Abstract:
One embodiment of the present invention includes a waveguide. The waveguide comprises an elongated member having a conductive bottom surface and a hollow channel. The hollow channel is defined by a first conductive sidewall, a second conductive sidewall, and a conductive inner surface. The waveguide also comprises a plurality of conductive ridge portions projecting from the conductive inner surface and extending between the first conductive sidewall and the second conductive sidewall. The conductive ridge portions can partition the hollow channel into a plurality of hollow recesses. The waveguide further comprises a plurality of switches associated with each of at least one of the plurality of conductive ridge portions. At least one of the plurality of switches associated with a respective one of the plurality of conductive ridge portions can be activated to couple the respective one of the plurality of conductive ridge portions to the conductive bottom surface.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to wave communications and, more particularly, to a programmable tunable filter waveguide. 
       BACKGROUND OF THE INVENTION 
       [0002]    The technology of information transfer continues to increase rapidly due to the climbing demand for wireless applications. Additionally, systems such as radar, signal intelligence (SigInt), and electronic warfare (EW) systems have ever increasing requirements for bandwidth while reducing size, weight and power. All of these micrometer (μm) or millimeter (mm) wave transceiver systems are typically equipped with antenna systems that include a configuration of antenna feeds that use downlink signals and/or receive uplink signals. In particular, as the demand for wireless communication applications increases, so also does the demand for systems to be capable of transmitting and/or receiving respective signals having wider bandwidth capacity. Furthermore, as systems are typically not reconfigurable once put into service, systems are typically equipped with an arrangement of components that are capable of handling only a fixed range of bandwidths. In particular, radar, SigInt, and EW systems are being placed on unmanned vehicles, both aerial and ground-based, with continuously decreasing size, where there are high electrical performance requirements with very little tolerance to weight and power consumption. 
         [0003]    Typically, a μm- and/or mm-wave signal received by the system is propagated to channelized filter banks prior to being frequency downconverted and digitized. The channelized filter banks include a plurality of different band-pass, high-pass and/or low-pass filters into which the μm- and/or mm-wave signal is switched based on the frequency pass-band intended to be received by the system. Therefore, a received μm- and/or mm-wave signal is switched to a desired filter bank in order to filter unwanted signals from being digitized in the receiver system. A system may likewise switch an outgoing modulated signal between a plurality of channelized filter banks prior to transmitting a μm- and/or mm-wave signal such that only desired signals are transmitted. 
         [0004]    By switching the transmitted and received μm- and/or mm-wave signals between the channelized filter banks, the system can be configured to modulate and demodulate wave signals occupying a number of channels of fixed bandwidths. However, because a given system may be configured to provide μm- and/or mm-wave signals over a broad range of frequencies, the system may require a large number of channelized filter banks, as well as a large number of switch manifolds to provide the transmitted and received μm- and/or mm-wave signals to the filter banks. The large number of channelized filter banks, switches, and other associated hardware, such as the interconnecting transmission lines, can occupy an excessive amount of the limited available space in a system. In addition, the switches that direct the μm- and/or mm-wave signal from one transmission line to a multitude of output transmission lines that are coupled to the filter banks can substantially affect an acquisition time of received μm- and/or mm-wave signals based on a slow speed of switching, and can also introduce excess signal loss. This can be particularly true in systems where the power level of the signals are high, such as on the order of one or more Watts, that require the use of switch technologies that can handle the higher power but have inherently slower switching speeds. 
       SUMMARY OF THE INVENTION 
       [0005]    One embodiment of the present invention includes a waveguide. The waveguide comprises an elongated member having a conductive bottom surface and a hollow channel. The hollow channel is defined by a first conductive sidewall, a second conductive sidewall, and a conductive inner surface. The waveguide also comprises a plurality of conductive ridge portions projecting from the conductive inner surface and extending between the first conductive sidewall and the second conductive sidewall. The plurality of conductive ridge portions can be conductive and can partition the hollow channel into a plurality of hollow recesses. The waveguide further comprises a plurality of switches associated with each of at least one of the plurality of conductive ridge portions. At least one of the plurality of switches associated with a respective one of the plurality of conductive ridge portions can be activated to couple the respective one of the plurality of conductive ridge portions to the conductive bottom surface. 
         [0006]    Another embodiment of the present invention includes a method for filtering a wave signal in an elongate waveguide structure. The method comprises determining a desired frequency pass-band for the wave signal. The method also includes selecting at least one pair of a plurality of conductive ridge portions disposed along a longitudinal surface of the elongate waveguide structure. The selected at least one pair of the plurality of conductive ridge portions can correspond to a respective at least one resonator pole based on a physical separation of the at least one pair of the plurality of conductive ridge portions relative to a wavelength of the wave signal that is associated with the respective at least one resonator pole. The respective at least one resonator pole can correspond to a respective at least one frequency within the desired frequency pass-band. The method also comprises activating a plurality of switches configured to conductively couple the selected at least one pair of the plurality of conductive ridge portions to a conductive outer surface of the elongate waveguide structure. 
         [0007]    Another embodiment of the present invention includes a wave signal waveguide. The waveguide comprises means for slowing propagation of a wave signal from a first end of the waveguide to a second end of the waveguide. The waveguide also comprises means for switchably generating at least one resonator pole associated with a respective at least one frequency of the wave signal. The at least one resonator pole can define a frequency pass-band for the wave signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  illustrates an example of a micrometer (μm) and/or millimeter (mm)-wave receive and/or transmit system in accordance with an aspect of the invention. 
