JPH0779205B2 - Antenna device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a linear antenna, and more particularly to an antenna device in which the characteristics are prevented from being deteriorated by the external environment.

[Prior Art] Conventionally, there are various kinds of antennas for wireless communication, and as an antenna for mobile communication, for example, a portable wireless device or a vehicle-mounted wireless device, a λ as shown in Fig. 6 (a) is used. A / 4 whip antenna, an h-shaped antenna shown in FIG. 6B, a brown antenna, a sleeve antenna, etc., which are not shown, are generally used.

There are various kinds of lengths of these antennas, but in principle, it is usually λ / 4 of the wavelength λ used or an integral multiple thereof.

The high frequency current and voltage distributions induced in these antennas are
The impedance Z _{0 of} these antennas as seen by the dotted line and the solid line in FIGS. 6 (a) and 6 (b), respectively, and seen from the feeding portion, is the ratio of the voltage V to the current I, that is, Z ₀ = V / I
(Ω).

Therefore, if the characteristic impedance of the coaxial cable used is, for example, 50 (Ω) or 75 (Ω), select a point where the above-mentioned antenna impedance Z ₀ = V / I is approximately these values, and match the two. It is generally made to measure.

Therefore, as is clear from FIGS. 6 (a) and 6 (b), at the tip of the antenna element, the current I is zero and the voltage V is maximum, so that the ratio V / I is extremely large (theoretical). Is infinite). This is natural because the antenna element length is determined so as to resonate at the used frequency, and is the same not only in the above example but also in the conventional linear antenna.

Conventionally, this has been taken as a matter of course, but as will be described later, when the tip or the bottom of the antenna has a high impedance, many problems occur.

[Problems to be Solved by the Invention] As described above, if there is a point having an extremely large impedance at the tip or the bottom of the antenna, it is seriously affected by the external environment and its gain and characteristics are deteriorated. There was a problem.

That is, when the antenna tip portion having a high impedance approaches a conductor or a dielectric substance such as a human body, the earth or the body of a vehicle, and a slight electrostatic capacitance is generated between these and the antenna tip portion, the antenna Since the tip end has a high impedance, a high frequency current flows through this electrostatic capacitance, resulting in various problems such as a decrease in antenna efficiency, a variation in radiation pattern and deterioration of VSWR.

More specifically, these problems will be described below.

FIG. 7 is a sectional view showing a situation in which the portable wireless device TRX is located in the cave 20.

As described above, since the tip of the conventional whip antenna exhibits extremely high impedance, even a slight stray capacitance C ₂₁ , C exists between the tip of the whip antenna 1 and the inner wall of the cavern 20, particularly the ceiling of the cavern 20. _{If 22} and C ₂₃ are present, the high-frequency standing wave induced in the antenna tip is disturbed because the antenna tip has a high impedance, and a part of the high-frequency current at the antenna tip causes stray capacitances C _{21 to} C _23. It will flow to Cave 20 via.

For this reason, the current and voltage distribution of the antenna becomes different from that shown in FIG. 6, and the original characteristics of the whip antenna cannot be maintained.

In other words, it can be easily understood that the antenna in such a situation has poor directional characteristics and gain because the impedance matching at the feeding point is disturbed.

Conventionally, it has been generally considered that the reason for the extremely short wireless communicable distance in such a cave is that the amount of energy attenuation when a radio wave propagates in a special terrain such as a cave is large. But not only for this reason,
As described above, the deterioration of the characteristics of the antenna used for this is considered to be one of the causes.

As described above, the phenomenon that the antenna is affected by the external environment and the characteristics thereof are deteriorated is not limited to the case of the portable wireless device operation in the cave as described above, but is generally widely seen. When a person holds the device in his hand or operates it over his shoulder, the whip antenna attached to it has the same characteristic deterioration.

That is, FIGS. 8 (a) and 8 (b) are schematic diagrams showing the relationship between the portable wireless device 2 equipped with the conventional λ / 4 whip antenna 1 and the ground 30, of which FIG. a) is a diagram showing a state in which the height of the portable wireless device 2 is kept from the ground 30 to H. The tip of the antenna 1 attached to the portable wireless device 2 and the portable wireless device 2 that can be regarded as the negative electrode element of the antenna 1 are shown. The lower end of the housing also exhibits high impedance.

