Abstract:
An improved multi-junction waveguide circulator overlaps two quarter-wave dielectric transformer sections so that the transitional sections occur concurrently in the same length of waveguide. Consequently, the two quarter-wavelength sections require a total length of between one-quarter wavelength and one-half wavelength, with no air gap between the two sections along the length of the internal cavity. The improved waveguide circulator can be implemented in variations from a minimum of two ferrite circulator elements held in close proximity to one another to any number of ferrite elements as required to achieve the desired isolation performance or to create a switch matrix with any combination of input and output ports. The improved waveguide circulator minimizes the length of the transitions between adjacent ferrite elements and thus reduces losses, component size, and mass.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract no. N00173-07-C-4000 awarded by the Naval Research Laboratory. 
     
    
     REFERENCE TO A “MICROFICHE APPENDIX” 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates in general to waveguide circulators for the non-reciprocal transmission of microwave energy; and more particularly to a novel system for reducing the size, mass, and insertion loss of the transition between adjacent circulators. 
         [0005]    2. Description of the Related Art 
         [0006]    Multi-junction waveguide ferrite circulator assemblies have a wide variety of uses in commercial and military, space and terrestrial, and low and high power applications. A waveguide circulator assembly may be implemented in a variety of applications, including but not limited to LNA redundancy switches, T/R modules, switch matrices, and switched-beam antenna systems. Ferrite circulators are desirable for these applications due to their high reliability, as there are no moving parts required. This is a significant advantage over mechanical switching devices. In most of the applications for multi-junction waveguide switching and non-switching circulators, small size, low mass, and low insertion loss are significant qualities, for example, in switched-beam antenna arrays where switches are located directly behind an antenna array. 
         [0007]    A commonly used type of waveguide circulator has three waveguide arms arranged at 120° and meeting in a common junction. This common junction is loaded with a non-reciprocal material such as ferrite. When a magnetizing field is created in this ferrite element, a gyromagnetic effect is created that can be used for circulating the microwave signal from one waveguide arm to another. By reversing the direction of the magnetizing field, the direction of circulation between the waveguide arms is reversed. Thus, a switching circulator is functionally equivalent to a fixed-bias circulator but has a selectable direction of circulation. Radio frequency (RF) energy can be routed with low insertion loss from one waveguide arm to either of the two output arms. If one of the waveguide arms is terminated in a matched load, then the circulator acts as an isolator, with high loss in one direction of propagation and low loss in the other direction. 
         [0008]    For applications where additional isolation is required between waveguide ports or where additional input/output ports are required, multiple waveguide circulators and isolators are used. The most basic building blocks for multi-junction waveguide circulator networks are single circulator junctions, optimized for an impedance match to an air-filled waveguide interface. For the purposes of this description, the terms “air-filled,” “empty,” “vacuum-filled,” or “unloaded” may be used interchangeably to describe a waveguide structure. The circulators can be connected in various configurations as required for the desired isolation and input/output port configuration. The direction of circulation may either be fixed or switchable. 
         [0009]    Conventional waveguide networks comprised of multiple ferrite elements typically have impedance-matching transition and an air-filled waveguide section between the ferrite elements. For example, conventional waveguide circulators may transition from one ferrite element to a dielectric-filled waveguide such as a quarter-wave dielectric transformer structure, to an air-filled waveguide section, and then back to another dielectric-filled waveguide section and the next ferrite element. The dielectric transformers are typically used to match the lower impedance of the ferrite element to that of the air-filled waveguide. The air-filled waveguide section between quarter-wave dielectric transformers is designed to be sufficiently long, generally at least a quarter-wavelength, so as to allow the fields to transition back to the standard waveguide TE 1,0  mode between circulators. Thus, the conventional transition between ferrite elements occurs over a length of three-quarters of a wavelength or greater between adjacent ferrite elements. This sets the minimum separation distance that can be obtained in multi-junction assemblies when the input/output ports of multiple circulators are intercoupled to provide a more complex microwave switching or isolation arrangement. This can result in a multi-junction waveguide structure that is undesirably large and heavy. Furthermore, the insertion loss of a multiple circulator assembly increases as the separation distance between ferrite elements is increased as a result of the finite conductivity of the waveguide structure. 