           [0009]      FIG. 2  illustrates an example of an exploded view of a programmable tunable filter waveguide in accordance with an aspect of the invention. 
           [0010]      FIG. 3  illustrates an example of a schematic representation of a portion of a programmable tunable filter waveguide in accordance with an aspect of the invention. 
           [0011]      FIG. 4  illustrates an example of different configurations of a programmable tunable filter waveguide in accordance with an aspect of the invention. 
           [0012]      FIG. 5  illustrates an example of a frequency response graph of the programmable tunable filter waveguide of the example of  FIG. 4  in accordance with an aspect of the invention. 
           [0013]      FIG. 6  illustrates an example of a configuration of a programmable tunable filter waveguide in accordance with an aspect of the invention. 
           [0014]      FIG. 7  illustrates diagrammatic examples of a programmable tunable filter waveguide in accordance with an aspect of the invention. 
           [0015]      FIG. 8  illustrates an example of a method of filtering signals in accordance with an aspect of the invention. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0016]    The present invention relates to micrometer (μm) and/or millimeter (mm)-wave systems that employ filters to select frequencies of interest for communication, radar, signal intelligence (SigInt), and electronic warfare (EW) applications, either in the receiver or transmit components. More particularly, this invention applies to replacing such filters with a programmable tunable miniature waveguide filter. The waveguide can be a ridged waveguide having a slow-wave configuration that includes a plurality of conductive ridge portions. The slow-wave configuration of a waveguide, including the plurality of conductive ridge portions, is described in detail in U.S. Pat. No. 7,023,302 to Peterson, et al., which is herein incorporated in its entirety by reference. At least some of the plurality of conductive ridge portions can include a plurality of switches. The plurality of switches for a given one of the plurality of conductive ridge portions can be activated to conductively couple the conductive ridge portion to a respective plurality of conductive shunts. The conductive shunts can be coupled to a conductive outer surface of the waveguide. The coupling of a given conductive ridge portion to one or more of the conductive shunts can affect the resonant coupling of a wave signal propagating through the waveguide. Therefore, by selecting specific conductive ridge portions and a number of switches to be activated to couple the specific conductive ridge portions to the conductive shunts, one or more resonator poles for specific frequencies can be formed on the waveguide. The one or more resonator poles can thus define a frequency pass-band for the μm- and/or mm wave signal propagating through the waveguide. 
         [0017]      FIG. 1  illustrates an example of a wave signal receive and/or transmit system  10  in accordance with an aspect of the invention. The wave signal receive and/or transmit system  10  could be implemented on a satellite, or any of a variety of other μm and/or mm-wave devices configured to transmit and receive wave signals, such as μm and/or mm-wave signals. The wave signal receive and/or transmit system  10  includes an antenna  12  configured to transmit and receive the signals. The signals could include μm and/or mm-wave signals in a frequency range of, for example, approximately 3 GHz to approximately 900 GHz. 
         [0018]    Signals that are received at the antenna  12  are input to a tunable filter waveguide  14 . The tunable filter waveguide  14  can be a slow-wave ridged waveguide that is configured as a programmable band-pass filter the received signal. The tunable filter waveguide  14  provides the band-pass filtered wave signal to a frequency converter  16  that is configured to downconvert the wave signal to a baseband signal, from which the baseband signal is provided to a digitizer  18 . The digitizer  18  is configured to convert the baseband signal into digitized spectral content, such that the signal can be provided to a controller or any of a variety of additional hardware for which the spectral content of the signal is intended. For example, the spectral content of the signal could include control instructions or could be data intended for re-transmission. 
         [0019]    The tunable filter waveguide  14  can be configured as a slow-wave waveguide element that is interposed between a first transmission medium  20  and a second transmission medium  22 . As an example, the first transmission medium  20  and the second transmission medium  22  can include any of a variety of different types of waveguides, such as a miocrostrip-line, coplanar strip-line, suspended strip-line, strip-line waveguide, rectangular waveguide, or ridged waveguide. As is explained in greater detail below, the tunable filter waveguide  14  can be programmable configured to include one or more resonator poles that define a given frequency pass-band for the received wave signal. As such, the wave signal receive and/or transmit system  10  includes a tunable filter controller  24  that is configured to control the frequency pass-band of the tunable filter waveguide  14 . 
         [0020]    As an example, the tunable filter waveguide  14  can include a plurality of switches that are activated to conductively couple two or more conductive ridge portions of the slow-wave waveguide element of the tunable filter waveguide  14  to an outside conductive surface of the tunable filter waveguide  14 . Each of the plurality of switches can be implemented as rapid switching field effect transistors, such as switches in a monolithic microwave integrated circuit (MMIC). The tunable filter controller  24  can control the state of each of the switches. As such, by conductively coupling the two or more conductive ridge portions to the outside conductive surface, a resonant coupling associated with the given two or more conductive ridge portions of the tunable filter waveguide  14  can be decreased with respect to the signal propagating through the tunable filter waveguide  14 . The two or more conductive ridge portions that are selected to be coupled to the outside surface can be predetermined to generate one or more resonator poles associated with one or more respective frequencies within a desired frequency pass-band. 
