuit board ground provided in the region, a first switch provided to the antenna area of the circuit board, a second switch provided in a different region from that of the antenna area before Symbol circuit board, and the first switch conductors between said second switch is provided, wherein the electrical conductor is connected to the ground and Than is.

  According to the antenna device of the present invention, the first switch is provided in the antenna region, the second switch is provided outside the antenna region, and the feeder circuit is held by the user of the portable device case that houses the antenna device. When the switch is operated with the case held by the user, the power supply circuit and a part of the human body held by the user are close to each other so that they are coupled in high frequency, and only the arrangement of the power supply circuit The antenna performance can be improved.

1 is a structural diagram schematically showing a portable device and an antenna device according to a first embodiment of the present invention. It is a figure which shows the operation state in Embodiment 1 of this invention. It is a figure which shows the operation state in Embodiment 2 of this invention. It is the schematic which shows operation | movement of the antenna apparatus in Embodiment 2 of this invention. It is a figure which shows the operation state in Embodiment 3 of this invention. It is a figure which shows the operation state in Embodiment 3 of this invention.

<Embodiment 1>
As shown in FIG. 1A, the appearance of the portable device that is the subject of the present invention is the same as that of a general portable device, and is provided with a first button 2 and a second button 3 in a dielectric case 1. An area (button area) where the first button 2 and the second button 3 are provided and an area (gripping area) for the user to hold the portable device are set. An antenna device 10 is provided inside the case 1 of the portable device, and a predetermined signal is transmitted when the user presses the first button 2 or the second button.

As shown in the plan view of FIG. 1B and the cross-sectional view of FIG. 1C, the structure of the antenna device 10 includes a CPU (Central Processing Unit) 12, a transmission circuit 13, a power feeding circuit 14, A loop antenna 15, a termination circuit 16, a first switch 17, and a second switch 18 are provided. The CPU 12, the transmission circuit 13, the power feeding circuit 14, the minute loop antenna 15, the termination circuit 16, and the second switch 18 are attached on the substrate ground 19. A battery 20 that supplies a voltage for driving the antenna device 10 is attached to the back surface of the circuit board 14.
As shown in FIG. 1B, the first switch 17 is disposed in a region surrounded by the minute loop antenna 15, and the second switch 18 is disposed on the substrate ground 19.

  When operating this portable device, as shown in FIG. 2, regardless of whether the hand to be used is a right hand or a left hand, the portable device case 1 is supported from the lower side, and the first button 2 or the second button from the upper side is supported. 2 button 3 is pressed. FIG. 2 shows an example of how the portable device is used, and shows a state in which the portable device is operated with the right hand. FIG. 2A shows a state where the first button 2 is being pressed, and FIG. 2B shows a state where the second button 3 is being pressed. In this operation, the first switch 17 or the second switch 18 of the antenna device 10 is pushed by the user holding the portable device so as to wrap and pressing a button corresponding to a desired remote keyless function. Become. For example, when the second switch 18 is pressed, the CPU 12 sends data corresponding to the pressed second switch 18 to the transmission circuit 13 by pressing the second switch 18.

  The transmission circuit 13 modulates data and outputs a high-frequency signal such as a UHF (Ultra High Frequency) band binary FSK (Frequency Shift Keying) modulated wave. This high-frequency signal is fed by the feeding circuit 14 and is radiated to the space by the elements of the minute loop antenna 15. The minute loop antenna 15 is configured by, for example, a pattern formed on the circuit board 11. The power feeding circuit 14 and the termination circuit 16 are circuits for adjusting the elements of the minute loop antenna 15 to operate in a desired frequency band. In the UHF band, for example, the power feeding circuit 14 is connected to the substrate ground 19 with a ground coil. Further, the termination circuit 16 is connected to the substrate ground 19 by a capacitor connected in series. The substrate ground 19 is formed on the circuit board 11 and is formed on the end side opposite to the end portion on which the element of the minute loop antenna 15 is provided so as not to inhibit the radiation from the minute loop antenna 15. ing.

  The power feeding circuit 14 is mounted on the circuit board 11. In particular, when the user performs a button operation on the portable device, a position where the portable device is supported or close to the portable device, for example, a quarter of a wavelength in a minute loop. A circuit having a length that can be regarded as being electrically close if the length is 1/10 or less of the wavelength, preferably 1/40 or less of the wavelength. Arranged on the substrate 11. For example, in FIG. 2A, in order to hold the portable device with the index finger and press the button with the thumb, a feeding point is provided at a position between the second joint and the third joint of the index finger. When the index finger and the power supply circuit 14 are close to each other, they are coupled in high frequency (electric field coupling), and when the power supply circuit 14 supplies power to the elements of the minute loop antenna 15, an electric field is excited by the user's index finger, that is, the human body. Will flow.

