JP2006191270A - Antenna assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small antenna assembly having a variable resonance frequency and a high gain. <P>SOLUTION: The antenna assembly comprises: a substrate 2; a ground conductor 3 formed on the surface of the substrate 2; a loading section 4 arranged on the substrate 2 with a linear conductor pattern being formed on an element; an inductor portion 5 being connected between one end of the conductor pattern and a ground conductor 3; and a feeding point 7 for feeding to one end of the inductor portion 5. A frequency regulating section 6 is provided between one end of the conductor pattern and the inductor portion 5. The frequency regulating section 6 comprises regulation chip inductors 21A-21C which can be connected in parallel with each other, and a switch section 22 for connecting one end of the conductor pattern with the inductor portion 5 by selecting at least one of the regulation chip inductors 21A-21C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an antenna device used for transmission / reception of a digital television broadcast band, for example.

In recent years, terrestrial television broadcasting has been digitized. This terrestrial digital broadcast can be a high-definition broadcast by digitizing a television broadcast, and a data broadcast can also be added. And in this terrestrial digital broadcast, it broadcasts using the frequency of a 470 MHz-770 MHz band which is a UHF band.
On the other hand, in a portable terminal, a quarter wavelength antenna is used in a band of 400 MHz or higher. In the 1/4 wavelength type antenna, an electric length of an antenna element is 1/4 wavelength, and a whip antenna having a length of 1/4 wavelength as a physical length is used for a portable terminal. The built-in antenna can be built in a portable terminal by reducing the physical length to less than 1/4, and the bandwidth and antenna gain are deteriorated compared to the whip antenna due to the downsizing. Note that the specific bandwidth of the whip antenna is generally about a dozen percent.

By the way, when receiving terrestrial digital broadcasting with a portable terminal, even if the whip antenna is adjusted at 470 MHz to 770 MHz required in the broadcasting band of terrestrial digital broadcasting, the bandwidth of the whip antenna is 100 MHz or less. It is impossible to cover a bandwidth of 300 MHz with one antenna. For this reason, the resonance frequency needs to be variable.
Therefore, as a method for making the resonance frequency variable, an antenna has been proposed in which the capacitance value of the capacitor is controlled by voltage using a varicap and the resonance frequency of the antenna is made variable. In addition, an antenna device has been proposed in which the resonance frequency of the antenna is variable by providing a resonance frequency variable means capable of short-circuiting and opening the end of the plate-shaped inverted F antenna at the end of the plate-shaped inverted F antenna (for example, , See Patent Document 1).
JP-A-8-307303

  However, the following problems remain in the conventional antenna device. That is, in the conventional antenna device, when the resonance frequency is made variable using a varicap in the former antenna device, an inductor and a capacitor are used, so that the applicable antenna type is only a loop antenna. In the latter antenna device, when the end of the plate-like inverted F antenna is short-circuited, a loop antenna shape is obtained. Here, since the gain of the antenna is proportional to the loop area, there is a problem that the gain becomes low when the loop antenna is downsized.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a small antenna device having a variable resonance frequency and a high gain.

  The present invention employs the following configuration in order to solve the above problems. That is, the antenna device of the present invention is an element body made of a composite material having a substrate, a ground conductor formed on the surface of the substrate, and a dielectric material or a magnetic material, or both, disposed on the substrate. In an antenna apparatus comprising a loading portion in which a linear conductor pattern is formed, an inductor portion connected between one end of the conductor pattern and the ground conductor, and a feeding point that feeds one end of the inductor portion, A frequency adjustment unit is provided between one end of the conductor pattern and the inductor unit, and the frequency adjustment unit includes a plurality of adjustment inductors that can be connected in parallel to each other, and at least one of the plurality of adjustment inductors. And a switch part for connecting one end of the conductor pattern and the inductor part.

According to the present invention, even if the electrical length of the antenna element alone is shorter than 1/4 of the antenna operating wavelength, by combining the loading unit and the inductor unit, 1/4 of the antenna operating wavelength is obtained as the overall electrical length. Satisfied. Thereby, for example, even if the frequency is 470 MHz to 770 MHz, which is a broadcasting band of terrestrial digital broadcasting, the antenna device can be significantly shortened.
In addition, among the plurality of adjustment inductors that can be connected in parallel to each other, an appropriate one is selected at the switch portion, and one end of the conductor pattern is connected to the inductor portion, thereby adjusting the inductance of the frequency adjustment portion. Here, for example, when three adjustment inductors that can be connected in parallel to each other are provided, when at least one of the plurality of adjustment inductors connects one end of the conductor pattern and the inductor portion, the adjustment in the frequency adjustment unit There are seven combinations of inductor connection patterns.
In this way, by appropriately adjusting the inductance of the frequency adjustment unit by the switch unit, the electrical length in the frequency adjustment unit changes, and the resonance frequency of the antenna device can be set. Then, by using an inductor having a predetermined inductance as each adjustment inductor, the resonance frequency is adjusted according to the channel even in a wide bandwidth such as 470 MHz to 770 MHz which is a broadcasting band of digital terrestrial broadcasting. Can be covered.

