GB2145569A - Reflector antenna - Google Patents

Reflector antenna Download PDF

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Publication number
GB2145569A
GB2145569A GB08408429A GB8408429A GB2145569A GB 2145569 A GB2145569 A GB 2145569A GB 08408429 A GB08408429 A GB 08408429A GB 8408429 A GB8408429 A GB 8408429A GB 2145569 A GB2145569 A GB 2145569A
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GB
United Kingdom
Prior art keywords
strut
antenna
supporting strut
waves
supporting
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB08408429A
Other versions
GB8408429D0 (en
GB2145569B (en
Inventor
Hideo Sato
Akiyoshi Ogawa
Naoto Matsunaka
Takashi Katagi
Takashi Ebisui
Katsuhiko Aoki
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Mitsubishi Electric Corp
KDDI Corp
Original Assignee
Kokusai Denshin Denwa KK
Mitsubishi Electric Corp
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Application filed by Kokusai Denshin Denwa KK, Mitsubishi Electric Corp filed Critical Kokusai Denshin Denwa KK
Publication of GB8408429D0 publication Critical patent/GB8408429D0/en
Publication of GB2145569A publication Critical patent/GB2145569A/en
Application granted granted Critical
Publication of GB2145569B publication Critical patent/GB2145569B/en
Expired legal-status Critical Current

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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q19/00Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
    • H01Q19/10Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
    • H01Q19/18Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces having two or more spaced reflecting surfaces
    • H01Q19/19Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces having two or more spaced reflecting surfaces comprising one main concave reflecting surface associated with an auxiliary reflecting surface
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q19/00Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
    • H01Q19/02Details
    • H01Q19/021Means for reducing undesirable effects
    • H01Q19/023Means for reducing undesirable effects for reducing the scattering of mounting structures, e.g. of the struts
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q19/00Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
    • H01Q19/10Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
    • H01Q19/12Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave

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  • Aerials With Secondary Devices (AREA)

Abstract

A reflector antenna such as a Cassegrain or Parabolic antenna which is intended for use in the microwave or millimeter wavebands has a supporting post or strut 4 which supports a component of the antenna and is located in the plane wave produced by the main reflector 1. The plane wave is therefore scattered and in order to improve the performance of the antenna the surface of the strut is modified so as to cause random scatter of the primary wave so that the field strength of the scattered waves is reduced. As shown the front of the strut comprises a triangular member. <IMAGE>