         [0010]    Referring now to  FIG. 1 , there is shown a top view of a conventional two-junction waveguide circulator structure. Magnetizing windings  109  are inserted through apertures in each leg of the ferrite elements  102  in order to establish a magnetizing field in each ferrite element. The polarity of this field can be switched back-and-forth by the application of current on the magnetizing winding to create a switchable circulator. Each of the ferrite elements have a quarter-wave dielectric transformer  110  or  111  attached to each leg. There are two transformers  110  attached to the adjacent legs of the ferrite elements and four transformers  111  attached to the remaining legs of the elements. As shown in  FIG. 1 , there is a substantial air gap of distance “G” between the quarter-wave dielectric transformers  110  that are attached to the adjacent legs of the ferrite elements. This distance “G” is typically longer than a quarter-wavelength. Dielectric spacers  112  are disposed on the top and bottom surfaces of the two ferrite elements. In  FIG. 1 , the bottom spacers are hidden from view. These dielectric spacers are used to properly position the ferrite elements in the conductive waveguide structure  100  and to provide a thermal path out of the ferrite elements to the conductive waveguide structure for high power applications. The conductive waveguide structure may include waveguide input/output ports  121 ,  122 ,  123 , and  124 . These ports provide interfaces, such as for signal input and output, for example. Empirical matching elements are not shown, but they may be disposed on the surface of the conductive waveguide structure to affect the performance. The matching elements may be capacitive/inductive dielectric or metallic buttons that are used to empirically improve the impedance match over the desired operating frequency band. 
         [0011]    Previous patents have described approaches for decreasing the spacing and loss between the ferrite elements by replacing the standard quarter-wave dielectric transformers with a reduced height waveguide transition. This method removes the quarter-wave dielectric transformers, but the reduced height transition is sensitive to dimensional variations, which results in a design that is expensive and difficult to manufacture and assemble. Other patents have described approaches for eliminating the quarter-wave dielectric transformers between ferrite elements. These methods provide size and insertion loss benefits, but this comes at the expense of isolation and frequency bandwidth. 
         [0012]    In view of the problems with the conventional waveguide circulator structures disclosed above, there is a need for a multi-junction waveguide circulator structure that provides improvements in the critical areas of size, mass, and insertion loss without sacrificing the manufacturability or isolation performance of the assembly. 
       SUMMARY 
       [0013]    The present invention improves upon traditional multi-junction waveguide circulators by overlapping two quarter-wave dielectric transformer sections so that these quarter-wave dielectric transformer sections occur concurrently in the same length of waveguide. Instead of using the typical method of transitioning from one ferrite element to a dielectric-filled waveguide to an air-filled waveguide and then back to another dielectric-filled waveguide section and into the next ferrite element, the invention eliminates the air-filled waveguide section resulting in a 0 to 100% overlap of adjacent quarter-wave dielectric transformers along the same length of waveguide. Consequently, the two quarter-wavelength sections require a total length of between one-quarter wavelength and one-half wavelength. In traditional multi-junction waveguide circulators, the length of the two quarter-wavelength transitional sections is generally greater than three-quarters of a wavelength. 
         [0014]    The quarter-wave dielectric transformers are generally relatively thin (for example, less than about 0.015″ (0.381 mm) thick for operations at about 40 GHz), which helps to minimize the impact of the additional dielectric loading of the overlapping section on the impedance match. Any effects of the additional dielectric loading can be accounted for by selecting different dimensions for the overlapping and non-overlapping quarter-wave dielectric transformers as determined using the traditional analytical and empirical means of optimization. As known in the prior art, empirical matching elements may also be disposed on the surface of the conductive waveguide structure to further affect the performance. The matching elements are generally capacitive/inductive dielectric or metallic buttons that are used to empirically improve the impedance match over the desired operating frequency band. 
         [0015]    The waveguide circulator in accordance with the invention can be implemented in variations from a minimum of two ferrite circulator elements held in close proximity to one another to any number of ferrite elements as required to achieve the desired isolation performance or to create a switch matrix with any combination of input and output ports. The waveguide circulator in accordance with the invention minimizes the length of the transitions between adjacent ferrite elements and thus reduces losses, component size, and mass. 
