Waveguide device (1) for guiding a radio frequency signal at a given frequency f, the device (1) including: a core (3) manufactured by additive manufacturing and including side walls with inner and outer surfaces (7, 8), the inner surfaces (7) delimiting a waveguide channel (2), wherein a cross-section of the channel (2) has two straight sides joined together by two half-portions, at least one of the two half-portions being rounded or formed of at least two straight segments the cross-section having a maximum length (a) and a maximum width (b), the ratio between the maximum length (a)/maximum width (b) being between 2.05 and 3.5, preferably between 2.05 and 2.4.