JP4835572B2 - Tunable antenna - Google Patents

Description

  The present invention relates to a tuning antenna including an antenna element and a tuning circuit.

  Terrestrial digital television broadcasting is television broadcasting performed using a digital radio station on the ground (land). In Japan, the analog television broadcast (VHF 1-12ch), which began broadcasting in 1953, will be replaced with a digital system using only UHF channels (13-62ch in the 470-770 MHz band) in July 2011. Is scheduled.

  In terrestrial digital television broadcasting, a multi-channel OFDM (Orthogonal Frequency Modulation) system is used, and the carrier can be divided into 13 segments and different digital modulation can be performed for each segment.

  Computers such as ordinary TVs and desktop and laptop computers can store 4 channels in 3 segments. In HDTV, 12 segments are used, and the remaining 1 segment is used for data transmission. One-segment (for mobile phones and mobile terminals) 1 segment partial reception service). One-seg reception is intended for reception by mobile / mobile devices such as mobile phones, car navigation systems, PDAs (portable information communication terminals), and game machines.

  As an antenna for receiving such terrestrial digital television broadcasting, there are a monopole antenna and a conventional tuned antenna 41 as shown in FIG.

  In the tuning antenna 41, a variable capacitance diode (VCD) 43 is electrically connected to one end of the wave receiving element 42. VCD is also called a varicap diode or a variable capacitor. A DC (direct current) cut capacitor 44 is electrically connected to the VCD 43, and one end of an RF (high frequency) cut resistor 45 is electrically connected between the VCD 43 and the DC cut capacitor 44. One end of the frequency control power supply 47 is electrically connected to the power supply side terminal, which is the other end side, via the control voltage cable 46, and the other end side of the frequency control power supply 47 is grounded. A reception circuit 49 including an amplifier is electrically connected to the other end of the wave receiving element 42 via an RF output (received RF signal output) cable 48.

  In more detail, in the tuning antenna 41, as shown in FIG. 5, the receiving element 42 and each element are mounted on a printed circuit board (PCB) 51, and the control voltage terminal 52 connected to the RF cut resistor 45 is controlled. The voltage cable 46 is electrically connected, and the RF output cable 48 is electrically connected to the RF output terminal 53 of the wave receiving element 42.

  In this tuning antenna 41, the capacity of the VCD 43 is changed by the control voltage of the frequency control power supply 46, the tuning frequency is changed according to the frequency of the radio wave received by the wave receiving element 42, and the broadcast of the desired channel is received.

  The prior art document information related to the invention of this application includes the following.

Japanese Patent Laid-Open No. 10-173426 (tuned type, especially see FIG. 2) JP 2000-151448 (tuned type) Japanese Patent Laid-Open No. 2003-298341 (tuned type, especially see FIG. 3) JP 2006-345042 A (microcomputer control type)

  However, in the conventional tuned antenna 41, in order to receive a received signal, a total of two input / output terminals of the control voltage terminal 52 and the RF output terminal 53, and a total of the control voltage cable 46 and the RF output cable 48 are included. Two cables are required.

  Further, in the tuning antenna 41, when the receiving element 42 and the receiving circuit 49 are separated from each other, two cables must be routed at the same time. Therefore, both the cable cost and the assembly cost are high.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a tuning antenna that reduces the number of cables connected to an antenna element and reduces cable cost and assembly cost.

The present invention has been devised to achieve the above object, and the invention of claim 1 is a tuning antenna comprising an antenna element and a tuning circuit electrically connected to the antenna element.
An RF output signal line electrically connected to the first terminal of the antenna element on one end side and outputting a reception signal received by the antenna element;
A control voltage superimposing circuit that is electrically connected to the other end of the RF output signal line and superimposes a control voltage of a frequency control power source that controls the tuning circuit;
One end side is electrically connected to the second terminal of the antenna element, and the other end side is provided with a first DC cut capacitor grounded,
The tuning circuit is
Variable capacitance means electrically connected to the third terminal of the antenna element;
One end side is electrically connected to the other end of the variable capacitance means, and the other end side is connected to the capacitance adjusting capacitor,
One end side is electrically connected to a connection point between the variable capacitance means and the capacitance adjusting capacitor, and the other end side includes a grounding element that is grounded.
The received signal output from the connection point between the RF output signal line and the control voltage superimposing circuit is a tuned antenna that is input to DC cut means.