Description

SPECIFICATION Reflector antenna The present invention relates to a reflector antenna intended for use in the microwave band or the millimeter wave band. More particularly, the invention relates to an antenna device having excellent wide angle radiation characteristics.
Fig. 1 shows the arrangement of a Cassegrain antenna, which is an example of a conventional reflector antenna.
In Fig. 1, reference numeral 1 designates a main reflector, 2 a subreflector, 3 a primary radiator, and 4 a supporting strut for supporting the subreflector. A spherical wave radiated by the primary radiator 3 of the reflector antenna thus constructed is converted into a plane wave upon being reflected by the subreflector mirror 2 and the main reflector 1. The plane wave is radiated outwardly. In this operation, the plane wave 5 reflected by the main reflector 1 is scattered by the supporting strut 4. In this case, the scattered wave 6 is composed of the reflected wave from the surface and the diffracted wave from the edge.
The section, on the main reflector side, of the conventional supporting strut 4 may be circular as shown in Fig. 2B or rectangular as shown in Fig. 2C. Therefore, the scattered waves 6 formed by these supporting struts have the radiation patterns as follows. If it is assumed that, as shown in Fig. 2A, the supporting strut 4 forms an angle 8 with the Z-axis when the plane wave 5 advances in the positive direction of the Z-axis, and if, as shown in Fig. 3A, the observation point P has the coordinates (H, 4 > ) in polar coordinates with the Z-axis as the polar axis, then the direction of advancement of the reflected wave due to the supporting strut 4 can be represented by the following expression (1)::
where + is the angle formed between the plane Z-X and a normal line extending from the point on a reflection surface 8 at which the plane wave 5 is applied.
The direction of the diffracted wave is in the form of a cone having an edge 7 as the cental axis and having a half vertical angle 8. In the case of Fig. 2B, the supporting strut 4 has a curved surface which has a continuously changing value 4'. Therefore, the reflected wave is radiated in the form of a circular cone which has the supporting strut 4 as its central axis and has a half vertical angle 0. On the other hand, in the case of the supporting strut 4 shown in Fig. 2C, a reflected wave is produced due to a reflection surface 8 where the value + is 90 degrees and waves are refracted due to edges 7. The reflected wave is radiated in the negative direction along the Z axis (- Z). while the diffracted waves are radiated conically.
The radiation patterns of the scattered waves due to the conventional supporting struts shown in Figs. 2B and 2C are as shown in Figs. 3B and 3C, respectively. In Figs. 3B and 3C, the higher the density of lines shown therein, the higher the field intensity level. As is apparent from these figures, the field intensity level is high in the direction of scattering, and it is not low even in the region where the value H is large. This degrades the wide angle radiation characteristics of the antenna. Therefore, the use of such an antenna may cause interference with other radio systems.
This difficulty may be eliminated by employing a technique whereby a microwave absorber is provided on the surface of the supporting strut, or a technique whereby, as shown in Fig. 4, metal plates 9 are arranged at a certain pitch on the supporting strut 4, or a technique whereby metal elements which are shorter than the wavelength employed and are irregularly arranged on the supporting strut. However, the first technique is disadvantageous in that it is impossible for the microwave absorber to completely absorb the scattered waves, and it is rather difficult to provide such a material which has satisfactory weather-proof characteristics. The second technique is also disadvantageous in that a grating lobe is formed according to the pitch at which the metal plates are arranged.The third technique has a drawback that, although the reflected wave can be scattered, it is difficult to scatter the diffracted wave.
The object of the present invention is to provide an antenna in a simple and convenient form.
According to the invention an antenna for the microwave or millimeter waveband comprises at least one supporting strut extending into an aperture of said antenna; at least one triangular strut provided on at least a part of said supporting strut, a section of said triangular strut perpendicular to a longitudinal axis of said supporting strut being in a form of a triangle having one side which is connected to said supporting strut, and the remaining two sides of which are longer than the wavelength of waves radiated by the antenna, and the length of said triangular strut in said longitudinal direction of said supporting strut being longer than said wavelength; and a planar member having a thickness less than said wavelength, said planar member having one edge connected to an outer edge of said triangular strut away from said supporting strut and an opposite edge cut in the form of a polygon having a plurality of segments each of which is longer than said wavelength, a plane of said planar member being parallel to a plane including said longitudinal direction of said supporting strut and a direction of propagation of said waves.
In the accompanying drawings: Figures 1 and 4 are cross-sectional views of prior art antennas used in the microwave or millimeter waveband; Figures 2A-2C and 3A-3C are diagrams used for illustrating radiation patterns from the antennas of Figs. 1 and 4; Figures 5A, 5B, 6-8, 10, 1 1A-16A and 17-19 are diagrams illustrating various supporting strut strutures for an antenna of the present invention; Figure 9 is a diagram illustrating a radiation pattern of an antenna utilizing the supporting strut structure shown in Fig. 8; Figure 16B is a diagram illustrating a radiation pattern of an antenna employing the supporting strut struture of the embodiment shown in Fig. 1 6A; and Figure 20A is an explanatory diagram showing wide angle radiation characteristics of the conventional antenna, and Figure 20B is also an explanatory diagram showing wide angle radiation characteristics of the antenna using a supporting strut having a struture shown in Fig. 6.
