JPH0136721B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly relates to an omnidirectional antenna that emits radio waves in the microwave band in all directions in a horizontal plane.

Conventionally, most of the omnidirectional antennas used in the microwave band were of the slot array type, which had a simple structure and could be made small. When this slot array type omnidirectional antenna is used as a transmitting antenna, it emits radio waves in a direction perpendicular to the antenna axis, so it is necessary to excite the electric field in each slot in the same phase. A resonant type chosen to be 1/2 of the tube wavelength has been used. FIG. 1 shows an example of such a conventional antenna.

In Fig. 1, 1 is a rectangular waveguide specially made flat in order to obtain omnidirectional characteristics, and 2 is a plurality of axially long slots formed on its wide surface 1a, and each slot 2 is They are arranged on the left and right sides of the center in the width direction of the wide surface 1a so that the interval between their center positions in the longitudinal direction is equal to 1/2 of the wavelength in the tube. Further, the slot 2 is also provided at an opposing position on the opposing surface 1b. This makes it possible to make the radiation direction of radio waves in a plane perpendicular to the tube axis of the antenna non-directional.

By the way, the conventional omnidirectional slot array antenna, in which the slot spacing is chosen to be 1/2 of the channel wavelength, has a narrow frequency bandwidth of the radio waves used, as is well known as a resonant type characteristic. There were flaws. In particular, when narrowing the vertical beam width in order to increase the antenna gain, the number of slots must be increased, which has the disadvantage of further narrowing the bandwidth.

In order to eliminate the above-mentioned drawbacks, the present invention constructs a slot array antenna of a non-resonant type that is shifted slightly more than 1/2 of the channel wavelength, so that the radio wave emission direction is shifted from the direction perpendicular to the antenna axis. A radio wave refraction medium is placed on the outer periphery to change and correct the radio wave propagation direction so that the radio wave emission direction is perpendicular to the antenna axis.The purpose of this is to provide a sufficiently wide frequency band and high gain. The aim is to realize an omnidirectional antenna.

FIG. 2 is a perspective view of one embodiment of the present invention. In Fig. 2, 3 is a flat rectangular waveguide, 4 is a plurality of axially long slots formed on its wide surface 4a, and each slot 4 has a center position in the longitudinal direction whose interval is equal to the guide wavelength. They are arranged on the left and right sides of the center in the width direction of the wide surface 3a, and at opposing positions on the opposing surface 3b, so as to be slightly longer than 1/2 of the width of the wide surface 3a. Reference numeral 5 denotes a hollow cylindrical radio wave refractive medium made of a material such as a dielectric material having a refractive index greater than 1 (for example, polyethylene, polystyrene, etc. with low loss of radio waves). The radio wave refractive medium 5 has a constant outer diameter, and an inner diameter that changes linearly in the axial direction from bottom to top, so that its thickness changes in the axial direction at an angle a. It has an axially symmetrical structure, and its central axis is arranged to coincide with the tube axis of the rectangular waveguide 3. It is assumed that a waveguide from a transmission radio wave generation source (not shown) is connected to the lower part of the rectangular waveguide 3, and the upper part thereof is non-reflection terminated.

In the above configuration, the transmitted radio wave is applied from the lower part of the rectangular waveguide 3 in TE ₁₀ mode, and is radiated to the outside from the slot 4. Since the interval between the slots 4 is slightly larger than 1/2 of the wavelength in the tube as described above, the phases of the electric fields induced in each slot 4 are not in phase,
The higher the position, the more delayed the phase. Therefore, the traveling direction of the radiated radio waves is inclined upward by an angle θ from the direction perpendicular to the tube axis of the rectangular waveguide 3. Therefore, the rectangular waveguide 3 emits radio waves having a conical wavefront. The radio waves make a constant angle with the tube axis, the electric field strength is almost uniform in all directions, and when they pass through the radio wave refraction medium 5, they are corrected in the direction perpendicular to the tube axis as described later. radiated into the air.

Next, we will explain how the radiation direction of radio waves is corrected by the radio wave refraction medium 5. As mentioned above, the electric field strength of radio waves is almost uniform in the direction around the tube axis, so here we will explain how the radio wave radiation direction is corrected. We will consider only one cross-section including . Figure 3 shows a part of the cross section of the omnidirectional antenna shown in Figure 2, including the tube axis.Since the radiated radio waves can be considered to be equivalently radiated from the wave source on the tube axis, it is rectangular. A cross section of the waveguide 3 is not shown. That is, 5a in the figure
and 5b are the outer wall and inner wall of the radio wave refractive medium 5,
O is the tube axis of the rectangular waveguide 3 (or the radio wave refractive medium 5
), P is the wave source on the tube axis O, E is the radio wave radiated from the wave source P, Q is the incident point of the radio wave E on the inner wall 5a, R is the emission point of the radio wave E on the outer wall 5b, S is the wave source Normal at P, T is normal at incident point Q, α
and β are the incident angle and refraction angle of the radio wave E at the incident point Q. If the refractive index of the radio wave refractive medium 5 is n, then the refraction of the radio wave E at the point of incidence Q is expressed by the following equation.

