Power Combiners, Impedance Transformers and Directional Couplers: Part IV

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  • Author: Andrei Grebennikov
The first directional couplers consisted of either a two-wire balanced line coupled to a second balanced line along a distance of quarter wavelength, or a pair of rods a quarter wavelength long between ground planes. Although the propagation of waves on systems of parallel conductors was investigated many decades ago—in connection with the problem of crosstalk between open wire lines or cable pairs in order to eliminate the natural coupling rather than use it—the first exact design theory for TEM (transverse electromagnetic) transmission-line couplers was introduced by Oliver.