JPH0680976B2 - Waveguide slot antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The waveguide slot antenna of the present invention is particularly suitable for an antenna used for a marine radar, and will also be used for wireless communication in the SHF (Ultra High Frequency) band in the future. It is expected that the application of will be expanded.

[Prior Art] A waveguide slot antenna has been conventionally used as a rotating antenna for some marine radar devices, but it is rarely touched by the general public and is not listed in an antenna-related manual. There are many types of antennas and they are not well known, so the following is the "Antenna Engineering Handbook" (edited by The Institute of Electronics and Communication Engineers, published by Ohmsha, October 30, 1955, first edition)
A more detailed excerpt is put.

Reprinted from page 223 of the Antenna Engineering Handbook "Fig. 8.2.
(Omitted) is a waveguide slot antenna which is an example of the simplest configuration of the series feeding circuit. The power coupling part from the waveguide that is the main line forms the element antenna as it is,
The degree of coupling is determined by the tilt angle of the slot. The slot spacing is half the wavelength in the waveguide, and the condition of co-phase excitation is satisfied by reversing the tilt direction for each element. Reprinted from page 249 of the Antenna Engineering Handbook "7/6/3
Nautical Radar Antenna [1] Ship-mounted radar antenna (b) Slot type radar antenna (Omitted) Currently, a slot antenna with a small aperture can be used for navigation radar. As shown in the figure (omitted), the slot antenna cuts a groove (slot) in the waveguide wall and uses the radio waves radiated from the slot as an array. It is light in weight, low in wind resistance, and moreover on the antenna. Has the advantage that it is easy to select the current distribution of. As the current distribution to be used, the Tiewisev distribution that minimizes both the beam width and the side rope level for a given antenna length, or the beam width expands slightly,
A Taylor distribution is used that has a low side rope and obtains a high gain pattern. The slot length has a wide band property as a non-resonant slot slightly shorter or longer than λg / 2.
Therefore, the beam direction is slightly deviated from the broadside direction. (The following is omitted.) ”The drawing of which reference is omitted is almost the same as FIG. 4 of the present specification. As is clear from this figure, the main body of the waveguide slot antenna is the rectangular waveguide itself,
Since the structure has the slots a to n provided on one side wall thereof,
Compared with other SHF band antennas, it has the advantages of high mechanical strength and small occupied volume.

[Problems to be Solved by the Invention]

In the waveguide slot antenna, each slot operates as a radiating element, so it can be considered as an array antenna in which as many elements as the number of slots are arranged in the central direction of the waveguide. By increasing the number, the radiation directivity in the plane including the center line of the waveguide and perpendicular to the slot plane (hereinafter referred to as the horizontal radiation plane for convenience) becomes sharp, and the center gain also increases. With respect to the radiation directivity in a plane orthogonal to both of the emission planes (hereinafter referred to as a vertical emission plane for convenience), only the degree of directivity of a single dipole element can be expected. It is good as a ship radar antenna for displaying the position of an object on the water surface by rotating the antenna along a horizontal plane and measuring the intensity and reflection time of the reflected radio wave in the horizontal direction, For wireless communication applications, it is desirable to have good omnidirectional directivity, such as a parabolic antenna, which is another SHF band antenna, and a horn antenna.

In the waveguide slot antenna, since the horizontal plane directivity is perfectly satisfactory, improving the vertical plane directivity improves the omnidirectional directivity. Further, it is desirable to improve the directivity of the vertical plane because it can reduce water surface reflection and aircraft reflection even for a line radar.

[Means for Solving the Problems]

In order to improve the vertical directivity of the waveguide slot antenna, two waveguide slot antennas are vertically stacked in the present invention.

It is well known that many directional antennas are improved in directivity and gain in the stacking direction by stacking the antenna units, and it is also in practical use. However, it is estimated that there is no data that there is no example of stack use in the waveguide slot antenna, but it is estimated that there was no obstacle to the intended purpose because the conventional application was limited to ship radar. In addition, in the stack antenna, it is necessary to feed power so that each antenna unit is excited in the same phase, but the feed waveguide is directly connected to one end of the antenna unit of FIG. 4 which is the basic form of the waveguide slot antenna. In the structure, the mechanism for feeding each unit from the main waveguide through the two-branch waveguide runs counter to the simplicity of the antenna unit and is completely unsuitable for use as a rotary antenna for radar.

Further, as a rotating antenna for radar, a structure in which a feeding probe is installed penetrating the rotation center part of an antenna unit is mainly used as shown in FIG. 5, but when a stack antenna is used, the feeding probe of each unit is the rotation center. This is also due to the fact that a power supply system that is an axis and is excited in the same phase has not been developed.

In order to solve the above-mentioned point, in the present invention, as shown in the partial cross-sectional schematic view of FIG. 1, the waveguide slot antenna unit 1 and the waveguide slot antenna unit 2 have the same slot surfaces 11 and 12. A three-quarter-wavelength feeding probe is provided by stacking in the same direction and penetrating the antenna units 1 and 2.

FIG. 2 is a vertical cross-sectional view for explaining the mechanical relationship and operation of the stacked antenna units 1 and 2 and the feeding probe 3.

Since the antenna units 1 and 2 are stacked so that the center distance is about one-half wavelength, depending on the size of the rectangular waveguide forming the unit, both units may come into close contact with each other or may have a space therebetween.

Since the excitation of this antenna system is performed by the three-quarter-wavelength feeding probe 3 that penetrates each antenna unit,
Necessary holes are provided in the waveguide wall passing through. Further, when there is a gap between the antenna units 1 and 2, it is appropriate to provide a spacer 4 having a shield effect in order to prevent direct radiation from that portion.

