JPH0324803B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure of a radiating element of a dipole antenna. More specifically, the present invention relates to a dipole antenna in which radiation directivity from the antenna is approximately equal over a wide frequency band.

As the use of radio waves increases, a wideband antenna that can be used for multiple channels has become required. In particular, the UHF broadcast wave band has a wide bandwidth.
Channel changes or multi-channel sharing are often performed. In this case, unless the directivity characteristics of the antenna are kept constant, the service area etc. will change, causing inconvenience.

Conventionally, turn style antennas, super gain antennas, etc. have been used as antennas for TV broadcasting, but since these have relatively narrow bands, recently dipole antennas with a reflector, which combine a dipole of about 1 wavelength and a reflector, have been used. is also beginning to be used. Although this antenna can have relatively good VSWR characteristics over a wide band by making the radiating element thicker, it is difficult to widen the directional characteristic, that is, to reduce the frequency dependence of the directional characteristic.

The reason for this is that if the radiating element is shortened, the gain will decrease at low frequencies, and if the radiating element is made long, the directivity will become sharper at higher frequencies and unnecessary side lobes will occur.

Therefore, when forming an omni-directional antenna by attaching reflector-equipped antennas to the four sides of a steel tower, for example, it has been difficult to achieve desired directional characteristics over a wide band.

An object of the present invention is to provide a dipole antenna which can receive electromagnetic waves over a wider band than conventional dipole antennas and whose directivity characteristics are almost the same over a wide frequency band.

For the purpose of simplifying the explanation, only the radiating element of the dipole antenna will be explained in the present invention, but it goes without saying that the dipole antenna can be used as a single dipole antenna or as a dipole antenna with a reflector.

The present invention will be described below with reference to the drawings.

FIG. 1, FIG. 2, and FIG. 3 are conceptual diagrams showing the current distribution when a current is supplied that makes the antenna length of the dipole antenna 1/2 wavelength, 1 wavelength, and 2 wavelengths.

The arrows in the figure indicate the direction of current at a certain moment. When calculating the radiation from each dipole using a known formula for calculating radiation from dipole antennas, we find that the dipole antenna in Figure 3 radiates less compared to the dipole antennas in Figures 1 and 2. . The reason for this is that in the cases of Figures 1 and 2, the direction of the current is the same throughout the radiating element 1, whereas in the case of Figure 3, the direction of the current is the same as the direction of the current near the dipole center 2. This is because the direction of the current near the dipole end 3 is in the opposite direction. That is, the current distribution has node 4.

The present invention is applicable not only when the length l between the dipole ends 3 and 3 is 1/2 (l = λ/2), 1 time (l = λ), but also twice (l = λ) the wavelength λ of the supplied current. An object of the present invention is to provide a wideband dipole antenna that can efficiently emit electromagnetic waves even when 2λ) and has almost the same directivity characteristics.

4 to 9 are conceptual diagrams showing various embodiments of the present invention.

The operating principle of the present invention will be explained using FIG. 4.
FIG. 4 shows the dipole antenna of FIG. 3, where l=2λ, with the vicinity of the end 3 bent loosely into a J-shape. Note that it is preferable that the radius of curvature at the bending point 5 is not too small from the viewpoint of impedance. At this time, the wavelength on the dipole radiating element changes slightly, but the current distribution has one node at the end 3 of the dipole antenna, an antinode near the bending point 5, and the direction of the current is reversed at the node 4. become. The direction of the current at a certain moment is indicated by an arrow in FIG.

Generally, the following relationship holds true for voltage and current on a line.

V=V ₀ e ^-j( 〓 ^{x- 0)} +V _r e ^j( 〓 ^{x+ r)} I=I ₀ e ^-j( 〓 ^{x- 0)} −I _r e ^j( 〓 ^{x+ r)} propagates on the line without attenuation If it does not flow at the tip (x = H) and is completely reflected, then at x = H and I = 0
is the boundary condition at the tip. If we rewrite this using Euler's formula, we get the following equation.

I = 2I ₀ sinβ (H - x) cos (ωt + ₀ - _r / 2) I ₀ = I _r , ₀ + _r = 2βl where x: Coordinate on the line t: Time V and I are the voltage and current at point x V ₀ I ₀ is the input end 〃 V _r I _r is the reflection end 〃 ₀ , _r is the phase of the input end and reflection end β = 2π / λ λ Wavelength ω = 2π Angular velocity: frequency This formula shows that the spatial distribution of the current is the tip of the dipole This means that it becomes a sine wave with zero amplitude.

The same holds true for the dipole antenna according to the present invention. However, in this case, since the tip of the die ball is bent, the following effect occurs.

When l=λ/2, the direction of the current flowing between the end 3 of the dipole and the bending point S is opposite to the direction of the current in the adjacent part, so the electromagnetic fields due to the current in that part cancel each other out, and in effect Basically, only the current in the center of the dipole antenna transmits and receives electromagnetic waves. The symmetry of the actual current distribution at this time is almost the same as that of the current distribution shown in FIG.

When l=λ, the currents at the end portions of the dipole cancel each other out, so that the symmetry of the actual current distribution is almost the same as that of the second current distribution.

