JPH062813U - Offset double reflector antenna - Google Patents

Abstract

(57) [Abstract] [Purpose] The phase of the electromagnetic wave radiated from the primary radiator of the offset double reflector depends on the radiation direction.
It prevents the flatness of the electromagnetic wave reflected by the main reflecting mirror from decreasing. The auxiliary reflecting mirror 3 is composed of a central reflecting mirror 3a and a peripheral reflecting mirror 3b, and the central reflecting mirror 3a and the peripheral reflecting mirror 3b are arranged so that the optical path of the electromagnetic wave reflected by the peripheral reflecting mirror 3b becomes long.
Shift.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an offset double reflector antenna used for terrestrial microwave communication or satellite communication.

[0002]

[Prior art]

 FIG. 1 is a conceptual sectional view of an offset double reflector antenna according to the prior art.

This antenna is composed of a main reflecting mirror 1, a sub-reflecting mirror 2, an auxiliary reflecting mirror 3, and a primary radiator 4.

Regarding the main reflecting mirror 1 and the sub-reflecting mirror 2, the focal points F1 and F2 are confocal.

Similarly, regarding the sub-reflecting mirror 2 and the auxiliary reflecting mirror 3, the focal points F2 and F3 have a confocal relationship. The radiation center of the primary radiator 4 is arranged so as to coincide with the focal point F3.

The antenna with this configuration is premised on that the electromagnetic wave emitted from the primary radiator 4 is a perfect spherical wave. In this case, the spherical wave emitted from the focus F3, which is the emission center of the primary radiator 4, becomes a spherical wave W1 centered on the focus F2 when it is reflected by the auxiliary reflecting mirror 3 (FIG. 2). Reach 2. Since the focal points F2 and F1 have a confocal relationship, the spherical wave reflected by the sub-reflecting mirror 2 reaches the main reflecting mirror 1 through the focal point F1. Since the focal point F1 is the focal point of the main reflecting mirror 1, it becomes a plane wave W0 when reflected by the main reflecting mirror 1.

[0007]

[Problems to be solved by the device]

 The electromagnetic wave actually emitted from the primary radiator is not a perfect spherical wave.

FIG. 3 is a characteristic curve showing the dependence of the amplitude and phase of the electromagnetic wave radiated from the primary radiator on the radiation direction. In FIG. 3, the solid line A shows the amplitude pattern, the broken line PH shows the phase pattern at high frequencies, and the broken line PL shows the phase pattern at low frequencies. As can be seen from FIG. 3, the phase advances in the peripheral portion of the auxiliary reflecting mirror 3, and this tendency becomes remarkable when the frequency is high.

As a result, the electromagnetic wave reflected by the auxiliary reflecting mirror 3 is not a perfect spherical wave W1 but a wave W2 having a phase advanced in the peripheral portion of the auxiliary reflecting mirror 3, as shown in FIG.

Therefore, the real image formed by being reflected by the sub-reflecting mirror 2 is also blurred near the focus F1, and the directivity and the gain of the electromagnetic wave W3 reflected by the main reflecting mirror 1 are adversely affected.

An object of the present invention is to propose an offset double reflector antenna that can reduce the influence of the phase characteristic on the radiation direction of the primary radiator.

[0012]

[Means for Solving the Problems]

 The above problem is due to the fact that the auxiliary reflecting mirror or sub-reflecting mirror has a multi-stage mirror surface so that the optical path becomes longer in the region where the phase of the electromagnetic wave radiated from the primary radiator leads the phase of the spherical wave. Resolved

More specifically, the above-mentioned problem is solved by a main reflecting mirror which is a rotating parabolic mirror and a spheroidal mirror or a rotating hyperboloidal mirror which has one focus at the focus of the main reflecting mirror. In an offset double reflector antenna comprising a reflecting mirror, a primary radiator that radiates electromagnetic waves, and an auxiliary reflecting mirror that forms an image of the radiation center of the primary radiator on the other focus of the sub-reflecting mirror, the auxiliary reflecting mirror has a central area. It consists of a substantially circular center reflector and a peripheral toroidal peripheral reflector, and the distance from the center reflector to the subreflector is larger than the distance from the center reflector to the subreflector. The problem was solved by the offset double reflector antenna, which is characterized in that the central reflector and the peripheral reflectors are arranged in a circular staircase pattern.