         [0021]    The tunable filter controller  24  can also control the number of switches per conductive ridge portion that are activated to selectively control the amount of resonant coupling of each of the resonator poles. For example, the tunable filter controller  24  can activate more switches for a given conductive ridge portion to increase the conductive coupling of the given conductive ridge portion to the outside conductive surface, thus decreasing the amount of resonant coupling of the associated resonator poles formed by the given conductive ridge portion. Conversely, the tunable filter controller  24  can activate less switches for a given conductive ridge portion to decrease the conductive coupling of the given conductive ridge portion to the outside conductive surface, thus increasing the amount of resonant coupling of the associated resonator poles formed by the given conductive ridge portion. The tunable filter controller  24  can also control the switches to adjust the input and output impedances of the tunable filter waveguide  14 , such that the input and output impedances of the tunable filter waveguide  14  can be substantially matched to the first transmission medium  20  and the second transmission medium  22 , respectively. Furthermore, the tunable filter controller  24  can be configured to switch between several different switching configurations, such that the tunable filter waveguide  14  can be configured to switch between several different predetermined frequency pass-bands based on commands received from the tunable filter controller  24 . 
         [0022]    By controlling the switches of the tunable filter waveguide  14  to form resonator poles that define a frequency pass-band, the tunable filter waveguide  14  is thus programmable configured as a bandpass filter. However, the configuration of the resonator poles formed on the tunable filter waveguide  14  can also result in the passing of harmonic frequencies of the frequency pass-band of the signal. Therefore, the tunable filter waveguide  14  can also be configured to include a plurality of ridge coupling switches. The ridge coupling switches can be controlled by the tunable filter controller  24  to conductively couple adjacent conductive ridge portions of the tunable filter waveguide  14  together to simulate a non-slow-wave ridged waveguide portion. One or more of the simulated non-slow-wave ridged waveguide portions can be interleaved with the slow-wave waveguide structure, such that the one or more simulated non-slow-wave ridged waveguide portions form a low-pass filter. Therefore, harmonic frequencies of the frequency pass-band can be filtered from the signal propagating through the tunable filter waveguide  14 . 
         [0023]    As is demonstrated in the example of  FIG. 1 , the tunable filter waveguide  14  can be programmed by the tunable filter controller  24  to filter any of a variety of frequency pass-bands of the received or transmitted signal. Therefore, a single one of the tunable filter waveguide  14  can be used to replace bulky and expensive sets of channelized filter banks that would be necessary to accomplish filtering of similar frequency pass-band ranges. Because the tunable filter waveguide  14  may occupy little more space than a typical single filter in a filter bank, the available space on a satellite or other structure that implements the wave signal receive and/or transmit system  10  can be greatly increased. In addition, because the signal does not propagate through physical switches, such as can be implemented in typical channelized filter banks, the signal is not subject to switching losses by being switched between different channelized filter banks. Accordingly, the signal power can be improved by approximately 10 dB over that of traditional channelized filter bank implementations. Also, because the switches can be implemented as rapid switching MMIC switches, the tunable filter waveguide  14  can be switched between different frequency pass-bands without substantially affecting acquisition time. Furthermore, since the plurality of switches are distributed in the programmable waveguide filter structure, the power handling requirements on any individual switch is substantially reduced. 
         [0024]    It is to be understood that the wave signal receive and/or transmit system  10  is not intended to be limited to the example of  FIG. 1 . Specifically, the example of  FIG. 1  demonstrates a very simplified example of a wave transmit and/or receive system, such that the wave signal receive and/or transmit system  10  can include any of a variety of additional components that have been omitted for the sake of simplicity and ease of explanation. In addition, it is to be understood that the components of the wave signal receive and/or transmit system  10  are not intended to be limited solely to received signals, as described above, but that the components of the wave signal receive and/or transmit system  10 , including the tunable filter waveguide  14  and tunable filter controller  24 , can be implemented for transmitted signals, as well. 
         [0025]      FIG. 2  illustrates an example of an exploded view of a programmable tunable filter waveguide  50  in accordance with an aspect of the invention. The programmable tunable filter waveguide  50  can be substantially similar to the tunable filter waveguide  14  in the example of  FIG. 1 . Therefore, reference is to be made to the example of  FIG. 1  in the discussion of the example of  FIG. 2 . The programmable tunable filter waveguide  50  can be fabricated in any of a variety of manners, such as through a micromachined etching process. Therefore, the components of the programmable tunable filter waveguide  50  can be formed from a substrate, such as silicon, that can be plated with a conductive material, such as gold. 
         [0026]    The programmable tunable filter waveguide  50  includes a conductive straight ridged waveguide structure  52 . The conductive straight ridged waveguide structure  52  includes a pair of conductive sidewalls  54  and a conductive top portion  56 . The conductive sidewalls  54  and the conductive top portion  56  define a hollow channel along the longitudinal length of the programmable tunable filter waveguide  50 . The programmable tunable filter waveguide  50  also includes a plurality of conductive ridge portions  58 . The conductive ridge portions  58  can be formed integral with the conductive top portion  56  and perpendicular with the conductive sidewalls  54 , and can extend along the entire length of the programmable tunable filter waveguide  50 . Thus, the conductive ridge portions  58  can be arranged such that a hollow recess is formed in-between each of conductive ridge portions  58 . Accordingly, the conductive ridge portions  58  form a slow-wave structure in the conductive straight ridged waveguide structure  52 . 