When l = 2λ, the current distribution is as shown in Fig. 4, so the direction of the current flowing between the end 3 of the dipole and the bending point 5, and the current flowing between the bending point 5 and the above-mentioned node 4. The direction of is opposite.
Therefore, the radiation from both parts has opposite phases, and the radiation weakens each other. As a result, the electromagnetic waves that weaken the electromagnetic waves radiated by the current between the center 2 of the dipole and the node 4 become weaker. In other words, the dipole antenna shown in FIG. 4 is substantially equivalent to an antenna covering only the portion between the center 2 of the dipole and the node 4. In other words, it is equivalent to the dipole antenna shown in Figure 2. Therefore, their radiation directivity characteristics are also approximately the same.

When the frequency of the current supplied to the dipole antenna of the present invention is sequentially changed from low frequency to high frequency, the current distribution at low frequencies has the symmetry shown in Figure 1 and emits electromagnetic waves, and then the symmetry shown in Figure 2. At high frequencies, the antenna emits electromagnetic waves with a current distribution as shown in FIG. 4, which radiates electromagnetic waves having the same symmetry as the dipole antenna in FIG. 2. That is, it is possible to radiate electromagnetic waves over a wide band without changing the dimensions of the dipole, and to make the directivity characteristics almost equal.

5 to 7 show other embodiments of the present invention.

The dipole antenna shown in FIG. 5 is an antenna in which the vicinity of the end 3 of the dipole is bent into a chevron shape, and the vicinity of the center 2 of the dipole is formed into a straight line.
When a high frequency current (a current with a frequency equivalent to that shown in FIG. 3) is supplied to this antenna, the current flow at a certain moment is as shown by the arrow in FIG. 5. Although the currents indicated by arrows a and b are not completely antiparallel, they contain antiparallel components as vectors, so the electromagnetic waves emitted from each of them weaken each other to some extent. Therefore, arrow c near the center of the antenna
The electromagnetic waves radiated from the current indicated by arrow a
It is not weakened by the electromagnetic waves radiated from the current shown by arrow b and is effectively radiated. As a result, the dipole antenna of FIG. 5 has substantially the same effect as the dipole antenna of FIG. 4.

The bent portion 6 in FIG. 5 is bent so that the current flowing through the bent portion has an antiparallel component vectorwise. Therefore, there are various variations in its implementation.

FIG. 6 is a conceptual perspective view of an embodiment in which a bent portion 6a is provided in the direction of the electromagnetic wave main lobe of a flat dipole antenna.

Figure 7 shows a bent portion 6b in a direction perpendicular to the main lobe.
This is a conceptual example of an embodiment provided with.

The antennas shown in Figs. 4 to 7 suppress radiation due to the current from node 4 of the current distribution in Fig. 3 to dipole end 3. A similar effect can be obtained by suppressing radiation due to the current between the two.

Figure 8 shows a bent portion 6 near the center of the dipole.
FIG. 3 is a conceptual diagram of a dipole antenna provided with a

The dipole antenna shown in FIG. 8 also radiates electromagnetic waves in a wide band. That is, the dipole end 3-
3, the wavelength λ is l=λ/2, l
=λ, l=3/2λ, l=2λ, electromagnetic waves are effectively radiated.

In FIGS. 5 to 8, the bent portions 6, 6
a, 6b, and 6c are formed by a single mountain curve, but based on the operating principle of the antenna of the present invention,
The same effect can be obtained with a small chevron or wavy curve.

FIG. 9 shows another embodiment of the present invention in which the bent portion 6 of the antenna shown in FIG. 5 is realized by a wave-shaped bent portion 6d.

[Brief explanation of the drawing]

FIGS. 1 to 3 show dipole antennas according to the prior art with l=λ/2, l=λ, and l=
A diagram showing the current distribution when a current of 2λ is supplied,
Figures 4 and 5 are diagrams showing the current distribution and direction of current when a current equivalent to the current distribution in Figure 3 is supplied to the dipole antenna of the present invention, and Figures 6 to 9 are diagrams showing the current distribution according to the present invention. This is an example. 2...Dipole center, 3...Dipole end, 4
...Node, 5...Bending point, 6, 6a, 6b, 6c,
6d...Bending part.

Claims (1)

[Claims] 1 The distance between both ends 3-3 of the dipole is l, and l
It is formed of a radiating element that has a straight part with a boundary near node 4 and a bent part symmetrically with respect to the dipole center 2 in the current distribution when supplying a current with a wavelength λ that satisfies the relationship 2λ. A dipole antenna featuring 2. The dipole antenna according to claim 1, wherein the bent portion is provided between the node 4 and the antenna terminal. 3. The dipole antenna according to claim 1, wherein the bent portion is formed by bending a dipole radiating element in the direction of the electromagnetic main lobe of the flat dipole antenna. 4. The dipole antenna according to claim 1, wherein the bent portion is formed by bending a dipole radiating element in a direction perpendicular to the main lobe of the flat dipole antenna. 5. The dipole antenna according to claim 1, wherein the bent portion is provided between the dipole center 2 and the node 4. 6. The dipole antenna according to claim 1, wherein the bent portion is a small wave-shaped bent portion.