Abstract:
An apparatus and method for providing adaptive control of the output of a radio frequency coupler. Adaptive control may include providing a transmission line having a plurality of branches extending therefrom and terminating, correspondingly, with a plurality of terminals and terminating, at its opposite end, with a single terminal, as well as, providing one or more proximate transmission lines inductively coupled with the transmission line and each having an input terminal at one end. Application of one or more input signals, respectively, to the one or more proximate transmission lines can adaptively control, via the inductive coupling, either a combination signal which is produced from a plurality of incoming signals when received at the plurality of terminals and is output from the single terminal or a plurality of outgoing signals which are produced from an incoming signal when received at the single terminal and divided among the plurality of branches and which are output from the plurality of terminals.

Description:
REFERENCE TO EARLIER-FILED APPLICATION 
   This is a Continuation Application of and incorporates by reference U.S. patent application Ser. No. 10/879,634, filed Jun. 30, 2004, titled “Variable Power Coupling Device.” 

   BACKGROUND 
   Microwave power combiners/dividers are used in different circuit applications. One such application is the combination of several incoming signals to achieve a coherent output signal having the desired output power. Conversely, an incoming signal may be divided to provide several output signals for digital signal processing devices. 
   Conventional combiners/dividers include a plurality of branches (fingers) couples to a unitary terminal. When used as a divider, an input signal is supplied to the unitary terminal and is transmitted to the several branches. When used as a power combiner, several input signals are supplied simultaneously to the respective branches and combined to one output signal at the unitary terminal. 
   A well-known combiner/divider is the Wilkinson power divider. The Wilkinson device is conventionally used for binary dividing/combining; that is, successive divisions or multiplications by two. Hence, the Wilkinson device is limited in that the divisions or multiplications are always a factor of 2 and the input and output impedances are equal to characteristic impedance Z 0 . Regardless of its application as a combiner or a divider, the Wilkinson device does not allow different input/output impedances. Moreover, since the Wilkinson device uses quarter-wavelength line in each division/multiplication operation and is binary, each subsequent operation requires additional space for the additional quarter-wavelength lines. Most importantly, the Wilkinson device does not allow N-way combination or division response in dimensional circuits. Circuits may be categorized in four groups according to their dimensions: zero dimensional, one dimensional, two dimensional and three dimensional. For example, in two dimensional circuits, two dimensions of the circuit are comparable or larger than the wavelength of the corresponding frequency. The other dimension is much smaller than the wavelength; therefore, these circuits may be categorized as two dimensional or 2D. 
   Other conventional combiners/dividers provide multi-prong impedance transforming power devices have a first terminal (corresponding to a first transmission line) and N transmission line fingers. The transmission lines have first and second ends. At their second end, the transmission lines are coupled to the first terminal while at their second terminal they are positioned to electromagnetically communicate with a power source. When used as a combiner, power is provided to each of the transmission lines. When combined, the power from each transmission line is combined to form an output from the first terminal. A drawback of the multi-prong impedance is the failure to provide control of the impedance transformation functions over a broad band of frequencies, while simultaneously achieving a wide range of possible impedance transformations. That is, the multi-prong device is limited to providing substantially linear output/input. 
   Clearly, there is a need in the art for power combiner/divider apparatus that overcomes the shortcoming of the prior art. 
   SUMMARY 
   Various exemplary embodiments as shown and described herein and in the accompanying drawings address these and related issues. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of a variable coupling device according to one embodiment of the invention. 
       FIG. 2   a  schematically represents a frequency coupler according to one embodiment of the invention. 
       FIG. 2   b  schematically represents a frequency divider according to one embodiment of the invention. 
       FIG. 3  shows a variable frequency coupler according to another embodiment of the invention. 
       FIG. 4   a  is a circuit diagram of another embodiment of the invention. 
