Abstract:
A reception signal of a horizontally polarized wave and a reception signal of a vertically polarized wave from one satellite are amplified by a first pair of low noise amplifiers, and a reception signal of a horizontally polarized wave and a reception signal of a vertically polarized wave from another satellite are amplified by a second pair of low noise amplifiers. One of the low noise amplifiers is selected in accordance with the polarized wave and the satellite, and the signal from the selected low noise amplifier is supplied to a further low noise amplifier through a coupling circuit. The coupling circuit includes extending portions extended in strip conductor shapes from the first pair of low noise amplifiers and an extending element extended in a strip conductor shape from an input of the next stage low noise amplifier. The extending portions and the extended element are arranged so as to closely face each other.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a low noise converting apparatus suitable for use in a case where, for example, radio waves from a plurality of satellites are received by one parabolic antenna. 
     2. Description of the Related Art 
     A satellite broadcasting receiving system is provided with a low noise converter (referred to as an LNB) for converting a signal of a band of, for example, 12 GHz received by a parabolic antenna to an intermediate frequency signal of a band of, for example, 1 GHz and transmitting the signal to an indoor IRD (Integrated Receiver Decoder) or a receiver such as television receiver, VTR, or the like having a receiving tuner of a satellite broadcasting through a connecting cable. FIG. 1 shows an example of such a conventional low noise converter. 
     In FIG. 1, reference numerals  111  and  112  denote current feeding devices. Radio waves are transmitted from a satellite existing on a geostationary satellite orbit by using a band of, for example, 12 GHz by radio waves having an orthogonal relation, for example, by a horizontally polarized wave and a vertically polarized wave. The radio waves from the satellite are received by a parabolic antenna. The reception signals are inputted to the current feeding devices  111  and  112 . The reception signals of the horizontally polarized wave and vertically polarized wave are obtained from the current feeding devices  111  and  112 , respectively. 
     The reception signal of the horizontally polarized wave from the current feeding device  111  is supplied to a low noise amplifier  121 . The reception signal of the vertically polarized wave from the current feeding device  112  is supplied to a low noise amplifier  122  and amplified. 
     Control signals are supplied to the low noise amplifiers  121  and  122  from a control unit  110 . Although not shown, a switching signal of the horizontally polarized wave and vertically polarized wave is supplied to the control unit  110  from a satellite tuner. A control is performed so that either the low noise amplifier  121  or  122  is made operative in response to the switching signal. Thus, the switching between the horizontally polarized wave and vertically polarized wave is performed. 
     An output of the low noise amplifier  121  or  122  is supplied to a low noise amplifier  104  through a coupling circuit  103 . The reception signal is further amplified by the low noise amplifier  104 . An output of the low noise amplifier  104  is supplied to a filter circuit  105 . Unnecessary band components in the reception signal are removed by the filter circuit  105 . An output of the filter circuit  105  is supplied to a mixer  106 . 
     A local oscillating signal from a local oscillator  107  is supplied to the mixer  106 . In the mixer  106 , the reception signal of a band of, for example, 12 GHz is converted to an intermediate frequency signal of a band of, for example, 1 GHz. An output of the mixer  106  is extracted from an output terminal  109  through a high frequency amplifier  108 . A signal from the output terminal  109  is supplied to the indoor receiver through a connecting cable. 
     The conventional low noise converter shown in FIG. 1 receives the signal transmitted from one satellite on the geostationary satellite orbit. The radio waves are transmitted from the satellite by two planes of polarization of the horizontally polarized wave and vertically polarized wave. Therefore, the low noise amplifier  121  for the horizontally polarized wave and the low noise amplifier  122  for the vertically polarized wave are provided for the low noise converter. The switching between the horizontally polarized wave and vertically polarized wave is performed by selectively making the low noise amplifier  121  for the horizontally polarized wave and the low noise amplifier  122  for the vertically polarized wave operative. 
     In recent years, in association with the development of broadcasting services, a number of satellites were launched. Among the satellites, there are satellites launched to close positions on the geostationary satellite orbit. Signals transmitted from the two satellites launched to close positions on the geostationary satellite orbit as mentioned above can be received by one antenna. 
     FIG. 2 shows a construction of a conventional low noise converter in the case where the signals from the two satellites existing at close positions on the geostationary satellite orbit are received by one antenna. 
     In FIG. 2, reference numerals  211  and  212  denote current feeding devices for a reception signal from one satellite and  213  and  214  indicate current feeding devices for a reception signal from the other satellite. The radio waves are transmitted from the two satellites existing at close positions on the geostationary satellite orbit by the horizontally polarized wave and vertically polarized wave by using a band of, for example, 12 GHz. The radio waves from the two satellites are received by one parabolic antenna. 
     Between the two reception outputs, the signal from one satellite is inputted to the current feeding devices  211  and  212  and the reception signals of the horizontally polarized wave and vertically polarized wave of one satellite are derived from the current feeding devices  211  and  212 , respectively. The signal from the other satellite is inputted to the current feeding devices  213  and  214  and the reception signals of the horizontally polarized wave and vertically polarized wave of one satellite are derived from the current feeding devices  213  and  214 , respectively. 
