Abstract:
A compact multilayer signal processing system. In the illustrative embodiment, the system is adapted for use with microwave signals. The system includes a first mechanism for receiving an input signal and selectively routing the input signal onto a first signal path. A second mechanism routes the input signal along the first signal path vertically through one or more layers to a first circuit component. The first circuit component outputs an adjusted signal in response to receipt of the input signal. A third mechanism directs the adjusted signal to the output of the system. In a specific embodiment, the one or more layers include one or more groundplane layers. In this embodiment, the first mechanism includes an input switching network in communication with a controller. The switching network is positioned on a switching layer and communicates with one or more controllers to facilitate selectively switching the input signal onto one of plural input signal paths. The second mechanism further includes a first input waveguide that extends from the input switching network vertically through at least one groundplane layer and to an input end of the first circuit component. The third mechanism includes a first output waveguide extending from an output end of the first circuit component, vertically through at least one groundplane layer to an output switching network disposed on the switching layer. In the specific embodiment, the circuit layer includes plural circuit components that are coupled to respective input waveguides and output waveguides that extend vertically through the first groundplane layer to the input switching network and the output switching network, respectively.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     This invention relates to circuits. Specifically, the present invention relates to systems and methods for packaging and isolating circuits, such as microwave frequency converter circuits.  
         [0003]     2. Description of the Related Art  
         [0004]     Circuit isolation and packaging systems are employed in various demanding applications including microwave filter banks. Such applications demand compact packaging that minimizes electrical interference between components.  
         [0005]     Compact circuit isolation systems are particularly useful in microwave frequency converters and filter banks, where crosstalk between switches, filters, amplifiers, and signal converters is especially problematic. Conventionally, microwave frequency-shifter components are individually packaged in expensive double-sided cavitized housing assemblies, which are interconnected via wire, ribbon, and/or solder interconnects. Such component assemblies are often undesirably large and expensive. Furthermore, the various interconnects are prone to breakage, which reduces system reliability.  
         [0006]     Hence, a need exists in the art for a cost-effective and space-efficient system and method for assembling and packaging circuit components requiring electrical isolation.  
       SUMMARY OF THE INVENTION  
       [0007]     The need in the art is addressed by the compact multilayer signal processing system of the present invention. In the illustrative embodiment, the system is adapted for use with microwave signals. The system includes a first mechanism for receiving an input signal and selectively routing the input signal onto a first signal path. A second mechanism routes the input signal along the first signal path through one or more layers, including one or more groundplane layers, to a first circuit component for modifying the input signal and providing an adjusted signal in response thereto. A third mechanism outputs the adjusted signal.  
         [0008]     In a specific embodiment, the first mechanism includes an input switching network in communication with one or more controllers for selectively switching the input signal onto one of plural input signal paths. The switching network is positioned on a switching layer. The second mechanism accommodates a first input signal that extends from the input switching network through at least one groundplane layer and to an input end of the first circuit component. The third mechanism accommodates a first output signal extending from an output end of the first circuit component, through the at least one groundplane layer and to an output switching network disposed on the switching layer. In the specific embodiment, the input switching network and the output switching network are microstrip switching networks. The first circuit component is a stripline circuit component that is disposed on a circuit layer. The circuit layer is positioned between a first groundplane layer and a second groundplane layer.  
         [0009]     In a more specific embodiment, the first circuit component is a microwave filter. The circuit layer includes plural circuit components that are each coupled to a respective input waveguide and output waveguide that extend through the first groundplane layer to the input switching network and the output switching network, respectively.  
         [0010]     In the illustrative embodiment, the system further includes one or more controllers coupled to the input switching network and/or to the output switching network. The one or more controllers are adapted to selectively activate or select a desired circuit component disposed on the circuit layer in response to a given operational mode of the multilayer signal processing system. The system further includes one or more additional circuit layers disposed substantially adjacent to and parallel to the second groundplane layer on a side of the second groundplane layer opposite the circuit layer. The one or more additional circuit layers include one or more additional microwave filters disposed therein. The various waveguides, including the first input waveguide and the first output waveguide, are equipped with mode-suppression holes that parallel the waveguides, which are circular waveguides.  
