Structure of primary radiator

Abstract: A primary radiator for use in antenna to be mounted in an artificial satellite has a structure for preventing an electrical charging caused by charged particles accumulated at the reflector (4). The subreflector (4) is isolated from the horn (3) by a resin cover (5). In order to prevent this electrical charging, a fine metallic conductor (7) is passed from the central part of a sub-reflector (4) to the axial central part where an influence for the electromagnetic field is less within the circular waveguide constituting the primary radiator and then connected to the ground at the part of the linear polarization of the rectangular and circular converter (1). Since the metallic conductor (7) crosses at a right angle the electric field of a dominant mode within the waveguide, disturbance of the electromagnetic field is reduced.

Description: This invention relates to a primary radiator which is a component element of an antenna to be mounted in an artificial satelite, more particularly a structure of a primary radiator for preventing an electrical charge caused by some charged particles and the like under an environment of space. In the conventional type of self-independent primary radiator, it is constructed such that a cap-like sub-reflection part is fixed to an opening of an electrical supplying waveguide and an insulator of resin material having a better penetration of electromagnetic wave is used for fixing the sub-reflector, so that there has been no arrangement for making a DC conduction between the sub-reflector and the electrical supplying waveguide. In case that the above-described primary radiator is mounted in a satelite and used in a space, there is no DC conduction between the sub-reflector and the electrical supplying waveguide, so that some charged particles are accumulated at the sub-reflector under a mutual action with plasma faced on an orbit of the satelite, and an electrical potential difference generated between both elements is increased to cause a certain discharged short circuit and the like. Such a discharged short circuit as above has some disadvantages that it becomes a source of noise and a trouble is applied to a communication system in the satelite so as to provide a bad influence against a function of the antenna. An issue of the present invention is to provide a self -independent type primary radiator having the countermeasure against an electrical charge of the above-described charged particles. The above-described issue is accomplished by passing a fine metallic conductor from a central part of a sub-reflector to an axial central part where a less influence is applied for an electromagnetic field within a circular waveguide constituting the self-independent primary radiator and then connecting the conductor to a ground in DC form at a linear polarization part of a rectangular and circular converter. As a method for making an electrical conduction between the sub-reflector and the electrical supplying waveguide, it is an easy method to arrange the metallic conductor along a cover. However, such a method as above can not be employed in an antenna where a non-symmetrical characteristic of directivity is high due to the fact that this high non-symmetrical characteristic appears in an opening surface type antenna radiating a circular polarization. In turn, since the axial central part in the circular waveguide is crossed at a right angle with an electric field of a dominant mode to be transmitted, the fine metallic conductor may restrict a disturbance of the electromagnetic field even if the conductor is fixed within the waveguide. Accordingly, if the fine metallic conductor is passed from the central part of the sub-reflector to the axial central part in the circular waveguide and connected to a ground in DC form at the part of the linear polarization of the rectangular and circular converter, it becomes possible to make an electrical conduction between the sub-reflector and the electrical supplying waveguide without applying any substantial influence over a directivity of the primary radiator or V.S.W.R. According to the present invention which is defined in claim 1, the mechanism for preventing an electrical charging is not realized by sacrificing an electrical characteristic of the primary radiator, but a basic design configuration of the conventional type of primary radiator is continued as it is, and some additional component parts are applied to the primary radiator as well as additional machining is applied, resulting in enabling a new function for providing a countermeasure for preventing an electrical charging to be added without influencing the electrical characteristic. In the drawings: Fig. 1 is a setional view for showing the present invention. Fig. 2 is an outer appearance view of the present invention. Fig. 3 is a perspective view for showing an assembled condition of the metallic wire of the present invention within a rectangular and circular converter with a part of the waveguide being broken away. Fig. 4 is a sectional view for showing a condition in which the metallic wire of the present invention is fixed to the sub-reflector. Fig. 5 is an outer appearance view for showing a preferred embodiment of the opening surface antenna of the present invention. Fig. 6 is a side elevational view for showing a preferred embodiment of the opening surface antenna of the present invention. One preferred embodiment of the present invention will be described in reference to the accompanying drawings. Fig. 1 is a sectional view for showing a self-independent type primary radiator assembled with the metallic conductor for preventing an electrical charging action, and Fig. 2 is an outer appearance view for showing the primary radiator of the present invention. As illustrated in the preferred embodiment of the present invention, the