Abstract:
A directional coupler characterized as having improved directivity. The directional coupler and methodology uses enhanced destructive interference to reduce the leakage at the output port of a signal incident at the coupled port of the coupler thereby giving the coupler improved directivity. The directional coupler creates this enhanced destructive interference by the introduction of impedance discontinuities in the coupled transmission lines. The impedance discontinuity in the coupled transmission lines can take on many forms, such as recesses at the coupling sides of the coupled transmission lines, protrusions at the non-coupling sides of the coupled transmission lines, or both. Another directional coupler is capable of being tuned for different coupling levels. This coupler comprises adjacent conductors between the coupled transmission lines that are connected, as required, to the coupled lines to change the coupling level.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to radio frequency (RF) and microwave circuits, and in particular, to a directional coupler having relatively high-directivity due to discontinuities that cause destructive interference of an incident signal at the coupled port of the coupler and to a directional coupler with an adjustable coupling level.  
         BACKGROUND OF THE INVENTION  
         [0002]    Directional couplers are extensively used in the radio frequency (RF) and microwave/millimeterwave field. They are typically used to sample a signal for further processing and/or control. For example, directional couplers are used in the frequency control of dielectric resonator oscillators (DROs). In this regard, a directional coupler is placed at the output of a DRO to provide a sample of the DRO&#39;s output signal. The sampled signal is applied to a phase detector for phase comparison with a highly frequency-stable crystal oscillator. The phase detector generates a phase error signal, which is subsequently filtered to produce a frequency control signal for the DRO. The frequency control signal causes the DRO to produce an output signal whose frequency stability is tied to that of the crystal oscillator.  
           [0003]    A directional coupler typically comprises four ports: an input port, an output port, a coupled port, and an isolated port. An incident signal is applied to the input port, and a first portion of the incident signal is produced at the output port and a second portion of the incident signal is produced at the coupled port. For example, if the coupling of a directional coupler is 10 dB, then one-tenth ({fraction (1/10)}) of the incident signal is produced at the coupled port, and nine-tenths ({fraction (9/10)}) of the incident signal is produced at the output port. In an ideal coupler, which has infinite directivity, none of the incident signal is produced at the isolated port.  
           [0004]    However, most if not all directional couplers do not perform the same as ideal couplers. Accordingly, they have a finite directivity. Therefore, some of the incident signal applied to the input port ends up at the isolated port. Typically, directional couplers have a directivity value that produces a signal level at the isolated port that is approximately 10 dB lower in amplitude than the coupling level. Taking the same example above, a typical 10 dB coupler will have a directivity of approximately 20 dB. That is, there is a signal generated at the isolated port that is 20 dB below the incident signal at the input port. Generally, for an incident signal at the input port, this is not a significant problem (other than a small contribution to the insertion loss of the coupler) since the signal generated at the isolated port is simply dissipated through a load typically connected to the isolated port.  
           [0005]    Relatively low directivity becomes a problem when there is an incident signal at the coupled port. This is because for an incident signal at the coupled port, the output port now becomes the “isolated port.” Thus, if a directional coupler has a relatively low directivity, an incident signal present at the coupled port ends up at the output port. In DRO applications, the coupled port of a directional coupler is coupled to the phase detector circuit for supplying a portion of the DRO RF/microwave/millimeterwave signal to the phase detector circuit. Thus, harmonics from the reference oscillator, reflected DRO signals with reference harmonic sidebands, and other spurious signals generated by the phase detector circuit may end up as incident signals at the coupled port. Since a directional coupler has a frequency response similar to a bandpass filter, the low frequency reference oscillator harmonics and spurious signals will be well attenuated on the way to the output port of the coupler. In a similar manner, reference oscillator harmonics and spurious signals beyond the passband of the coupler will also be attenuated. Only the directivity of the directional coupler will attenuate any signals within the passband of the directional coupler. Thus, if the coupler has poor directivity, these unwanted signals propagate to the output port and degrade the purity of the DRO output spectrum.  
           [0006]    Thus, there is a need for a directional coupler and method therefor that exhibits improved directivity. Such a need and others are met herein in accordance with the invention.  
