JPS6347041Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is installed in, for example, automobiles, and is used for transmitting and receiving VHF communication waves with a frequency of 150 MHz (140 to 160 MHz) and FM broadcasting, which is used for general and simple business wireless communication and amateur wireless communication. wave,
It relates to an antenna device that is commonly used for receiving AM broadcast waves (medium waves), and in particular between the feed point of the rod antenna element and the splitter that separates each radio wave and transmits it to radio equipment and radio receivers. The present invention relates to impedance matching means provided on a coaxial power supply cable to be connected.

Multiband antenna devices commonly used for transmitting and receiving VHF communication waves and receiving FM-AM broadcast waves are well known. Impedance matching between the rod antenna element in such an antenna device and the antenna element and the duplexer is usually performed by impedance matching means installed within the duplexer. However, in conventional antenna devices with the above configuration, if the antenna element length is set to match radio waves in a specific frequency band, the impedance at the antenna element feeding point becomes abnormally large for radio waves in other frequency bands. 50Ω
When you connect the coaxial power supply cable to the above power supply point,
There was a problem in that standing waves were generated in the cable, causing the entire power supply cable to generate heat, resulting in large losses.

Therefore, the present invention provides impedance matching means with a simple configuration in the coaxial feed cable that connects the rod antenna element and the branching filter.This cable generates less heat and the loss associated with it is significantly reduced. The purpose of the present invention is to provide a three-wave antenna device that can effectively transmit and receive communication waves (up to 160 MHz) and receive FM broadcast waves and AM broadcast waves (medium waves).

The present invention provides a simple impedance matching means consisting of a reactance correction capacitor and a short-circuit stub at a predetermined position in the middle of the coaxial feed cable, thereby improving the relationship between the antenna element and the coaxial feed cable against VHF communication waves. Impedance matching is possible, and it is possible to provide practically acceptable matching for FM broadcast waves, which suppresses heat generation in the coaxial cable and significantly reduces antenna loss, as well as for AM waves. The capacitor prevents short-circuiting of the coaxial cable due to short-circuiting stubs, allowing for good transmission and reception of VHF communication waves and reception of FM-AM broadcast waves.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram showing the connection relationship between impedance matching means, which is the main part of the embodiment, and a coaxial power supply cable.

In FIG. 1, 1 is, for example, a plurality of different diameter conductive tubes 1a,
1b, . . . 1n are slidably connected to each other, and the length when fully extended is L.
It is adapted to be telescopically driven by a drive mechanism 3 attached to the inside of the vehicle body wall 2. 4 is a coaxial feeding cable, one end of which is connected to the feeding end A of the rod antenna element 1, and the other end connected to the branching filter 5.
It can be detachably connected to the common terminal T0 of the terminal. The branching filter 5 has an FM broadcast wave trap F1 which has a coil and a capacitor connected in parallel between the common terminal T0 and the first branch terminal (radio device connection terminal) T1 to block FM broadcast waves, and a coil and a capacitor connected in parallel. Filter F2 connects capacitors in series to pass 150MHz communication waves and block medium waves (AM waves).
A first channel is provided by connecting these in series, and a coil and a capacitor are connected in parallel between the common terminal T0 and the second branch terminal (radio receiver connection terminal) T2 to block 150MHz communication waves. A second channel is provided by connecting in series the communication wave trap F3 and an adjustment capacitor CX for electrostatic matching (80pF) to the AM wave input circuit of the receiver. . Note that 6 is a relay cable that connects the radio to the first branch terminal T1, and 7 is a relay cable that connects the FM-AM receiver to the second branch terminal T2.

Incidentally, an impedance matching means 8 is provided in the middle of the coaxial power supply cable 4. As shown in FIG. 2, this impedance matching means includes a reactance consisting of a finely adjustable variable capacitor in a matching box 9 disposed at a point B which is a distance l1 from the feeding point A of the antenna element 1. A correction capacitor C is housed, one end of this capacitor C is connected to the internal conductor (core wire) 4a of the coaxial power supply cable 4, and this capacitor C
A short-circuit stub S having a length 12 and having a short-circuited end is connected in series to the other end. Note that the short-circuit stub S uses a cable having the same structure as the coaxial power supply cable 4.

Here, the means for setting the length L of the antenna element 1, the distance l1 between points A and B, the length i2 of the shorting stub S, etc. will be described with specific numerical values. For convenience of explanation, each of the above-mentioned band waves will be defined as follows.

