New photonic filter structures for interference mitigation of microwave signals are presented. These novel fibre-based filters have a parallel topology, and overcome the problem of synthesising both a narrow stopband and a very-wide and flat passband. Results for these filters showed a stopband 6-dB width of 10 MHz at a frequency of 1.5 GHz, with flat passband, and a shape factor for -40 dB interference rejection of 7.8, which is the lowest reported for a photonic filter.