Abstract:
A flexible matching circuit topology defined by rules maximizes transfer efficiency for an amplified input signal over a wide band of operation. The circuit includes an impedance matching circuit suitable for transforming an electromagnetic signal transmission path of a first impedance into an electromagnetic signal transmission path having a second impedance. A first transmission line element is connected to at least one intermediate transmission line element. At least one pair of perpendicularly juxtaposed transmission line stub elements are connected across said intermediate transmission line element. At least one last transmission line element is connected to the intermediate transmission line element. An optional number of single-sided stub elements may be connected perpendicularly to the first transmission line element, the intermediate transmission line elements or the last transmission line element.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims priority of Provisional Patent Application 61/364,218 filed Jul. 14, 2010, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE PRESENT SUBJECT MATTER 
       [0002]    1. Field of the Present Subject Matter 
         [0003]    The present subject matter relates to dielectric waveguides such as microstrips or planar waveguides, and more specifically to impedance matching within a transmission line. 
         [0004]    2. Background 
         [0005]    One form of high-frequency, high-power, wideband amplifier is formed on a semiconductor substrate. In one context, a nominal power level is 100 W. Other power levels may be accommodated. The amplifier is coupled to an output terminal by a planar transmission line. The transmission line may comprise a microstrip. However, the present context is not limited to microwave frequency apparatus. The amplifier may provide power for any number of applications. Examples include communications and microwave oven power supply. 
         [0006]    Of course, impedance matching of the amplifier to the transmission line is extremely important. In impedance mismatch causes power to be reflected. One measure of our reflection is VSWR, or voltage standing wave ratio. Reflected power is not provided to an output stage. The output stage can be an antenna directly, a circulator, diplexer, another amplifier, or many other forms of output stages. Efficiency is reduced, often significantly. 
         [0007]    One conventional response to this problem is the use of adequate heat sinks or active cooling devices. While problems due to overheating or avoided, inefficiency remains. 
         [0008]    Another approach is the inclusion of linearization electronics for amplifiers. Linearization techniques used in power amplifiers compensate for significant nonlinearity exhibited by, for example, transistors in power driving amplifier stages. Efficiency is improved results. However thermal run-away may still occur. 
         [0009]    Impedance matching techniques may be very complex. For example, United States Patent Application Publication No. 20110143687 discloses a matching circuit in the context of a transmitter on a substrate. Several reactance circuits must be included to accomplish matching. Expense and complexity are increased with respect a circuit that utilizes a modified transmission line. 
         [0010]    United States Patent Application Publication No. 20080136552 discloses a scheme for impedance matching due to wire bonding between a microstrip transmission line and a conductor backed coplanar waveguide. Here, the problem is addressed by use of particular materials rather than a particular geometry. 
         [0011]    Accordingly, there exists a need for improving impedance matching in high power amplifier applications utilizing a transmission line on a dielectric substrate. 
       SUMMARY 
       [0012]    In accordance with the present subject matter, a structure is provided which allows a wideband width signal to propagate as a traveling wave across the matching circuit in such a way as to allow an amplifying device to operate simultaneously at peak efficiency and output power level. The foregoing, and various other needs, are addressed, at least in part, by the present subject matter, wherein power added efficiency is dramatically improved over an arbitrarily, seemingly limitless bandwidth via use of the matching circuit topology and design methods of the present subject matter. 
         [0013]    According to one preferred form, a flexible matching circuit topology defined by rules is provided to maximize transfer efficiency for an amplified input signal over a wide band of operation. The circuit includes an impedance matching circuit suitable for transforming an electromagnetic signal transmission path of a first impedance into an electromagnetic signal transmission path having a second impedance. A first transmission line element is connected to at least one intermediate transmission line element. At least one pair of perpendicularly juxtaposed transmission line stub elements are connected across said intermediate transmission line element. At least one last transmission line element is connected to the intermediate transmission line element. An optional number of single-sided stub elements may be connected perpendicularly to the first transmission line element, the intermediate transmission line elements or the last transmission line element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a plan view of a first form of transmission line for inclusion on a substrate utilizing a wideband matching circuit topology; 
           [0015]      FIG. 2  is a plan view of a further form of transmission line; 
           [0016]      FIG. 3  is a plan view illustrating further details of a wideband matching circuit topology; 
           [0017]      FIG. 4  is a plan view of a further embodiment of transmission line incorporating wideband matching circuit topology; 
           [0018]      FIG. 5  is a plan view of yet another form of wideband matching circuit topology which is in a transmission line; 
           [0019]      FIG. 6  is an isometric view of a wideband matching circuit topology, which may include metal deposited on an insulating substrate material and a ground plane underneath the insulating substrate material; 
           [0020]      FIG. 7  is a block diagram illustrating the use of the first embodiment wideband matching circuit topology of the present subject matter within an amplifying system; 
           [0021]      FIG. 8  is a plan view useful in describing desired dimensions in a dimensions matching circuit topology; 
           [0022]      FIG. 9  is a graph illustrating a nominal case of power added efficiency and output power performance of the amplifying apparatus according to the present subject matter; and 
           [0023]      FIG. 10  is an isometric view of an embodiment comprising metal sandwiched between two insulating substrate materials and a ground plane above the upper insulating substrate material and underneath the lower insulating substrate material. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    It is to be understood that the present subject matter is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The present subject matter is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
         [0025]    Reference now will be made in detail to the presently preferred embodiments of the present subject matter. Such embodiments are provided by way of explanation of the present subject matter, which is not intended to be limited thereto. Various modifications and variations can be made. 
         [0026]    For example, features illustrated or described as part of one embodiment can be used on other embodiments to yield a still further embodiment. Additionally, certain features may be interchanged with similar devices or features not mentioned yet which perform the same or similar functions. It is therefore intended that such modifications and variations are included within the totality of the present subject matter. 
         [0027]    Prior art matching impedance stubs have been commonly and exclusively either of simple rectangular in shape or of semicircular (pie) in shape. The reflection behavior along the rectangular shape is represented mathematically as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       ρ 
                       = 
                       
