Abstract:
A phase error adjustment device configured to connect to an end of a waveguide polarizer and correct phase errors that the waveguide polarizer might generate. In accordance with this embodiment, the phase error adjustment device comprises an aperture having a height and a width, and changes in the dimension of the height or width will change the phase error adjustment quantity. In accordance with another embodiment of the invention, the phase error adjustment device comprises a thickness, and changes in the thickness will change the phase error adjustment quantity.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to a waveguide polarizer, and more specifically to waveguide polarizer differential phase error adjustment device. 
   Satellite antenna systems frequently utilize circularly polarized beams to send and receive communication signals. As one skilled in the art will appreciate, the circularly polarized beams can be generated in a number different of ways. For example, in many instances, a microwave polarizer can be used to convert linear polarized signals to circularly polarized signals. The polarizer essentially converts linearly polarized TE10 mode input signals into circularly polarized signals by decomposing the input linearly polarized signal (TE10 mode) into TE10 mode and TE01 mode signals and introducing a precise 90 degree phase shift between the two (TE10/TE01) modes. When the TE10 mode and TE01 mode signals propagate with equal amplitude and 90 phase difference, the signal is circularly polarized. 
     FIGS. 1   a  and  1   b  illustrate a well known corrugated square waveguide polarizer  100  used to create circularly polarized waves. This particular polarizer design simultaneously achieves a low input match of the TE10 and TE01 modes, as well as a precise 90-degree phase shift between the two orthogonal electric field modes over the usable frequency bands. 
   During design of the corrugated square waveguide polarizer  100 , the 90-degree phase shift is accurately predicted using mode matching techniques and predictions confirmed by known measurements. Performance problems for the waveguide polarizer, however, can occur because of tolerances in the physical structure of the polarizer created during the manufacturing process. As one skilled in the art will appreciate, the phase shift is very sensitive to the fabricated dimensions of the polarizer. 
   In order to obtain less then 1 degree phase error, the polarizer needs to be fabricated with dimensional accuracy of &lt;0.001″ at Ku/Ka bands. These very tight manufacturing tolerances are extremely difficult to achieve on a consistent basis and performance essentially comes down to how well you can manufacture the polarizer. Even the best manufacturing processes typically will create polarizers with tolerance errors that make the polarizers inoperable at certain frequencies. Thus, a device and/or method is needed that will offset or fix the phase shift errors caused by manufacturing tolerance errors. 
   BRIEF SUMMARY OF THE INVENTION 
   One embodiment of the invention relates to a phase error adjustment device configured to connect to an end of a waveguide polarizer and correct phase errors that the waveguide polarizer might generate. In accordance with this embodiment, the phase error adjustment device comprises an aperture having a height and a width, and wherein changes in the dimension of the height or width will change the phase error adjustment quantity. 
   In accordance with another embodiment of the invention, the phase error adjustment device comprises a thickness, and changes in the thickness will change the phase error adjustment quantity. Further, in another embodiment, the phase error adjustment device has an outer shape that matches the outer shape of the end of the waveguide polarizer. 
   In accordance with yet another embodiment, the waveguide polarizer comprises a square waveguide polarizer. In some embodiments, the waveguide polarizer comprises a corrugated square waveguide polarizer, other square input/output polarizers, and the like. In addition, in another embodiment, the waveguide polarizer comprises an aperture, and the height and the width of the aperture of the phase error adjustment device is different from a height and a width of the waveguide polarizer aperture. In yet another embodiment, the material of the phase error adjustment device comprises the same material as the waveguide polarizer. 
   In accordance with another embodiment, the present invention relates to a device for converting a linearly polarized electromagnetic wave signal into a circularly polarized electromagnetic wave signal which comprises a TE10 mode signal and a TE01 mode signal. The TE10 mode signal and the TE01 mode signal have the same signal amplitude and are approximately 90 degrees out of phase. In accordance with this embodiment, the device comprises a waveguide polarizer adapted to convert the linear polarized electromagnetic wave signal into the circularly polarized electromagnetic wave signal. In addition, the device further comprises a phase error adjustment device connected to an end of the waveguide polarizer. The phase error adjustment device is adapted to correct phase errors that may be generated between the TE10 mode signal and the TE01 mode signal by the waveguide polarizer. Accordingly, the phase error adjustment device comprises an aperture having a height and a width, and changes in the dimension of the height or width will change the phase error adjustment quantity of the phase error adjustment device. In accordance with one embodiment, the phase error adjustment device is adapted to correct phase errors, so that the phase between the TE10 mode signal and the TE01 mode signal is approximately 90 degrees. 
   In accordance with yet another embodiment, the present invention relates to a method for adapting a waveguide polarizer to correct for manufacturing tolerances in the waveguide polarizer that might cause phase errors in the circularly polarized electromagnetic signals generated by the waveguide polarizer. In accordance with this embodiment, the method comprises: a) measuring phase errors in the circularly polarized signal caused by the waveguide polarizer; b) determining aperture dimensions of a phase error adjustment device that will correct the phase errors; and c) attaching the phase error adjustment device in cascade with the waveguide polarizer so that the phase errors are corrected, the phase error adjustment device having the aperture dimensions determined in the determining step. 