         [0011]     One embodiment of the present invention is a stacked multilayer microwave filter with several filter elements. The unique positioning of the filter elements between or adjacent to groundplanes facilitates improved input/output isolation and significantly reduces the form factor required to implement the filter. Versatility and scalability of the filter is enhanced via use of unique input and output switching networks. The switching networks can switch a filter input signal to an appropriate layer and accompanying filter element and then selectively output the resulting filtered output signal while achieving minimal interference and maximum electrical isolation between filter input and output terminals. The vertical waveguides that couple the filter elements to the switching networks and that extend through one or more layers of the filter are equipped with special mode-suppression holes that further enhance filter response characteristics.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is an exploded view of a stacked multilayer programmable microwave filter according to an embodiment of the present invention.  
         [0013]      FIG. 2  is a magnified view illustrating filter layers of the stacked multilayer programmable filter of  FIG. 1 .  
         [0014]      FIG. 3  is a more detailed view illustrating a Radio Frequency (RF) switching layer and control signal routing layer of the stacked multilayer programmable filter of  FIG. 1 .  
         [0015]      FIG. 4  is a magnified view illustrating exemplary vertical RF transitions of the programmable filter of  FIG. 1 .  
         [0016]      FIG. 5  is a further magnified view of an exemplary vertical RF transition of  FIG. 4 . 
     
    
     DESCRIPTION OF THE INVENTION  
       [0017]     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.  
         [0018]      FIG. 1  is an exploded view of a stacked multilayer programmable microwave filter  10  according to an embodiment of the present invention. For clarity, various well-known components, such as power supplies, antennas, and so on, have been omitted from the figures. However, those skilled in the art with access to the present teachings will know which components to implement and how to implement them to meet the needs of a given application.  
         [0019]     The stacked programmable microwave filter  10  includes, from top to bottom, a switching layer  14 , a control-routing layer  16 , a first groundplane layer  18 , a first filter layer  20 , a second groundplane layer  22 , and a second filter layer  24 . The various layers  14 - 24  are approximately parallel and coincident as shown in  FIG. 1 . The various layers  14 - 24  have a low-loss dielectric substrate core, which in the present embodiment is Duroid. Duroid may be ordered from Rogers Corp.  
         [0020]     The switching layer  14  includes an input switching network  24  and an output switching network  26 , which are positioned on opposite ends of a top surface  48  of the switching layer  14 . The switching networks  24 ,  26  are implemented via microstrip with a common groundplane implemented via the first groundplane layer  18 .  
         [0021]     The input switching network  24  includes an input terminal  28  for receiving an input microwave signal. In the present specific embodiment, the input terminal  28  connects to an input of a first 1-4 switch  30 . The first 1-4 switch  30  selectively provides input to a second 1-4 switch  32 , a first vertical RF transition  34 , a second vertical RF transition  36 , and a third 1-4 switch  38 .  
         [0022]     The second 1-4 switch  32  selectively provides input to a third vertical RF transition  50 , a fourth vertical RF transition  52 , a fifth vertical RF transition  54 , and a sixth vertical RF transition  56 . The third 1-4 switch  38  selectively provides input to a seventh vertical RF transition  58 , an eighth vertical RF transition  60 , a ninth vertical RF transition  62 , and a tenth vertical waveguide RF transition  64 . The 1-4 switches  30 ,  32 ,  38  are responsive to control signals received from a first Application-Specific Integrated Circuit (ASIC) controller  40 . The control signals are routed through the control-routing layer  16  via a first set of routing paths  42 , which are connected to the first ASIC controller and to the input switching network  24  via vertical connections (not shown) extending through the switching layer  14 .  
         [0023]     The output switching network  26  includes a first 4-1 switch  68 , an output of which represents the output of the programmable stacked microwave filter  10  as provided at an output terminal  78 . In response to receipt of control signals from a second controller  44 , the 4-1 switch  68  selectively switches inputs from a second 4-1 switch  70 , a first output vertical RF transition  72 , a second output vertical RF transition  74 , and a third 4-1 switch  76  to the output terminal  78 .  
         [0024]     The second 4-1 switch  70  selectively switches input from third, fourth, fifth, and sixth output vertical RF transitions  80 - 86 , respectively, to an input of the first 4-1 switch  68  in response to receipt of specific control signals from the second controller  44 . Similarly, the third 4-1 switch  76  selectively switches input from seventh, eighth, ninth, and tenth vertical RF transitions  88 - 94 , respectively, to an input of the first 4-1 switch  68 .  
         [0025]     The various switches  68 ,  70 ,  76  are responsive to control signals received from the second ASIC controller  44 . The control signals are routed through the control-routing layer  16  via a second set of routing paths  46 , which are connected to the second ASIC controller and to the output switching network  26  via vertical connections (not shown) extending through the switching layer  14 .  
