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A parallel-plate waveguide (PPW), composed of a metal plane above a high impedance surface, based on periodic arrangement of unit cells, realized in microstrip technology is introduced. The novel unit cell consists of a combination of a concentric circular and an annular patch, where each patch is connected to one of the two closing planes through a different number of vias. The structure presents several electromagnetic band-gaps in the microwave range and may be used as a multi-band filter. When diodes are connected within the device, its behavior may be switched from band-stop to band-pass filtering in the lower frequency range. The proposed solution allows eliminating the biasing network, and consequently significantly simplifying the design and manufacturing, since switches can be biased through the continuous closing planes.