Two filters using Defected Ground Structures have been proposed. First,
a multiple frequency band stop filter utilizing a semi-H defect in the
ground plane is presented. This structure is then prototyped on a Rogers
4350B substrate of overall size 45 mm $\times$ 15 mm,
and external SMD capacitors have been employed to control the resonance
of the circuit, for the stopband frequencies of 433 MHz, 700 MHz and 915
MHz. An equivalent circuit is also proposed for this multi-band design.
The second filter is a combination of a band-stop and band-pass filter
in one structure. The filter, operating with a controllable passband and
stopband frequency is fabricated, on Rogers 4350B lossy substrate, to
validate the EM and circuit simulation results. Two SMD capacitors have
been loaded in the filter to control the pass band and stop band
frequencies of the filter with a structure size of 20 mm x 20 mm.
Furthermore, a novel equivalent circuit model encompassing the band-pass
and band-stop frequency response of the DGS based filter is proposed.