Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a separation and a combination of electromagnetic signals and a multiplexer suitable for use in a satellite and a system for communication via satellite and, more particularly, to a multiplexer for accomplishing the foregoing functions in a unitary structure of reduced size and mass.  
           [0002]    In a satellite carrying communication equipment for the processing of signals of numerous channels of a communication system, the communication equipment may have the task of arranging a set of received uplink signals to produce a set of downlink signals for transmission by antenna elements to different geographic locations. This is accomplished by the separation of various signal channels of the received uplink signals, and the combining of various ones of the separated channels to produce a desired set of channels for transmission to a geographic location. Such separation and combining has been accomplished at microwave frequencies by use of multiplexers which include manifolds operative with bandpass filters that serve to segregate the respective signal channels. Previous designs of multiplexer units (input, combining or output) have accommodated the separation of signals into separate channels or subgroups of channels or the combining of multiple signals or signal groups. This has been accomplished by use of separate units to combine some channels while separating other channels, wherein routing from one input signal path to a choice of output paths and routing multiple input paths to a single output path have been implemented with separate devices. Such separate assemblies of microwave equipment tend to be bulky and heavy, thus presenting the disadvantage of necessitating a design of the satellite to carry a larger and a heavier payload than is desirable.  
         SUMMARY OF THE INVENTION  
         [0003]    The aforementioned disadvantage is overcome and other benefits are provided by a multiplexer forming a multiple channel routing multiplexer wherein, in accordance with the invention, a plurality of manifolds are interconnected by bandpass filters. The filters serve to segregate signal channels from each other during a process of separating the microwave signals associated with various ones of the channels found in one of the manifolds. The filters also serve to segregate signal channels from each other during a process of combining the microwave signals associated with various ones of the channels by use of another of the manifolds.  
           [0004]    In accordance with a feature of the invention, one or more of the bandpass filters are employed as connecting filters for coupling a signal channel directly between a first of the manifolds and a second of the manifolds, wherein the construction of the manifold and the connecting filters is in the form of a rigid assembly which replaces the numerous separate assemblies of the prior art. The rigid assembly of manifolds and filters in the multiplexer of the invention is more compact and of reduced mass as compared to the system of numerous separate assemblies of the prior art.  
           [0005]    As an example in the construction of a preferred embodiment of the invention, there is provided a first manifold serving as an input manifold and having an input port for receiving a plurality of signals in differing spectral bands, and a plurality of output ports respectively for outputting signals in differing spectral bands. There is provided a second manifold and a third manifold each serving as an output manifold and having an output port for outputting a plurality of signals in differing spectral bands, and a plurality of input ports respectively for receiving signals in differing spectral bands. Bandpass filters, each having differing fixed spectral passbands, provide for connection of output ports of the first manifold to input ports of the second and the third manifolds as well as for segregating signal channels of further output ports of the first manifold. The bandpass filters also provide for receiving input signals at input ports of each of the second and the third manifolds. A base may be provided for supporting each of the manifolds and each of the bandpass filters in a unitary structure.  
           [0006]    By way of further example in the construction of the foregoing embodiment of the invention, each of the bandpass filters comprises a cylindrical sidewall terminated by opposed end walls defining a resonant cavity. Each of the manifolds is constructed as a section of waveguide of rectangular cross-section having a pair of broad sidewalls connected by a pair of opposed narrow sidewalls. A sidewall, preferably a broad sidewall of a manifold is suitable for the rigid mounting of a filter thereon with the end wall of the cavity in contact with the side wall of the manifold. If desired, at a location of connection between a cavity and a manifold, the sidewall of the manifold may serve as the end wall of the cavity. At the location of connection between the bandpass filter and the manifold there is electromagnetic coupling between the bandpass filter and the manifold via a slot extending through the end wall of the filter and the sidewall of the manifold. The filters may include tuning elements, may have single or multiple cavities, and may include mode coupling elements for generating plural modes of electromagnetic waves within a filter cavity.  
           [0007]    The invention provides for a reconfiguration of multiple input channels into multiple output channels with minimization of mass and insertion loss within the routing configuration. Minimization of mass, along with a compact assembly, occurs in the routing assembly by use of a single filter providing both the function of separating signals and the function of combining signals. A concept of the invention is to integrate filtering and multiplexing functions normally performed by separate assemblies. The assembly of the invention allows for the separation of multiple signals, each having its own carrier frequency, from one signal path for routing on separate paths, and the combining of other signals from separate paths to be combined for a single output. The routing multiplexer filtering concept allows the combining of multiple input paths and the creation of multiple output paths consisting of a different combination of input and output signal groups or groups of channels.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]    The aforementioned aspects and other features of the invention are explained in the following description, taken in connection with the accompanying drawing figures wherein:  
         [0009]    [0009]FIG. 1 shows diagrammatically a multiple channel routing multiplexer of the invention serving as part of a communication system with communication via a satellite link;  
         [0010]    [0010]FIG. 2 is a stylized perspective view of the multiplexer of FIG. 1;  
         [0011]    [0011]FIG. 3 is a fragmentary stylized perspective view showing detail in the interconnection of a filter between manifolds in the multiplexer of FIGS. 1 and 2; and  
         [0012]    [0012]FIG. 4 is a stylized perspective view of an alternative embodiment of a bandpass filter having dual mode operation in the multiplexer of FIGS. 1 and 2. 
