Abstract:
The high order mode electromagnetic wave coupler and coupling method uses one or more Y-shaped bifurcated waveguides to divide the wave to one or more order, so as to divide the target electromagnetic wave proportionally into equal shares. The waveguide is used to inject the electromagnetic wave to a main waveguide, so that the electromagnetic wave is converted into high order mode in the main waveguide. For example, a rectangular waveguide TE 10  mode can be converted to a circular TE 01  mode, wherein this conversion can also be applied to higher order modes and microwave guide-shaped modes. The coupling method includes a electromagnetic wave power dividing section and mode converting section, of which the power divider and dividing method can divide the electromagnetic wave proportionally. The coupler and coupling method feature high converting efficiency, high mode purity, high bandwidth, and convenient operation.

Description:
RELATED U.S. APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       REFERENCE TO MICROFICHE APPENDIX  
       [0003]     Not applicable.  
       FIELD OF THE INVENTION  
       [0004]     The present invention relates generally to a high order mode electromagnetic wave coupler and coupling method using proportional distributing waves, and more particularly to a coupling technology that converts the rectangular waveguide TE 10  mode to the circular waveguide TE 01  mode.  
       BACKGROUND OF THE INVENTION  
       [0005]     The TE 01  mode, having advantages of field azimuthal symmetry and low propagating loss, is widely used in microwave applications, such as in gyrotron microwave sources. When applied to microwave plasma heating, the symmetrical distribution of the circular TE 01  mode is expected to make heating more evenly.  
         [0006]     Two methods have been classified to generate the TE 01  mode with a cylindrical waveguide. One method is in-line coupling, and another is sidewall coupling. The former uses a deformed waveguide structure to convert a wave into the desired mode gradually. The transition length is generally long, and multiple modes could be excited during the converting process, wherein a Tantawi converter is commonly used. The latter, sidewall coupling, often uses a long and straight waveguide with coupling holes on the sidewall. Like the in-line converter, this type of converter needs converter components with longer lengths so that the electric wave can be converted slowly to the desired mode. However, during the converting process, the waves of the unwanted modes will interact with the electron beam, which will result in serious mode competition. Therefore, shortening the transition length and improving the mode purity could effectively lower the possibility of mode competition.  
         [0007]     Thus, to overcome the aforementioned problems of the prior art, it would be an advancement in the art to provide an improved structure that can significantly improve the efficacy.  
         [0008]     To this end, the inventor has provided the present invention of practicability after deliberate design and evaluation based on years of experience in the production, development and design of related products.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The primary objective of the present invention is to provide a high order mode electromagnetic wave coupler using proportional distributing waves. The invention comprises an electromagnetic wave power divider, being comprised of a Y-shaped bifurcated waveguide to divide the wave to one or more orders. The divided wave is proportional so that the electromagnetic wave has a symmetric magnitude after passing through the bifurcated rectangular waveguide, and so that the electromagnetic wave can distribute the waves to a position with a suitable angle after passing through the curved waveguide. The wave is then injected into the mode converter; therefore, the coupler features high converting efficiency, high mode purity, high bandwidth, and convenient operation.  
         [0010]     Another objective of the present invention is to provide a high order mode electromagnetic wave coupling method using proportional distributing waves, being comprised of a power divider and mode-converter. The high order mode electromagnetic wave coupler, using a coupling method based upon proportional distributing waves, includes an electromagnetic wave power divider (section), having one or more Y-shaped bifurcated waveguides to divide the wave to one or more orders. The input end of the Y-shaped bifurcated waveguide is a rectangular waveguide, and the other end is split into two rectangular waveguides. Each Y-shaped bifurcated waveguide is connected to the power divider by a curved waveguide. The divided wave is proportional so that the electromagnetic wave has a symmetric magnitude after passing through the bifurcated rectangular waveguide, and so that the electromagnetic wave can distribute the waves to a position with a suitable angle, after passing through the curved waveguide. Then, the wave is injected into the mode converter (section). The other end of Y-shaped bifurcated waveguide is split into two rectangular waveguides, so that a slightly tapered section is connected to the end of the Y-shaped bifurcated waveguide through a curved waveguide.  
         [0011]     The invention also includes a mode-converter (section), which comprises a main waveguide, which has corresponding coupling holes on the sidewall. The electromagnetic wave is coupled by the rectangular waveguides that are connected to the curved waveguide into a polarized wave.  
         [0012]     The present invention provides a new high-efficiency TE 01  mode coupler, specifically a high order mode electromagnetic wave coupler and coupling method. The coupler features reduced converting components (main waveguide  21 ), high converting efficiency (shortened transition length), high mode purity (99.99%), high bandwidth, and convenient operation.  