When the micro loop antenna 15 is fed from the power feeding circuit 14 on the circuit board 11 as in the first embodiment, as shown in FIG. 2C, a micro loop mode current (path a) that flows through the elements of the micro loop antenna 15 In addition, a dipole mode current flows through the substrate ground 19 (path b). For this reason, the signal radiated from the portable device is a signal of the sum of the radiation by the minute loop mode current and the radiation by the dipole mode current.
For this reason, by providing the substrate ground 19 on the human body side, the dipole mode current flowing in the substrate ground 19 flows to the human body through the index finger by high-frequency coupling (path c). Since the human body has a length on the order of a wavelength, radiation from a dipole mode current becomes strong. For this reason, since the feeding circuit 14 is arranged at the index finger position (that is, the position where the portable device is supported), a minute loop antenna current and a dipole mode current with the human body as the ground are generated. The antenna performance as a machine is improved.
As described above, the antenna performance can be improved by providing the feeding circuit 14 at a position held by the portable device.

  FIG. 1 shows an example in which two switches, such as a first switch 17 and a second switch 18, are mounted. Here, at least one switch is arranged in the minute loop antenna 15 and the other is arranged on the substrate ground 19. Although the shape of the circuit board 11 is shown as a flat rectangle, the shape of the circuit board 11 is not limited to a rectangle, and may be an ellipse or a square. However, it is considered that the circuit board 11 is preferably an elliptical shape that is long in one direction and short in one direction from the viewpoint of ease of handling when operated by the user of the portable device. Further, in the first embodiment, an example of holding with the right hand has been shown, but in the case of holding with the left hand as well, since the back is supported on the back side of the portable device, the feeding point is arranged at the place to support. .

<Embodiment 2>
Generally, the antenna performance is deteriorated by providing a conductor in the element of the minute loop antenna 15. This is because the electric field generated in the element of the minute loop antenna 15 is disturbed. When the human body is used as an antenna ground as in the first embodiment, the user's hand also functions as a part of the antenna ground. Therefore, if the button to be pressed is different as in the case of pressing the first button 2 as shown in FIG. 3A and the case of pressing as the second button 3 as shown in FIG. The ground approaches or leaves. For this reason, the intensity of the radio wave radiated from the element of the minute loop antenna 15 is changed as shown in FIGS. 3B to 3D by the button to be pressed. In this manner, in the remote keyless entry system, the following describes how to deal with a case where it is necessary to avoid that the antenna radio wave intensity is extremely different due to the operation of pressing a button.

In the second embodiment, improvements are made to prevent changes in radio wave intensity.
The second embodiment will be described with reference to FIG. FIG. 4A shows the antenna device and shows the arrangement of the substrate ground 19. The power supply circuit 14, the termination circuit 16, and the like are the same as those in the first embodiment, and are not shown.
In the second embodiment, a second substrate ground 192 which is a conductor is provided between the first switch 17 and the second switch 18 and connected to the ground. Here, the second substrate ground 192 is shown as being provided on the circuit board 11. However, when the circuit board 11 is a multilayer board, it is not necessarily provided on the surface. Two substrate grounds 192 may be provided.

Here, when a high-frequency signal is supplied to the power supply circuit 14, an electric field is generated by current flowing through the elements of the minute loop antenna 15. An electric field is also generated in the minute loop antenna 15. As shown in FIG. 4B, this electric field has a strong radio wave intensity in the area of the minute loop antenna 15, but the second substrate ground provided between the first switch 17 and the second switch 18. Blocked at 192. For this reason, the radio field intensity around the second substrate ground 192 decreases.
In the second embodiment, the switch operation is performed with the thumb. In order to eliminate the influence of the user's thumb in the element of the minute loop antenna 15, the second substrate ground 192 to be connected is, for example, a width of about 3 mm, which is thinner than a general finger size in order not to deteriorate the antenna performance. It is said.
Note that the shape of the second substrate ground 192 may be not only a rectangular shape as shown in FIG. 4 but also an arc shape.

By providing a structure having the function of the second ground substrate 192 as a shielding plate for reducing the radio field intensity, even when a finger approaches or separates when the switch is pressed, the radio field intensity greatly changes. It will not occur. That is, a difference in antenna performance caused by selection of a button to be pressed can be reduced.
As described above, the strength of the radio wave radiated from the element of the minute loop antenna 15 is provided by providing a member that shields the radio wave like the second board ground 192 between the switches mounted on the circuit board 11. Therefore, even if the buttons to be pressed are different, the antenna performance is not so different.

