Abstract:
An apparatus and method for building three-dimensional spatial power combiners for efficiently combining power from a large number of active devices are being disclosed. The apparatus discloses a plurality of grid amplifiers, each having a major surface, the plurality of grid amplifiers are arranged along an axis that is perpendicular to the major surface of each grid amplifier and spatially separated from each other by a selected resonant distance to generate a standing wave between adjacent grid amplifiers. The method discloses selecting a plurality of grid amplifiers each having a major surface, arranging the plurality of grid amplifiers along an axis that is perpendicular to the major surface of each grid amplifier, selecting a resonance distance, and spatially separating said plurality of grid amplifiers by the resonant distance to generate a standing wave between adjacent grid amplifiers.

Description:
FIELD 
   This invention relates to three-dimensional spatial power combiners. 
   BACKGROUND AND PRIOR ART 
   Broadband communications, radar and other imaging systems require the generation and transmission of radio frequency (“RF”) signals in the microwave and millimeter wave bands. In order to efficiently achieve the levels of output transmission power needed for many-applications at these high frequencies, a technique called “power combining” has been employed, whereby the output power of individual components are coupled, or combined, thereby creating a single power output that is greater than an individual component can supply. Conventionally, power combining has used resonant waveguide cavities or transmission-line feed networks. These approaches, however, have a number of shortcomings that become especially apparent at higher frequencies. First, conductor losses in the waveguide walls or transmission lines tend to increase with frequency, eventually limiting the combining efficiency. Second, these resonant waveguide cavities or transmission-line combiners become increasingly difficult to machine as the wavelength gets smaller. Third, in waveguide systems, each device often must be inserted and tuned manually. This is labor-intensive and only practical for a relatively small number of devices. 
   Several years ago, “spatial power-combining” was proposed as a potential solution to these problems. Spatial power combining provides enhanced RF efficiency by coupling the components to beams or modes in free space rather than via transmission lines in corporate combining structures. 
   If components are combined using transmission line circuits there is an upper limit to the number of elements (and hence a limit to the power which can be generated) due to transmission line and combining structure losses that depend on the number of elements in a nonlinear relation or due to the accumulating complexity of the circuit.  FIGS. 1   a  and  1   b  capture the concepts of corporate and spatial power combining, respectively.  FIG. 1   a  shows a circuit for a corporate combiner of power amplifiers integrated on a planar geometry. It can be seen that as additional elements are added the lengths of transmission line and the number of nodal combining circuits increases. The losses in the added line and combining circuits accumulate. They reduce and eventually eliminate the advantages of the combined power. Hence, it becomes necessary to use a spatially combined architecture as shown in  FIG. 1   b.    
     FIGS. 2   a ,  2   b  and  2   c  depict several spatially combined configurations to control the RF EM field of spacefed active arrays.  FIG. 2   a  shows a quasi-optical system using lenses and polarizers to control the RF field. Similar configurations can use an open array with no lenses and may use phase control circuitry in each of the active antenna elements to provide beam control.  FIG. 2   b  portrays an active array inside a waveguide, where the waveguide walls controls the EM field and defines its modal structure.  FIG. 2   c  presents a waveguiding structure controlling EM field, but expanding to allow a larger number of amplifier elements to be combined. 