         SUMMARY OF THE INVENTION  
         [0007]    An aspect of the invention relates to a new and improved directional coupler and method therefor characterized in having improved directivity. The directional coupler and methodology uses enhanced destructive interference to suppress the leakage at the output port of a signal incident at the coupled port of the coupler. It has long been known that for an ideal coupler there is no signal present at the coupler&#39;s isolated port. A non-ideal coupler may have a low-level signal at this port. The design of the improved directional coupler more successfully suppresses this signal through the use of a more finely tuned destructive interference, thereby providing improved directivity. For a signal incident at the coupled port, the output port behaves as if it is the isolated port. The directional coupler of the invention creates destructive interference of a signal that is incident at the coupled port by the introduction of one or more impedance discontinuities in the coupled transmission lines. If the impedance discontinuities are properly configured, destructive interference of the signal incident at the coupled port occurs, resulting in less leakage of this signal at the output port.  
           [0008]    More specifically, the directional coupler comprises an input port, an output port, a coupled port, an isolated port, and a pair of coupled transmission lines having a first coupling transmission line with ends respectively coupled to the input and output ports, and a second coupling transmission line with ends respectively coupled to the coupled and isolated ports. The coupled transmission lines each or both include one or more impedance discontinuities which are configured to cause further destructive interference of a signal that is incident at the coupled port, resulting in less leakage of this signal at the output port. The signal incident at the coupled port is split into two parts. The first part of the signal is propagated along one part of the coupler while the second part of the signal is propagated along the adjacent second part of the coupler. Due to the discontinuities present in the design of the coupler, these two signals are caused to have substantially equal amplitudes and substantially opposite phases. This causes the two signals to substantially interfere destructively with each other. Since the signal that is incident at the coupled port has its level reduced at the output port due to the destructive interference, the directional coupler has improved directivity. Assuming that there is little to no resistive loss in the coupler&#39;s transmission lines, the level of the signal is reduced at the output port due to substantially destructive interference. The remaining energy is reflected back from the output port and dispersed out the other ports of the coupler.  
           [0009]    The impedance discontinuity in the coupled transmission lines can take on many forms. In one exemplary embodiment, the impedance discontinuity is a pair of recesses symmetrically positioned on respective coupling sides of the coupled transmission lines. In another embodiment, the impedance discontinuity is a pair of recesses symmetrically positioned on respective coupling sides of the coupled transmission lines, and a pair of protrusions symmetrically positioned on the non-coupling sides of the coupled transmission lines. In this exemplary embodiment, the recess and protrusion coincide positionally along the coupled transmission lines. Another embodiment may include coupled transmission lines having respective non-coupling sides that are tapered from the ends of the coupled transmission lines to the discontinuities on the lines.  
           [0010]    Another aspect of the invention is a directional coupler that is capable of being tuned for different coupling levels. This directional coupler comprises an input port, an output port, a coupled port, an isolated port, and a pair of coupled transmission lines. One of the pair of coupled transmission lines has ends coupled respectively to the input and output ports, and the other pair has ends coupled to the coupled and isolated ports. Adjacent conducting areas are provided between the coupled transmission lines to allow higher coupling when the pair of coupled transmission lines are connected to the adjacent conducting areas. Another set of adjacent conducting areas are provided on respective non-coupling sides of the coupled transmission lines to give the coupled transmission lines the proper characteristic impedance when the coupling-side adjacent conducting areas are not connected to the coupled transmission lines.  
