Microwave and Millimeter-wave switches are key components in communication systems. They are used for signal routing and for realizing a wide range of reconfigurable microwave and millimeter-wave devices. Phase Change Materials (PCM) have been widely used in optical storage media and non-volatile memory device applications. Over the past recent years, there have been interest in exploiting the PCM materials such as germanium telluride (GeTe) and metal insulator transition materials such as vanadium oxides (VO2) for RF applications. The principle of operation of PCM devices is based on the ability of the material to transform from a high-resistivity state (amorphous phase) to a low-resistivity state (crystalline phase) and vice versa with the application of short duration pulses. Several orders of magnitude in resistivity change can be achieved by PCM technology allowing the realization of highly miniature microwave and millimeter-wave switches. In addition to miniaturization, GeTe based switches offer latching functionality and ease of monolithic integration with other RF circuits. This talk will address recent developments in PCM switches and their applications to the realization of reconfigurable filters, switch matrices, phase shifters, variable attenuators, and reflective intelligent surfaces. It outlines major design considerations for tunable filters presenting techniques to realize tunable filters that maintain filter performance over tuning range, illustrating examples of tunable filters tuned only a by single tuning element. The talk also addresses existing tuning technologies, providing a comparison between Semiconductor, MEMS and PCM tuning elements in terms of linearity, insertion loss, suitability for use at millimeter-wave frequencies and ease of integration with high-Q filters. Very recent results for PCM-based reconfigurable acoustic filters are also presented.

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