Regarding the antenna characteristics in this state, the current and voltage distributions distributed in the whip antenna as the positive electrode element and the portable wireless device as the negative electrode element are generally unbalanced. Therefore, the horizontal directional characteristics and the feeding point impedance are It will be considerably deformed compared to the antenna. Further, it is easily understood that if a person holds the portable wireless device by hand or lowers it from the shoulder, the deformation becomes large and the antenna characteristic deteriorates.

In addition, such a portable wireless device 2 is placed on the ground 30 as shown in FIG.
It is possible to obtain the original antenna characteristics for the first time in the state where an image can be formed, but it is rare to use in such a state.

Next, FIGS. 9A and 9B show the case of a λ / 2 vertical dipole antenna.

As shown in FIG. 9 (a), if a feeding point is provided at the midpoint of the λ / 2 dipole, both ends of the λ / 4 length elements 4 and 5 have high impedance as described above. It is clear that when the tip of the element 5 is brought close to the ground 30 as shown in b), the antenna characteristics are deteriorated as described above.

As described above, in the conventional antenna, since the tip of the element is in an extremely high impedance state, if the element is brought close to the ground or other dielectric material, the original performance of the antenna cannot be maintained and it is extremely unstable. And it was an inefficient antenna.

In addition, even in the case of an on-vehicle antenna, which was generally considered to be relatively stable in the past, when the external environment changed due to movement, it was affected by this and its characteristics changed variously. Is discussed as a fading phenomenon in mobile communications without being clearly identified as a variation due to the combination of radio waves that propagate through multiple propagation paths, which is the original cause of fading. It was recognized that the fading associated with mobile communications was extremely large with the inclusion.

[Means for Solving the Problems] The present invention has been made in view of the problems of the conventional antenna as described above, and is intended to reduce the influence of the external environment existing in the direction from the power feeding portion to the tip of the antenna. In order to realize a reduced antenna, the following measures are taken.

That is, by adding a matching circuit based on the principle to be described later to the extremely high impedance portion of the tip portion or the lower end portion or both of the conventional antenna, the high impedance of the tip portion or the lower end portion of the antenna or both ends thereof is added. There is provided an antenna device in which is converted to low impedance (value substantially close to zero).

The means for converting the high impedance at the tip of the antenna into a low impedance is substantially equivalent to a parallel 2 line of (2n-1) λ / 4 length or a coaxial line of the same length with one end short-circuited to the end of the antenna. An antenna device in which the above circuit is realized by a lumped constant circuit, a distributed constant circuit or a mixed circuit thereof is added to the tip of the antenna.

Further, based on the same idea, when the power feeding to the linear antenna is voltage feeding, that is, when feeding from the antinode of the voltage, by inserting the above-mentioned matching circuit in the feeding portion of the antenna, the feeding point of the antenna and the wireless The impedance matching between the wireless device including the input / output terminal of the device or the housing and the power feeding portion is achieved, and the antenna is electrically separated and independent.

However, in this case, it is necessary to terminate the input / output terminal of the wireless device with a low impedance (for example, 50Ω or 75Ω), so between the feeding point of the antenna and the input / output terminal of the wireless device (2n
-1) Impedance matching is performed by an electrical equivalent circuit that is approximately λ / 4 long.

[Operation] The operation of the matching circuit added in the present invention will be described below.

As is well known, (2n-1) λ / 4 length, for example, λ / 4,3 / 4λ, 5/4
The impedance seen from the other end (open end) of one of the parallel two lines of λ ... or the coaxial line of the same length which is short-circuited is extremely large (theoretical infinity).

Further, the relationship between both impedances of the impedance Z ₂ viewed from the other open end which is terminated at a predetermined value Z ₁ instead of shorting one end of such a line is expressed by the following equation.

Z ₀ ² = Z ₁ · Z ₂ (1) where Z ₀ is the characteristic impedance of the parallel line or the coaxial line.

