Current needs in the telecommunication area lead to drastic strains on the performances of circuits, either active devices or passive ones. In this context, the use of agile devices should allow one to cut down the number of circuits in the front-end while keeping all the functions desired by users. Since a few years, our investigations have been focused on the assessment of the capabilities of KTN ferroelectric thin-films for the realization of agile devices at microwave frequencies. Our circuits have been realised in coplanar technology, which is well-suited to the use of ferroelectrics especially as thin-films. High variations of the propagation constant under a bias field should be exclusively controlled by designing coplanar waveguides (CPWs). Though the width of the feed line, W, has no effect on the DC bias field and, thus, likely on the tuning properties of the line, we wondered about its impact on the electrical parameters, i.e. attenuation factor, phase-change coefficient, agility, impedance dispersion... We, thus, realized CPWs with the same slot width together with feed lines of different widths. Measurements highlighted that, for example, not only the attenuation factor, but also the agility on the phase-change coefficient were both elevated by reducing the width of the feed line. Our experimental data suggest that the differences observed are mainly induced by a change in the distribution of microwave field lines caused by a variation of the feed line width. The coplanar technology also allows one to get the same impedance for different couples of slot width and feed line width. Thus, we realized 50-Ω impedance transmission lines with different side-dimensions in order to determine the optimum (W,G) couple in term of losses. Once again, the electrical parameters of these CPWs were highly dependent upon their geometrical dimensions.