  A second aspect of the present invention is the tuning antenna according to the first aspect, wherein the DC cut means is a second DC cut capacitor or a DC cut element built in an amplifier.

According to a third aspect of the present invention, the variable capacitance means is a variable capacitance diode,
3. The tuned antenna according to claim 1, wherein the variable capacitance diode has a cathode connected to a third terminal of the antenna element and an anode connected to the capacitance adjusting capacitor.

According to a fourth aspect of the present invention, in the tuning antenna according to any one of the first to third aspects, the grounding element is a resistor or an inductor.

The invention of claim 5 is a tunable antenna according to claim 1 or 2 wherein the M EMS variable capacitance.

  According to the present invention, the number of cables connected to the antenna element can be reduced, and the cable cost and the assembly cost can be reduced.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a circuit diagram of a tuning antenna showing a preferred embodiment of the present invention, and FIG. 2 is a schematic plan view thereof.

  As shown in FIG. 1 and FIG. 2, the tunable antenna 1 according to the present embodiment mainly receives terrestrial digital television broadcasts. For example, a computer such as a desktop or laptop computer, a mobile phone, It is mounted (built in) and used in mobile / mobile devices such as car navigation systems, PDAs, and game machines. In addition, the tuning antenna 1 may be used as a tunable receiving antenna.

  As shown in FIG. 6 (an example of a general monopole antenna), a tuning antenna used in terrestrial digital television broadcasting needs to maintain reception characteristics in a wide band of 470 to 770 MHz. For this reason, when receiving a broadcast of a desired channel, it is important to reduce the variation of the tuning frequency to prevent the reception characteristics from being deteriorated.

  The present inventors completed the present invention as a result of diligent research in consideration of the above points.

  Now, the tuning antenna 1 according to the present embodiment includes a wave receiving element 2 as an antenna element and a tuning circuit 3. The wave receiving element 2 is formed of a conductive metal plate such as Cu or Al, or a microstrip line provided on a printed circuit board. The variable capacitance means 4 is electrically connected to the wave receiving element 2. In this embodiment, a VCD is used as the variable capacitance means 4.

  In the present embodiment, an antenna element in which a metal plate is formed in an approximately F shape in plan view is used as the wave receiving element 2. The wave receiving element 2 includes an elongated third terminal (receiving unit) 2r, a second terminal (grounding unit) 2e that protrudes laterally from one end of the third terminal 2r, and whose tip is grounded, and a side of the third terminal 2r The first terminal (feeding unit) 2d protrudes from the end along the second terminal 2e and receives radio waves. A receiving circuit 49 including an amplifier is electrically connected to the tip of the first terminal 2d via an RF output (receiving RF signal output) signal line 5 that outputs a receiving signal. As the RF output signal line 5, a thin coaxial cable or a wiring pattern provided on the printed circuit board 21 is used.

  The cathode of the variable capacitor means 4 is electrically connected in series to the other end of the third terminal 2r of the wave receiving element 2. One end of a capacitance adjustment capacitor (first DC cut capacitor) 6 is electrically connected in series to the anode of the variable capacitance means 4 and the other end of the capacitance adjustment capacitor 6 is grounded (ground (GND) connection). The

  Thus, by connecting the capacitance adjusting capacitor 6 in series to the variable capacitance means 4, the capacitance value (variable width) of the variable capacitance means 4 can be adjusted.

  In the present embodiment, a capacitance adjusting capacitor 6 having a capacitance value of 5 pF is connected in series to the variable capacitance means 4 (capacitance value 1 to 4.5 pF). As a result, the capacitance value (variable width) of the variable capacitance means 4 could be adjusted to 0.8 to 2.4 pF. Thus, by reducing the capacitance value of the variable capacitance means 4, the inductance of the antenna element can be increased, the gain can be increased, and the reception sensitivity of the antenna can be improved.

  Between the variable capacitance means 4 and the capacitance adjusting capacitor 6, the receiving element side terminal r of the grounding element 7 is electrically connected in parallel, and the opposite terminal is grounded. For grounding, a ground portion such as a ground wiring pattern or a ground layer provided on the printed circuit board 21 is used.

  In this embodiment, a chip capacitor is used as the capacitance adjusting capacitor 6, and the capacitance value is 5 pF. Further, as the grounding element 7, a resistor is used to stably operate the tuning antenna 1 in a high frequency band. A chip resistor was used as this resistor, and the resistance value was set to 100 kΩ.

