Abstract:
The present invention discloses a method and apparatus for simultaneously receiving linear polarization signals and circular polarization signals. First, the present invention gathers a plurality of signals and separates them into a first linear polarization signal and a circular polarization signal in a predetermined way. The present invention transforms the circular polarization signal into a second linear polarization signal. The first linear polarization signal and the second linear polarization signal are transferred to an electric circuit.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority of Taiwan Patent Application Serial No.091104245 filed on Mar. 7, 2002. 
   FIELD OF INVENTION 
   The present invention relates to a method and apparatus for simultaneously receiving signals, and more particularly, to a method and apparatus for simultaneously receiving linear polarization signals and circular polarization signals. 
   BACKGROUND OF THE INVENTION 
   Satellite signal transmission techniques improve substantially to meet people&#39;s needs in many ways, such as communication, astronomical observation, meteorological observation, and so forth. As a result, the number of the operating satellites in space grows rapidly as the need for satellites increases in recent years. Sometimes, the space is so crowded that two satellites may even be set in almost the same orbit. 
   As to current techniques of satellite signal transmission, the Fixed-Satellite Service (FSS) is used to receive linear polarization signals with frequencies about 10.95 GHz to 11.7 GHz. The Broadcasting-Satellite Service (BSS) is used to receive circular polarization signals with frequencies about 12.2 GHz to 12.7 GHz. Those two types of satellite services have close frequency bands and usually are set in almost the same orbit. Thus, the corresponding receivers or feeds for receiving satellite signals must have the ability to receive linear polarization signals from FSS satellites and to receive circular polarization signals from BSS satellites. However, it is quite difficult to receive two types of signals by one single receiver or feed with current techniques. Also, the issue for avoiding interference between two types of signals needs to be solved for the time being. Therefore, receivers or feeds of the prior art are not able to take up the challenge. Instead, most traditional receivers or feeds could only receive one type of signals. For example, it takes two different feeds to receive linear polarization signals and circular polarization signals respectively. 
   As shown in  FIG. 1 , in the prior art, two antenna disks  11  and  12  are used to receive a linear polarization signal  111  and a circular polarization signal  121  respectively. This kind of method of implementing two antenna disks is quite uneconomical. 
   The U.S. Pat. No. 3,731,236 discloses an apparatus for transferring and receiving two types of signals. As shown in  FIG. 2 , the apparatus includes a transformer  14  connecting to a four-port ortho-mode transducer (OMT)  13 . The four-port ortho-mode transducer (OMT)  13  connects to four rectangular waveguides  21 ,  22 ,  23 , and  24  respectively. While receiving signals, low frequency signals are transferred through the four rectangular waveguides  21 ,  22 ,  23 , and  24 . However, when the transferred low frequency signals, including circular polarization signals, passing through the four rectangular waveguides  21 ,  22 ,  23 , and  24 , the circular polarization signals will be distorted or destroyed. That is to say, instead of receiving signals of any frequencies, the apparatus could only operates normally when the frequency of the linear polarization signals is lower than that of the circular polarization signals. 
   Consequently, with current techniques for satellite signal transmission, a novel apparatus and method for receiving all types of signals with any frequencies, without serious interference, is desired. 
   SUMMARY OF THE INVENTION 
   The objective of the present invention is to provide a method and apparatus for simultaneously receiving linear polarization signals and circular polarization signals. 
   In the present invention, the linear polarization signals and the circular polarization signals received in the same orbit are separated first and then integrated to at least a low noise block (LNB). 
   In the method of the present invention, signals including the linear polarization signal and the circular polarization signal are received in a predetermined way and separated into a first linear polarization signal and a circular polarization signal. The circular polarization signal is then transformed into a second linear polarization signal. The first linear polarization signal and the second linear polarization signal are then transferred to an electric circuit. 
   The apparatus of the present invention includes a receiver, an ortho-mode transducer (OMT), a polarizer, and an electric circuit. The receiver is used to receive signals. The ortho-mode transducer (OMT) is used to separate the received signals into a first linear polarization signal and a circular polarization signal. The polarizer is used to transform the circular polarization signal into a second linear polarization signal. 
   Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practicing the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of an apparatus for receiving signals with two antenna disks according to the prior art. 
       FIG. 2  is a schematic diagram of an apparatus for receiving signals according to the prior art. 
       FIG. 3  is a schematic diagram of an apparatus for receiving signals with one antenna disk according to the present invention. 
       FIG. 4  is a schematic flowchart of a first exemplary embodiment of the method for receiving signals according to the present invention. 