           [0011]    Other aspects of the invention include a local oscillator, receiver and transmitter that use the directional couplers of the invention. Other aspects, features and techniques of the invention will become apparent to one skilled in the relevant art in view of the following detailed description of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 illustrates a top view of an exemplary directional coupler in accordance with the invention;  
         [0013]    [0013]FIG. 2 illustrates a top view of another exemplary directional coupler in accordance with the invention;  
         [0014]    [0014]FIG. 3 illustrates a top view of yet another exemplary directional coupler in accordance with the invention;  
         [0015]    [0015]FIG. 4A illustrates a top view of still another exemplary directional coupler in accordance with the invention without connection to adjacent conductors;  
         [0016]    [0016]FIG. 4B illustrates a top view of still another exemplary directional coupler in accordance with the invention with connections to adjacent conductors in a manner that provides looser coupling;  
         [0017]    [0017]FIG. 4C illustrates a top view of still another exemplary directional coupler in accordance with the invention with connections to adjacent conductors in a manner that provides medium coupling;  
         [0018]    [0018]FIG. 4D illustrates a top view of still another exemplary directional coupler in accordance with the invention with connections to adjacent conductors in a manner that provides tighter coupling;  
         [0019]    [0019]FIG. 5 illustrates a block diagram of an exemplary local oscillator that includes a directional coupler in accordance with the invention;  
         [0020]    [0020]FIG. 6 illustrates a block diagram of an exemplary receiver that includes at least one directional coupler in accordance with the invention; and  
         [0021]    [0021]FIG. 7 illustrates a block diagram of an exemplary transmitter that includes at least one directional coupler in accordance with the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    [0022]FIG. 1 illustrates a top view of an exemplary directional coupler  100  in accordance with the invention. The directional coupler  100  comprises an input port  104 , an output port  106 , a coupled port  108 , and an isolated port  110 . As with all couplers, the act of defining a port as the input port determines the function of the remaining ports. For example, if port  108  was used as the input port, the output of the coupler would be at port  110 , the signal would be coupled out to port  104 , and port  106  would be the isolated port. The coupler  100  further comprises a pair of coupled transmission lines  120  and  122 . The directional coupler  100  may also include leading transmission lines  112 ,  114 ,  116  and  118  with corresponding 90-degree bends  124 ,  126 ,  128  and  130  which respectively couple the input port  104 , output port  106 , coupled port  108 , and isolated port  110  to the coupled lines  120  and  122 . The leading transmission lines, the 90 degree bends, and the coupled transmission lines are all formed as a continuous electrical conductive layer disposed on a substrate  102 , which can be a dielectric substrate such as alumina, quartz, silicon, or gallium arsenide. Dashed lines are shown in FIG. 1 to indicate the respective boundaries between the leading transmission lines, the 90-degree bends, and the coupled transmission lines.  
         [0023]    As previously discussed, a problem with traditional couplers is that they typically have relatively low directivity. That is, an incident signal at the coupled port typically leaks out the output port. This leakage is typically about 10 dB lower than the coupling level for the coupler. For example, if a 10-dB coupler is used, it is expected that the leaked signal at the output port is approximately 20 dB below the level of the signal incident at the coupled port. For DRO applications, this leaked signal at the output port contaminates the output spectrum of the DRO, generally requiring external filtering to better clean the DRO output. In many circumstances, the spectrum of the leaked signal from the coupled port is so close in frequency to the signal from the input port that it is not possible to filter out the unwanted spectral lines. In this case, the performance of the system is degraded and there are no means to correct the problem. Thus, there is a need for a directional coupler with higher directivity, such as about 40 dB. If such were the case, the leaked signal at the output port would be 40 dB below the level of the signal incident at the coupled port. This is a substantial reduction of the leaked signal power by about 20 dB or a factor of 100.  
         [0024]    In order to provide this improved directivity, the directional coupler  100  includes coupled transmission lines  120  and  122  having respectively impedance discontinuities  132  and  134  that create additional destructive interference (beyond the destructive interference of this signal produced by the conventional directional coupler) of the signal incident at the coupled port  108 , resulting in less leakage of this signal at the output port  106 . More specifically, the discontinuities generated at the changes in line width before and after regions containing recesses  132  and  134  are designed to generate two signals that originate from the signal that is incident at the coupled port  108  (a first part and a second part) that are substantially equal in amplitude and substantially opposite in phase. Destructive interference occurs when a signal combines with another signal that is propagating in the same direction as the first signal, but cycling with opposite phase and equal amplitude. Since these two signals are substantially equal in amplitude and substantially opposite in phase, the leakage signal from the coupled port  108  is substantially reduced at the output port  106  thereby improving the directivity of the coupler  100 . Since there is substantially no leakage signal from the coupled port  108  present at the output port  106 , this signal power is then caused to exit out one or more of the other ports.  
         [0025]    In the exemplary embodiment, the impedance discontinuities  132  and  134  are in a form of respective recesses on the coupling side of the coupled transmission lines  120  and  122 . The recesses are generally positioned near the middle of the coupled transmission lines  120  and  122 . The ends of the recesses are tapered to make a smoother transition to the non-recessed portions of the coupled transmission lines  120  and  122 . The depth and length of the recesses are selected to obtain a desired directivity for the coupler  100 . The recesses are generally symmetrical about the coupling axis (the axis that extends parallel to the coupled transmission lines, and is midway between the coupled transmission lines), but they need not be symmetrical.  