In the antenna device according to the present invention, the switch unit includes a bias voltage input unit that is connected to the plurality of adjustment inductors between the one end of the conductor pattern and the inductor unit. A switching element whose impedance changes according to the voltage applied to the bias voltage input unit, and the connection between the adjustment inductor and one end of the inductor unit or the conductor pattern by the voltage applied to the bias voltage input unit The state is preferably variable.
According to the present invention, the impedance of the switching element connected to each adjustment inductor varies depending on the voltage value applied to the bias voltage input connected to each adjustment inductor,
The connection state between the adjustment inductor and the inductor portion or the conductor pattern changes. In this way, the inductance of the frequency adjustment unit is adjusted, and the resonance frequency of the antenna device is set.

In the antenna device according to the present invention, it is preferable that the switch unit includes a shunt-type switch circuit in which the switching element is disposed between the adjustment inductor and a ground.
According to the present invention, when a bias voltage that is forward with respect to the switching element is applied to the bias voltage input section, the impedance of the switching element is lowered, and the adjustment inductor and the ground are short-circuited. Thereby, the connection state between the inductor section and the conductor pattern is turned off with respect to the high-frequency signal. On the other hand, when a reverse bias voltage is applied to the switching element, since the impedance of the switching element is high, the adjustment inductor and the ground are opened. Thereby, the connection state between the inductor portion and one end of the conductor pattern is turned on with respect to the high-frequency signal. In this way, the connection state of the adjustment inductance is changed according to the voltage applied to the bias voltage input unit.

Further, in the antenna device according to the present invention, the switch unit has the switching element connected in series to the adjustment inductor between the adjustment inductor and one end of the inductor unit or the conductor pattern. It is preferable to provide a series type switch circuit arranged as described above.
According to the present invention, when a bias voltage that is forward with respect to the switching element is applied to the bias voltage input section, the impedance of the switching element is lowered, and the inductor section and one end of the conductor pattern are short-circuited. Thereby, the connection state between the inductor portion and one end of the conductor pattern is turned on with respect to the high-frequency signal. On the other hand, when a reverse bias voltage is applied to the switching element, since the impedance of the switching element is high, the inductor portion and one end of the conductor pattern are in an open state. Thereby, the connection state between the inductor section and one end of the conductor pattern is turned off with respect to the high-frequency signal. As described above, the connection state of the adjustment inductance is changed according to the voltage applied to the bias voltage input unit.

In the antenna device according to the present invention, it is preferable that the conductor pattern has a spiral shape wound in the longitudinal direction of the element body.
According to this invention, by making the conductor pattern into a spiral shape, the conductor pattern becomes longer and the gain of the antenna device can be increased.

In the antenna device according to the present invention, it is preferable that the conductor pattern has a meander shape formed on a surface of the element body.
According to the present invention, by making the conductor pattern a meander shape, the conductor pattern becomes longer and the gain of the antenna device can be improved. Further, the conductor pattern is easily formed by forming the conductor pattern on the surface of the element body.

  According to the antenna device of the present invention, by combining the loading unit and the inductor unit, the electrical length can satisfy ¼ of the antenna operating wavelength, and the antenna device can be significantly shortened. In addition, the switch unit can easily adjust the inductance of the frequency adjusting unit by selecting at least one of a plurality of adjusting inductors that can be connected in parallel and connecting one end of the conductor pattern and the inductor unit. . Thereby, since the electrical length in a frequency adjustment part changes, the resonant frequency of an antenna apparatus can be set. Therefore, by using an adjustment inductor having an appropriate inductance, it is possible to cover by adjusting the inductance of the frequency adjustment unit with the switch unit even when the bandwidth is wide, such as a broadcasting band of digital terrestrial broadcasting.

Hereinafter, an antenna device according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3.
The antenna device 1 according to the present embodiment is an antenna device used for, for example, a portable terminal capable of receiving terrestrial digital broadcasting.

