Changing the Electromagnetic Bandgap and Stopbands in a Multistate Periodic Circuit

Changing the electromagnetic bandgaps (EBGs) and hence the stopbands in a multistate periodic microwave circuit is investigated experimentally. The state of the prototype circuit, consisting of 24 unit cells, is changed by closing or opening gaps in selected unit cells. This varies the periodic loading along the circuit and hence the EBG. In most states, the circuit behaves as a bandstop filter, and its stopband width and location are determined by the circuit state. Experimental results confirm that the first stopband width can be as large as 63% (at 4.92 GHz) or can be absent. The EBG leads to excellent isolation around 40 dB in the stopbands. Sharp roll-off between passbands and stopbands (upto 120 dB/octave) and small length compared to microstrip filters with similar cut-off and roll-off characteristics are other advantages of the proposed platform.