         [0013]     For example, converting a linear polarized wave from rectangular waveguide TE 10  mode to a circular waveguide TE 01  mode is based on the above-mentioned principles. The method extends to other high order and microwave guide-shaped mode conversions. The TE 01  mode has drawn much attention in a variety of applications, such as Electron Cyclotron Maser (ECM) based gyrotron microwave sources, microwave systems, electromagnetic input and output devices, including microwave equipment, microwave plasma sources, microwave material processing, as well as applications in telecommunications industry and national defense industry. Among a wide range of selection in couplers for microwave, the circular TE 01  mode is commonly used due to its features of azimuthally symmetric electric field and low ohmic loss. The TE 01  mode in the present invention has high mode purity of 99.9%, and the converting efficiency is 98.5%, which is superior to conventional methods.  
         [0014]     The electromagnetic wave power divider A of the present invention has two Y-shaped bifurcated waveguides  11  to divide the wave to one or more orders. The divided wave is proportional so that the electromagnetic wave has symmetric magnitude after passing through the bifurcated rectangular waveguide  111 , and so that the electromagnetic wave can distribute the waves to a position with suitable angle after passing through the curved waveguide  110 . Then, the wave is injected into the mode converter B. The coupler features high converting efficiency, high mode purity, high bandwidth, and convenient operation. The coupler can generate multiple coupling modes, TE 01 , TE 21 , TE 31 , TE 41 , TE 51 .  
         [0015]     Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]      FIG. 1  shows a perspective view of the assembled electromagnetic wave coupler.  
         [0017]      FIG. 2   a  shows a cross-section view of the electric field distribution and the electric field direction with HFSS at the power dividing section.  
         [0018]      FIG. 2   b  shows a schematic view of the reflection coefficient of the input port.  
         [0019]      FIG. 3   a  shows a cross-section view of the electric field distribution with HFSS.  
         [0020]      FIG. 3   b  shows a graph illustration of the transmission frequency reaction of the four rectangular TE 10  modes to circular TE 01  mode.  
         [0021]      FIG. 4   a  shows a graph illustration of the distribution of the electric field strength of the converter coupler with HSFF.  
         [0022]      FIG. 4   b  shows a graph illustration of the first five modes&#39; transmission losses and the reflection loss.  
         [0023]      FIG. 5  shows an exploded perspective view of the model of the electromagnetic wave coupler.  
         [0024]      FIG. 6   a  shows a perspective view of two similar electromagnetic wave couplers.  
         [0025]      FIG. 6   b  shows a graph illustration of the transmission frequency reaction of the two similar electromagnetic wave couplers in connection.  
         [0026]      FIG. 7   a  shows a graph illustration of the HFSS electromagnetic field intensity distribution of the two identical electromagnetic wave couplers with different angles.  
         [0027]      FIG. 7   b  shows a graph illustration of the transmission frequency reaction of the two identical electromagnetic wave couplers with different angles.  
         [0028]      FIG. 8  shows the schematic view of a diagram of the experimental setup and result.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     The features and the advantages of the present invention will be more readily understood upon a thoughtful deliberation of the following detailed description of a preferred embodiment of the present invention with reference to the accompanying drawings.  
         [0030]     As shown in  FIG. 1 , there a high order mode electromagnetic wave coupler using proportional distributing waves.  
         [0031]     The invention includes an electromagnetic wave power divider A, which has one or more Y-shaped bifurcated waveguides  11  to divide the wave to one or more orders. The input end of the Y-shaped bifurcated waveguide  11  is a rectangular waveguide, and the other end is split into two rectangular waveguides. Each Y-shaped bifurcated waveguide  11  is connected to the power divider by a curved waveguide  110 . The divided wave is proportional so that the electromagnetic wave has symmetric magnitude after passing through the bifurcated rectangular waveguide  111 , and so that the electromagnetic wave can distribute the waves to a position with suitable angle after passing through the curved waveguide  110 . Then, the wave is injected into the mode converter B. The other end of Y-shaped bifurcated waveguide  11  is split into two rectangular waveguides  111 , so that a slightly tapered section  112  is connected to the end of the Y-shaped bifurcated waveguide  111  through a curved waveguide  110 . The curved waveguide  110  is connected to the mode converter B, so that an optimized connector  113  could be set.  
         [0032]     The invention also includes a mode-converter B, which has a main waveguide  21  with corresponding coupling holes  22  on the sidewall. The electromagnetic wave is coupled by the rectangular waveguides  111  that are connected to the curved waveguide  110  into a polarized wave.  
