Antenna device

Abstract

 There is provided an antenna device that can change its resonant frequency depending on a received frequency, has a simple configuration, and facilitates miniaturization. A radiating electrode 19 to which a high-frequency feeding voltage is supplied, and a variable capacitive element (a varactor diode) 16 to which a direct current bias voltage is supplied and whose capacitance value varies depending on the bias voltage are provided on the surface of a dielectric block 18 of an antenna element 12. The variable capacitive element 16 is electrically connected to the radiating electrode 19 so that the capacitance value of the variable capacitive element 16 is an additional capacitance value for changing the resonant frequency of the antenna. The resonant frequency of the antenna is appropriately changed depending on a received frequency using the direct current bias voltage supplied to the variable capacitive element 16 as a control signal. The antenna element 12 is preferably an inverted F-type antenna or a loop-type antenna, and the variable capacitive element 16 is preferably provided in a vacant area on the surface of the dielectric block 18.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to an antenna device suitable as a small-sized antenna used for a portable information terminal apparatus and having a tuning control function that changes a resonant frequency of the antenna depending on a received frequency.

2. Description of the Related Art

[0002] Retractable rod antennas are generally used as antenna devices used for portable television receivers. In order to obtain the optimum reception sensitivity in the rod antenna, however a user must perform complicated sensitivity settings, such as adjusting the length of the antenna depending on a received channel (a received frequency) or changing the angle or direction of the antenna. Further, since the rod antenna is used in an extended state, the rod antenna tends to be considered to be a troublesome projection and is easily broken. Thus, it is conceivable that various antenna devices that are more easily miniaturized than the rod antenna can be useful. However, since a small-sized antenna has a narrow bandwidth of a resonant frequency, in order to cope with the wide range of received frequencies, a tuning control function is required which appropriately changes the resonant frequency of the antenna depending on the received frequency.

[0003] As a small-sized antenna device having such a tuning control function, there has conventionally been proposed an antenna device in which a variable capacitive element for changing an additional capacitance value of an antenna element is mounted on a circuit board in which the antenna element, such as an inverted F-type antenna or a loop-type antenna, is provided, and a direct current bias voltage (a control voltage) is supplied to the variable capacitive element (for example, refer to Patent Document 1). In the above antenna device, the variable capacitive element and the bias control circuit thereof are inserted in series into a feeding line on the circuit board side connected to a feeding point of the antenna element, and the capacitance value of the variable capacitive element varies depending on the magnitude of a direct current bias voltage supplied from the bias control circuit. Also, when the capacitance value of the variable capacitive element varies, an additional capacitance value of the antenna element varies and the resonant frequency of the antenna varies. Thus, it is possible to perform tuning control for changing the resonant frequency of the antenna depending on a received frequency by setting the magnitude of the direct current bias voltage depending on the received frequency.

[Patent Document 1]

[0004] Japanese Unexamined Patent Application Publication No. 10-107671 (Pages 2 and 3, Fig. 1)

[0005] In the aforementioned conventional proposal, a configuration is adopted in which a variable capacitive element and a bias control circuit thereof are attached to a feeding line on a circuit board side so as to make an antenna device with a tuning control function. However, such a configuration has a problem in that it is hard to achieve desired miniaturization because space for arranging the variable capacitive element and the bias control circuit should be provided on the circuit board side. In other words, high package density is required for a circuit board in a portable information terminal apparatus, such as a portable television receiver, and space on the circuit board that can be used for an antenna is also limited. Thus, a configuration in which tuning control means, such as a variable capacitive element, is separately arranged from an antenna element and a tuner unit interferes with miniaturization. For example, in the case of the terrestrial digital television broadcasting that will be introduced soon, it is assumed that the broadcast will be received by personal digital assistants (PDAs) and portable telephones as well as television-only receivers. In this case, it is indispensable to design a compact antenna device for receiving television broadcasting signals in a portable information terminal apparatus of this type.

SUMMARY OF THE INVENTION

[0006] The present invention has been made in light of the actual circumstances of conventional design. It is therefore an object of the present invention to provide an antenna device which can change its resonant frequency depending on a received frequency, has a simple configuration, and facilitates miniaturization.

[0007] In order to achieve the aforementioned object, an antenna device according to the present invention comprises a radiating electrode to which a high-frequency feeding voltage is supplied, and a variable capacitive element to which a direct current bias voltage is supplied and whose capacitance value varies depending on the bias voltage, the radiating electrode and the variable capacitive element being provided on the surface of a dielectric block, wherein the variable capacitive element is electrically connected to the radiating electrode so that the capacitance value of the variable capacitive element is an additional capacitance value for changing the resonant frequency of the antenna, and wherein the resonant frequency of the antenna is changed depending on a received frequency using the direct current bias voltage as a control signal.

