Abstract:
A power combining array and method of increasing performance in a power combining array includes a waveguide enclosure having a plurality of slotline modules disposed therein. The slotline modules include input and output antennas that have varying physical characteristics to overcome differences in field intensity across the slotline module configuration and to account for phase changes. The varying physical characteristics include differences in longitudinal position, thickness, dielectric constant, and circuit element configurations. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or the meaning of the claims.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to the provisional patent application having Ser. No. 60/660,029 filed on Mar. 8, 2005, which is hereby incorporated by reference in its entirety as if fully set forth herein. 

   FIELD OF THE INVENTION 
   The present invention generally relates to amplification, generation, and control of microwave signals. Specifically, the present invention relates to increasing performance of spatially-combined arrays for microwave signals used in telecommunications and radar/imaging systems. 
   BACKGROUND OF THE INVENTION 
   Transmission line-to-waveguide transitions are used extensively in microwave communications systems such as radar and satellite systems. The systems may include a waveguide antenna for phased array applications or a conventional waveguide of arbitrary cross-section. In these systems the microwave signal may be bi-directionally coupled between a waveguide and a transmission line with minimal power (insertion) loss and maximum signal clarity. 
   One example of a known waveguide-based spatially combined amplifier is shown in  FIG. 1(   a ). Microwave power is incident from the waveguide structure on the left. This energy illuminates a two-dimensional array of several slotline modules, with each slotline module forming a column of the array. Each slotline module consists of a dielectric card, upon which at least two circuit elements are mounted. The input energy is coupled to these circuit elements through an antenna which tapers to a slotline transmission line. Structures transform the microwave energy from the slotline mode to a microstrip mode, with the microstrip conductor printed on the side of the card opposite to the slotline. Energy on the microstrip is coupled to the input of the circuit elements. The outputs of the circuit elements are coupled to the waveguide in a similar manner. 
   Another known waveguide-based spatially combined amplifier is shown in  FIG. 1(   b ). In  FIG. 1(   b ), microwave power is incident from the coaxial waveguide structure on the left. This energy illuminates a two-dimensional annular array of several slotline modules, with each slotline module forming a radial column of the array. Each slotline module consists of a dielectric card, upon which at least two circuit elements are mounted. The input energy is coupled to these circuit elements through an antenna which tapers to a slotline transmission line. Structures transform the microwave energy from the slotline mode to a microstrip mode, with the microstrip conductor printed on the side of the card opposite to the slotline. Energy on the microstrip is coupled to the input of the circuit elements. The outputs of the circuit elements are coupled to the output coaxial waveguide in a similar manner. 
   The use of the word slotline is intended to include any and all of the family of balanced microwave transmission line structures where the signal power is concentrated in a gap between two substantially symmetric conductors printed on one or both sides of a dielectric substrate. Common terms for these transmission line structures include slotline, finline, antipodal finline, unilateral finline, bilateral finline, and insulated finline. The use of the term “slotline” in this application is therefore intended to be consistent with standard terminology widely known in the art. 
   In existing rectangular waveguide spatial power combiner configurations such as that of  FIG. 1(   a ), the field intensity in the rectangular waveguide follows a sinusoidal distribution, with the result that the slotline modules in the center of the structure receive more power than the slotline modules along the edge. Similarly, the outputs of the central modules couple to the waveguide more effectively than the edge modules. This imbalance in the signal amplitude reduces the power-combining efficiency of the entire array. 
   SUMMARY OF THE INVENTION 
   In one embodiment, the present invention provides a power combiner apparatus comprising a waveguide enclosure defined on an input side by an input waveguide section supporting an input field, and on an output side by an output waveguide section supporting an output field. The power combining apparatus includes an array of slotline modules disposed within the waveguide enclosure between the input waveguide section and the output waveguide section along an H-direction defined as a direction perpendicular to both a direction of propagation and a direction of an electric field in a fundamental mode supported by the waveguide enclosure, each slotline module in the array of slotline modules including a circuit element having an input portion and an output portion, an input slotline antenna disposed between the input waveguide section and the input portion of the circuit element, and an output slotline antenna disposed between the output waveguide section and the output portion of the circuit element. Different slotline modules within the array of slotline modules are configured to have varying characteristics according to a position of each slotline module in the array of slotline modules within the waveguide enclosure to cause a signal amplitude balance among the slotline modules to substantially follow a specified amplitude contour. 
   The present invention also includes a method of increasing performance in a power combining array comprising applying a microwave signal to a waveguide enclosure having a plurality of slotline modules positioned therein, each slotline module having at least one pair of slotline antennas, wherein a field intensity of the microwave signal applied to the waveguide enclosure is stronger at a center of the waveguide enclosure and weaker at edges of the waveguide enclosure, and varying characteristics of the slotline modules to cause an amplitude balance among the slotline modules to substantially match a specified amplitude contour through each slotline module. 