  The antenna device 1 includes a substrate 2 made of an insulating material such as a resin, a rectangular ground conductor 3 formed on the surface of the substrate 2, and a parallel to the ground conductor 3 on the surface of the substrate 2. Arranged between the loading section 4 disposed, the inductor section 5 that can be connected to the base end of the loading section 4 and the other connected to the ground conductor 3, and between the one end of the loading section 4 and the inductor section 5. A frequency adjustment unit 6, a power supply unit 7 that supplies power to a connection point P <b> 1 between the inductor unit 5 and the frequency adjustment unit 6, and a power supply conductor 8 that connects the connection point P <b> 1 and the power supply unit 7 are provided.

The loading unit 4 includes a loading element 11 and lands 12 </ b> A and 12 </ b> B that are formed on the surface of the substrate 2 and place the loading element 11 on the substrate 2. And
The land 12 </ b> A and the frequency adjusting unit 6 are connected by the connecting conductor 13.
As shown in FIG. 2, the loading element 11 is a rectangular parallelepiped element body 14 made of a dielectric material such as alumina, and is wound around the surface of the element body 14 in a spiral shape with respect to the longitudinal direction of the element body 14. And a linear conductor pattern 15.
Both ends of the conductor pattern 15 are connected to connection conductors 16A and 16B formed on the back surface of the element body 14 so as to be connected to the lands 12A and 12B.

  The inductor unit 5 is a chip inductor that connects a ground connection pattern 17 that connects the frequency adjustment unit 6 and the ground conductor 3, and a dividing unit (not shown) that is formed in the ground connection pattern 17 and divides the ground connection pattern 17. 18.

  The frequency adjustment unit 6 selects at least one of the three adjustment chip inductors 21A to 21C that can be connected in parallel to each other and the adjustment chip inductors 21A to 21C, and connects one end of the conductor pattern 15 and the connection point P1. And a switch unit 22 to be connected.

As shown in FIG. 3, the switch unit 22 includes switch circuits 23A to 23C provided between the adjustment chip inductors (adjustment inductors) 21A to 21C and the connection point P1, respectively.
The switch circuit 23A is a so-called shunt type switch circuit, and includes a bias voltage input terminal (bias voltage input unit) 31A for applying a bias voltage to the connection point P2 shown in FIG. PIN diode (switching element) 33A, a bypass capacitor 34A for removing noise from bias voltage input terminal 31A, between connection point P2 and connection point P1, and between connection point P2 and adjustment chip inductor 21A. A DC block capacitor 35A that is provided and removes a direct current from the bias voltage input terminal 31A, and a high-frequency signal that is provided between the bias voltage input terminal 31A and the connection point P2 and flows to the adjustment chip inductor 21A is input with a bias voltage. RF block coil 36 for preventing backflow to terminal 31A When, is constituted by.

  When the bias voltage higher than the threshold value is applied to the bias voltage input terminal 31A, the switch circuit 23A lowers the impedance of the PIN diode 33A and becomes conductive, and the connection point P2 and the ground G are short-circuited. As a result, the high-frequency signal does not flow between the connection point P1 and the adjustment chip inductor 21A, resulting in a non-connection state. Further, when the bias voltage applied to the bias voltage input terminal 31A is equal to or lower than the threshold value, the impedance of the PIN diode 33A is high and non-conductive, so that the connection between the connection point P2 and the ground G is open. . As a result, a high frequency signal flows between the connection point P1 and the adjustment chip inductor 21A, and a connection state is established.

Similarly to the switch circuit 23A, the switch circuits 23B and 23C are bias voltage input terminals 31B and 31C, PIN diodes (switching elements) 33B and 33C, bypass capacitors 34B and 34C, and DC block capacitors 35B and 35C, respectively. And RF block coils 36B and 36C.
Similar to the switch circuit 42A, the switch circuits 23B and 23C are disconnected when a bias voltage higher than the threshold is applied to the bias voltage input terminals 31B and 31C, and are connected when the applied bias voltage is equal to or lower than the threshold. It is comprised so that.

  Then, by appropriately adjusting the bias voltage applied to the bias voltage input terminals 31A to 31C, the connection state of the three adjustment chip inductors 21A to 21C that can be connected in parallel changes, and the inductance in the frequency adjustment unit 6 is set. be able to. Here, assuming that the inductances of the adjustment chip inductors 21A to 21C are La to Lc, respectively, Leq of the inductor in the frequency adjustment unit 6 is expressed by the following equation. Here, SWn in the following equation is 1 when each of the adjustment chip inductors 21A to 21C is turned on, which is connected to the connection point P1, and is 0 when it is turned off, which is a non-connected state.