                         
                           ρ 
                           0 
                         
                          
                         
                            
                           
                             ( 
                             
                               2 
                                
                               
                                   
                               
                                
                               j 
                                
                               
                                   
                               
                                
                               β 
                                
                               
                                   
                               
                                
                               l 
                             
                             ) 
                           
                         
                       
                     
                      
                     
                       
 
                     
                      
                     where 
                      
                     
                       
 
                     
                      
                     
                       ρ 
                       ≡ 
                       
                         reflection 
                          
                         
                             
                         
                          
                         coefficient 
                       
                     
                      
                     
                       
 
                     
                      
                     β 
                     = 
                     
                       
                         
                           2 
                            
                           π 
                         
                         λ 
                       
                       ≡ 
                       
                         propagation 
                          
                         
                             
                         
                          
                         constant 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     l 
                     ≡ 
                     
                       line 
                        
                       
                           
                       
                        
                       length 
                        
                       
                           
                       
                        
                       
                         ( 
                         m 
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0028]    The impedance along on an open circuit straight rectangular stub that is juxtaposed to a transmission line of similar rectangular shape is given by: 
         [0000]        Z   OC   =−jZ   0  cot(β/ l )  (2)
 
         [0029]    The initial reflection as a function of impedance along an exponential tapered transmission line similar to the shapes presented in the present subject matter is given by: 
         [0000]    
       
         
           
             
               
                 
                   
                     ρ 
                     0 
                   
                   = 
                   
                     
                       1 
                       2 
                     
                      
                     
                       ln 
                        
                       
                         ( 
                         
                           
                             Z 
                             OC 
                           
                           
                             
                               Z 
                               0 
                             
                              
                             
                                 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0030]    Upon substitution of expression (2) into expression (3) an initial reflection as function of impedance for an exponentially tapered open circuit stub is found as: 
         [0000]    
       
         
           
             
               
                 
                   
                     ρ 
                     0 
                   
                   = 
                   
                     
                       1 
                       2 
                     
                      
                     
                       ln 
                        
                       
                         ( 
                         
                           
                             - 
                             j 
                           
                            
                           
                               
                           
                            
                           
                             cot 
                              
                             
                               ( 
                               
                                 β 
                                 / 
                                 l 
                               
                               ) 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0031]    And by further substitution of expression (1) into expression (4) a general expression for open circuit stub reflection of an exponential taper as a function of propagation constant and line length is found as: 
         [0000]    
       
         
           
             
               
                 
                   ρ 
                   = 
                   
                     
                       1 
                       2 
                     
                      
                     
                       ( 
                       
                          
                         
                           2 
                            
                           j 
                            
                           
                               
                           
                            
                           β 
                            
                           
                               