     The reception signal of the horizontally polarized wave of one satellite which is supplied from the current feeding device  211  is sent to a low noise amplifier  221  and amplified. The reception signal of the vertically polarized wave of one satellite which is supplied from the current feeding device  212  is sent to a low noise amplifier  222  and amplified. Control signals are supplied from a control unit  230  to the low noise amplifiers  221  and  222 . A switching signal of the horizontally polarized wave and vertically polarized wave is supplied to the control unit  230 . A control is performed so that either the low noise  20  amplifier  221  or  222  is made operative in response to the switching signal. Thus, the switching between the horizontally polarized wave and vertically polarized wave is performed. 
     An output of the low noise amplifier  221  or  25   222  is supplied to a low noise amplifier  241  through a coupling circuit  231 . The reception signal is further amplified by the low noise amplifier  241 . An output of the low noise amplifier  241  is supplied to a coupling circuit  233 . 
     The reception signal of the horizontally polarized wave of the other satellite which is supplied from the current feeding device  213  is sent to a low noise amplifier  223  and amplified. The reception signal of the vertically polarized wave of the other satellite which is supplied from the current feeding device  214  is sent to a low noise amplifier  224  and amplified. Control signals are supplied from the control unit  230  to the low noise amplifiers  223  and  224 . The switching signal of the horizontally polarized wave and vertically polarized wave is supplied to the control unit  230 . A control is performed so that either the low noise amplifier  223  or  224  is made operative in response to the switching signal. Thus, the switching between the horizontally polarized wave and vertically polarized wave is performed. 
     An output of the low noise amplifier  223  or  224  is supplied to a low noise amplifier  242  through a coupling circuit  232 . The reception signal is further amplified by the low noise amplifier  242 . An output of the low noise amplifier  242  is supplied to the coupling circuit  233 . 
     The control signals are supplied from the control unit  230  to the low noise amplifiers  241  and  242 . A switching signal of two satellites is supplied to the control unit  230 . A control is performed so that either the low noise amplifier  241  or  242  is made operative in response to the switching signal. Thus, the switching between the two satellites is performed. 
     An output of the coupling circuit  233  is supplied to a filter circuit  225 . Unnecessary band components in the reception signal are removed by the filter circuit  225 . An output of the filter circuit  225  is supplied to a mixer  206 . 
     A local oscillating signal from a local oscillator  207  is supplied to the mixer  206 . In the mixer  206 , the reception signal of a band of, for example, 12 GHz is converted to an intermediate frequency signal of a band of, for example, 1 GHz. An output of the mixer  206  is extracted from an output terminal  209  through a high frequency amplifier  208 . A signal from the output terminal  209  is supplied to the indoor receiver through a connecting cable. 
     As mentioned above, the signals from the two satellites existing at close positions on the geostationary satellite orbit can be received by one antenna by providing: the low noise amplifiers  221  and  222  at the first stage for amplifying the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave which are transmitted from one satellite; the coupling circuit  231  for switching the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave from one satellite; the low noise amplifier  241  at the next stage for amplifying the reception signal of the horizontally polarized wave or the reception signal of the vertically polarized wave from one satellite; the low noise amplifiers  223  and  224  at the first stage for amplifying the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave which are transmitted from the other satellite; the coupling circuit  232  for switching the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave from the other satellite; the low noise amplifier  242  at the next stage for amplifying the reception signal of the horizontally polarized wave or the reception signal of the vertically polarized wave from the other satellite; and the coupling circuit  233  for switching the reception signals of two satellites. 
     However, if the signals from two satellites are enabled to be received by one antenna as mentioned above, problems such that the number of amplifiers arranged in the low noise converter increases, the number of coupling circuits increases, the costs rise, and it is difficult to realize a small size and a light weight occur. 
     That is, in the example shown in FIG. 1, since it is intended to receive the signals from one satellite and the signal of the horizontally polarized wave and the signal of the vertically polarized wave from one satellite are transmitted, the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave are amplified by the low noise amplifiers  121  and  122  and the coupling circuit  103  is provided to select the signal of the horizontally polarized wave and the signal of the vertically polarized wave. 
     However, in case of enabling the signals from two satellites to be received, since the signal of the horizontally polarized wave and the signal of the vertically polarized wave are transmitted from each satellite, the circuits for amplifying and selecting the signal of the horizontally polarized wave and the signal of the vertically polarized wave and the circuit to switch the satellites are necessary. 
     That is, in case of enabling the signals from two satellites existing at close positions on the geostationary satellite orbit to be received by one antenna, as shown in FIG. 2, there are necessary: the low noise amplifiers  221  and  222  for amplifying the signal of the horizontally polarized wave and the signal of the vertically polarized wave from one satellite; the low noise amplifiers  223  and  224  for amplifying the signal of the horizontally polarized wave and the signal of the vertically polarized wave from the other satellite; the coupling circuit  231  for switching the signal of the horizontally polarized wave and the signal of the vertically polarized wave from one satellite; the coupling circuit  232  for switching the signal of the horizontally polarized wave and the signal of the vertically polarized wave from the other satellite; the low noise amplifiers  241  and  242  for further amplifying the signals from the satellites; and the coupling circuit  232  for switching the signals of two satellites. 