         [0026]    [0026]FIG. 2 illustrates a top view of another exemplary directional coupler  200  in accordance with the invention. The directional coupler  200  comprises an input port  204 , an output port  206 , a coupled port  208 , and an isolated port  210 . The coupler  200  further comprises a pair of coupled transmission lines  220  and  222 . The directional coupler  200  may also include leading transmission lines  212 ,  214 ,  216  and  218  with corresponding 90-degree bends  224 ,  226 ,  228  and  230  which respectively couple the input port  204 , output port  206 , coupled port  208 , and isolated port  210  to the coupled transmission lines  220  and  222 . The leading transmission lines, the 90 degree bends, and the coupled lines are all formed as a continuous electrical conducting layer disposed on a substrate  202 , which can be a dielectric substrate such as alumina, quartz, silicon, or gallium arsenide. The 90-degree bends each have an added step at the inner corner of the bends. Dashed lines are shown in FIG. 2 to indicate the respective boundaries between the leading transmission lines, the 90-degree bends, and the coupled transmission lines.  
         [0027]    The directional coupler  200  also includes coupled transmission lines  220  and  222  having respectively impedance discontinuities  232  and  234  that create additional destructive interference of an signal incident at the coupled port  208 , resulting in less leakage of this signal at the output port  206 , thereby improving the coupler&#39;s directivity. In the exemplary directional coupler  200 , the impedance discontinuities  232  and  234  are in a form of respective recesses  236  and  238  on the coupling side of the coupled transmission lines  220  and  222 , and corresponding protrusions  240  and  242  on the non-coupling side of the transmission lines  220  and  222 . The recesses  236  and  238  and protrusions  240  and  242  generally coincide along and are positioned near the middle of the coupled transmission lines  220  and  222 . The ends of the recesses  236  and  238  and protrusions  240  and  242  are tapered to make a smoother transition to the non-recessed and non-protruded portions of the coupled transmission lines  220  and  222 . The depth and length of the recesses  236  and  238  and corresponding protrusions  240  and  242  are selected to obtain a desired directivity for the coupler  200 . The recesses and protrusions are generally symmetrical about the coupling axis, but they need not be symmetrical.  
         [0028]    [0028]FIG. 3 illustrates a top view of yet another exemplary directional coupler  300  in accordance with the invention. The directional coupler  300  comprises an input port  304 , an output port  306 , a coupled port  308 , and an isolated port  310 . The coupler  300  further comprises a pair of coupled transmission lines  320  and  322 . The directional coupler  300  may also include leading transmission lines  312 ,  314 ,  316  and  318  with corresponding 90-degree bends  324 ,  326 ,  328  and  330  which respectively couple the input port  304 , output port  306 , coupled port  308 , and isolated port  310  to the coupled transmission lines  320  and  322 . The leading transmission lines, the 90 degree bends, and the coupled lines are all formed as a continuous electrical conducting layer disposed on a substrate  302 , which can be a dielectric substrate such as alumina, quartz, silicon, or gallium arsenide. Dashed lines are shown in FIG. 3 to indicate the respective boundaries between the leading transmission lines, the 90-degree bends, and the coupled transmission lines.  
         [0029]    The directional coupler  300  also includes coupled transmission lines  320  and  322  having respectively impedance discontinuities  332  and  334  that create additional destructive interference of a signal incident at the coupled port  308 , resulting in less leakage of this signal at the output port  306 , thereby improving the coupler&#39;s directivity. In the exemplary directional coupler  300 , the impedance discontinuities  332  and  334  are in a form of respective recesses  336  and  338  on the coupling side of the coupled transmission lines  320  and  322 , and corresponding protrusions  340  and  342  on the non-coupling side of the transmission lines  320  and  322 . The recesses  336  and  338  and protrusions  340  and  342  generally coincide along and are positioned near the middle of the coupled transmission lines  320  and  322 . The ends of the recesses  336  and  338  and protrusions  340  and  342  are tapered to make a smoother transition to the non-recessed and non-protruded portions of the coupled transmission lines  320  and  322 . The depth and length of the recesses  336  and  338  and corresponding protrusions  340  and  342  are selected to obtain a desired directivity for the coupler  300 . The recesses and protrusions are generally symmetrical about the coupling axis, but they need not be symmetrical.  
