JPH0314807Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a resistive plate-terminated antenna that can be used, for example, as an antenna for an underground radar that searches for underground objects.

``Prior Art'' In short-range radars that detect buried objects within several meters underground from the ground surface, the time from the time the radio waves are transmitted until the radio waves are reflected back is extremely short. For this reason, the transmitted radio wave uses a single pulse wave that ends in a short time.

However, when transmitting a single pulse wave, the antenna must instantly stop resonating and must have a characteristic that no residual vibration occurs. In other words, when using an antenna that generates residual vibrations, if the antenna is still vibrating when the reflected waves return, the reflected waves cannot be detected. For this reason, the antenna must have low sharpness, that is, it must have broadband characteristics.

In response to these demands, the applicant developed a resistor-loaded dipole antenna as shown in Figure 2.
-172260, Utility Model Application Publication No. 1985-85912. FIG. 3 shows an electrical equivalent circuit of the resistor-loaded dipole antenna shown in FIG. 2. Third
In the figure, 1A and 1B indicate antenna conductors constituting a plate-shaped broadband dipole antenna 1. The antenna conductors 1A and 1B are formed by cutting a conductive plate into a triangular shape and placing the vertices facing each other. Furthermore, the mutually opposing vertices are used as feeding points, and a single pulse wave-shaped transmission pulse is supplied to these feeding points through the feeding line 2.

A connecting conductor 3 is connected to both ends of the antenna conductors 1A and 1B. This connecting conductor 3 is formed into a band shape so as to have a cross-sectional area that does not have an inductance component with respect to high-frequency signals, and a loading resistor 4 is connected between both ends of the antenna conductors 1A and 1B by the connecting conductor 3.
Connect.

As the loading resistor 4, a strip-shaped resistor is used as shown in FIG. In other words, the resistor is also made to have a sufficiently large cross-sectional area so that it does not have an inductance component.

The antenna conductors 1A and 1B are supported by being attached to an insulating plate 5 as shown in FIG. At the same time, a bowl-shaped radio wave shield 6 is placed over one surface of the antenna conductor. In the example shown in FIG. 2, the radio wave shielding body 6 is constituted by a bowl-shaped body 6A formed of, for example, a conductive plate and a radio wave absorber 6B stuck to the inner wall surface of the bowl-shaped body 6A. For example, a ferrite plate can be used as the radio wave absorber 6B.

When a transmission pulse is applied to a feeding point using such a structure, the high-frequency current component of the transmission pulse travels from the feeding point toward the opposite side of the feeding point and is radiated as an electromagnetic wave. On the other hand, the low frequency current component of the transmission pulse is hardly radiated as an electromagnetic wave due to the short dimensions of the antenna conductors 1A and 1B, and most of the low frequency current component flows through the loading resistor 4 and is dissipated as heat.
In this way, the high frequency component of the transmission pulse applied to the feeding point is radiated as electromagnetic waves. Since the loading resistor 4 is connected between both ends of the antenna conductors 1A and 1B, the sharpness of the antenna is reduced, and a broadband dipole antenna with less residual vibration can be obtained.

Furthermore, by providing the radio wave shield 6, the radio waves radiated from the antenna conductors 1A and 1B are radiated only in the underground direction, and the radio waves radiated in directions other than the underground direction are blocked by the radio wave shield 6. Therefore, the amount of radio waves leaking to the outside can be reduced, and radio waves can be prevented from entering the antenna 1 from the outside.

Further, since no reflection occurs at the radio wave shield 6, reflected waves are not emitted underground. Therefore, there is also the advantage that the SN ratio of the received signal received from underground can be improved.

Further, the connecting conductor 3 and the loading resistor 4 are formed in a band shape,
Since the cross-sectional area is large in the current path direction, no inductance component is generated. Therefore, the short circuit consisting of the connecting conductor 3 and the loading resistor 4 can maintain the sharpness at a low value over a wide band.

``Problem that the invention attempts to solve'' By the way, the radio wave shield 6 shown in Figure 2 absorbs most of the radio waves emitted in directions other than underground, but it cannot completely absorb 100%. It's difficult.
This has the disadvantage that radio waves leak a little and that underground exploration is obstructed if strong radio waves arrive from the outside.

``Means for Solving the Problems'' This invention has a structure in which a waterproof cover is placed over the resistive plate-terminated antenna and a shielding coating is applied to the inner wall surface of the waterproof cover.

``Operation'' According to the structure of this invention, radio waves leaking from the resistive plate-terminated antenna are reflected or absorbed by the shielding coating formed on the inner wall surface of the waterproof cover, thereby reducing the amount of leakage to the outside.

In other words, the shielding film may be a metal film or a resistive film. When a metal coating is used as the shielding coating, the radio waves are reflected by the shielding coating and returned to the resistive plate-terminated antenna side. The outer peripheral surface of the resistance plate terminated antenna is a bowl-shaped body 6A.
, the radio waves are repeatedly reflected between the shielding film and the outer peripheral surface of the bowl-shaped body 6A, and gradually attenuate and disappear.