         [0016]    In one aspect of the invention, a ferrite circulator having a waveguide structure with an internal cavity is provided. The waveguide structure includes a plurality of ports extending from the internal cavity and at least two ferrite elements disposed in the internal cavity. A first ferrite element has a first quarter-wave dielectric transformer and an adjacent second ferrite element has a second quarter-wave dielectric transformer, wherein at least a portion of the first and second quarter-wave dielectric transformers overlap along a length of the internal cavity. 
         [0017]    In another aspect of the invention, a ferrite circulator having a waveguide structure with an internal cavity is provided. The waveguide structure includes a plurality of ports extending from the internal cavity and at least two ferrite elements disposed in the internal cavity. A single transformer is located between the at least two ferrite elements. The single transformer has the functionality of two quarter-wave dielectric transformers, the first ferrite element and the second ferrite element being separated by a distance between no more than the length of two quarter-wave dielectric transformers at an operating frequency. 
         [0018]    In still another aspect of the invention, a ferrite circulator having a waveguide structure with an internal cavity, the waveguide structure including a plurality of ports extending from the internal cavity is provided. A first ferrite element is disposed in the internal cavity, the first ferrite element having at least a first and a second quarter-wave dielectric transformer. A second ferrite element is disposed in the internal cavity adjacent to the first ferrite element, the second ferrite element having a third quarter-wave dielectric transformer disposed such that at least a portion of the first and third quarter-wave dielectric transformers overlap along a length of the internal cavity so that first and second ferrite element are separated by a distance between no more than the length of two quarter-wave dielectric transformers at an operating frequency. A third ferrite element is disposed in the internal cavity adjacent to the first ferrite element, the third ferrite element having a fourth quarter-wave dielectric transformer. The third ferrite element is disposed such that no portions of the second and fourth quarter-wave dielectric transformers overlap along a length of the internal cavity. 
         [0019]    Additional advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The accompanying drawings are included to provide further understanding of the invention and are incorporated in and constitute a part of this specification. The accompanying drawings illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the Figures: 
           [0021]      FIG. 1  shows a top view of a conventional two-junction waveguide circulator structure; 
           [0022]      FIG. 2  shows a perspective view of the internal portion of a two-junction waveguide circulator structure incorporating two partially overlapping dielectric quarter-wave transformers slightly offset from center according to one embodiment of the present invention; 
           [0023]      FIG. 3  shows a top view of the structure shown in  FIG. 2 ; 
           [0024]      FIG. 4  compares measured data for a prototype of the design shown in  FIG. 2  to measured data for a conventional design as shown in  FIG. 1 , exemplary of the Ka-band of operating frequency; 
           [0025]      FIG. 5  shows a perspective view of the internal portion of a two-junction waveguide circulator structure incorporating two partially overlapping dielectric quarter-wave transformers manufactured as a single piece according to one embodiment of the present invention; 
           [0026]      FIG. 6  shows a top view of the structure shown in  FIG. 5 ; 
           [0027]      FIG. 7  shows a perspective view of the internal portion of a two-junction waveguide circulator structure incorporating two partially overlapping dielectric quarter-wave transformers offset from center and aligned with the opposite edges of the ferrite elements according to one embodiment of the present invention; 
           [0028]      FIG. 8  shows a top view of the structure shown in  FIG. 7 ; 
           [0029]      FIG. 9  shows a perspective view of the internal portion of a two-junction waveguide circulator structure incorporating two partially overlapping dielectric quarter-wave transformers offset from center and aligned beyond the opposite edges of the ferrite elements according to one embodiment of the present invention; 
           [0030]      FIG. 10  shows a top view of the structure shown in  FIG. 9 ; 
           [0031]      FIG. 11  shows a perspective view of the internal portion of a two-junction waveguide circulator structure incorporating two partially overlapping dielectric quarter-wave transformers with one dielectric quarter-wave transformer centered to a ferrite element and the other dielectric quarter-wave transformer offset from the centerline of the ferrite element according to one embodiment of the present invention; 
           [0032]      FIG. 12  shows a top view of the structure shown in  FIG. 11 ; 
           [0033]      FIG. 13  shows a perspective view of the internal portion of a two-junction waveguide circulator structure incorporating two fully overlapping dielectric quarter-wave transformers offset from center and aligned with the opposite edges of the ferrite elements according to one embodiment of the present invention; 