                           
                            
                           l 
                         
                       
                       ) 
                     
                      
                     
                       ln 
                        
                       
                         ( 
                         
                           
                             - 
                             j 
                           
                            
                           
                               
                           
                            
                           
                             cot 
                              
                             
                               ( 
                               
                                 β 
                                 / 
                                 l 
                               
                               ) 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0032]    This expression shows high degree of frequency dependent variability and when juxtaposed to a transmission line of similar characteristics, a very rich set of frequency modes may exist on the waveguide structure represented by the preferred embodiment. 
         [0033]      FIG. 1  is a plan view of an exemplary transmission line  100  embodying matching circuit topology according to the present subject matter. The transmission line is designed for improving power transfer efficiency over a very wide bandwidth and at a prescribed power level. Further features and embodiments are described in further detail with respect to  FIGS. 2-5 . 
         [0034]      FIG. 2  is a plan view of a further form of transmission line. As shown in  FIG. 2  from the left, a receiving or transmitting signal generated from an external signal source enters or exits a first transmission line element  101 , which has a specific characteristic impedance value. In the case of an entering, or source, wave, a traveling wave is further propagated across element  104 . For purposes of the present description, the wave propagated across junction is referred to as a propagating wave. The propagating wave sets up a non-uniform standing wave between a pair of resonance stub elements  102  and  103 . At the stub elements  102  and  103 , the propagating standing wave&#39;s power and frequency characteristics are modified. Propagation continues into a long and tapered edge intermediate transmission line element  105 , where the power and frequency characteristics of the standing wave are further modified. The standing wave continues along an L-shaped junction element  108 . The designation L is arbitrary. The junction  108  which could alternatively be described as a T-shaped or cross shaped junction element. At the L-shaped junction element  108  may be coupled to a non-uniform standing wave resonance tuning element, which in the present illustration comprises a single-sided tuning stub  106  and  107 . Inclusion of the non-uniform standing wave resonance tuning element is optional. 
         [0035]    The standing wave is further propagated along a second tapered edge intermediate transmission line element  109 , where its power and frequency characteristics are again modified. The standing wave propagates along L-shaped junction element  110 . The designation L is arbitrary. The junction element  110  could alternatively be described as a T-shaped or cross shaped junction element. The standing wave also propagates across single-sided tuning stubs  111  and  112 . The standing wave is again modified in frequency and power characteristic before reaching a final transmission line element  113 . The final transmission line element  113  has a specific characteristic impedance value, almost assuredly different from that specific to the first transmission line element,  101 . 
         [0036]    It is important to note that the characteristic impedance value of any previously described element of the matching circuit topology is variable throughout the topology. It is likewise important to note that the standing wave propagating throughout the matching circuit topology is essentially bi-directional. A transmission and a reflection aspect of the propagating wave simultaneously exist. Transmission line element geometry directs a wave along the direct transmission path, i.e., the horizontal signal propagation path as seen in  FIG. 1 . Various resonance members connect to the transmission line vertically as seen in  FIG. 1 , perpendicular to the transmission path. These comprise perpendicular tuning stubs of various forms and geometry. At least one of the perpendicularly juxtaposed transmission line stubs or said single-sided stub elements is open circuit or shunt circuit configured. Additional variations illustrating this unique combination exist and a partial list of exemplary embodiments will now be illustrated by  FIGS. 3 ,  4 , and  5 . 
         [0037]    “Perpendicular” is used here as a nominal specification. It need not mean exactly 90°. Deviation from 90° tends to degrade preference. Performance characteristics can be measured, and a user can select a maximum permissible level of degradation. 
         [0038]      FIG. 3  is a plan view illustrating further details of a wideband matching circuit topology.  FIG. 3  illustrates the details of a second exemplary embodiment in accordance with one or more embodiments of the present subject matter. The main difference between the circuit of  FIG. 2  and the circuit of  FIG. 3  is in the substitution of tuning stub elements  106  and  107  with tuning stub element  114  and modification of resonance tuning elements  111  and  112  by deletion of element  112 . 