  The variable capacitance means 4, the capacitance adjusting capacitor 6, and the grounding element 7 constitute a tuning circuit 3 that changes the tuning frequency according to the frequency of the radio wave received by the wave receiving element 2.

  Between the RF output signal line 5 and the receiving circuit 49, a frequency control power source 8 as a variable DC power source for controlling the tuning circuit 3 is electrically connected in parallel. This frequency control power supply 8 is for applying a frequency control voltage to the variable capacitance means 4 as a positive voltage.

  The range of the frequency control voltage of the frequency control power supply 8 is about 0 to 6 V in the case of terrestrial digital television broadcasting. Further, the electrostatic capacity of the variable capacitance means 4 changes in the range of about 1.0 to 4.5 pF by this frequency control voltage.

  Further, a control voltage superposition circuit 9 made of an inductor (inductance 270 nH) is electrically connected in series between the frequency control power supply 8 and the RF output signal line 5. Between the RF output signal line 5 and the receiving circuit 49, the receiving circuit 49 side is closer to the receiving circuit 49 than the connection point j between the control voltage superimposing circuit 9 and a receiving side DC cutting capacitor (second DC cutting capacitor). 10b is electrically connected in series. The capacitance value of the receiving side DC cut capacitor 10b was set to 1000 pF.

  The tuning antenna 1 according to this embodiment is characterized in that a frequency control voltage of a frequency control power supply 8 that controls the tuning circuit 3 is superimposed on an RF output signal line 5 that outputs a reception signal.

  In addition, one end of a DC cut capacitor (first DC cut capacitor) 10a for applying a frequency control voltage to the tuning circuit 3 is electrically connected to the ground portion 2e of the wave receiving element 2, and the DC cut capacitor The other end of the capacitor 10a is grounded. A chip capacitor was also used as the DC cut capacitor 10a, and its capacitance value was set to 1000 pF.

  The operation of this embodiment will be described.

  In the tuning antenna 1, the capacity of the variable capacity means 4 is changed by superimposing the frequency control voltage of the frequency control power supply 8 on the RF output signal line 5, and according to the frequency of the radio wave received by the wave receiving element 2. The tuning frequency is changed to receive a broadcast of a desired channel. The frequency of the radio wave received by the wave receiving element 2 is transmitted as a received signal from the first terminal 2d to the receiving circuit 49.

  As described above, the tuning antenna 1 outputs a signal from the RF output signal line 5 electrically connected to the wave receiving element 2, while controlling the frequency to the variable capacitance means 4 via the RF output signal line 5. A voltage is applied.

  Therefore, in the tuning antenna 1, the RF output signal line 5 can be used for reception and control voltage superposition, and the control voltage terminal and the control voltage cable, which are conventionally required, are unnecessary.

  Further, the tuning antenna 1 need only route one of the RF output signal lines 5 even when the receiving element 2 and the receiving circuit are separated from each other.

  Therefore, according to the tuning antenna 1, the number of cables connected to the wave receiving element 2 and terminals for connection are reduced, the wiring pattern length can be shortened, and both the cable cost and the assembly cost can be reduced.

  Further, since the tuning antenna 1 is electrically connected with a control voltage superposition circuit 9 made of an inductor between the frequency control power supply 8 and the RF output signal line 5, the frequency control voltage is applied to the RF output signal line 5. Can be easily superimposed.

  Further, in the tuning antenna 1, the tuning circuit 3 is composed of a variable capacitance means 4, a capacitance adjusting capacitor 6, and a grounding element 7. One end of the capacitance adjusting capacitor 6 and one end of the grounding element 7 are both connected. Connected to ground.

  For this reason, in the tuning antenna 1, the electric charge that easily accumulates between the variable capacitance means 4 and the capacitance adjusting capacitor 6 and destabilizes the tuning frequency is released to the ground by the grounding element 7. It is possible to control the tuning frequency. When there is no grounding element 7 as in the conventional tuned antenna, there is no line for escaping the electric charge accumulated between the variable capacitance means 4 and the capacitance adjusting capacitor 6 to the outside. For this reason, the frequency control voltage applied to the variable capacitor means 4 becomes unstable under the influence of the electric charge, and therefore the tuning frequency control becomes unstable.

  In addition, since the tuning antenna 1 has the DC cut capacitor 10a electrically connected to the second terminal 2e of the receiving element 2, the frequency control voltage is surely applied not to the second terminal 2e but to the variable capacitance means 4. Can be applied.

