Reflection mirror antenna device

A first region of a reflection mirror including a center point of the paraboloid of revolution is formed of a conductor. A second region, which is an outer peripheral side of the first region, of the reflection mirror is a region where a plurality of reflection elements, which are conductor patterns, is arranged on a dielectric body overlaid on a base plate conductor. An arrangement pitch of the plurality of reflection elements corresponds to a wavelength of a radio wave in the second frequency band.

TECHNICAL FIELD

The present invention relates to a reflection mirror antenna device having a primary radiator and a reflection mirror.

BACKGROUND ART

For example, in a communication system used for satellite communication in the Ka band, which is the frequency band of 27 GHz to 40 GHz, in order to achieve large-capacity and high-speed communication, a system in which a desired coverage area is covered with a plurality of pencil beams has become a mainstream.

As communication bands in the Ka band, the transmission band is set at 20 GHz, and the reception band is set at 30 GHz, and thus a gap exists between the transmission band and the reception band.

For this reason, a reflection mirror antenna for both transmission and reception has different illuminance distributions of radio waves radiated from a primary radiator on a reflection mirror, and a beam width in the reception band is narrower than that in the transmission band. As a result, there arises a problem of difference between gain of a beam in the transmission band and gain of a beam in the reception band at ends of the desired coverage area.

The following Patent Literature 1 discloses a reflection mirror antenna that has a step on the mirror surface of a reflection mirror such that a phase at a center portion of the reflection mirror is different from a phase in an outer peripheral portion by 180 degrees in order to bring the gain of a beam in the transmission band and the gain of a beam in the reception band at ends of a desired coverage area as close as possible.

CITATION LIST

Patent Literatures

SUMMARY OF INVENTION

Technical Problem

A conventional reflection mirror antenna device configured as described above can bring the gain of a beam in the transmission band and the gain of a beam in the reception band at ends of a desired coverage area close to each other. However, manufacturing a step on a mirror surface of a reflection mirror is difficult, and forming the step that meets design values is difficult, so that the gain of a beam in the reception band at the ends of the coverage area becomes lower than that in the transmission band at the ends of the coverage area in some cases.

As a result, there is a problem that, when the reflection mirror antenna device is used as a shared antenna serving as both of a transmission antenna and a reception antenna, even in a case where the gain of a beam in the transmission band at ends of the coverage area is high, communication characteristics of the reflection mirror antenna device is limited in accordance with the gain of the beam in the reception band.

The present invention is made to solve the above-described problem, and an object of the present invention is to achieve a reflection mirror antenna device capable of adjusting the gain of a beam in a transmission band and the gain of a beam in a reception band to coincide with each other at ends of a coverage area.

Solution to Problem

A reflection mirror antenna device according to the invention includes: at least one primary radiator radiating a radio wave in a first frequency band and a radio wave in a second frequency band higher than the first frequency band; and a reflection mirror having a surface of a paraboloid of revolution reflecting radio waves in the first and second frequency bands radiated from the at least one primary radiator. A first region of the reflection mirror including a center point of the paraboloid of revolution is formed of a conductor. A second region, which is an outer peripheral side of the first region, of the reflection mirror is a region where a plurality of reflection elements, which are conductor patterns, is arranged on a dielectric body overlaid on a base plate conductor. An arrangement pitch of the plurality of reflection elements corresponds to a wavelength of a radio wave in the second frequency band. The plurality of reflection elements arranged in the second region cause phase difference between a reflection phase of a radio wave on the first region and a reflection phase of a radio wave on the second region. The phase difference between a reflection phase of a radio wave at the center point included in the first region and a reflection phase of a radio wave on the second region is in a range between 90 and 180 degrees.

Advantageous Effects of Invention

According to the invention, a first region of the reflection mirror including a center point of the paraboloid of revolution is formed of a conductor. A second region, which is an outer peripheral side of the first region, of the reflection mirror is a region where a plurality of reflection elements, which are conductor patterns, is arranged on a dielectric body overlaid on a base plate conductor. An arrangement pitch of the plurality of reflection elements corresponds to a wavelength of a radio wave in the second frequency band. Thus, an effect of adjusting gain of a beam in a transmission band and gain of a beam in a reception band to coincide with each other at ends of a coverage area without forming a step on the mirror surface of the reflection mirror can be achieved.

DESCRIPTION OF EMBODIMENTS

In order to describe the present invention in more detail, some embodiments for carrying out the present invention will be described below with reference to the accompanying drawings.

First Embodiment

FIG. 1is a configuration diagram illustrating a reflection mirror antenna device according to a first embodiment of the invention.