   Active arrays for space-fed spatial combining systems have been demonstrated in the two classic array topologies—tile and tray—shown in  FIGS. 3   a  and  3   b , respectively. In the case of the tile approach shown in  FIG. 3   a , two distinct design approaches have been developed, shown in  FIGS. 4   a  and  4   b . In the Rutledge “grid” array of  FIG. 4   a , active devices are integrated at the vertical and horizontal intersections of a metallic mesh. The vertical wires connect either the input circuits or the output circuits of the amplifiers, while the horizontal wires connect the other circuit. An incoming wave can thus be polarized to interact only with the amplifiers input circuits, while the outgoing wave will be orthogonally polarized. Polarizer grids used on either side of the grid array insure isolation between input and output circuits. In the grid array, the active elements are generally spaced much closer than a half wavelength. The entire length of the grid wires act as single antenna elements. In the active antenna array of  FIG. 4   b , separate antenna elements are integrated directly with active devices or a MMIC amplifier, with each element acting as an independent cell. The array acts as a periodic antenna array with the elements spaced at roughly half wavelength intervals. The EM wave is received on one side of the array, active devices can be placed on either or both sides of the array, and the array radiates on the other side. The antenna elements can be various combinations of patch and slot elements, with the possibility that in some configurations a common ground plane can isolate the input from the output. The tray approach, illustrated in  FIG. 3   b , uses a tray of end-fire antenna elements, with multiple trays stacked to provide a 2-dimensional array. The tray then acts to receive an input signal, to excite an electrical circuit that runs perpendicular to the plane of the antenna array, and to radiate from the other side of the trays. 
   Conventional spatial power-combiners do not efficiently combine power from a large number of active devices; do not obtain an equal share of power from each of the active device, irrespective of where the active device is located within the grid, and delivering the sum of the individual contributions to a load; and in high-power, high-frequency applications drawing heat away from spatial power combiners also remains a problem. 
   To overcome the problem of insufficient heat sinking a three-dimensional power combiner has been proposed as shown in  FIGS. 5   a  and  5   b . See W. A. Shiroma, B. L. Shaw and Z. B. Popovic, “Three-Dimensional Power Combiners,” 1994 IEEE MTT-S Int. Microwave Symp. Dig., pp. 831–834, May 1994; and W. A. Shiroma, B. L. Shaw and Z. B. Popovic, “A 100-Transistor Quadruple Grid Oscillator,” IEEE Microwave and guided Wave Lett., vol. 4, no. 10, pp. 350–351, October 1994.  FIG. 5   a  depicts two planar oscillator grids placed back to back against a dielectric spacer and  FIG. 5   b  depicts four planar oscillator grids separated by dielectric spacers. 
   However, there is still a need to more efficiently combine power from a large number of active devices. The present description addresses these problems by disclosing a three-dimensional power combiner to efficiently combine power from a large number of active devices (e.g. transistors, negative resistance diodes) in a series manner while obtaining an equal share of power from each active device, independent of where the active device is located along the series chain, and delivering the sum of the individual contributions to a load. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1   a  depicts a conventional corporate combiner using binary Wilkinson splitter/combiner networks; 
       FIG. 1   b  depicts a special combining architecture; 
       FIG. 2   a  depicts a quasi-optical beam amplifier concept using a lens-focused arrangement; 
       FIG. 2   b  depicts an active array of amplifier elements inside of a waveguide; 
       FIG. 2   c  depicts an active array in oversized waveguide with tapered “horn” feed to accommodate more amplifiers; 
       FIG. 3   a  depicts a “tile” topology of spatial combining systems; 
       FIG. 3   b  depicts a “tray” topology of spatial combining systems; 
       FIG. 4   a  depicts a Rutledge “grid” for a “tile” topology shown in  FIG. 3   a;    
       FIG. 4   b  depicts a conventional antenna array design for a “tile” topology shown in  FIG. 3   a;    
       FIG. 5   a  depicts a three-dimensional power combiner with two planar oscillator grids placed back to back against a dielectric spacer; 
       FIG. 5   b  depicts a three-dimensional power combiner with four planar oscillator grids separated by dielectric spacers; 
       FIG. 6  depicts a three-dimensional power amplifier composed of grid amplifiers separated by a resonant distance θ according to the present disclosure; 
       FIG. 7  depicts a schematic diagram of the three-dimensional power amplifier shown in  FIG. 6  wherein the grid amplifiers comprise two-dimensional array of two terminal devices; 
