This is because the BPF is a two-pole filter; at its cut-off frequency (when output is 50 per cent) the output power of a true LPF of the same cut-off would be in fact 70.7 per cent.
This is because the BPF is a two-pole filter; at its cut-off frequency (when output is 50 per cent) the output power of a true LPF of the same cut-off would be in fact 70.7 per cent.
这是因为带通滤波器是一个两极滤波器；在其截止频率下（输出为50%），真正的具有相同截止频率的低通虑波器的输出功率事实上为70.7%。