A novel switchable lowpass filter constructed with electromagnetic bandgap and illumination-sensitive cadmium sulfide

A novel construction of microwave switchable lowpass filter based on electromagnetic bandgap (EBG) and cadmium sulfide (CdS) thin film is proposed. Linearly tapered slot-array EBG structure is well known for its exceptional stopband ability and compact physical size. When the illumination-sensitive CdS thin film is deposited on the perforations of the EBG structure, the stopband phenomenon induced by tapered slot-array can be controlled by optical means. Innovative “conductive islands” were introduced to reside in the center of each perforation in order to enhance the optical switching. It has been demonstrated in both simulation and experimental measurement that the transmission coefficient is switched from 31.3 to 5.6 dB at 13 GHz when the gap width between the conductive island and the perforation is 30 μm. As the gap width decreases, the insertion loss can be reduced. Simulation result indicates that the insertion loss can be improved to around 1 dB at 13 GHz when the gap width is decreased to 5 μm. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2238–2242, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22665