     
    
       [0013]    Identically labeled elements appearing in different ones of the figures refer to the same element but may not be referenced in the description for all figures.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    [0014]FIG. 1 presents electronic equipment  10  carried by a satellite  12  and forming part of a communication system  14 . Included within the equipment  10  is a multiplexer  16  constructed in accordance with the invention. In the operation of the equipment  10 , signals communicate via an uplink channel from the earth  18  to the satellite  12 , and are received by a receiver  20  followed by processing in a signal processor  22 . Various well-known signal-processing functions may be performed by the processor  22 . An additional function of routing the signals is provided by the multiplexer  16 . The processor  22  outputs to the multiplexer  16  a set of microwave signals disposed in separate signal channels  24  on separate carrier frequencies. The multiplexer  16  receives the signals via a set of input ports  26  of the multiplexer  16 , and outputs the signals via a set of output ports  28  of the multiplexer  16 . By way of example in the implementation of the satellite electronic equipment  10 , the output ports  28  of the multiplexer  16  apply their respective output signals in channels  30  to various components, such as feed elements, of an antenna system  32  which, in turn, produces a set of beams directing various output signal channels  30  and to corresponding locations on the earth&#39;s surface.  
         [0015]    As shown in FIGS. 1, 2 and  3 , the multiplexer  16  comprises a plurality of manifolds of which three manifolds  34 ,  36  and  38  are shown by way of example. The plurality of manifolds are interconnected by a plurality of the bandpass filters of which two interconnecting bandpass filters  40  and  42  are shown by way of example. The filter  40  interconnects the manifold  34  with the manifold  36 , and the filter  42  interconnects the manifold  34  with the manifold  38 . In accordance with a feature of the invention, the assembly of the three manifolds  34 ,  36  and  38  with their interconnecting bandpass filters  40  and  42  constitute a rigid unitary assembly wherein, if desired, the rigidity may be enhanced by a mounting of the manifolds to a supporting base plate  44 . The manifold  34  has an input port  46  which also serves as one of the input ports  26  of the multiplexer  16 . The manifold  36  has an output port  48  it also serves as one of the output ports  28  of the multiplexer  16 . The manifold  38  has an output port  50  which also serves as one of the output ports  28  of the multiplexer  16 . Two bandpass filters  52  and  54  connect to output ports of the manifold  34 , and to serve to output signals from the multiplexer  16  via output ports  28 . Two bandpass filters  56  and  58  connect to input ports of the manifold  36 , and serve to receive signals for the multiplexer  16  via input ports  26 . Two bandpass filters  60  and  62  connect to input ports of the manifold  38 , and serve to receive signals for the multiplexer  16  via input ports  26 .  
         [0016]    It is noted that the use of the terms input port and output port is intended to facilitate the description of the invention, and conforms to the direction of signal flow shown in FIG. 1. However, is to be understood that the components of the multiplexer  16 , namely, the manifolds and the bandpass filters of the multiplexer  16 , operate in reciprocal fashion such that signals could be inputted via the output ports  28  to exit via the input ports  26  of the multiplexer  16 .  
         [0017]    Each of the manifolds  34 ,  36  and  38  is constructed of a section of waveguide which, by way of example, is shown as a waveguide of rectangular cross-section having four sidewalls consisting of opposed broad walls  64  and  66  joined by narrow walls  68  and  70 . Furthermore, by way of example in the construction of any one of the manifolds  34 ,  36  and  38 , the section of waveguide is terminated by an end wall  72  at one end of the waveguide section, and at an opposite and thereof is open for formation of a port such as the port  46 ,  48  or  50 . The sidewalls and the end wall in each of the manifolds is constructed of an electrically conducting material such as copper.  
         [0018]    Each of the bandpass filters  40  and  42 , as well as other ones of the bandpass filters has a cylindrical form, such as a right circular cylinder by way of example, and comprises a cylindrical sidewall  74  terminated by opposed end walls  76  and  78  that define a cavity  80  (as shown for the filter  42  in FIG. 3). The sidewalls and the end wall in each of the filters is constructed of an electrically conducting material such as copper. The cavity  80  resonates as a frequency of microwave radiation dependent on the dimensions of the cavity  80  and on the position of a tuning element, such as a tuning screw  82  which extends through the sidewall  74  into the cavity  80 . Rotation of the screw  82  advances the screw  82  to a desired position for adjustment of the resonant frequency of the cavity  80 . The construction of the filter  42  with a single cavity  80  is presented by way of example, it being understood that a filter, such as the filter  62  (as shown in FIG. 2) may be constructed of two cavities  84  and  86  separated by a transverse wall  88 . The transverse wall  88  has a coupling aperture  90  having the configuration of a linear slot. Each of the cavities  84  and  86  is provided with a tuning screw  92 , disposed in the sidewall  74 , for adjustment of resonant frequency in the cavity.  