         [0027]    The programmable tunable filter waveguide  50  also includes a plurality of switches  60  coupled to a plurality of conductive shunts  62 . The switches  60  and the conductive shunts  62  can be formed in an integral layer that is coupled to a bottom surface of the conductive ridge portions  58 , such that the switches  60  can be implemented as MMIC switches. In addition, each of the conductive shunts  62  can be conductively coupled to a conductive bottom surface  64  of the programmable tunable filter waveguide  50 , which could also be formed integral with the switches  60  and the conductive shunts  62 . The switches  60  and the conductive shunts  62  can be configured in rows, such that each row corresponds to a given one of the conductive ridge portions  58 , with each of the switches  60  in a given row being coupled to one of the conductive ridge portions  58 . Therefore, a given switch can be activated to conductively couple a given one of the conductive ridge portions  58  to a respective one of the conductive shunts  62 . It is to be understood that the programmable tunable filter waveguide  50  could be configured such that not all of the conductive ridge portions  58  are coupled to switches  60 . For example, some of the conductive ridge portions  58  may not ever be coupled to the conductive bottom surface  64  depending on the desired frequencies within the frequency pass-band, as described in greater detail below. 
         [0028]    As an example, each of the conductive ridge portions  58  can be coupled to a group of, for example, between four and eight switches  60 , demonstrated as seven in the example of  FIG. 2 , with each of the switches  60  being coupled to a respective one of the conductive shunts  62 . The conductive shunts  62  in each of the rows can be arranged in the hollow recesses between the conductive ridge portions  58 , such that the conductive ridge portions  58  can be conductively coupled to the conductive shunts  62  through a lateral conductive via (not shown), as demonstrated in more detail in the example of  FIG. 3  below. Therefore, parasitic effects associated with the conductive shunts  62  that could provide interference on the signal propagating through the programmable tunable filter waveguide  50  can be substantially reduced. As a result of the arrangement of the switches  60  and the conductive shunts  62 , the tunable filter controller  24  can control the activation state of each of the switches  60  separately to conductively couple one or more of the conductive ridge portions  58  to the conductive bottom surface  64  via one or more of the switches  60  and conductive shunts  62  in a respective one or more of the rows. 
         [0029]    As described above, two or more of the conductive ridge portions  58  can be selected to be coupled to the conductive bottom surface  64  to generate one or resonator poles associated with one or more respective frequencies within a desired frequency pass-band. For example, a resonator pole for a frequency having an associated wavelength λ can be formed by coupling two of the conductive ridge portions  58  that are separated relative to each other by a length of approximately λ/2 to the conductive bottom surface  64 . Based on the number of the switches  60  that are activated to couple the respective two or more of the conductive ridge portions  58  to the conductive bottom surface  64 , the amount of resonant coupling of the signal to the resonator poles can be controlled. For example, the more switches  60  that are activated for a given conductive ridge portion  58 , the more the conductive coupling of the given conductive ridge portion  58  to the conductive bottom surface  64  is increased, and thus the more the resonant coupling of the associated resonator poles formed by the given conductive ridge portion  58  is decreased. In addition, as also described above, the switches  60  can also be controlled to adjust the input and output impedances of the programmable tunable filter waveguide  50 , such that the input and output impedances of the programmable tunable filter waveguide  50  can be substantially matched to the transmission mediums that are coupled to both ends of the programmable tunable filter waveguide  50 . 
         [0030]      FIG. 3  illustrates an example of a schematic representation of a portion of a programmable tunable filter waveguide  100  in accordance with an aspect of the invention. The portion of the programmable tunable filter waveguide  100  can be substantially similar to the programmable tunable filter waveguide  50  in the example of  FIG. 2 . Therefore, reference is to be made to the example of  FIG. 2  in the discussion of the example of  FIG. 3 . 
         [0031]    The portion of the programmable tunable filter waveguide  100  demonstrates a first conductive ridge portion  102 , a second conductive ridge portion  104 , and a third conductive ridge portion  106  arranged perpendicular between a first conductive sidewall  108  and a second conductive sidewall  110 . The portion of the programmable tunable filter waveguide  100  also includes a first plurality of switches  112  that are each configured to conductively couple the first conductive ridge portion  102  to a respective one of a first plurality of conductive shunts  114 . The portion of the programmable tunable filter waveguide  100  further includes a second plurality of switches  116  that are each configured to conductively couple the second conductive ridge portion  102  to a respective one of a second plurality of conductive shunts  118 . The first conductive ridge portion  102  is coupled to the switches  112  through conductive compressible stud bumps  120 , which could be fabricated from gold. Similarly, the second conductive ridge portion  104  is coupled to the switches  116  through conductive compressible stud bumps  122 . The conductive shunts  114  are fabricated in a hollow recess formed between the first conductive ridge portion  102  and the second conductive ridge portion  104 , and the conductive shunts  118  are fabricated in a hollow recess formed between the second conductive ridge portion  104  and the third conductive ridge portion  106 . Therefore, parasitic effects associated with the conductive shunts  114  and  118  that could provide interference on the signal propagating through the programmable tunable filter waveguide in which the portion  100  is included can be substantially reduced. 