Wireless communication wave...1 (wavelength λ1), as an example
Radio waves of 150MHz (140-160MHz) shall be used.

FM broadcast wave...2 (wavelength λ2), the frequency of FM broadcast wave in Japan at the moment is 76
~90MHz, and the frequency of FM broadcast waves in Europe and America is 88~108MHz.

AM broadcast wave (medium wave)...3 (wavelength λ3) <A> Setting of antenna element length L The length L of the rod antenna element 1 when fully extended is
It is set to 1/2 to 5/8 of the wavelength λ1 of the VHF communication wave 1, and is set to be close to 1/4 of the wavelength λ2 of the FM broadcast wave 2. For example, if L is set to 1/2 of the wavelength λ1 of communication wave 1 of 150MHz, the length L
is approximately 1000 mm, which is approximately 1/4 of the wavelength λ2 of FM broadcast wave 2 in Japan. Thus 1,
It resonates with both. However, when the antenna element length L is set to 1/2λ1 as described above, the impedance Z1 of the feeding point A of the antenna element 1 with respect to the communication wave 1 becomes capacitive, and its magnitude is 1 kΩ.
It also depends on the degree. Therefore, for example, a coaxial feed cable 4 with a characteristic impedance of 50Ω is connected to the feed point A.
If connected, standing waves will occur in the power supply cable 4, resulting in a large loss.

<B> Selection of short-circuit stub placement position Therefore, in order to minimize the range in which the above loss occurs, an impedance matching means is provided in the coaxial cable 4. In this case, the stub placement position is determined by the characteristic impedance. Point B is selected where the impedance resistance component R1 is approximately 50Ω for the 150MHz communication wave 1 distributed on the 50Ω coaxial cable. At this time, the distance l1 from the feeding point A becomes l1<1<1/4λ1, and the reactance component X1 of the point B with respect to 1 becomes -j (capacitive).

<C> Arrangement of short-circuit stub for point 1 In order to obtain a short-circuit stub S that can cancel the capacitance reactance -jX1 for point B 1, first consider the admittance at point B. Then, since the imaginary part of this admittance, that is, the susceptance, is +jb1, it is sufficient to provide a short-circuit stub S having a susceptance of -jb1 to offset this. Therefore, the length l2 of the short-circuiting stub S is selected to be 1/4 to 1/2λ1. By doing this,
The antenna element 1 whose length L is 1/2λ1 is matched to 50Ω with respect to 1. Furthermore, stub S
In order to be able to finely adjust the reactance changes due to variations in the length l2 and how it is installed on the vehicle body, etc.
In addition, in order to prevent a direct short circuit of the coaxial power supply cable 4 due to the short circuit stub S from occurring for AM waves (medium waves), there is a variable distance between the core wire of the coaxial power supply cable 4 and the core wire of the short circuit stub S. Insert a capacitor C for type reactance correction.

<D> Securing the reception function of FM broadcast wave 2 As mentioned above, the length L of antenna element 1 is 1/2
If set to λ1, then 1/4λ2 for 2
Although the antenna element 1 is set to be slightly longer, the antenna element 1 almost resonates with the antenna element 2. Therefore, the impedance Z2 of the feeding point A with respect to 2
The resistance component is several tens of Ω, and the reactance component is small +j (inductive).

On the other hand, at point B where the short-circuit stub S is connected, the cable length l1 from the feeding point A is l1<1/4λ1 for a wavelength λ1 of 1, so that l1<< for a wavelength λ2 of 2. It is 1/4λ2. Therefore, the resistance component R2 at point B becomes larger than the resistance component at the feeding point A, resulting in reactance X2+j (inductive). That is, when the inductance reactance X2 with respect to 2 at the point B is converted into admittance, it becomes -jb2 in susceptance. Therefore, to offset this +
Requires susceptance jb2. However, since the 1 is also used for transmission, matching to the 1 cannot be made worse. Therefore, 1/4λ1<
Within the condition l2<1/2λ1, the length l2 of the shorting stub S is made close to the length l2<1/4λ2 so that a susceptance of -jb2 can be obtained. By doing this, a certain degree of consistency can be obtained for 2 as well. Note that since 2 is an FM broadcast wave and a reception-only wave, the VSWR only needs to be about 3 or less, for example. Therefore by a single stub S
Matching can be obtained for the 150MHz communication wave 1, and there is no practical problem with FM broadcast waves.

