JPS6363122B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a so-called shot backfire antenna in which a main reflector and a small reflector are arranged three-dimensionally at short intervals before and after a feeding radiator. .

<Prior art> As an antenna, the length in the axial direction of the antenna can be configured to be shorter than that of an endfire array (for example, Yagi/Uda antenna), and the antenna has good aperture efficiency.
A short backfire antenna, the components of which are shown in FIG. 1, has been considered. This short fire antenna is basically the first antenna.
As shown in the figure, it consists of a planar main reflector 1, a side reflector 2, a small reflector 3, and a feeding radiator (die ball in the figure) 4, which are provided in a cylindrical shape on its outer periphery in parallel with the central axis. It is configured.

The radiation characteristics of this antenna are influenced by the specifications of the constituent elements (also shown with symbols in Figure 1), and an analytical design method for this has not yet been established.
Typical specifications when obtaining a gain of about 14 dB are: Diameter of main reflector 1 (D _R ) 2 wavelengths Depth of side reflector 2 (W _B ) 0.25 wavelength Diameter of small reflector 3 (D _r ) 0.5 wavelength Distance between main reflector 1 and small reflector 3 (S _R )
Distance between 0.5 wavelength feeding dipole 4 and small reflector 3 (S _r )
0.25 wavelength is used.

Among the above specifications, the diameter D _R of the main reflector 1 is of course the most dominant factor in the gain, but the distance S _R between the main reflector 1 and the small reflector 3 is also deeply related to the basic operation of this antenna. , this short-backfire antenna is selected to have the narrowest interval among 1/2 wavelengths (N) times an integer (N) of 1/2 wavelengths (N=1).

In FIG. 1, the electromagnetic waves radiated from the feeding radiator 4, which is made up of, for example, a 1/2 wavelength dipole, are transmitted through a leakage cavity made up of a main reflector 1, a small reflector 3, and a side reflector 2. Internally, between the main reflector 1 and the small reflector 3, the distance between them S _R
is selected as 1/2 wavelength as above, so
The electromagnetic waves emitted from the feeding radiator 4 are reflected many times, and as a result, a standing wave is excited at the aperture between the tip of the side reflector 2 and the small reflector 3, and a single wave is generated in the antenna axis direction. A tropic beam is emitted.

<Problems to be Solved by the Present Invention> However, the operating frequency of the short-backfire antenna according to the prior art with such a configuration is, as a matter of course, based on the above-mentioned basic operating principle.
A planar main reflector 1 and a side reflector 2 on its outer periphery
, a small reflector 3 parallel to the planar main reflector 1, and a feeding radiator 4. Since this is a radiation antenna based on the leakage cavity resonance phenomenon, the distance S _R between the main reflector 1 and the small reflector 3 is 1. /2 wavelength, which is a narrow frequency band near the basic operating frequency, and the input impedance of the feeding radiator 4 also exhibits a rapid change near the basic operating frequency, which makes it difficult to use this antenna in practical terms. becomes narrow.

FIG. 2 shows an example of actually measured frequency characteristics of the input standing ratio (VSWR) for a conventional short-backfire antenna configured with the above specifications.

This antenna is intended for use in the frequency band allocated to the maritime mobile satellite service between 1535MHz and 1644MHz, and a sleeve dipole designed to widen the band has been adopted as the feeding radiator 4. It is clear that the VSWR characteristics shown in Figure 2 result in an extremely narrow frequency band and are difficult to put into practical use.

Therefore, in order to widen the frequency characteristics of the input VSWR to some extent, the distance S _R between the main reflector 1 and the small reflector 3 should be set to about 0.6 wavelength, which is wider than 1/2 wavelength, or It is necessary to reduce the diameter D _r of 0.3 to 0.4 wavelength. However, if this is done, the operation of the antenna deviates from the basic operation and the aperture efficiency decreases. Therefore, in order to obtain the required gain, it is necessary to increase the diameter of the main reflector 1 by 20 to 30% from its original size.

Conversely, the gain can be increased by making the diameter of the small reflector 3 larger than 0.5 wavelength and making the depth WB of the side reflector 2 0.4 to 0.7 wavelength without changing the diameter of the main reflector 1. However, since the leakage cavity resonance phenomenon formed by the main reflector 1, side reflector 2, and small reflector 3 is further strengthened, the operating frequency band is further narrowed.

An object of the present invention is to provide a short-backfire antenna that solves the above-mentioned problems.

<Means for solving the above-mentioned problems> In order to solve the above-mentioned problems, the short-backfire antenna of the present invention has an aperture diameter of 1 to 3 wavelengths and an aperture angle of 120° to 120°.
a main reflector having a conical shape of 160°; and a side reflector projecting forward in a cylindrical shape parallel to the central axis of the aperture of the main reflector along the periphery of the aperture of the main reflector; , a feeding radiator disposed in front on the central axis of the aperture surface of the main reflector, and a feeding radiator disposed on the central axis of the aperture surface of the main reflector, perpendicular to the central axis, A small reflector is provided in front of the main reflector, which is arranged at an interval of 0.5 to 1 wavelength from the center of the aperture of the main reflector.