Figs. 5A and 5B show a preferred embodiment of an antenna in accordance with the invention. In Figs. 5A and 5B, reference numeral 4 designates a supporting strut, 5 a plane wave passing the supporting strut, 10 a triangular strut, and 11 a plate structure. The corsssection of the strut 10, which is positioned parallel to the longitudinal axis of the supporting strut 4, is in the form of a triangle. The length of one side of the triangle adjacent the supporting strut 4 is equal to the width of the supporting strut 4, and the length of each of the remaining sides is longer than the wavelength of radiated waves. The length of the triangular strut 10 in the longitudinal direction of the supporting strut is longer than the wavelength. The plate structure 11 is a flat plate having a thickness less than the radiated wavelength.One edge of the structure 11 is connected to the lateral edge of the triangular strut 10 while the other edge is formed as a polygonal line having a number of sides each of which is longer than the wavelength. For a Cassegrain antenna, the triangular strut 10 is provided on the surface, faced to the main reflector side, of the supporting strut. For a parabolic antenna, the triangular strut 10 is provided on the surface of the supporting strut faced to the main reflector side. The structure 11 is coupled to the lateral edge of the of the triangular strut 10 in such a manner that it is parallel to a plane which includes both the longitudinal direction of the supporting strut and the direction of advancement of the plane wave 5.
In Fig. 5A, reference character 7a designates the aforementioned lateral edge which is the connecting line between the structure 11 and the triangular strut, 7b and 7c edges which are the connecting lines between the triangular strut 10 and the supporting strut 4, and 7c an edge of the structure 11 which forms the aforementioned polygonal line. With the above-described arrangement, the scattered wave of a plane wave 5 due to the supporting strut 4 can be represented by the superposition of diffracted waves due to edges 7a, 7b, 7c and 7d and reflected waves due to the surfaces 8a and 8b. The reflected waves 1 3 due to the surfaces 8a and 8b are radiated in directions which are defined by the values 8 and + in expression (1).As the value + decreases, the direction of reflection approaches the direction of advancement of the plane wave 5.
The plane wave 5 incident on the struture 10 is scattered as diffracted waves by the edge 7d.
As the edge 7d is irregularly polygonally-shaped having sides each longer than the radiated wavelength, the diffracted waves due to the edge 7d are scattered over a wide range. Thus, as the directions of advancement of the reflected waves approaches the direction of advancement of the plane wave and the diffracted waves are scattered over a wide range, the radiation levels of the scattered waves in the region where the value H is large are reduced.
Another embodiment of the invention is shown in Fig. 6. In this embodiment, the surface of a supporting strut 4, on which a triangular strut 10 is mounted, is made up of a plurality of planes which are perpendicular to a plane which includes both the longitudinal direction of the supporting strut 4 and the direction of advancement of a plane wave 5.
With this arrangement, the directions and phases of waves reflected by surfaces 8a, 8d and 8e are different, and the directions and phase of diffracted waves due to edges 7a, 7b, 7e, 7f, 7g and 7h is also made different. Therefore, the radiation levels of the scattered waves re reduced.
Figs. 20A and 20B are explanatory diagrams showing wide angle radiation characteristics of the antenna using a conventional supporting strut and the present antenna using a supporting strut having a structure shown in Fig. 6 for the purpose of comparison, where E, designates an etevation angle. As is clear from Figs. 20A and 20B, according to the invention, the radiation levels of the scattered waves due to the supporting strut are effectively decreased.
A third embodiment of the invention is shown in Fig. 7. In this embodiment, the structure 11 includes a plurality of polygonal members the sides of which are different in length and which are arranged irregularly to form a polygonal line. In this case also, the radiation levels of the scattered waves are reduced. In this embodiment, each of the polygonal members is triangular.
However, the same effect can be obtained by employing rectangular members as the polygonal members or by employing rectangular members and triangular members in combination.
Furthermore, the same effect can be obtained by rounding off some or all of the corners of the polygonal members.
As is apparent from the above description, according to the invention, the radiation levels of the scattered waves due to the supporting strut are decreased. Accordingly, an antenna having excellent wide-angle radiation characteristics is provided.
Fig. 8 shows another embodiment of the invention. In Fig. 8, reference numeral 4 designates a supporting strut, 5 a radiated plane wave, 7 edges along which quadrangular prisms are connected to the supporting strut 4, and 1 5 the quadrangular prisms. Two sides of the bottom of each quadrangular prism 1 5 which extend in the longitudinal direction of the supporting strut have a length and height equal to or larger than the radiated wavelength while the width of the remaining two sides of the bottom is equal to the width of the supporting strut.A plurality of plural types or shapes or quadrangular prisms, which are different in the length or height of the sides extending in the longitudinal direction of the supporting strut, are irregularly arranged on a surface, on the main reflector side, of the supporting strut in the case of a Cassegrain antenna, and on a surface, on the reflecting mirror side, of the supporting strut in the case of a parabolic antenna.