This device described above has the following effects.

[1] It is possible to reduce the heat generated due to the generation of standing waves in the coaxial feed cable 4, and accordingly the loss of the antenna is significantly reduced.

[] 140~
The reactance component of the VHF communication wave 1 having a band of 130 MHz can be canceled out, and the reactance component of the FM broadcast wave 2 can be reduced at the same time.

[] For AM broadcast waves 3 (medium waves), the reactance correction capacitor C prevents the short-circuiting stub S from short-circuiting the coaxial feed cable 4, so one rod antenna element 1 can support communication and FM broadcasting using 150MHz band waves. It can receive frequency band waves and medium wave AM broadcast frequency band waves, and can configure a so-called three-wave antenna.

[] By making the reactance correction capacitor C of the impedance matching means 8 of a variable capacitance type and housing it in the matching box 9, the short-circuit stub constant can be finely adjusted as needed. As a result, even if the reactance of the feeding point A changes due to the installation condition or other factors after the antenna device is mounted on the vehicle, this can be easily readjusted.

In the above embodiment, the rod antenna element length L is matched to 1 (150MHz).
As described above, the antenna element length L was selected to be 1016 mm to match 1 (145 MHz), and 2 (145 MHz) was selected. 1 (158M) even if shared in Japan).
800mm to match the
2 (in the United States), it was possible to obtain an antenna device with similar effects using a single short-circuit stub S. Further, in the above embodiment, the present invention is applied to a vehicle antenna device, but it is of course applicable to antenna devices other than vehicles.

As explained above, the present invention has one end connected to the feed point of an antenna element installed to enable transmission and reception of VHF communication waves and reception of FM-AM broadcast waves, and the other end connected to a duplexer. An impedance matching means is provided in the middle of the coaxial power supply cable, and the impedance matching means selects a point on the cable where the impedance to the communication wave is equal to the characteristic impedance of the cable, and can be finely adjusted to this point. One end of a reactance correction capacitor made of a variable capacitor is connected to the other end of the capacitor, and the reactance component with respect to the communication wave at the connection point between the cable and the capacitor is canceled out,
A short-circuit stub whose length is set so as to reduce the reactance component to the FM broadcast wave at the connection point is connected.

Therefore, according to the present invention, the antenna element and the coaxial feed cable are well matched for VHF communication waves, and the matching for FM broadcast waves can be achieved without any practical problem. Heat generation in the coaxial power supply cable due to waves is suppressed, resulting in less loss, and in the case of AM waves, the reactance correction capacitor prevents shorting of the coaxial power supply cable by the shorting stub, which interferes with the reception of AM broadcast waves. There is no fear, and in the end, in the main case
It is possible to provide a device with a three-wave antenna that can satisfactorily transmit and receive VHF communication waves and receive FM-AM broadcast waves.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram showing impedance matching means of the embodiment. 1... Rod antenna element, 2... Car body wall, 3
...Drive mechanism, 4...Coaxial power supply cable, 5...
Duplexer, 8... Impedance matching means, A...
Feeding point, B... Connection point, C... Capacitor for reactance correction, S... Short circuit stub.

Claims (1)

[Scope of claim for utility model registration] (1) Having a frequency band of approximately 140 to 160 MHz
A rod antenna element installed to enable transmission and reception of VHF communication waves and reception of FM and AM broadcast waves, and a coaxial feed cable with one end connected to the feeding point of this antenna element and the other end connected to a branching filter. and an impedance matching means provided in the middle of the coaxial power supply cable,
The impedance matching means includes a reactance correction capacitor including a finely adjustable variable capacitor whose one end is connected to a point on the coaxial power supply cable where the impedance to the communication wave is equal to the characteristic impedance of the cable, and the other capacitor. a short-circuit stub connected at one end to the end and set to a length that cancels a reactance component to the communication wave at the connection point between the cable and the capacitor and reduces a reactance component to the FM broadcast wave at the connection point; An antenna device comprising: (2) The capacitance value of the reactance correction capacitor is set so that the shorting stub does not short-circuit the coaxial power supply cable for AM broadcast waves.
The antenna device described in (1). (3) The antenna device according to claim (1) of the utility model registration, wherein the short-circuit stub is formed of a cable having the same structure as the coaxial power supply cable.