[0008] The dielectric antenna in which the radiating electrode is provided on the surface of the dielectric block is suitable for miniaturization because the wavelength of the antenna can be reduced due to a dielectric. If the variable capacitive element, which is tuning control means, is provided in a vacant area on the surface of the dielectric block, space for forming the antenna on the circuit board can be reduced, and a circuit for the antenna can be simplified. Also, when a direct current bias voltage supplied to the variable capacitive element increases, a capacitance value of the variable capacitive element decreases, and the resonant frequency of the antenna increases with a decrease in an additional capacitance value. It is thus possible to perform tuning control for appropriately changing the resonant frequency of the antenna depending on the received frequency by appropriately setting the magnitude of the direct current bias voltage according to the received frequency. Therefore, a small-sized antenna device capable of performing tuning control can be produced at a low cost, and the antenna device can be used as an antenna device for receiving terrestrial digital television broadcasting signals in a portable information terminal apparatus.

[0009] Further, if the antenna device is configured as an inverted F-type antenna obtained by providing the radiating electrode on the upper surface of the dielectric block that is mounted on a ground conductor, or a loop-type antenna obtained by providing the radiating electrode on the side surface of the dielectric block mounted in a region where the ground conductor does not exist, the antenna device can be further miniaturized. Also, when the antenna device is configured as the inverted F-type antenna, it is preferable that the variable capacitive element be provided on the side surface of the dielectric block. In addition, when the antenna device is configured as the loop-type antenna device, it is preferable that the variable capacitive element be provided on the side surface or the upper surface of the dielectric block.

[0010] Moreover, if a chip-shaped varactor diode is adopted as the variable capacitive element, the antenna device can be relatively easily mounted on the surface of the dielectric block. As a result, an antenna device can be obtained with stable performance at a low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

Fig. 1 is a view showing the schematic structure of a television signal receiving card comprising an antenna device according to a first embodiment of the present invention;

Fig. 2 is an explanatory view showing a state in which the card shown in Fig. 1 is mounted on a portable information terminal apparatus;

Fig. 3 is a perspective view of an antenna element built in the card shown in Fig. 1;

Fig. 4 is a bottom view of the antenna element shown in Fig. 3;

Fig. 5 is a characteristic diagram showing the relationship between a resonant frequency and a control voltage supplied to a varactor diode of the antenna element shown in Fig. 3;

Fig. 6 is an explanatory view showing a radiating pattern of the antenna element shown in Fig. 3;

Fig. 7 is a perspective view showing an antenna element according to a modification of the first embodiment;

Fig. 8 is a view showing the schematic structure of a television signal receiving card comprising an antenna device according to a second embodiment of the present invention;

Fig. 9 is a perspective view of an antenna element built in the card shown in Fig. 8;

Fig. 10 is a bottom view of the antenna element shown in Fig. 9;

Fig. 11 is a perspective view showing an antenna element according to a modification of the second embodiment;

Fig. 12 is a view showing the schematic structure of a television signal receiving card comprising an antenna device according to a third embodiment of the present invention;

Fig. 13 is a perspective view of an antenna element built in the card shown in Fig. 12;

Fig. 14 is a bottom view of the antenna element shown in Fig. 13; and

Fig. 15 is a perspective view showing an antenna element according to a modification of the third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a view showing the schematic structure of a television signal receiving card comprising an antenna device according to a first embodiment of the present invention; Fig. 2 is an explanatory view showing a state in which the card is mounted on a portable information terminal apparatus; Fig. 3 is a perspective view of an antenna element built in the card; Fig. 4 is a bottom view of the antenna element; Fig. 5 is a characteristic diagram showing the relationship between a resonant frequency and a control voltage supplied to a varactor diode of the antenna element; and Fig. 6 is an explanatory view showing a radiating pattern of the antenna element.

[0013] A television signal receiving card 11 shown in Fig. 1 is a card-type electronic device for receiving signal waves (horizontally polarized waves) for the terrestrial digital television broadcasting having the frequency range of 470 to 770 MHz, which is mounted and used on a portable information terminal apparatus 1 shown in Fig. 2. The card 11 is generally configured such that a circuit board 14 on which an antenna element 12, a tuner unit 13, etc., are mounted is inserted inside an outer case 15, and a chip-shaped varactor diode 16 and a resistor 17 are attached to the side surface of the antenna element 12 (see Fig. 3).