With this arrangement, waves scattered due to the quadrangular prisms 1 5 can be represented by the superposition of reflected waves from the surfaces 1 6a and 1 6b forming the quadrangular prisms 15, waves diffracted due to the connecting lines or edges of the surfaces 1 6a and 1 6b, and waves diffracted due to the connecting lines or the edges 7 of the quadrangular prisms 1 5 and the supporting strut 4. Among these waves, the waves reflected due to the surfaces 1 6a including an edge 7 are radiated in a direction which is defined by an angle 8 formed between the direction of advancement of the plane wave 5 and the edge 7 and by half the angle formed between confronting surfaces 1 6b. The angle O of the plural quadrangular prisms are equal to one another but the value of + is different.Therefore, the waves reflected due to the surfaces 1 6a are scattered along the generating line of a circular cone which has the supporting strut as its central axis and a half vertical angle 8. The waves reflected due to the other two surfaces 1 6b forming each quadrangular prism 1 5 are scattered along the H-axis with z = 0 where the value of + is 90 degrees. As the plural quadrangular prisms have different angles between the surface 1 6b and the Z-axis, the waves reflected due to the surfaces 1 6b are scattered along the H-axis. The waves diffracted due to the edge are scattered in the form of a circular cone which is defined by a half vertical angle 8 with the supporting strut as its central axis.The waves diffracted due to the other edges are scattered over a wide range as the angles formed between the edges and the Z-axis are different from one another. Since these quadrangular prisms are irregularly arranged, no grating lobe is produced.
The radiation pattern of the scattered waves due to the plural quadrangular prisms is as shown in Fig. 9. In Fig. 9, reflection points 14a indicate the directions of the reflected waves due to the surfaces 1 6a, and reflection points 1 4b indicates the directions of the reflected waves due to the surfaces 1 6b. As is apparent from the above description, as a plane wave incident on the supporting strut is scattered over a wide range, the field intensity levels of the scattered waves is reduced.
Fig. 10 shows yet another embodiment of the invention. In this embodiment, the abovedescribed quadrangular prisms are mounted on a surface of a supporting strut which includes a plurality of surfaces which are perpendicular to a plane which includes both the direction of advancement of transmitted waves and the longitudinal direction of the supporting strut. In this arrangement, waves reflected due to the surfaces of the quadrangular prisms and waves diffracted due to the edges are scattered in a wider range, and the phases of the waves reflected due to the surfaces of the quadrangular prisms and of the waves diffracted due to the edges can be changed. Thus, in this case, the radiation level of the scattered waves is more effectively reduced.
Reference has been made to the case where the length of two sides of the bottom of each quadrangular prism which are perpendicular to the longitudinal direction of the supporting strut is equal to the width of the supporting strut. However, the same effect can be obtained even if the length of the two sides is made smaller than the width of the supporting strut.
As was described above, the scattered waves due to the supporting strut for the primary radiator or the subreflector obstructing the passage of the transmitted waves in the antenna of the invention are scattered over a wide range by irregularly arranging on a part or the whole of a surface of the supporting strut a plurality of plural types or shapes of quadrangular prisms with the length and height of two sides of the bottom of each quadrangular prism which extend in the longitudinal direction of the supporting strut being equal to or larger than the wavelength, the length of the remaining two sides being equal to or smaller than the width of the supporting strut, and the lengths or heights of the sides of the bottoms of the quadrangular prisms which extend in the longitudinal direction of the supporting strut being different from one another.
Therefore, the radiation level of the scattered waves is reduced.
Fig. 1 1A shows another preferred embodiment of the invention. In Fig. 1 1A, reference numeral 4 designates the supporting strut, 5 a radiated plane wave, and 1 9 surfaces of the supporting strut. A part or the whole of a surface, on the main reflector side, of the supporting strut is made up of a plurality of surfaces 1 9 perpendicular to a plane which includes both the longitudinal direction of the supporting strut 4 and the direction of advancement of the plane wave 5 in the case of a Cassegrain antenna. In the case of a parabolic antenna, a part or the whole of a surface, on the reflector side, of the supporting strut is made up of a plurality of surfaces 1 9 similar to those described above.Sections of the supporting strut in planes including the aforementioned two directions have the same configuration, and each section has an edge in the form of a polygonal line with sides each longer than the radiated wavelength.
With this arrangement, waves scattered due to the supporting strut 4 can be represented by the superposition of reflected waves 10 due to the surfaces 1 9 and diffracted waves due to the polygonal edge 7. The surfaces 1 9 are perpendicular to the plane including both the direction of advancement of the plane wave 5 and the longitudinal direction of the supporting strut 4 and facing irregular directions. Therefore, the reflected waves 20 are scattered on the H-axis with = = Oin Fig. 3. The diffracted waves are scattered over a wide range as the edge 1 8 is in the form of an irregular polygonal line.
Thus, plane waves incident on the supporting strut are scattered in one particular region, and accordingly the field strength of the scattered waves in the other regions is reduced. In the case of the above-described supporting strut, the configurations of the sections in given planes perpendicular to the ''shadow'' of the supporting strut projected onto the effective area of the surface on the reflector side are the same and are linear.