Therefore, the ratio of Z ₁ and Z ₂ is set to Z ₂ / Z ₁ = m (2), and the value of m is set to a desired value out of m = 0 to 1 to obtain a desired index. Pieces can be matched.

That is, for example, if the center conductor of a coaxial line of λ / 4 is connected to the tip (point of high impedance) of the linear antenna, and the outer conductor and the inner conductor are short-circuited at the other end of the line, the original antenna tip The impedance of the coaxial line viewed from the connection point of the part is the Z ₁ of the equation (1) set to zero,
From Z ₂ = Z ₀ ² / Z ₁ , Z ₂ becomes infinite. Therefore, the impedance of the new antenna tip with the coaxial line added becomes zero.

Since the impedance of the newly formed antenna tip portion is zero, it is not affected by the external environment existing in the antenna tip direction from the feeding portion.

Similarly, when voltage supply is performed, (2n-1) λ
/ 4 length line is inserted between the feeding point of the linear antenna that feeds the voltage and the input / output terminal of the radio, etc. It is possible to electrically separate this antenna from the radio device including the housing.

That is, for example, when the feeding point of the λ / 2-length single antenna by voltage feeding and the input / output terminal of the radio are matched, the lower end of the λ / 2-length single antenna is Since the impedance is extremely high like the tip portion, the central conductor of the above-mentioned (2n-1) λ / 4 length coaxial line is connected to the lower end portion of the antenna, and the other end of the coaxial line is connected to the radio terminal. Connect to the input / output terminal. Also in this case, the impedance matching between the feeding point of the antenna, the coaxial line and the input / output end of the wireless device, and the coaxial line is performed so as to satisfy the equation (1).

At this time, the (2n-1) λ / 4 length coaxial line inserted between the feeding point and the input / output end of the wireless device has an input / output impedance of the wireless device, for example, the input / output impedance of the wireless device. 50Ω or 75
Although it is terminated with a value such as Ω, it is considered to be almost zero because it is extremely small compared to the impedance of the lower end of the λ / 2 length single antenna, and (2n-1) for the antenna tip. Impedance matching can be achieved similarly to the case of adding a λ / 4-length coaxial line, and as a result, a function of electrically separating the radio device and the antenna is exhibited.

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

FIG. 1 is a structural diagram showing the principle when the present invention is applied to a dipole antenna.

In FIG. 1, 1 and 2 each have a length of approximately λ.
/ 4 long antenna elements, each tip 1
Matching circuits 3 and 4 surrounded by dotted lines are connected to a and 2a. The matching circuits 3 and 4 are short circuits in which the λ / 4 long parallel lines 5 and 5 ′ are connected at their tip portions 6. Further, the feeding portion of the antenna is provided in the middle between the element 1 and the element 2 as in the conventional antenna.

The operation of the elements 1 and 2 of the antenna is no different from the conventional one, but by adding the matching circuits 3 and 4, the tip of the new antenna becomes the shorted tip 6. . Therefore, the impedance of the antenna tips 1a and 2a before adding the matching circuits 3 and 4 was high impedance, but the matching circuits 3 and 4 made the tip 6 of the new antenna have a low impedance, and In the direction of the tip 6 of the antenna, it is stable without being affected by the outside. That is, in an extreme case, the matching circuit
The characteristics of the antenna will not change even if the tips 6 of the antennas 3 and 4 are brought into contact with the ground or touched by a person. In addition,
The operation of the matching circuits 3 and 4 is as described in detail above, and therefore its explanation is omitted.

FIG. 2 is a structural sectional view for explaining a specific example of the matching circuit based on the above principle.

In FIG. 2, 7 is a coaxial line used in place of the parallel lines 5 and 5'of FIG. 1, and its length is λ / 4,
The center conductor 8 is connected to the tip 1a of the antenna element 1, and the center conductor 8 and the outer conductor 9 are short-circuited at the other end of the coaxial line 7.

