A transition arrangement (100;100 1 ;100A;100B;100C;100D;100E; 100F) for providing at least one transition between at least one substrate integrated waveguide, SIW, (20;20A,20A; 20B,20B;20C,20C;20D,20E 20E;20F), said at least one SIW forming part of, or comprised by a circuit arrangement (11;11A;...;11F), , and an at least one other waveguide and/or antenna structure or antenna interface (10;10A,10A;10B;10C,10C;10D,10D;10E;10F), wherein the transition arrangement comprises said at least one SIW comprising an upper first ground plane (9;9 1 ;9A,9A;....;9E;9F) and a lower second ground plane (9';9 1 ';9A',9A';....;9E';9F'), the transition arrangement further comprising a first conducting plate or block (1;1 1 ;1A;1B;1C;1D;1E;1F) and a second conducting plate or block (2;2 1 ;2A;2B;2C;2D;2E;2F) comprising a plate or split-block assembly comprising at least one waveguide port and/or antenna port , wherein said at least one SIW (20;20A,20A;20B,20B;20C,20C;20D,20D;20E;20F) is arranged on said first conducting plate or block (1;1 1 ;1A;1B;1C;1D;1E;1F), and a number of ridges and/or impedance matching or transforming structures (4;4 1 ;4A,4A; 14B,14B;4C,4C;14D,14D;4E;14F) are connected to the second conducting plate or block (2;2 1 ;2A;2B;2C; 2D;2E;2F), such that for the at least one transition between said at least one SIW, (20;20A,20A;20B,20B; 20C,20C;20D,20D;20E;20F) and said at least one other waveguide and/or antenna structure or antenna interface (10;10A,10A;10B;10C,10C; 10D,10D;10E;10F), each ridge and/or impedance matching or transforming structure (4;4A;14B;4C;14D;4E;14F) is extended with an open circuit λ g /4 stub (5;5 1 ;5A,5A;5B,5B;5C,5C;5D,5D; 5E;5F) for inverting impedance and providing a short-circuit for electromagnetically coupling the EM-field between the at least one SIW(20;20A,20A;20B,20B;20C,20C;20D,20D;20E;20F) and each ridge and/or impedance matching or transforming structure (4;4 1 ;4A,4A; 14B,14B;4C,4C;14D,14D;4E;14F) in an assembled state of the first and second conducting plates or blocks (1,2;1A,2A;...;1F;2F), characterized in that each ridge and/or the impedance matching or transforming structure (4;4 1 ;4A,4A;14B,14B;4C,4C;14D,14D;4E;14F) and the open circuit λ g /4 stub (5;5 1 ;5A,5A;5B,5B;5C,5C;5D,5D;5E;5F) are so arranged that, when the first and second conducting plates or blocks (1,2; 1 1 ,2 1 ;1A,2A;...;1F;2F) are assembled, a side or surface of the open circuit λ g /4 stub (5;5 1 ;5A,5A;5B,5B;5C,5C; 5D,5D;5E;5F) being located opposite to the side or surface of the stub (5;5 1 ;5A,5A;5B,5B;5C,5C;5D,5D;5E;5F) that is connected to the second plate (2;2 1 ;2A;2B;2C;2D;2E;2F), is disposed at a slight distance from a portion of said upper first ground plane (9;9 1 ;9A;....;9F) of said at least one SIW (20;20A,20A; 20B,20B;20C,20C;20D,20D;20E;20F), without any galvanic contact between the at least one SIW (20;20A,20A;20B,20B;20C,20C;20D,20D;20E;20F) and each ridge and/or impedance matching or transforming structure (4;4 1 ;4A,4A;14B,14B;4C,4C;14D,14D;4E;14F) and between the at least one SIW (20;20A,20A;...;20F) and the open circuit λ g /4 stub (5;5 1 ;5A,5A; 5B,5B;5C,5C;5D,5D;5E;5F), such that a contactless, substantially planar, transition is formed between the at least one SIW (20;20A,20A;... ;20F) and the at least one other waveguide and/or antenna structure or antenna interface (10;10A,10A; 10B;10C,10C;10D,10D;10E;10F), wherein λg is guide wavelength of a waveguide section formed by the stub (5;5 1 ;5A,5A;5B,5B;5C,5C;5D,5D; 5E;5F) and the upper first ground plane (9;9 1 ;9A;....;9F). <EOS>