FIG. 1Ais a configuration diagram illustrating the reflection mirror antenna device according to the first embodiment of the invention, andFIG. 1Bis an enlarged view of a main portion surrounded by a dotted circle inFIG. 1A.

InFIG. 1, a primary radiator1radiates a radio wave in a first frequency band, and radiates a radio wave in a second frequency band which is higher than the first frequency band.

A reflection mirror2has a surface of a paraboloid of revolution2areflecting a radio wave in the first and second frequency bands radiated from the primary radiator1.

A first region4includes a center point3of the paraboloid of revolution2a, and is formed of a conductor11.

A second region5is an outer peripheral side of the first region4.

In the second region5, a plurality of reflection elements14, which are conductor patterns, respectively, is arranged on a dielectric body13overlaid on a base plate conductor12.

The base plate conductor12is formed on the back side of the reflection mirror2, the back side not receiving radio waves radiated from the primary radiator1, and the reflection elements14are formed on the front side of the reflection mirror2, the front side receiving radio waves radiated from the primary radiator1.

N (N represents an integer of equal to or more than two) reflection elements14are arranged in the second region5.

An arrangement pitch of the N reflection elements14corresponds to a wavelength of the radio wave in the second frequency band. For example, when the wavelength of the radio wave in the second frequency band is λ, the arrangement pitch of the N reflection elements14is in the range of approximately 0.5×λ to 0.7×λ.

In the first embodiment, since the arrangement pitch of the N reflection elements14is designed to correspond to the wavelength of the radio wave in the second frequency band, the N reflection elements14influence phase distribution on the reflection mirror2in the second frequency band.

On the other hand, in the first frequency band lower than the second frequency band, the N reflection elements14merely act as conductors, and do not contribute to change in a reflection phase.

The N reflection elements14thus do not influence the phase distribution on the reflection mirror2in the first frequency band.

In the enlarged view ofFIG. 1B, as seen in a macroscopic vision, the reflection mirror2is described in a plane. However, since the reflection mirror2is actually the paraboloid of revolution2a, it has a curved surface.

In the first embodiment, the N reflection elements14arranged in the second region5cause the difference between a reflection phase of a radio wave on the first region4and a reflection phase of a radio wave on the second region5, and the phase difference between a reflection phase of a radio wave at the center point3included in the first region4and the reflection phase of a radio wave on the second region5is in the range between 90 and 180 degrees.

Operations will now be described.

The primary radiator1radiates a radio wave in the first frequency band and a radio wave in the second frequency band.

The reflection mirror2has a surface of a paraboloid of revolution2areflecting radio waves in the first and second frequency bands radiated from the primary radiator1, and reflects the radio waves in the first and second frequency bands radiated from the primary radiator1to a desired direction.

FIG. 2is an explanatory diagram illustrating amplitude distribution and phase distribution on the reflection mirror in the reflection mirror antenna device.

FIG. 2Aillustrates amplitude distribution and phase distribution on the reflection mirror in the reflection mirror antenna device, the entire reflection mirror being formed of a conductor, andFIG. 2Billustrates amplitude distribution and phase distribution on the reflection mirror in the reflection mirror antenna device of the first embodiment.

In the reflection mirror antenna device whose reflection mirror2is entirely formed by a conductor, as illustrated inFIG. 2A, the amplitude distribution on the reflection mirror2in the first frequency band is different from that in the second frequency band.

On the other hand, as illustrated inFIG. 2A, by designing the primary radiator1appropriately, as illustrated inFIG. 2A, it is possible to adjust the phase distribution on the reflection mirror2in the first frequency band and that in the second frequency band to be approximately the same.

In such a design, the beam width of a beam, which is a radio wave reflected by the reflection mirror2, in the first frequency band is narrower than that in the second frequency band. This is because tapering of the amplitude distribution on the reflection mirror2in the first frequency band is more moderate than that in the second frequency band since the first frequency band is lower than the second frequency band.

Since the beam width in the first frequency band is different from that in the second frequency band, when a desired coverage area is set, gain of a beam in the first frequency band is different from that in the second frequency band at ends of the coverage area.

In the reflection mirror antenna device of the first embodiment, the N reflection elements14arranged in the second region5cause the difference between the reflection phase of a radio wave on the first region4and the reflection phase of a radio wave on the second region5.

In the example ofFIG. 2B, the phase difference between the reflection phase of a radio wave at the center point3included in the first region4and the reflection phase of a radio wave on the second region5is 180 degrees.

Thus, synthesis of the beam reflected by the first region4and the beam reflected by the second region5can adjust the gain of the beam in the first frequency band and the gain of the beam in the second frequency band to coincide with each other at ends of the coverage area.

