JPH09130132A - Small-sized antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the small-sized antenna for FM teletext broadcasting receiver based on a portable information terminal device where problems on tuning and matching accompanied with miniaturization of a dipole antenna are resolved to eliminate restrictions on the use place, anxiety about accidents, trouble on design, unnecessary functions, etc. SOLUTION: A reduction dipole antenna consists of an antenna element 31, loading coils 321 and 322, a varactor diode 33, a DC cut capacitor 34, a matching capacitor 35, a feed point 36, and a varactor diode application voltage terminal 37, and one loading coil 322 out of divided loading coils and the varactor diode are connected in parallel to constitute a parallel circuit, and the apparent reactance on the parallel circuit side is changed by the capacitance variance of the varactor diode on the market, and a reception voltage detection part 4 and a tuning control circuit part 5 are used together to automatically perform tuning in the FM frequency band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small antenna for an FM broadcast receiver having a function of automatically tuning the frequency of an antenna, and more particularly to a display section of a portable information terminal device such as an electronic notebook or a handy terminal. F to display characters
The present invention relates to a small antenna for an M character multiplex broadcasting receiver.

[0002]

2. Description of the Related Art The antenna of a small portable FM broadcast receiver is usually housed in the receiver, and a rod type antenna which is extended from the main body of the receiver when used is generally used. In recent years, an FM receiver using an earphone type antenna that also serves as an antenna for a connection cable of an earphone or a headphone has been commercialized for convenience of carrying. The cable length of the earphones and headphones is about 1 m, and in consideration of the convenience of carrying the earphones and headphones when not in use, the cables are wound and stored in a reel case or wound in the receiver body. There is also a storage type.

On the other hand, a receiver incorporating the rod type antenna has a good receiving sensitivity, and therefore, when used, it is extended from the main body of the receiver and the length of the antenna at this time is extended up to about 70 to 90 cm. There are also things.
The most recently commercialized FM text multiplex receiver antenna is the same as the existing FM broadcast receiver (pocket radio).
It is similar to the antenna.

[0004]

In recent years, the FM multiplex broadcasting service has been started. In this broadcasting, text information is multiplexed with ordinary FM broadcasting to provide news, weather information, traffic information, and so on.
It is designed to serve program information and the like, and FM character multiplex broadcast receivers for receiving this broadcast have been prototyped by various companies, and some of them have already been commercialized.

Further, in order to popularize FM character multiplex broadcasting in the future, receivers for receiving this broadcasting are portable type, stationary type, car stereo type, personal computer tuner board type, etc.
Various types are being considered. Of these, at least the following two types are conceivable especially for portable types.

One of them is a portable receiver type dedicated to FM character multiplex broadcasting similar to the conventional portable FM broadcasting receiver, and this type is based on a portable FM broadcasting receiver and demodulates character information. Both the FM voice broadcasting and the character multiplex broadcasting can be performed by adding a decoder circuit for
It is a type that can be received by one device.

The other is to use portable information terminal equipment such as electronic notebooks and handy terminals which have been rapidly spread in recent years, and an FM character multiplex broadcasting receiver is externally provided or built in the portable information terminal equipment. It is the type that was made.
The type based on the portable information terminal basically receives only FM text multiplex broadcasting, and the received text information such as news, weather information, traffic information, program information, etc. is received by the portable information terminal. The display is provided on the device so that it can be visually displayed.

The type based on a portable information terminal device is generally placed on a desk or a knee, or is often held in a hand for operation. Therefore, for receiving FM character multiplex broadcasting. In the type that uses a rod-type antenna, a rigid antenna must be extended and used for a long time, and not only does it look smart, but it also has problems such as poor operability in narrow places and portability. Had. In order to solve this problem, it is possible to change to an earphone type antenna composed of a flexible cord, but even in the earphone type antenna, it is necessary to extend the antenna cord when using, so the cord is It is entangled or twisted, and as a result, the reception sensitivity is lowered, or it has an unnecessary function for listening to voice, and is not suitable for use only as an antenna.