[0014]

[Action]

 FIG. 4 is a conceptual sectional view of an offset double reflector antenna according to the present invention. FIG. 5 is a conceptual cross-sectional view of an example of an auxiliary reflecting mirror used in the offset double reflecting mirror antenna according to the present invention.

The antennas of FIGS. 4 and 5 are improvements of the antennas of FIGS. 1 and 2, and the structures other than the auxiliary reflecting mirror are the same. Therefore, the same reference number is given to members having a common structure for both, and the description thereof is omitted.

As can be seen by comparing FIGS. 1 and 4, the auxiliary reflecting mirror 3 is a single reflecting mirror in FIGS. 1 and 2, whereas the auxiliary reflecting mirror 3 is a single reflecting mirror in FIGS. The difference is that it is composed of a substantially circular center reflecting mirror 3a and a substantially annular peripheral reflecting mirror 3b.

In this example, the auxiliary reflecting mirror is composed of one central reflecting mirror 3a and one peripheral reflecting mirror 3b. The central reflecting mirror 3a and the peripheral reflecting mirror 3b are mirror surfaces having the same curvature, and are displaced from each other so that a step having a height d is formed at the boundary portion.

As a result, the distance of the peripheral reflecting mirror 3b from the sub reflecting mirror 2 is larger than the distance of the central reflecting mirror 3a from the sub reflecting mirror 2.

On the other hand, the electromagnetic wave radiated from the primary radiator has its phase advanced as it deviates from the direction of the main lobe, as described in FIG.

In other words, the phase of the electromagnetic wave with which the peripheral reflecting mirror 3b is irradiated is ahead of that of the electromagnetic wave with which the central reflecting mirror 3a is irradiated.

This phase difference is compensated by the optical path difference in the step portion.

When an electromagnetic wave having a wavelength of λ and a wave number of k is incident on the step portion at an angle θ / 2 with respect to the normal to the mirror surface of the auxiliary reflecting mirror, the phase modification amount ΔΦ at the step portion is Given by the formula. ΔΦ = kd (1 + cos θ) / cos (θ / 2) k = 2π / λ

As a result, the phase difference between the electromagnetic wave reflected by the peripheral reflecting mirror 3b and the electromagnetic wave reflected by the central reflecting mirror 3a becomes small, and as shown in FIG. 5, both reflecting mirrors which are auxiliary reflecting mirrors. The electromagnetic wave W5 reflected by is close to the ideal spherical wave W1 although a slight discontinuity in phase remains.

This means that the electromagnetic wave incident on the sub-reflecting mirror 2 is close to a spherical wave centered on one focus F 2 shown in FIG.

Therefore, the electromagnetic wave reflected by the sub-reflecting mirror 2 enters the main reflecting mirror 1 through the other focal point F1.

As a result, as shown in FIG. 4, the reflected wave W4 reflected by the main reflecting mirror 1 becomes close to the ideal plane wave W0.

[0027]

【Example】

 Fig. 6 shows a main reflector with an aperture of 1800 mm and a focal length of 775 mm, a sub-reflector with an aperture of 553 mm and a focal length of 1626 mm, and a peripheral reflector with an outer diameter of 442 mm, an inner diameter of 147 mm and a focal length of 1497 mm. And the directional characteristics of the antenna according to the present invention, which is constructed by using a central reflector whose outer diameter and focal length are equal to the inner diameter and focal length of the peripheral reflector and a primary radiator with an aperture of 174 mm, respectively. It is a characteristic curve shown in comparison with the directional characteristic of the antenna by a prior art in 7-13 GHz. The height d of the step was 0.9 mm.

The directional characteristics of the antenna (d = 0) according to the prior art shown by the dotted line are free from the dip at the shoulder portion B of the main lobe, but the antenna of the present invention shown by the broken line is In the main lobe with directional characteristics (d ≠ 0), the shoulder portion A is depressed.

FIG. 7 is a gain efficiency characteristic curve showing the gain efficiency of the (d ≠ 0) antenna of FIG. 6 as a variable in comparison with the case of the antenna (d = 0) according to the related art. In the case of the conventional antenna (d = 0) shown by the broken line, the efficiency changes from the lowest frequency FL to the highest frequency FH used, whereas when the antenna of the present invention (d ≠ 0) shown by the solid line is used. , The efficiency is almost constant in the used band.