         [0039]      FIG. 4  is a plan view illustrating the details of a third exemplary embodiment in accordance with one or more embodiments of the present subject matter. The circuit of  FIG. 4  comprises a non-linear intermediate transmission line element  115  rather than the linear tapered intermediate transmission line element  105  of  FIG. 3 . 
         [0040]      FIG. 5  is a plan view of yet another form of wideband matching circuit topology in a transmission line. A cross shaped junction element  116  and associated additional juxtaposed tuning stub,  117  are utilized in the alternative to the L-shaped junction element  108  of  FIG. 3 . 
         [0041]      FIG. 6  is an isometric view of a wideband matching circuit topology, which may include metal deposited on an insulating substrate material and a ground plane underneath the insulating substrate material. The embodiment of  FIG. 6  comprises the transmission line  100  of  FIG. 1  on a substrate  119 . The transmission line  118  comprises the metallization layer on top of the insulating substrate  119 , which comprises a dielectric material. A metallic ground, or reference, plane  120  is formed at a lower, preferably planar, surface of the substrate  119 . The ground plane  120  is used to support the travelling wave within the medium. 
         [0042]      FIG. 7  is a block diagram illustrating the use of the first embodiment wideband matching circuit topology of the present subject matter within an amplifier system.  FIG. 7  represents a use of the present subject matter within an amplifier system. The amplifier system comprises an input impedance matching circuit  121 / 124 , an active device  122 , and an output impedance matching circuit  123 / 125 . The geometries of the impedance matching circuits used for input and output impedance matching of the amplifying apparatus are not necessarily commensurate in geometry or in size. 
         [0043]      FIG. 8  is a plan view useful in describing desired dimensions in a dimensions matching circuit topology.  FIG. 8  illustrates a series of lengths and widths  126  used to specify some of the geometry of each of the individual elements of the wideband matching circuit topology from exemplary embodiment of the present subject matter illustrated by  FIG. 3 . Lengths and widths to provide a center frequency of operation can be calculated from known principles. The impedance transformation required can be measured or otherwise calculated. 
         [0044]    The frequency of operation corresponds to a particular wavelength. The resonant stubs are sized to correspond to a selected fraction, e.g., ¼, of the standing wave wavelength. Widths are specified according to the impedance transformation needed. Such prior art was more narrowband due to dependence on a center frequency of operation. In the present subject matter, the prior art requirement to be dependent on a single center frequency is lost in favor of choosing through some other means the various dimensions of the circuit to represent a much larger number of frequencies over which the circuit may operate. 
         [0045]    A computer tuning and optimization algorithm in a computer program may be used to calculate the desired dimensions of the circuit elements. One program is Microwave Office published by Applied Wave Research Corporation. A user may input frequency design specification frequency. Additionally, the user may input an approximate dimension. In many cases ¼ wavelength is a useful dimension. Also, the program can be informed of the user&#39;s design criteria. The program will calculate tradeoffs and optimize an element design to maximize the level of the parameter sought most by the user. Parameters may include maximum power level, efficiency, or other parameters. The program will provide an output indicating shapes and dimensions of elements cooperating with the transmission line. These dimensions and shapes comprise elements formed in a rule-based geometry. Another suitable program is Advanced Design System by Agilent Technologies. 
         [0046]      FIG. 9  illustrates by way of example a performance graph  131  showing the PAE  132  and power  133  performances of an actual amplifying apparatus built in correspondence with the embodiment of  FIG. 7  using an actual wideband matching circuit topology. This amplifying apparatus exhibits wideband behavior in terms of output power and efficiency of operation. 
         [0047]      FIG. 10  is an isometric view of an embodiment comprising metal sandwiched between two insulating substrate materials and a ground plane above the upper insulating substrate material and underneath the lower insulating substrate material.  FIG. 10  illustrates by way of example a performance graph  131  showing the power added efficiency (PAE)  132  and power  133  performances of an actual amplifying apparatus as illustrated in  FIG. 7  using an actual exemplary wideband matching circuit topology not unlike the exemplary embodiment described by  FIG. 4 . This amplifying apparatus exhibits wideband behavior in terms of output power and efficiency of operation. 
         [0048]      FIG. 10  illustrates another embodiment by which designs with the features represented by the present subject matter may also be fabricated.  FIG. 10  is an isometric view of an alternative embodiment to that of  FIG. 1 .  FIG. 10  comprises a wideband matching circuit in a sandwiched physical embodiment. Transmission line  134  illustrates the metallization layer in-between a top and bottom insulating substrate components,  136  composed of a dielectric material, and  135  represents a metallic ground, or reference, plane used to support the travelling wave within the medium. 
         [0049]    Those skilled in the art will appreciate that the present subject matter may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the present subject matter. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present subject matter.