Therefore, at present, there is a strong demand for the development of a highly sensitive small antenna, and preferably a small antenna which can be incorporated therein, which eliminates the above problems. On the other hand, a small antenna generally has a small input resistance, which is the real part of the antenna input impedance, and therefore has a high Q of the antenna, and has a problem of a frequency bandwidth such as a narrow bandwidth when viewed from the impedance matching bandwidth. There is.

With respect to the above problem, in view of the sudden increase in mismatch loss, the receiving gain is lowered and the receiving sensitivity is deteriorated unless some measure for tuning and matching is taken. Generally, in order to miniaturize a dipole antenna, a loading coil (loading coil) is arranged at any of the top, middle, and root of the antenna element so that it can be tuned at a desired frequency to form a shortened dipole antenna. A smaller and shorter coil requires a loading coil with a larger inductance.

Further, the loading coil having a large inductance has a large number of coil turns, and as a result, the antenna becomes long and the loss resistance increases. When the loss resistance increases, the electric power received by the antenna element is lost by the resistance and the reception sensitivity deteriorates.

The frequency band of FM broadcasting is 76 to 90 MHz in Japan, and in order to receive the desired frequency during this period, the value of the loading coil must be adjusted for tuning. Generally, in order to adjust the value of the loading coil, a variable capacitor is connected in series or in parallel to perform the adjustment. To make the adjustment electronically,
A variable capacitance diode is used instead of the variable capacitor. However, from the viewpoint of manufacturing cost, the capacitance value of the variable capacitance diode which is currently commercially available and can be used is several pF to several tens pF for an applied voltage of several volts, that is, 1 in the FM frequency band.
It is about 0 to 100 ohms.

On the other hand, the desired value of the above-mentioned loading coil is 10 to 15 cm for the antenna element length in the FM frequency band.
Since it is about several thousand ohms, the conventional general tuning method cannot cover the FM frequency band because the variable value of the variable capacitor or the variable capacitance diode is small.

As described above, if the dipole antenna is downsized, it is necessary to add a tuning circuit, and it is difficult to adjust the loading coil even if tuning means is added. As a result, broadband rod-type antennas and earphone-type antennas have been conventionally used.

An object of the present invention is to eliminate the tuning and matching problematic adjustment that accompanies the miniaturization of dipole antennas.
FM character multiplex broadcasting based on portable information terminal devices without problems of rod type antennas and earphone type antennas, that is, restrictions on places of use, concerns about accidents, design inconvenience, functional waste, etc. It is to provide a small antenna for a receiver.

[0016]

In order to solve the above-mentioned problems, in the present invention, a loading coil composed of a ferrite material as a core material is used as a loading coil of a shortened dipole antenna, and this loading coil is divided into two. Then, one of the divided loading coils and the variable capacitance diode are connected in parallel to form a tuning loading coil.

Further, the received voltage detection circuit and the automatic tuning control circuit adjust the applied voltage of the variable capacitance diode to automatically perform frequency tuning, thereby providing an antenna having a small structure which can be built in the housing.

[0018]

In the shortened dipole antenna configured as described above, the size can be reduced by 1/10 to 1/20 as compared with the normal dipole antenna (length: about 1.8 m), and therefore the device housing. It is possible to provide a small antenna for an FM teletext broadcast receiver based on a portable information terminal device that can be built in.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram for explaining the structural principle of the shortened dipole antenna of the present invention.

The shortened dipole antenna of the present invention comprises an antenna element 31, loading coils 321, 322,
It is composed of a variable capacitance diode 33, a DC blocking capacitor 34, a matching capacitor 35, a feeding point 36, and a variable capacitance diode applied voltage terminal 37.