         [0030]    Directional coupler  300  differs from coupler  200  in that the non-coupling sides of the coupled transmission lines  320  and  322  is respectively tapered  344  and  346  as they extend from their respective 90-degree bends  324 ,  326 ,  328  and  330  to the impedance discontinuities  332  and  334 . Also, the inner corners of the 90-degree bends  324 ,  326 ,  328  and  330  do not include steps, but are part of tapered transitions  344  and  346 . The tapered transitions  344  and  346  improve the impedance match of the coupler  300 .  
         [0031]    [0031]FIG. 4A illustrates a top view of still another exemplary directional coupler  400  in accordance with the invention without connection to adjacent conductors. Directional coupler  400  facilitates tuning of the coupler to provide different coupling levels. This feature is particularly useful for prototyping with directional couplers. The directional coupler  400  comprises input port  404 , output port  406 , coupled port  408 , and isolated port  410 . The coupler  400  further comprises a pair of coupled transmission lines  420  and  422 . The directional coupler  400  may also include leading transmission lines  412 ,  414 ,  416  and  418  with corresponding 90-degree bends  424 ,  426 ,  428  and  430  which respectively couple the input port  404 , output port  406 , coupled port  408 , and isolated port  410  to the coupled transmission lines  420  and  422 . The leading transmission lines, the 90 degree bends, and the coupled transmission lines are all formed as a continuous electrical conducting layer disposed on a substrate  402 , which can be a dielectric substrate such as alumina, quartz, silicon, or gallium arsenide. Dashed lines are shown in FIG. 4 to indicate the respective boundaries between the leading transmission lines, the 90-degree bends, and the coupled transmission lines.  
         [0032]    To give the directional coupler  400  coupling level tuning capability, the coupled transmission lines  420  and  422  each comprises a primary transmission line  432 , one or more adjacent conductors  434   a - f  on the coupling side of the primary transmission line  432 , and one or more adjacent conductors  436   a - e  on the non-coupling side of the primary transmission line  432 . In the exemplary embodiment, the adjacent conductors  434   a - f  and  436   a - e  extend generally parallel with and are spaced apart from the primary transmission line  432 . Also, they are symmetrical about a central and coupling axes of the coupler  400 . Without wire or ribbon bonds connecting the primary transmission line  432  to the adjacent conductors  434   a - f  and  436   a - e,  the adjacent conductors  434   a - f  and  436   a - f  are substantially signal isolated from the line  432 . Once they are fully connected to the primary transmission line  432  by one or more ribbon or wire bonds, they are then signally coupled to the line  432 .  
         [0033]    [0033]FIG. 4B illustrates a top view of the exemplary directional coupler  400  in accordance with the invention with connections to adjacent conductors in a manner that provides looser coupling. For looser coupling, the adjacent conductors  434   a  and  434   f  on the coupling-side are respectively electrically connected to the corresponding primary transmission lines  432  by one or more wire or ribbon bonds  440 , and the adjacent conductors  436   a - e  on the non-coupling side are respectively electrically connected to the corresponding primary transmission lines  432  by one or more ribbon bonds  442 . Looser coupling is achieved because only a relatively small portion (i.e. the combined lengths of adjacent conductors  434   a  and  434   f ) of the total coupling length is coupled closer due to the bridging of the primary transmission lines  432  to the corresponding adjacent conductors  434   a  and  434   f.    
         [0034]    The electrical connection of the primary transmission lines  432  to the corresponding adjacent coupling-side conductors  434   a  and  434   f  gives the coupled transmission lines  420  and  422  a particular width at that region, which translates to a particular characteristic impedance. In order to maintain substantially the same characteristic impedance for the coupled transmission lines  420  and  422  throughout their lengths, the primary transmission lines  432  are electrically connected to the adjacent non-coupling conductors  436   a - e  at the portions of the coupled transmission lines  420  and  422  where there is no bridging of the primary transmission lines  432  to the corresponding adjacent coupling-side conductors  434   a  and  434   f.  In this manner, the widths of the coupled transmission lines  420  and  422  are substantially constant throughout their lengths, thereby maintaining substantially the same characteristic impedance throughout the lengths of the coupled transmission lines  420  and  422 .  