In this way, the impedance of the matching circuit 3 connected to the tip 1a of the antenna element 1 as viewed from the tip 1a is infinite, and the impedance of the tip 6 of the newly formed antenna is zero. The matching circuit 4 shown in FIG. 1 can be the same as the matching circuit shown in FIG.

However, when a λ / 4-length parallel line or a coaxial line is used as in the matching circuit shown in FIG. 1 or 2, the total length of the antenna becomes double by adding the matching circuit. This causes inconvenience.

Therefore, in the embodiment of the present invention, FIG.
A matching circuit having characteristics similar to those of the matching circuit shown in the figure is configured by a lumped constant circuit element or the like to reduce the size of the antenna.

FIG. 3 (a) is an equivalent circuit diagram of a line having a parallel line length l ₀ of λ / 4, and FIG. 3 (b) is an equivalent circuit diagram of a line having a parallel line length l ₀ of 3λ / 4. It is a circuit diagram. In FIGS. 3 (a) and 3 (b), the inductances L ₁ and L ₂ and the capacitances C ₁ and C ₂ are values obtained from the equations (1) and (2), and the lumped constant circuit element having these values is used. Can be realized with.
For the parallel line length l ₀ , λ / 4 and 3λ / 4 are the third
Since it is cyclically repeated every λ / 2 as shown in FIG. 7C, if the parallel line lengths of λ / 4 and 3λ / 4 are considered, (2n−1) λ / 4 of the parallel line length l ₀ is obtained. Can be applied to all of.

FIG. 4 is a diagram showing a configuration of a matching circuit which is an embodiment of the present invention.

In the matching circuit in FIG. 4 (a), 10 is a hollow conductive cap, and a coil 11 is connected between the lower inner wall of the matching conductive circuit and the tip of the antenna element 1, and both ends of the coil 11 and the hollow conductive cap. Between each of the 10 side walls,
The capacitors 41 and 42 having a predetermined value are connected to each other, and the space between the opening of the hollow conductive cap 10 and the tip of the antenna element 1 is supported by an insulating material space 12.
However, when stray capacitance exists between the hollow conductive cap 10 and the coil 11, the stray capacitance is added to determine the capacitance of the capacitors 41 and 42 and the inductance of the coil 11.

The matching circuit in FIG. 4 (b) is a desired matching circuit by positively utilizing the stray capacitance between the hollow conductive cap 10 and the coil 11 in FIG. 4 (a). That is, this matching circuit uses the hollow conductive cap 13 in which the inner shape of the hollow conductive cap 10 is formed to form a desired capacitance between the convex portion of the hollow conductive cap 13 and the lead portion of the coil 11. As a result, Fig. 3 (a)
The capacitors 41 and 42 shown in are omitted.

In this way, the parallel line or the coaxial line composed of the distributed constant circuit is made into a lumped constant circuit in consideration of its length, so that the matching circuit having a desired size can be downsized.

Next, a description will be given of an embodiment of the present invention in the case where the feeding portion of the antenna has a high impedance instead of the tip portion of the antenna. That is, a matching circuit in the case where the antenna power feeding method is voltage power feeding will be described.

FIG. 5 is a structural diagram showing another embodiment of the present invention,
The matching circuit shown in FIG. 4 (a) is inserted between the feeding portion of the linear antenna 14 of nλ / 2 length by voltage feeding and the input / output terminal 15 of the radio device TRX. The structure of this matching circuit is
At the upper end of the hollow conductive pipe 16, the lower end of the linear antenna 14 having a length of nλ / 2 is fixed by an insulating material support 17, and the lower end of the linear antenna 14 and the input / output end 15 of the radio TRX are connected. And the capacitors C ₃ and C ₄ are inserted and connected between the both ends of the coil 11 and the hollow conductive pipe 16, and the lower end of the hollow conductive pipe 16 is outside the radio TRX. It is electrically connected to the housing 18. In addition, coil 1
1, the value of the lumped constant circuit elements such as capacitors C ₃ and C ₄ is 4th
Obtained in the same way as in the figure. In this case, as described above, the impedance of the input / output terminal 15 of the wireless device is low impedance (50Ω or 75Ω, etc.), and the matching circuit must match this low impedance. Since the impedance never becomes zero, the electrical length of the matching circuit is either slightly longer or shorter than the (2n-1) λ / 4 length. However, since this electrical length can change depending on the value of the lumped constant circuit element, it has almost no effect on the physical size of the matching circuit. Of course, the matching circuit shown in FIG. 4 (b) may be applied.