   In another embodiment, the present invention provides a power combiner apparatus comprising a waveguide enclosure defined on an input side by an input waveguide section supporting an input field, and on an output side by an output waveguide section supporting an output field. The power combining apparatus includes an array of slotline modules disposed within the waveguide enclosure between the input waveguide section and the output waveguide section along an H-direction defined as a direction perpendicular to both a direction of propagation, defined as the longitudinal direction, and a direction of an electric field in a fundamental mode supported by the waveguide enclosure, defined as the E-direction, each slotline module in the array of slotline modules including a circuit element having an input portion and an output portion, and a pair of slotline antennas including an input slotline antenna disposed between the input waveguide section and the input portion of the circuit element, and an output slotline antenna disposed between the output waveguide section and the output portion of the circuit element. At least one of the input antennas and output antennas includes an associated slotline-to-microstrip transition having a slotline transmission line on one face of a dielectric layer upon which the slotline antenna is disposed, and having a conducting strip oriented substantially perpendicular to the slotline antenna on an opposite face of the dielectric layer, the conducting strip forming a pair of differentially driven microstrip lines coupling the slotline antenna to an associated circuit element. 
   The foregoing and other aspects of the present invention will be apparent from the following detailed description of the embodiments, which makes reference to the several figures of the drawings as listed below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1(   a ) is a perspective view of a prior art waveguide-based spatially combined amplifier; 
       FIG. 1(   b ) is a perspective view of a prior art coaxial waveguide-based spatially combined amplifier; 
       FIG. 2  is a perspective view of a waveguide-based spatially combined amplifier array according to one embodiment of the present invention; 
       FIG. 3  are side views of different slotline modules for a waveguide enclosure according to one embodiment of the present invention; 
       FIG. 4  are side views of different slotline modules for a waveguide enclosure according to another embodiment of the present invention; 
       FIG. 5  is a perspective view of a waveguide-based spatially combined amplifier array according to another embodiment of the present invention; 
       FIG. 6  is a side view of a slotline module according to another embodiment of the present invention; and 
       FIG. 7  is a circuit diagram showing circuit elements and a microstrip transitions according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   In the following description of the present invention reference is made to the accompanying drawings which form a part thereof, and in which is shown, by way of illustration, exemplary embodiments illustrating the principles of the present invention and how it may be practiced. It is to be understood that other embodiments may be utilized to practice the present invention and structural and functional changes may be made thereto without departing from the scope of the present invention. 
   The embodiments of the invention include systems and methods that can be implemented to increase the performance of spatially-combined arrays, a class of microwave devices. These devices compete with conventional solid state and vacuum tube microwave amplifiers and sources (oscillators). The present invention discloses several architectures that increase the performance of these spatially combined arrays by adjusting the amplitude balance of the signals among individual slotline modules according to a specified amplitude contour, accomplished by varying some property of the slotline modules. Further, the embodiments of the invention include slotline-to-microstrip transitions and delay equalization structures that further enhance the power combining efficiency. These architectures need not be used exclusively; one or more of the techniques could be used together to improve the performance of the spatially combined amplifier. 
     FIG. 2  is a perspective view of power combining array according to one embodiment of the present invention. In  FIG. 2 , a power combining array  100  includes a waveguide enclosure  110  having an input first end  120  and an output second end  130 . Transversely disposed along an H-direction, and substantially aligned with an E-direction and a longitudinal direction extending between the input end  120  and the output end  130 , are a plurality of slotline modules  140 . Each slotline module  140  in the plurality of slotline modules  140  includes a pair of slotline antennas comprising an input slotline antenna  150  and an output slotline antenna  160 . Each input slotline antenna  150  is disposed between the input end  120  of the waveguide enclosure  110  and a circuit portion  170 . Each output slotline antenna  160  is disposed between the output end  130  of the waveguide enclosure  110  and the circuit portion  170 . 
   The present invention increases performance of the power combining array  100  by varying characteristics of the slotline modules  140  to cause the signal amplitude applied to each module to substantially follow a specified amplitude contour according to the modules position along the H-direction within the waveguide enclosure  110 . When a signal is applied, signal intensity is strongest across a center  180  of the waveguide enclosure and gets weaker at edges  190  of the waveguide enclosure. Therefore, signal amplitudes across slotline modules  140  at the center of the waveguide enclosure  110  are different from those across slotline modules  140  at the edges of the waveguide enclosure  110 , resulting in a lack of uniformity in amplitude balance. 