         [0035]    [0035]FIG. 4C illustrates a top view of the exemplary directional coupler  400  in accordance with the invention with connections to adjacent conductors in a manner that provides medium coupling. For medium coupling, the adjacent conductors  434   a - b  and  434   e - f  on the coupling-side are respectively electrically connected to the corresponding primary transmission lines  432  by one or more wire or ribbon bonds  440 , and the adjacent conductors  436   b - d  on the non-coupling side are respectively electrically connected to the corresponding primary transmission lines  432  by one or more ribbon bonds  442 . Medium coupling is achieved because about half (i.e. the combined lengths of adjacent conductors  434   a - b  and  434   e - f ) of the total coupling length is coupled closer due to the bridging of the primary transmission lines  432  to the corresponding adjacent conductors  434   a - b  and  434   e - f.  In order to maintain substantially the same characteristic impedance for the coupled transmission lines  420  and  422  throughout their lengths, the primary transmission lines  432  are electrically connected to the adjacent non-coupling conductors  436   b - c  at the portions of the coupled transmission lines  420  and  422  where there is no bridging of the primary transmission lines  432  to the corresponding adjacent coupling-side conductors  434   a - b  and  434   e - f.    
         [0036]    [0036]FIG. 4D illustrates a top view of the exemplary directional coupler  400  in accordance with the invention with connections to adjacent conductors in a manner that provides tighter coupling. For tighter coupling, the adjacent conductors  434   a - f  on the coupling-side are respectively electrically connected to the corresponding primary transmission lines  432  by one or more wire or ribbon bonds  440 , and the adjacent conductors  436   c  on the non-coupling side are respectively electrically connected to the corresponding primary transmission lines  432  by one or more ribbon bonds  442 . Tighter coupling is achieved because a major portion (i.e. the combined lengths of adjacent conductors  434   a - f ) of the total coupling length is coupled closer due to the bridging of the primary transmission lines  432  to the corresponding adjacent conductors  434   a - f.  In order to maintain substantially the same characteristic impedance for the coupled transmission lines  420  and  422  throughout their lengths, the primary transmission lines  432  are electrically connected to the adjacent non-coupling conductors  436   c  at the portions of the coupled transmission lines  420  and  422  where there is no bridging of the primary transmission lines  432  to the corresponding adjacent coupling-side conductors  434   a - f.    
         [0037]    [0037]FIG. 5 illustrates a block diagram of an exemplary local oscillator  500  using a directional coupler in accordance with the invention. The local oscillator  500  comprises a DRO  502  (which can also be any type of tunable RF/microwave/millimeterwave oscillator), an amplifier  504  (or other device that isolates the output of the DRO  502  from the load connected to the LO output port, such as an attenuator or isolator), a directional coupler  506  (e.g. directional couplers  100 ,  200 ,  300  or  400 ), a crystal oscillator  508 , a phase detector  510 , and a loop filter  512 . The coupler&#39;s input port is coupled to the output of the amplifier  504 , the coupled port is coupled to the phase detector  510 , the isolated port is coupled to a load impedance of Z 0 , and the output port serves as the output of the local oscillator  500 .  
         [0038]    The DRO  502  generates a relatively low phase noise LO signal, which is amplified by amplifier  504 . A portion of the amplified LO signal is coupled to the phase detector  510  by the coupler  506 . The phase detector  510  compares the phase of the reference signal from the crystal oscillator  508  to the phase of the sampled LO signal, and generates a phase error signal. The phase error signal is applied to the loop filter  512  to filter out unwanted frequency components so as to generate the tuning voltage V TUNE  for the DRO  502  to maintain the DRO output within a frequency specification.  
         [0039]    [0039]FIG. 6 illustrates a block diagram of an exemplary receiver  600  using a directional coupler in accordance with the invention. The directional couplers of the invention can be used in many applications, even as part of the receiver  600 . The receiver  600  comprises a low noise amplifier  604  having an input for receiving an RF/microwave/millimeterwave signal from an antenna  602  or other transmission source. The output of the low noise amplifier  604  is coupled to a first down-converting stage comprising a first mixer  606  and a first local oscillator (LO) comprising DRO  614 , optional amplifier  612  (or other device that isolates the output of the DRO  614  from the mixer  606 , such as an attenuator or isolator), a directional coupler  607  (e.g. couplers  100 ,  200 ,  300  and  400 ), phase detector  610 , a reference crystal oscillator  608 , and a loop filter  613 . The output of the DRO  614  is optionally coupled to the input of the amplifier  612  for isolating the output of the DRO  614 . A portion of the local oscillator signal at the output of the amplifier  612  is coupled to the phase detector  610  to phase compare the local oscillator signal with the reference from the crystal oscillator  608 , and to generate a phase error signal. The phase error signal is applied to the loop filter  613  to generate a tuning voltage V TUNE  for the DRO  614  to keep the DRO output within a frequency specification.  