self-independent type primary radiator of the present invention is comprised of a rectangular and circular converter 1 for converting a transmittance mode TE₁₀ of the rectangular waveguide into a transmittance mode TE₁₁ of the circular waveguide, a circular polarization generator 2 for converting a linear polarization into a circular polarization and a horn 3 for radiating the wave outwardly. The horn part fixes a cap-like sub-reflector part 4 to an opening part of the electrical supplying waveguide through a resin cover 5. A reference numeral 6 denotes an aligner for performing an impedance alignment with the circular waveguide fixed so as to provide an efficient radiation from the sub-reflector part in an outward direction. In this self-independent type primary radiator, a fine metallic wire 7 for use in preventing an electrical charging is passed and arranged through an axial central part where less influence is applied to the electromagnetic fields in the circular waveguide, the circular polarization generator and the rectangular and circular converter and then fixed to an interior part of the rectangular and circular converter through a short circuit plate 8. In case that the antenna is to be used in the space, surplus amount of local charged particles generated at the sub -reflector can be transmitted along an electrical discharging path of this metallic wire formed in the primary radiator and flowed into the main body of the antenna, so that both sub -reflector and the main body of the antenna can be kept substantially at the identical potential. The short-circuit plate within the rectangular and circular converter is fixed in a direction crossing at a right angle with the polarization plane of the linear polarization in such a way as an influence against the electromagnetic field may be kept low. In addition, if a diameter of the metallic wire is made to have a value less than 1/100λ (λ : a wave length), a less influence over the transmittance mode of the circular waveguide is found, so that it is possible to make an influence over V.S.W.R. or a directivity as one which shows practically less problems in case that the device is constructed as a primary radiator operating at a circular polarization. Fig. 3 and 4 show one preferred embodiment in which the metallic wire for preventing an electrical charging is assembled in the self-independent type primary radiator. Fig. 3 is a perspective view in which a condition having the metallic wire assembled in the rectangular and circular converter is illustrated with a part of the waveguide being partly cut away. The metallic wire is wound around the short circuit plate in the rectangular and circular converter and fixed in it. As a fixing means for this metallic wire, a press fitting at 9 is utilized, wherein two metallic wires to be wound around the short circuit plate are passed through the fine metallic pipe and then the metallic pipe is crushed to form the fixing part. In order to prevent the wound metallic wire from being moved on the short circuit plate, a small groove 10 is made at the part where the wire is wound. The short circuit plate is directed in a direction crossing at a right angle with a polarization plane of the linear polarization transmitted within the central part of the rectangular and circular converter, so that the electromagnetic field can pass without being influenced by the short circuit plate. Fig. 4 is a sectional view for showing a condition in which the metallic wire is fixed at the cap-like sub-reflector. The metallic wire is passed from the central part of the sub-reflector through the axial central part of the primary radiator and arranged. A terminal end of the metallic wire is fixed with a metallic threaded column 12 for fitting a nut 11 being press contacted. The sub-reflector is provided with a block 13 for fixing the metallic column together with the nut and the metallic wire is fixed to the block under a tensioned condition with the nut. In addition if, as a meterial quality of the metallic wire, twisted metallic wires of tens to several tens elements are employed, it is possible to improve a mechanical strength and a reliability. Fig. 5 and 6 illustrate a preferred embodiment of the opening surface antenna constructed with the primary radiator of the present invention, wherein Fig. 5 is an outer appearance and Fig. 6 is a side elevational view. A reference numeral 14 designates a main reflection mirror and a reference numeral 15 denotes a primary reflector. An electromagnetic wave rediated from the primary radiator is reflected by the main reflection mirror and then radiated outwardly. The preferred embodiment of the present invention is mounted on the inspecting satelite and this embodiment corresponds to the preferred embodiment of the opening surface antenna for radiating a broad beam and the main reflection mirror has a conical special shape.

Claims: A primary radiator of a self-independent type which is used as a primary radiator acting as a component element of an open surface antenna, the primary radiator comprising a sub-reflection part of cap shape, for use in radiating against a main reflection mirror, fixed to an opening part of an electrical supplying waveguide by an insulating supporting item, characterized in that a conductor is inserted and arranged at a central part within the electrical supplying waveguide where an influence for an electromagnetic field is less, so as to provide DC conduction between said sub-reflector part and the electrical supplying waveguide.

Inventors: OGAWA KAZUHISA - HONCHO, OHGI HIROKAZU C O SEIYORYO TOT, USUI IKURO, OGAWA, KAZUHISA, 3-149 HONCHO, OHGI, HIROKAZU,C/O SEIYORYO 3514, TOTSUKACHO, USUI, IKURO
Applicants: AGENCY IND SCIENCE TECHN, THE AGENCY OF INDUSTRIAL SCIENCE AND TECHNOLOGY
Application year: 1989
Main classification: H01Q1
IPC codes: H01Q19, H01Q1