Here,FIG. 3is an explanatory diagram illustrating a means for determining the reflection phase on the second region5.

InFIG. 3, the phase center of the primary radiator1is defined as the origin O of an orthogonal coordinate system.

r0is a unit vector representing a main beam direction of the reflection mirror2. The primary radiator1is inclined at an offset angle β with respect to the reflection mirror2having the paraboloid of revolution2a.

The distance from the origin O to the center point3of the paraboloid of revolution2ais represented as a distance R0, and the reflection phase at the center point3of the paraboloid of revolution2ais represented as Φ0.

The distance R0can be expressed by the following expression (1).

In the expression (1), f represents the focal distance of the reflection mirror2.

In addition, the reflection phase Φ0at the center point3of the paraboloid of revolution2acan be expressed by the following expression (2).
Φ0=k0R0(2)

In the expression (2), k0represents a wave number (=2π/wavelength).

In addition, inFIG. 3, a reflection phase at a position where the n (n=1, 2, . . . , and N)-th reflection element14, among the N reflection elements14arranged in the second region5, is arranged is represented as Φn, and the distance from the origin O to the n-th reflection element14is represented as Rn. rnis a position vector pointing the reflection phase Φnfrom the reflection phase Φ0.

The reflection phase Φnat the position where the n-th reflection element14is arranged can be expressed by the following expression (3).
Φn=k0(Rn−rn·r0)  (3)

Consequently, it is possible to set the phase difference between the reflection phase of a radio wave at the center point3and the reflection phase of a radio wave at the position where the n-th reflection element14is arranged in the range between 90 and 180 degrees, by setting the reflection phase Φnas in the expression (4) by using the expressions (2) and (3).

FIG. 4is an explanatory diagram illustrating a simulation result of beam gain at ends of the coverage area of the reflection mirror antenna device.

In the example ofFIG. 4, the opening diameter of the reflection mirror2is set at 1500 mm, the first frequency band, which is a transmission band, is set at 20 GHz, and the second frequency band, which is a reception band, is set at 30 GHz.

In addition, in the example ofFIG. 4, the diameter of the first region4in the reflection mirror2is set at 1000 mm, and the phase difference between the reflection phase of a radio wave at the center point3of the first region4and the reflection phase of a radio wave on the second region is set at 180 degrees.

In the example ofFIG. 4, an angular range between ends, where dropping from the peak of the directivity gain in the first frequency band (directivity gain in the first frequency band at an angle of 0 degrees) by 4 dBi is exhibited, is defined as the coverage area, and the angular range is shown as one degree (−0.5 to +0.5). The ends of the coverage area in this case are at −0.5 degrees and +0.5 degrees.

Here, the angular range between ends, where the dropping from the peak of the directivity gain by 4 dBi is exhibited, is defined as the coverage area. However, this is merely an example, and angular ranges between ends where the dropping from the peak of the directivity gain by more or less than 4 dBi is exhibited may be defined as the coverage area.

InFIG. 4, a dotted line represents a beam in the first frequency band, a solid line represents a beam in the second frequency band in the first embodiment, and a dashed line represents a beam in the second frequency band in a case where the entire reflection mirror2is formed of a conductor (inFIG. 4, this case is expressed as a conventional case).

As illustrated inFIG. 4, the beam in the second frequency band in the case where the entire reflection mirror2is formed of a conductor has a beam width narrower than that of the beam in the first frequency band, so that the gain of the beam in the first frequency band at the ends of the coverage area is different from that in the second frequency band.

That is, the gain of the beam in the second frequency band, which is the reception band at the ends of the coverage area, is lower than that in the first frequency band, which is the transmission band.

As illustrated inFIG. 4, in the reflection mirror antenna device of the first embodiment, the beam width of a beam in the first frequency band is substantially the same as that in the second frequency band, and the gain of the beam in the first frequency band at the ends of the coverage area coincides with the gain of the beam in the second frequency band.

FIG. 5is an explanatory diagram illustrating a simulation result of beam gain at the ends of the coverage area when the reflection phase of the second region is changed from 0 to 180 degrees in each of the cases where the first region4has the diameter of 1000 mm and where the first region4has the diameter of 900 mm.

InFIG. 5, gain at the ends of the coverage area of 20 GHz means gain of a beam in the first frequency band, which is the transmission band, at the ends of the coverage area, and the gain of the beam is approximately 42 dBi.

