Patent Publication Number: US-7907031-B2

Title: Transit structure between a waveguide and a dielectric waveguide having a matching cavity

Description:
TECHNICAL FIELD 
     The present invention relates to a transit structure of two waveguides, one of which is a dielectric waveguide; more particularly, to a transit structure to implement a matching (impedance matching) with a simple structure when a dielectric waveguide is connected to a waveguide. 
     BACKGROUND ART 
     Wireless communication in a knowledge information era is expected to be developed from a second generation wireless communication based on sound and text, and a third generation mobile communication of image information transmission (IMT2000), to a fourth generation system having a transmission speed larger than 100 Mbps. The fourth generation system having such a broad bandwidth requires use of a new frequency in place of a conventional frequency, as the conventional frequency bandwidth has already become saturated, and it is very important to use a millimeter wave bandwidth as the frequency to realize such a broad bandwidth and high-speed communication. 
     However, the communication system of a millimeter wave bandwidth is expensive and bulky as a result of being constructed with a plurality of individual devices, which are the shortcomings in commercializing this bandwidth. In order to overcome these shortcomings and to use millimeter wave RF components, many studies have been developed for the miniaturization of the devices, devices having a low cost and a low loss, and a related packaging technology. 
     Particularly, in case that a System in a Package (SiP) technology employs a low temperature Co-fired ceramics (LTCC), various types of such devices have been proposed, such as a point to multi-points communication transceiver with 26 GHz bandwidth, and a short range wireless communication system with 60 GHz and 70 GHz bandwidths. 
     In such a millimeter wave system, various types of transit structures are used for connecting the transmitters or the receivers to the antennas. 
     Generally, a conventional transit structure is a micro strip line, or a transit structure of a strip line and a waveguide, by using a single layer substrate technology. A rear side cavity shape is generally required through fabrication of a mechanical structure. 
     Recently, a transit structure using a stack process has appeared; this is a structure using a dielectric cavity and an aperture with a lowest surface as a dielectric waveguide and another waveguide. In such conventional technology, there are several shortcomings in realizing a structure having an optimum performance, due to a complex matching structure and dielectric resonator, and many parameters the aperture may have. 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     The present invention has been proposed in order to overcome the above-described problems in the related art. A dielectric waveguide and another waveguide are placed in an orthogonal direction, and a matching is implemented by providing a simple structure with a cavity for a matching between the two dielectric waveguides. It is, therefore, an object of the present invention to provide a transit structure to reduce a size thereof and to shorten a design time thereof. 
     It is another object of the present invention to provide a transit structure of two waveguides including a dielectric waveguide, capable of easily compensating a frequency and matching error generated during practical manufacturing, by varying an impedance characteristic of the dielectric waveguide by allowing a change in the degree of insertion of a tuning rod into the dielectric waveguide. 
     In order to achieve the above-described objects, the present invention is a transit structure generally including a dielectric waveguide, a cavity and another waveguide, wherein the cavity is placed between the dielectric waveguide and the another waveguide. 
     Technical Solution 
     In accordance with an aspect of the present invention, there is provided a transit structure of two waveguides including a dielectric waveguide, characterized in that: the dielectric waveguide is positioned in a direction orthogonal to the other waveguide to connect the two waveguides; and the transit structure includes a cavity to match the dielectric waveguide with the other waveguide. 
     In accordance with another aspect of the present invention, there is provided a transit structure for connecting a waveguide to a dielectric waveguide, the transit structure including: a cavity to match the dielectric waveguide and the other waveguide, wherein the dielectric waveguide and the other waveguide are orthogonal to each other. 
     It is preferable that the dielectric waveguide includes: a first ground surface existing at a top surface of the dielectric waveguide; a second ground surface existing at a bottom surface of the dielectric waveguide where a pattern at a portion thereof connected to the cavity is removed; a dielectric substrate is placed between the first ground surface and the second ground surface to form the dielectric waveguide; and a plurality of conductive vias arranged in at least one row connected to the first ground surface and the second ground surface to form a wall of the dielectric waveguide. 
     It is preferable that if the plurality of conductive vias is arranged in at least two rows, the conductive vias of a front row and the conductive vias of a rear row are placed to connect with each other. 
     It is preferable that the dielectric waveguide is made of many folded dielectric substrates and a top via and a bottom via are connected by a pattern. 
     It is preferable that the cavity is formed by removing a portion of the dielectric substrate placed between a top of a second ground surface where a pattern of a cavity portion is removed and a bottom of a third ground surface where a pattern of the cavity portion is removed, and a cavity wall is formed by a plurality of conductive vias arranged in at least one row to connect the second ground surface to the third ground surface. 