Yet another embodiment of the invention is shown in Fig. 1 2A. In this embodiment, the configurations of sections in given planes including both the longitudinal direction of the supporting strut and the direction of advancement of a plane wave 5 are the same, and each of the sections is in the form of an irregular polygonal line having segments each longer than the radiated wavelength. The configuration, on the reflector side, of a section in a plane perpendicular to the "shadow" of the supporting strut projected onto the effective area is formed by two sides which form an angle + with the direction of advancement of the plane waves 5. Therefore, by decreasing the angle +, it is possible to make the directions of the relfected waves 10 approach the direction of advancement of the plane waves 5.Furthermore, since the surface 1 9 of the supporting strut is irregular, the phases of the reflected waves are made different, and accordingly the field strengths of the scattered waves is reduced.
In still another embodiment of the invention, as shown in Fig. 1 2B, a plurality of surfaces are formed which are symmetrical with a plane which includes both the longitudinal direction of the supporting strut 4 and the direction of advancement of the plane waves 5 facing in various directions. The configuration of a section in the plane of symmetry is in the form of an irregular polygonal line composed of segments each being longer than the radiated wavelength. With the supporting strut thus constructed, waves reflected by the surfaces 8 are directed in various directions, and therefore the field strength of the scattered waves is decreased.
Fig. 1 3A shows an embodiment of the present invention in which 4 is the support pole structure, 5 is an incident plane wave and 21 is a planar member. The planar member 21 is a plate having a thickness smaller than the radiated wavelength. One end of the planar member 21 is connected to the supporting strut 4 along the length thereof while the other end is irregularly zig-zag shaped and has a length greater than the radiated wavelength. The planar member 21 is connected to a main reflector side surface of the supporting strut 4 if the antenna is of Cassegrain type or to a reflector side surface of the supporting strut 4 if the antenna is a parabolic type, wherein the member lies in a plane parallel to a plane containing the lengthwise direction of the supporting strut 4 and the propagating direction of the plane waves 5.
With this arrangement, a plane wave 5 incident on the planar member 21 becomes a diffraction wave due to the edge 7 and is scattered. Since the length of the edge 7 is greater than the radiated wavelength and the shape thereof is an irregularly zigzag, waves diffracted by the edge 7 are widely scattered thereby reducing the field strength of the diffracted waves.
The same effect may be obtained by irregularly arranging a plurality of protrusions each having different length or size instead of the planar member having the zigzag shape, as shown in Fig. 1 3B. Therefore, since a portion of the incident plane waves 5 are widely scattered, the field strength of the waves scattered by the support pole structure is reduced.
In Fig. 1 3B, the protrusions are shown as being triangular in shape. However, the same effect cen be obtained by providing protrusions having rectangular shapes or combination of rectangular shapes and triangle shapes. The same effect is also obtainable by rounding corners of a portion or the whole of the irregular zigzag shapes.
Fig. 1 4A shows an embodiment of the present invention in which 4 is the supporting strut, 5 is the incident plane wave and 23 indicates two planar members. Each planar member 23 is a plate having a thickness less than the radiated wavelength. One end of the planar member 23 is connected to the supporting strut 4 along the length thereof while the other end is irregularly zigzag shaped having segments with a length greater than the radiated wavelength.The planar members 23 are attached on either side of a main reflector side surfsce of the supporting strut 4 if the antenna is of Cassegrain type or to both sides of a reflector side surface of the supporting strut 4 if the antenna is a parabolic type, such that the planar members lie in planes parallel to a plane containing the lengthwise direction of the supporting strut 4 and the propagating direction of the plane waves 5.
With this arrangement, a plane wave 5 incident on the plane member 23 reflected by the supporting strut 4 becomes a diffracted wave due to an edge 7 of the planar members. The diffracted waves are scattered as shown in Fig. 1 4B. A portion of a reflected wave 25 which propagates toward the planar members 23 is scattered again by the edges 7. Since the length of each edge 7 is greater than the radiated wavelength and the shape thereof is an irregularly zigzag, waves diffracted due to the edges 7 are widely scattered. Since the phases thereof are different, the field strength of the scattered waves, which are a combination of the waves reflected and the diffracted waves, is reduced.
The same effect may be obtained by irregularly arranging a plurality of protrusions each having different length oe size instead of the planar members having the zigzag shape as shown in Fig. 15.
In Fig. 15, the protrusions are triangular in shape. However, the same effect can be obtained by providing protrusions having a rectangular shape or combinations of rectangular and triangle shapes. Further in Figs. 14A, 1 4B and 1 5 although a case where the plate members 23 have the same configuration are attached to the both sides of the supporting strut 4 has been described, the same effect may be obtained by making the shapes of the plate member 23 different or by rounding corners of a portion or the whole of the irregular zigzag shapes.