         [0032]    Similar to as described above, the activation state of each of the switches  112  can be separately controlled to conductively couple the first conductive ridge portion  102  to a conductive outer surface, such as the conductive bottom surface  64  in the example of  FIG. 2 , via the lateral conductive coupling of the compressible stud bumps  120  to the conductive shunts  114 . The amount of conductive coupling, and thus the inversely proportional resonant coupling of a signal to one or more resonator poles formed by the coupling of the conductive ridge portion  102  to the conductive shunts  114 , can be controlled based on the number of the switches that are activated. For example, the greater the number of the switches  112  that are activated, the greater the conductive coupling of the first conductive ridge portion  102  to the conductive outer surface, and thus the less the resonant coupling of the associated resonator poles formed by the coupling of the first conductive ridge portion  102 . In addition, because the energy of a given signal is greatest along a central axis of a slow-wave ridged waveguide, the switches  112  that are nearest the center of the first conductive ridge portion  102  have the greatest effect on the resonant coupling. Thus, the amount of conductive coupling, and thus also resonant coupling, can be controlled based on the location of the switches  112  that are activated to couple the first conductive ridge portion  102  to the conductive shunts  114 . In a like manner, the activation state of each of the switches  116  can be separately controlled to conductively couple the second conductive ridge portion  104  to a conductive outer surface via the lateral conductive coupling of the compressible stud bumps  122  to the conductive shunts  118 , such that conductive and resonant coupling of the second conductive ridge portion  104  can also be controlled. 
         [0033]    In addition to the switches  112  and  116 , the portion of the programmable tunable filter waveguide  100  demonstrates a first plurality of ridge connection switches  124  configured to conductively couple the compressible stud bumps  120  and the compressible stud bumps  122 . Thus, the first ridge connection switches  124  are configured to conductively couple the adjacent first conductive ridge portion  102  and second conductive ridge portion  104 . Likewise, the portion of the programmable tunable filter waveguide  100  demonstrates a second plurality of ridge connection switches  126  configured to conductively couple the compressible stud bumps  122  and a plurality of compressible stud bumps  128  that are included in the conductive ridge portion  106 . Thus, the second ridge connection switches  126  are configured to conductively couple the adjacent second conductive ridge portion  104  and third conductive ridge portion  106 . As described in greater detail below, by conductively coupling adjacent conductive ridge portions, the physical slow-wave waveguide structure can be reconfigured to simulate a non-slow-wave ridged waveguide structure. One or more simulated non-slow-wave ridged waveguide portions that are interleaved with slow-wave waveguide portions of a given programmable tunable filter waveguide can thus be configured as a series-connected low-pass filter. Therefore, undesired harmonic frequencies associated with the desired frequency pass-band can be filtered from the signal. The number of the ridge connection switches  124  or  126  that are activated at an end of a series of coupled adjacent conductive ridge portions can adjust the length of the simulated non-slow-wave ridged waveguide structure. 
         [0034]      FIG. 4  illustrates an example of a first configuration  150 , a second configuration  152 , and a third configuration  154  of a programmable tunable filter waveguide  151  in accordance with an aspect of the invention. The programmable tunable filter waveguide  151  of which the first configuration  150 , the second configuration  152 , and the third configuration  154  represent can be substantially similar to the programmable tunable filter waveguide  50  in the example of  FIG. 2 . Therefore, reference is to be made to the example of  FIG. 2  in the discussion of the example of  FIG. 4 . 
         [0035]    The first configuration  150  of the programmable tunable filter waveguide  151  includes a first conductive ridge portion  156  at a first end  157  of the programmable tunable filter waveguide  151  and a second conductive ridge portion  158  at a second end  159  of the programmable tunable filter waveguide  151 . Each of the first conductive ridge portion  156  and the second conductive ridge portion  158  have a single switch activated. It is to be understood that, in the example of  FIG. 4 , an activated switch is demonstrated as a solid black circle, and a deactivated switch is demonstrated as an open circle. Thus, both the first conductive ridge portion  156  and the second conductive ridge portion  158  may be weakly conductively coupled to a conductive outer surface, such as the conductive bottom surface  64  in the example of  FIG. 2 , and thus very strongly resonantly coupled. The single switch coupling of the first conductive ridge portion  156  and the second conductive ridge portion  158  may be implemented to substantially match an impedance of the first end  157  and the second end  159 , respectively, of the programmable tunable filter waveguide  151  to respective connected transmission media. 
         [0036]    The first configuration  150  of the programmable tunable filter waveguide  151  also includes a third conductive ridge portion  160  having two switches activated and a fourth conductive ridge portion  162  having four switches activated. Thus, the third conductive ridge portion  160  is more strongly conductively coupled than the first conductive ridge portion  156 , and the fourth conductive ridge portion  162  is more strongly conductively coupled than the third conductive ridge portion  160 . The third conductive ridge portion  160  and the fourth conductive ridge portion  162  are separated by a length of approximately λ 1 /2. Therefore, the third conductive ridge portion  160  and the fourth conductive ridge portion  162  form a resonator pole  164  for a frequency having a corresponding wavelength of approximately λ 1 . 