Note that the antenna length is not limited to the λ / 4 length and the λ / 2 length described above, and it is obvious that the antenna length can be widely applied to an antenna having an antenna length that is an integral multiple thereof.

[Effects of the Invention] As described above, the present invention reduces the high impedance of the conventional linear antenna tip portion or the antenna lower end portion by using the above-described matching circuit to newly form the antenna tip. In addition to providing a linear antenna with extremely stable performance, there is no influence of the external environment in the direction from the feeding part to the tip of the antenna or the direction of the bottom of the antenna by setting the impedance of the antenna part or the bottom of the antenna to zero or extremely low. It has a remarkable effect.

[Brief description of drawings]

FIG. 1 is a structural diagram showing the principle when the present invention is applied to a dipole antenna. FIG. 2 is a structural cross-sectional view for explaining a specific example of a matching circuit based on the principle shown in FIG. FIG. 3 is a diagram showing an equivalent circuit diagram of a matching circuit. FIG. 4 is a diagram showing a configuration of a matching circuit which is an embodiment of the present invention. FIG. 5 is a diagram showing the configuration of another embodiment when the present invention is applied between a linear antenna and a radio device. FIG. 6 is a diagram showing a conventional antenna. FIG. 7, FIG. 8 and FIG. 9 are state diagrams for explaining defects of the conventional antenna. 1,2,14 …… Linear antenna, 3,4 …… Matching circuit, 5,5 ′ ……
Parallel 2 lines 6 ... Tip, 7 ... Coaxial line, 8 ... Coaxial line center conductor, 9 ... Dielectric 10,13 ... Hollow conductive cap, 11 ... Coil, 12 ... Support 15 ... … Radio input / output end, 16 …… Hollow conductive pipe, 30 ……
Earth, TRX ... radio

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tokki Oba 4-1-37 Kamikizaki, Urawa-shi, Saitama Antenna Giken Co., Ltd. (72) Inventor Akihisa Mori 753 Otani, Samukawa-cho, Takaza-gun, Kanagawa Toyo Communication Equipment Co., Ltd. Within the corporation (56) References Japanese Patent Publication Sho 23-870 (JP, B1)

Claims (4)

[Claims] 1. A structure in which a coil is arranged along the central axis of a conductive cap whose one end is electrically closed, and a capacitor is inserted between both ends of the coil and the inner wall of the conductive cap, the end of a unipole antenna. And an electrical equivalent circuit of the structure is substantially a parallel line or a coaxial line having a (2n-1) λ / 4 length (λ is a wavelength at which the antenna resonates, n is an integer) short-circuited at one end. The antenna device is characterized in that they are made equal to each other. 2. The antenna device according to claim 1, wherein one end of the unipole antenna serves as a power feeding portion, and the antenna length of the unipole antenna is nλ / 2 length (λ is a wavelength at which the antenna resonates, and n is an integer). In this case, a structure consisting of a coil, a conductive pipe surrounding the coil, and a capacitor inserted between both ends of the coil and the inner wall of the conductive pipe is connected to the power supply part, and the electrical structure of the structure is electrically connected. The equivalent circuit is (2n−
1) Matching the impedance of the feeding part of the antenna and the impedance of the communication device or the feeding line connecting the antenna by making them substantially equal to a parallel line or a coaxial line of λ / 4 length. An antenna device characterized in that 3. The antenna device according to claim 1, wherein a floating capacitance between the coil and the conductive cap or the conductive pipe is used instead of the capacitor of the structure. 4. The capacitor of the structure is replaced with a concavity and convexity provided on the inner wall of the conductive pipe or the conductive cap, and the stray capacitance between the concavity and convexity is used. ) Or (2) the antenna device.