In the embodiment shown in Fig. 16A, 4 is the supporting strut, 5 is an incident plane wave and 27 is a triangular strut. In this case, the cross-sectional shape of the strut 27 taken alone a plane orthogonal to the lengthwise direction of the supporting strut 4 is triangular with the length of the base of the triangle , with which the triangular strut is connected to the supporting strut, being equal to the width of the supporting strut 4. The lenmgths of the remaining two sides of the triangle are longer than the radiated wavelength, and the length of the triangular strut 27 along the supporting strut is longer that the radiated wavelength.The triangular strut 27 is formed on the supporting strut on the side of a surface of a main reflector if the antenna is of the Cassegrain type or formed on the supporting strut on the side of the reflector supported thereby if the antenna is of a parabolic type. An edge 28a is formed by connecting apexes of cross-sectional triangles of the triangular strut 27 and edges 28b and 28c form connecting portions to the supporting strut 4.
With this arrangement, a portion of incident plane waves 5 scattered by the supporting strut 4 is represented by a combination of waves diffraction due to the edges 2boa, 28b and 28c and waves reflected due to planes 29a and 29b. The direction of the waves reflected due to the planes 29a and 29b are determined by 8 and + according to equation 1. Therefore, by making the value of + small, the reflected direction 30 is made closer to the propagating direction of the plane waves 5. Therefore, the radiation pattern of the scattered waves is as shown in Fig. 16B.
Although there may be left some diffraction waves due to the edge 28a, it is possible to reduce the field strength of the scattered waves in the area where H is large.
Fig. 1 7 shows another embodiment in which the surface configuration of the supporting strut 4 to be mounted on the triangular strut structure 27 is composed of a plurality of planes orthogonal to the plane containing the lengthwise direction of the supporting strut 4 and the propagating direction of the plane waves 5.
With this arrangement, the direction and the phases of the reflected wave are changed from the planes 29a, 29d and 29e, respectively, as well as changing the direction and phases of the waves diffracted due to the edges 28a, 28d and 28e. Therefore, it is possible to further reduce the field strengths of the waves scattered due to the supporting strut struture.
In the embodiment of Fig. 18A, reference numeral 4 designates the supporting strut, 5 the incident plane wave, 33 a triangular prism, and 30a-30c planar members. The configuration of a section of the strut 33 perpendicular to the longitudinal axis of the supporting strut 4 is such that the length of two sides of the bottom of the triangular strut, which is mounted to the supporting strut 4, is equal to the width of the supporting strut 4, the remaining two sides are longer than the radiated wavelength, and the length of the triangular strut 33 along the longitudinal axis of the supporting strut 1 is no longer than the radiated wavelength.Each planar member 30a-30c is in the form of a flat plate having one edge connected to a longitudinal edge of the triangular strut 33 and another edge which is in the form of a polygonal line composed of segments each longer than the radiated wavelength. The triangular strut is mounted on a surface, on the main reflector mirror side, of the supporting strut in the case of a Cassegrain antenna, and on a surface on the reflector side of the supporting strut in the case of a parabolic antenna. The planar members 30a-30b are connected to respective three longitudinal edges of the triangular strut 33 in such a manner that they are in parallel with a plane which includes both the longitudinal direction of the supporting strut and the direction of advancement of the plane waves 5.The planar members 30a, 30b and 30c have edges 31 a, 31b and 31 c, respectively. An edge 31d is the connecting line of the member 30a and the triangular strut 33.
The triangular strut 33 has side surfaces 32a and 32b extending longitudinally.
With this arrangement, the scattered waves can be represented by the superposition of waves diffracted due to the edges 31a, 31b, 31 c and 31d and waves reflected due to the surfaces 32a and 32b. If the half vertical angle + of the triangular section of the triangular strut 33 is decreased, then the field strength of the waves diffracted due to the edge 31d are reduced.
Also, the directions of advancement of the waves reflected due to the edge 31d then approaches the planar members 30b and 30c. As the edges 31 a, 31 b and 31 c of the planar members 30a, 30b and 30c are each in the form of an irregular polygonal line composed of segments longer than the radiated wavelength, the plane waves 5 incident on these edges and the resulting scattered waves are scattered as diffracted waves with different phases over a wide range. Therefore, the scattered waves are reduced in field strength.
Fig. 1 9 shows another embodiment of the invention in which a surface of the supporting strut 4 on which a triangular strut 33 and planar members 30a, 30b and 30c are mounted is made up of a plurality of surfaces which are perpendicular to a plane which includes both the longitudinal direction of the supporting strut and the direction of advancement of plane waves 5. With this arrangement, the reflected waves and the diffracted waves are made different in direction and in phase. Therefore, the scattered waves are reduced in radiation level.
The planar members used in the embodiments of Figs. 18A and 1 9 are formed with a plurality of triangular or rectangular members. The same effect can be obtained by employing planar members which include a plurality of triangular or rectangular members which have different side lengths or sizes and are arranged irregularly. Furthermore, the same effect can be obtained by rounding off the protruding corners of some or all of the triangular or rectangular members.
Although the foregoing explanation relates to the electromagnetic waves being plane waves, the present invention is also applicable to spherical electromagnetic waves with a similar effect.
In such a case, the shape of each through-hole should be conicai.