         [0026]     The first, third, fifth, seventh, and ninth input vertical RF transitions  34 ,  50 ,  54 ,  58 ,  62 , respectively, extend approximately perpendicularly through the switching layer  14 , the control-routing layer  16 , and the first groundplane layer  18  to the first filter layer  20 . At the first filter layer  20 , the input vertical RF transitions  34 ,  50 ,  54 ,  58 ,  62  couple to inputs of five respective first-layer filter elements  96 , three of which are visible in  FIG. 1 . The three visible first-layer filter elements include a first filter element  98 , a second filter element  100 , and a third filter element  102 , which are coupled to the third input vertical RF transition  50 , the fifth input vertical waveguide  54 , and the first input vertical waveguide  34 , respectively.  
         [0027]     The corresponding first, third, fifth, seventh, and ninth output vertical RF transitions  72 ,  80 ,  84 ,  88 ,  92 , respectively, extend approximately perpendicularly through the switching layer  14 , the control-routing layer  16 , and the first groundplane layer  18 , and couple to outputs of the respective first-layer filter elements  96 . Outputs of the first filter element  98 , second filter element  100 , and third filter element  102  are coupled to the third output vertical RF transition  80 , fifth output vertical RF transition  84 , and the first output vertical RF transition  74 , respectively.  
         [0028]     The second, fourth, sixth, eighth, and tenth input vertical RF transitions  36 ,  52 ,  56 ,  60 ,  64 , respectively, extend approximately perpendicularly through the switching layer  14 , the control-routing layer  16 , the first groundplane layer  18 , the first filter layer  20 , and the second groundplane layer  22 . The input vertical RF transitions,  36 ,  52 ,  56 ,  60 ,  64  couple to inputs of five respective second-layer filter elements  104 , three of which are visible in  FIG. 1 . The three visible second-layer filter elements include first, second, and third second-layer filter elements  106 ,  108 ,  110 , respectively. Inputs of the visible second-layer filter elements  106 ,  108 ,  110  are coupled to the fourth input vertical RF transition  52 , the sixth input vertical waveguide  56 , and the second input vertical RF transition  36 , respectively.  
         [0029]     The second, fourth, sixth, eighth, and tenth output vertical RF transitions  74 ,  82 ,  86 ,  90 ,  94 , respectively, extend approximately perpendicularly through the switching layer  14 , the control-routing layer  16 , the first groundplane layer  18 , the first filter layer  20 , and the second groundplane layer  22 . The output vertical RF transitions  74 ,  82 ,  86 ,  90 ,  94  couple to outputs of the five respective second-layer filter elements  104 . Outputs of the visible second layer filter elements  106 ,  108 ,  110  are coupled to the fourth output vertical RF transition  82 , the sixth output vertical RF transition  86 , and the second output vertical RF transition  74 , respectively.  
         [0030]     In the present specific embodiment, the control-routing layer  16  is constructed substantially from dielectric material, such as Duroid. A top surface  112  of the control-routing layer  16  is shown lacking surface metalization, but exhibiting plated through holes, i.e., coaxial structures corresponding to the various vertical RF transitions, such as the input vertical waveguides  34 ,  36 ,  50 - 56  shown.  
         [0031]     In the present embodiment, the first groundplane layer  18  is implemented via a dielectric substrate exhibiting a first metal-plated top surface  114  with vertical RF transition holes therein, which correspond to the various vertical RF transitions  34 ,  36 ,  50 - 64 ,  74 ,  76 ,  80 - 94 . Similarly, the second groundplane layer  22  is implemented via a dielectric substrate exhibiting a second metal-plated top surface  118  with vertical RF transition holes therein. The second filter layer  24  also exhibits a metallic surface  120  disposed on a dielectric core.  
         [0032]     In the filter  10  of  FIG. 1 , the various vertical waveguides  34 ,  36 ,  50 - 64 ,  74 ,  76 ,  80 - 94  are shown extending perpendicularly through the various horizontal layers  14 - 24 . However, the various vertical RF transitions  34 ,  36 ,  50 - 64 ,  74 ,  76 ,  80 - 94  may extend vertically through the horizontal layers  14 - 24  at an angle through the layers  14 - 24  without departing from the scope of the present invention. For the purposes of the present discussion, the term vertically through is taken to mean either perpendicularly through or at an angle through.  
         [0033]     The first filter layer  20  exhibits a dielectric core with a top surface metalization  116  with strategically cleared areas corresponding to the filter elements  96 . Metalization within the strategically cleared areas is shaped to provide desired filtering operations on microwave signals passing through the filter elements  96 . The second filter layer  24  is constructed similarly to the first filter layer  20  with the exception that the metallic surface  120  of the second filter layer  24  lacks waveguide holes therethrough.  