           [0034]      FIG. 14  shows a top view of the structure shown in  FIG. 13 ; 
           [0035]      FIG. 15  shows a perspective view of the internal portion of a two-junction waveguide circulator structure incorporating two fully overlapping dielectric quarter-wave transformers manufactured as a single piece according to one embodiment of the present invention; 
           [0036]      FIG. 16  shows a top view of the structure shown in  FIG. 15 ; 
           [0037]      FIG. 17  shows a perspective view of the internal portion of a two-junction waveguide circulator structure incorporating two minimally overlapping dielectric quarter-wave transformers slightly offset from center according to one embodiment of the present invention; 
           [0038]      FIG. 18  shows a top view of the structure shown in  FIG. 17 ; 
           [0039]      FIG. 19  shows a perspective view of the internal portion of a two-junction waveguide circulator structure incorporating two minimally overlapping dielectric quarter-wave transformers manufactured as a single piece according to one embodiment of the present invention; 
           [0040]      FIG. 20  shows a top view of the structure shown in  FIG. 19 ; 
           [0041]      FIG. 21  shows a perspective view of the internal portion of a four-junction waveguide circulator structure incorporating three pairs of partially overlapping dielectric quarter-wave transformers slightly offset from center according to one embodiment of the present invention; 
           [0042]      FIG. 22  shows a top view of the structure shown in  FIG. 21 ; 
           [0043]      FIG. 23  shows a perspective view of the internal portion of a twelve-junction waveguide circulator structure incorporating ten pairs of partially overlapping dielectric quarter-wave transformers slightly offset from center according to one embodiment of the present invention; and 
           [0044]      FIG. 24  shows a top view of the structure shown in  FIG. 23 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0045]    Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. It important to note that while the embodiments below illustrate the ferrite element as having a Y-shape with three legs, the invention also includes a variety of differing shapes, including a triangular puck or rectangular puck shape. While these shapes may not be considered to have legs as described below, they nevertheless have particularly protruding portions which may operate in a manner similar to the toroid legs described below. 
         [0046]      FIG. 2  shows a perspective view of a two-junction waveguide circulator structure in accordance with a first embodiment of the invention. Magnetizing windings  209  and  216  are inserted through apertures in each leg of the ferrite elements  202  and  203 , respectively, in order to establish a magnetizing field in the ferrite element. The polarity of this field can be switched back-and-forth by the application of current on the magnetizing windings  209 ,  216  to create a switchable circulator. Dielectric spacers  212  are disposed on the top and bottom surfaces of the two ferrite elements. The bottom spacers are partially hidden from view. These dielectric spacers are used to properly position the ferrite elements in the conductive waveguide structure  200  and to provide a thermal path out of the ferrite elements to the conductive waveguide structure for high power applications. The conductive waveguide structure may include waveguide input/output ports  221 ,  222 ,  223 , and  224 . These ports provide interfaces, such as for signal input and output, for example. As known in the prior art, empirical matching elements (shown, e.g., as  219  in  FIGS. 7 and 8 ) may be disposed on the surface of the conductive waveguide structure to affect the performance. The matching elements may be capacitive/inductive dielectric or metallic buttons that are used to empirically improve the impedance match over the desired operating frequency band. 
         [0047]    Each of the ferrite elements have a quarter-wave dielectric transformer  210  or  211  attached to each leg. Note that, as in conventional designs, the length of the quarter-wave dielectric transformers may deviate in length from a standard calculation of a quarter-wavelength. The standard calculation of a quarter-wavelength distance can be determined given the height and width of the waveguide and the width and dielectric constant of the quarter-wave dielectric transformer. In an exemplary design for the 37 to 40 GHz frequency range, the waveguide dimensions are those of standard WR-22 waveguide, the width of the dielectric transformer is 0.011 inches (0.279 mm) and the relative dielectric constant is 4.5. Given these values, a quarter-wavelength is approximately 0.080 inches (2.032 mm) using standard calculation methods. However, optimal performance was realized using a length of 0.067 inches (1.702 mm) for the quarter-wave dielectric transformers. In practice, the length of the quarter-wave dielectric transformer may deviate from the standard calculation due to discontinuities in the propagation modes between the ferrite-loaded, dielectric-loaded, and air-filled waveguide sections. It is not uncommon for the standard calculation and the actual length of the quarter-wave dielectric transformers to differ by up to 25%. 