         [0033]     The Y-shaped bifurcated waveguide  11  of the electromagnetic wave power divider A forms an included angle of less than  180 . For the mode converter B, the cross-section shape of the main waveguide  21  is optimized for coupling efficiency between the rectangular and columnar waveguides.  
         [0034]     Based on the structure, a high order mode electromagnetic wave coupling method uses proportional distributing waves.  
         [0035]     A first section is the electromagnetic wave power dividing section, which has one or more Y-shaped bifurcated waveguides  11  to divide the wave to one or more orders. The divided wave is proportional. A slightly tapered section  112  is connected to the end of the Y-shaped bifurcated waveguide  11  so that the electromagnetic wave has a symmetric magnitude after passing through the bifurcated rectangular waveguide  111 , which is then connected through a curved waveguide  110  to distribute the waves to a position with suitable angle. An optimized connector  113  can now be set.  
         [0036]     A second section uses a main waveguide  21 , in which the electromagnetic wave is coupled into a polarized wave by injecting into the rectangular waveguides  111  that are connected to the curved waveguide  110 .  
         [0037]     For the electromagnetic wave power divider A, the possible converting modes based on different amounts of evenly distributed energy are shown below: 
        (one time division)     split to 2: use the TE 21 , mode as the main converting mode, and the remaining includes TE mn , m=0,1,2,4,6,8 . . . , n=1,2,3,4,5 . . . whereas, m=multiples of 0, 1 and 2, n=1 or above;     (multiple divisions)     split to 3: use the TE 01 , TE 31  modes as the main converting modes, and the remaining includes TE mn , m=0,3,6,9,12 . . . , n=1,2,3,4,5 . . . whereas, m=multiples of 0 and 3, n=1 or above;     split to 4: use the TE 01 , TE 41  modes as the main converting modes, and the remaining includes TE mn , m=0,4,8,12,16 . . . , n=1,2,3,4,5 . . . whereas, m=multiples of 0 and 4, n=1 or above; and     split to 5: use the TE 01 , TE 51  modes as the main converting modes, and the remaining includes TE mn , m=0,5,10,15 . . . , n=1,2,3,4,5 . . . whereas, m=multiples of 0 and 5, n=1 or above, and so on.        
 
         [0044]     The present invention uses a polarized TE 01  mode converter as an example. The mode converting process consists of two sections. The first section is the electromagnetic wave power dividing section, which has one or more Y-shaped bifurcated waveguides  11  to divide the wave to one or more orders. The input end of the Y-shaped bifurcated waveguide  11  is a rectangular waveguide, and the other end is split into two rectangular waveguides. Each Y-shaped bifurcated waveguide  11  is connected to the power divider by a curved waveguide  110 . A slightly tapered section  112  is connected to the end of the Y-shaped bifurcated waveguide  11  to minimize the reflection. The divided wave is proportional so that the electromagnetic wave has symmetric magnitude after passing through the bifurcated rectangular waveguide  111 , and so that the electromagnetic wave can distribute the waves to a position with a suitable angle after passing through the curved waveguide  110 . Then, the wave is injected into the mode converter B, to generate multiple signals with equal amplitude and electric fields. The second section is the mode converting section, in which the signal is transmitted into a main waveguide  21  to form a pure polarized TE 01  mode. The following discusses the operating principles and design details of each section.  
         [0045]     A. Power Dividing Section: Minimize the Input Reflection  
         [0046]     The reflection is minimized by optimizing the geometry of the Y-splitters. An input power is first divided into two equal amplitude signals through a Y-shaped bifurcated power divider  11 . A slightly tapered section  112  is connected to the end of the Y-shaped bifurcated waveguide  11  to minimize the reflection. The signal is divided in the bifurcated rectangular waveguide  111  after passing through the curved waveguide  110 . The curved waveguide  110  and slightly tapered horn  112  can be shut completely to minimize multiple reflections. Then, multiple signals are outputted with suitable angles and equal amplitudes after passing through the waveguide  11  or optimized connector  113 .  FIG. 2   a  shows the cross-section view of the electric field distribution and the electric field direction with HFSS at the power dividing section.  FIG. 2   b  shows the reflection coefficient of the input port. The reflection of input port P 1 —rectangular waveguide  11  is minimized by optimizing the geometry of the Y-splitters. The figure shows the reflection of the entire frequency band below 20 dB. At the end of the four output ports (ports  1   a - d ), the color spectrums are the same, but the electric field orientations are differed. This means, at this moment, all the field strengths are the same but the direction is clockwise. The electric field distribution and the electric field direction with HFSS shown in the cross-section view ( FIG. 2   a ) show the reflection coefficient of the input port and can minimize multiple reflections. The only reflection signal is detected at input port P 1 . The reflection coefficient of the entire frequency range is better than that of 20 dB. Therefore, though the optimized frequency is not at the center, it has an insignificant effect on the performance of the coupling device. The mode converter determines the bandwidth of the coupling device, as shown below and discussed herein.  