         [0034]     The filter elements  96 , sandwiched between the first groundplane layer  114  and the second groundplane layer  118 , are stripline filter elements. Consequently, the filter elements  96  are homogenous and exhibit improved filter responses over certain other conventional filter elements. The second filter layer  24  is constructed similarly to the first filter layer  20 , with the exception that no waveguide holes through the second filter layer  24  are needed.  
         [0035]     In operation, the ASIC controllers  40 ,  44  configure the input switching network  24  and the output switching network  26  to select a particular filter element from the filter elements  96  of the first filter layer  20  or from the filter elements  104  of the second filter layer  104 . A particular filter element is selected when the appropriate switches of the input network  24  and the output network  26  enable an input signal to pass through the input switching network  14 ; through a corresponding input vertical RF transition; through the selected filter element; through the corresponding output vertical waveguide; and through the output switching network  26  to the output terminal  78 .  
         [0036]     In the present specific embodiment, the compact stacked filter  10  configuration is adapted to filter electromagnetic energy within a microwave frequency band, such as between 4-15 GHz. Furthermore, in the present embodiment, only one filter element at a time is selected via the controllers  40 ,  44 .  
         [0037]     Strategic use of the input switching network  24  and the output switching network  26  in combination with the use of groundplane layers  18 ,  22  between the input/output terminals  28 , 78  and a selected filter element greatly enhance electrical isolation between the terminals  28 ,  78  and between the input and output of the selected filter element. This obviates the need for special independent adjacent cavatized housings for each filter element to ensure sufficient input/output isolation. Consequently, the footprint of the filter  10  significantly reduces filter space requirements, which is very important in various applications including missile, aircraft, and satellite systems.  
         [0038]     Note that various layers, including the filter layers  20 ,  24  are coated with metal  134 . The metalization  134  is connected to all ground planes  18 ,  22 , which further improves signal isolation and cross talk. Note that the bottom filters  104 - 110  are stripline filters. Consequently, an additional groundplane layer (not shown) is included below the bottom filter layer  24 .  
         [0039]     The ASIC controllers  40 ,  44  store information about filtering characteristics of each filter element  96 ,  104  and run algorithms that choose the appropriate filter for a given signal environment. In addition, the ASIC controllers  40 ,  44  may send tuning signals, via the routing paths  42 ,  46 , to various circuit paths extending to/from the switches  30 ,  32 ,  38  and switches  68 ,  70 ,  76  to improve overall filter performance. Tuning signals may be computed by the ASIC controllers  40 ,  44  based on a predetermined algorithm that may be readily developed by those skilled in the art with access to the present teachings without undue experimentation.  
         [0040]     In the present embodiment, the ASIC controllers  40 ,  44  select the appropriate filter elements  96 ,  104  according to the frequency of electromagnetic energy that is provided to the input terminal  28 . The controllers  40 ,  44  may communicate with a frequency-measuring device (not shown). Alternatively, appropriate functionality may be built into the controllers  40 ,  44 , to facilitate determining the frequency of the input signal to facilitate selecting the appropriate filter element  96 ,  104  accordingly. Alternatively, the controllers  40 ,  44  may be manually pre-configured to select a particular filter element  96 ,  104 . The controllers  40 ,  44  and accompanying algorithm may be implemented via a user-programmable computer or other ASIC by those skilled in the art without undue experimentation.  
         [0041]     In the present specific embodiments, the various vertical RF transitions  34 ,  36 ,  50 - 64 ,  74 ,  76 ,  80 - 94  exhibit mode-suppression holes, which are optimized to suppress undesirable signal modes travelling in the vertical RF transitions as discussed more fully below. The mode suppression holes  122  are implemented via metal-metal-plated through holes running substantially parallel to the vertical RF transitions  34 ,  36 ,  50 - 64 ,  74 ,  76 ,  80 - 94 . In this embodiment, the vertical RF transitions  34 ,  36 ,  50 - 64 ,  74 ,  76 ,  80 - 94  are implemented via coaxial structures or circular waveguides. Waveguides other than circular waveguides may be employed without departing from the scope of the present invention.  
         [0042]     Those skilled in the art will appreciate that the stacked filter  10  may be scaled to accommodate additional layers, additional filter elements per layer, or fewer layers with fewer filter elements per layer without departing from the scope of the present invention. Furthermore, the filter elements  96 ,  104  may be replaced with other types of circuit components, such as frequency converters, amplifiers, and so on, without departing from the scope of the present invention.  