         [0048]    There are two quarter-wave dielectric transformers  210  attached to the adjacent legs of the ferrite elements and four transformers  211  attached to the remaining legs of the elements. As shown in  FIG. 2 , the quarter-wave dielectric transformers  210  that are attached to the adjacent legs of the ferrite elements overlap along the length of the transformers so that portions of both transformers are contained within the same section of waveguide.  FIG. 3  shows a top view of the structure of  FIG. 2 . In  FIG. 3 , the length of the overlapping region between the adjacent quarter-wave dielectric transformers  210  is denoted as “D.” It is important to note that there is no air-filled waveguide section separating the adjacent ferrite elements  202  and  203 . The waveguide region between the ferrite elements contains either one or two quarter-wave dielectric transformers  210  along the entire length. As illustrated in  FIG. 3 , the overlap of the two quarter-wave dielectric transformers in this embodiment is roughly 50% of their length or one-eighth of a wavelength. This results in a spacing of approximately three-eighths of a wavelength between the ferrite elements. The additional embodiments described below will show that the overlap can vary from 0% to 100%. As shown in  FIG. 3 , the adjacent quarter-wave dielectric transformers  210  are spaced very closely to one another along the waveguide width (the direction perpendicular to the transformers  210 ), leaving a de minimus air gap. The additional embodiments described below will show that this separation distance along the waveguide width is not critical. 
         [0049]    In operation as a 1 input/3 output switch, an RF signal is provided as input to the waveguide port  221  and is delivered as output through either waveguide port  222 ,  223 , or  224 . The signal enters the waveguide structure  200  through waveguide port  221  and, depending upon the direction of magnetization of ferrite element  202 , either passes through ferrite element  202  and out waveguide port  222  or passes through both ferrite elements  202  and  203  and out waveguide port  223  or  224 . The direction of signal propagation through a ferrite element can be described as clockwise or counter-clockwise with respect to the center of the ferrite element. For example, if the signal input through waveguide port  221  passes in a clockwise direction through ferrite element  202 , it will propagate in the direction of the second ferrite element  203 . For this signal to continue through the second ferrite element  203  towards port  224 , the magnetization of ferrite element  203  should be established so as the propagating signal passes in the counter-clockwise direction. The RF signal will thereby exit through waveguide port  224  with low insertion loss. Summarizing the above-described scenario, the RF signal propagates from the input port  221  to the output port  224  with low insertion loss (effectively ON) and from the input port  221  to the other two output ports  222  and  223  with high insertion loss (effectively OFF or isolated). 
         [0050]    To change the low loss output port from output port  224  to output port  223 , a magnetizing current is now passed through magnetizing winding  216  so as to cause circulation through ferrite element  203  in the clockwise direction. The magnetic bias of ferrite element  202  is also established so that the input signal will propagate in a clockwise direction with respect to the center junction of ferrite element  202 . This allows the RF signal to propagate from the input port  221  to output port  223  with low insertion loss (effectively ON) and from the input port  221  to the other two output ports  222  and  224  with high insertion loss (effectively OFF or isolated). 
         [0051]    In the conventional designs, as was shown in  FIG. 1 , a distance “G” of air-filled waveguide is employed in the transition from one ferrite element to another. In the embodiment of  FIG. 2  and  FIG. 3 , the air-filled waveguide section is removed and the ferrite elements are moved closer to one another by an additional distance of “D,” which is the overlap in the length of the quarter-wave dielectric transformers  210 . Thus, the distance between the ferrite elements is decreased by a total length of G+D in embodiments of the present invention. This reduction in transition length leads to lower insertion loss as well as smaller size and weight for multi-junction circulator assemblies. In an exemplary design for the 37 to 40 GHz frequency range, the air-filled waveguide length “G” would generally be at least 0.1 inches for a conventional design and the overlap length “D” is designed to be 0.030 inches in the new invention. This length of “D” provides a quarter-wave dielectric transformer overlap of approximately 40% in comparison to the 0.075 inch length of the quarter-wave dielectric transformers. In this example, the invention provides a savings of 0.13 inches in the spacing between ferrite elements or roughly one-third of a waveguide wavelength. This size improvement becomes more important in larger groupings of circulators, as will be illustrated in additional embodiments described below. The improvement in size also leads to improvements in loss, as shown in  FIG. 4 .  FIG. 4  contains a plot comparing the insertion loss per circulator for the new invention and the prior art. The conventional design has approximately 0.04 dB more loss per circulator junction due to the additional waveguide losses over the longer length. The other RF performance parameters, such as isolation and return loss are similar for the conventional designs and the new invention. The dimensions of the ferrite element, dielectric spacers, and waveguide cross-section are the same as in conventional designs, so the conventional methods of design through empirical methods or proprietary or commercially-available design software can be employed. Although the exemplary design is for the 37 to 40 GHz range, it should be understood that this invention can be applied to any frequency of operation for waveguide circulators using quarter-wave dielectric transformers, typically encompassing the 1 to 10 GHz frequency range. 
