**Abstract**

Dielectric and conducting liquids with varying electromagnetic properties can offer novel alternatives for building tunable microwave passive components as well as antennas. Injecting these fluidics in or around microwave substrates alters their overall electrical characteristics, enabling circuit reconfigurability. Alternatively, changing the shapes and dimensions of conductors by using liquid metals can achieve similar reconfigurability. An overview of different liquids and their electromagnetic properties is first given. The principles behind the reconfigurability of the electrical characteristics of typical guiding structures based on mode shape variation in the presence of fluids are discussed. The realization of an N-bit programmable impedance tuner in 3D LTCC technology based on these principles is presented.

**Keywords:** liquid metal, liquid dielectric, cavities, impedance tuners, RF reconfigurability, 3D substrate, LTCC, transmission lines