sinα/sinβ=n...(1) Here, in order for the radio wave E radiated into the air from the radiation point R to travel in a direction perpendicular to the tube axis O, that is, in a direction parallel to the normal S, α−β= θ...(2) The following equation must hold. By eliminating α from the above equations (1) and (2), the following equation is obtained: sin(θ+β)/sinβ=n (3). Here, since the refraction angle β is equal to the inclination angle a of the inner wall 5a of the radio wave refraction medium 5, the above (3)
The formula is expressed as follows.

sin(θ+a)/sin a=n (4) Since the angle θ is determined by the spacing between the slots 4 of the rectangular waveguide 3, and the refractive index n is determined by the material, By giving the numerical values of the angle θ and the refractive index n, the inclination angle a that satisfies the above equation (4) can be obtained, and the radio wave E is radiated by the radio wave refractive medium 5 having the inclination angle a thus obtained. The direction can be corrected to be perpendicular to the tube axis O.

As explained above, in the above embodiment, a non-resonant slot array antenna is used to obtain omnidirectional characteristics in the direction perpendicular to the tube axis. The well-known wideband property can be expected, and since this broadband property is not significantly related to the number of slots, it is possible to increase the number of slots and increase the antenna gain while maintaining the broadband property.

FIG. 4 shows another embodiment of the radio wave refraction medium, in which 6 is a hollow cylindrical radio wave refraction medium, 6a is its inner wall, and 6b is its outer wall. The radio wave refraction medium 6 is made of the same material as the radio wave refraction medium 5 in the above embodiment with a refractive index n greater than 1, and has a constant inner diameter and an outer diameter extending linearly from top to bottom in the axial direction. As the thickness increases, the thickness changes uniformly in the axial direction, forming an axially symmetrical structure. Therefore, according to the radio wave refracting medium 6, the radiation direction of radio waves can be corrected to the direction perpendicular to the tube axis, as in the previous embodiment.

FIG. 5 shows still another embodiment of the radio wave refraction medium, in which 7 is a hollow cylindrical radio wave refraction medium;
7a is its inner wall, and 7b is its outer wall. The radio wave refraction medium 7 is made of aluminum, brass, etc., and has a large number of disc-shaped metal conductor plates 8 having a hole 8a in the center arranged parallel to the electric field, and spacers 9 made of foamed polystyrene or the like are placed between the metal conductor plates 8. By setting the interval between the large number of metal conductor plates 8 to 1/2 or less of the wavelength used, the refractive index n of the radio wave is equivalently made smaller than 1, and the hole 8a
By gradually decreasing the diameter from the bottom to the top, the distance between the inner wall 7a and the outer wall 7b, that is, the thickness, can be uniformly changed in the opposite direction to that of the radio wave refractive medium 5 of the above embodiment. It's summery. Therefore, even by using the radio wave refraction medium 7, the radiation direction of radio waves can be corrected, and an omnidirectional antenna with a wide band and high gain can be realized. Note that the spacer 9 may be made of any material as long as the loss of radio waves is small and the refractive index n is about 1, and the spacer 9 may not be provided as long as the distance between the metal conductor plates 8 can be maintained by other means.

The non-resonant slot array antenna may be constructed using a circular waveguide, a coaxial line, etc. in addition to a rectangular waveguide. In this case, the position of the slot and the operation mode will be different from those of the above embodiment.

As explained above, according to the present invention, a hollow cylindrical radio wave refraction medium is provided around the outer periphery of a non-resonant slot array antenna to refract the direction of radio waves radiated from the antenna in a direction perpendicular to the tube axis. Since it is disposed coaxially with the antenna, it is possible to realize an antenna that can radiate radio waves omnidirectionally in a horizontal plane perpendicular to the tube axis, has a wide usable frequency band, and can increase gain. Therefore, it is extremely effective for use in frequency sweep type raymark beacons, raycons, etc. for a large number of marine radars.

[Brief explanation of drawings]

The drawings serve to explain the present invention; FIG. 1 is a perspective view showing an example of a conventional resonant slot array antenna, and FIG. 2 is a perspective view showing an embodiment of the omnidirectional antenna of the present invention. , FIG. 3 is a partially omitted vertical cross-sectional view for explaining the operation of the omnidirectional antenna shown in FIG. 2, FIG. 4 is a vertical cross-sectional view showing another embodiment of the radio wave refraction medium, and FIG. FIG. 7 is a longitudinal cross-sectional view showing still another example of the refractive medium. 3... Rectangular waveguide, 4... Slot, 5... Radio wave refraction medium.

Claims (1)

[Claims] 1. A hollow cylindrical radio wave refraction medium that refracts the direction of radio waves radiated from the antenna in a direction perpendicular to the tube axis is disposed on the outer periphery of a non-resonant slot array antenna coaxially with the antenna. An omnidirectional antenna featuring