Improved design of modal filter for electronics protection

A new structure of modal filter which is more relevant for lightning protection of electronics than previously considered structures is proposed. Decrease of modal filter length or increase of original pulse width by factor of 10 and increase of modal filter attenuation from factor of 2 up to factor of 5 is shown. Condition for equal magnitudes of decomposed pulses and analytic formula for their values against a ratio of even to odd mode characteristic impedances are derived. Dependence of these values on coupling is shown for practical parameters of the new structure based on FR-4. On the basis of the calculated data an experimental prototype of an improved modal filter has been made. An experimental investigation has been performed.