  In the frequency adjustment unit 6, if at least one of the adjustment chip inductors 21A to 21C is connected to the connection point P1, there are seven combinations among the adjustment chip inductors 21A to 21C. Then, by adjusting the inductance Leq of the frequency adjusting unit 6, the resonance frequency can be set by adjusting the electrical length of the antenna device 1.

  The power supply conductor 8 is a linear pattern that connects the frequency adjustment unit 6 and the power supply unit 7 connected to the high-frequency circuit RF.

  The loading unit 4 has a physical length shorter than ¼ of the antenna operating wavelength of the antenna device 1, so that the self-resonant frequency of the loading unit 4 is the antenna operating frequency of the antenna device 1. The higher frequency side. Accordingly, when the resonance frequency of the antenna device 1 is considered as a reference, the loading unit 4 cannot be said to be self-resonant, and thus has a different property from a helical antenna that self-resonates at the antenna operating frequency. Yes.

  Here, Table 1 shows values of the inductance Leq of the frequency adjusting unit 6 when the inductances of the adjustment chip inductors 21A to 21C are 100 nH, 68 nH, and 30 nH, respectively. Here, the connection states of the adjustment chip inductors 21 </ b> A to 21 </ b> C in the switch unit 22 are referred to as patterns 1 to 7 as shown in Table 1, respectively.

Further, the resonance frequency of the antenna device 1 in each connected state is as shown in FIG. As shown in FIG. 4, it can be seen that the resonance frequency of the antenna device 1 can be set from 470 MHz to 770 MHz, which is a broadcasting band of digital terrestrial broadcasting, by changing the connection state of the adjustment chip inductors 21A to 21C. .
FIG. 5 shows the VSWR (Voltage Standing Wave Ratio) characteristics of the antenna device 1. Here, the curves C1 to C7 shown in FIG. 5 indicate the VSWR characteristics in each connection state of the patterns 1 to 7 in Table 1. As shown in FIG. 5, it is possible to cover a wide frequency range from 470 MHz to 770 MHz without deteriorating impedance characteristics. Therefore, in digital terrestrial broadcasting, voltage is applied to the bias voltage input terminals 31A to 31C so that the resonance frequency of the antenna device 1 corresponds to the channel to be received, and the connection state of the adjustment chip inductors 21A to 21C is set. The broadcast of the desired channel is received.

In the antenna device 1 configured as described above, even if the electric length of the antenna element alone is shorter than ¼ of the antenna operating wavelength, the antenna operation can be performed as the entire electric length by combining the loading unit 4 and the chip inductor 5. Satisfies ¼ of the wavelength. Thereby, for example, even if the frequency is 470 MHz to 770 MHz, which is a broadcasting band of terrestrial digital broadcasting, the antenna device can be significantly shortened.
Further, the adjustment chip inductors 21 </ b> A to 21 </ b> C having a predetermined inductance are used, and the inductance in the frequency adjustment unit 6 shows seven values. As a result, even in a wide frequency band such as 470 MHz to 770 MHz, by controlling the voltage applied to the bias voltage input terminals 31A to 31C and appropriately changing the connection state of the adjustment chip inductors 21A to 21C, impedance Can cover without degrading the characteristics.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
For example, as shown in FIG. 6, the frequency adjustment unit 41 is configured by so-called series type switch circuits 42A to 42C provided between the adjustment chip inductors 21A to 21C and the connection point P1, respectively. 43 may be provided.
The switch circuit 42A includes a bias voltage input terminal 31 for applying a bias voltage to the connection point P2 shown in FIG. 6, a PIN diode 33A disposed between the connection point P2 and the connection point P3, a bypass capacitor 34A, a DC A block capacitor 35A and RF block coils 36A disposed between the bias voltage input terminal 31 and the connection point P2 and between the connection point P3 and the ground G are provided.

  When the bias voltage higher than the threshold value is applied to the bias voltage input terminal 31A, the switch circuit 42A decreases the impedance of the PIN diode 33A and short-circuits between the connection point P2 and the connection point P3. A high frequency signal flows between the point P1 and the adjustment chip inductor 21A, and the connection state is established. Further, when the bias voltage applied to the bias voltage input terminal 31A is equal to or lower than the threshold value, the impedance of the PIN diode 33A is high, so that the high frequency signal does not flow between the connection point P2 and the connection point P3. It is configured to be in a disconnected state.