     It is preferable that if the conductive vias are arranged in at least two rows, the conductive vias of a front row and the conductive vias of a rear row are placed to connect with each other. 
     It also is preferable that the dielectric waveguide is made of many folded dielectric substrates, and a top via and a bottom via are connected by a pattern. 
     It is preferable that the dielectric waveguide allows a tuning rod to be inserted, and is capable of controlling a degree of insertion of the tuning rod. 
     It is preferable that the insertion of the tuning rod is performed by inserting the tuning rod into a hole to face a cavity connection unit on the dielectric waveguide. 
     It also is preferable that the transit structure further includes: a dielectric substrate formed on a dielectric waveguide; and a most upper ground surface, wherein the plurality of holes for insertion of the tuning rod is formed on the upper most ground surface and the dielectric substrate. 
     Advantageous Effects 
     The present invention can drastically reduce a design time by simply implementing a transit structure by using only a dielectric waveguide, a cavity and another waveguide on a dielectric substrate, and remarkably reduce a size thereof in comparison with a conventional transit structure, since all designs are finished in a metal waveguide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a concept diagram showing a transit structure of two waveguides, wherein one is a dielectric waveguide, in accordance with one embodiment of the present invention; 
         FIG. 2  is a plan view of the transit structure of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of  FIG. 1 ; 
         FIG. 4  is a three-dimensional exploded perspective view of the transit structure of  FIG. 1  in accordance with one embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of another embodiment of the transit structure; and 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, preferred embodiments of the present invention are described in detail with respect to the accompanying drawings in such a manner that it may easily be carried out by a person having ordinary skilled in the art to which the invention pertains. Similar components are labeled with the same reference numbers in these drawings. 
       FIG. 1  is a concept diagram showing a transit structure of two waveguides including a dielectric waveguide in accordance with one embodiment of the present invention. 
     An overall transit structure includes 3 types of elements i.e., a dielectric waveguide  10 , a cavity  20 , and another waveguide  30 , as shown in  FIG. 1 , and a housing  40  (as illustrated in  FIGS. 2 and 3 ). Sizes of the dielectric waveguide  10  and the waveguide  30  are generally determined by a frequency of the overall system and a structure of a transceiver or the like, and, a width and a height of the cavity  20  positioned between the dielectric waveguide  10  and the waveguide  30  become important factors to determine a performance of the transit structure. 
       FIG. 2  and  FIG. 3  are respectively a plan view and a cross-sectional view of the structure shown in  FIG. 1 . 
     The sizes wg_a and wg_b of the waveguide  30  shown in  FIG. 2  are parameters that are previously determined by a frequency of the system. For example, in case of a WR-22 rectangular waveguide, wg_a×wg_b=5.8 mm×2.9 mm. 
     In order to design the dielectric waveguide based on the other waveguide with an inside thereof being filled with air, overall sizes of the designed waveguide must be constantly reduced by a ratio of 1/√{square root over (∈)} r  in all three dimensions according to the change of the dielectric constant as shown in the following mathematical equation (1).
 
λ g =2π/β=2π√{square root over ( k   2   −k   c   2 )}  Eq. (1)
 
     Wherein, in the equation (1), λ g  is a wavelength of the waveguide, β is a propagation constant, κ is a frequency of the material, κ c  is a blocking wave number, and k=ω√{square root over (μ∈)}, k c =√{square root over ((mπ/a) 2 +(nπ/b) 2 )}{square root over ((mπ/a) 2 +(nπ/b) 2 )} (where ω denotes an angular frequency, μ is a permeability, ∈ is a permittivity, m and n are two integers representing orders, a is a length of a longitudinal axis and b is a length of a vertical axis). 
     Since, at a high frequency on the order of a millimeter wave, a relation of k&gt;&gt;k c  exists, it is noted that λ g  is inversely proportional to √{square root over (∈)} r  as a simplification, where ∈ r  is the relative permittivity of the material thereof. Since a waveguide filter utilizes a TE10 mode, z-axis, i.e., the height, does not affect the performance except for resulting in a slight incremental loss. 
     That is, in case when a dielectric constant of 7.1 is used, the size of a WR-22 waveguide is 5.8 mm×2.9 mm, whereas the size of the dielectric waveguide becomes 5.8/√{square root over (7.1)}=2.18 mm×2.9/√{square root over (7.1)}=1.09 mm. 
     In  FIG. 2 , a length di_ 1  from a center of the cavity  20  to an end of the dielectric waveguide  10  is a very important parameter to determine the transit frequency, and the sizes cav_a and cav_b of the cavity  20  play roles in matching the dielectric waveguide  10  with the waveguide  30 —the overall performance is largely determined by those parameters. 
     In  FIG. 3 , a height di_h of the dielectric waveguide  10  and a height cav_h of the cavity  20  are shown. Herein, the height of the dielectric waveguide  10  does not greatly affect the performance as described above when the dielectric waveguide  10  is operated as a waveguide, but it becomes a major parameter to control the frequency and to control the matching when the transit structure is designed. The height cav_h of the cavity  20  is a major parameter to perform the matching, together with the widths cav_a and cav_b of the cavity  20 , as shown in  FIG. 2 . 
     Therefore, the transit structure in accordance with the present invention determines the performance thereof according to the height di_h and the width di_ 1  of the dielectric waveguide  10  and the widths cav_a and cav_b of the cavity. Since the height of the dielectric waveguide  10  and the height of the cavity  20  depend on a previously determined height of the multi-layered substrate (and also, it is possible that the height of the multi-layered substrate is controlled by folding various sheets, but a continuous change is difficult), the performance of the waveguide transit structure in accordance with the present invention is determined according to the length of the dielectric waveguide  10  and the cavity  20 . 
       FIG. 4  is a three-dimensional exploded perspective view in accordance with one embodiment of the present invention. 
       FIG. 4  shows a structure that a dielectric substrate  12  forming the dielectric waveguide  16  has a first ground surface  11  and a second ground surface  13 , and the first ground surface  11  and the second ground surface  13  are connected through a plurality of conductive vias  14 . The plurality of conductive vias  14  can be at least one row to form a wall of the dielectric waveguide  16 , since it prevents a signal from leaking from the dielectric waveguide. If two rows of the conductive vias are placed to connect with each other, as shown in the drawings, the performance of the dielectric waveguide  16  is further improved. In the second ground surface  13 , a pattern formed on a surface adjacent to the cavity  25  is removed (as referred to by reference numeral  15  in  FIG. 4 ). 
     The cavity  25  is formed by removing a portion of the dielectric substrate  21 . The second ground surface  13  formed on a top of the dielectric substrate  21 , and a third ground surface  22  formed on a bottom of the dielectric substrate  21  are connected through the conductive vias  23 . The conductive vias  23  are positioned with maximal access to the sidewall of the cavity  25  to form a complete cavity  25 . At least one row of the conductive vias  23  can be used in a similar manner to that for the dielectric waveguide. Similar to the second ground surface  13 , a pattern at a portion contacting the cavity  25  is removed (as referred to by reference numeral  24  in  FIG. 4 ). Cavity  32  is a path in which a wave is guided. 
     The waveguide  30  is placed below the cavity  25 . Herein, the waveguide  30  is generally made of metal, but it can give a effect similar to that of the metal by coating metal on a surface of a general dielectric material. Therefore, the present invention is not limited to the metal. 
       FIG. 5  is a cross-sectional view showing application of the transit structure of the present invention to a practical circuit board. It is a drawing of a cross-sectional view of the transit structure shown in  FIG. 4  , but also shows a tuning rod and dielectric substrate  12  of multiple layers. As shown in the drawing, the first ground surface  11  and the second ground surface  13  for the circuit substrate  2  and the dielectric waveguide  16  placed in the module are formed inside of the multi-layered substrate. A plurality of layers  12 - 1 ,  12 - 2  and  12 - 3  can be formed between the first ground surface and the second ground surface  13 . In this case, the plurality of conductive vias  14  are formed in each layer to connect the first ground surface  11  and the second ground surface  13 , and a plurality of patterns  17  and  18  are formed to connect the plurality of conductive vias  14 . A hole  50  is formed to insert the tuning rod  51  from the most upper ground surface  1  to the dielectric waveguide  16 . The second ground surface  13  and the third ground surface  22  are formed on a bottom portion of the dielectric waveguide  16  to construct the cavity  25 , and a plurality of layers can be formed between the second ground surface  13  and the third ground surface  22  similar to the multiple layers for the dielectric waveguide  16 . A plurality of conductive vias  23  is formed along a plurality of wall surfaces of the cavity  25  to connect the plurality of layers. 
     Finally, a waveguide  30  is placed on the third ground surface  22 , and is formed to be connected to a device having an external waveguide interface such as an external filter and an antenna or the like. 
     While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.