         [0040]    The output of the mixer  606  is coupled to an intermediate frequency (IF) filter  616  to remove the higher frequency products and other unwanted signals from the down-converted received signal. If two-stage down-conversion is desired, the output of the IF filter  616  is coupled to a second down-converting stage comprising a second mixer  620  and a second local oscillator (LO) comprising DRO  624 , optional amplifier  622  (or other device that isolates the output of the DRO  624  from the mixer  620 , such as an attenuator or isolator), a directional coupler  621  (e.g. couplers  100 ,  200 ,  300  and  400 ), a phase detector  626 , the reference crystal oscillator  608  (being common to both down-converting stages), and a loop filter  625 . The output of the DRO  624  is optionally coupled to the input of the amplifier  622  for isolating the output of the DRO  624 . A portion of the local oscillator signal at the output of the amplifier  622  is coupled to the phase detector  626  to phase compare the local oscillator signal with the reference from the crystal oscillator  608 , and to generate a phase error signal. The phase error signal is applied to the loop filter  625  to generate the tuning voltage V TUNE  for the DRO  624  to keep the DRO output within a frequency specification. The output of the mixer  620  is coupled to a baseband filter  630  to remove the higher frequency products and other unwanted signals from the second down-converted received signal to generate a baseband signal.  
         [0041]    [0041]FIG. 7 illustrates a block diagram of an exemplary transmitter  700  using a directional coupler in accordance with the invention. The directional couplers of the invention can be used in many applications, even as part of the transmitter  700 . The transmitter  700  comprises a first up-converting stage for up-converting a baseband signal. The first up-converting stage comprises a first mixer  702  and a first local oscillator (LO) comprising DRO  710 , optional amplifier  708  (or other device that isolates the output of the DRO  710  from the mixer  702 , such as an attenuator or isolator), a directional coupler  703  (e.g. couplers  100 ,  200 ,  300  and  400 ), phase detector  706 , a reference crystal oscillator  704 , and a loop filter  709 . The output of the DRO  710  is optionally coupled to the input of the amplifier  708  for isolating the output of the DRO  710 . A portion of the local oscillator signal at the output of the amplifier  708  is coupled to the phase detector  706  to phase compare the local oscillator signal with the reference from the crystal oscillator  704 , and to generate a phase error signal. The phase error signal is applied to the loop filter  709  to generate a tuning voltage VTUNE for the DRO  710  to keep the DRO output within a frequency specification.  
         [0042]    The output of the mixer  702  is coupled to an intermediate frequency (IF) filter  712  to remove the lower frequency products and other unwanted signals from the up-converted signal. If two-stage up-conversion is desired, the output of the IF filter  712  is coupled to a second up-converting stage comprising a second mixer  714  and a second local oscillator (LO) comprising DRO  718 , optional amplifier  716 , a directional coupler  715  (e.g. couplers  100 ,  200 ,  300  and  400 ), phase detector  720 , the reference crystal oscillator  704  (being common to both up-converting stages), and a loop filter  719 . The output of the DRO  718  is coupled to the input of the amplifier  716  for increasing the power of the local oscillator signal sufficiently to drive the mixer  714 . A portion of the local oscillator signal at the output of the amplifier  716  is coupled to the phase detector  720  to phase compare the local oscillator signal with the reference from the crystal oscillator  704 , and to generate a phase error signal. The phase error signal is applied to the loop filter  719  to generate a tuning voltage V TUNE  for the DRO  718  to keep the DRO output within a frequency specification.  
         [0043]    The output of the mixer  714  is coupled to a radio frequency (RF)/microwave/millimeterwave filter  724  to remove the lower frequency products and other unwanted signals from the second up-converted signal to generate the RF/microwave/millimeterwave signal for transmission via a wireless medium or other transmission medium. The output of the RF/microwave/millimeterwave filter  724  is coupled to the input of a power amplifier  726  (which can comprise of one or more amplification stages) for increasing the power of the RF/microwave/millimeterwave signal for transmission over the wire medium via the antenna  728  or transmission over other types of transmission mediums.  
         [0044]    In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.  
