In this paper, we present a sensor suitable for performing the spectroscopy on a localized micrometric volume of a generic liquid, in the spectral range comprised between 1 GHz and 20 GHz. The sensor is based on two ungrounded, open-ended coplanar waveguides, acting as Input/Output ports, with a microfluidic channel passing through them to perform also transmission through the liquid analysis. The sensor has been designed and numerically simulated to obtain the electromagnetic response in different conditions: an empty channel for having a zero-reference response and for observing variations as a function of liquids filling the channel.