   In an amplifying array, full utilization of the power-handling capability of the circuit elements requires that each circuit element is driven at the same fraction of its maximum signal power capability. In the case of modules having substantially identical circuit elements, the specified amplitude contour for maximum power-handling capacity would be a substantially equal distribution of amplitudes among the modules. If the different modules have differing circuit elements, the specified amplitude contour may be tailored to provide each circuit a signal strength matched to its power-handling capacity. Further, a non-uniform amplitude contour may be specified for a set of modules having either identical or differing circuit elements in order to optimize a performance metric other than power-handling capacity, such as spectral regrowth performance. 
   In the present invention, one method of causing the signal amplitude to follow a specified amplitude contour is by varying a longitudinal position of at least one of the slotline antennas on at least one slotline module  140 . Referring to  FIG. 2 , the longitudinal position of slotline antennas are varied according to a specified physical contour  200  at the input end  120  of the waveguide enclosure and at the output end  130  of the waveguide enclosure in order to achieve the specified amplitude contour. In one embodiment, the longitudinal position of the slotline antennas in different slotline modules are varied according each module&#39;s position along the H-direction within the waveguide enclosure  110  to achieve a specified amplitude contour. Increasing the distance between the waveguide ends  120  and  130  and the antennas of the slotline modules positioned nearer to the center of the waveguide enclosure  110  along the H-direction relative to the antennas of the modules positioned further from the center increases the relative amount of power in the modules further from the center. In another embodiment, varying the characteristics of the slotline modules includes varying the shape of the input and output slotline antennas to adjust the amplitude balance among individual slotline modules. 
   In another embodiment, a delay equalization portion  210  may be implemented with the circuit portion  170  of the slotline module to reduce delay imbalance among the slotline modules. Delay equalization may be characterized in the time domain as a time delay, or the frequency domain as a phase delay. Time delay equalization can be accomplished, for example, by inserting extra length into a transmission line path or by altering the propagation constant along a transmission path by varying dielectric loading. Time delay equalization generally has the advantage of operating over a broad range of frequencies. Phase delay equalization can be accomplished by altering reactive elements in the circuit or the transmission path. Phase delay equalization often has the advantage of small size and ease of adjustment. The delay equalization portion may be configured for phase delay equalization for narrowband applications, and may be configured for time delay equalization for broadband applications. It is noted that the delay equalization portion  210  may be implemented in conjunction with any technique for adjusting amplitude balance among the slotline modules. 
     FIG. 3  and  FIG. 4  are close-up views of slotline modules disposed on a dielectric substrate  220  have one or more dielectric layers.  FIG. 3  shows a variation in slotline antenna  160  tapering for a slotline module  140  positioned at or near the center  180  of the waveguide enclosure  110  as compared to tapering for a slotline antenna  160  for a slotline module  140  positioned near an edge  190  of the waveguide enclosure  100 . 
     FIG. 5  is a perspective view of a power combining array  100  according to another apparatus and method for performing the present invention. Performance of the power combining array  100  is increased by varying the physical thickness of the dielectric substrate  220  that the input slotline antennas  150 , the output slotline antennas  160 , the microstrip-to-slotline transition, and the circuit element  170  are printed on. Slotline modules  140  disposed upon thicker dielectric substrates  220  couple to the input and output fields more strongly than slotline modules  140  with thinner dielectric substrates  220 . Accordingly, slotline modules  140  with thicker dielectric substrates  220  are positioned near edges  190  of the waveguide enclosure  110 , while slotline modules  140  with thinner dielectric substrates  220  are positioned near the center  180  of the waveguide enclosure  110 , thereby adjusting the coupling of the various slotline modules  140  to the input and output fields to match a specified amplitude contour. A dielectric constant  230  of the material comprising the dielectric substrate  220  may also be varied to affect the signal amplitude. By varying the thickness of the dielectric substrate  220  and/or the dielectric constant  230  in one or more slotline modules, the balance of signal amplitude applied across the plurality of slotline modules can be adjusted to increase performance in the power combining array  100 . A delay equalization section  210  may also implemented with this embodiment to further balance the amplitude of the signal delay. 
   Another technique for performing the present invention involves varying the number of circuit elements on a slotline module  140 .  FIG. 6  and  FIG. 7  are a close-up view and a circuit diagram, respectively, of a slotline module  140  illustrating different embodiments in which the number of circuit elements comprising the circuit element portion  170  on a slotline module  140  is increased. Input slotline antennas  140  and output slotline antennas  150  are connected to circuit portions  170  on the slotline modules  140  by microstrip-to-slotline transitions  240 . These slotline-to-microstrip transitions  240  may include different configurations as shown in  FIG. 6  and  FIG. 7 . For example, a slotline-to-microstrip transition  240  may be a slotline-to-2 way microstrip transition  250 , or a slotline-to-4-way microstrip transition  260 . It is to be understood that the present invention contemplates that slotline-to-microstrip transitions  240  can be implemented in any number of ways to increase performance in a power combining array  100 . 
