This special issue presents devices and the results of a tunable microwave microsystem associating RF circuits and microfluidic components. A channel is buried inside the substrate of a microstrip waveguide. This channel is located beneath a resonant stub. With this configuration a microfluidic passive tunable filter can be fabricated. Dielectric fluids are used to disrupt the electric field in a microstrip structure and thus modify the effective permittivity of the substrate. In this work, a notch filter is realized with an open-ended quarter-wavelength stub placed on top of a hollow SU-8 structure. This structure offers two advantages: channels can easily be fabricated and a reduction of SU8 losses. The filter shows a good performance; the initial cut-off frequency of 25 GHz shifts more than 20% when deionized water is used in fluidic channels. And the shape of RF function is kept throughout the range.

International audienceA new approach for the development of tunable and reconfigurable microstrip (MS) devices is proposed. The basic idea consists of using a suspended substrate with an integrated network of plastic tubes, which can be selectively filled in with a high-permittivity dielectric fluid, e.g., water. The local change of the substrate effective permittivity achieved in such a way enables one to change, in a controlled and reversible manner, the electrical length of certain elements of MS circuits. As a proof-of-concept, tunable stub resonators based on suspended and inverted MS lines are designed and characterized in frequency and time domains. The same principle is then applied for the development of a fourth-order bandpass filter with 40% fractional bandwidth operating at 5 GHz. A tunable range of 19.5% with the insertion loss of 0.6 dB is demonstrated. The performance of the stub resonators and filter is validated successfully via prototypin

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