The　printed　windows　in　rectangular　waveguides　have　been　investigated　using　a　combined　method　of　modal　analysis　and　generalised　scattering　matrix　for　the　first　time.　The　method　takes　into　account　the　influences　of　the　nonzero　metallisation　thickness　and　the　mounting　grooves.　The　frequency　characteristics　of　the　unilateral　and　bilateral　windows　are　illustrated.　©　1989,　The　Institution　of　Electrical　Engineers.　All　rights　reserved.