Electronically or magnetically tunable band-pass or band-stop filters, having more than 5 tunable resonators capable of tuning across a 1,5:1 frequency band (fmax/fmin) in less than 10 μs and having any of the following: (a) A band-pass bandwidth of more than 0,5 % of centre frequency; or (b) A band-stop bandwidth of less than 0,5 % of centre frequency;