  The frequency control voltage applied from the frequency control power supply 8 via the first terminal 2d is prevented from being applied to the second terminal 2e side by the DC cut capacitor 10a, and a predetermined frequency control voltage is applied to the variable capacitance means 4. This is because is applied.

  Further, as shown in FIG. 1, a receiving side DC cut capacitor 10b is further electrically connected between the RF output signal line 5 and the receiving circuit 49 on the receiving circuit 49 side from the connection point j with the control voltage superimposing circuit 9. Thus, if they are connected in series, the frequency control voltage can be applied more reliably to the variable capacitance means 4 rather than to the receiving circuit 49 side.

  The frequency control voltage from the frequency control power supply 8 is prevented from being applied to the receiving circuit 49 side by the receiving side DC cut capacitor 10b, and a predetermined frequency control voltage is applied to the first terminal 2d. It is. Further, for the same reason as described above, a predetermined frequency control voltage is applied to the variable capacitance means 4 by the DC cut capacitor 10a.

  As the DC cut means, the above effect can be obtained even if an amplifier including a receiving DC cut element (for example, a capacitor, a high-pass filter, etc.) is used instead of the receiving side DC cut capacitor 10b. In the example of FIG. 1, an amplifier incorporating this DC cut element can be used as the receiving circuit 49.

  In order to mount the tuning antenna 1 in the above-described computer or mobile / mobile device, for example, as shown in FIG. 2, a printed circuit board 21 is placed in a case (housing) 23 at a predetermined distance from one end thereof. In addition to mounting, the tuning antenna 1 may be mounted at one end.

  Further, when a thin coaxial cable is used as the RF output signal line 5, an RF output terminal (received RF signal output terminal) 22 is formed on the first terminal 2d of the wave receiving element 2, and the RF output terminal. The central conductor of the coaxial cable is electrically connected to 22 and the external conductor is electrically connected to the ground portion.

  In the above-described embodiment, an example in which a VCD is used as the variable capacitor unit 4 has been described. However, a MEMS (Micro Electro Mechanical System) variable capacitor may be used as the variable capacitor unit 4.

  In particular, unlike the VCD, the MEMS variable capacitor can be used not only as a reception antenna but also as a transmission antenna by configuring the tunable antenna 1 according to the present embodiment using the MEMS variable capacitor.

  This is because a VCD made of a semiconductor material is a non-linear device, and thus causes waveform distortion when used at a relatively large power (0 dBm = 1 mW) or more. In the case of a receiving antenna, a large amount of power is not input, but in the case of a transmitting antenna, a large amount of power amplified by a power amplifier is input, so that it is difficult to use. However, if it is a MEMS variable capacitance, since it is a linear device which changes a capacity | capacitance by the mechanical fluctuation | variation of a parallel plate without using a semiconductor material, it will not cause waveform distortion. Therefore, it can also be used as an antenna for transmission.

  Further, as the grounding element 7, an inductor (for example, an inductance of 270 nH) may be used as long as the tuning frequency is relatively high (400 MHz or higher) and the frequency control does not become unstable.

  As the control voltage superimposing circuit 9, in addition to a single inductor, a series circuit or parallel circuit of an inductor and a resistor may be used.

  Next, an example in which the tuning antenna 1 is used for a mobile phone will be described. Here, since the tuning antenna 1 is used as a transmission / reception antenna, a MEMS variable capacitor is used as the variable capacitor means 4.

  As shown in FIG. 3A and FIG. 3B, the mobile phone 31 includes a case 32 that is provided so as to be opened and closed in half by a rotating means such as a hinge.

  The case 32 has a battery side case 32a containing a battery that is also used as the frequency control power supply 8 (see FIG. 1), and a liquid crystal display (LCD) is housed on the battery side case 32a side. On the opposite side, in the same manner as in FIG. 2, the printed circuit board 21 and the LCD side case 32b in which the tuning antenna is housed, and the back cover that covers the housed printed circuit board 21 and the tuning antenna and is attached to the LCD side case 32b. 32c. The tunable antenna receiving element 2 also operates as a radiating element as an antenna element in the case of transmission.

  The printed circuit board 21 includes a CPU 33 electrically connected to the battery, a tuner 34 that is independently connected to the CPU 33, a transmission circuit 35, and a reception unit (a transmission unit in the case of a radiation element) of the wave receiving element 2. A transmission / reception switch (SW) 36 that is electrically connected independently and switches between the tuner 34 and the transmission circuit 35 by a switching signal from the CPU 33 is mounted.