         [0043]     In the present specific embodiment, interfacing between the switching networks  24 ,  26  and the vertical RF transitions are implemented via stripline-to-circular transitions. Similarly, interfacing between the vertical RF transitions  34 ,  36 ,  50 - 64 ,  74 ,  76 ,  80 - 94  and the filters  96 - 102 ,  104 - 110  are implemented via circular-to-stripline transitions. Conventional stripline-to-circular transitions and/or circular-to-stripline transitions may be employed without departing from the scope of the present invention.  
         [0044]     Those skilled in the art will appreciate that the stacked programmable microwave filter  10  may be adapted for use with electromagnetic energy exhibiting frequencies other than microwave frequencies without departing from the scope of the present invention. Furthermore, the various microwave filters  96 ,  104  may be replaced with circuit components other than filters, such as amplifiers, frequency converters, and so on, without departing from the scope of the present invention. In addition, the switching networks  24 ,  26  may be replaced with different types of switching networks. For example, the 1-4 switches  30 ,  32 ,  38  may be replaced with a single 1-10 switch. A 1-20 switch could be employed in implementations wherein the stacked filter  10  exhibits twenty filter elements.  
         [0045]     The unique use of the switching networks  24 ,  26  in combination with a stacked approach exhibiting isolation-enhancing groundplanes  18 ,  22  yields compact circuit implementations while minimizing cross-talk between components and maximizing electrical isolation between the input terminal  28  and the output terminal  78 .  
         [0046]      FIG. 2  is a magnified exploded view illustrating filter layers  20 ,  24  of the stacked multilayer programmable filter of  FIG. 1 . For clarity, the intervening groundplane layer  22  of  FIG. 1  is not shown in  FIG. 2 .  
         [0047]     In the present specific embodiment, the five first-layer filter elements  96  and the five second-layer filter elements  104  are implemented as stripline filter elements with strategically patterned filter metalization  130  surrounded by clearance areas  132  in surrounding metal surfacing  134 . Various input vertical RF transitions  52 ,  56 ,  36 ,  60 ,  64  and output vertical RF transitions  82 ,  86 ,  74 ,  90 ,  94  and accompanying mode-suppression holes  122  are more clearly visible in  FIG. 2 .  
         [0048]      FIG. 3  is a more detailed view illustrating a Radio Frequency (RF) switching layer  14  and control-routing layer  16  of the stacked multilayer programmable filter  10  of  FIG. 1 . The first ASIC controller  40  connects with the corresponding first set of routing paths  42  in the control-routing layer  16 . Similarly, the second ASIC controller  44  connects to the second set of routing paths  46  in the control-routing layer  16 .  
         [0049]     In the present specific embodiment, the various connecting paths  42 ,  46  connect the ASIC controllers  40 ,  44  to various circuit-tuning stubs  140  in the input switching network  24  and the output switching network  26 . Additional circuit paths connect the first ASIC controller  40  and the second ASIC controller  44  to the input switches  2 - 32  and the output switches  68 ,  70 ,  76 , respectively. For clarity, the control lines  42 ,  46  of  FIG. 1  are not shown in  FIG. 3 .  
         [0050]      FIG. 4  is a magnified view illustrating exemplary vertical waveguides  50 ,  52 ,  80 ,  82  of the programmable filter of  FIG. 1 . The vertical RF transitions  50 ,  52 ,  80 ,  82  are implemented via center circular waveguide sections  142  surrounded by strategically positioned mode suppression holes  122 . The exact numbers, sizes, and positions of the mode suppression holes  122  are application specific and may be readily determined by those skilled in the art with access to the present teachings to meet the needs of a given application. Well-known methods for transitioning stripline and microstrip circuits to/from circular waveguides, such as the exemplary vertical RF transitions  50 ,  52 ,  80 ,  82 , may be employed to implement embodiments of the present invention without departing from the scope thereof.  
         [0051]      FIG. 5  is a further magnified view of an exemplary vertical RF transition of  FIG. 4 . The mode-suppression holes  122  and accompanying surface metalization facilitate coupling the microstrip switching network circuitry (see switching network  24  of  FIG. 1 ) to the vertical circular waveguide  50  and constituent center circular waveguide  142  while suppressing undesirable microwave signal propagation modes.  
         [0052]     Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications, and embodiments within the scope thereof. It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.  
         [0053]     Accordingly,