   In accordance with one embodiment of the invention, a circularly polarized electromagnetic signal comprises a TE10 mode signal and a TE01 mode signal, both signals having approximately the same signal amplitude and being approximately 90 degrees out of phase, and the phase error adjustment device is adapted to correct phase errors so that the phase between the TE10 mode signal and the TE01 mode signal is approximately 90 degrees. 
   A more complete understanding of the present invention may be derived by referring to the detailed description of preferred embodiments and claims when considered in connection with the figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the Figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
       FIG. 1   a  is perspective view of a prior art corrugated square waveguide polarizer; 
       FIG. 1   b  is a cross-sectional view of the polarizer of  FIG. 1   a;    
       FIG. 2  side view of a square waveguide polarizer having one embodiment of a phase error adjustment device attached thereto; 
       FIG. 3  is an end view of one embodiment of a phase error adjustment device in accordance with the present invention; 
       FIGS. 4   a  and  4   b  are graphs illustrating the differential phase versus frequency for unadjusted square waveguide polarizers; 
       FIGS. 5   a  and  5   b  are graphs illustrating the differential phase versus frequency for the square waveguide polarizers of  FIGS. 4   a  and  4   b , respectively, but with phase error adjustment devices attached thereto; and 
       FIG. 6  is a graph illustrating predicted differential phase shift values versus corrugation depths for two embodiments of phase error adjustment devices. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As noted above, waveguide polarizer manufacturing or fabrication errors may create phase errors in the circularly polarized signals generated by the polarizer. Thus, the present invention relates to devices and methods for correcting those phase errors. More specifically, the present invention involves cascading a separate external phase adjustment device (namely, phase trimmer) to compensate for the phase shift errors caused by imperfect manufacturing. The present invention also relates to methods for determining the phase shift errors, and compensating for those errors by manufacturing suitable phase adjustment devices. 
   Referring now to  FIGS. 2 and 3 , one embodiment of waveguide polarizer  100  (see  FIG. 2 ) and a phase adjustment device  110  is shown. In accordance with this embodiment, waveguide polarizer  100  comprises a corrugated waveguide polarizer. As one skilled in the art will appreciate, waveguide polarizer  100  can be manufactured using any suitable material that can propagate electromagnetic waves, such as aluminum, steel, or the like. In addition, while the illustrated embodiment shows a square waveguide polarizer, other suitable polarizer devices can be used, such as, for example, a septum polarizer, or the like. 
   In accordance with the illustrated embodiment, phase adjustment device  110  comprises a device that can be connected to an end of (i.e., in cascade with) waveguide polarizer  100 . Phase adjustment device  110  includes an aperture  111  having a height (“H”) 114  and a width (“W”  116  (see  FIG. 3 ), and device  110  has a thickness (“T”)  112  (see  FIG. 2 ). As discussed in more detail below, the phase adjustment qualities of phase adjustment device  110  can be changed by changing the dimensions of aperture  111  and/or the thickness (“T”)  112 . Also, as illustrated in  FIG. 3 , phase adjustment device  110  can be connected to waveguide polarizer  100  using any suitable fastener or fastening device, for example, using fasteners through attachment holes  118 . 
   As discussed briefly above, phase adjustment device  110  is configured to offset or remedy any phase errors that a waveguide polarizer  100  may have as a result of manufacturing tolerances or other defects. As one skilled in the art will appreciate, for a circularly polarized wave, the phase between the TE01 mode signal and the TE10 mode signal should be 90 degrees or as close to 90 degrees as possible. The manufacturing tolerances or other defects many times will cause the phase between the TE01 mode and the TE10 mode to be sufficiently large that the wave is no longer circularly polarized. Phase adjustment device  10  will add phase lead or lag (+ or − phase adjustment), so that the phase between the two modes are as close to 90 degrees as possible. As mentioned above, adjusting the height  114  and/or width  116  of aperture  111 , and/or adjusting the thickness  112  of phase adjustment device  110  will add the necessary phase lead or lag, as appropriate. 
   To determine the necessary dimensions for phase adjustment device  110 , the phase errors for the waveguide polarizer  100  first are determined, which indicates the amount of phase lead or lag adjustment that is need. Then, modeling software can be used to calculate the phase adjustment device aperture dimensions  114 ,  116  and thickness  112  that will generate the necessary phase lead or lag. 
   Table 1 illustrates an example of how phase adjustment device  110  can correct phase shift errors across the widely separated frequency bands around 20/30 GHz. In this example, the predicted phase values are the expected phase shift values between the TE01 mode signal and the TE10 mode signal for a properly fabricated waveguide polarizer over various frequency values. As one can see, the predicted phase values are all within a degree or so of the desired 90 degree value. The “As Built” values show the actual phase values for a manufactured waveguide polarizer. As one can see, the “As Built” values are as much as 7 degrees off. By inserting a phase adjustment device  110 , the actual phase values can be corrected so that they are close to 90 degrees, making the waveguide polarizer operable. 
   