       FIG. 4   b  is a circuit diagram of another embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic illustration of a variable coupling device according to one embodiment of the invention. Referring to  FIG. 1 , a coupler  100  has a first transmission line  110  and a second transmission line  120 . The first transmission line  110  includes a first terminal  112  that can receive an incoming signal (not shown) or provide an output signal. The first transmission line  110  also includes a first branch  111  and second branch  113 . The first branch  111  ends in a second terminal  114  while the second branch  113  ends in a third terminal  116 . Both the second terminal  113  and third terminal  116  can receive an incoming signal or transmit an output signal. 
   The second transmission line  120  has a fourth terminal  122  and a fifth terminal  124  each of which may receive an incoming signal or transmit an output signal, depending on the application of the coupler  100  and can be positioned in close proximity to the first transmission line  110  such that the second transmission line  120  is inductively engaged to the first transmission line  110 . Although not specifically shown in the exemplary embodiment of  FIG. 1 , the second transmission line  120  can be inductively couples to the first branch  111  or second branch  113 . To provide the desired inductive effect, the proximity of the first and the second terminals can be in the range of 5 to 40 mil (0.13 to 1 mm) with a dielectric constant (εr) of 3.5 and thickness of 20 mil (0.5 mm) at frequencies up to 8 GHz in 1D circuits. Thus, if a terminal of the second transmission line  120  receives an incoming signal, a portion of the power from the incoming signal inductively engages the first transmission line  110  to thereby alter the power signal output of the first transmission line  110 . 
   The coupler may be positioned on a dielectric substrate or other suitable medium and comprised of conductive or semi-conductive materials. Further, the coupler may function over a broad range of frequencies and is suitable for use in various technologies employing microstrip techniques including but not limited to microwave communications, millimeter wave communications, point-to-point and point-to-multipoint wireless communications, satellite communications, and fixed and mobile radar systems. 
   Each of the first and second terminals can be constructed of conductive or semi-conductive material such as those used in conventional couplers. For example, any microstrip (planar) media, such as microwave monolithic integrated circuitry (MMIC) can be used to implement the embodiment of  FIG. 1 . In such an embodiment, the parallel transmission line spacing  121  can range from approximately 5 to 40 mil (0.13 to 1 mm) with a dielectric constant (εr) of 3.5 and thickness of 20 mil (0.5 mm) at frequencies up to 8 GHz in 1D circuits. In 2D circuits, the frequencies may extend up to 100 GHz. 
   A key feature of the disclosed invention is the compact size of the variable coupler. Compact designs are particularly important when considering semiconductor die fabrication, particularly when gallium arsenide (GaAs) is used as a substrate. For example, the length and impedance of the first branch  111  and the second branch  113  may be determined by a divider (or sum) ration with the length and impedance of the first terminal  112 . The impedance of the second transmission line  120  may match the impedance of the coupled branch. In this example, the impedance of the second transmission line  120  may match the impedance of the first branch  111 . 
   When used as a variable power divider, the coupling device  100  can be positioned to receive an incoming signal at the first terminal  112  and provide outputs at each of the second terminal  114  and the third terminal  116 . To provide a variable power output, the second transmission line  120  can be place in electromagnetic proximity of either the first branch  111  or the second branch  113 . In the embodiment of  FIG. 1 , the second transmission line  120  is positioned adjacent to the first branch  111 . If power is supplied to the second transmission line  120  via the fourth terminal  122 , electromagnetic inductance will be formed in the second transmission line  120 . The inductance will affect the current flowing through the first branch  111  so as to increase or decrease the signal power output at the second terminal  114 . A desired signal output at each of the second and third terminals can be obtained by varying the power supplied to the second transmission line  120 , by adjusting the proximity (or length) of the second transmission line  120  and the first branch  111 , or both. While not specifically shown in  FIG. 1 , the fifth terminal  124  can be terminated to a proper load. 
