Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1999-06-11
2001-03-27
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S246000
Reexamination Certificate
active
06208220
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to microwave couplers, such as a coupler constructed in a multilayer, vertically-connected stripline architecture. More particularly, this invention discloses couplers having a vertically-connected stripline structure in which multiple sets of stripline layers are separated by interstitial groundplanes, wherein more than one set of layers has a segment of coupled stripline.
BACKGROUND OF THE INVENTION
Over the decades, wireless communication systems have become more and more technologically advanced, with performance increasing in terms of smaller size and robustness, among other factors. The trend toward better communication systems puts ever-greater demands on the manufacturers of these systems. These demands have driven many developments in microwave technology.
Looking at some of the major developments historically, the early 1950's saw development of planar transmission media, creating a great impact on microwave circuits and component packaging technology. Developments in the engineering of microwave printed circuits and the supporting analytical theories applied to the design of striplines and microstrips contributed to improvements in microwave circuit technology. A historical perspective on some of the developments of microwave integrated circuits and their applications is provided by Howe, Jr., H., “Microwave Integrated Circuits—An Historical Perspective”,
IEEE Trans. MIT
-
S,
Vol. MTT-32, September 1984, pp. 991-996.
The early years of microwave integrated circuit design were devoted mostly to the design of passive circuits, such as directional couplers, power dividers, filters, and antenna feed networks. Despite continuing refinements in the dielectric materials used in the fabrication of such circuits and improvements in the microwave circuit fabrication process, microwave integrated circuit technology was characterized by bulky metal housings and coaxial connectors. The later development of case-less and connector-less couplers helped reduce the size and weight of microwave integrated circuits. These couplers, sometimes referred to as filmbrids, are laminated stripline assemblies that are usually bonded together by fusion or by thermoplastic or thermoset films.
Traditionally, the size of a coupler in the X-Y-plane is governed by the length of the stripline sections being coupled. A coupler designed to perform over wide bandwidths requires additional sections of coupled striplines, which would further increase the overall size of the coupler. Furthermore, since the length of the coupled sections is inversely proportional to the operational frequency of the coupler, a coupler designed to operate at lower frequencies would have longer stripline sections. Coupled lines are often meandered to decrease their effective outline size.
Today, the demands of satellite, military, and other cutting-edge digital communication systems are being met with microwave technology. The growth in popularity of these systems has driven the need for compact, lightweight, and surface-mountable packaging of microwave integrated circuits. Although advances in microwave integrated circuit technology, such as those outlined above, have helped decrease the size, weight and cost of the circuits, it would be advantageous to decrease the size, weight and cost of such circuits even further. In sum, present technologies have limitations that the present invention seeks to overcome.
SUMMARY OF THE INVENTION
The present invention relates to improved microwave couplers which take advantage of novel multilayer, vertically-connected stripline architecture to gain performance benefits over narrow and wide bandwidths while reducing the size and weight of the couplers. Multiple sets of stripline layers are separated by interstitial groundplanes, wherein more than one set of layers has only a segment of coupled stripline.
The vertically-connected stripline structure comprises a stack of dielectric substrate layers preferably having a thickness of approximately 0.002 inches to approximately 0.100 inches, with metal layers, preferably made of copper, which may be plated with tin, with a nickel/gold combination or with tin/lead, between them. Some metal layers form groundplanes, which separate the stack into at least two stripline levels, wherein each stripline level consists of at least one center conducting layer with a groundplane below and a groundplane above, and wherein groundplanes may be shared with other stripline levels. It therefore becomes possible to place segments of a coupler in different stripline levels and connect the segments using plated-through via holes. In this way, couplers are formed on multiple substrate layers by etching and plating copper patterns and via holes on substrates of various thickness and bonding the layers together in a prescribed order.
Preferably, the vertically-connected stripline structure comprises a homogeneous structure having at least four substrate layers that are composites of polytetrafluouroethylene (PTFE), glass, and ceramic. Preferably, the coefficient of thermal expansion (CTE) for the composites are close to that of copper, such as from approximately 7 parts per million per degree C to approximately 27 parts per million per degree C, although composites having a CTE greater than approximately 27 parts per million per degree C may also suffice. Although the substrate layers may have a wide range of dielectric constants such as from approximately 1 to approximately 100, at present substrates having desirable characteristics are commercially available with typical dielectric constants of approximately 2.9 to approximately 10.2.
A means of conduction, such as plated-through via holes, which may have various shapes such as circular, slot, and/or elliptical, by way of example, are used to connect center conducting layers of the stacked stripline structure and also to connect groundplanes. By way of example only, ground slots in proximity to circular via holes carrying signals can form slab transmission lines having a desired impedance for propagation of microwaves in the Z-direction.
Although the vertically-connected stripline structure disclosed typically operates in the range of approximately 0.5 to 6 GHz, other embodiments of the invention can operate at lower and higher frequencies. Furthermore, although the structure disclosed utilizes dielectric material that is a composite of PTFE, glass, and ceramic, the invention is not limited to such a composite; rather, co-fired ceramic or other suitable material may be used.
It is an object of this invention to provide a novel coupler constructed in a multilayer, vertically-connected stripline architecture.
It is another object of this invention to reduce the size and weight of microwave integrated circuits that utilize couplers, by dividing the couplers into segments and arranging the segments on different stripline levels.
It is another object of this invention to reduce the costs of manufacturing microwave integrated circuits that utilize couplers, by dividing the couplers into segments and arranging the segments on different stripline levels, thereby reducing the area of a microwave integrated circuit and allowing more circuits to fit in a given area.
It is another object of this invention to provide an implementation of a broad bandwidth coupler constructed in a multilayer, vertically-connected stripline architecture, by combining a series of uncoupled interconnections with a series of coupled sections.
It is another object of this invention to provide an implementation of a coupler capable of operating over a very wide range of frequencies and having a high pass frequency response, wherein the coupler is constructed in a multilayer, vertically-connected stripline architecture, by connecting non-uniform coupled structures tandem.
REFERENCES:
patent: 3761843 (1973-09-01), Cappucci
patent: 5369379 (1994-11-01), Fujiki
patent: 5557245 (1996-09-01), Taketa et al.
patent: 5576669 (1996-11-01), Ruelke
patent: 5841328 (1998-11-01), Hagashi
patent: 5929729 (1999-
Bettendorf Justin P.
Chadbourne & Parke LLP
Merrimac Industries, Inc.
Montgomery Francis G.
Wintringham Drew M.
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