Low-Complexity High-Bandwidth Multiport Matching Networks for Coupled Loads

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Wireless devices that transmit and receive signals usually have antenna elements as part of their design. These antenna elements need to be "matched" to the radio-frequency amplifiers they are connected to, much in the way audio speakers need to be matched to amplifiers to optimize the sound of a music system. Matching circuits can be complicated when there are many antennas in a compact device since these antennas interact and couple with each other. Because of this coupling, any connection with one antenna disturbs the connections with neighboring antennas. Hence, the problem of connecting amplifiers to antennas when they are closely spaced requires careful consideration and a systematic circuit design process. Existing designs tend to be complicated, non-systematic, and difficult to implement in a compact manner; as a result, much transmitter power is lost to a poor match. This research effort looks at simple systematic circuit designs that achieve a good match across a wide range of transmitter frequencies. Since wireless devices are being asked to operate in many bands simultaneously and with high data rates, such circuits can yield great improvements in wireless connectivity in existing frequency bands as well as next-generation bands where the demands on the number of antennas, data rates and device performance are expected to be even more extreme. The theory and experimental validation developed under this effort for low-complexity, high-bandwidth networks is expected to have significant impact on the performance of low-cost high-performance devices, with benefit to society at large, including applications in personal communications and medical telemetry. The effort also has significant educational benefits since it will train an interdisciplinary mix of graduate students in topics within communications, circuits, and microwave engineering. This research effort advocates the design and analysis of low-complexity high-bandwidth multiport matching networks to compensate for coupling in radio-frequency transmitters, receivers, and circuits. The ideal multiport matching network inserted between independent sources and coupled loads compensates for the coupling by eliminating both reflected power and also power transferred from one source through a load to another source. Among the design limitations of such networks, complexity and bandwidth are usually the most important, especially for compact wideband wireless communication devices. These limitations have not been well studied, and this effort includes an integrated two-pronged exploration of these issues in microwave and millimeter-wave matching networks. The first prong uses network-theoretic analyses to explore systematic, unified, design methods that work for any load structure. The effort also seeks standardized limits against which network performance in both complexity and bandwidth can be measured. The second prong couples an experimental program to both validate as well as inform the modeling choices made in the design and optimization of the matching networks. Practical issues such as undesired parasitic coupling and electromagnetic discontinuities in distributed circuit implementations will be examined. Of particular interest are the microwave (2.4 GHz) and millimeter-wave (60 GHz) frequencies with both lumped and distributed radio-frequency components, and an emphasis on simple module layouts. The effort is transformative because it will offer a comprehensive unified set of metrics, design criteria, and methodologies for complexity and bandwidth of multiport matching networks applicable to compact radio-frequency devices.