   When used as a power combiner, each of the second terminal  114  and third terminal  116  receives an input signal. The input signals can be uniform or can have different signal powers. That is, the input signal to each of the second terminal  114  and third terminal  116  may have the same or different frequencies. In a conventional Wilkinson combiner, the input signals to each of the second and third terminals are combined to form an output signal from the first terminal  112 . An obvious drawback is that the conventional coupler provides a linear combination of the input signal. In contrast, according to one embodiment of the invention an input signal can be provided to the fifth terminal  124  to inductively control the signal flow through the first branch  111  (that is, the inductive coupling between the first branch  111  and the second transmission line  120  can actively increase/decrease the power magnitude supplied to the first terminal  112 ). As with the variable power divider embodiment described above, the output signal power from the first terminal  112  can be adjusted by adjusting the proximity and/or length of the second transmission line  120  and the first branch  111 . 
     FIG. 2   a  schematically represents a frequency coupler according to one embodiment of the invention. As shown in  FIG. 2   a , the variable frequency divider  200  includes a first transmission line  210  having a first terminal  212  that receives an incoming signal  211  of frequency f 1 . The first terminal  212  can be represented as having an equivalent characteristic impedance  213  with a value of Z 213 . The first terminal  212  divides to a first branch  218  and second branch  219  which terminate in a second terminal  214  and third terminal  216 , respectively. A second transmission line  220  includes a fourth terminal  222  that receives an incoming signal  221  of frequency F 2 . In the exemplary embodiment of  FIG. 2   a , the fourth terminal  222  is represented as having an equivalent characteristic impedance Z 223 . The proximate positioning of the first terminal  212  and fourth terminal  222  allows for electromagnetic influence among Z 213  and Z 223 . Consequently, the output at each of the second and third terminals ( 214 ,  216 , respectively) can be adjusted by controlling signal frequency f 2 . 
     FIG. 2   b  schematically represents a frequency combiner according to one embodiment of the invention. The variable frequency combiner  250  has similar elements as the elements of the variable frequency divider  200  represented in  FIG. 2   a.  Therefore, similar elements will maintain like reference numbers. The variable frequency combiner  250  comprises a first transmission line  210  and a second transmission line  220 . The first transmission line  210  is defined by an output terminal  212 , a first branch  218  and a second branch  219 . The first branch  218  is shown with an impedance  251  (Z 251 ) and receives an incoming signal  253 . Similarly, the second branch  219  is shown with an impedance  255  (Z 255 ) receiving an incoming signal  257 . The second transmission line  220  is positioned proximally to the first branch  218  and comprises an impedance  259  (Z 259 ) and a fourth terminal  222  and receives an incoming signal  261 . Each of the incoming signals  253 ,  257  and  261  may be signals of different frequency and power. Each of the incoming signals  253 ,  257  and  261  may be generated by a signal generator (not shown). Proximity of the second transmission line  220  to the first branch  218  of the first transmission line  210  enables electromagnetic coupling between the impedance  259  of the second transmission line  220  and the impedance  251  of the first branch  218 . Depending on the respective values of Z 251  and Z 259 , the electromagnetic coupling will affect the signal being transmitted through the second terminal  214  and the second transmission line  220 . Consequently, the signal output from an output terminal can be more than a linear combination of the incoming signals  253  and  257 . 
   The inventive embodiment of  FIGS. 1 ,  2   a  and  2   b  can be represented as an equivalent circuit satisfying the following relationships: 
               [   S   ]     =     [             [   S   ]     w             [   S   ]     c                 [   S   ]       c   ⁢           ⁢   1               [   S   ]     j           ]       ,         [   R   ]     o     =     [           R     o   ⁢           ⁢   1           0       0       0       0           0         R     o   ⁢           ⁢   2           0       0       0           0       0         R     o   ⁢           ⁢   3           0       0           0       0       0         R     o   ⁢           ⁢   4           0           0       0       0       0         R     o   ⁢           ⁢   5             ]             
where [S] w  is 3×3, [S] c  is 2×3, [S] ct  is 3×2, [S] l  is 2×2 and [R] o  is a termination matrix. The [S] depends upon a Wilkinson, balanced/unbalanced coupler arm that should be matched with an associated Wilkinson arm, termination matrix and frequency.
 
