 A common application of waffle @-@ iron filters is to remove the harmonics of transmitters , such as high power radar , before applying to the antenna . Legislation in most jurisdictions requires strict limits on out @-@ of @-@ band transmissions since these can cause serious interference with other stations . This is an application that usually requires a very wide stopband , a characteristic of waffle @-@ iron filters . For instance , to remove all harmonics up to the fifth it is necessary for a low @-@ pass filter to have a stopband greater than three times the passband . 
