In microwave circuit design, it is often necessary to interface circuit boards with other circuit components such as microwave waveguides. Circuit boards typically communicate via one of various conductor-based transmission lines, such as microstrip, stripline, coplanar waveguide or slotline. Three-dimensional microwave waveguides typically have rectangular or circular cross sections, and are hollow with metallic shells or are filled with a conductive dielectric material. These three-dimensional waveguides are referred to herein as microwave waveguides or simply waveguides.
Adaptors or transitions, also referred to herein as probe launches or simply probes, are mechanisms employed to interface conductor-based transmission lines with waveguides. Such transitions typically suffer from losses due to attenuation and impedance mismatches (reflections), and also may result in perturbations in microwave signals sent or received by the probe.
Conventional transitions to a microwave waveguide are from stripline or microstrip transmission lines. The transition may be disposed at an end of a microwave waveguide section, or laterally through a side of a microwave waveguide
A method and apparatus for coupling a conductor-based transmission line, such as a strip transmission line, to a waveguide is provided. The transmission line, which may be a microstrip, stripline, coplanar waveguide or slotline, among others, may be separated from a corresponding conducting ground plane by a first dielectric substrate layer. The ground plane may be adhesively coupled to a portion of the waveguide, and may be offset from the interior of the waveguide. Thus, adhesive squeezed out between the ground plane and the waveguide may be shielded from the probe and thus does not significantly perturb electromagnetic signals within the waveguide.
In one embodiment, a second dielectric substrate layer may be mounted to the first substrate, and a conducting probe, or launch, may be attached to the second substrate. The conducting probe may extend into the interior of the waveguide for sending and receiving electromagnetic signals. The attachment of the second substrate to the first substrate may be made by mounting the conducting probe onto the microstrip signal conductor.
In another embodiment, the first substrate may extend completely across the waveguide, and an attached microstrip may extend partially across the waveguide so as to act as a probe launch. In this case, the substrate and/or its associated ground plane may entirely cover the waveguide aperture.
Various embodiments of a transition for interfacing a microwave waveguide with an external circuit are now described in more detail with reference to
A substantially planar second dielectric substrate 20, also referred to as a probe substrate, has an attached conducting probe 22. Substrate 20 may be directly mounted onto substrate 12 using conductive mounting bumps 24, so that probe 22 faces signal conductor 18 and is in electrical contact with the signal conductor through one or more of the mounting bumps. Direct mounting, which may also be referred to as flip mounting, may reduce the length of the electrical connection between the conducting probe and the microstrip signal conductor, since connection through or around a substrate may be avoided. Alternatively, if probe substrate 20 is not directly mounted onto microstrip substrate 12, then probe 22 may make electrical contact with signal conductor 18 through any other suitable means, such as through the use of conducting wires, strip conductors or vias.
Transition 10 may be configured to transmit electrical signals between an external circuit, not shown, and three-dimensional microwave waveguide 9. Waveguide 9 in this example generally includes a metal or otherwise conductive base 32 and a waveguide end 33, shown as a metal or otherwise conductive cover 34. The waveguide end may function as a backshort of waveguide 9, and in some embodiments the base and end may be formed as an integral unit. The waveguide may be shaped such that it defines a substantially hollow interior corresponding to an air dielectric, although in some embodiments the interior of the waveguide maybe filled with a solid or liquid dielectric material. The interior of the waveguide defines a direction of electric field propagation parallel to a first direction longitudinal to the waveguide, represented by arrow 35.
Waveguide 9 may have a transverse opening 36, including a lip 38 having an inner edge 40 and an outer edge 42. Opening 36 may be formed in base 32, in end 33, or in a combination of base 32 and end 33. Opening 36 may be configured to accommodate transition 10, so that the transition may be partially inserted into the waveguide with probe 22 extending over inner edge 40 of lip 38. As depicted in
As indicated in
Alternatively, as indicated at 44′ in
A third alternative is indicated at 44″ in
Waveguide 102 may include a metal or otherwise conductive base 132 and a waveguide end 133, shown as a metal or otherwise conductive a removable cover 134. The waveguide end may function as a backshort of waveguide 102. A first aperture 136 in base 132 may define a substantially hollow interior of the waveguide, although as previously mentioned, in some embodiments the interior of the waveguide may be filled with a dielectric material. The interior of the waveguide defines a direction of electric field propagation, represented by arrow 137, parallel to a first direction longitudinal to the waveguide. Cover 134 may define a hollow recess 138 greater in cross-sectional area than the area of aperture 136, and the cover may be configured to seat directly onto the base and to substantially enclose aperture 136. The cover further defines a transverse opening 140 configured to accept a portion of transition 110 when the cover is in place. Opening 140 may also be in base 132, or in a combination of base 132 and cover 134.
As is particularly seen in
As indicated in
To avoid unpredictable signal perturbations from adhesive squeezed out at the interface of conducting ground plane 116 and base 132, aperture 146 in the ground plane may be offset in some manner from aperture 136 in the base of the waveguide. For example, as indicated in
It should be appreciated that in the embodiments depicted in
Accordingly, while embodiments have been particularly shown and described with reference to the foregoing disclosure, many variations may be made therein. The foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be used in a particular application. Where the claims recite “a” or “a first” element or the equivalent thereof, such claims include one or more such elements, neither requiring nor excluding two or more such elements. Further, ordinal indicators, such as first, second or third, for identified elements are used to distinguish between the elements, and do not indicate or imply a required or limited number of such elements, and do not indicate a particular position or order of such elements unless otherwise specifically stated.
The methods and apparatus described in the present disclosure are applicable to the telecommunications and other communication frequency signal processing industries involving the transmission of signals between circuits or circuit components.