The antenna element 31 need not be limited to a rectangular element as shown in FIG. 1, and even if it is a round bar-shaped element, its shape is not limited as long as it has a short length. In addition, the material is formed of a good conductor such as copper, aluminum, or silver, which is suitable as an antenna element. Since the loading coils 321 and 322 are required to have high inductance matching the impedance of the antenna element, a ferrite material is used as the core material. Further, as the ferrite material, a material having a low loss at a desired frequency is used so as not to lower the Q of the antenna.

Due to recent advances in material technology, for example, 9 ×
By winding a conductor wire having a diameter of about 1 mm around 8 to 10 turns around a commercially available prismatic ferrite material having a size of about 5 × 20 mm, a low loss inductance (1
000-1500 ohms) is easily obtained.

The loading coils 321 and 322 are divided into two, as will be described later, and each coil may be formed of the same ferrite material or separate ferrite materials. The variable capacitance diode 33 has a terminal 3
It is a diode whose capacitance value changes according to the voltage applied from 7, and is connected in parallel with the loading coil 322 to form a tuning circuit. The DC blocking capacitor 34 is a capacitor provided for the purpose of blocking the DC voltage and conducting the high frequency component so that the DC voltage can be properly applied to the variable capacitance diode 33. The matching capacitor 35 is a capacitor for matching with the receiving circuit section after the feeding point 36. The receiving circuit section is connected at the feeding point 36, and the variable capacitance diode applied voltage terminal 37 is connected to the tuning control circuit section described later.

The operation of the tuning circuit portion (mainly the loading coils 321, 322 and the variable capacitance diode 33) of the shortened dipole antenna having the above-mentioned structure will be described below. When configuring a shortened dipole antenna using a short antenna element, a loading coil having an inductance matching the impedance of the antenna element is required. In this case, the inductance value required for the loading coil is very large, and the conventional tuning method for a shortened dipole antenna using a relatively long antenna element, that is, for the entire loading coil without dividing the loading coil is used. With a method of connecting a variable capacitor or variable capacitance diode in series or in parallel with each other, sufficient tuning adjustment cannot be performed because the amount of capacitance change of the variable capacitor or variable capacitance diode is small, and the number of windings and length of the loading coil are mechanically adjusted. It is
It was necessary to change the size and shape.

According to the present invention, the loading coil 321
322 is divided into two, and one of the divided loading coils 322 and the variable capacitance diode are connected in parallel to form a parallel circuit. It is possible to perform tuning in the FM frequency band by changing the apparent reactance of a parallel circuit composed of the a-b or cd loading coil 322 and the variable capacitance diode.

The following is a specific description using numerical values. If the reactance component of the impedance of the short antenna element is -j2000 [Ω] at a frequency of 80 MHz, the required inductance value of the loading coil is + j200.
Since it is 0 [Ω] and two sets of loading coils 321 and 322 are arranged around the feeding point 36 in FIG. 1, the inductance value of each of the loading coils 321 and 322 is + j1000 [Ω].

Here, the applied voltage is 1 to 5 V and 20 to
If an FM tuner electronic tuning variable capacitance diode with a large capacitance change ratio of about 50 pF is used at a frequency of 80 MHz, the reactance change amount of this diode is -j4.
It is 0 [Ω] to −j100 [Ω].

In consideration of this, for example, the inductance value of the loading coil 322 is + j120 [Ω], and the inductance value of the loading coil 321 is + j1.
When 330 [Ω] is selected, the apparent reactance value when the parallel circuit side of the loading coil 322 and the variable capacitance diode is viewed from ab or cd of FIG. 1 is the reactance change amount of the variable capacitance diode 33: − j40 [Ω] ~
Corresponding to -j100 [Ω], -j60 [Ω] to -j60
Changes to 0 [Ω] and loading coils 321 and 322
The amount of change of the loading coil including the variable capacitance diode 33 is 540 [Ω] of + j730 [Ω] to + j1270 [Ω].

