Finlines are guiding structures for electromagnetic waves that consist of one or several metallic fins suspended in the
E
plane of a waveguide enclosure. They are the basic transmission media for the so‐called integrated
E
‐plane circuit technology.
Finlines are applied predominantly in the frequency range between 10 and 100 GHz; but some applications at frequencies up to 170GHz have been realized. Having losses of typically 0.1 dB per wavelength, finlines are not suitable for long‐distance transmission. However, they excel as a circuit medium for millimeter‐wave components and systems due to their low manufacturing cost, wide single‐mode bandwidth, compatibility with discrete active and passive devices, and suitability for integration with other hybrid circuit techniques as well as with standard rectangular waveguides.