       FIG. 5  is a schematic flowchart of a second exemplary embodiment of the method for receiving signals according to the present invention 
       FIG. 6  is a schematic flowchart of a third exemplary embodiment of the method for receiving signals according to the present invention. 
       FIG. 7  is a schematic diagram of a first exemplary embodiment of an apparatus for receiving signals according to the present invention. 
       FIG. 8  is a schematic diagram of a second exemplary embodiment of an apparatus for receiving signals according to the present invention. 
       FIG. 9  is a schematic diagram of a third exemplary embodiment of an apparatus for receiving signals according to the present invention. 
   

   DETAILED DESCRIPTION 
   In order to achieve the objective of simultaneously receiving linear polarization signals and circular polarization signals, the present invention separates linear polarization signals and circular polarization signals first, and then integrates them to at least a low noise block (LNB). 
   As shown in  FIG. 3 , the apparatus for receiving signals of the present invention only needs one antenna disk  31 . In comparison with the prior art, the present invention substantially reduces the required space and cost for building more antenna disks for receiving all types of signals. 
     FIG. 4  is a schematic flowchart of a first exemplary embodiment of the method for receiving a signal according to the present invention. In the first embodiment, the method for receiving a signal includes the step  401  to the step  413 . 
   First, in the step  403 , a signal received from a receiver is transferred to a waveguide. 
   Next, in the step  405 , the signal is separated into a first linear polarization signal and a circular polarization signal by respectively transferring them to a first waveguide and a second waveguide. The first waveguide and the second waveguide respectively have different cutoff frequencies. The first linear polarization signal selectively includes a first signal in a first direction and a second signal in a second direction. In the embodiment, the first direction and the second direction are orthogonal to each other. For example, if the first direction is horizontal, the second direction will be vertical. 
   Additionally, the cross-section dimensions of the waveguides, the first waveguide and the second waveguide, are different and could be adjusted to vary the value of their cutoff frequencies. In the embodiment, the first linear polarization signal and the circular polarization signal are separated by adjusting the cross-section dimensions of the waveguides. 
   Besides, the phrase “selective include” mentioned above and below means to include any one, all of them, or combination of some of them. 
   Then, in the step  407 , the circular polarization signal is transformed into a second linear polarization signal. The second linear polarization signal selectively includes a third signal in the first direction and a fourth signal in the second direction. In particular, the circular polarization signal selectively includes a left-hand circular polarization (LHCP) and a right-hand circular polarization (RHCP). In the step  407 , the left-hand circular polarization (LHCP) and the right-hand circular polarization (RHCP) are transformed into the third signal and the fourth signal respectively. 
   Assume that the frequency of the first linear polarization signal is lower than that of the circular polarization signal. In the step  409 , the first linear polarization signal in the first waveguide is filtered by a low pass filter to filter out an undesired high frequency noise. Thus, the first signal and the second signal with lower frequencies are preserved. On the other hand, if the frequency of the circular polarization signal is lower than that of the first linear polarization signal, in the step  409 , the circular polarization signal in the second waveguide will be filtered by a low pass filter to filter out an undesired high frequency noise. Accordingly, the present invention is not restricted to any limitation to the frequencies of the linear polarization signal and the circular polarization signal. 
   To simplify the description, in the following description, we assume that the frequency of the linear polarization signal is lower than that of the circular polarization signal. 
   Next, proceed to the step  411 . In the step  411 , after filtering, the first signal and the second signal of the first linear polarization signal and the third signal and the fourth signal of the second linear polarization signal are transferred respectively to two low noise blocks (LNB). Thus, the signal with the linear polarization signal and the circular polarization signal are completely received and become a new signal with only one polarization-type. 
     FIG. 5  is a schematic flowchart of a second exemplary embodiment of the method for receiving a signal according to the present invention. In the embodiment, the method for receiving a signal includes the step  501  to the step  515 . 
   The steps, from the step  501  to the step  509 , are respectively identical to the step  401  to the step  409 . After the step  509 , the first linear circular polarization signal with lower frequency is separated from the circular polarization signal. For the time being, the first linear polarization signal has a first signal and a second signal, which are low pass filtered. The circular polarization has a third signal and a fourth signal respectively transformed from the left-hand circular polarization (LHCP) and the right-hand circular polarization (RHCP). 
   The difference between the above two embodiments is in the step  511 . In the step  511 , the first signal, the second signal of the first linear polarization signal, and the third signal, the fourth signal of the second linear polarization signal are integrated to become an integration signal. The integration signal is then transferred to a waveguide. It could be understood that the integration signal in the step  511  is a reverse operation of the step  505 . 
