Realization of a microwave interdigital filter using electrically conducting liquids

A cavity type band pass interdigital filter has been designed and developed using electrically conducting liquid: mercury. This filter has an insertion loss of -5.0 dB at a center frequency of 4.46 Ghz and a 1:2 VSWR bandwidth of 63 Mhz respectively. Further, the property of thermal expansion of liquids, under certain specific & controlled conditions has been utilized, to vary the characteristics of this filter. This has been achieved by exercising suitable control over temperature (external-environmental) and pressurization (internal) of certain components / parts made of liquid: mercury while fabricating the interdigital filter. The development of this interdigital filter has demonstrated that: ldquoit´s possible to shift/move the frequency-band window of the filter by few tenths of megahertz´s in the frequency domainrdquo.