  The tuner 34 includes a receiving amplifier, a high-frequency circuit, a demodulator, and the like that are generally necessary for receiving radio waves, excluding the tuning circuit. The transmission circuit 35 includes a frequency generator, a transmission amplifier, a modulator, a power amplifier, and the like that are generally necessary for transmitting radio waves.

  In the mobile phone 31, when receiving a one-segment broadcast, if a desired channel is selected by operating a button, the CPU 33 outputs a switching signal to the SW 36 via the tuner 34, and the SW 36 switches to the receiving circuit.

  On the other hand, the CPU 33 outputs a control signal corresponding to the tuning frequency of the selected channel to the frequency control power supply 8 (see FIG. 1) of the tuning antenna 1 via the tuner 34, and the frequency control power supply 8 selects the selected channel. A corresponding constant frequency control voltage is applied to the variable capacitance means 4 (see FIG. 1) via the RF output signal line 5.

  The radio wave received by the wave receiving element 2 is input as a received signal from the first terminal 2d to the tuner 34 via the SW 36, and then an image is displayed on the LCD. When transmitting a radio wave, the transmission signal is radiated as a radio wave from the wave receiving element 2 through the transmission circuit 35, the SW 36, and the first terminal 2d that operates as a power feeding unit.

  Thus, if the tunable antenna 1 is used, unlike the conventional case, the hardware on the antenna module side does not need to be changed, and a low-cost mobile phone 31 can be realized.

  In addition, if the tuning antenna 1 is mounted on an electric device such as a notebook personal computer having severe space restrictions, the total length of the cable to be used can be significantly shortened compared to the conventional case, which is particularly effective.

1 is a circuit diagram of a tuning antenna showing a preferred embodiment of the present invention. FIG. 2 is a schematic plan view of the tuning antenna shown in FIG. 1. 3A is a plan view showing a mounting example of the tuning antenna shown in FIG. 1, and FIG. 3B is a perspective view of the back surface of the printed circuit board. It is a circuit diagram of the conventional tuning type antenna. It is the plane schematic diagram of the conventional tuning type antenna. It is a figure which shows the antenna gain characteristic of a common monopole antenna in Japanese terrestrial digital television broadcasting.

Explanation of symbols

1 Tunable antenna 2 Receiving element (antenna element)
2d 1st terminal 2e 2nd terminal 2r 3rd terminal 3 Tuning circuit 4 Variable capacity means (example of VCD)
5 RF output signal line 6 Capacitance adjustment capacitor 8 Frequency control power supply 9 Control voltage superimposing circuit 10a DC cut capacitor (first DC cut capacitor)
10b Receiving side DC cut capacitor (DC cut means: second DC cut capacitor)

Claims (5)

In a tuning antenna comprising an antenna element and a tuning circuit electrically connected to the antenna element,
An RF output signal line electrically connected to the first terminal of the antenna element on one end side and outputting a reception signal received by the antenna element;
A control voltage superimposing circuit that is electrically connected to the other end of the RF output signal line and superimposes a control voltage of a frequency control power source that controls the tuning circuit;
One end side is electrically connected to the second terminal of the antenna element, and the other end side is provided with a first DC cut capacitor grounded,
The tuning circuit is
Variable capacitance means electrically connected to the third terminal of the antenna element;
One end side is electrically connected to the other end of the variable capacitance means, and the other end side is connected to the capacitance adjusting capacitor,
One end side is electrically connected to a connection point between the variable capacitance means and the capacitance adjusting capacitor, and the other end side includes a grounding element that is grounded.
The tuning antenna according to claim 1, wherein the reception signal output from a connection point between the RF output signal line and the control voltage superimposing circuit is input to a DC cut means.   2. The tuned antenna according to claim 1, wherein the DC cut means is a DC cut element built in a second DC cut capacitor or an amplifier. The variable capacitance means is a variable capacitance diode,
The tuning antenna according to claim 1 or 2, wherein a cathode of the variable capacitance diode is connected to a third terminal of the antenna element, and an anode is connected to the capacitance adjusting capacitor. The tuned antenna according to claim 1, wherein the grounding element is a resistor or an inductor. The tuning antenna according to claim 1 or 2 , wherein the variable capacitance means is a M EMS variable capacitance.

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