The operation and embodiment of the present invention have been described with respect to the auxiliary reflecting mirror using one central reflecting mirror 3a and one peripheral reflecting mirror. However, depending on the phase characteristics of the primary radiator 4, it is also possible to realize the peripheral reflecting mirror with a plurality of substantially annular reflecting mirrors.

Further, although the three-reflecting mirror offset antenna has been described, this method is also effective for the two-reflecting mirror offset antenna.

Further, it is also possible to use a modified mirror surface in which the step portion is continuous.

[0033]

[Effect of device]

 Even if the deviation of the phase characteristics of the electromagnetic wave emitted from the primary radiator is large, it can be corrected to improve the flatness of the electromagnetic wave reflected by the main reflecting mirror.

[Brief description of drawings]

FIG. 1 is a conceptual cross-sectional view of an offset double reflector antenna according to the related art.

FIG. 2 is a conceptual cross-sectional view of an auxiliary reflecting mirror used in an offset double reflecting mirror antenna according to the related art.

FIG. 3 is a characteristic curve showing the dependence of the amplitude and phase of the electromagnetic wave emitted from the primary radiator on the emission direction.

FIG. 4 is a conceptual sectional view of an offset double reflector antenna according to the present invention.

FIG. 5 is a conceptual cross-sectional view of an example of an auxiliary reflecting mirror used in the offset double reflecting mirror antenna according to the present invention.

FIG. 6 is a characteristic curve showing the directional characteristics of the offset double reflector antenna according to the present invention in comparison with those of the prior art.

FIG. 7 is a gain efficiency characteristic curve showing the gain efficiency of the offset double reflector antenna according to the present invention as a variable in comparison with the gain efficiency according to the prior art.

[Explanation of symbols]

 1 Main Reflector 2 Sub Reflector 3 Auxiliary Reflector 3a Center Reflector 3b Peripheral Reflector 4 Primary Radiator

Claims (3)

[Scope of utility model registration request] 1. A main reflecting mirror which is a paraboloid of revolution, a sub-reflecting mirror which is a spheroidal mirror or a hyperboloid of revolution having one focal point at the focal point of the main reflecting mirror, and primary radiation which radiates electromagnetic waves. And a sub-reflector antenna that includes an auxiliary reflector that creates an image of the radiation center of the primary radiator on the other focal point of the sub-reflector, wherein the auxiliary reflector has a substantially circular center reflector in the central region and the periphery. The area consists of a circular ring-shaped peripheral reflector, and the central reflector and peripheral reflector are circular so that the distance from the central reflector to the secondary reflector is larger than the distance from the central reflector to the secondary reflector. An offset double reflector antenna, which is arranged in a staircase shape. 2. A main reflecting mirror that is a rotating parabolic mirror, a sub-reflecting mirror that is a spheroidal mirror or a rotating hyperboloidal mirror having one focus at the focus of the main reflecting mirror, and primary radiation that emits electromagnetic waves. And a sub-reflector antenna that includes an auxiliary reflector that creates an image of the radiation center of the primary radiator on the other focal point of the sub-reflector, wherein the auxiliary reflector has a substantially circular center reflector in the central region and the periphery. The area consists of a circular ring-shaped peripheral reflector, and the central reflector and peripheral reflector are circular so that the distance from the central reflector to the secondary reflector is larger than the distance from the central reflector to the secondary reflector. An offset double-reflecting mirror antenna, which is composed of a modified mirror surface that is arranged in a staircase shape and continuously moves from a central reflecting mirror to a peripheral reflecting mirror without any step. 3. A main reflecting mirror which is a rotating parabolic mirror, a sub-reflecting mirror which is a spheroidal mirror or a rotating hyperboloidal mirror having one focus at the focus of the main reflecting mirror, and primary radiation which emits electromagnetic waves. An offset double reflector antenna in which the radiation center of the primary radiator is located on the other focal point of the sub-reflector, the sub-reflector having a substantially circular central reflector in the central region and a substantially annular ring in the peripheral region. It consists of peripheral reflectors, and the central reflector and peripheral reflectors are arranged in a circular staircase so that the distance from the main reflector to the peripheral reflector is larger than the distance from the main reflector to the central reflector. A double reflector type offset double reflector antenna.