       FIG. 8  depicts a schematic diagram of the three-dimensional power amplifier shown in  FIG. 6  wherein the grid amplifiers comprise two-dimensional array of three terminal devices; 
       FIG. 9  depicts a three-dimensional oscillator composed of grid amplifiers separated by a resonant distance θ according to the present disclosure; 
       FIG. 10  depicts a schematic diagram of the three-dimensional oscillator shown in  FIG. 9  wherein the grid amplifiers comprise two-dimensional array of two terminal devices; and 
       FIG. 11  depicts a schematic diagram of the three-dimensional oscillator shown in  FIG. 9  wherein the grid amplifiers comprise two-dimensional array of three terminal devices; 
       FIG. 12  depicts another three-dimensional oscillator composed of grid amplifiers separated by a resonant distance θ according to the present disclosure; 
       FIG. 13  depicts a schematic diagram of the three-dimensional oscillator shown in  FIG. 12  wherein the grid amplifiers comprise two-dimensional array of three terminal devices; 
   

   DETAILED DESCRIPTION 
   According to the present disclosure a three-dimensional power combiner may be constructed to efficiently combine power from a large number of active devices (e.g. transistors, negative resistance diodes) in a series manner while obtaining an equal share of power from each active device, independent of where the active device is located along the series chain, and delivering the sum of the individual contributions to a load. Unlike in the prior art, this disclosure utilizes resonance between grids of active devices so that the impedance seen from each active device is equal to all the others, thereby extracting equal power from all active devices. 
   Referring to  FIG. 6 , an exemplary embodiment of a three-dimensional amplifier  100  is composed of four “grid” amplifiers  10  separated by distance d. The grid amplifiers  10  may, for example, contain a two dimensional array of two terminal active devices, such as, for example, IMPATT, Gunn or tunnel diodes or three terminal active devices, such as, for example, FET transistors. The grid amplifiers  10  are well known in the art and are not discussed in great detail herein for clarity purposes. The grid amplifiers are discussed in more detail in “A 44–60 GHz monolithic pHEMT grid amplifier,” M. P. DeLisio, S. W. Duncan, D. W. Tu, S. Weinreb, C. M. Liu, D. B. Rutledge, 1996 IEEE MTT-S Int. Microwave Symp. Dig., pp. 1127–1130, 1996, which is incorporated herein by reference. 
   Referring to  FIG. 7 , schematic diagram  110  of the three-dimensional amplifier  100  with of grid amplifiers  10  composed of a two dimensional array of two terminal devices is shown. The grid amplifiers  10  are periodically arranged on transmission lines  15  and  16 , with a resonant distance θ 
           (     θ   =     kd   =     n   ⁢           ⁢   π   ⁢     d   λ           )         
separating the grid amplifiers  10  where d is the physical distance between grid amplifiers  10 , k is a propagation constant and is related to wavelength as
 
             k   =       2   ⁢           ⁢   π     λ       ,         
and λ is wavelength of the energy to be amplified. According to Circuit theory, separating the grid amplifiers by multiples of half a wavelength effectively placed the grid amplifiers in parallel. Thus each grid “sees” the same external admittance, and therefore delivers the same power to the load, independent of their proximity to the load admittance Y L .
 
   Referring to  FIG. 8 , schematic diagram  120  of the three-dimensional amplifier  100  with grid amplifiers  10  composed of a two dimensional array of three terminal devices is shown. There are two sets of loaded transmission lines  17  and  18 , one for the input (gate) side and one for the output (drain) side. As above, the lengths of transmission line between grid amplifiers  10  are multiples of half a wavelength so that the inputs and outputs of the three terminal devices in the grid amplifiers  10  appear in parallel. For the gate circuit, this creates equal voltages across all of the gates, and on the drain circuit, power from each of the transistors adds in phase, delivering the sum power to the load Y L . 
   The three terminal devices in each grid amplifier  10  may have cross polarized inputs and outputs, which may allow each polarization through the three-dimensional amplifier  100  to act like a separate transmission line. The vertical input polarization couples into the grid amplifier  10 , delivering a fraction of the power to the three terminal devices, with remainder either reflected back or transmitted through. The power delivered to the three terminal devices is amplified by the three terminal devices and then radiated into the cross polarized component to adjacent grid amplifiers  10 . The resonant distance θ between the grid amplifiers  10  creates standing waves between grid amplifiers  10 , thus creating equal admittances at each grid amplifiers  10  so that each sources the same power. 