         [0047]     B. Mode Converting Stage: Optimize the Transmission Effect  
         [0048]     The first section generates multiple signals with equal magnitude but different electric field orientations. In the second section, the signals excite the desired TE 01  mode, the size of the optimized connector  113  of the sidewall being optimized to provide effective coupling between the rectangular and cylindrical waveguide.  FIG. 3   a  shows the cross-section view of the electric field distribution with HFSS. The wave is injected into each rectangular waveguide  111  after passing through the optimized connector  113  of the curved waveguide  110 , and it forms a polarized TE 01  mode at the main waveguide  21 .  
         [0049]      FIG. 4   a  shows the distribution of the electric field strength of the converter coupler with HSFF. The mode converting process can be seen in this figure. With a radius of 6.0 mm, the cutoff frequencies for the first five modes are 14.7, 19.1, 24.3, 30.5, and 30.5 GHz for TE  11 , TM 01 , TE 21 , TM 11 , and TE 01 , respectively. Therefore, when exciting the desired TE 01  mode, the concentration of the other four modes shall be kept as low as possible. The sidewall couplings rule out the possibility of exciting TM waves due to the electric field orientation. In addition, the quad-feed structure is unfavorable to TE 11  and TE 21  modes. Instead, it is suitable for a four-fold or a circular symmetric field pattern. Thus, in the operating frequency range, only the TE 01  mode could be formed and high mode purity is expected.  
         [0050]      FIG. 4   b  shows the first five modes&#39; transmission losses and the reflection loss. A TE 10  rectangular waveguide mode injected into port  1  can be converted to five different circular waveguide modes at port  2 . The converting efficiency of a specific mode is defined as the output power of this mode at port  2  divided by the input power at port  1 . The converting efficiency of the desired mode is very high, and those of the other four modes are extremely low (less than 0.1%). Close to the center frequency, the converting efficiency of the desired mode is about 98.5%, mainly due to the reflection and the ohmic loss. As to the spurious modes, all the concentrations are less than −40 dB, except for some ripples. These ripples are mainly due to the phase imbalance in the power-dividing section.  
         [0051]      FIG. 5  shows the design drawing of the coupler: electromagnetic wave power divider A and mode converter B. The rectangular TE 10  mode is converted into a polarized TE 01  mode in the main waveguide  21 . All components are machined with Computer Numerical Control (CNC) lathe with a tolerance of 0.01 mm, and are aligned with pins and fastened with screws.  
         [0052]     Two identical electromagnetic couplers are joined back-to-back to measure the mode (as seen in  FIG. 6   a ), and the frequency reaction of the transmission between the two electromagnetic couplers (as seen in  FIG. 6   b ) is the simulate result of two identical polarized TE 01  mode converters. Butt transmission measurement is often used to display the coupling features. The setup for the simulation and measurement is the same as shown in  FIG. 5 . Between the two couplers, there is a uniform middle section of 1.0 cm. A well calibrated two-port VNA (Agilent 8510C) is employed. The measured results exhibit excellent agreement with the simulation results. The ohmic loss from the metal wall accounts for the main converting loss. As shown in  FIG. 7   a , in examining the field symmetry and other competition modes, the angle θ between the two identical converters can be adjusted. Three specific angles are 0°, 45°, and 90°.  FIG. 7   b  shows the transmission frequency reaction of the two identical electromagnetic wave couplers with different angles.  
         [0053]     Although the simulation and measurement results are consistent, further evidence is required to show the effectiveness of the converting coupler. One of the methods is to show the field mode of TE 01 .  FIG. 8  shows the schematic diagram of the experimental setup and result. The 0.5 W RF power is provided by the traveling wave tube amplifier (Hughes 1077H) driven by a synchronizer (Agilent 8357a). A slightly tapered section is connected at the end of the converter to enlarge the size of the field pattern for visual inspection. A temperature sensitive liquid crystal display (LCD) sheet, displaying full color spectrum when the temperature changes from 25 to 30° C., is placed in front of the horn. The circular and azimuthal symmetric field pattern evidences the purity of the circular TE 01  mode. If a converting mode were mixed with a non-converting mode, irregular field distribution would appear.