     Particularly, providing the three coupling circuits  231 ,  232 , and  233  causes an increase in size when they are mounted. 
     That is, those coupling circuits are constructed on a microstrip line as shown in FIG.  3 . As shown in FIG. 3, the coupling circuit  231  is constructed by extending portions  151 ,  152 , and  153  of strip conductors each having a length of almost λ/4 (λ denotes a wavelength at a center frequency of a reception band). The extending portion  151  is extended from an output of the low noise amplifier  221  and the extending portion  152  is extended from an output of the low noise amplifier  222 . The extending portion  153  is extended from an input of the low noise amplifier  241 . The extending portions  151  and  152  are arranged so as to face the extending portion  153  with predetermined intervals. 
     As mentioned above, by arranging the extending portion  153  extended from the input of the low noise amplifier  241  so as to face the extending portions  151  and  152  extended from the outputs of the low noise amplifiers  221  and  222 , the outputs of the low noise amplifiers  221  and  222  and the input of the low noise amplifier  241  are electrically coupled. 
     Similarly, as shown in FIG. 3, the coupling circuit  232  is constructed by extending portions  161 ,  162 , and  163  of strip conductors each having a length of almost λ/4. The extending portion  161  is extended from an output of the low noise amplifier  223  and the extending portion  162  is extended from an output of the low noise amplifier  224 . The extending portion  163  is extended from an input of the low noise amplifier  242 . The extending portions  161  and  162  are arranged so as to face the extending portion  163  with predetermined intervals. 
     As mentioned above, by arranging the extending portion  163  extended from the input of the low noise amplifier  242  so as to face the extending portions  161  and  162  extended from the outputs of the low noise amplifiers  223  and  224 , the outputs of the low noise amplifiers  223  and  224  and the input of the low noise amplifier  242  are electrically coupled. 
     Similarly, as shown in FIG. 3, the coupling circuit  233  is constructed by extending portions  171 ,  172 , and  173  of strip conductors each having a length of almost λ/4. The extending portion  171  is extended from an output of the low noise amplifier  241  and the extending portion  172  is extended from an output of the low noise amplifier  242 . The extending portion  173  is extended from an input of the filter circuit  225  (refer to FIG.  2 ). The extending portions  171  and  172  are arranged so as to face the extending portion  173  with predetermined intervals. 
     As mentioned above, by arranging the extending portion  173  extended from the input of the filter circuit  225  so as to face the extending portions  171  and  172  extended from the outputs of the low noise amplifiers  241  and  242 , the outputs of the low noise amplifiers  241  and  242  and the input of the filter circuit  225  are electrically coupled. 
     As mentioned above, the coupling circuit comprises the extending portions of the strip conductors each having a length of almost λ/4 and the position to arrange the coupling circuit is restricted by a circuit construction. Therefore, when the number of coupling circuits increases, an area on a circuit board to construct the coupling circuits increases, a degree of freedom in a layout of circuit parts is small, and a circuit scale is enlarged. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is, therefore, an object of the invention to provide a low noise converting apparatus which can receive radio waves from a plurality of satellites by one antenna and realize a miniaturization and a reduction in costs. 
     According to one aspect of the invention, there is provided a low noise converting apparatus comprising: a plurality of first-stage low noise amplifying means each provided in a path of a reception signal of a polarized wave of each of a plurality of satellites; control means for selectively making one of the plurality of first-stage low noise amplifying means operative in accordance with the satellite to be selected and the polarized wave of a radio wave; one next-stage low noise amplifying means for further amplifying an output of the first-stage low noise amplifying means; coupling means for coupling the plurality of first-stage low noise amplifying means and the one next-stage low noise amplifying means; and frequency converting means for frequency converting an output of the next-stage low noise amplifying means. 
     The reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave of one satellite are amplified by the first-stage low noise amplifiers, respectively. The reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave of the other satellite are amplified by the first-stage low noise amplifiers, respectively. Outputs of the first-stage low noise amplifiers are selected, coupled by the coupling circuit, and supplied to the next-stage low noise amplifier. With this construction, a plurality of coupling circuits needed in the conventional low noise converter are constructed by one coupling circuit and miniaturized and the costs are reduced. The next-stage low noise amplifier is used in common by one low noise amplifier, the number of parts is reduced, and a construction, connecting lines, and the like are simplified. 
     According to another aspect of the invention, there is further provided a low noise converting apparatus comprising: coupling means for synthesizing radio waves of different frequencies among radio waves of a plurality of satellites and outputting a synthesized radio wave; first-stage low noise amplifying means for amplifying a reception signal of the plurality of satellites synthesized by the coupling means; next-stage low noise amplifying means for further amplifying an output of the first-stage low noise amplifying means; and frequency converting means for frequency converting an output of the next-stage low noise amplifying means. 
     For example, in case of receiving signals from two satellites, the reception signals of different frequencies are synthesized and sent to the first-stage low noise amplifier. Thus, the first-stage low noise amplifier is used in common for the reception signals from two satellites and the miniaturization and reduction of costs are accomplished. 
