Wave transmission lines and networks – Coupling networks – Balanced to unbalanced circuits
Reexamination Certificate
1998-11-25
2001-03-20
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Balanced to unbalanced circuits
C455S326000
Reexamination Certificate
active
06204736
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to microwave mixers, such as a mixer constructed in a multilayer, microwave integrated circuit, with rectangular coaxial transmission lines. More particularly, this invention discloses a new mixer design, in which baluns composed of rectangular coaxial transmission lines typically operating at 0.9 to 6 GHz are implemented in a multilayer topology, and are utilized to reduce the size, weight, and cost of microwave mixers.
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, operation at higher frequencies and the accompanying increase in bandwidth, lower power consumption for a given power output, and robustness, among other factors. The trend toward better communication systems puts ever-greater demands on the manufacturers of these systems.
Today, the demands of satellite, military, and other cutting-edge digital communication systems are being met with microwave technology.
Many of these systems use mixers to multiply signals and translate frequency. Mixers are used in both transmitter and receiver applications. Examples of microwave mixers that are built for this purpose are disclosed in Maas, S.,
Microwave Mixers,
2nd Edition, Artech House, 1993.
Microwave mixers may be categorized by the technology used for construction. For example, microwave integrated circuits (MICs) typically include discrete semiconductor components for microwave applications. Monolithic microwave integrated circuits (MMICs) often incorporate semiconductor devices directly on the circuit substrates, also for microwave applications. An alternative type of MMIC includes ceramic substrates with attached beamlead devices. In either case, copper or other appropriate metal is incorporated into the circuitry.
Another class of mixers utilizes Lumped Element Technology. Baluns comprising wire-wound transformers provide relatively broad bandwidths and small size, but have an upper frequency limitation. In addition, Lumped Element Technology is labor-intensive and therefore costly to produce.
Typical MIC mixers are single-layered or double-sided and incorporate Schottky diodes. These mixers are usually passive devices, which do not require DC bias. Such circuits are suspended on metal frames or packaged in housings having pins, leads, or other connectors. MIC mixers perform well at high frequencies and over wide bandwidths. Generally, size increases as frequency decreases.
Thick film MMIC mixers, on the other hand, typically integrate passive Schottky diodes on ceramic substrates. The substrates themselves may form a surface-mount interface requiring no additional packaging for connecting to other electronic components. Thus, thick film MMIC mixers are generally small relative to MIC mixers. However, thick film MMIC mixers usually operate over narrow bandwidths relative to MIC mixers.
Thin film MMIC mixers typically incorporate diodes or field-effect transistors (FETs) directly on silicon or gallium arsenide substrates. Thin film MMIC mixers are smaller than MIC mixers, and are available in die form, but are commonly packaged as surface-mount components. Although such mixers are capable of operating at high frequencies, they usually also operate over narrow bandwidths relative to MIC mixers. Wide bandwidth operation is possible, but development cost is high, with associated design and foundry costs.
In sum, present technologies have several shortcomings that the present invention seeks to overcome. The bandwidth provided by MMIC technology is typically limited, and the development cost is high. Lumped Element Technology has an upper frequency limitation, and is labor-intensive to produce. MIC technology produces circuits that are physically larger, and utilizes metal frames or housings that further increase the size of the packaging.
SUMMARY OF THE INVENTION
The present invention relates to an improved multilayer, microwave mixer which takes advantage of a novel realization of distributed balun technology to gain superior performance benefits over classic MIC and MMIC mixers at reduced size and cost. The balun structure disclosed utilizes rectangular coaxial transmission lines, and operates in range of approximately 0.9 to 6 GHz. Other embodiments of the invention can operate at lower or higher frequencies.
Preferably, the microwave mixer comprises a homogeneous structure having approximately seven substrate layers that are composites of polytetrafluouroethylene, 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 these 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.
Preferably, these layers have a thickness of approximately 0.005 inches to approximately 0.100 inches, and are metalized with copper or other suitable conductor. The copper may be plated, for example, with tin, with a nickel/gold combination or with tin/lead.
Preferably, via holes, which may have various shapes such as circular, slot, and/or elliptical, by way of example, are used to connect the circuitry between layers and form portions of the baluns.
It is an object of this invention to provide a novel balun structure having performance benefits over existing baluns while reducing size and weight.
It is another object of this invention to provide a novel balun structure having performance benefits over existing baluns while reducing manufacturing costs.
It is another object of this invention to provide a balun utilizing substrates that form a compact, surface-mount interface.
It is another object of this invention to provide a balun utilizing substrates that eliminate the need for additional packaging.
It is another object of this invention to provide a balun having an effective bandwidth that is wider than lumped-equivalent baluns used in MMIC mixers.
REFERENCES:
patent: 5534830 (1996-07-01), Ralph
patent: 5745017 (1998-04-01), Ralph
Gunston, M.A.R.,Microwave Transmission-Line Impedance Data, Noble Publishing (1996), pp. 23-24, 26, 61.
Chadbourne & Parke LLP
Glenn Kimberly E
Merrimac Industries, Inc.
Montgomery Francis G.
Pascal Robert
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