         [0037]    The first configuration  150  of the programmable tunable filter waveguide also includes a fifth conductive ridge portion  166  and a sixth conductive ridge portion  168  each having six switches activated. Thus, the fifth and sixth conductive ridge portions  166  and  168  are the most strongly conductively coupled of the conductive ridge portions, and thus also the least resonantly coupled. The fourth conductive ridge portion  162  and the fifth conductive ridge portion  166  are separated by a length of approximately λ 2 /2. Likewise, the fifth conductive ridge portion  166  and the sixth conductive ridge portion  168  are separated by a length of approximately λ 3 /2. Therefore, the fourth and fifth conductive ridge portions  162  and  166  form a resonator pole  170  for a frequency having a corresponding wavelength of approximately λ 2 , and the fifth and sixth conductive ridge portions  166  and  168  form a resonator pole  172  for a frequency having a corresponding wavelength of approximately λ 3 . Accordingly, the first configuration  150  of the programmable tunable filter waveguide has a frequency pass-band for a signal that is defined by the series connection of the three resonator poles  164 ,  170 , and  172 . 
         [0038]    As described above, the conductive ridge portion  168  is highly conductively coupled. As a result, the high conductive coupling at the conductive ridge portion  168  has a substantial effect on the impedance of the programmable tunable filter waveguide  151 . Therefore, additional switches for additional conductive ridge portions may be activated to further affect the impedance of the programmable tunable filter waveguide  151 , such that the impedance at the first end  157  can be substantially balanced relative to the second end  159 . Therefore, the first configuration  150  of the programmable tunable filter waveguide  151  includes a seventh conductive ridge portion  174  having four switches activated and an eighth conductive ridge portion  176  having two switches activated. 
         [0039]    The sixth conductive ridge portion  168  and the seventh conductive ridge portion  174  are separated by a length of approximately λ 2 /2, and the seventh conductive ridge portion  174  and the eighth conductive ridge portion  176  are separated by a length of approximately λ 1 /2. The separation of the sixth conductive ridge portion  168  and the seventh conductive ridge portion  174  is therefore approximately the same as the separation of the fourth conductive ridge portion  162  and the fifth conductive ridge portion  166 . Therefore, the resonator pole  170  includes two portions that are symmetrical about the resonator pole  172 , with each of the portions having resonant couplings that are also symmetrical about the resonator pole  172 . Similarly, the resonator pole  164  likewise has two symmetrical portions with respect to spacing and resonant coupling about the resonator pole  172  based on the spacing between the seventh conductive ridge portion  174  and the eighth conductive ridge portion  176 . Therefore, the impedance at each of the first end  157  and the second end  159  of the programmable tunable filter waveguide  151  is balanced with respect to each other, and can thus be matched to associated coupled transmission media. In addition, because the resonant coupling is substantially greater at each of the first end  157  and the second end  159 , signal nodes of the signal in the desired frequency pass-band defined by the resonator poles  164 ,  170 , and  172  are more closely coupled to the first end  157  and the second end  159 . Accordingly, the first configuration  150  can result in a substantially effective out-of-band frequency rejection of the signal. Furthermore, because the portions of the resonator poles  164  and  170  are symmetrical with respect to length, the desired frequency pass-band is substantially unaffected as the signal is affected by each portion of the resonator poles  164  and  170  substantially the same. 
         [0040]    The second configuration  152  of the programmable tunable filter waveguide  151  is substantially the same as the first configuration  150  with regard to conductive and resonant coupling. However, the second configuration  152  includes a resonator pole  178  having two portions, each separated by a length of λ 4 /2, a resonator pole  180  having two portions, each separated by a length of λ 5 /2, and a resonator pole  182  separated by a length of λ 6 /2. The lengths λ 4 , λ 5 , and λ 6  are wavelengths corresponding to frequencies in a desired frequency pass-band that is defined by the resonator poles  178 ,  180 , and  182 . The resonator poles  178 ,  180 , and  182  are each demonstrated in the example of  FIG. 4  as having a substantially shorter length than the resonator poles  164 ,  170 , and  172  of the first configuration  150 , and thus correspond to shorter wavelengths of correspondingly higher frequencies. Therefore, the frequency pass-band of the second configuration  152  can be substantially greater than the frequency pass-band defined by the first configuration  150 . 
         [0041]    In a similar manner, the third configuration  154  of the programmable tunable filter waveguide  151  includes a resonator pole  184  having two portions, each separated by a length of λ 7 /2, a resonator pole  186  having two portions, each separated by a length of λ 8 /2, and a resonator pole  186  separated by a length of λ 9 /2. The resonator poles  184 ,  186 , and  188  are each demonstrated in the example of  FIG. 4  as having a substantially shorter length than the resonator poles  178 ,  180 , and  182  of the second configuration  152 , and thus correspond to shorter wavelengths of correspondingly higher frequencies. Therefore, the frequency pass-band of the third configuration  154  can be substantially greater than the frequency pass-band defined by the second configuration  152 . 
         [0042]    It is to be understood that, in the example of  FIG. 4 , the distances λ X /2 are intended to be drawn loosely to scale relative to each other. However, it is also to be understood that each of the resonator poles that have different wavelength variables are intended to have different wavelengths for the purpose of the discussion of the example of  FIG. 4 . Therefore, the resonator poles  164 ,  170 ,  172 ,  178 ,  180 ,  182 ,  184 ,  186 , and  188  are not intended to be limited to the wavelengths depicted in the example of  FIG. 4 , and are not intended to be of the same wavelength relative to each other. 