       Appendix A  
       [0045]    I hereby appoint BLAKELY, SOKOLOFF, TAYLOR &amp; ZAFMAN LLP, a firm including: William E. Alford, Reg. No. 37,764; Farzad E. Amini, Reg. No. 42,261; William Thomas Babbitt, Reg. No. 39,591; Carol F. Barry, Reg. No. 41,600; Jordan Michael Becker, Reg. No. 39,602; Lisa N. Benado, Reg. No. 39,995; Bradley J. Bereznak, Reg. No. 33,474; Michael A. Bernadicou, Reg. No. 35,934; Roger W. Blakely, Jr., Reg. No. 25,831; R. Alan Burnett, Reg. No. 46,149; Gregory D. Caldwell, Reg. No. 39,926; Andrew C. Chen, Reg. No. 43,544; Thomas M. Coester, Reg. No. 39,637; Donna Jo Coningsby, Reg. No. 41,684; Dennis M. deGuzman, Reg. No. 41,702; Justin Dillon, Reg. No. 42,486; Stephen M. De Klerk, Reg. No. P46,503; Michael Anthony DeSanctis, Reg. No. 39,957; Daniel M. De Vos, Reg. No. 37,813; Sanjeet Dutta, Reg. No. P46,145; Matthew C. Fagan, Reg. No. 37,542; Tarek N. Fahmi, Reg. No. 41,402; George Fountain, Reg. No. 36,374; Paramita Ghosh, Reg. No. 42,806; James Y. Go, Reg. No. 40,621; James A. Henry, Reg. No. 41,064; Willmore F. Holbrow III, Reg. No. P41,845; Sheryl Sue Holloway, Reg. No. 37,850; George W Hoover II, Reg. No. 32,992; Eric S. Hyman, Reg. No. 30,139; William W. Kidd, Reg. No. 31,772; Sang Hui Kim, Reg. No. 40,450; Walter T. Kim, Reg. No. 42,731; Eric T. King, Reg. No. 44,188; Erica W. Kuo, Reg. No. 42,775; George B. Leavell, Reg. No. 45,436; Gordon R. Lindeen III, Reg. No. 33,192; Jan Carol Little, Reg. No. 41,181; Robert G. Litts, Reg. No. 46,876; Kurt P. Leyendecker, Reg. No. 42,799; Joseph Lutz, Reg. No. 43,765; Michael J. Mallie, Reg. No. 36,591; Andre L. Marais, under 37 C.F.R. § 10.9(b); Paul A. Mendonsa, Reg. No. 42,879; Clive D. Menezes, Reg. No. 45,493; Chun M. Ng, Reg. No. 36,878; Thien T. Nguyen, Reg. No. 43,835; Thinh V. Nguyen, Reg. No. 42,034; Dennis A. Nicholls, Reg. No. 42,036; Daniel E. Ovanezian, Reg. No. 41,236; Kenneth B. Paley, Reg. No. 38,989; Marina Portnova, Reg. No. P45,750; William F. Ryann, Reg. 44,313; James H. Salter, Reg. No. 35,668; William W. Schaal, Reg. No. 39,018; James C. Scheller, Reg. No. 31,195; Jeffrey S. Schubert, Reg. No. 43,098; George Simion, Reg. No. P-47,089; Jeffrey Sam Smith, Reg. No. 39,377; Maria McCormack Sobrino, Reg. No. 31,639; Stanley W. Sokoloff, Reg. No. 25,128; Judith A. Szepesi, Reg. No. 39,393; Vincent P. Tassinari, Reg. No. 42,179; Edwin H. Taylor, Reg. No. 25,129; John F. Travis, Reg. No. 43,203; Joseph A. Twarowski, Reg. No. 42,191; Mark C. Van Ness, Reg. No. 39,865; Thomas A. Van Zandt, Reg. No. 43,219; Lester J. Vincent, Reg. No. 31,460; Glenn E. Von Tersch, Reg. No. 41,364; John Patrick Ward, Reg. No. 40,216; Mark L. Watson, Reg. No. P46,322; Thomas C. Webster, Reg. No. P46,154; and Norman Zafman, Reg. No. 26,250; my patent attorneys, and Firasat Ali, Reg. No. 45,715; and Justin M. Dillon, Reg. No. 42,486; Raul Martinez, Reg. No. 46,904; my patent agents, with offices located at 12400 Wilshire Boulevard, 7th Floor, Los Angeles, Calif. 90025, telephone (714) 557-3800, with full power of substitution and revocation, to prosecute this application and to transact all business in the Patent and Trademark Office connected herewith.