JPH0447482B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse radar antenna that measures a nearby object using pulses with a narrow time width.

Generally a rod-shaped dipole antenna with a large diameter,
It is known that a flat triangular dipole antenna has constant impedance characteristics over a wide band, and the above antenna is used for transmitting and receiving signals having a wide band spectrum. In the antenna described above, a current that travels on the antenna surface from the feeding point toward the open end and a backward wave that is reflected at the open end and returns to the feeding point coexist, resulting in standing wave excitation. When a pulse with such a narrow time width that the time required for flowing from the feeding point of the antenna toward the open end of the antenna cannot be ignored is applied to such an antenna, the pulse is generated by the traveling wave current flowing from the feeding point toward the open end. , and the remaining energy is reflected at the open end and re-radiated when it returns to the feeding point as a backward wave.When the above antenna is used as a pulse radar antenna, it has the disadvantage of producing a false echo. In order to suppress this phenomenon, the dipole antenna is made longer than 1/2 wavelength, and an appropriate resistor is loaded at a position of 1/4 wavelength from the feed point of the antenna toward the open end. A part of the current that should become a backward wave is absorbed by the resistor, and the remaining current is passed through the 1/4 wavelength position and reflected at the open end.
This problem was solved by further absorbing this backward wave with the resistor and exciting the area from the feeding point to the loading position with only the forward wave current, but this problem resulted in an increase in the aperture area of the antenna, and an increase in the open end of the antenna. Reflected waves exist between the loading resistors, which contribute to radiation. In addition, in order to provide directivity in only one direction and eliminate unnecessary radiation components, a reflector or a shield case that also serves as a reflector is required at a distance of 1/4 wavelength from the antenna.
If the distance R between the reflector and the antenna is made shorter than 1/4 wavelength in order to reduce the size, there is a drawback that the band becomes narrower.

The present invention eliminates this drawback and provides a pulse radar antenna that is small and simple in structure, does not impair broadband constant impedance characteristics, and can suppress reflected waves from the open end of a triangular dipole antenna. This will be explained in detail below based on the drawings.

1 and 2 are a longitudinal cross-sectional view and an A-A' cross-sectional view of an embodiment of the antenna of the present invention.
2 is a feeding connector, 2 is a broadband balun as a balanced/unbalanced converter, 3 is a dielectric substrate, 4 is a triangular dipole antenna formed by etching a metal plate fixed on the substrate 3, and 5 is a conductive antenna. A dielectric material having an inverted concave shape, such as a dielectric material made by coating particles of foamed polystyrene with graphite, 6 a metal plate shield case which is used both as a metal plate and a reflection plate, 7 a triangular dipole antenna 4 This is a space surrounded by a metal plate shield case. Narrow pulses sent from a transmitter (not shown) through the feed connector 1 are passed through the broadband balun 2 to
The current is applied to the central feeding terminal of the triangular dipole antenna 4 having a length of 1/2 wavelength of the pulse fundamental wave, and the current travels toward the outside of the triangular dipole antenna 4 from the feeding point. When the fundamental wave component travels by 1/4 wavelength, the current is absorbed by the inverted concave dielectric 5 made of, for example, expanded polystyrene particles coated with graphite. The dielectric 5 is connected to both open ends of the triangular dipole antenna 4, and extends vertically from one open end toward the reflector (corresponding to 6), and is recessed between the antenna 4 and the reflector. It is folded back into a shape and connected to the other open end, and there is a space 7 between the dielectric 5 and the central part of the antenna. For example, a current flowing through graphite travels from one end of the triangular dipole antenna 4 to the other end, but because the resistivity of the graphite is large, the traveling wave current is converted into thermal energy, which is absorbed by the dielectric 5. be done. Therefore, the pulse current returning from the open end of the triangular dipole antenna 4 to the feeding point is only due to the mismatch between the open end and the dielectric 5, and the amount thereof is very small. In addition, the dielectric material 5 has the property of absorbing radio waves over a wide band, and the pulses radiated from the triangular dipole antenna 4 toward the metal plate shield case 6 are attenuated when they are incident on the shield case 6 and reflected, and the reflected waves are has a small effect on the antenna impedance, making it possible to take advantage of the wideband characteristics of the triangular dipole.

As explained above, by utilizing the space between the triangular dipole antenna 4 and the shield case 6, both ends of the triangular dipole antenna 4 are short-circuited with, for example, an inverted concave dielectric material 5 coated with graphite. The structure is small and simple, and reflection from the open end of the antenna is suppressed with such a simple structure, and the pulses radiated to the shield case 6 side are absorbed by the dielectric 5, so that the reflection plate and the distance R between the antenna
can be made small while maintaining broadband characteristics, and when the antenna 4 is used as a pulse radar antenna, it has the effect of suppressing pseudo echoes.

[Brief explanation of drawings]

FIGS. 1 and 2 are a longitudinal cross-sectional view and an A-A' cross-sectional view, respectively, showing an embodiment of the antenna of the present invention. 1...Power supply connector, 2...Broadband balun, 3
... Dielectric substrate, 4 ... Triangular dipole antenna, 5 ... Reverse concave dielectric with conductivity, 6 ... Metal plate shield case, 7 ... Space part.

Claims (1)

[Claims] 1. A triangular dipole antenna fixed on one side of a dielectric substrate with the apex angles of triangular metal plates facing each other, and a triangular dipole antenna arranged parallel to the triangular dipole antenna in order to radiate electromagnetic waves from the triangular dipole antenna in a single direction. the arranged metal plate shield case; and both leg ends disposed in a space formed by the triangular dipole antenna and the metal plate shield case and abutting both open ends of the triangular dipole antenna to electrically short-circuit each other; What is claimed is: 1. A pulse radar antenna characterized in that it has an inverted concave dielectric material that is both electrically conductive and suppresses reflected waves from both open ends of the triangular dipole antenna.