Conversion of tem-wave in higher waves on the cascades from three unequally-period diaphragms or gratings

Acquired earlier experience of an optimization of the TE-waves converters we use for creation of TM-waves converters in flat (rectangular) waveguides, which are more interesting to usage in an electronics. We also optimize interaction of the TEM-wave with higher of TE- and TM-waves to create converters on the basis of the cascade from three unequally-period gratings in free-space. However there were difficulties of providing flat-topped (and from this broadband ) amplitude-frequency response of converters on TM- and TEM-waves. The search of modified constructions of such devices for overcoming these difficulties is necessary.