   An exemplary approximate normalized matrix with termination may be represented by the following relationship: 
   
     
       
         
           S 
           = 
           
             [ 
             
               
                 
                   0 
                 
                 
                   0.7 
                 
                 
                   0.5 
                 
                 
                   0 
                 
                 
                   0.55 
                 
               
               
                 
                   0.7 
                 
                 
                   0.7 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   0 
                 
               
               
                 
                   0.5 
                 
                 
                   0 
                 
                 
                   0.7 
                 
                 
                   0.55 
                 
                 
                   0 
                 
               
               
                 
                   0 
                 
                 
                   0 
                 
                 
                   0.55 
                 
                 
                   0.7 
                 
                 
                   0.45 
                 
               
               
                 
                   0.55 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   0.45 
                 
                 
                   0.7 
                 
               
             
             ] 
           
         
       
     
   
   Although in the exemplary embodiments of  FIGS. 2   a  and  2   b , the characteristic impedances are positioned in the represented location, it shall be understood by those of skill in the art that such placements are only exemplary and do not limit the principles of the invention disclosed herein. Moreover, the respective impedances are provided to illustrate an equivalent circuit function of the variable coupler, as known to those of skill in the art. 
     FIG. 3  shows a variable frequency coupler  300  according to another embodiment of the invention. Depending on how it is configured, the variable frequency coupler  300  can be used as a signal divider or a combiner. The coupler of  FIG. 3  can be considered as a conceptual extension of the exemplary coupler of  FIG. 1  in that the device of  FIG. 3  enables additional signal manipulation by providing a third transmission line for electromagnetically affecting the second branch of the first transmission line. 
   Referring to  FIG. 3 , a first transmission line  310  is defined by a first terminal  312 , second terminal  314  and third terminal  316  interconnected through a first branch  311  and a second branch  313 . If the coupler  300  is used as a variable power divider, the first terminal  312  is used as input and the second terminal  314  and third terminal  316  are used as outputs. Conversely, if the coupler  300  is used as a variable power combiner, the first terminal  312  is used as output and the second terminal  314  and third terminal  316  are used as inputs. For use as a variable power divider, the first terminal divider  312  can receive an input signal. When used as a variable combiner, the second terminal  314  and third terminal  316  can receive signals having the same or different frequencies. A second transmission line  320  and third transmission line  330  can be positioned in proximity of the first branch  311  and second branch  313 , respectively. Referring to the second transmission line  320 , either of the fourth terminal  322  or the fifth terminal  324  can receive an input signal. While not specifically shown in  FIG. 3 , the fourth terminal  322  or fifth terminal  324  can be terminated to a proper load. Similarly, the third transmission line  330  can be adapted to have either of a sixth terminal  332  or a seventh terminal  334  receive an input signal. While not specifically shown in  FIG. 3 , the sixth terminal  332  or seventh terminal  334  may be coupled to proper loads or sources. 
   For example, if used as a power divider, variable frequency coupler  300  can be positioned to receive an incoming signal at the first terminal  312  and provide subsequent outputs at each of the second terminal  314  and third terminal  316 . To provide variable output at each of the second terminal  314  and third terminal  316 , the second transmission line  320  and third transmission line  330  can be positioned in electromagnetic proximity to the first branch  311  and the second branch  313 , respectively. If power is supplied to the second transmission line  320  via the fourth terminal  322  or fifth terminal  324 , electromagnetic inductance will be formed in the second transmission line  320 . The inductance will affect the current flowing through the first branch  311  so as to increase or decrease the signal power output at the second terminal  314 . Similarly, if power is supplied to the third transmission line  330  via the sixth terminal  322  or seventh terminal  332 , electromagnetic inductance will be formed in the third transmission line  330 . The inductance will affect the current flowing through the second branch  313  so as to increase or decrease the signal power output at the third terminal  316 . Each of the transmission lines can be charged with an input signal of similar or different magnitude. The current flow direction can be optionally consistent with that of the first transmission line  310 . Thus, the terminals in the second transmission line  320  and third transmission line  330  can be coupled to a signal specifically calculated to induce the desired electromagnetic coupling on the respective first branch  311  and second branch  313 . 