         [0052]    Other patents have described approaches for eliminating the quarter-wave dielectric transformers between ferrite elements. In an exemplary design for the 37 to 40 GHz frequency range, the spacing between ferrite elements is approximately 0.1 inches longer in the new invention than in the prior patents. However, the new invention operates over a broader frequency range than the prior patents due to the use of the quarter-wave dielectric transformers. Furthermore, the new invention provides higher isolation of approximately 20 to 25 dB per circulator junction versus 15 to 20 dB per circulator junction for the prior patent. 
         [0053]    Referring now to  FIG. 5 , there is shown a perspective view of another embodiment of the device according to the present invention. This embodiment is different from that of  FIG. 2  in that the two quarter-wave dielectric transformers  210  have been replaced by a single transformer  231 , which has the functionality of two quarter-wave dielectric transformers. The  FIG. 2  embodiment utilizes a de minimus air gap between the two quarter-wave dielectric transformers. If a multi-junction waveguide circulator is used in a high power application or in an application that sees a wide range of temperatures, differences in the coefficients of thermal expansion between the ferrite elements  202  and  203  and the conductive waveguide structure  200  could stress the adhesive bond lines that constrain all of the individual pieces to the waveguide structure. The higher the stress in the bond lines, and the greater the chances of breaking an adhesive bond line or damaging a ferrite element. Thus, the embodiment of  FIG. 2  may be preferable in certain applications. However, if adhesive bond line stress is not a concern, then the embodiment of  FIG. 5  has the advantage of a lower parts count and lower cost. The dimensions of the transformer  231  in  FIG. 5  would be the same as the combination of the two  FIG. 2  quarter-wave dielectric transformers  210  with no air gap. This is illustrated in  FIG. 6 , which is a top view of the  FIG. 5  embodiment. 
         [0054]    Referring now to  FIG. 7 , there is shown a perspective view of another embodiment of the device according to the present invention.  FIG. 8  contains a top view of the embodiment of  FIG. 7 . Whereas the  FIG. 2  and  FIG. 3  embodiment utilizes a de minimus air gap between the two quarter-wave dielectric transformers  210 , the embodiment of  FIG. 7  and  FIG. 8  shows that the two quarter-wave dielectric transformers  232  can be moved closer to the outside edges of the ferrite elements  202  and  203 , resulting in a gap between the transformers that is several times greater than the width of the transformers. Note that the  FIG. 7  and  FIG. 8  embodiment utilizes the same overlap length “D” between the two quarter-wave dielectric transformers  232  as in the  FIG. 2  and  FIG. 3  embodiment.  FIGS. 7 and 8  also include optional empirical matching elements  219  disposed on the surface of the conductive waveguide structure  200  to affect the performance. The matching elements  219  may be capacitive/inductive dielectric or metallic buttons that are used to empirically improve the impedance match over the desired operating frequency band. Although the matching elements  219  are shown only in  FIGS. 7 and 8 , they may be similarly included in any of the other embodiments described herein. 
