New and improved types of waffle-iron filters

Waffle-iron filters are waveguide low-pass filters with wide stop-bands. The waffle-iron filter was first described in 1957 in a report of the Stanford Research Institute, and upon this all subsequent designs have been based. The pass-band fractional bandwidths were generally in the order of 10¿20%, and the unpressurized pulse power-handling capacity was about 1.5 MW at the L-band. The stop-band attenuation was typically more than 60 dB from below the second harmonic to beyond the fourth harmonic frequency. New filters have recently been developed with pass-band fractional bandwidths of over 40% (covering almost the whole recommended frequency band of a standard waveguide) and pulse power-handling capacity, without pressurization, of up to about 8 MW at the L-band, while the stop-band attenuation and bandwidth remain as good as before.