Patent Application
20100097158
This invention relates in general to radio frequency transmission, and in particular to a radio frequency coaxial transition.
The transition between a vertical and horizontal radio frequency (“RF”) propagation path within circuit boards has proven to be inefficient. Such transitions are typically mismatched and include inductive discontinuities in the circuit path and have relatively high insertion loss and poor return loss. Previous attempts have included capacitance compensation on the center conductor of the vertical coaxial structure, processing smaller external vertical coaxial features, or using smaller size external surface mount coaxial parts to reduce the inductive parasitic.
The teachings of the present disclosure relate to a coaxial transition that includes a first conductor aligned along a first axis. The transition also includes a ground shield surrounding the first conductor such that a first gap exists between the first conductor and the ground shield. An electric field radiates between the first conductor and the ground shield through the first gap. The transition further includes a second conductor aligned along a second axis and coupled to the first conductor. The second conductor forms a second gap between the second conductor and a portion of the ground shield. A first portion of the electric field radiates between the second conductor and the ground shield through the second gap. The transition also includes a top ground plane aligned substantially parallel to the second conductor. A third gap exists between the top ground plane and the second conductor. The second gap and the third gap are substantially parallel with the second conductor therebetween.
Technical advantages of particular embodiments include a coaxial transition that has little or no inductive break therein. Accordingly, a coaxial transmission line may transition (e.g., change directions from horizontal to vertical) more efficiently than a traditional coaxial transition. This may reduce insertion loss and obtain an improved return loss compared to a similarly sized traditional coaxial transition.
Other technical advantages will be readily apparent to one of ordinary skill in the art from the following figures, descriptions, and claims. Moreover, while embodiments may include all, some, or none of the enumerated advantages.
A more complete understanding of particular embodiments will be apparent from the detailed description taken in conjunction with the accompanying drawings in which:
Coax transition 100 may be used anywhere where a change in direction of the propagation path of an RF signal or transition between a coaxial interface and a planar transmission line is desired (e.g., a microstrip transmission line). Thus, coax transition 100 may be used in a variety of tasks covering a wide range of RF frequencies. For example, in certain embodiments, such as those involving an RF or microwave circuit board, coax transition 100 may be used to transition from a surface mounted vertical coaxial launcher to a horizontal stripline transmission line coupled to the circuit board. This may allow for RF signals to be received from a surface mounted coaxial interface and communicated to another part of the circuit board. By employing coax transition 100, a better RF/microwave transition from the coaxial surface mount to the circuit board may be achieved. Furthermore, particular embodiments may allow for a vertical conductor 110 (and thus the corresponding surface mounted coaxial parts) to have a larger diameter while maintaining and/or improving on the efficiency of RF/microwave/millimeter transitions compared to a standard coax transition. The increased size may result in easier printed circuit board manufacturing.
Coax transition 100 includes a vertical conductor 110, a horizontal conductor 120, a ground plane 130, outer ground walls 140, and via connectors 160. These components form the structure of coax transition 100, which reduces the problem of mismatched coaxial transitions. In the depicted embodiment vertical conductor 110 is a coaxial interface that is transitioning to horizontal conductor 120a, which in this example begins as a microstrip (120a) and then continues as a stripline (120b) transmission line. This transition may occur over the diameter of vertical conductor 110 while maintaining a continuous transmission line.
The components of coax transition 100 are arranged such that electric field 150 is able to pass through gaps 170 created between vertical conductor 110 and outer ground walls 140, between horizontal conductor 120 and ground plane 130, and between horizontal conductor 120b and ground wall 140b. Gaps 170 may comprise any desired dielectric material. Because coax transition 100 includes gap 170d between ground plane 130 and the top surface of horizontal conductor 120, there may be little or no inductive break during the transition. Also, a greater percentage of electric field 150 may be able to make the transition from a vertical propagation path to a horizontal propagation path, as compared to certain prior coax transitions, such as the one depicted in
In the depicted embodiment, gap 170a is substantially the same as gap 170b. This consistent gap may continue until the top surface of outer ground walls 140 is reached. At this point coax transition 100 begins to transition from a vertical direction to a horizontal direction. More specifically, the coaxial portion of coax transition 100 begins to transition to the predominantly microstrip portion (120a).
Electric field 150 on both sides of vertical conductor 110 is able to transition from the vertical propagation path to the horizontal propagation path. Furthermore, horizontal conductor 120 is able to maintain electric field 150 on both of its sides. This may be facilitated by ground plane 130. Ground plane 130 may continue for the entire length of horizontal conductor 130. This may reduce or eliminate inductive discontinuities in the propagation path of electric field 150. As can be seen in
In
In the illustrated embodiment, horizontal conductor 220 includes quarter-wave impedance transformer 280. Quarter-wave impedance transfer 280 may aid in transitioning from the substantially cylindrical vertical conductor 210 of the coaxial interface to the substantially planar horizontal conductor 220 of the stripline transmission line.
Via connectors 260 may electrically connect the top ground plane to outer ground wall 240. In the depicted embodiment, via connectors 260 surround both vertical conductor 210 and horizontal conductor 220. Thus, both vertical conductor 210 and horizontal conductor 220 remain enclosed as coax transition 200 transitions from vertical to horizontal. This may be different than a traditional coax transition (shown in
Although particular embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope the appended claims.