     The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram for use in explanation of a conventional low noise converter; 
     FIG. 2 is a block diagram for use in explanation of a conventional low noise converter; 
     FIG. 3 is a schematic diagram showing a layout on a circuit board of a main portion of the conventional low noise converter; 
     FIG. 4 is a block diagram showing a construction of the first embodiment of the invention; 
     FIG. 5 is a schematic diagram showing a layout on a circuit board of a main portion of the first embodiment of the invention; 
     FIG. 6 is a block diagram showing a construction of the second embodiment of the invention; 
     FIG. 7 is a schematic diagram showing a layout on a circuit board of a main portion of the second embodiment of the invention; 
     FIG. 8 is a block diagram showing a construction of the third embodiment of the invention; and 
     FIG. 9 is a schematic diagram showing a to layout on a circuit board of a main portion of the third embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Three embodiments of the invention will now be described hereinbelow with reference to the drawings. First, the first embodiment among them will be described. FIG. 4 shows a construction of the first embodiment. 
     In FIG. 4, reference numerals  11  and  12  denote current feeding devices for a reception signal from one satellite and  13  and  14  indicate current feeding devices for a reception signal from the other satellite. The radio waves are transmitted from the two satellites existing at close positions on the geostationary satellite orbit by the horizontally polarized wave and vertically polarized wave by using a band of, for example, 12 GHz. The radio waves from the two satellites are received by one parabolic antenna. 
     Between the reception outputs, the signal from one satellite is inputted to the current feeding devices  11  and  12  and the reception signals of the horizontally polarized wave and vertically polarized wave of one satellite are derived from the current feeding devices  11  and  12 , respectively. The signal from the other satellite is inputted to the current feeding devices  13  and  14  and the reception signals of the horizontally polarized wave and vertically polarized wave of the other satellite are derived from the current feeding devices  13  and  14 , respectively. 
     The reception signal of the horizontally polarized wave of one satellite which is supplied from the current feeding device  11  is sent to a low noise amplifier  21  and amplified. The reception signal of the vertically polarized wave of one satellite which is supplied from the current feeding device  12  is sent to a low noise amplifier  22  and amplified. The reception signal of the horizontally polarized wave of the other satellite which is supplied from the current feeding device  13  is sent to a low noise amplifier  23  and amplified. The reception signal of the vertically polarized wave of the other satellite which is supplied from the current feeding device  14  is sent to a low noise amplifier  24  and amplified. 
     Control signals are supplied from a control unit  10  to the low noise amplifiers  21  to  24 . A switching signal of the horizontally polarized wave and vertically polarized wave and a switching signal of the satellites are supplied to the control unit  10 . A control is performed so that one of the low noise amplifiers  21  to  24  is made operative in response to the switching signals. Thus, the switching between the horizontally polarized wave and vertically polarized wave and the switching between the satellites are simultaneously performed. 
     Outputs of the low noise amplifiers  21  to  24  are supplied to a low noise amplifier  4  through a coupling circuit  3 . The reception signal is further amplified by the low noise amplifier  4 . An output of the low noise amplifier  4  is supplied to a filter circuit  5 . Unnecessary band components in the reception signal are removed by the filter circuit  5 . An output of the filter circuit  5  is supplied to a mixer  6 . 
     A local oscillating signal from a local oscillator  7  is supplied to the mixer  6 . In the mixer  6 , the reception signal of a band of, for example, 12 GHz is converted to an intermediate frequency signal of a band of, for example, 1 GHz. An output of the mixer  6  is extracted from an output terminal  9  through a high frequency amplifier  8 . A signal from the output terminal  9  is supplied to the indoor receiver through a connecting cable. 
     According to the first embodiment constructed as mentioned above, the three coupling circuits  231 ,  232 , and  233  (refer to FIG. 2) needed in the conventional low noise converter are constructed by one coupling circuit  3  and miniaturized and the costs are reduced. Since the low noise amplifiers  241  and  242  at the second stage are used in common by one low noise amplifier  4 , the parts corresponding to one low noise amplifier are reduced and the construction, the connecting lines, and the like of the control unit  10  for the low noise amplifiers  21 ,  22 ,  23 , and  24  are simplified. 
     That is, FIG. 5 shows an example of a specific layout on a circuit board of the low noise amplifiers  21 ,  22 ,  23 ,  24 , and  4  and the coupling circuit  3  according to the embodiment. 
     A dielectric material such as Teflon (registered trade mark), ceramics, or the like is used as a material of the circuit board and strip conductors are formed on the circuit board. For example, a copper foil material is used as a strip conductor. Therefore, a distribution constant line path of the microstrip lines, strip lines, or the like is constructed. 
     For example, an FET (Field Effect Transistor), an HEMT (High Electron Mobility Transistor), or the like is used as each of the low noise amplifiers  21 ,  22 ,  23 ,  24 , and  4 . The signals from the current feeding devices  11  and  12  are amplified by the low noise amplifiers  21  and  22  and sent to the coupling circuit  3 . The signals from the current feeding devices  13  and  14  are amplified by the low noise amplifiers  23  and  24  and sent to the coupling circuit  3 . 
