Fixed-frequency, commercial filter designs in 1-3GHz RF bands can satisfy stopband rejections in the range of 20-40dB.The challenges of a notch filter design for a chosen 0.2% proximity (!S
!J)
are highlighted in Fig. 3.5, where !0 = !J (absolute accuracy). In order to achieve 40dB SIR improvement better than 57dB rejection is warranted when Q=30; while fixed-frequency microwave filter have trouble meeting such specification, the task becomes impractical with tunable ones.