<Function> In this way, the aperture diameter of the main reflector is 1 to 3 wavelengths,
Main reflector 1
Since the facing distance between the small reflector and the small reflector is not constant,
The cavity resonance phenomenon is alleviated, resulting in a broadband characteristic, and the position of the front end of the side reflector on the plane perpendicular to the central axis of the main reflector can be adjusted without increasing the length of the side reflector in the axial direction. Since the small reflector can be placed close to the arrangement surface, the electric field irradiation distribution due to standing wave excitation on the aperture surface between the small reflector and the small reflector can be made uniform without intensifying the cavity resonance phenomenon, and the aperture efficiency can be improved. It gets expensive.

<Example of the present invention> Next, an embodiment of the present invention is shown in FIG.

The main reflector 1 has a conical opening in the direction of the feeding radiator 4 at an aperture angle α.

The aperture angle α of the main reflector 1 must be selected in relation to other specifications, especially the diameter D _R of the main reflector 1.
For a diameter D _R of 1 to 3 wavelengths, the aperture angle α
A suitable angle is 120° to 160°.

The side reflector 2 and the feed radiator 4 are similar to those shown in FIG.

Also in this structure, the electromagnetic waves radiated from the feeding radiator 4 are reflected several times between the main reflector 1 and the small reflector 3, thereby exciting a standing wave and radiating the electromagnetic waves.

However, by making the main reflector 1 have a simple geometric shape and tilting it at an appropriate aperture angle α in front of the antenna, that is, in the radiation or incidence direction of radio waves, the main reflector 1 and the small reflector 3 can be Since the facing distance between the reflector and the reflector is no longer constant, even though the standing wave excitation radiation is carried out, the main reflector 1 and the small reflector 3 are parallel to each other as seen in conventional short backfire antennas. Cavity resonance phenomena such as this are alleviated, and good broadband characteristics can be obtained.

In addition, compared to the case of a conventional planar main reflector, the main reflector 1 has a conical shape with an aperture angle α;
Since the front end of the side reflector 2 approaches the placement surface of the small reflector 3 without forming the side reflector 2 deeply, the feeding radiator 4 for the peripheral part of the main reflector 1 is
The electric field irradiation distribution by the small reflector 3 is optimized, and as a result, the aperture efficiency is improved and an excellent radiation pattern with low side lobes is obtained.

Next, this will be explained in more detail.

That is, in the conventional short-backfire antenna, in order to narrow the beam angle of the reflected main lobe and increase the gain while keeping the dimensions of the main reflector 1 constant, (i) the diameter D of the small reflector 3; It is clear from the experimental results that it is effective to increase _r to 0.5 to 0.6 wavelengths and (ii) to increase the depth WB of the side reflector 2 to 0.4 to 0.7 wavelengths.

In particular, increasing the depth WB of the side reflector 2 means moving the tip P to P' as shown in FIG. The electric field irradiation distribution due to standing wave excitation on the aperture between P′ is made uniform, the radiation from P′ is strengthened,
It acts so that the phase of the radiation matches the phase of radiation from other apertures (for example, radiation from near the periphery Q of the small reflector 3) in a far-field electric field.
However, if the diameter of the small reflector 3 is increased and the depth WB of the side reflector 2 is increased as described in (i) and (ii) above, the main reflector 1, the side reflector 2, and the small reflector The leaky cavity resonance phenomenon formed in the antenna 3 is further strengthened, and it is inevitable that the operating band of the antenna will be further narrowed.

However, in the short-backfire antenna according to the present invention, as shown by the dotted line in FIG.
The side reflector 2 remains at its front end without changing its depth.
P' is placed approximately 0.25 wavelength ahead of the tip P of the side reflector 2 according to the conventional technology (a position corresponding to approximately 0.5 wavelength in depth of the side reflector 2 according to the conventional technology, near point P' in Fig. 8). has been done. Furthermore, the diameter of the small reflector 3 is also kept at 0.5 wavelength.

Therefore, the electric field irradiation distribution due to the standing wave excitation on the aperture between the peripheral edge Q and P' of the small reflector 3 is made uniform, as described above, without intensifying the leakage cavity resonance phenomenon. , P' is intensified, and its radiation phase acts to match the phase of radiation from other apertures (for example, radiation from near the periphery Q of the small reflector 3) in the far electric field.

By forming the main reflector 1 into a conical shape with an aperture angle α, the resonance characteristics of the leakage cavity formed by the main reflector 1, side reflectors 2, and small reflectors 3 can be improved compared to the conventional technology. Due to the resonance characteristics of the cavity part, the sharpness of resonance is significantly reduced,
The depth of the side reflector 2 in the conventional technology is 0.5 to 0.6
It is possible to obtain broader band characteristics than in the case of wavelength.

In addition, by forming the main reflector 1 in a conical shape, as a result of the effect acting in combination with the effect of the side reflector 2, an opening in the peripheral part of the main reflector 1 is formed as shown in FIG. The surface electric field distribution (indicated by arrows in the figure) is such that the irradiation is stronger than when it is formed using a flat plate-shaped main reflector in the conventional technology, and
The phase is also optimized by making it conical rather than a flat plate, so side lobes are suppressed,
This increases the aperture efficiency.