     
       
             
           
             
             
           
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Predict and Corrected Measured Differential Phase Shift 
             
           
        
         
             
                 
               Frequency GHz 
             
           
        
         
             
               Test Case 
               19.70 
               19.95 
               20.20 
               29.50 
               29.75 
               30.00 
             
             
                 
             
           
        
         
             
               Predicted Phase (deg) 
               −91.2 
               −90.1 
               −89.1 
               −89.0 
               −90.3 
               −90.4 
             
             
               As Built Measured 
               −86.0 
               −84.0 
               −83.0 
               −83.1 
               −94.2 
               −85.5 
             
             
               (deg) 
             
             
               Corrected with Device 
               −90.6 
               −89.6 
               −88.7 
               −88.1 
               −89.0 
               −90.1 
             
             
               (deg) 
             
             
               Corrected Phase Error 
               4.6 
               5.6 
               5.7 
               5.0 
               5.2 
               4.6 
             
             
               (deg) 
             
             
                 
             
           
        
       
     
   
     FIGS. 4   a ,  4   b ,  5   a , and  5   b  illustrate additional examples of how phase adjustment device  110  corrects phase errors in polarizers.  FIG. 4   a  shows a differential phase curve  400  for a manufactured waveguide polarizer. As one can see, the differential phase is near 90 degrees at the frequency of about 18.75 GHz (point  402 ). In this example, however, the operational frequency is around 20 GHz, which has a differential phase of about 83 degrees or so (point  404 ). A value well off of the desired 90 degrees.  FIG. 4   b  shows a differential phase curve  410  for a waveguide polarizer that includes a phase adjustment device  110 . As illustrated in this example, at the operating frequency of 20 GHz, the differential phase value is corrected so that it is about 89.5 degrees (point  412 ). In this example, with the phase adjustment device in place, the wave guide polarizer will have an operational frequency range between about 19.7 GHz and about 20.2 GHz (illustrated as lines  414  and  416 ). 
   Similarly,  FIGS. 5   a  and  5   b  illustrate an example for an operating frequency of about 30 GHz. In this example,  FIG. 5   a  shows a differential phase curve  500  for a manufactured waveguide polarizer. As one can see, the differential phase is not close to 90 degrees for the illustrated operational frequency. For the operational frequency of about 30 GHz, the differential phase is about 85 degrees or so (point  502 ). Again, a value well off of the desired 90 degrees.  FIG. 5   b  shows a differential phase curve  510  for a waveguide polarizer that includes a phase adjustment device  110 . As illustrated in this example, at the operating frequency of about 30 GHz, the differential phase value is corrected so that it is about 90 degrees (point  512 ). In this example, with the phase adjustment device in place, the wave guide polarizer has an operational frequency range between about 29.5 GHz and about 30 GHz (illustrated as lines  514  and  516 ). 
   Referring now to  FIG. 6 , a chart showing the amount that various phase adjustment devices will adjust phase is shown. In this chart, curve  600  illustrates the amount of phase adjustment for a phase adjustment device having an aperture height of 0.400 inches, an aperture width of 0.4355 inches and a thickness of 0.050 inches. As can be seen, this particular device provides a phase lead adjustment of about 3.75 degrees at 20.00 GHz (point  602 ) and about 3.5 degrees at 30.00 GHz (point  604 ). 
   Similarly, curve  610  illustrates the amount of phase adjustment for a phase adjustment device having an aperture height of 0.415 inches, an aperture width of 0.4355 inches, and a thickness of 0.05 inches. As can be seen, this particular device provides a phase lead adjustment of about 1.7 degrees at 20.00 GHz (point  612 ) and about 1.5 degrees at 30.00 GHz (point  614 ). 
   Curves  620  and  630  illustrate the amount of phase adjustment for the same devices as are illustrated by curves  610  and  600 , respectively, except that the devices are rotated 90 degrees. Thus, curve  620  illustrates the amount of phase adjustment for a device having an aperture height of 0.4355 inches, an aperture width of 0.415 inches, and a thickness of 0.05 inches. This particular device provides a phase lag of about −1.7 degrees at 20.00 GHz (point  622 ) and about—1.5 degrees at 30.00 GHz (point  624 ); the same phase adjustment as curve  610  except a lag instead of a lead. 
   Similarly, curve  630  illustrates the amount of phase adjustment for a device having an aperture height of 0.4355 inches, an aperture width of 0.400 inches, and a thickness of 0.05 inches. This particular device provides a phase lag of about −3.75 degrees at 20.00 GHz (point  632 ) and about −3.5 degrees at 30.00 GHz (point  634 ). Again, the same phase adjustment as curve  600  except a lag instead of a lead. 
   In conclusion, the present invention provides devices and methods for correcting phase shift errors in waveguide polarizers. While detailed descriptions of one or more embodiments of the invention have been given above, various alternatives, modifications, and equivalents will be apparent to those skilled in the art without varying from the spirit of the invention. Therefore, the above description should not be taken as limiting the scope of the invention, which is defined by the appended claims.