     As shown in FIG. 5, the coupling circuit  3  is constructed by extending portions  31 ,  32 ,  33 ,  34 ,  35   a , and  35   b  of strip conductors each having a length of almost λ/4. The extending portion  31  is extended from an output of the low noise amplifier  21  and the extending portion  32  is extended from an output of the low noise amplifier  22 . The extending portion  33  is extended from an output of the low noise amplifier  23 . The extending portion  34  is extended from an output of the low noise amplifier  24 . The extending portions  35   a  and  35   b  are extended from an input of the low noise amplifier  4 . The extending portions  31  and  32  are arranged so as to face the extending portion  35   a  with predetermined intervals. The extending portions  33  and  34  are arranged so as to face the extending portion  35   b  with predetermined intervals. 
     As mentioned above, by arranging the extending portion  35   a  extended from the input of the low noise amplifier  4  so as to face the extending portions  31  and  32  extended from the outputs of the low noise amplifiers  21  and  22 , the outputs of the low noise amplifiers  21  and  22  and the input of the low noise amplifier  4  are electrically coupled. By arranging the extending portion  35   b  extended from the input of the low noise amplifier  4  so as to face the extending portions  33  and  34  extended from the outputs of the low noise amplifiers  23  and  24 , the outputs of the low noise amplifiers  23  and  24  and the input of the low noise amplifier  4  are electrically coupled. 
     When the mounting parts such as low noise amplifiers  21 ,  22 ,  23 ,  24 , and  4  and the like are installed, for example, a cream solder is filled into each part pad on the strip conductors, thereby installing the mounting parts. By heating the cream solder by heating means such as a reflow furnace or the like in this state, the soldering is performed. 
     The first embodiment has been described above with respect to the case of receiving the radio waves from two satellites of a band of, for example, 12 GHz transmitted from two satellites on the geostationary satellite orbit. The invention, however, can be also similarly applied to the case of receiving radio waves from three or more satellites. 
     In the foregoing first embodiment, although each satellite transmits the radio wave of the horizontally polarized wave and the radio wave of the vertically polarized wave, the invention can be also similarly applied to the case of transmitting a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn from each satellite. 
     That is, in the above example, although both two satellites transmit the radio wave of the horizontally polarized wave and the radio wave of the vertically polarized wave, the invention can be also applied to the case where one satellite transmits a radio wave of a horizontally polarized wave and a radio wave of a vertically polarized wave and the other satellite transmits a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. The invention can also cope with the case where both satellites transmit a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. Further, the invention can also cope with the case where one satellite transmits a radio wave of a horizontally polarized wave and a radio wave of a vertically polarized wave and the other satellite transmits a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. 
     The invention can also cope with the case where one satellite transmits a radio wave of one polarized wave and the other satellite transmits radio waves of two polarized waves. For example, the invention can also cope with the case of receiving radio wave from a satellite which broadcasts only a radio wave of a circularly polarized wave of the right or left turn and radio waves from a satellite which transmits a radio wave of a horizontally polarized wave and a radio wave of a vertically polarized wave. The invention can also cope with the case of receiving a radio wave from a satellite which broadcasts only a radio wave of a circularly polarized wave of the right or left turn and radio waves from a satellite which transmits a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. The invention can also cope with the case of receiving a radio wave from a satellite which broadcasts only a radio wave of a horizontally or vertically polarized wave and radio waves from a satellite which transmits a radio wave of a horizontally polarized wave and a radio wave of a vertically polarized wave. The invention can also cope with the case of receiving a radio wave from a satellite which broadcasts only a radio wave of a horizontally or vertically polarized wave and radio waves from a satellite which transmits a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. 
     Each of the low noise amplifiers  21 ,  22 ,  23 ,  24 , and  4  and the high frequency amplifier  8  does not need to be always constructed by one active device but they can be realized as an integrated circuit. Further, the mixer  6 , local oscillator  7 , and amplifier  8  can be constructed as an integrated circuit and used. It is also possible to use a construction in which the high frequency amplifier  8  is omitted. 
     Although the first embodiment has been described with respect to the case where the strip conductor of a copper foil material is formed on the circuit board, the invention can be also easily applied to, for example, a circuit board on which a pattern is formed by a thick film print, a circuit board on which a pattern is formed by electroless plating, or the like. Further, although the embodiment has been described with respect to the case of using the parts enclosed in a package for surface mounting, the devices can be formed on one chip or chip-shaped devices can be integrated by using the die bonding or wire bonding technique. 
     The second embodiment of the invention will now be described with reference to the drawings. FIG. 6 shows a construction of the second embodiment. 
     In FIG. 6, reference numerals  311  and  312  denote current feeding devices for a reception signal from one satellite and  313  and  314  indicate current feeding devices for a reception signal from the other satellite. The radio waves are transmitted from the two satellites existing at close positions on the geostationary satellite orbit by the horizontally polarized wave and vertically polarized wave by using a band of, for example, 12 GHz. The radio waves from the two satellites are received by one parabolic antenna. 
     Between the two reception outputs, the signal from one satellite is inputted to the current feeding devices  311  and  312  and the reception signals of the horizontally polarized wave and vertically polarized wave of one satellite are derived from the current feeding devices  311  and  312 , respectively. The signal from the other satellite is inputted to the current feeding devices  313  and  314  and the reception signals of the horizontally polarized wave and vertically polarized wave of the other satellite are derived from the current feeding devices  313  and  314 , respectively. 
