JP5305994B2 - Antenna device - Google Patents

Description

  The present invention relates to an antenna device for information communication provided with a double reflector used in a microwave and millimeter wave band, and in particular, is disposed apart from a first reflector having a conductive grid and the first reflector. The present invention relates to an antenna device for dual orthogonal polarization using a double reflecting mirror composed of a second reflecting mirror.

  Conventionally, a double grid offset parabolic reflector antenna device having low cross polarization performance has been proposed as an antenna device that improves communication efficiency and suppresses reflection of cross polarization (for example, Patent Document 1, Non-patent document 1).

  In this type of antenna device, in order to improve communication efficiency (radiation efficiency of radio waves), the central axis of the parabolic reflector is offset with respect to the radiator, and the radiator and its peripheral equipment are It is configured not to interfere with the incident path and the radiation path.

  Of the double reflecting mirrors that individually reflect radio waves in two orthogonal polarization directions, the first reflecting mirror arranged on the incident side and the radiation side of the radio wave and the back side of the first reflecting mirror are arranged. Of the double reflecting mirrors including the second reflecting mirror, at least the first reflecting mirror is made of a dielectric, and a conductive grid aligned in a certain direction is formed near the surface of the front reflecting mirror.

  Thus, by forming a conductive grid on the first reflecting mirror of the double reflecting mirror, the first radio wave having the conductive grid direction as the main electric field direction is reflected by the first reflecting mirror. The second radio wave in the orthogonal direction passes through the first reflecting mirror and reaches the second reflecting mirror. At this time, the radiation level of unnecessary cross polarized waves in the direction orthogonal to the conductive grid direction of the first reflecting mirror is significantly reduced.

  The mirror surface thickness of the first reflecting mirror cancels out the phase of the substantially reflected radio wave on the front and back surfaces of the first reflecting mirror with respect to the second radio wave (reduces the loss of the passing radio wave to the second reflecting mirror). Therefore, as is well known, it is set to a natural number multiple (nλ / 4) of about ¼ wavelength.

The second radio wave in the direction orthogonal to the conductive grid on the first reflecting mirror passes through the first reflecting mirror made of a dielectric, reaches the second reflecting mirror, and is reflected by the second reflecting mirror.
At this time, some of the radio waves reflected on the second reflecting mirror are converted into polarized waves in a direction parallel to the conductive grid on the first reflecting mirror. Since it is reflected by the radiating grid and is not radiated in the main radiation direction, the radiation level of unnecessary cross-polarized waves also decreases in the second reflector.

JP-A 63-026005

“Double Grid Facet Parabolic Reflector Antenna”, edited by IEICE, Antenna Engineering Handbook (2nd edition), p. 323, 6.6.2

  However, in the conventional antenna device, the mirror surface thickness of the first reflecting mirror is set uniformly to about nλ / 4, so that the incident angle varies depending on the difference in the incident position of the second radio wave on the first reflecting mirror. If it increases, the substantial passage path length of the second radio wave at the first reflecting mirror changes, the phase cancellation of the reflected radio wave of the second radio wave becomes insufficient, and the passage loss of the second radio wave increases. There was a problem that the gain decreased.

  The present invention has been made in order to solve the above-described problems, and by setting the mirror surface thickness of the first reflecting mirror to an optimum value corresponding to the incident angle of the second radio wave, An object of the present invention is to obtain an antenna device that suppresses a decrease in gain due to an increase in radio wave passage loss.

An antenna device according to the present invention includes a first primary radiator that radiates a first radio wave excited in a first polarization direction, and a second polarization direction that is orthogonal to the first polarization direction. A second primary radiator that radiates the excited second radio wave, and a double reflector having a central axis offset with respect to the radio wave radiation directions of the first and second primary radiators, provided, the double reflector, for emitting first and second radio wave in a predetermined direction, and reflecting the first wave, and, a second reflected by the second radio wave and a second reflecting mirror A first reflecting mirror having a conductive grid for passing radio waves, and a second reflecting mirror that reflects the second radio waves emitted from the second primary radiator and passed through the first reflecting mirror. In the antenna device, the mirror thickness of the first reflecting mirror differs depending on the incident position of the second radio wave. That in accordance with the incidence angle of the second radio wave, different set to the optimum value, the mirror thickness of the first reflecting mirror, an incident angle of the second radio wave predetermined angle emitted from the second primary radiator At the antenna position below, it is set to about 1/4 of the wavelength of the second radio wave, and at the antenna position where the incident angle exceeds a predetermined angle, it is set to a value larger than 1/4 of the wavelength. is there.