   The present invention generally contemplates a slotline-to-microstrip transition  240  that transforms energy in a slotline mode to a two-way microstrip mode. In the embodiments of  FIG. 6 and 7 , the present invention employs a more sophisticated slotline-to-4-way-microstrip transition  260 . Impedance matching structures may also be incorporated into these slotline-to-microstrip transitions  240 . In this embodiment, the number of circuit elements that can couple from or to a slotline module  140  is doubled to allow the circuit elements to be physically arranged such that their outputs are very close to the slotline-to-microstrip transition  240 , minimizing output losses and maximizing power combining efficiency. A delay equalization section  210  may also be used with this embodiment to further increase performance in the power combining array. 
   The embodiment of  FIG. 7 , as described above, shows the output of a slotline module  140  with a slotline-to 4-way microstrip transition  260 . In this embodiment, the input uses a slotline-to 2-way microstrip transition  250  and at least one two-way microstrip power divider  270 . Microstrip power dividers  270  are commonly used devices in the field of power combining arrays  100 . In addition, certain microstrip power dividers  270 , such as a Wilkinson power divider, isolate two divided ports from each other. Therefore, in this embodiment, the individual circuit elements on the slotline modules  140  are isolated from each other by the two-way microstrip power dividers  270 . The entire spatially combined array  100  is therefore less susceptible to crosstalk between the circuit elements and thus is more stable, and less sensitive to variations or failures in the individual circuit elements. A delay equalization section  210  may also be implemented to further increase the performance of the power combining array  100 . Also, as before, this embodiment may be generalized to incorporate slotline-to N-way microstrip transitions  240 . 
   In this embodiment, at least one of the input slotline antennas  150  and output slotline antennas  160  includes an associated slotline-to-microstrip transition  240  having a slotline transmission line on one face of a dielectric layer upon which the slotline antenna is disposed. Also included may be a conducting strip oriented substantially perpendicular to the slotline antenna on an opposite face of the dielectric layer. The conducting strip forms two or more pair of differentially driven microstrip lines coupling the slotline antenna to an associated circuit element  170 . The two or more pair of differentially driven microstrip lines may be separated by a distance along the slotline module  140  substantially equal to an integral number of quarter-wavelengths at the operating frequency. Additionally, the two or more differentially driven microstrip lines may separate a signal applied to the waveguide enclosure  110  through at least two sets of components in the circuit element  170  of a slotline module  140 . The power divider  270  connects the slotline-to-microstrip transition to a component of a circuit element  170  and is configured to isolate components in the circuit element  170 . 
   It is further understood that the embodiments illustrated in  FIG. 6  and  FIG. 7  and described in the preceding paragraphs may be applied to spatial power combiner arrays  100  using a coaxial architecture to increase the number of circuit elements coupled to or from a single slotline module  140 . Additionally, any number of different circuit elements and different slotline-to-N-way microstrip transitions  240  may be combined to achieve the desired result in the present invention. Therefore, the present invention is not limited to circuit configurations shown in the accompanying drawings, and one of skill in the art will recognize the different slotline modules  140  in the waveguide enclosure  110  may have different circuit configurations designed to achieve increased performance in the power combining array  100 . 
   Yet another technique for performing the present invention involves varying properties of circuit elements in the circuit element portion  170  for a slotline module  140 . In this technique, properties of the circuit elements, such as the power-handling capacity, are varied to substantially match the signal amplitude. In one embodiment, a bias of an amplifier is varied in a circuit element portion  170  of at least one slotline module  140  to increase performance in the power combining array  100 . It is understood that any property of a circuit element on any number of slotline modules  140  may be employed, which when varied substantially matches element characteristics to the signal amplitude contour. Additionally, any combination of varied circuit elements on any number of slotline modules  140  are contemplated by the present invention. As with other techniques and embodiments discussed herein, a delay equalization section  210  may be employed to further increase performance in the power combining array  100 . 
   It is to be understood that other embodiments may be utilized and structural and functional changes may be made without departing from the scope of the present invention. The foregoing descriptions of embodiments of the invention have been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Accordingly, many modifications and variations are possible in light of the above teachings. For example, varying any combination of characteristics of circuit elements and slotline antennas may produce acceptable performance increases in a power combining array  100 . Additionally, varying an amount of space between each slotline module may also increase performance in a power combining array  100 . Also, the embodiments of the present invention may be utilized to substantially equalize signal amplitude as a means of increasing performance in a power combining array. It is therefore intended that the scope of the invention be limited not by this detailed description.