     The reception signal of the horizontally polarized wave of one satellite which is supplied from the current feeding device  311  and the reception signal of the horizontally polarized wave of the other satellite which is supplied from the current feeding device  313  are sent to a low noise amplifier  331  through a coupling circuit  302 . The reception signal of the vertically polarized wave of one satellite which is supplied from the current feeding device  312  and the reception signal of the vertically polarized wave of the other satellite which is supplied from the current feeding device  314  are sent to a low noise amplifier  332  through the coupling circuit  302 . 
     Control signals are supplied from a control unit  310  to the low noise amplifiers  331  and  332 . A switching signal of the horizontally polarized wave and vertically polarized wave is supplied to the control unit  310 . A control is performed so that either the low noise amplifier  331  or  332  is made operative in response to the switching signal. Thus, the switching between the horizontally polarized wave and vertically polarized wave is performed. 
     Outputs of the low noise amplifiers  331  and  332  are supplied to a low noise amplifier  333  through a coupling circuit  304 . The reception signal is further amplified by the low noise amplifier  333 . An output of the low noise amplifier  333  is supplied to a filter circuit  305 . Unnecessary band components in the reception signal are removed by the filter circuit  305 . An output of the filter circuit  305  is supplied to a mixer  306 . 
     A local oscillating signal from a local  25  oscillator  307  is supplied to the mixer  306 . In the mixer  306 , the reception signal of a band of, for example, 12 GHz is converted to an intermediate frequency signal of a band of, for example, 1 GHz. An output of the mixer  306  is extracted from an output terminal  309  through a high frequency amplifier  308 . A signal from the output terminal  309  is supplied to the indoor receiver through a connecting cable. 
     According to the embodiment of the invention, the signals of two systems comprising the reception signal of the horizontally polarized wave of one satellite from the current feeding device  311  and the reception signal of the horizontally polarized wave of the other satellite from the current feeding device  313  are supplied to the low noise amplifier  331 , and the reception signal of the horizontally polarized wave of one satellite and the reception signal of the horizontally polarized wave of the other satellite are amplified by the low noise amplifier  331 . As mentioned above, the amplifier at the first stage for the reception signal of the horizontally polarized wave of one satellite and the amplifier at the first stage for the reception signal of the horizontally polarized wave of the other satellite are used in common by the low noise amplifier  331 . If a frequency of the signal from one satellite and a frequency of the signal from the other satellite differ, the signals of two systems can be selected on the receiver side later. Therefore, the amplifier at the first stage for the reception signal of the horizontally polarized wave of one satellite and the amplifier at the first stage for the reception signal of the horizontally polarized wave of the other satellite are used in common by the low noise amplifier  331 . 
     Similarly, the signals of two systems comprising the reception signal of the vertically polarized wave of one satellite from the current feeding device  312  and the reception signal of the vertically polarized wave of the other satellite from the current feeding device  314  are supplied to the low noise amplifier  332 , and the reception signal of the vertically polarized wave of one satellite and the reception signal of the vertically polarized wave of the other satellite are amplified by the low noise amplifier  332 . As mentioned above, the amplifier at the first stage for the reception signal of the vertically polarized wave of one satellite and the amplifier at the first stage for the reception signal of the vertically polarized wave of the other satellite are used in common by the low noise amplifier  332 . If a frequency of the signal from one satellite and a frequency of the signal from the other satellite differ, the signals of two systems can be selected on the receiver side later. Therefore, the amplifier at the first stage for the reception signal of the vertically polarized wave of one satellite and the amplifier at the first stage for the reception signal of the vertically polarized wave of the other satellite are used in common by the low noise amplifier  332 . 
     FIG. 7 shows an example of a specific layout on a circuit board of the coupling circuit  302  and the low noise amplifiers  331 ,  332 , and  333  provided as an input section of the foregoing second embodiment. 
     A dielectric material such as Teflon (registered trade mark), ceramics, or the like is used as a material of the circuit board and strip conductors are formed on the circuit board as shown in FIG.  7 . For example, a copper foil material is used as a strip conductor. 
     In FIG. 7, reference numerals  311 P and  312 P denote probes for receiving the signals of the horizontally polarized wave and vertically polarized wave of one satellite. The probes correspond to the current feeding devices  311  and  312 , respectively. Reference numerals  313 P and  314 P denote probes for receiving the signals of the horizontally polarized wave and vertically polarized wave of the other satellite. The probes correspond to the current feeding devices  313  and  314 , respectively. An HEMT (High Electron Mobility Transistor) or an FET (Field Effect Transistor) is used as each of the low noise amplifiers  331 ,  332 , and  333 . 
     As shown in FIG. 7, the coupling circuit  302  is constructed by: a coupling portion  302   a  comprising extending portions  321 ,  322 , and  323  of strip conductors each having a length of almost λ/4; and a coupling portion  302   b  comprising extending portions  324 ,  325 , and  326  of strip conductors each having a length of almost λ/4. 