On the other hand, when a resistive film is used as the shielding film, radio waves leaking from the resistive plate-terminated antenna are absorbed by the shielding film. Therefore, the amount of leakage to the outside can be significantly reduced.

``Example'' Figure 1 shows an example of this invention. 11 in the diagram
shows the resistor plate terminated antenna explained in FIG.
In this example, a resistive plate-terminated antenna 11 is mounted on a plastic truck 12, and a waterproof cover 13 is placed over the top of the truck 12. Note that 14 indicates a wheel. The waterproof cover 13 is formed in the shape of a bowl, and the bowl-shaped waterproof cover 13 is placed over the top of the truck 12 and its four circumferences are connected to the flange portion 12A formed on the truck 12 with screws or the like to prevent rainwater from entering the interior of the truck 12. The structure is designed to prevent this from happening.

This invention has a structure in which a shield coating 15 is applied to the inner wall surface of the waterproof cover 13. As the shield coating 15, as described above, a conductor coated by vapor deposition or a resistor coated by uniform spray coating can be used.

As the conductor, for example, copper foil or aluminum foil can be formed by, for example, vapor deposition. In addition, in the case of a resistor layer, for example, a carbon film is sprayed,
Alternatively, it can be formed by vapor deposition. Further, the shield coating 15 can be formed not only on the inner wall surface of the waterproof cover 13 but also on the inner wall surface of the truck 12 excluding the portion facing the bottom surface of the resistive plate-terminated antenna 11.

Although not particularly shown in the drawings, the bogie 12 has a structure in which a plurality of holes for attaching axles are provided in the vertical direction, and the height of the bogie 12 from the ground can be changed by appropriately selecting the positions of the holes. .
By having a structure that allows the height of the trolley 12 from the ground to be changed, the height of the trolley can be changed according to the ground conditions, and the trolley 12 can be set in a state where it can run smoothly. This has the advantage that the radiation surface of the antenna can always be set closest to the ground.

"Effects of the invention" As mentioned above, according to this invention, the radio wave shield 6
Since the shielding film 15 that is attached to the inner wall surface of the waterproof cover 13 is further provided on the outside of the radio wave shielding body 6,
Even if a radio wave passes through, the transmitted radio wave is reflected or absorbed by the shield coating 15 provided on the outside. In other words, when the shielding film 15 is a conductive foil, the radio waves are reflected by the shielding film 15,
The reflected wave is returned to the radio wave shield 6 and
It is absorbed by and disappears.

In addition, when a resistor layer is used as the shield coating 15, the radio waves transmitted through the radio wave shield 6 are transferred to the shield coating 15 formed on the inner wall surface of the waterproof cover 13.
It is absorbed by and disappears.

In this way, according to this invention, the amount of radio wave leakage from the resistor plate-terminated antenna can be reduced.

Furthermore, since the radio wave shielding body 6 is structured to absorb radio waves, it is possible to prevent radio waves emitted upward from being reflected and directed underground. In this respect, reflected waves from the target can be received with a good signal to noise ratio. Furthermore, since it has a double shield structure of the radio wave absorber 6 and the shield coating 15 attached to the inner surface of the waterproof cover 13, it is possible to obtain a short-range radar antenna with excellent performance that is less likely to be interfered with by external radio waves. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a sectional view for explaining one embodiment of this invention, Fig. 2 is a partially sectional perspective view for explaining the structure of the resistor plate-terminated antenna proposed earlier, and Fig. 3 is a sectional view for explaining an embodiment of the invention. FIG. 3 is a connection diagram for explaining an electrical equivalent circuit of the resistor plate-terminated antenna shown in FIG. 2; 1: dipole antenna, 1A, 1B: antenna element, 2: feed line, 3: connection conductor, 4: loading resistor, 5: insulating plate, 6: radio wave shield, 6A: bowl-shaped conductor, 6B: radio wave absorber, 11: Resistance plate terminated antenna, 12: Trolley, 13: Waterproof cover, 14: Wheel, 15: Shield coating.

Claims (1)

[Claims for Utility Model Registration] A: A pair of antenna conductors constituting a dipole antenna; B: A bowl-shaped body formed by a conductive plate that covers the upper part of the pair of antenna conductors; and C: The outer peripheral surface of this bowl-shaped body. D: a band-shaped resistor which is attached to the antenna conductor and is placed between both ends of the pair of antenna conductors and electrically connected to both ends of the antenna conductor; D: a waterproof cover that covers the upper surface of the bowl-shaped body; and E: A resistive plate-terminated antenna comprising: a radio wave absorber coated on the inner peripheral surface of the body; and a shielding film coated on the inner wall surface of the waterproof cover.