   After the step  511 , the integration signal is transferred to a low noise block (LNB). Thus, the signal with the linear polarization signal and the circular polarization signal is completely received and becomes a new signal with only one polarization-type. 
   In the second embodiment, the present invention reduces the required space and cost not only for building more antenna disks for receiving all types of signals, but also for a set of low noise block (LNB). Thus, the present invention becomes much simpler and inexpensive. 
     FIG. 6  is a schematic flowchart of a third exemplary embodiment of the method for receiving a signal according to the present invention. In the embodiment, the first signal and the second signal of the first linear polarization signal are respectively separated. The method of the present invention includes the step  601  to the step  621 . 
   First, in the step  603 , a signal received from a receiver is transferred to a main waveguide. Next, in the step  605 , the signal is separated into a first separation signal and a second separation signal via the main waveguide, which is the waveguide for transferring majority of the circular polarization signals. The first separation signal, selectively including a first signal in a first direction, is transferred to a first waveguide. 
   Next, in the step  607 , the second separation signal is separated into a third separation signal and a fourth separation signal via the main waveguide. The third separation signal, selectively including a second signal in a second direction, is transferred to a second waveguide. The fourth separation signal includes the circular polarization signal. In the embodiment, the first signal and the second signal are both linear polarization signals. The first direction and the second direction are orthogonal to each other. 
   In the step  609 , the first separation signal in the first waveguide is filtered by a low pass filter. Thus, the undesired high frequency noise is filtered out from the first separation signal. The first signal with low frequency is preserved. Similarly, in the step  611 , the third separation signal in the second waveguide is also filtered by another low pass filter. Thus, the undesired high frequency noise is filtered out from the third separation signal. The second signal with low frequency is preserved. 
   In the step  613 , the circular polarization signal in the main waveguide is transformed into a first linear polarization signal. The first linear polarization signal includes a third signal in the first direction and a fourth signal in the second direction. The circular polarization signal includes a left-hand circular polarization (LHCP) and a right-hand circular polarization (RHCP), which are transformed into a third signal and a fourth signal respectively. 
   In the step  615 , the second signal, the third signal, and the fourth signal are integrated to become a first integration signal, which is transferred to the main waveguide. 
   Next, in the step  617 , the first signal and the first integration signal are integrated to become a second integration signal, which is also transferred to the main waveguide. 
   In the step  619 , the second integration signal in the main waveguide is transferred to a low noise block (LNB). Thus, the signal with the linear polarization signal and the circular polarization signal is completely received and becomes a new signal with only one polarization-type. 
   In the embodiment, the present invention reduces the required space and cost not only for building more antenna disks for receiving all types of signals, but also for a set of low noise block (LNB). Thus, the present invention becomes much simpler and inexpensive. Furthermore, since the present invention separates the first signal and the second signal before filtering them, a high performance filter, with optimum performance costing much more, is not necessary. 
   The above description shows the method for receiving a signal according to the present invention. Further description for an exemplary apparatus in accordance with the above method is showed below. 
   As shown in  FIG. 7 , the present invention provides an apparatus for simultaneously receiving linear polarization signals and circular polarization signals. The apparatus includes a receiver  701 , an ortho-mode transducer (OMT)  703 , a polarizer  705 , a filter  707 , and two low noise blocks  709  and  711 . 
   The receiver  701  receives a signal and transfers it to a waveguide  71 . The ortho-mode transducer (OMT)  703  separates the signal into a first linear polarization signal  72  and a circular polarization signal  74 . The first linear polarization signal  72  and the circular polarization signal  74  are transferred to a first waveguide  73  and a second waveguide  75  respectively. The first linear polarization signal  72  selectively includes a first signal  722  in a first direction and a second signal  724  in a second direction. The first direction and the second direction are orthogonal to each other. 
   On the other hand, by adjusting the cross-section dimensions of the waveguides  73  and  75 , signals with different cutoff frequencies may be separated. In the embodiment, the first linear polarization signal  72  and the circular polarization signal  74  are separated by respectively adjusting the cross-section dimensions of the waveguides  73  and  75 . 
   After the separation of the signals  72  and  74 , the polarizer  705  transforms the circular polarization signal  74  in the second waveguide  75  into a second linear polarization signal. The second linear polarization signal selectively includes a third signal  746  in the first direction and a fourth signal  748  in the second direction. In particular, the circular polarization signal  74  includes a left-hand circular polarization (LHCP)  742  and a right-hand circular polarization (RHCP)  744 . The polarizer  705  transforms the left hand circular polarization  742  and the right hand circular polarization  744  into the third signal  746  and the fourth signal  748  respectively. 