[0014] The antenna element 12 is an inverted F-type dielectric antenna which is obtained by providing a radiating electrode 19, an earth electrode 20, a feeding terminal 21, a control terminal 22, etc., on the surface of a rectangular parallelepiped dielectric block 18. The dielectric block 18 is made of a dielectric material, such as ceramic or resin, and the respective electrode 19 and 20 and the respective terminals 21 and 22 are made of a conductive layer, such as a copper foil. The radiating electrode 19 has two capacitive coupling portions C1 and C2 on the upper surface of the dielectric block 18, and these capacitive coupling portions C1 and C2 perform impedance matching or adjustment of an additional capacitance value. Further, the earth electrode 20 is connected to a ground conductor 23 on the circuit board 14 side on the bottom face of the dielectric block 18, and the feeding terminal 21 and the control terminal 22 are connected to the tuner unit 13. Also, a high-frequency feeding voltage is supplied to the feeding terminal 21 so that a direct current bias voltage (a control voltage) is supplied to the control terminal 22.

[0015] The varactor diode 16 is a variable capacitive element whose capacitance value varies depending on the magnitude of the applied direct current bias voltage. One end of the varactor diode 16 is connected to the resistor 17, and the other end of the varactor diode 16 is connected to the earth electrode 20. The resistor 17 for blocking high frequencies is connected to the control terminal 22 so that a direct current bias voltage is supplied to the varactor diode 16 through the resistor 17. In addition, the direct current bias voltage does not influence the radiating electrode 19 because it is intercepted by the capacitive coupling portion C2.

[0016] The tuner unit 13 is a tuner for receiving television signals, and a received signal (an RF signal) is input to the tuner unit 13 from the antenna element 12. After the tuner unit 13 has processed the received signal, it outputs the processed signal to a liquid crystal display unit 2 of the portable information terminal apparatus 1 as an IF signal.

[0017] A slot 3 for detachably mounting the television signal receiving card 11 is provided in the portable information terminal apparatus 1. When the television signal receiving card 11 is mounted on the portable information terminal apparatus 1, as shown in Fig. 2, the antenna element 12 built on one side of the card 11 is held in a state that protrudes to the outside of the portable information terminal apparatus 1. In other words, when a terrestrial digital television broadcasting signal is received to display an image on a liquid crystal display unit 2, as shown in Fig. 2, the television signal receiving card 11 is mounted on the portable information terminal apparatus 1, and the antenna element 12 is operated as an inverted F-type antenna in order to receive the signal. Further, when the reception of the terrestrial digital television broadcasting signal is finished and when another card is mounted to use the portable information terminal apparatus 1 for other purposes, the television signal receiving card 11 is pulled out from the slot 3.

[0018] Next, the operation of the antenna element 12 will be described in detail. Since an additional capacitance value of the antenna element 12 varies depending on a capacitance value of the varactor diode 16, which is a variable capacitive element, the resonant frequency of the antenna can be changed according to the magnitude of the direct current bias voltage (the control voltage) to be supplied from the tuner unit 13 to the varactor diode 16. In other words, when the direct current bias voltage increases, as shown in Fig. 5, a capacitance value of the varactor diode 16 (solid line A) decreases, and the resonant frequency (broken line B) of an antenna rises with a decrease in an additional capacitance value. Therefore, the resonant frequency of an antenna can be tunably controlled depending on a received frequency by appropriately setting the magnitude of a direct current bias voltage depending on the received frequency. As a result, it is possible to receive terrestrial digital television broadcasting signals having the frequency range of 470 to770 MHz while setting the antenna element 12 to such a small-sized size that the long side of the antenna element is 35 mm, the short side thereof is 11 mm, and the height thereof is 5 mm. Also, after a video signal received by the antenna element 12 is processed in the tuner unit 13, the video signal is output to the liquid crystal display unit 2 of the portable information terminal apparatus 1 and is displayed on the screen based on the signal.

