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Over the last decade, mobile communication and its associated mass volume market has become one of the driving forces in the technology evolution of semiconductor and microwave circuits. For handheld communication devices, it is now mainstream to support increasing numbers of communication standards and localization services that occupy ever-expanding wide frequency ranges and bandwidths. At the same time, the physical dimensions of handheld user devices are shrinking, leading to even tighter specifications for the highly integrated front-end architectures of mobile radios. Todays radio front-end architectures use dedicated receive and transmit paths for each covered communication standard, thus the overall complexity and occupied area is increasing as well. The wide frequency allocation of the regulated communication bands along with the variety of standards, which have to be covered by these radios, calls for reconfigurable and frequency agile microwave subsystems. The scope of this article is to provide a comprehensive understanding of design principles for frequency agile and reconfigurable microwave circuits such as power dividers and couplers and how they can be used in radio-frequency (RF)-transceiver subsystems to pave the way toward reconfigurable radio front-end architectures. Introducing reconfigurability in microwave circuits is achieved by tunable passive components. Tunable passives can be implemented in a variety of technologies such as ferroelectric varactors, semiconductor diodes, and microelectromechanical systems (MEMS) components. Attractive applications for tunable circuits in the RF front end are tunable matching networks, filters, reconfigurable power amplifiers, tunable voltage controlled oscillator (VCO) circuits, and finally, couplers and dividers.
Date of Publication: Jan.-Feb. 2012