   Placement of the second and third transmission lines  320  and  330  in proximity to the first transmission line  310  can be in a range of 5 to 40 (0.13 to 1 mm) with a dielectric constant (εr) of 3.5 and thickness of 20 mil (0.5 mm) at frequencies up to 8 GHz in 1D circuits. 
     FIG. 4   a  schematically represents a frequency coupler of another embodiment of the invention. As shown in  FIG. 4   a , the variable frequency divider  400  includes a first transmission line  410  having a first terminal  412  receiving an incoming signal  411  of frequency f 1 . The first terminal  412  can be represented as having an equivalent characteristic impedance  413  with and impedance value of Z 413 . The first terminal  412  divides to a first branch  418  and second branch  419  which terminate in a second terminal  414  and third terminal  416 , respectively. A second transmission line  420  includes a fourth terminal  422  receiving an incoming signal  421  of frequency f 2 . A third transmission line  430  includes a sixth terminal  432  receiving an incoming signal  431  of frequency f 3 . In the exemplary embodiment of  FIG. 4   a , the fourth terminal  422  is represented as having an equivalent characteristic impedance Z 423  and the sixth terminal  432  is represented as having an equivalent characteristic impedance Z 433 . 
   The length and proximate positioning of the first branch  418  and second transmission line  420  allow for electromagnetic influence among Z 413  and Z 423 . The length and proximate positioning of the second branch  419  and third transmission line  430  allow for electromagnetic influence among Z 413  and Z 433 . Consequently, the output at each of the second and third terminals ( 414 ,  416 , respectively) can be adjusted by controlling signal frequency f 2  or signal frequency f 3  or both. 
     FIG. 4   b  schematically represents a frequency combiner according to yet another embodiment of the invention. The variable frequency combiner  450  has similar elements as the elements of the variable frequency divider  400  represented in  FIG. 4   a.  Therefore, similar elements will maintain like reference numbers. The variable frequency combiner  450  comprises a first transmission line  410 , second transmission line  420  and third transmission line  430 . The first transmission line  410  is defined by an output terminal  412  (also first terminal  412 ), a first branch  418  and a second branch  419 . The first branch  418  is shown with an impedance  451  (Z 451 ) and receives an incoming signal  453 . Similarly, the second branch  419  is shown with an impedance  455  (Z 455 ) receiving an incoming signal  457 . The second transmission line  420  is positioned proximally to the first branch  418  and comprises an impedance  459  (Z 459 ) and a fifth terminal  424  receiving an incoming signal  461 . The third transmission line  430  is positioned proximally to the second branch  419  and comprises an impedance  463  (Z 463 ) and a seventh terminal  434  receiving an incoming signal  465 . 
   Each of the incoming signals  453 ,  457 ,  461  and  465  may optionally be signals of different frequency and power. Proximity of the second transmission line  420  to the first branch  418  enables electromagnetic coupling between the impedance  459  of the second transmission line  420  and the impedance  451  of the first branch  418 . Proximity of the third transmission line  430  to the second branch  419  enables electromagnetic coupling between the impedance  463  of the third transmission line  430  and the impedance  455  of the second branch  419 . Depending on the respective values of Z 451 , Z 455 , Z 459  and Z 463 , the electromagnetic coupling will affect the power of the signal being transmitted through the first terminal  412  and the first transmission line  410 . Consequently, the signal output from an output terminal can be more than a linear combination of the incoming signals  453 ,  457 , and  461  and  465 . 
   The inventive embodiments of  FIGS. 3 ,  4   a  and  4   b  can be represented as an equivalent circuit satisfying the following relationships: 
               [   S   ]     =     [             [   S   ]     w             [   S   ]       c   ⁢           ⁢   1               [   S   ]       c   ⁢           ⁢   2                   [   S   ]       ct   ⁢           ⁢   1               [   S   ]       l   ⁢           ⁢   1             [   0   ]                 [   S   ]       ct   ⁢           ⁢   2             [   0   ]             [   S   ]       i   ⁢           ⁢   2             ]       ,         [   R   ]     o     =     [           R     o   ⁢           ⁢   1                                                                                                     R     o   ⁢           ⁢   2                                                                                                     R     o   ⁢           ⁢   3                                                                                                     R   o4                                                                                                   R     o   ⁢           ⁢   5                                                                                                     R   o6                                                                                                   R     o   ⁢           ⁢   7             ]             
where [S] w  is 3×3, [S] ci  is 2×3, [S] cti  is 3×2, [S] li  is 2×2 and [R] o  is a termination matrix. The [S] depends upon a Wilkinson, balanced/unbalanced coupler arm that should be matched with an associated Wilkinson arm, termination matrix and frequency.
 