This is the change amount of a set of loading coils, which is doubled to 1080 [Ω] as a whole. Converting this amount of change into a change in frequency, approximately 71 [MHz]
.About.94 [MHz], which can sufficiently cover the FM broadcast frequency band. On the other hand, when the same value is applied to the conventional method, that is, the method of connecting the variable capacitance diode in series to the entire loading coil without dividing the loading coil, the reactance change amount of the variable capacitance diode is −j40. Corresponding to [Ω] to −j100 [Ω], the frequency changes only about 2 [MHz], and F
It cannot cover the M broadcast frequency band.

Next, an example of means and method for automatically tuning using the shortened dipole antenna of the present invention is shown in FIG.
It will be described based on. FIG. 2 is a block circuit diagram for explaining the operation relating to the tuning method of the shortened dipole antenna of the present invention.

A circuit for automatically tuning using the shortened dipole antenna of the present invention is roughly classified into a shortened dipole antenna 3, a reception voltage detection unit 4, and a tuning control circuit unit 5.
Consists of The reception voltage detection unit 4 is a circuit that converts a high frequency voltage of the FM broadcast reception frequency output from the feeding point 36 of the shortened dipole antenna 3 into a DC voltage, which is substantially proportional to the intensity (magnitude of amplitude) of the high frequency voltage. It is a circuit in which the amplitude of the DC voltage changes.

This circuit is already installed as an S meter output terminal in the front end portion which is the first-stage integrated circuit of the FM broadcast receiver currently in use. If this S-meter output terminal is not provided in the front end, an RSSI circuit (DC voltage corresponding to the input high frequency voltage) is added with the output from the AGC (automatic gain control) terminal or IF (intermediate frequency output) terminal. Can be used to perform the same function as the S meter output terminal.

For example, when a DC voltage is applied to the variable capacitance diode 33 so that the shortened dipole antenna 3 is tuned at a desired frequency (f), the reception frequency and the output value of the reception voltage detection unit 4 The relationship is as shown in FIG. FIG. 3 is an explanatory diagram showing the relationship between the reception frequency and the output value of the reception voltage detection unit during tuning.

As is clear from this figure, if the tuning frequency of the shortened dipole antenna 3 and the received frequency match, the output voltage output from the feeding point of the shortened dipole antenna 3 becomes maximum, and accordingly, the output voltage becomes maximum. The output value of the reception voltage detector also becomes maximum as shown in FIG.

The tuning control circuit section 5 is a circuit which judges the voltage output from the reception voltage detection section 4 and supplies a required voltage to the variable capacitance diode applied voltage terminal 37. An example of the tuning control circuit unit is shown in FIG. This circuit is an A / A for converting the analog voltage output from the reception voltage detection unit 4 into a pulsed digital voltage that is easily processed by the CPU 52.
It can be configured by a D converter 51, a CPU 52, and a D / A converter 53 for converting a digital voltage output from the CPU 52 into an analog voltage which is a variable capacitance diode applied voltage.

The tuning control circuit section 5 thus configured
Receives the output voltage from the reception voltage detector 4 and receives the CPU 5
In step 2, the D / A converter 5 performs processing according to a program written in the CPU 52 and the peripheral memory, such as whether this voltage is a certain voltage or more or is the maximum value.
It is possible to output the required voltage through 3.

The reception voltage detection unit 4 and the tuning control circuit unit 5 described above are examples of the present invention, and other circuits may be used as long as they have the same function. next,
An example of automatic tuning will be described below. For example, with a variable capacitance diode applied voltage of 1 [V], 76 [MH
z], 2 [V] to 80 [MHz], and 5 [V]
It is assumed that the shortened dipole antenna 3 is configured so as to tune to 90 [MHz].

On the other hand, it is assumed that the radio tuner selects 80 [MHz]. Here, the CPU 52 outputs a digital signal to the D / A converter 53 so that the D / A converter 53 outputs a voltage of 1 [V], and the digital signal is output to the cathode end of the variable capacitance diode 33 configured in the shortened dipole antenna 3. A voltage of 1 [V] is applied through the applied voltage terminal 37. In this case, the output voltage at the feeding point 36 shown in FIG.
It becomes the maximum at 6 [MHz], but the reception tuning frequency is 80 [M
[Hz], the output voltage is low as shown in the example of FIG. 2, and the voltage output from the reception voltage detection unit 4 is also low. This voltage is sent to the CPU 5 through the A / D converter 51.
Processing is performed in 2 and the read value is stored in the memory.