  According to the present invention, by setting the mirror surface thickness of the first reflecting mirror to an optimum value according to the incident angle of the second radio wave, it is possible to suppress a decrease in gain due to an increase in the passage loss of the second radio wave. .

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows schematically the antenna apparatus which concerns on Embodiment 1 of this invention. It is sectional drawing which expands and shows the A section of the 1st reflective mirror in FIG. It is sectional drawing which expands and shows the B section of the 2nd reflective mirror in FIG. It is explanatory drawing which shows the difference in the incident angle of the 2nd electromagnetic wave according to the antenna position of a 1st reflective mirror with a block diagram. It is explanatory drawing which shows the difference in the incident angle of the 2nd electromagnetic wave according to the antenna position of a 1st reflective mirror by distribution characteristics. It is explanatory drawing which shows the passage loss characteristic of the 2nd electromagnetic wave with respect to the mirror surface thickness of a 1st reflective mirror for every incident angle. It is explanatory drawing which shows the setting value distribution of the mirror surface thickness with respect to the antenna position (incident angle) of the 1st reflective mirror by Embodiment 1 of this invention. It is a block diagram which shows roughly the antenna apparatus which concerns on Embodiment 2 of this invention.

Embodiment 1 FIG.
1 is a block diagram schematically showing an antenna apparatus according to Embodiment 1 of the present invention. 2 and 3 are cross-sectional views showing enlarged two-dot chain line regions A and B in FIG.
In FIG. 1, the antenna device includes a first primary radiator 1, a second primary radiator 2, and a double reflecting mirror 3.
The double reflecting mirror 3 includes a first reflecting mirror 4 disposed on the front surface side for transmitting and receiving radio waves, and a second reflecting mirror 5 disposed on the rear surface side of the first reflecting mirror 4.

The first primary radiator 1 is composed of a horn antenna or the like, and radiates a first radio wave W1 (refer to a one-dot chain line arrow) excited in a first polarization direction. On the other hand, the 2nd primary radiator 2 consists of a horn antenna etc., and radiates | emits the 2nd electromagnetic wave W2 (refer broken line arrow) excited in the 2nd polarization direction orthogonal to the 1st polarization direction. .
The first radio wave W 1 is reflected by the first reflecting mirror 4, and the second radio wave W 2 passes through the first reflecting mirror 4 and is reflected by the second reflecting mirror 5.

In FIG. 2, the first reflecting mirror 4 is laid in a fixed direction (polarization direction of the first radio wave W1) in the front skin 4a, the front skin 4a, the rear skin 4b, and the spacer 4c made of a dielectric. And a conductive grid G1.
The spacer 4c has a known honeycomb structure, and the mirror thickness T between the front skin 4a and the rear skin 4b is set to a predetermined value (usually λ / 4).
The mirror surface thickness T of the first reflecting mirror 4 is optimized according to the incident angle, as will be described later.

  In FIG. 3, the second reflecting mirror 5 includes a front skin 5a, a rear skin 5b, a spacer 5c made of a dielectric material, and a fixed direction (a direction perpendicular to the polarization direction of the first radio wave W1) in the front skin 5a. 2 and a conductive grid G2 laid in line with the polarization direction of the second radio wave W2.