<Embodiment 3>
In the second embodiment, by providing the second substrate ground 192 between the first switch 17 and the second switch 18, the difference in antenna performance that occurs according to the button to be pressed is reduced.
However, it is necessary to consider the arrangement positions of the termination circuit 16 and the power feeding circuit 14. That is, as shown in FIG. 5A and FIG. 5B, in the state where the termination circuit 16 is closer to the minute loop antenna 15 than the feeder circuit 14 in the longitudinal direction of the circuit board 11, for example, as shown in FIG. When the first button 2 is pressed with the thumb, the terminal circuit 16 and the user's thumb are coupled at a high frequency. For this reason, in addition to the dipole mode current flowing from the termination circuit 16 to the user's thumb by high-frequency coupling (path 1), a human body dipole mode current (path 2) to the termination circuit 16 is generated through the user's thumb. Therefore, when the path 2 is increased, the dipole mode current becomes the sum of the substrate dipole mode current, the human body dipole mode current through the path 1 and the human body dipole mode current through the path 2. Therefore, when the first button 2 is pressed and when the second button 3 is pressed as shown in FIG. 5B, the antenna performance is different. In the third embodiment, improvements are made to prevent a situation in which the antenna performance varies greatly depending on the button to be pressed.

The third embodiment will be described with reference to FIGS. 6A and 6B. Note that illustration and description of the same parts as those of the second embodiment such as the portable device and the antenna device are omitted.
In the third embodiment, the termination circuit 16 and the power feeding circuit 14 are arranged at the same position when viewed from the minute loop antenna 15. That is, as shown in FIGS. 6A and 6B, the circuit boards are arranged at symmetrical positions with respect to the minute loop antenna having the same distance in the longitudinal direction of the circuit board. In other words, in the longitudinal direction of the circuit board 11, the termination circuit 16 is disposed at the same position as the power feeding circuit 14 when viewed from the position of the minute loop antenna 15. The substrate ground 19 is disposed on the opposite side of the element of the minute loop antenna 15 with respect to the power feeding circuit 14 and the termination circuit 16.

  With this arrangement, the dipole mode current flowing from the termination circuit 16 to the human body via the thumb is, for example, as shown in FIG. 6A, when the user presses the first button 2 with the thumb. Since the thumb is separated from the termination circuit 16, the coupling amount between the thumb and the termination circuit 16 is reduced. Similarly, as shown in FIG. 6B, when the user presses the second button 3 with the thumb, the dipole mode current is the same as that when the first button 2 is pressed, It flows to the path 4 by the combination with the thumb. In this state, the amount of coupling between the first button 2 and the termination circuit 16 and the amount of coupling between the second button 3 and the termination circuit 16 are the same as the minimum distance between the termination circuit 16 and the thumb regardless of which button is pressed. For this reason, the amount of each coupling becomes approximately the same.

For this reason, a difference in antenna performance can be reduced when the first button 2 is pressed and when the second button 3 is pressed.
As described above, by arranging the termination circuit 16 and the power feeding circuit 14 at the same position with respect to the longitudinal direction of the circuit board 11, the change in antenna performance caused by the button to be pressed can be reduced.

  In the present invention, any constituent element of the embodiment can be appropriately changed or omitted within the scope of the invention.

1 case, 2 first button, 3 second button, 10 antenna device,
11 circuit board, 12 CPU, 13 transmitting circuit, 14 feeding circuit,
15 micro loop antenna, 16 termination circuit, 17 first switch,
18 second switch, 19 substrate ground, 20 battery,
192 Second substrate ground

Claims (2)

A circuit board housed in a case of a portable device, a minute loop antenna attached to the circuit board, disposed on the circuit board in the vicinity of the holding portion of the case of the portable device, connected to the minute loop antenna, A feeding circuit that feeds power to the minute loop antenna, a termination circuit that adjusts the minute loop antenna to a desired frequency band, a ground provided in a region different from the antenna region in which the minute loop antenna is provided on the circuit board, a first switch provided in the antenna area of the circuit board, the second provided in a region different from the said antenna region before Symbol circuit board switches, and said first switch of the second switch An antenna device , wherein a conductor is provided therebetween, and the conductor is connected to the ground . The antenna device according to claim 1 , wherein the termination circuit and the power feeding circuit are arranged symmetrically with respect to the minute loop antenna having the same distance in the longitudinal direction of the circuit board.

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