We have studied the effects of introducing phaseshifts in the active section of a m phaseshift-controlled DFB wavelength tunable filter on tuning range, peak power transmissivity and side-mode suppression ratio (SMSR). The analysis indicates that when the filter wavelength tuning range is 22.1 Å for the grating coupling coefficient while maintaining almost constant transmissivity (gain) of more than 35 dB. The filter SMSR ranges from 11.1 to 25.4 dB. The results for asymmetric values of and are also given.