The spacer 5c has a known honeycomb structure, and the mirror thickness T between the front skin 5a and the rear skin 5b is set to a predetermined value (usually λ / 4).
Although the second conductive grid G2 is provided in the second reflecting mirror 5 here, the second reflecting mirror 5 is made of a metal since it is focused on the second radio wave W2 when passing through the first reflecting mirror 4. The second conductive grid G2 can be omitted by replacing with a reflector made of metal or a reflector having a radio wave reflection characteristic equivalent to that of metal (for example, a reflector made of a carbon fiber fabric).

Next, the operation according to the first embodiment of the present invention shown in FIGS. 1 to 3 will be described.
The first radio wave W1 radiated from the first primary radiator 1 is in the vicinity of the surface of the first reflecting mirror 4 made of a dielectric whose mirror surface thickness T is optimized. Is reflected by the conductive grid G1 formed in the same direction as the polarization direction of, and radiated in a predetermined direction on the front surface of the antenna.

  On the other hand, since the second radio wave W2 radiated from the second primary radiator 2 has a polarization direction orthogonal to the laying direction of the conductive grid G1, the second radio wave W2 passes through the first reflecting mirror 4 and is second. After being reflected by the reflecting mirror 5, it is radiated in a predetermined direction on the front surface of the antenna, similarly to the first radio wave W1.

Next, the set value of the mirror thickness T according to the first embodiment of the present invention will be specifically described with reference to FIGS. 4 to 7 together with FIGS.
FIG. 4 is an explanatory diagram showing the incident angle θ of the second radio wave W2 with respect to each antenna position of the first reflecting mirror 4 in a configuration diagram.

  FIG. 4 shows incident angles θb, θm, and θt at each antenna position (Y coordinate) corresponding to the lower end portion, the middle portion, and the upper end portion of the first reflecting mirror 4. Further, here, a case is shown in which the antenna aperture diameter of the double reflector 3 is about 75 wavelengths (75λ).

FIG. 5 is an explanatory diagram showing the incident angle θ of the second radio wave W2 with respect to each antenna position of the first reflecting mirror 4 as distribution characteristics.
In FIG. 5, the horizontal axis represents the antenna position (Y coordinate position) of the first reflecting mirror 4 normalized by the wavelength λ, and the vertical axis represents the incident angle θ [degrees]. The black circles on the distribution curve of the incident angle θ indicate the incident angles θb (= 8 degrees), θm (= 25 degrees), and θt (= 40 degrees) in FIG. 4, respectively.

FIG. 6 is an explanatory diagram showing the characteristics of the passage loss of the second radio wave W2 with respect to the mirror surface thickness T, and shows the simulation calculation result of the passage loss depending on the incident angle.
In FIG. 6, the horizontal axis represents the mirror surface thickness T (λ) of the first reflecting mirror 4 normalized by the wavelength λ, and the vertical axis represents the passage loss of the second radio wave W2.

  Further, in FIG. 6, the solid line indicates the passage loss characteristic in the case of the incident angle θb (= 8 degrees) at the lower end portion of the first reflecting mirror 4, and the broken line indicates the incidence at the intermediate portion of the first reflecting mirror 4. The transmission loss characteristic in the case of the angle θm (= 25 degrees) is shown, and the dotted line shows the transmission loss characteristic in the case of the incident angle θt (= 40 degrees) at the upper end of the first reflecting mirror 4.

FIG. 7 is an explanatory diagram showing a set value distribution of the mirror thickness T according to the first embodiment of the present invention, and shows values set based on the passage loss characteristics of FIG.
In FIG. 7, the horizontal axis represents the antenna position (Y coordinate position) normalized by the wavelength λ, and the vertical axis represents the mirror surface thickness T (λ) of the first reflecting mirror 4 normalized by the wavelength λ.

  As described above, the mirror surface thickness T of the first reflecting mirror 4 is to suppress the loss when the second radio wave W2 radiated from the second primary radiator 2 passes through the first reflecting mirror 4. Usually, it is set to about ¼ wavelength.