     In the coupling portion  302   a , the extending portion  321  is extended from the probe  311 P to receive the signal of the horizontally polarized wave of one satellite and the extending portion  322  is extended from the probe  313 P to receive the signal of the horizontally polarized wave of the other satellite. The extending portion  323  is extended from an input of the low noise amplifier  331 . As mentioned above, by arranging the extending portion  323  extended from the input of the low noise amplifier  331  so as to face the extending portion  321  extended from the probe  311 P and the extending portion  322  extended from the probe  313 P with predetermined intervals, the outputs of the probes  311 P and  313 P and the input of the low noise amplifier  331  are electrically coupled. 
     In the coupling portion  302   b , the extending portion  324  is extended from the probe  312 P to receive the signal of the vertically polarized wave of one satellite and the extending portion  325  is extended from the probe  314 P to receive the signal of the vertically polarized wave of the other satellite. The extending portion  326  is extended from an input of the low noise amplifier  332 . As mentioned above, by arranging the extending portion  326  extended from the input of the low noise amplifier  332  so as to face the extending portion  324  extended from the probe  312 P and the extending portion  325  extended from the probe  314 P with predetermined intervals, the outputs of the probes  312 P and  314 P and the input of the low noise amplifier  332  are electrically coupled. 
     The coupling circuit  304  is constructed by extending portions  341 ,  342 , and  343  of strip conductors each having a length of almost λ/4. The extending portion  341  is extended from an output of the low noise amplifier  331 . The extending portion  342  is extended from an output of the low noise amplifier  332 . The extending portion  343  is extended from an input of the low noise amplifier  333 . As mentioned above, by arranging the extending portion  343  extended from the input of the low noise amplifier  333  so as to face the extending portion  341  extended from the output of the low noise amplifier  331  and the extending portion  342  extended from the output of the low noise amplifier  332  with predetermined intervals, the outputs of the low noise amplifiers  331  and  332  and the input of the low noise amplifier  333  are electrically coupled. 
     When the mounting parts such as low noise amplifiers  331 ,  332 , and  333  and the like are installed, for example, a cream solder is filled into each part pad on the strip conductors, thereby installing the mounting parts. By heating the cream solder through heating means such as a reflow furnace or the like in this state, the soldering is performed. 
     As mentioned above, according to the embodiment, the signals of two systems comprising the reception signal of the horizontally polarized wave of one satellite from the current feeding device  311  and the reception signal of the horizontally polarized wave of the other satellite from the current feeding device  313  are coupled and the signals of two systems comprising the reception signal of the vertically polarized wave of one satellite from the current feeding device  312  and the reception signal of the vertically polarized wave of the other satellite from the current feeding device  314  are coupled by the coupling circuit  302 . Therefore, the six low noise amplifiers  221 ,  222 ,  223 ,  224 ,  241 , and  242  (refer to FIG. 6) needed in the conventional low noise frequency converting apparatus are reduced to the three low noise amplifiers  331 ,  332 , and  333  and the miniaturization and the reduction of costs are realized. Since the number of low noise amplifiers is reduced, the construction, connecting lines, and the like of the control unit  310  for the low noise amplifiers are simplified. 
     Although the second embodiment has been described above with respect to the case of receiving the radio waves from two satellites of a band of, for example, 12 GHz transmitted from two satellites existing on the geostationary satellite orbit, the invention can be also similarly applied to the case of receiving radio waves from three or more satellites. 
     Although each satellite transmits the radio wave of the horizontally polarized wave and the radio wave of the vertically polarized wave in the second embodiment, the invention can be also similarly applied to the case of transmitting a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn from each satellite. 
     That is, although both two satellites transmit the radio wave of the horizontally polarized wave and the radio wave of the vertically polarized wave in the foregoing example, the invention can be also applied to the case where one satellite transmits a radio wave of a horizontally polarized wave and a radio wave of a vertically polarized wave and the other satellite transmits a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. The invention can also cope with a case where both two satellites transmit a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. The invention can also cope with a case where one satellite transmits a radio wave of a horizontally polarized wave and a radio wave of a vertically polarized wave and the other satellite transmits a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. 
     The invention can also cope with the case where one satellite transmits a radio wave of one polarized wave and the other satellite transmits radio waves of two polarized waves. For example, the invention can also cope with the case of receiving radio wave from a satellite which broadcasts only a radio wave of a circularly polarized wave of the right or left turn and radio waves from a satellite which transmits a radio wave of a horizontally polarized wave and a radio wave of a vertically polarized wave. The invention can also cope with the case of receiving a radio wave from a satellite which broadcasts only a radio wave of a circularly polarized wave of the right or left turn and radio waves from a satellite which transmits a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. The invention can also cope with the case of receiving a radio wave from a satellite which broadcasts only a radio wave of a horizontally or vertically polarized wave and radio waves from a satellite which transmits a radio wave of a horizontally polarized wave and a radio wave of a vertically polarized wave. The invention can also cope with the case of receiving a radio wave from a satellite which broadcasts only a radio wave of a horizontally or vertically polarized wave and radio waves from a satellite which transmits a radio wave of a circularly polarized wave of the right turn and a radio wave of a circularly polarized wave of the left turn. 