Claims (5)

1. An antenna for the microwave or millimeter waveband comprising: at least one supporting strut extending into an aperture of said antenna; and a triangular strut formed on at least a portion of a surface of said supporting strut, the shape of said triangular strut in a plane orthogonal to a longitudinal direction of said supporting strut being triangular, a length of a side of said triangular strut where said triangular strut is connected to said supporting strut being equal to the width of said supporting strut, lengths of remaining two sides of said triangular strut being longer than a wavelength of waves radiated from said antenna, and a length of said triangular strut along said supporting strut being longer than said wavelength of said radiated waves.
2. The antenna as claimed in claim 1 wherein said supporting strut has surfaces on which said trinagular strut is positioned having at least one plane orthogonal to a plane including said longitudinal direction of said supporting strut and a direction of propagation of said radiated waves.
3. An antenna for the microwave or millimeter waveband comprising: at least one supporting strut extending into an aperture of said antenna; at least one triangular strut provided on at least a part of said supporting strut, a section of said triangular strut perpendicular to a longitudinal axis of said supporting strut being in a form of a triangle having one side which is connected to said supporting strut, said one side being equal in length to a width of said strut, and the remaining two sides of which are longer than the wavelength of waves radiated by the antenna and the length of said triangular strut in said longitudinal direction of said supporting strut being longer than said wavelength; and a planar member having a thickness less than said wavelength, said planar member having one edge connected to an outer edge of said triangular strut away from said supporting strut and an opposite edge cut in the form of a polygon having a plurality of segments each of which is longer than said wavelength, a plane of said planar member being parallel to a plane including said longitudinal direction of said supporting strut and a direction of propagation of said waves.
4. An antenna for use in the microwave or millimetre wave band substantially as hereinbefore described with reference to Fig. 7 of the accompanying drawings.
4. The antenna as claimed in claim 3 wherein said surface of said supporting strut upon which said triangular strut is provided includes at least one surface which is perpendicular to a plane including both said longitudinal direction of said supporting strut and the direction of propagation of said waves.
5. The antenna as claimed in claim 3 or 4 wherein at least some of said segments are of different lengths.
6. The antenna as claimed in claim 3 or 4 wherein at least some of said segments are of different lengths, and wherein at least some of the corners of said segments are rounded.
7. An antenna for the microwave or millimeter waveband comprising: at least one supporting strut extending into an aperture of said antenna; and a plurality of quadrangular prisms arranged irregularly on at least a part of a surface of said supporting strut, the length and height of two sides of a quadrangular prism extending in a longitudal direction of said supporting strut and being equal to or greater than the wavelength of waves radiated by said antenna, a length of two remaining sides of each quadrangular prism being equal to or less than a width of said supporting strut, and at least some lengths of said sides of said bottoms of said quadrangular prisms being different from one another.
8. The antenna as claimed in claim 7 wherein said supporting strut has a surface upon which said quadrangular prisms are mounted including a plurality of surfaces perpendicular to a plane including both said longitudinal direction of said supporting strut and a direction of propagation of waves radiated by said antenna.
9. In a Cassegrain antenna for the microwave or millimeter waveband having at least one supporting strut extending into an aperture of said antenna, the improvement comprising said supporting strut having a surface on a main reflector side composed of a plurality of surfaces which are symmetrical with a plane including both a longitudinal direction of said supporting strut and a direction of propagation of waves radiated by said antenna, the configuration of a section of said supporting strut in said plane being in the form of an irregular polygonal line having a plurality of segments each of which is longer than said wavelengths of said radiated waves.
10. In a parabolic antenna for the microwave or millimeter waveband having at least one supporting strut extending into an aperture of said antenna, the improvement comprising said supporting strut having a surface on a reflector side composed of a plurality of surfaces which are symmetrical with a plane including both a longitudinal direction of said supporting strut and a direction of propagation of waves radiated by said antenna, the configuration of a section of said supporting strut in said plane being in the form of an irregular polygonal line having a plurality of segments each of which is longer than said wavelengths of said radiated waves.
11. An antenna for the microwave or millimeter waveband comprising: at least one supporting strut extending into an aperture of said antenna, and at least one planar member having one edge connected to said supporting strut and the opposite edge thereto having an irregular zigzag shape, said planar member extending along at least a portion of the length of said said supporting strut and being in a plane parallel to a plane containing the lengthwise direction of said supporting post and a direction of propagation of waves radiated from said antenna, a thickness of said planar member being less than said wavelength of said radiated waves, and the length of segments of said end having said irregular zigzag shape being longer than said wavelength of said radiated waves.
1 2. The antenna as claimed in claim 9 wherein at least a portion of corners of said irregular zigzag shaped edge are rounded.
1 3. The antenna as claimed in claim 11 wherein one of said planar member is provided along a center line of said supporting strut.
1 4. The antenna as claimed in claim 11 wherein first and second ones of said planar members are provided disposed on opposite side surfaces of siad supporting post.
1
5. The antenna as claimed in claim 14 wherein the shapes of said irregular zigzag edges are similar to one another between said first and second planar members.
16. The antenna as claimed in claim 14 wherein the shapes of said irregular zigzag edges are different from one another.
1 7. An antenna for the microwave or millimeter waveband comprising: at least one supporting strut extending into an aperture of said antenna; a triangular strut provided on at least a part of a surface of said supporting strut, a section of said triangular strut perpendicular to a longitudinal axis of said supporting strut being in the form of a triangle having one side which is connected to said supporting strut, said side connected to said supporting strut being equal in length to a width of said supporting strut, and remaining two sides of said section being longer than a wavelength of waves radiated by said antenna, a length of said triangular strut in said longitudinal direction of said supporting strut being longer than said radiated wavelength; and first through third planar members each having a thickness less than said wavelength of said radiated waves, each of said planar members having a first edge which is connected to a corresponding longitudinal edge of said triangular strut and a second edge formed in the shape of an irregular polygonal line having segments each of which is longer than said wave length of said radiated waves, said planar members each being parallel to a plane including both said longitudinal direction of said supporting strut and a direction of propagation of said radiated waves.
1 8. An antenna for the microwave or millimeter waveband substantially as hereinbefore described with reference to the accompanying drawings.
1. An antenna for use in the microwave or millimetre wave band comprising a main reflector of generally parabolic form, a subreflector or radiator positioned in front of the main reflector, a supporting strut acting to support the subreflector or radiator relative to the main reflector, said supporting strut being positioned so that in the use of the antenna, waves reflected from the radiating surface of the main reflector strike the supporting strut, the surface of said supporting strut which is struck by the waves from said radiating surface being defined by a strut portion which is of a triangular section and is integral with the supporting strut, the length of the strut portion in the direction of the strut and the lengths of the sides of the strut portion being longer than the wavlength, and the width of the base of the strut portion being equal to the width of the supporting strut.
2. An antenna according to Claim 1 in which the strut portion is defined by a series of interconnected elements of triangular section, the planar bases of the elements lying in planes orthoganal to the plane containing the lengthwise direction of the strut and the propagating direction of the reflected waves, some of the planar bases being inclined in the longitudinal direction of the strut.
3. An antenna for use in the microwave or millimetre wave band substantially as hereinbefore described with reference to Fig. 5 of the accompanying drawings.
GB08408429A 1980-06-03 1984-04-02 Reflector antenna Expired GB2145569B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP7454880A JPS56169906A (en) 1980-06-03 1980-06-03 Antenna device