However, as shown in FIG. 6, the mirror surface thickness T that minimizes the passage loss varies depending on the difference in the incident angle θ when the second radio wave W2 is incident on the first reflecting mirror 4.
That is, with respect to the incident angles θb and θm (solid line and broken line) at the lower end portion and the intermediate portion of the first reflecting mirror 4, a mirror surface thickness T (λ) (≈0.25) of about ¼ wavelength is obtained. Although optimal, a mirror surface thickness T (λ) of 0.5 (λ / 2) or more is appropriate for the incident angle θt (dotted line) at the upper end of the first reflecting mirror 4.

Accordingly, as shown in FIG. 7, the mirror surface thickness T (λ) normalized by the wavelength λ is shifted from the uniform distribution, and the antenna position where the incident angle θ becomes a predetermined angle (value normalized by the wavelength λ). It increases when it exceeds “near“ 45 ”). The predetermined angle varies depending on the specifications of the antenna device, but the incident angle θ is preferably set to a value within a range of 30 degrees to 50 degrees.
As a result, as is clear from the characteristics of FIG. 6, an improvement in gain of about 0.1 dB can be realized.

  As described above, the antenna device according to Embodiment 1 (FIGS. 1 to 3) of the present invention is the first primary radiator that radiates the first radio wave W1 excited in the first polarization direction. 1, a second primary radiator 2 that radiates a second radio wave W2 excited in a second polarization direction orthogonal to the first polarization direction, and first and second primary radiators A double reflecting mirror 3 whose center axis is offset with respect to the radio wave radiation directions 1 and 2, and the double reflecting mirror 3 radiates the first and second radio waves W1 and W2 in a predetermined direction. Furthermore, the first reflecting mirror 4 having the conductive grid G1 for reflecting the first radio wave W1 and allowing the second radio wave W2 to pass through, and the second reflecting mirror 5 for reflecting the second radio wave W2 are provided. It is configured.

The mirror surface thickness T of the first reflecting mirror 4 varies depending on the incident position of the second radio wave W2, as shown in FIGS. 4 to 7, and depends on the incident angle θ of the second radio wave W2 with respect to the first reflecting mirror 4. Are set to different optimum values.
Specifically, the mirror surface thickness T is the wavelength of the second radio wave W2 at the antenna position where the incident angle θ of the second radio wave W2 is equal to or smaller than a predetermined angle (value within a range of 30 degrees to 50 degrees). At an antenna position where the incident angle θ is set to approximately ¼ of λ and the incident angle θ exceeds a predetermined angle, the value is set to a value larger than ¼ of the wavelength λ.

Further, the mirror surface thickness T of the first reflecting mirror 4 is set to a larger value as the incident angle θ increases as shown in FIG. 7 at the antenna position where the incident angle θ exceeds the predetermined angle.
Thus, by setting the mirror surface thickness T of the first reflecting mirror 4 to an optimum value corresponding to the incident angle θ of the second radio wave W2, the passage loss of the second radio wave W2 with respect to the first reflecting mirror 4 is achieved. Can be suppressed, and the antenna gain can be improved.

  As shown in FIG. 2, the first reflecting mirror 4 includes a front skin 4a in which a conductive grid G1 is embedded, a rear skin 4b disposed opposite to the front skin 4a, and a distance between the front skin 4a and the rear skin 4b. And a spacer 4c for holding the mirror surface thickness T, and the conductive grid G1 is laid in the same direction as the first polarization direction.

As shown in FIG. 3, the second reflecting mirror 5 has a second conductive grid G2 for reflecting the second radio wave W2, and the second conductive grid G2 has a second polarization direction. Are laid in the same direction.
Thereby, in the 2nd reflective mirror 5, only the 2nd electromagnetic wave W2 can be reflected reliably, and communication efficiency can be improved further.

  In FIGS. 2 and 3, the first and second reflecting mirrors 4 and 5 are arranged in a fixed direction, taking as an example the case where the electric field directions of the first and second radio waves W1 and W2 are constant. Although the uniform conductive grids G1 and G2 are formed, the present invention can also be applied to a circularly polarized wave whose electric field direction rotates with time. In this case, the conductive grid provided on each surface of the first reflecting mirror 4 and the second reflecting mirror 5 may be formed in a pattern such as a circle.