     Each of the low noise amplifiers  331 ,  332 , and  333  and the high frequency amplifier  308  does not need to be always constructed by one active device but they can be realized as an integrated circuit. It is not always necessary to provide the high frequency amplifier  308 . Further, the invention is not limited to the presence or absence of the filter circuit  305 , the inserting position thereof, and the number of filter circuits. It is not always necessary to limit the local oscillator  307  to a single construction but a local oscillating circuit comprising a plurality of oscillators can be used. 
     FIG. 8 shows a construction of the third embodiment of the invention. Although each satellite transmits the signals of two polarized waves which cross perpendicularly each other in the second embodiment, the third embodiment shows an example in the case where each satellite transmits a signal of one polarized wave. Each satellite transmits the signal of one of a horizontally polarized wave, a vertically polarized wave, a circularly polarized wave of the right turn, a circularly polarized wave of the left turn, and the like. 
     In FIG. 8, reference numeral  361  denotes a current feeding device for a reception signal from one satellite and  362  denotes a current feeding device for a reception signal from the other satellite. Radio waves are transmitted from two satellites existing at close positions on a geostationary satellite orbit by using a band of, for example, 12 GHz. The radio waves from two satellites are received by one parabolic antenna. 
     Between the reception outputs, the signal from one satellite is inputted to the current feeding device  361  and the reception signal of one satellite is obtained from the current feeding device  361 . The signal from the other satellite is inputted to the current feeding device  362  and the reception signal of the other satellite is obtained from the current feeding device  362 . 
     The reception signal of one satellite from the current feeding device  361  and the reception signal of the other satellite from the current feeding device  362  are supplied to a low noise amplifier  381  through a coupling circuit  377 . An output of the low noise amplifier  381  is supplied to a low noise amplifier  383  and further amplified. 
     An output of the low noise amplifier  383  is supplied to a filter circuit  355 . Unnecessary band components in the reception signal are removed by the filter circuit  355 . An output of the filter circuit  355  is supplied to a mixer  356 . 
     A local oscillating signal from a local oscillator  357  is supplied to the mixer  356 . In the mixer  356 , the reception signal of a band of, for example, 12 GHz is converted to an intermediate frequency signal of a band of, for example, 1 GHz. An output of the mixer  356  is extracted from an output terminal  359  through a high frequency amplifier  358 . A signal from the output terminal  359  is supplied to the indoor receiver through a connecting cable. 
     According to the embodiment of the invention, the signals of two systems comprising the reception signal of one satellite from the current feeding device  361  and the reception signal of the other satellite from the current feeding device  362  are supplied to the low noise amplifier  381 . If a frequency of the signal from one satellite and a frequency of the signal from the other satellite differ, the signals of two systems can be selected later on the receiver side. Therefore, the amplifier at the first stage for the reception signal of the horizontally polarized wave of one satellite and the amplifier at the first stage for the reception signal of the horizontally polarized wave of the other satellite can be used in common by the low noise amplifier  381 . 
     FIG. 9 shows an example of a specific layout on a circuit board of the coupling circuit  377  and low noise amplifier  381  provided as an input section of the foregoing third embodiment. 
     In FIG. 8, reference numerals  361 P and  362 P denote probes for receiving the signal of one satellite and the signal of the other satellite. The probes correspond to the current feeding devices  361  and  362 , respectively. 
     As shown in FIG. 9, the coupling circuit  377  is constructed by extending portions  378 ,  379 , and  380  of strip conductors each having a length of almost λ/4 (λ denotes a wavelength at a center frequency of a reception band). The extending portion  378  is extended from the probe  361 P to receive the signal from one satellite and the extending portion  379  is extended from the probe  362 P to receive the signal from the other satellite. The extending portion  380  is extended from an input of the low noise amplifier  381 . As mentioned above, by arranging the extending portion  380  extended from the input of the low noise amplifier  381  so as to face the extending portion  378  extended from the probe  361 P and the extending portion  379  extended from the probe  362 P with predetermined intervals, the outputs of the probes  361 P and  362 P and the input of the low noise amplifier  381  are electrically coupled. 
     According to the third embodiment constructed as mentioned above, the signal from the current feeding device  361  and the signal from the current feeding device  362  are synthesized through the coupling circuit  377 , the synthesized output is supplied to the low noise amplifier  381 , and the first-stage low noise amplifiers for two satellites are used in common by the low noise amplifier  381 . There is no need to provide a control unit, connecting lines, and the like for the low noise amplifier. Thus, the number of low noise amplifiers is reduced and the miniaturization and the reduction of costs are realized. 
     According to the invention, a plurality of coupling circuits needed in the conventional low noise converter are constructed by one coupling circuit. The low noise amplifiers at the second stage are used in common by one low noise amplifier. According to the invention, therefore, it can cope with three or more different radio wave signals and the miniaturization and the reduction of costs are realized. 
     Further, according to the invention, for example, in the case where the signals from two satellites are received by one antenna, by synthesizing the signals of different frequencies between the radio waves of two satellites and supplying the synthesized signal to the first-stage low noise amplifier, the first-stage low noise amplifier is used in common. Thus, the number of low noise amplifiers needed in the conventional low noise frequency converting apparatus is reduced and the miniaturization and the reduction of costs are realized. 
     The present invention is not limited to the foregoing embodiments but many modifications and variations are possible within the spirit and scope of the appended claims of the invention.