[0019] In the present embodiment as described above, the antenna element 12 built in the television signal receiving card 11 is an inverted F-type dielectric antenna, and the varactor diode 16 for changing the resonant frequency of an antenna depending on the received frequency is mounted on a vacant area of the dielectric block 18 of the antenna element 12. Therefore, as shown in Fig. 6, good receiver sensitivity can be obtained by the small-sized antenna element 12. Accordingly, space for forming an antenna on the circuit board 14 can be reduced, a circuit for the antenna can be simplified, and the entire size of the television signal receiving card 11 can be made compact. In addition, Fig. 6A is a radiating pattern showing directivity in a x-y plane of Fig. 1, and Fig. 6B is a radiating pattern showing directivity in a x-z plane of Fig. 1, and Fig. 6C is a radiating pattern showing directivity in a y-z plane of Fig. 1. It can be understood from these drawings that, even if the antenna element 12 is directed to any direction, an extreme decrease in gain does not occur.

[0020] Further, since the antenna element 12 is configured as an inverted F-type antenna which can receive both a horizontally polarized wave and a vertically polarized wave, it is possible to expect good receiver sensitivity even in a room where turbulence of a polarized wave occurs easily. Moreover, since the antenna element 12 is modularized by attaching the varactor diode 16 to the dielectric block 18, the antenna element 12 can be simply and precisely mounted on the circuit board 14. In addition, the chip-shaped varactor diode 16 can be relatively easily mounted in the surface of the dielectric block 18 so that stable performance and a low price can be expected.

[0021] Fig. 7 is a perspective view showing an antenna element according to a modification of the aforementioned first embodiment, wherein the same reference numerals are given to the same components as those in Fig. 3. An antenna element 28 shown in Fig. 7 is configured such that one end of the varactor diode 16 is connected to the feeding terminal 21 through the resistor 17, and a feeding voltage and a direct current bias voltage (a control voltage) are overlapped with each other and are supplied from the tuner unit 13 to the feeding terminal 21. Therefore, the control terminal 22 that was required in the antenna element 12 is omitted in the antenna element 28.

[0022] Fig. 8 is a view showing the schematic structure of a television signal receiving card comprising an antenna device according to a second embodiment of the present invention, Fig. 9 is a perspective view of an antenna element built in the card, and Fig. 10 is a bottom view of the antenna element. In addition, in these Figs. 8 to 10, the same reference numerals are given to the same components as those in Figs. 1 to 4.

[0023] A television signal receiving card 31 shown in Fig. 8 is greatly different from that of the first embodiment in that an antenna element 32 is configured as a loop-type antenna. In other words, the antenna element 32 shown in Figs. 8 to 10 is a loop-type dielectric antenna in which a strip-shaped radiating electrode 19 is provided along the side surface of a rectangular parallelepiped dielectric block 18, and a capacitor 24 is interposed between a radiating electrode 19 and a feeding terminal 21. The feeding terminal 21, a control terminal 22, and an earth terminal 25 are provided on the end of one side of the bottom face of the dielectric block 18, the feeding terminal 21 and the control terminal 22 are connected to the tuner unit 13, and the earth terminal 25 is connected to a ground conductor 23 on a circuit board 14 side. One end of the varactor diode 16 is connected to the resistor 17, and the other end thereof is connected to the earth terminal 25 through the radiating electrode 19. The resistor 17 for blocking high frequencies is connected to the control terminal 22 so that a direct current bias voltage (a control voltage) is supplied to the varactor diode 16 through the resistor 17. Moreover, as shown in Fig. 8, although the ground conductor 23 does not exist in the mounting region of the antenna element 32 and in the vicinity thereof on the circuit board 14, the basic configuration of the circuit board 14 side is the same as that of the first embodiment.

[0024] Since the antenna element 32 is configured as a loop-type antenna in the television signal receiving card 31 according to the second embodiment as described above, the radiating pattern of a horizontally polarized wave is non-directional. Accordingly, even if the portable information terminal apparatus on which the television signal receiving card 31 is mounted is arbitrarily rotated along the circuit board 14, it is possible to receive terrestrial digital television broadcasting signals with constant sensitivity. Further, if the antenna element 32 is a loop-type antenna, there is an advantage in that the human body hardly affects the antenna element.

[0025] Fig. 11 is a perspective view showing an antenna element according to a modification of the aforementioned second embodiment, wherein the same reference numerals are given to the same components as those in Fig. 9. An antenna element 33 shown in Fig. 11 is configured such that one end of a varactor diode 16 is connected to a feeding terminal 21, and a feeding voltage and a direct current bias voltage (a control voltage) are overlapped with each other and are supplied from a tuner unit 13 to the feeding terminal 21. Therefore, the control terminal 22 and the resistor 17 which are required in the antenna element 32 are omitted in the antenna element 33.