Similarly to the switch circuit 42A, the switch circuits 42B and 42C are bias voltage input terminals 31B and 31C, PIN diodes 33B and 33C, bypass capacitors 34B and 34C, DC block capacitors 35B and 35C, and an RF block, respectively. The coils 36B and 36C are configured.
Similar to the switch circuit 42A, the switch circuits 42B and 43C are connected when a bias voltage higher than the threshold is applied to the bias voltage input terminals 31B and 31C, and are disconnected when the applied bias voltage is equal to or lower than the threshold. It is comprised so that it may be in a state.
Then, by appropriately adjusting the bias voltage applied to the bias voltage input terminals 31A to 31C, the connection state of the three adjustment chip inductors 21A to 21C that can be connected in parallel changes, and the inductance in the frequency adjustment unit 6 is set. be able to.
Note that the shunt-type switch circuit and the series-type switch circuit may be used in an appropriate combination for the switch unit. Further, a switch circuit having another configuration may be used.

In this embodiment, the antenna device is used for a portable terminal capable of receiving terrestrial digital broadcasting, but may be used for other wireless communication devices such as a cellular phone.
Further, although a PIN diode is used as the switching element, a MESFET (Metal Semiconductor Field Effect Transistor) or the like may be used.
Further, although alumina as a dielectric material is used as the element body, a magnetic material or a composite material having both a dielectric material and a magnetic material may be used.
In addition, the conductor pattern has a spiral shape wound on the surface of the element body, but may have a meander shape formed on the surface of the element body, or may have another shape.
Further, a dividing portion may be formed in the power supply conductor, and the dividing portion may be connected by a chip capacitor. Here, by appropriately setting the capacitance of the chip capacitor, it is possible to easily match the impedance in the power feeding unit. The impedance adjusting unit is not limited to the chip capacitor, and an inductor can be used.
Further, although three adjusting inductors are provided, two or four or more inductors may be provided.

It is a top view which shows typically the antenna apparatus in one Embodiment of this invention. It is a perspective view of the loading element in FIG. FIG. 2 is a schematic diagram showing an antenna device for explaining a switch unit in FIG. 1. It is a graph which shows the resonant frequency of the antenna apparatus with respect to the inductance of the frequency adjustment part in FIG. It is a graph which shows the VSWR characteristic of the antenna apparatus in each connection state of the frequency adjustment part in FIG. It is this schematic diagram which shows the antenna apparatus for demonstrating the switch part which can apply this invention except one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna apparatus 2 Board | substrate 3 Ground conductor 4 Loading part 5 Inductor part 6 Frequency adjustment part 7 Feeding part 8 Feeding conductor 14 Element body 15 Conductor patterns 21A-21C Adjustment chip inductor (Adjustment inductor)
22, 43 Switch units 23A to 23C, 42A to 42C Switch circuits 31A to 31C Bias voltage input terminal (bias voltage input unit)
33A-33C PIN diode (switching element)
P1 connection point

Claims (6)

A substrate,
A ground conductor formed on the surface of the substrate;
A loading part in which a linear conductor pattern is formed on an element body made of a composite material disposed on the substrate and having a dielectric material or a magnetic material or both;
An inductor connected between one end of the conductor pattern and the ground conductor;
In an antenna device comprising a feeding point that feeds one end of the inductor section,
A frequency adjustment unit is provided between one end of the conductor pattern and the inductor unit,
The frequency adjustment unit includes a plurality of adjustment inductors that can be connected in parallel to each other, and a switch unit that selects at least one of the plurality of adjustment inductors and connects one end of the conductor pattern to the inductor unit. An antenna device comprising: The switch unit has a bias voltage input unit connected to each of the plurality of adjustment inductors between one end of the conductor pattern and the inductor unit, and an impedance according to a voltage applied to the bias voltage input unit. A switching element that changes,
2. The antenna device according to claim 1, wherein a connection state between the adjustment inductor and the inductor section or one end of the conductor pattern is variable depending on a voltage applied to the bias voltage input section.   The antenna device according to claim 2, wherein the switch unit includes a shunt-type switch circuit in which the switching element is disposed between the adjustment inductor and a ground.   A series type switch circuit in which the switch unit is arranged such that the switching element is connected in series with the adjustment inductor between the adjustment inductor and one end of the inductor unit or the conductor pattern. The antenna device according to claim 2, further comprising:   5. The antenna device according to claim 1, wherein the conductor pattern has a spiral shape wound in a longitudinal direction of the element body. 6. 5. The antenna device according to claim 1, wherein the conductor pattern has a meander shape formed on a surface of the element body. 6.

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