   The filter  707  filters out an undesired high frequency noise from the first linear polarization signal  72  in the first waveguide  73 . The first signal  722  and the second signal  724  with lower frequencies are preserved. In the embodiment, the present invention assumes that the frequency of the first linear polarization signal is lower than that of the circular polarization signal. On the other hand, if the frequency of the circular polarization signal is lower than that of the first linear polarization signal, the circular polarization signal will be filtered by a low pass filter. Accordingly, the present invention is not restricted to any limitation to the frequencies of the linear polarization signal and the circular polarization signal. 
   The first signal  726  and the second signal  728  of the first linear polarization signal  72  and the third signal  746  and the fourth signal  748  of the second linear polarization signal  74  are transferred respectively to the low noise block  711  and  709  for further integration. Thus, the signal with the linear polarization signal and the circular polarization signal is completely received and becomes a new signal with only one polarization-type. 
   As shown in the  FIG. 8 , the present invention provides an apparatus for simultaneously receiving a signal having a first linear polarization signal  72  and a circular polarization signal  74 . The first linear polarization signal  72  includes a first signal  722  in a first direction and a second signal  724  in a second direction. The first direction and the second direction are orthogonal to each other. 
   The apparatus includes a receiver  701 , an ortho-mode transducer (OMT)  703 , a polarizer  705 , a filter  707 , an ortho-mode integrator  801 , and a low noise block  803 . 
   As set forth in the first embodiment, the cross-section dimensions of the waveguides  73  and  75  are different so as to separate the first linear polarization signal  72  and the circular polarization signal  74  with different frequencies. After passing through the polarizer  705  and the filter  707 , the present invention obtains the first signal  722 , the second signal  724  of the first linear polarization signal  72  and the third signal  742 , the fourth signal  744  of the second linear polarization signal  74 . 
   The difference between the above two embodiments is that the present invention uses an ortho-mode integrator  801  to integrate the above four signals to obtain a integration signal  82  which is transferred to a waveguide  81 . The integration signal  82  is transferred to the low noise block  803 . 
   In the embodiment, the present invention reduces the required space and cost not only for building more antenna disks for receiving all types of signals, but also for a set of low noise block (LNB). Thus, the present invention becomes much simpler and inexpensive. 
   As shown in  FIG. 9 , the apparatus for receiving a signal includes a receiver  701 , two ortho-mode transducers (OMT)  901  and  903 , a polarizer  705 , two filters  905  and  907 , two ortho-mode integrators  909  and  911 , and a low noise block  803 . 
   Person skilled in the art could understand that the difference between the above two embodiments is that the first signal  722  and the second signal  724  of the first linear polarization signal  72  are separated respectively via the waveguide  71  and are integrated respectively with the circular polarization signal  74 . Therefore, the present invention reduces the required space and cost not only for building more antenna disks for receiving all types of signals, but also for a set of low noise block (LNB). Thus, the present invention becomes much simpler and inexpensive. Furthermore, since the present invention separates the first signal and the second signal before low pass filtering them, a high performance filter, which is much more expensive, is not necessary. 
   The above description shows the apparatus and method for receiving signals having linear polarization signals and circular polarization signals. 
   Furthermore, the above embodiments assume the following two conditions: first, the frequency of the linear polarization signal is lower than that of the circular polarization signal; second, the received signal includes four signals, including the linear polarization signal having two orthogonal signals and the circular polarization signal having a left-hand circular polarization (LHCP) and a right-hand circular polarization (RHCP). However, the present invention could also implement in conditions, such as the frequency of the linear polarization signal is not lower than that of the circular polarization signal, receiving a signal including any one, two, or three of the above four signals. For example, the method and apparatus could be used to receive a signal with a left-hand circular polarization with lower frequency and a linear polarization signal in a vertical direction with higher frequency simultaneously. 
   Besides, as to oblique polarization signals, the present invention could also receive the oblique polarization signals by adjusting the angle of the receiving apparatus or by collocating with other devices, which are able to rotate the polarization angle. Consequently, the present invention is able to receive many types of signals, with whatever frequencies and polarization types. 
   In the foregoing specification the invention has been described with reference to specific embodiments. It will, however, be evident that various modification and changes may be made to thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense. Thus, it is intended that the present invention covers the modification and variations of this invention provided they come within the scope of the appended claims and their equivalents.