In the above description, the transmitting antenna device has been described. Needless to say, the transmitting antenna device can also be applied to a receiving antenna device that receives radio waves of two orthogonal polarizations.
In this case, a first receiver and a second receiver (not shown) may be installed at the same position as the first and second primary radiators 1 and 2, and the first and second primary radiators are provided. 1 and 2 may be configured to also have a reception function.

Embodiment 2. FIG.
In the first embodiment (FIGS. 1 to 7), the case where the first and second radio waves W1 and W2 are radiated in a predetermined direction as the radiation pattern of the perfect circle distribution is shown. In consideration of the case where the communication target area (service area) is not a perfect circle, the first reflecting mirror 4C having a shape whose radiation direction is adjusted may be used as shown in FIG.

FIG. 8 is a block diagram schematically showing an antenna apparatus according to Embodiment 2 of the present invention. Components similar to those described above (see FIG. 1) are denoted by the same reference numerals as those described above or after the reference numerals. A detailed description is omitted with “C”.
In FIG. 8, the mirror surface shape of the first reflecting mirror 4C of the double reflecting mirror 3C is modified so that the first and second radio waves W1 and W2 can be efficiently irradiated to the service area. Yes.

The double reflecting mirror 3C is a front mirror surface modified reflecting mirror, and the first reflecting mirror 4C suppresses passage loss when the second radio wave W2 radiated from the second primary radiator 2 passes. As described above, the mirror surface thickness T is set to an optimum value according to the incident angle θ of the second radio wave W2 as described above.
As shown in FIG. 8, the antenna device using the first reflecting mirror 4 </ b> C whose radiation direction has been corrected can achieve the same effects as described above.

  1 1st primary radiator 2 2nd primary radiator 3 3C double reflector 4, 4C 1st reflector 5, 5C 2nd reflector, W1 1st radio wave, W2 1st 2 radio wave, T mirror surface thickness, θ, θb, θm, θt Incident angle.

Claims (5)

A first primary radiator that radiates a first radio wave excited in a first polarization direction;
A second primary radiator that radiates a second radio wave excited in a second polarization direction orthogonal to the first polarization direction;
A double reflector having a central axis offset with respect to the radio wave radiation direction of the first and second primary radiators,
In order for the double reflector to radiate the first and second radio waves in a predetermined direction,
Reflecting the first wave, and, a first reflecting mirror having a conductive grid for passing the second radio wave reflected by the second radio wave and a second reflecting mirror,
A second reflecting mirror for reflecting the second radio wave radiated from the second primary radiator and passed through the first reflecting mirror ;
In the antenna device configured by
The mirror surface thickness of the first reflecting mirror varies depending on the incident position of the second radio wave, and is set to a different optimum value according to the incident angle of the second radio wave with respect to the first reflecting mirror .
The mirror surface thickness of the first reflecting mirror is equal to the wavelength of the second radio wave at the antenna position where the incident angle of the second radio wave radiated from the second primary radiator is a predetermined angle or less. At an antenna position where the incident angle is set to about 1/4 and the incident angle exceeds the predetermined angle, a value larger than 1/4 of the wavelength is set.
An antenna device characterized by that. 2. The antenna device according to claim 1 , wherein the mirror surface thickness of the first reflecting mirror is set to a larger value as the incident angle increases at an antenna position where the incident angle exceeds the predetermined angle. . The antenna device according to claim 1 , wherein the predetermined angle is set to a value within a range of 30 degrees to 50 degrees. The first reflecting mirror is
A front skin in which the conductive grid is embedded;
A rear skin disposed opposite to the front skin;
A spacer for maintaining the distance between the front skin and the rear skin as the mirror thickness, and
4. The antenna device according to claim 1, wherein the conductive grid is laid in the same direction as the first polarization direction. 5. The second reflecting mirror has a second conductive grid for reflecting the second radio wave,
5. The antenna device according to claim 1 , wherein the second conductive grid is laid in the same direction as the second polarization direction. 6.

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