We introduce a novel structure of inhomogeneous parallel plate waveguide suitable for advanced applications requiring frequency tunability. The structure relies on microstrip technology and consists of a periodic metallic lattice embedded in dielectric materials. The basic metal pattern is connected to the upper layer by a metallic post in each unit cell, and can be in the same time selectively connected to the lower metallic plane through two vias. The presence or absence of the connection is determined by the states of two incorporated diodes. The frequency characteristics of the structure can be changed through a cost effective, two-way DC supplier, which sets the states of the two diodes positioned across two slots, which in turn avoid short-circuit between the two closing planes. The biasing network as a source of generation of spurious noise is completely eliminated since the control voltage is applied through the existing metal walls of the structure.