Here, as an example, the specifications for a maritime satellite communication antenna are shown below.

Aperture diameter of main reflector 1 (D _R ) 400 mm (2.05 wavelength at 1.54 GHz) Depth of side reflector 2 (W _B ) 48 mm (0.25 wavelength at 1.54 GHz) Diameter of small reflector 3 (D _r ) 90 mm ( (0.46 wavelength at 1.54GHz) Distance between the center of main reflector 1 and small reflector 3 (S _R ) 120mm (0.62 wavelength at 1.54GHz) Distance between feeding dipole 4 and small reflector 3 (S _r )
60mm (0.26 wavelength at 1.54GHz) Aperture angle (α) of main reflector 1 150° The antenna in this example (actually for circularly polarized waves composed of dipoles with intersecting feeding radiators 4)
The directivity gain at 1.54 GHz is 15.5 dB, the side lobe level is 20 dB or less, and the aperture efficiency of the main reflector 1 is as high as 85%.

The input VSWR vs. frequency characteristics of this antenna are shown in the fourth section.
This is shown by the solid line curve A in the figure. Compared to the conventional short-backfire antenna shown in Fig. 2, it shows significantly improved wideband characteristics, and the desired frequency band of this antenna, i.e.
The VSWR value is sufficient for practical use across the 1.54/1.64 GHz reception/transmission frequency band.

FIG. 6 shows a comparative example of the radiation pattern characteristics of the present invention and the conventional short-backfire antenna shown in FIG. 1 when the diameter of the main reflector 1 is approximately three wavelengths. In the figure, the pattern shown by the dotted line in A is the case of the conventional short-backfire antenna, and the pattern shown by the solid line in B is the case according to the present invention. In both cases, the aperture diameter of the main reflector was 2.6 wavelengths, and the other structural parameters were variously changed to maximize the gain.

In the conventional short backfire antenna,
The directivity gain is 15.6dB and the aperture efficiency is 54%.
In the embodiment of the present invention in which the aperture angle (α) of the main reflector is 150°, the directional gain is 17.1 dB and the aperture efficiency is 70%.
In this example, the diameter of the main reflector is
Compared to the case where D _R is set to 2.05 wavelength as mentioned above,
Although the aperture efficiency has decreased slightly, it still shows good radiation characteristics.

FIG. 5 shows another embodiment of the invention. In this embodiment, a second small reflector 3' whose diameter is slightly smaller (approximately 5%) is placed in front of the small reflector 3 (radiation direction of radio waves) and is placed concentrically with the conventional small reflector 3. , are arranged in parallel with an interval of about 0.1 wavelength.

By providing the two small reflectors 3 and 3' in this way, it is possible to further widen the input VSWR band without substantially changing the radiation pattern.

That is, the frequency characteristics of VSWR shown by the dotted line _B in FIG. Small reflector 3'
This is an embodiment in which the reflectors are added in front of the small reflectors 3 at intervals of 0.09 wavelength, and is even better than the case in which the second small reflectors 3' are not provided in A of the figure.

<Effects of the Present Invention> As described above, the short-backfire antenna of the present invention can achieve a wide operating frequency band and a high aperture efficiency.

[Brief explanation of drawings]

Figure 1A is a sectional view showing the configuration of a typical conventional short-backfire antenna, Figure 1B is its front view, and Figure 2 is the conventional antenna shown in Figure 1.
FIG. 3 is a diagram showing a VSWR vs. frequency characteristic diagram. FIG. 3A is a sectional view showing one embodiment of the present invention, and FIG. 3B is a front view thereof. FIG. 4 is a VSWR vs. frequency characteristic diagram for the embodiment of FIG. 3 and the embodiment of FIG. 5. FIG. 5A is a sectional view showing another embodiment of the present invention, and FIG. 5B is a front view thereof. Figure 6 is the first
FIG. 4 is a radiation pattern diagram for the conventional example shown in the figure and the embodiment shown in FIG. 3; Fig. 7 is an explanatory diagram for explaining the conventional operation, Fig. 8 is an explanatory diagram for showing the difference between the conventional example and the embodiment of the present invention, and Fig. 9 A and B are respectively the conventional example and the present invention. FIG. 3 is an explanatory diagram showing a structure and aperture surface electric field distribution in comparison with an example. 1...Main reflector, 2...Side reflector, 3...Small reflector, 4...Feeding radiator.

Claims (1)

[Scope of Claims] 1. A main reflector having an aperture diameter of 1 to 3 wavelengths and a conical aperture surface with an aperture angle of 120° to 160°; a side reflector protruding forward in a cylindrical shape parallel to the central axis of the aperture of the reflector; a feeding radiator disposed in front of the central axis of the aperture of the main reflector; and the main reflector. a small reflector arranged on the central axis of the aperture surface of the vessel, perpendicular to the central axis and in front of the feeding radiator at an interval of 0.5 to 1 wavelength from the aperture center of the main reflector; A short back fire antenna with