         [0043]      FIG. 5  illustrates an example of a frequency response graph  200  of the first configuration  150 , the second configuration  152 , and the third configuration  154  of the programmable tunable filter waveguide  151  of the example of  FIG. 4  in accordance with an aspect of the invention. The frequency response graph  200  includes a first curve  202  that corresponds to the first configuration  150 , a second curve  204  that corresponds to the second configuration  152 , and a third curve  206  that corresponds to the third configuration  154 . In the example of  FIG. 5 , the first curve  202  demonstrates a frequency pass-band between approximately 17.5 GHz and 19.5 GHz, the second curve  204  demonstrates a frequency pass-band between approximately 21.5 GHz and 23.5 GHz, and the third curve  206  demonstrates a frequency pass-band between approximately 25.5 GHz and 27.5 GHz. Thus, as described above in the example of  FIG. 4 , the third configuration  154  of the programmable tunable filter waveguide  151  is configured with a substantially greater frequency pass-band than the second configuration  152 , which is configured with a substantially greater frequency pass-band than the first configuration  150 . 
         [0044]    In addition, as also described above in the example of  FIG. 4 , each of the configurations  150 ,  152 , and  154  are configured with high resonant coupling at each end of the programmable tunable filter waveguide  151 . Therefore, each of the configurations  150 ,  152 , and  154  can result in a substantially effective out-of-band frequency rejection of the signal, as demonstrated by the sharp out-of-band power loss of each of the curves  202 ,  204 , and  206  in the example of  FIG. 5 . Adjustments to the resonant coupling of the programmable tunable filter waveguide  151  can be made based on the switch configuration to change the out-of-band slope of the curves  202 ,  204 , and  206 . In addition, although the example of  FIG. 5  demonstrates substantially no losses in the frequency pass-band of each of the curves  202 ,  204 , and  206 , it is to be understood that the frequency pass-band could be subject to loss based on insertion losses and/or the configuration of the switches. Furthermore, it is to be understood that the programmable tunable filter waveguide  151  is not limited to the configurations  150 ,  152 , and  154  in the example of  FIG. 4 , but can include more or less poles than three, each with different amounts of resonant coupling. Accordingly, the programmable tunable filter waveguide  151  can be configured in any of a variety of ways. 
         [0045]      FIG. 6  illustrates an example of a configuration  250  of a programmable tunable filter waveguide  252  in accordance with an aspect of the invention. The programmable tunable filter waveguide  151  of which the configuration  250  represents can be substantially similar to the portion of the programmable tunable filter waveguide  100  in the example of  FIG. 3 . Therefore, reference is to be made to the example of  FIG. 3  in the discussion of the example of  FIG. 6 . 
         [0046]    The configuration  250  of the programmable tunable filter waveguide  252  includes a slow-wave waveguide portion  253 . The slow-wave waveguide portion  253  includes a plurality of conductive ridge portions  254  that include activated switches, as demonstrated similar to the example of  FIG. 4 , for coupling the conductive ridge portions  254  to respective conductive shunts (not shown). Therefore, the conductive ridge portions  254  are conductively coupled to a conductive outer surface, such as the conductive bottom surface  64  in the example of  FIG. 2 . Similar to as described above, the conductive ridge portions  254  are conductively coupled to the conductive outer surface to form one or more resonator poles defining a frequency pass-band, with the number of activated switches for each of the conductive ridge portions  254  being determinative of the amount of resonant coupling for the signal propagating through the programmable tunable filter waveguide  252 . 
         [0047]    The configuration  250  of the programmable tunable filter waveguide  252  also includes a first plurality of conductive ridge portions  256  that are conductively coupled together via a plurality of ridge connection switches, demonstrated in the example of  FIG. 6  as solid lines connecting open circles. By conductively coupling the first group of adjacent conductive ridge portions  256  together, the physical slow-wave waveguide structure of the programmable tunable filter waveguide  252  can be reconfigured to simulate a non-slow-wave ridged waveguide portion  258 . The length of the simulated non-slow-wave ridged waveguide portion  258  can be controlled not only by the number of the first group of adjacent conductive ridge portions  256  that are coupled together, but also by the number of the ridge connection switches used to couple a set of adjacent conductive ridge portions  256  together. Specifically, in the example of  FIG. 6 , conductive ridge portions  260  are demonstrated as coupled to an adjacent conductive ridge portion  256  via only four ridge connection switches, as opposed to all of them. As such, the length of the simulated non-slow-wave ridged waveguide portion  258  may not be limited to just digital lengths between adjacent coupled conductive ridge portions  256 . Instead, by activating less than all of the ridge connection switches to interconnect adjacent conductive ridge portions  256 , a length that is a fraction of the length between the adjacent conductive ridge portions can be included in the total length of the simulated non-slow-wave ridged waveguide portion  258 . 
