2. