This application is based on and incorporates herein by reference Japanese Patent Application No. 2006-31067 filed on Feb. 8, 2006.
The present invention relates to a transmission line transition having a dielectric substrate and a waveguide tube disposed on the dielectric substrate.
Recently, development of a millimeter wave system for large, high-speed communication or vehicular radar has been advanced. In such a millimeter wave system, a transmission line transition is used for coupling electromagnetic energy, for example, between a waveguide tube and a planar line (e.g., a microstrip line) formed on a dielectric substrate.
As shown in
The millimeter wave system consists of very small components. Therefore, manufacturing variations may be caused when the components are formed and assembled. The manufacturing variations cause characteristic variations between the manufactured systems.
For example, in the case of the transition shown in
A distance between the tip of the antenna P5 and the ground plane P6 determine characteristics of the transition. As shown in
To reduce the manufacturing variations, the components of the transition need to be highly accurately formed and assembled. As a result, manufacturing time and cost of the transition is increased.
In view of the above-described problem, it is an object of the present invention to provide a transmission line transition having a structure that prevents a characteristic variation caused by a manufacturing variation so that the transition can be mass-produced.
A transmission line transition for coupling electromagnetic energy includes first and second dielectric substrates laminated to each other and a waveguide tube attached to the first dielectric substrate. The laminated dielectric substrate provides a dielectric waveguide having a first end short-circuited and a second end communicating with an interior of the waveguide. An antenna connected to a planar line is placed in the dielectric waveguide and spaced from the short-circuited end of the dielectric waveguide by a predetermined distance to excite the waveguide tube.
The short-circuited end reflects a signal propagating through the waveguide tube and the dielectric waveguide and a standing wave occurs in the dielectric waveguide. The antenna is positioned at an anti-node of the standing wave. In such an approach, the electromagnetic energy can be efficiently coupled between a first transmission line consisting of the waveguide tube and the dielectric waveguide and a second transmission line consisting of the planar line.
The transition achieves the short-circuited end of the dielectric waveguide without using a second waveguide member P2 of the conventional transition. In other words, while the transition uses a single-piece waveguide tube, the conventional transition uses a two-piece waveguide tube. Therefore, the transition can be accurately and easily assembled, at least compared to the conventional transition, so that the transition can be mass-produced.
The above and other objectives, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:
A planar line-to-waveguide transition 1 for coupling electromagnetic energy between a planar line and a waveguide is shown in
The first dielectric substrate 3 may be, for example, made of alumina. The first dielectric substrate 3 has a first surface on which the first ground plane 9 is disposed and a second surface on which the second ground plane 11 is disposed.
The waveguide tube 5 may be, for example, a hollow rectangular tube made of aluminum. The waveguide tube 5 has a hollow interior 15 with a rectangular cross section. One open end of the waveguide tube 5 is fixedly secured to the first dielectric substrate 3 through the first ground plane 9 by brazing, screws, or the like. The waveguide tube 5 has a longitudinal direction 10 shown in
The second dielectric substrate 7 may be, for example, made of alumina. The second dielectric substrate 7 has a first surface on which the second ground plane 11 is disposed and a second surface on which the third ground plane 13 is disposed. Thus, the second ground plane 11 is sandwiched between the first and second dielectric substrates 3, 7.
The first ground plane 9 is made of electrically conductive material (e.g., metal thin film) and has a rectangular opening 17 in its center, as shown in
Specifically, a bottom edge of the interior 15 is aligned with a bottom edge of the opening 17 so that the first ground plane 9 has a project portion 9a projecting from a top edge of the interior 15 by a distance Q1. Also, the first ground plane 9 projects from side edges of the interior 15 by a certain distance. Thus, the first ground plane 9 is positioned relative to the waveguide tube 5 such that the opening 17 is entirely within the interior 15 in the longitudinal direction 10.
The second ground plane 11 is made of electrically conductive material and has a rectangular opening 19 in its center, as shown in
The third ground plane 13 is made of electrically conductive material and has no opening. As described above, the third ground plane 13 is disposed on the second surface of the second dielectric substrate 7. The third ground plane 13 covers most of the second surface of the second dielectric substrate 7 as shown in
The first and second ground planes 9, 11 are electrically connected to each other by through holes 23 provided in the first dielectric substrate 3. The second and third ground planes 11,13 are electrically connected to each other by through holes 25 provided in the second dielectric substrate 7. Thus, the first, second, and third ground planes 9,11,13 are electrically connected to one another.
As shown in
A first wavelength Ar of a signal propagating in the first and second dielectric substrates 3, 7 is given by:
In the equation (1), λo represents a second wavelength of the signal propagating in free space and εγ represents a relative permittivity (i.e., a dielectric constant) of the first and second dielectric substrates 3, 7. A distance between the adjacent through holes 23 is less than or equal to a half of the first wavelength λr. Likewise, a distance between the adjacent through holes 25 is less than or equal to a half of the first wavelength λr . Thus, the signal can be efficiently propagating in the transition 1 without leaking between the first, second, and third ground planes 9, 11, 13.
The signal propagates through the interior 15 of the waveguide tube 5, a first dielectric portion surrounded by the through holes 23 of the first dielectric substrate 3, and a second dielectric portion surrounded by the through holes 25 of the second dielectric substrate 3. The first and second dielectric portions form a dielectric waveguide.
A cross-sectional area of the dielectric wave member (i.e., substantially the area of each of the openings 17,19) is determined based on a third wavelength λp of the signal propagating in the dielectric waveguide. Specifically, the cross-sectional area of the dielectric waveguide is reduced, as the third wavelength λp is small. The third wavelength λp is given by:
As shown in
The third ground plane 13 acts as a short-circuited end of the dielectric waveguide. A distance S between the short-circuit end and an antenna 29 in the longitudinal direction 10 is about a quarter of the third wavelength λp . The antenna 29 excites and is excited by the waveguide tube 5.
A feeder 21 is disposed on the second surface of the first dielectric substrate 3. The feeder 21 includes a planar line 27 and the antenna 29 connected to the tip of the planar line 27. For example, the planar line 27 is a microstrip line. The planar line 27 is arranged in the cutout portion 20 and the antenna 29 is arranged in the opening 19 so that the feeder 21 has no physical contact with the second ground plane 11. Specifically, the tip of the antenna 29 and the bottom edge of the opening 19 are spaced from each other by a distance L in a direction perpendicular to the longitudinal direction 10. The distance L determines coupling.(reflection) characteristics of the transition 1.
As described above, in the transition 1 according to the first embodiment, the first dielectric substrate 3 and the second dielectric substrate 7 are laminated to each other to provide the dielectric waveguide. The short-circuit end of the dielectric waveguide is achieved by the third ground plane 13 disposed on the second dielectric substrate 7. Thus, as with the conventional transition shown in
The short-circuited end (i.e., the third ground plane 13) reflects the signal propagating through the waveguide tube 5 and the dielectric waveguide. As a result, a standing wave occurs in the dielectric waveguide. The antenna 29 is positioned at an anti-node of the standing wave. In such an approach, the electromagnetic energy can be efficiently coupled between a first transmission line consisting of the waveguide tube 5 and the dielectric waveguide and a second transmission line consisting of the planar line 27.
The dielectric waveguide is positioned within the cross-sectional area of the interior 15 in the longitudinal direction 10 to prevent occurrence of high-order mode electromagnetic wave. Thus, propagation loss between the dielectric waveguide and the waveguide tube 5 can be reduced.
As shown in
As described above, the first and second dielectric substrates 3, 7 are made of ceramic such as alumina. In this case, conductive patterns as the ground planes 9, 11, 13 are printed on ceramic green sheets, and then the sheets are laminated to each other and burned. Alternatively, the first and second dielectric substrates 3, 7 may be made of resin. In this case, conductive sheets as the ground planes 9, 11, 13 are adhered on resin sheets.
The second embodiment of the present invention is shown in
The distance L is kept constant even when the waveguide tube 35 is improperly fixed to the project portion 31a of the first ground plane 31. Thus, the project portion 31a serves as the margin for error in fixing the waveguide tube 35 to the first ground plane 31 and allows the transition 1 having the desired coupling characteristic to be mass-produced.