         [0048]    The configuration  250  of the programmable tunable filter waveguide  252  also includes a second simulated non-slow-wave ridged waveguide portion  262  which is configured substantially the same as the non-slow-wave ridged waveguide portion  258 . The simulated non-slow-wave ridged waveguide portions  258  and  262  are thus interleaved with the slow-wave waveguide portion  253 . The programmable tunable filter waveguide  252  can thus include alternating sections of simulated non-slow-wave ridged waveguide portions, such as the simulated non-slow-wave ridged waveguide portions  258  and  262 , and slow-wave waveguide portions, such as the slow-wave waveguide portion  253 . 
         [0049]      FIG. 7  illustrates a first diagrammatic example  300  and a second diagrammatic example  302  of a programmable tunable filter waveguide  303 , which can be configured substantially similar to the programmable tunable filter waveguide  252  in the example of  FIG. 6 , in accordance with an aspect of the invention. It is to be understood that, although it is not depicted in the example of  FIG. 7 , the programmable tunable filter waveguide  303  may also include a conductive straight ridged waveguide structure having a pair of conductive sidewalls and a conductive top portion, such as described above in the example of  FIG. 2 . 
         [0050]    Each of the first diagrammatic example  300  and the second diagrammatic example  302  demonstrate a first slow-wave waveguide portion  304 , a second slow-wave waveguide portion  306 , and a third slow-wave waveguide portion  308 . Each of the slow-wave waveguide portions  304 ,  306 , and  308  can include conductive ridge portions that are coupled to a conductive outer surface of the programmable tunable filter waveguide  303 , thus generating one or more resonator poles for a signal propagating through the programmable tunable filter waveguide  303 . In addition, each of the slow-wave waveguide portions  304 ,  306 , and  308  can have arrangements of resonator poles that differ relative to each other. 
         [0051]    The first diagrammatic example  300  also demonstrates a first simulated non-slow-wave ridged waveguide portion  310  and a second simulated non-slow-wave ridged waveguide portion  312 , demonstrated in the example of  FIG. 7  as dashed lines to depict the conductive ridge portions that are conductively coupled to each other. Similar to as described above regarding the example of  FIG. 6 , the simulated non-slow-wave ridged waveguide portions  310  and  312  are thus interleaved with the slow-wave waveguide portions  304 ,  306 , and  308 . Because the coupling of adjacent conductive ridge portions simulates a non-slow-wave ridged waveguide portion, the second diagrammatic portion  302  of the programmable tunable filter waveguide  304  demonstrates a physical representation of the first diagrammatic example  300  of the programmable tunable filter waveguide  304 . Specifically, the second diagrammatic example  302  demonstrates actual non-slow-wave ridged waveguide portions  314  in place of the simulated non-slow-wave ridged waveguide portions  310  and  312 . Thus, the example of  FIG. 7  demonstrates the effect of coupling adjacent conductive ridge portions together, as it would affect the signal propagating through the programmable tunable filter waveguide  303 . 
         [0052]    The interleaving of simulated non-slow-wave ridged waveguide portions, such as the non-slow-wave ridged waveguide portions  258  and  262  in the example of  FIG. 6 , with slow-wave waveguide portions, such as the slow-wave waveguide portion  253  in the example of  FIG. 6 , forms a low-pass filter that is connected in series with the resonator poles of the slow-wave waveguide portions. As a result, the low-pass filter is configured to remove undesired harmonic frequencies associated with the desired frequency pass-band from the signal. Specifically, because the high frequency harmonic components cannot effectively propagate through the simulated slow-wave ridged waveguide portions, the high-frequency harmonic components are prevented from propagating through the programmable tunable waveguide filter. Therefore, only the desired frequency pass-band can pass through the programmable tunable filter waveguide. 
         [0053]    In view of the foregoing structural and functional features described above, methodologies in accordance with various aspects of the present invention will be better appreciated with reference to  FIG. 8 . While, for purposes of simplicity of explanation, the methodology of  FIG. 8  is shown and described as executing serially, it is to be understood and appreciated that the present invention is not limited by the illustrated order, as some aspects could, in accordance with the present invention, occur in different orders and/or concurrently with other aspects from that shown and described herein. Moreover, not all illustrated features may be required to implement a methodology in accordance with an aspect the present invention. 
         [0054]      FIG. 8  illustrates an example of a method  350  for filtering signals in accordance with an aspect of the invention. As an example, the signals can be micrometer and/or millimeter wave signals. At  352 , a desired frequency pass-band for a signal is determined. The desired frequency pass-band can correspond to a frequency pass-band that is normally implemented in a typical channelized filter bank. At  354 , at least one pair of conductive ridge portions of a slow-wave waveguide structure is selected based on a wavelength of a frequency within the desired frequency pass-band. The selected at least one pair of conductive ridge portions can be separated by a length of λ/2, where λ is a wavelength of the frequency within the desired frequency pass-band. 
         [0055]    At  356 , a plurality of switches are activated to conductively couple the selected at least one pair of conductive ridge portions to a conductive outer surface of the waveguide structure. The conductive outer surface can be a conductive bottom surface of the waveguide structure. The at least one pair of conductive ridge portions that are conductively coupled to the outer surface can form a respective at least one resonator pole of a frequency that is within the desired frequency pass-band. An amount of resonant coupling of the at least one resonator pole can be controlled by the number of switches that are activated to couple each of the conductive ridge portions to the conductive outer surface. 
         [0056]    What has been described above includes exemplary implementations of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications, and variations that fall within the scope of the appended claims.