FIG. 19 shows an arrangement of an antenna apparatus for shared use of left/right-handed circularly polarized waves and two frequency bands set forth, for example, in Takashi Kitsuregawa, “Advanced Technology in Satellite Communication Antennas: Electrical & Mechanical Design”, ARTECH HOUSE INC., pp. 193–195, 1990.
In the figure, reference numeral 61 denotes a primary radiator for transmitting both left- and right-handed circularly polarized waves in a first frequency band to a main- or sub-reflector and for receiving both left- and right-handed circularly polarized waves in a second frequency band from the main- or sub-reflector; 62, a polarizer; 63, an orthomode transducer; 64a and 64b, diplexers; P1, an input terminal for radio waves in the first frequency band transmitted from the primary radiator 61 in a left-handed circular polarized wave; P2, an output terminal for radio waves in the second frequency band received by the primary radiator 61 in a left-handed circular polarized wave; P3, an input terminal for radio waves in the first frequency band transmitted from the primary radiator 61 in a right-handed circular polarized wave; and P4, an output terminal for radio waves in the second frequency band received by the primary radiator 61 in a right-handed circular polarized wave.
Next, an operation will be described.
Now, a linearly polarized radio wave in the first frequency band inputted from the input terminal P1 passes through the diplexer 64a, is inputted to the orthomode transducer 63 and is outputted as a vertically polarized wave. The vertically polarized wave is then converted by the polarizer 62 to a left-handed circularly polarized wave, passes through the primary radiator 61 and is radiated from the reflector into the air. Furthermore, a left-handed circularly polarized radio wave in the second frequency band received by the reflector passes through the primary radiator 61, is converted by the polarizer 62 to a vertically polarized wave, and is inputted to the orthomode transducer 63. The radio wave is then carried to the diplexer 64a and is extracted from the output terminal P2 as a linearly polarized wave.
In the meantime, a linearly polarized radio wave in the first frequency band inputted from the input terminal P3 passes through the diplexer 64b, is inputted to the orthomode transducer 63 and is outputted as a horizontally polarized wave. The horizontally polarized wave is then converted by the polarizer 62 to a right-handed circularly polarized wave, passes through the primary radiator 61 and is radiated from the reflector into the air. Furthermore, a right-handed circularly polarized radio wave in the second frequency band received by the reflector passes through the primary radiator 61, is converted by the polarizer 62 to a horizontally polarized wave, and is inputted to the orthomode transducer 63. The radio wave is then carried to the diplexer 64b and is extracted from the output terminal P4 as a linearly polarized wave.
Here, the radio waves in the first frequency band inputted from the input terminals P1 and P3 hardly leak into the output terminals P2 and P4 owing to isolation characteristics of the diplexers 64a and 64b. Furthermore, since the radio waves are converted by the orthomode transducer 63 into polarized waves which are mutually orthogonal, little interference occurs between the two radio waves. Accordingly, two transmission waves using the same frequency band and having both left- and right-handed circular polarized waves will be efficiently radiated from the primary radiator 61.
Moreover, two radio waves using the same frequency band and having both left- and right-handed circular polarized waves, received at the primary radiator 61, are converted into two linearly polarized waves which are mutually orthogonal without any interference therebetween and isolated by the polarizer 62 and the orthomode transducer 63. Furthermore, each isolated radio wave hardly leaks into the input terminals P1 and P3 owing to the isolation characteristics of the diplexers 64a and 64b. Accordingly, two transmission waves using the same frequency band and having differently rotating circular polarized waves will be efficiently outputted from the terminal 2 and the terminal 4.
In a conventional antenna apparatus, in order to efficiently extract the radio wave received at the reflector and to carry the extracted wave to a receiver connected to the output terminals P2 and P4, it has been necessary to suppress transmission loss along a path from the primary radiator 61 to the receiver as small as possible. This has resulted in a problem in that the primary radiator 61, the polarizer 62, the orthomode transducer 63, the diplexers 64a and 64b and the receiver must be located in proximity, which restricts flexibility of a configuration of those circuits.
Furthermore, in general, for machine-driven scanning of antenna beams, the primary radiator 61, the polarizer 62 and the orthomode transducer 63 rotate with the reflector. In this situation, because of the above-mentioned need for reduction of transmission loss, the diplexers 64a and 64b and the receiver must also be located at places where they rotate with the reflector. This has resulted in a problem in that a machine-driven part of the antenna apparatus grows large and heavy, and its rotating mechanism and rotation supporting mechanism grow large and heavy.