The third embodiment of the present invention is shown in
In such an approach, double resonance occurs in the dielectric waveguide so that frequency characteristics of propagation of the electromagnetic energy become broadband characteristics. Further, a distance G between the antenna 49 and the first ground plane 41 is kept constant even when the waveguide tube 45 is improperly fixed to the project portion 41a of the first ground plane 41. Thus, the project portion 41a serves as the margin for error in fixing the waveguide tube 45 to the first ground plane 41 and allows the transition 1 having the desired coupling characteristic to be mass-produced.
The first ground plane may includes both the project portion 31a shown in
The Fourth embodiment of the present invention is shown in
Specifically, a first ground plane 69 is disposed on a first surface of a first dielectric substrate 55. The antenna 53 and a second ground plane 57 are disposed on a second surface of the first dielectric substrate 55. The planar line 51 and a third ground plane 61 are disposed on a second surface of the second dielectric substrate 59. The planar line 51 and the antenna 53 are electrically connected to each other by a through hole 63 provided in the second dielectric substrate 59.
As shown in
The first and second ground planes 69, 57 are electrically connected to each other by through holes 71 provided in the first dielectric substrate 55. The second and third ground planes 57, 61 are electrically connected to each other by through holes 73 provided in the second dielectric substrate 59. Thus, the first, second, and third ground planes 69, 57, 61 are electrically connected to one another.
As shown in
According to the fourth embodiment, the planar line 51 and the antenna 53 are disposed on the different ground planes. In such an approach, flexibility in designing the transition 1 can be improved.
The fifth embodiment of the present invention is shown in
Specifically, a transition 1 according to the fifth embodiment includes first, second, and third dielectric substrates 81, 83, 85 and first, second, third, and fourth ground planes 87, 89, 91, 93.
As shown in
The first and second ground planes 87, 89 are electrically connected to each other by through holes 95 provided in the first dielectric substrate 81. The second and third ground planes 89, 91 are electrically connected to each other by through holes 97 provided in the second dielectric substrate 83. The third and fourth ground planes 91, 93 are electrically connected to each other by through holes 99 provided in the third dielectric substrate 85. Thus, the first, second, third, and fourth ground planes 87, 89, 91, 93 are electrically connected to one another.
As with the fourth embodiment, a planar line 101 and an antenna 103 are formed on the different dielectric substrates. Specifically, the antenna 103 is disposed on a second surface of the first dielectric substrate 81 and the planar line 101 is disposed on the second surface of the third dielectric substrate 85. The planar line 101 and the antenna 103 are electrically connected to each other by a through hole 105 provided in the second and third dielectric substrates 83, 85.
As shown in
In the fifth embodiment, a distance S between the antenna 103 and the short-circuited end of the dielectric waveguide can be easily increased so that the flexibility in designing the transition 1 can be improved.
The sixth embodiment of the present invention is shown in
A transmission line transition 141 according to the seventh embodiment is shown in
The area of an opening 155 of the ground plane 153 is smaller than a cross-sectional area of the hollow interior 157 and the opening 155 is positioned within the interior 157 in a longitudinal direction of the waveguide tube. Specifically, the ground plane 153 has a project portion 153a projecting from a bottom edge of the interior 157 by a distance Q2. Therefore, a distance L between the tip of the antenna 151 and the ground plane 153 of the seventh embodiment is smaller than that between the tip of the antenna 29 and the first ground plane 9 of the first embodiment.
The distance L is kept constant even when the second waveguide member 145 is improperly fixed to the project portion 153a. Thus, the project portion 153a serve as the margin for error in fixing the second waveguide member 145 to the ground plane 153 and allows the transition 141 having the desired coupling characteristic to be mass-produced.
The embodiment described above may be modified in various ways. For example, the dielectric waveguide may be provided by four or more dielectric substrates laminated to each other. The planar line may be a slot line, a coplanar line, a tri-plate type line, or the like that can be formed on the dielectric substrate. The through holes may be via holes.
Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.
Number | Date | Country | Kind |
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2006-031067 | Feb 2006 | JP | national |