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GB8408429D0 GB8408429D0 (en) 1984-05-10
GB2145569A true GB2145569A (en) 1985-03-27
GB2145569B GB2145569B (en) 1985-09-18

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2637130A1 (en) * 1988-09-23 1990-03-30 Alcatel Transmission Cassegrain optical antenna with high output
EP0361294A1 (en) * 1988-09-23 1990-04-04 Alcatel Telspace Revolution reflector antenna
US5182569A (en) * 1988-09-23 1993-01-26 Alcatel N.V. Antenna having a circularly symmetrical reflector
EP2493020A1 (en) * 2009-10-21 2012-08-29 Mitsubishi Electric Corporation Antenna device

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4884670B2 (en) * 2004-12-24 2012-02-29 株式会社デバイス Antenna lifting device

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Publication number Priority date Publication date Assignee Title
GB609060A (en) * 1946-03-05 1948-09-24 Athur Harold Stevens Improvements in or relating to an absorption device for ultra high frequency radiant energy
GB1162312A (en) * 1967-02-16 1969-08-27 Mini Of Technology London Improvements in or relating to Microwave Aerial Assemblies
GB1205014A (en) * 1966-10-04 1970-09-09 Gen Electric & English Elect Improvements in or relating to directional aerial systems

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Publication number Priority date Publication date Assignee Title
JPS53105343A (en) * 1977-02-26 1978-09-13 Nippon Telegr & Teleph Corp <Ntt> Antenna unit
JPS54134959A (en) * 1978-04-12 1979-10-19 Mitsubishi Electric Corp Radio-wave shielding board

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB609060A (en) * 1946-03-05 1948-09-24 Athur Harold Stevens Improvements in or relating to an absorption device for ultra high frequency radiant energy
GB1205014A (en) * 1966-10-04 1970-09-09 Gen Electric & English Elect Improvements in or relating to directional aerial systems
GB1162312A (en) * 1967-02-16 1969-08-27 Mini Of Technology London Improvements in or relating to Microwave Aerial Assemblies

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2637130A1 (en) * 1988-09-23 1990-03-30 Alcatel Transmission Cassegrain optical antenna with high output
EP0361294A1 (en) * 1988-09-23 1990-04-04 Alcatel Telspace Revolution reflector antenna
US5182569A (en) * 1988-09-23 1993-01-26 Alcatel N.V. Antenna having a circularly symmetrical reflector
EP2493020A1 (en) * 2009-10-21 2012-08-29 Mitsubishi Electric Corporation Antenna device
EP2493020A4 (en) * 2009-10-21 2014-04-16 Mitsubishi Electric Corp Antenna device
US8766865B2 (en) 2009-10-21 2014-07-01 Mitsubishi Electric Corporation Antenna device

Also Published As

Publication number Publication date
JPH0221169B2 (en) 1990-05-14
JPS56169906A (en) 1981-12-26
GB8408429D0 (en) 1984-05-10
GB2145569B (en) 1985-09-18

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