It is unquestionable that a great effort is currently being directed toward the implementation of fully reconfigurable and multipurpose radio-frequency (RF) systems, aimed at developing quasiuniversal high-frequency transceiver modules. Examples of modern applications demanding such vast RF frequency agility are manifold; they encompass emerging cognitive/software-defined radios and multifunction radars with dynamic spectrum access capabilities to optimize their operation [1]-[3]. As a consequence, the research into very sophisticated frequency-controllable RF/microwave electronics incorporating high levels of reconfiguration has been reactivated. High-frequency tunable filters are among the best exponents of this trend, as they are the most critical and challenging devices to perform the adaptive frequency-band selection processes needed by these systems [4], [5]. It is desirable for them to exhibit full control in terms of center frequency, bandwidth, selectivity, and even group-delay performance in their transfer functions so that RF signals with arbitrary spectral characteristics can be properly processed. Thus, out-of-system interference and noise can be efficiently removed in each situation, which ultimately results in the correct operation and high quality-ofservice (QoS) of the whole radio system.