It can be seen that, in the range where the phase difference between the reflection phase of a radio wave at the center point3of the first region4and the reflection phase of a radio wave on the second region is between 90 and approximately 170 degrees, when the first region4has the diameter of 900 mm, the gain of the beam in the second frequency band, which is the reception band, at the ends of the coverage area is larger than that in the first frequency band, which is the transmission band.

Further, it can be seen that, in the range where the phase difference between the reflection phases is between approximately 110 and 180 degrees, when the first region4has the diameter of 1000 mm, the gain of the beam in the second frequency band, which is the reception band, at the ends of the coverage area is larger than that in the first frequency band, which is the transmission band.

By increasing power of the beam in the first frequency band radiated from the primary radiator1, it is possible to increase the gain of the beam in the first frequency band, which is the transmission band. Therefore, an effect is achieved in which the gain of the beam in the transmission band and the gain of the beam in the reception band at the ends of the coverage area can be adjusted to coincide with each other.

As understood from the above, a first region4of the reflection mirror2including a center point3of the paraboloid of revolution2ais formed of a conductor11. A second region5, which is an outer peripheral side of the first region4, of the reflection mirror2is a region where a plurality of reflection elements14, which are conductor patterns, is arranged on a dielectric body13overlaid on a base plate conductor12. An arrangement pitch of the plurality of reflection elements14corresponds to a wavelength of a radio wave in the second frequency band. As a result, an effect can be achieved in which gain of a beam in a transmission band and gain of a beam in a reception band at ends of a coverage area can be adjusted to coincide with each other without forming a step on the mirror surface of the reflection mirror2.

In this first embodiment, an example is illustrated in which the N reflection elements14arranged in the second region5cause delay of the reflection phase of a radio wave on the second region5in the range between 90 and 180 degrees compared to the reflection phase of a radio wave at the center point3included in the first region4.

In this embodiment, the reflection phase of a radio wave on the second region5is different from that at the center point3included in the first region4in the range between 90 and 180 degrees. If this condition is satisfied, the configuration is not limited to the above-described example.

Therefore, as illustrated inFIG. 6, the reflection phase of a radio wave on the second region5may be advanced with respect to that at the center point3included in the first region4in the range between 90 and 180 degrees.

FIG. 6is an explanatory diagram illustrating amplitude distribution and phase distribution on a reflection mirror in another reflection mirror antenna device according to the first embodiment of the invention.

Second Embodiment

The N reflection elements14arranged in the second region5may have any shape. In the second embodiment, an example in which each of the reflection elements14has a circular ring shape will be illustrated.

FIG. 7is a configuration diagram illustrating a reflection mirror antenna device according to the second embodiment of the present invention.

Each of the N reflection elements14of the reflection mirror antenna device inFIG. 7has the circular ring shape.

Also in the second embodiment, similarly to the above-described first embodiment, an effect can be achieved in which gain of a beam in a transmission band and gain of a beam in a reception band at ends of a coverage area can be adjusted to coincide with each other without forming a step on the mirror surface of the reflection mirror2.

Third Embodiment

The N reflection elements14arranged in the second region5may have any shape. In the third embodiment, an example in which each of the reflection elements14has a rectangular ring shape will be illustrated.

FIG. 8is a configuration diagram illustrating a reflection mirror antenna device according to the third embodiment of the present invention.

Each of the N reflection elements14of the reflection mirror antenna device inFIG. 8has the rectangular ring shape.

Also in the third embodiment, similarly to the above-described first embodiment, an effect can be achieved in which gain of a beam in a transmission band and gain of a beam in a reception band at ends of a coverage area can be adjusted to coincide with each other without forming a step on the mirror surface of the reflection mirror2.

The reflection elements14having the rectangular ring shape can change the reflection phase more easily than those having the circular ring shape.

Fourth Embodiment

In the above-described example of the first embodiment, a reflection mirror antenna device includes one primary radiator1. In the fourth embodiment, an example of a reflection mirror antenna device including a plurality of primary radiators1will be described.

FIG. 9is a configuration diagram illustrating the reflection mirror antenna device according to the fourth embodiment of the present invention.

In the example ofFIG. 9, the reflection mirror antenna device includes the plurality of primary radiators1having a phase center at the origin O, and the reflection mirror2has a paraboloid of revolution2areflecting radio waves radiated from the plurality of primary radiators1.

This configuration enables the reflection mirror antenna device to be operated as a multi-beam antenna.

It should be noted that, within the scope of the present invention, the embodiments can be freely combined to each other, any components of the embodiments can be modified, and any components of the embodiments can be omitted.

INDUSTRIAL APPLICABILITY

The invention is suitable for a reflection mirror antenna device having a primary radiator and a reflection mirror.

REFERENCE SIGNS LIST