A radiofrequency, RF, power amplifier pallet (200; 300; 400), comprising: a first dielectric substrate; a second dielectric substrate, arranged on the first dielectric substrate and comprising a first dielectric layer and a second dielectric layer, said second dielectric substrate comprising a cavity extending through the first and second dielectric layers; an RF amplifying unit comprising a RF power transistor and being arranged in said cavity, said RF amplifying unit comprising an input and an output; wherein the RF power amplifier pallet further comprises: a coin on which the RF amplifying unit is arranged, said coin being arranged in a cavity within the first dielectric substrate and having a higher thermal conductivity than the first dielectric substrate; a coupled line coupler comprising a first line segment (4; 140) and a second line segment (5; 141) that is electromagnetically coupled to the first line segment, wherein a first end of the first line segment is electrically connected to the output of the RF amplifying unit; a dielectric filled waveguide comprising an end section of the first dielectric substrate, an end section of the second dielectric substrate, and a plurality of electrically connected metal wall segments covering the end sections of the first and second dielectric layers, said plurality of wall segments being arranged spaced apart from the first line segment and being electrically connected to a first end of the second line segment; wherein the plurality of wall segments comprises an upper wall segment covering a top surface of the first dielectric layer and a lower wall segment covering a bottom surface of the first dielectric substrate, wherein either the RF power amplifier pallet further comprises a first plurality of vias (131; 501) that connect the upper wall segment to the lower wall segment or wherein the RF power amplifier pallet comprises one or more side wall segments (132; 502) that cover a side surface of the first and second dielectric substrate and that electrically connect the upper and lower wall segments. a first dielectric substrate; a second dielectric substrate, arranged on the first dielectric substrate and comprising a first dielectric layer and a second dielectric layer, said second dielectric substrate comprising a cavity extending through the first and second dielectric layers; an RF amplifying unit comprising a RF power transistor and being arranged in said cavity, said RF amplifying unit comprising an input and an output; wherein the RF power amplifier pallet further comprises: a coin on which the RF amplifying unit is arranged, said coin being arranged in a cavity within the first dielectric substrate and having a higher thermal conductivity than the first dielectric substrate; a coupled line coupler comprising a first line segment (4; 140) and a second line segment (5; 141) that is electromagnetically coupled to the first line segment, wherein a first end of the first line segment is electrically connected to the output of the RF amplifying unit; a dielectric filled waveguide comprising an end section of the first dielectric substrate, an end section of the second dielectric substrate, and a plurality of electrically connected metal wall segments covering the end sections of the first and second dielectric layers, said plurality of wall segments being arranged spaced apart from the first line segment and being electrically connected to a first end of the second line segment; wherein the plurality of wall segments comprises an upper wall segment covering a top surface of the first dielectric layer and a lower wall segment covering a bottom surface of the first dielectric substrate, wherein either the RF power amplifier pallet further comprises a first plurality of vias (131; 501) that connect the upper wall segment to the lower wall segment or wherein the RF power amplifier pallet comprises one or more side wall segments (132; 502) that cover a side surface of the first and second dielectric substrate and that electrically connect the upper and lower wall segments. a coin on which the RF amplifying unit is arranged, said coin being arranged in a cavity within the first dielectric substrate and having a higher thermal conductivity than the first dielectric substrate; a coupled line coupler comprising a first line segment (4; 140) and a second line segment (5; 141) that is electromagnetically coupled to the first line segment, wherein a first end of the first line segment is electrically connected to the output of the RF amplifying unit; a dielectric filled waveguide comprising an end section of the first dielectric substrate, an end section of the second dielectric substrate, and a plurality of electrically connected metal wall segments covering the end sections of the first and second dielectric layers, said plurality of wall segments being arranged spaced apart from the first line segment and being electrically connected to a first end of the second line segment; wherein the plurality of wall segments comprises an upper wall segment covering a top surface of the first dielectric layer and a lower wall segment covering a bottom surface of the first dielectric substrate, wherein either the RF power amplifier pallet further comprises a first plurality of vias (131; 501) that connect the upper wall segment to the lower wall segment or wherein the RF power amplifier pallet comprises one or more side wall segments (132; 502) that cover a side surface of the first and second dielectric substrate and that electrically connect the upper and lower wall segments.