In the above structure, since the feeding probe 3 has a length of 3/4 wavelength, the current distribution on the feeding probe 3 is roughly indicated by a dotted line, and the excitation phase in each antenna unit is indicated by an arrow. It is in reverse phase. In order to improve directivity and gain in the stack antenna, the radiated electromagnetic waves of each antenna unit must be in phase, but in the present invention, the slots of the antenna units 1 and 2 are located at the same distance from the feeding probe 3. (For example, the slots 12a and 22a or the slots 11n and 22n) are reversed in inclination direction so that the phases of the electromagnetic waves radiated from all the slots can be easily aligned.
Details of the structure will be described in Examples below.

Note that the center distance of the antenna units to be stacked is set to about ½ wavelength because the stacking antenna is a simple numerical combination of the directional characteristics of the individual units as shown in Fig. 3 due to mutual interference of the antenna units. Unlike
Since side ropes may be generated, it is common knowledge for those skilled in the art to determine the optimum dimension for the purpose of use by actual measurement. It must also be considered that the current distribution on the feeding probe is different from the distribution in free space.

A converter for converting the TE mode of the feed waveguide into the TEM mode of the probe is provided at the base of the feed probe. In the case of coaxial feeding, mode conversion is not necessary, but an impedance matching section is provided. At this time, in the present invention, a three-quarter wavelength probe is used, and power is supplied by the antinode of the current, so that the impedance is low and matching is easy.

〔Example〕

FIG. 6 is a front view of a horizontally polarized two-stage stacked waveguide slot antenna for marine radar to which the present invention is applied.
Both antenna units 1 and 2 are approximately λg in length with an interval of λg / 2.
/ 2 slots 12a to 12n are provided, and the tilt directions of the slots are alternately inverted to invert the antiphase excitation wave due to the λg / 2 difference and radiate in phase. Further, in the units 1 and 2, the slots at the same distance from the power supply probe 3 are made to have opposite inclination directions, and the phase due to antiphase excitation is corrected so that all radiated waves are aligned in the same phase. Further, a spacer 4 also serving as a shield is provided around the feeding probe 3, and auxiliary spacers 5A and 5B are provided between both ends of the antenna units 1 and 2 to secure a stack interval. Here, λg is the wavelength in the waveguide and is slightly shorter than the wavelength λo in free space.

FIG. 7 is a vertical sectional view of a feeding portion of the two-stage stacked waveguide slot antenna of FIG.

Antenna units 1 and 2 are waveguides with slots 12a-12n.
22a to 22n and the feed probe through hole are processed and used, and the spacer 4 is inserted and stacked.

The feeding probe 3 is mounted on the inner wall of the feeding waveguide 6 and has a tapered ridge 7 for mode and impedance conversion.
The antenna units 1 and 2 are mounted vertically on the abutment 8 via bearings 9 so that the antenna units 1 and 2 rotate horizontally around the power supply probe 3.

The feed probe 3 and the tapered ridge 7 are shown in FIG. 8, but the ridge 7 is usually made of the same material as the waveguide 6, and the tapered portion may be a straight line.

The feeding probe 3 is vertically implanted on the upper end surface of the ridge 7, and the probe 3 is usually a silver-plated hard copper wire.

In this structure, the feeding probe 3 is fixed, and only the antenna units 1 and 2 rotate, so there is an advantage that a rotary joint is not required in the feeding circuit.

〔The invention's effect〕

In the waveguide slot antenna according to the present invention, by utilizing the narrow directivity characteristic of the horizontal in-plane directivity, which is an advantage of the conventional waveguide slot antenna, and improving the vertical in-plane directivity which is a weak point, Even as a radar antenna for ships, which is an application, it reduces unnecessary reflection from the water surface and flying objects,
Not only is it effective in reducing false images on radar display drawings, but it is also expected that the applications for general communications and satellite broadcasting reception will be expanded by improving the directivity and gain in the vertical plane.

Mechanically, two antenna units are brought into close contact with each other or stacked at relatively narrow intervals with a spacer interposed therebetween, which has the effect of increasing the strength as compared with the antenna units alone.

Furthermore, since the structure is such that only one 3/4 wavelength probe is passed through and held by both antenna units for power feeding, the structure is extremely simple, and the antenna for radar is also shown in FIG. As can be seen from the above, since only the antenna unit is rotated around the fixed feeding probe as the central axis, it is convenient that the conventional radar antenna rotating mechanism can be used almost as it is.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a waveguide slot antenna of the present invention, FIG. 2 is a vertical cross-sectional view of FIG. 1, FIG. 3 is a combined radiation characteristic diagram of a stack antenna, and FIG. FIG. 5 is a plan view of a probe-fed waveguide slot antenna, FIG. 6 is a front view of an embodiment of the present invention, and FIG. 7 is an embodiment of the present invention. FIG. 8 is a vertical cross-sectional view of the feeding portion shown, and FIG. 8 is an external view of the feeding probe and the tapered ridge. 1-2: Waveguide slot antenna unit, 11/21 ...
… Slot surface, 12a-12n, 22a-22n …… Slot, 3…
… Feed probe, 4 ・ 5A ・ 5B …… Spacer, 6 …… Feed waveguide, 7 …… Tapered ridge, 8 …… Abutment, 9 ……
bearing.

Claims (1)

[Claims] 1. A waveguide slot antenna unit is formed by stacking two waveguide slot antenna units so that the slot surfaces have a center distance of about one-half wavelength, and penetrate each antenna unit to provide three-quarter wavelengths. A waveguide slot antenna, characterized in that a feed probe is provided, and the tilting direction of slots at the same distance from the feed probe of each antenna unit is reversed.