   An exemplary approximate normalized matrix with termination may be represented by the following relationship: 
   
     
       
         
           S 
           = 
           
             [ 
             
               
                 
                   0 
                 
                 
                   .45 
                 
                 
                   .45 
                 
                 
                   0 
                 
                 
                   .55 
                 
                 
                   0 
                 
                 
                   .55 
                 
               
               
                 
                   .45 
                 
                 
                   .7 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   .55 
                 
                 
                   0 
                 
               
               
                 
                   .45 
                 
                 
                   0 
                 
                 
                   .7 
                 
                 
                   .55 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   0 
                 
               
               
                 
                   0 
                 
                 
                   0 
                 
                 
                   .55 
                 
                 
                   .7 
                 
                 
                   .45 
                 
                 
                   0 
                 
                 
                   0 
                 
               
               
                 
                   .55 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   .45 
                 
                 
                   .7 
                 
                 
                   0 
                 
                 
                   0 
                 
               
               
                 
                   0 
                 
                 
                   .55 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   .7 
                 
                 
                   .45 
                 
               
               
                 
                   .55 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   0 
                 
                 
                   .45 
                 
                 
                   .7 
                 
               
             
             ] 
           
         
       
     
   
   Although in the exemplary embodiments of  FIGS. 4   a  and  4   b , the characteristic impedances are positioned in the represented location, it shall be understood by those of skill in the art that such placements are only exemplary and do not limit the principles of the invention disclosed herein. Moreover, the respective impedances are provided to illustrate an equivalent circuit function of the variable coupler, as known to those of skill in the art. 
   The variable frequency coupler of the present disclosure may be used for many different frequencies, i.e., 500 MHz to 8 GHz in 1D circuits and up to 60 GHz in 2D circuits, and many different waveforms and modulations. Further, the variable frequency coupler is suitable for use in microwave communications, millimeter wave communications, point-to-point and point-to-multipoint wireless communications and satellite communications as well as fixed and mobile radar systems as a modulated or non-modulated signal. The adaptive output control provided by the present disclosure also allows for versatility in a multiple frequency system with differing coupling values that are determined based on coupler geometrical structure and materials. 
   A device according to the principles of the invention can be used, for example, to receive radio frequency, microwave frequency as well as high power and high frequency applications and optical and laser applications. 
   While preferred embodiments of the present inventive apparatus and method have been described, it is to be understood that the embodiments described are illustrative only and that the scope of the embodiments of the present inventive apparatus and method is to be defined solely by the appended claims when accorded a full range of equivalence, many variations and modifications naturally occurring to those of skill in the art from a perusal thereof.