   This disclosure is not limited to four grid amplifiers  10  within the three-dimensional amplifier  100  as depicted in  FIG. 8 . One skilled in the art would understand that there could be a plurality of grid amplifiers  10  within the three-dimensional amplifier  100 . 
   Although the above exemplary embodiments disclose amplifiers, the above approach can be used in either an amplifier mode or an oscillator mode, depending on the terminations of the transmission lines. There are a number of methods that one can use to make the structure oscillate. To achieve oscillation one must couple outputs (scattered waves) from layers back to inputs (incident waves) from the same or other layers. When the amount of coupling increases beyond a certain point, determined partly by the gain of the layers, the structure will oscillate. The three-dimensional structure shown in  FIG. 6  may be configured as an oscillator array as shown in  FIG. 9 . 
   Referring to  FIG. 9 , an exemplary embodiment of a three-dimensional oscillator  125  composed of four “grid” amplifiers  10  separated by distance d, total reflector  20  and partial reflector  30  is shown. The total reflector  20  and the partial reflector  30  may be used to terminate sides of the three-dimensional oscillator  125  in order to provide feedback to initiate oscillations. The output of the three-dimensional oscillator  125  consists of the power transmitted through the partial reflector  30 . In this embodiment the outputs and input are cross polarized to reduce parasitic coupling between the inputs and outputs. 
   The grid amplifiers  10  may, for example, contain a two dimensional array of two terminal active devices, such as, for example, IMPATT, Gunn or tunnel diodes or three terminal active devices, such as, for example, FET transistors. As stated above, the grid amplifiers  10  are well known in the art and are not discussed in great detail herein for clarity purposes. 
   Referring to  FIG. 10 , schematic diagram  130  of the three-dimensional oscillator  125  with of grid amplifiers  10  composed of a two dimensional array of two terminal devices is shown. The grid amplifiers  10  are periodically arranged on transmission lines  21  and  22 , with a resonant distance θ 
           (     θ   =     kd   =     n   ⁢           ⁢   π   ⁢     d   λ           )         
separating the grid amplifiers  10  where d is the physical distance between grid amplifiers  10 , k is a propagation constant and is related to wavelength as
 
             k   =       2   ⁢           ⁢   π     λ       ,         
and λ is wavelength of the energy to be amplified. According to Circuit theory, separating the grid amplifiers by multiples of half a wavelength effectively placed the grid amplifiers in parallel. Thus each grid “sees” the same external admittance, and therefore delivers the same power to the load, independent of their proximity to the load admittance Y L .
 
   Referring to  FIG. 11 , schematic diagram  140  of the three-dimensional oscillator  125  with grid amplifiers  10  composed of a two dimensional array of three terminal devices is shown. There are two sets of loaded transmission lines  17  and  18 , one for the input (gate) side and one for the output (drain) side. As above, the lengths of transmission line between grid amplifiers  10  are multiples of half a wavelength so that the inputs and outputs of the three terminal devices in the grid amplifiers  10  appear in parallel. For the gate circuit, this creates equal voltages across all of the gates, and on the drain circuit, power from each of the transistors adds in phase, delivering the sum power to the load Y L . 
   The three terminal devices in each grid amplifier  10  may have cross polarized inputs and outputs, which may allow each polarization through the three-dimensional oscillator  125  to act like a separate transmission line. The vertical input polarization couples into the grid amplifier  10 , delivering a fraction of the power to the three terminal devices, with remainder either reflected back or transmitted through. The power delivered to the three terminal devices is amplified by the three terminal devices and then radiated into the cross polarized component to adjacent grid amplifiers  10 . The resonant distance between the grid amplifiers  10  creates standing waves between grid amplifiers  10 , thus creating equal admittances at each grid amplifiers  10  so that each sources the same power. 