         [0055]    Referring now to  FIG. 9 , there is shown a perspective view of another embodiment of the device according to the present invention.  FIG. 10  contains a top view of the embodiment of  FIG. 9 . This embodiment shows that the two quarter-wave dielectric transformers  233  can extend beyond the edges of the ferrite elements  202  and  203 . Note that the  FIG. 9  and  FIG. 10  embodiment utilizes the same overlap length “D” between the two quarter-wave dielectric transformers  233  as in previous embodiments; however, the transformers  233  have been made thicker in width than in the previous embodiments. This embodiment illustrates the fact that as the quarter-wave dielectric transformers  233  are moved farther from the center line of the waveguide, the width of the transformers can be increased to provide similar impedance to that of a centered transformer. The size and location of the overlapping quarter-wave dielectric transformers can be determined empirically, either through design prototypes or by the use of finite element analysis software. Additionally, empirical matching elements (not shown) may be disposed on the surface of the conductive waveguide structure to affect the performance as known in the prior art. 
         [0056]    Referring now to  FIG. 11 , there is shown a perspective view of another embodiment of the device according to the present invention.  FIG. 12  contains a top view of the embodiment of  FIG. 1 . This embodiment illustrates that the quarter-wave dielectric transformers  234  and  235  may be located asymmetrically with respect to the center line of the waveguide width.  FIG. 12  shows that quarter-wave dielectric transformer  234  is centered with respect to ferrite element  202  and the center line of the waveguide, but quarter-wave dielectric transformer  235  is aligned to the outside edge of ferrite element  203 . Note that the  FIG. 11  and  FIG. 12  embodiment utilizes the same overlap length “D” between the two quarter-wave dielectric transformers  233  as in previous embodiments. 
         [0057]    Referring now to  FIG. 13 , there is shown a perspective view of another embodiment of the device according to the present invention.  FIG. 14  contains a top view of the embodiment of  FIG. 13 . This embodiment is similar to that of  FIG. 7  and  FIG. 8 , but the ferrite elements  202  and  203  are separated by a shorter distance “D 1 ,” which is equal in length to a single quarter-wave dielectric transformer  236 . This embodiment reflects a complete 100% overlap of the quarter-wave dielectric transformers  236  and thus “D 1 ” is the minimum separation distance possible using the new invention, equal to one-quarter wavelength. 
         [0058]    Referring now to  FIG. 15 , there is shown a perspective view of another embodiment of the device according to the present invention.  FIG. 16  contains a top view of the embodiment of  FIG. 15 . This embodiment is similar to that of  FIG. 5  and  FIG. 6  in that two individual quarter-wave dielectric transformers have been replaced by a single transformer  237 , but the ferrite elements  202  and  203  are now separated by a shorter distance “D 1 ,” which is equal in length to a single quarter-wave dielectric transformer  237 . This embodiment reflects a complete 100% overlap of the quarter-wave dielectric transformers  236  and thus “D 1 ” is the minimum separation distance possible using the new invention, equal to one-quarter wavelength. 
         [0059]    Referring now to  FIG. 17 , there is shown a perspective view of another embodiment of the device according to the present invention.  FIG. 18  contains a top view of the embodiment of  FIG. 17 . This embodiment is similar to that of  FIG. 2  and  FIG. 3 , but the ferrite elements  202  and  203  are separated by a longer distance “D 2 ,” which is equal in length to the sum of the lengths of the two quarter-wave dielectric transformers  238 . This embodiment reflects a minimum 0% overlap of the quarter-wave dielectric transformers  238  and thus “D 2 ” is the maximum separation distance possible using the new invention, equal to one-half wavelength. As made clear in  FIGS. 17 and 18  for the purposes of this invention, a 0% overlap is defined as being equal to (and no greater than) the length of the sum of the lengths of the two quarter-wave dielectric transformers. Thus, this embodiment differs from the  FIG. 1  prior art in that there is no air-filled waveguide section of length “G” between the two quarter-wave dielectric transformers  238 . 
         [0060]    Referring now to  FIG. 19 , there is shown a perspective view of another embodiment of the device according to the present invention.  FIG. 20  contains a top view of the embodiment of  FIG. 19 . This embodiment is similar to that of  FIG. 17  and  FIG. 18 , but the two quarter-wave dielectric transformers  238  have been combined into a single half-wave dielectric transformer  239 . This half-wave dielectric transformer  239  can be aligned with the center line of the ferrite elements  202  and  203  as shown in  FIG. 20 . This embodiment reflects a minimum 0% overlap of the quarter-wave dielectric transformers  239  and thus “D 2 ” is the maximum separation distance possible using the new invention, equal to one-half wavelength. Note that this embodiment differs from the  FIG. 1  prior art in that there is no air-filled waveguide section of length “G” between the two quarter-wave dielectric transformers  239 . 
