JPH0640602B2 - Isolated monopole antenna - Google Patents

Description

The present invention relates to a base-insulated monopole antenna having a height of about 0.6 wavelength or less.

[Conventional technology]

As shown in FIG. 5, a conventional antenna for receiving a medium wave has a height H of an antenna column insulated by a base glass 2 on a ground 1.
= 0.2 to 0.6 wavelength, that is, a height of about 30 m to 200 m, and a crown 3 is installed on the upper part of the branch lines glass 4a, 4
It was supported by the branch line 5 insulated by b, .... Therefore, the land area occupied by the antenna is large, the antenna pillar needs to be strong, and the price is high, and a huge cost is required to construct a broadcasting station.

[Problems to be solved by the invention]

At present, there is a problem of interference from foreign radio waves in medium-wave broadcasting, and improvement is desired. To improve the interference, the electric field strength of the broadcast wave should be increased, but it is conceivable to install a large number of small relay stations in order to do so without affecting the foreign countries. In this case, a small and efficient antenna is needed to keep the construction cost as low as possible. Various proposals have been made in the past for improving the efficiency of a small antenna, but all of them are based on the top loading approach.

As for the efficiency of the antenna, it is known that the higher the antenna height is, the better the efficiency is when the antenna height is shorter than the wavelength. Therefore, if the construction cost is sufficient, it is recommended to increase the antenna height. This is the best way to improve efficiency. However, in order to reduce the construction cost, it is not possible to purchase a site with a large area that is usually required, and it is necessary to make the antenna self-supporting within a small site. For this reason, the base insulating portion is strengthened, so that the antenna height is limited. But,
If the material is light and flexible, it can be connected to the top of the antenna to further increase the antenna height. For example, when a rod such as a carbon fiber-containing rod is connected, the wind pressure can be reduced by bending the tip in the case of strong wind.

The present invention has been made in view of the above points, the antenna height can be sufficiently increased even in a relatively narrow site, and
An object is to provide an isolated monopole antenna that can reduce wind pressure.

Example of Invention

Embodiments of the present invention will be described below with reference to the drawings. First
As shown in the figure, an iron pillar having a diameter of 300 mm, for example, is used as the lower antenna 13 on the ground 11 via the base insulator 12.
m (H ₁ ), and a flexible thin rod made of carbon fiber having a length of 10 m (H ₂ ) is connected to the upper part thereof as the upper antenna 14. The antenna is self-supporting, has a small occupied area for installation, and is connected to a transmitter (not shown) from below via a feeder line 15. As described above, carbon is used for the upper antenna 14, and the molding material for molding this carbon fiber into a rod is, for example, polyethylene, polycarbonate, epoxy resin, or the like.

The above-mentioned molded article is coated with an insulating paint having good weather resistance in order to keep the weather resistance of the molded product, and in order to hold it mechanically, it is firmly held from above the insulating paint. Therefore, in order to establish electrical continuity, insulating paint is peeled off from a portion other than the holding portion of the upper antenna 14, one of the jumper wires 16 is directly connected to the carbon fiber, and the other is connected to the lower antenna 16. As a result, the upper antenna 14 and the lower antenna 13 can be electrically connected well.

In the above configuration, the lower antenna 13 has a diameter of 300
mm, and the average diameter of the upper antenna 14 is 2a, the wind pressure is proportional to the area of the antenna, so the ratio is (2
the ^{a / 300) 2 = a 2} /22500. Where a = 50mm
Then, the ratio becomes 11%, and if the strength of the lower antenna 13 is slightly increased, it is possible to sufficiently support the strength. In particular, when the upper antenna 14 is made thin so as to have flexibility, the upper antenna 14 has a shape that does not oppose the wind in a strong wind, and the wind pressure resistance is increased.

The conductivity H of the lower antenna 13 is set to σ = (s / m) = ∞, and the height H of the lower antenna 13 is set to σ = 100, σ = 316.2 and σ = 1000 (s / m) of the upper antenna 14. _{When 1 is set} to 20 m, the calculated value of the input impedance Zin = R + j × (s / m) with respect to the frequency of the monopole is shown in FIG.
In the vicinity of 1.5MHz, the resistance value R is large and the reactance is small compared to the monopole. Therefore, if the ground resistance loss is γ, the efficiency η is Is represented as When R << γ, the resistance of the monopole antenna is 1/3 of the resistance R of the antenna of the present invention.
Since it is ~ 1/4, the efficiency of the antenna of the present invention is increased 3 to 4 times.

Similar to FIG. 2, FIG. 3 shows calculated gain values when the conductivity is changed. The horizontal axis represents frequency and the vertical axis represents relative gain, and 0 dB is the gain of the half-wave dipole. 20
The conductivity is 1000 (s
/ M), the overall gain increases. The frequency is 1.
In the case of 5 (MHz), when the conductivity is 1000, the gain of the monopole is about 0.2 dB larger. Therefore, too thin ones are disadvantageous. If a material with a large radius a is used,
On the contrary, the gain is larger than that of the monopole antenna. The height H ₁ of the lower antenna 13 is set to a predetermined height, for example, 20 m,
By using a carbon fiber for the upper antenna 14 and increasing the antenna height, the resistance component of the input impedance becomes large, so that the efficiency and the gain can be increased.

For the lower antenna 13, a cylindrical column, a steel tower, a Panzer mast, etc. are used.

FIG. 4 shows an application example of the present invention. The lower antenna 13 is firmly supported by the branch line 22 insulated by the branch line glasses 21a, 21b, ... And the upper antenna 14 is made of a light and strong conductive material, so that efficiency and gain are improved.

〔The invention's effect〕

As described above, according to the present invention, in a base insulated monopole antenna having a relatively low height of about 0.6 wavelength or less for frequencies such as medium waves, the lower antenna is composed of a thick metal pillar, and the upper antenna is Since it is composed of a thin and flexible conductive member to keep both electrically connected,
Even on a small site, the antenna height can be increased sufficiently and the wind pressure can be reduced. Also, the input impedance, gain, efficiency, etc. of the antenna can be greatly improved.

[Brief description of drawings]

1 is a configuration diagram of an antenna according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing an input impedance characteristic and a relative gain when the conductivity of the antenna is changed in the embodiment, and FIG. Antenna configuration diagram showing an application example of the present invention,
FIG. 5 is a block diagram of a conventional antenna. 11 ... Earth, 12 ... Insulator, 13 ... Lower antenna, 14 ... Upper antenna, 15 ... Feed line, 16 ...
Jumper.

Claims (1)

[Claims] 1. A base-insulated monopole antenna having a wavelength of about 0.6 wavelength or less, wherein the lower antenna is composed of a thick metal column, and the upper antenna is made of a plastic material made of a carbon fiber having a conductivity different from that of the lower antenna. An insulating monopole antenna, characterized in that it is formed into a thin rod shape having electrical properties, and is configured to be held in an electrically conductive state and fed from the lower antenna.