         [0019]    In FIG. 3, portions of the sidewalls of the manifold  34  and of the filter  42  have been cut away to show a mode of coupling of electromagnetic energy between the manifold  34  and the filter  42 , and between the filter  40  to the manifold  38 . At the interface between the filter  42  and the manifold  34 , electromagnetic energy is coupled by way of a linear slot  94  extending from the cavity  80  through the end wall  76  and the broad wall  64  to the interior space of the manifold  34 . At the interface between the filter  42  and the manifold  38 , electromagnetic energy is coupled by way of a linear slot  96  extending from the cavity  80  through the end wall  78  and the broad wall  66  to the interior space of the manifold  38 . The slot  94  extends perpendicularly to the longitudinal direction of the manifold  34 , and the slot  96  extends perpendicularly to the longitudinal direction of the manifold  38 . The coupling by means of slots, such as the slots  94  and  96  depicted in FIG. 3 at the interfaces between the bandpass filter  42  and the manifolds  34  and  38 , is employed also for other ones of the interfaces at various ones of the bandpass filters with respective ones of the manifolds depicted in FIG. 2. By way of alternative embodiment in the construction at the interface between a filter and a manifold, such as the interface between the filter  62  and the manifold  38 , the broad wall  64  can serve as the end wall  78  wherein the sidewall  74  contacts the broad wall  64 , thereby simplifying construction by omitting the additional wall  78 .  
         [0020]    [0020]FIG. 4 shows, by way of example in an alternative construction of bandpass filter, a construction of the bandpass filter  62  of two cavities  84  and  86  separated by a transverse wall  98 . The transverse wall  98  has a coupling aperture  100  in the configuration of a crossed slot for the coupling of electromagnetic energy between the cavities  84  and  86 . By way of comparison of the operation of the filter  60  with the filter  62 , in the filter  62  the two cavities  84  and  86  each operate with a single mode of vibration of electromagnetic wave, and only the single tuning screw  92  is in each of the cavities  84  and  86  for tuning the respective cavity. However, in the filter  60 , each of the cavities  84  and  86  supports two orthogonal modes of vibration of electromagnetic wave and, accordingly, the tuning screw  92  tunes one of the electromagnetic waves in a respective one of the cavities, and an additional tuning screw  102  is provided for each of the cavities  84  and  86  for tuning the orthogonal wave. A mode coupling screw  104  is also provided in each of the cavities  84  and  86  of the filter  60  for the coupling of electromagnetic energy between the two modes. In the filter  62 , the linear slot of the coupling aperture  90  suffices to communicate electromagnetic energy between the single modes of vibration in the two cavities while, in the filter  60 , the crossed slot of the coupling aperture  100  serves to communicate electromagnetic energy between the dual orthogonal modes of vibration in the two cavities. With respect to the filter  60 , the manifold input ports  26  may be constructed, by way of example, as a coaxial connector  106  with a post or loop extending through the sidewall  74  into the cavity  84 . Alternatively, a waveguide connection (not shown) can be employed at the input port  26 .  
         [0021]    In the operation of the multiplexer  16 , and with reference to FIG. 1, the input signals may be the signals of either single input channels or groups of channels to be routed as output signals by different outputs via single channels or groups of channels. All signals are input either through an input multiplexer type of configuration (manifold or other splitting network) or are output through an output multiplexer type of configuration (manifold or other combining network), or both. Input signals to be routed as a group (or single channel) are filtered and are combined with other signals in an output manifold or combining device. Other signals connect to filters through a manifold or separation network and then pass through grouping or isolation filters. These latter signals are then either combined with other signals in an output combining device or are output directly through a filter.  
         [0022]    In the general configuration for a routing multiplexer, as depicted in FIG. 1, the input signals (c, d, w, x) are provided in single input channels. Input signal (A+B++a++y) is a group of channels to be routed to different outputs. The capitalization of the letters identifying some of the signals indicates that the signals (A, B) in a single channel will be divided out in separate channels, while the lower case letters identifies signals that will be combined with other signals before being outputted. On the output side, the signals of single channels A and B are separated from other input signals in an input multiplexer configuration, and are output directly to other elements of a payload, such as the antenna system  32 . Grouping signal channels and subgroups of channels in output manifolds (such as w+x++y and z++c+d) creates other output signals.  
         [0023]    The benefit of a routing multiplexer, such as the multiplexer  16 , is the improvement in mass and size, and performance associated with implementation in a single device. Mass and size are minimized by implementation of a single filtering component with appropriate manifolds to perform the separation function and the combining function. This eliminates a need for interconnection of coax or waveguide and the use of an additional filter. Performance is also improved in terms of the benefit of reduced insertion loss associated with a single filter and an absence of interconnecting cabling harness. The integration of microwave components into a single unit also insures unit performance with tuning and verification at the unit level, and simplifies testing of the nultiplexer.  
         [0024]    It is to be understood that the above described embodiments of the invention are illustrative only, and that modifications thereof may occur to those skilled in the art. Accordingly, this invention is not to be regarded as limited to the embodiments disclosed herein, but is to be limited only as defined by the appended claims.

Technology Category: 5