         [0061]    Referring now to  FIG. 21 , there is shown a perspective view of another embodiment of the device according to the present invention.  FIG. 22  contains a top view of the embodiment of  FIG. 21 . This embodiment is similar to that of  FIG. 2  and  FIG. 3 , but it contains four ferrite elements  301 ,  302 ,  303 , and  304  instead of two. In operation as a 1 input/5 output switch, an RF signal is provided as input to the waveguide port  321  and is delivered as output through either waveguide port  322 ,  323 ,  324 ,  325 , or  326 . The center ferrite element  304  has adjacent ferrite elements  301 ,  302 , and  303  on all three legs. As shown in  FIG. 21  and  FIG. 22 , the quarter-wave dielectric transformers  311 ,  312 , and  313  that are attached to the adjacent legs of the ferrite elements overlap along the length of the transformers so that portions of both transformers are contained within the same section of waveguide. In  FIG. 22 , the length of the overlapping region between the adjacent quarter-wave dielectric transformers  311 ,  312 , and  313  is denoted as “D 3 ,” “D 4 ,” and “D 5 ,” respectively. It is important to note that there are no air-filled waveguide section separating the center ferrite element  304  from the adjacent ferrite elements  301 ,  302 , and  303 . The waveguide region between the ferrite elements contains either one or two quarter-wave dielectric transformers  311 ,  312 , and  313  along the entire length. As illustrated in  FIG. 22 , the overlap “D 3 ,” “D 4 ,” and “D 5 ,” of the adjacent quarter-wave dielectric transformers  311 ,  312 , and  313  is roughly 50% of their length or one-eighth of a wavelength. This results in a spacing of approximately three-eighths of a wavelength between the ferrite elements. The overlap percent of the adjacent quarter-wave dielectric transformers  311 ,  312 , and  313  can vary independent of one another and can range from 0% to 100%. As shown in  FIG. 22 , the adjacent quarter-wave dielectric transformers  311 ,  312 , and  313  are spaced very closely to one another along the waveguide width (the direction perpendicular to “D 3 ,” “D 4 ,” and “D 5 ”), leaving a de minimus air gap. As previously illustrated for the two-junction waveguide circulator structures, variations ranging from a zero length gap to a gap several times wider than the quarter-wave dielectric transformers are possible. 
         [0062]    Referring now to  FIG. 23 , there is shown a perspective view of another embodiment of the device according to the present invention.  FIG. 24  contains a top view of the embodiment of  FIG. 23 . This embodiment is similar to that of  FIG. 21  and  FIG. 22 , but it contains twelve ferrite elements instead of four. In operation as a 1 input/13 output switch, an RF signal is provided as input to the waveguide port  401  and is delivered as output through either waveguide port  402 ,  403 ,  404 ,  405 ,  406 ,  407 ,  408 ,  409 ,  410 ,  411 ,  412 ,  413 , or  414 . This embodiment further illustrates the value of this invention in reducing the size of large multi-port circulator networks. In an exemplary design for the 37 to 40 GHz frequency range, this embodiment has a diameter of approximately 2.1 inches as compared to 3.5 inches using the conventional design methods. Therefore, the new invention provides a 40% reduction in size over the conventional design. 
         [0063]      FIGS. 23 and 24  also illustrate how embodiments of the present invention may be combined with elements of conventional waveguide circulator structures to provide desired spacing to create a multi-output switch. Thus, ferrite elements  420  and  421  utilize a conventional air-filled transition between elements  420  and  421 , while the remaining transitions include embodiments of the present invention. 
         [0064]    Although the exemplary embodiments of the invention are described with respect to a latching circulator switch junction, such as in  FIG. 2 , the invention can be applied to a fixed circulator junction that uses a current pulse of only one polarity through the magnetizing winding, or to a circulator for which a permanent magnet is used to bias the ferrite element. 
         [0065]    While exemplary embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous insubstantial variations, changes, and substitutions will now be apparent to those skilled in the art without departing from the scope of the invention disclosed herein by the Applicant. Accordingly, it is intended that the invention be limited only by the spirit and scope of the claims, as they will be allowed.