   This disclosure is not limited to four grid amplifiers  10  within the three-dimensional oscillator  125  as depicted in  FIG. 9 . One skilled in the art would understand that there could be a plurality of grid amplifiers  10  within the three-dimensional oscillator  125 . 
   This disclosure is not limited to the grid amplifiers  10  and the reflectors  20  and  30  being rectangular shape as depicted in  FIG. 9 . One skilled in the art would understand that the grid amplifiers  10  and the reflectors  20  and  30  may be other shapes like, for example, circular as depicted in  FIG. 12 . 
   The three-dimensional structure shown in  FIG. 6  may also be configured as an oscillator array as shown in  FIG. 12 . where the input/output coupling can be achieved by rotating each of the grid amplifiers  10  with respect to the other grid amplifiers  10 . With the grid amplifiers  10  rotated, the output polarization from one grid amplifier  10  will partly couple to the other grid amplifier  10 , with the coupling depending on the angle of rotation. The rotation of the grid amplifiers  10  is an easy way to couple the grid amplifiers  10  together to achieve oscillation and it also allows the coupling strength grid amplifiers  10  to be controlled by varying the rotation angle of grid amplifiers  10 . 
   Referring to  FIG. 12 , another exemplary embodiment of a three-dimensional oscillator  225  composed of four “grid” amplifiers  10  separated by distance d, total reflector  20  and partial reflector  30  is shown. The total reflector  20  and the partial reflector  30  may be used to terminate sides of the three-dimensional oscillator  225  in order to provide feedback to initiate oscillations. The output of the three-dimensional oscillator  225  consists of the power transmitted through the partial reflector  30 . 
   The grid amplifiers  10  of  FIG. 12  may, for example, contain a two dimensional array of two terminal active devices, such as, for example, IMPATT, Gunn or tunnel diodes or three terminal active devices, such as, for example, FET transistors. As stated above, the grid amplifiers  10  are well known in the art and are not discussed in great detail herein for clarity purposes. 
   Referring to  FIG. 13 , schematic diagram  240  of the three-dimensional oscillator  225  with grid amplifiers  10  composed of a two dimensional array of three terminal devices is shown. There are two sets of loaded transmission lines  17  and  18 , one for the input (gate) side and one for the output (drain) side. As above, the lengths of transmission line between grid amplifiers  10  are multiples of half a wavelength so that the inputs and outputs of the three terminal devices in the grid amplifiers  10  appear in parallel. For the gate circuit, this creates equal voltages across all of the gates, and on the drain circuit, power from each of the transistors adds in phase, delivering the sum power to the load Y L . 
   This disclosure is not limited to four grid amplifiers  10  within the three-dimensional oscillator  225  as depicted in  FIG. 12 . One skilled in the art would understand that there could be a plurality of grid amplifiers  10  within the three-dimensional oscillator  225 . 
   The foregoing Detailed Description of exemplary and preferred embodiments is presented for purposes of illustration and disclosure in accordance with the requirements of the law. It is not intended to be exhaustive nor to limit the invention to the precise form(s) described, but only to enable others skilled in the art to understand how the invention may be suited for a particular use or implementation. The possibility of modifications and variations will be apparent to practitioners skilled in the art. No limitation is intended by the description of exemplary embodiments which may have included tolerances, feature dimensions, specific operating conditions, engineering specifications, or the like, and which may vary between implementations or with changes to the state of the art, and no limitation should be implied therefrom. Applicant has made this disclosure with respect to the current state of the art, but also contemplates advancements and that adaptations in the future may take into consideration of those advancements, namely in accordance with the then current state of the art. It is intended that the scope of the invention be defined by the Claims as written and equivalents as applicable. Reference to a claim element in the singular is not intended to mean “one and only one” unless explicitly so stated. Moreover, no element, component, nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element, component, or step is explicitly recited in the Claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for . . . ” and no method or process step herein is to be construed under those provisions unless the step, or steps, are expressly recited using the phrase “step(s) for . . . . ”