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.