[0026] Fig. 12 is a view showing the schematic structure of a television signal receiving card comprising an antenna device according to a third embodiment of the present invention, Fig. 13 is a perspective view of an antenna element built in the card, and Fig. 14 is a bottom view of the antenna element. In addition, in Figs 12 to 14, the same reference numerals are given to the same components as those in Figs. 8 to 10.

[0027] An antenna element 42 of a television signal receiving card 41 shown in Fig. 12 is a loop-type antenna slightly different from that of the second embodiment. In other words, in the antenna element 42 shown in Figs 12 to 14, an elongated radiating electrode 19 is spirally provided along the side surface of a rectangular parallelepiped dielectric block 18. A varactor diode 16 and a resistor 17 arranged on the upper surface of the dielectric block 18 are respectively connected to the feeding terminal 21 and the control terminal 22 through via holes 26 and 27 passing through the dielectric block 18. Since one end of the spirally extending radiating electrode 19 is connected to the varactor diode 16 on the upper surface of the dielectric block 18, the radiating electrode 19 is finally connected to the feeding terminal 21 through the via hole 26. Further, the other end of the radiating electrode 19 is connected to an earth terminal 25 on the bottom face of the dielectric block 18. Moreover, the basic configuration of the circuit board 14 is the same as that of the second embodiment.

[0028] Since the radiating electrode 19 of the antenna element 42 spirally extends in the television signal receiving card 41 according to the third embodiment as described above, it is possible to remarkably increase the length of the antenna without increasing the size of the dielectric block 18. Therefore, the antenna according to the present invention is preferably used as a small-sized antenna for receiving a signal wave having a long wavelength. Further, since the antenna element 42 is a loop-type antenna, the radiating pattern of a horizontally polarized wave is non-directional as in the second embodiment. As a result, even though a portable information terminal apparatus is arbitrarily rotated along the circuit board 14, terrestrial digital television broadcasting signals can be received with constant sensitivity, and the human body hardly affects the antenna element.

[0029] Fig. 15 is a perspective view showing an antenna element according to a modification of the aforementioned third embodiment, wherein the same reference numerals are given to the same components as those in Fig. 13. An antenna element 43 shown in Fig. 15 is configured such that the control terminal 22, the resistor 17, and the via hole 27 is omitted, and a feeding voltage and a direct current bias voltage (a control voltage) are overlapped with each other and are supplied from the tuner unit 13 to the feeding terminal 21.

[0030] Moreover, a case in which an antenna device for receiving terrestrial digital television broadcasting signals is built in a card has been described in the aforementioned respective embodiments. However, it goes without saying that the present invention can be applied to an antenna device for receiving other signals or an antenna device which is built in the main body of an apparatus, such as a portable information terminal apparatus.

[0031] According to the embodiments of the present invention as described above, the following effects can be obtained.

[0032] The present invention provides an antenna device in which the resonant frequency of the antenna can be appropriately changed depending on a received frequency by attaching a variable capacitive element, such as a varactor diode, to the surface of a dielectric block. According to the above antenna device, since space for forming the antenna on the circuit board can be reduced and a circuit for the antenna can be also simplified, a small-sized antenna device capable of performing tuning control can be produced at a low cost. Accordingly, the antenna device according to present invention can be used as an antenna device for receiving terrestrial digital television broadcast signals in a portable information terminal apparatus. As a result, a high utility of the antenna device can be expected.

Claims

1. An antenna device comprising a radiating electrode to which a high-frequency feeding voltage is supplied, and a variable capacitive element to which a direct current bias voltage is supplied and whose capacitance value varies depending on the bias voltage, the radiating electrode and the variable capacitive element being provided on the surface of a dielectric block,
   wherein the variable capacitive element is electrically connected to the radiating electrode so that the capacitance value of the variable capacitive element is an additional capacitance value for changing a resonant frequency of the antenna, and
   wherein the resonant frequency of the antenna is changed depending on a received frequency using the direct current bias voltage as a control signal.

2. The antenna device according to Claim 1, wherein the antenna device is configured as an inverted F-type antenna obtained by providing the radiating electrode on the upper surface of the dielectric block that is mounted on a ground conductor, and the variable capacitive element is provided on the side surface of the dielectric block.

3. The antenna device according to Claim 1, wherein the antenna device is configured as a loop-type antenna obtained by providing the radiating electrode on the side surface of the dielectric block that is mounted in a region where the ground conductor does not exist, and the variable capacitive element is provided on the side surface or the upper surface of the dielectric block.

4. The antenna device according to any one of Claims 1 to 3, wherein the variable capacitive element is a chip-shaped varactor diode.

Drawing