Next, the CPU 52 uses the D / A converter 53.
From O.I. The variable capacitance diode 3 of the shortened dipole antenna 3 outputs a digital signal to the D / A converter 53 so as to output a voltage of 1.1 [V] which is increased by 1 [V].
3 through the applied voltage terminal 37 to the cathode end of 3
The voltage of [V] is applied, and the output voltage of the reception voltage detection unit 4 at this time is similarly read. Thereafter, the CPU 52 is sequentially processed in the same manner.
The output voltage of the reception voltage detector 4 with respect to the output voltage is read to determine the maximum value.

When it is determined that the maximum voltage, for example, the tuning voltage 2 [V] of 80 [MHz] is the maximum value, the CPU 52 operates automatically so as to apply this voltage to the variable capacitance diode applying voltage terminal 37. The tuning operation will be performed. The operation method described above is an example of a method of automatically tuning using the shortened dipole antenna of the present invention. For example, the frequency characteristic of the antenna is stored in the CPU in advance, and the direct characteristic is selected according to the selected frequency. Various methods such as a method of setting a variable capacitance diode applied voltage to a nearby voltage and searching only a narrow range and a method of searching a maximum value by a three-point comparison method are taken, but in order to realize the object of the present invention. Any method may be used, and the method is not particularly limited to the examples of the present invention.

The tuning control circuit section described above, particularly the CPU
The unit is a circuit unit included in the portable information terminal device, and by using this together, it is possible to realize a desired antenna without the need to add a new circuit for the shortened dipole antenna of the present invention. This is one of the important advantages of the present invention.

[0042]

As described in detail above, according to the present invention, a small antenna that can be built in the housing of the device is constructed, and the decrease in the antenna gain due to this is prevented to the minimum, and the portable information terminal device is provided. There is an excellent effect that it is possible to provide a small antenna for an FM teletext broadcast receiver capable of automatic tuning by effectively utilizing the CPU in the inside and the circuit part such as the reception voltage detecting part in the receiving part.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining a structural principle of a shortened dipole antenna of the present invention.

FIG. 2 is a block circuit diagram for explaining an operation relating to a tuning method for a shortened dipole antenna of the present invention.

FIG. 3 is an explanatory diagram for explaining a relationship between a reception frequency and an output value of a reception voltage detection unit at the time of tuning.

[Explanation of symbols]

 1 Portable Information Terminal Equipment 2 FM Character Multiplex Broadcasting Receiver 3 Shortened Dipole Antenna 4 Reception Voltage Detector 5 Tuning Control Circuit 31 Antenna Element 33 Variable Capacitance Diode 34 DC Blocking Capacitor 35 Matching Capacitor 36 Feed Point 37 Variable Capacitance Diode Apply Voltage terminal 51 A / D converter 52 CPU 53 D / A converter 321, 322 Loading coil

Claims (4)

[Claims] 1. A compact dipole-type small antenna that can be built-in, comprising at least a radiating element, a loading coil and a variable capacitance diode, wherein the loading coil is divided into two, and one of the divided loading coils and the variable capacitance diode is divided. A small antenna that is connected in parallel to form a tuning loading coil. 2. The small antenna according to claim 1, wherein the applied voltage of the variable capacitance diode is adjusted by the reception voltage detection circuit and the automatic tuning control circuit to perform frequency tuning. 3. The small antenna according to claim 1, wherein a ferrite material is used as a core material of the loading coil. 4. The small antenna according to claim 2, wherein the received voltage detection circuit and the automatic tuning control circuit are shared with the device main body circuit section for frequency tuning.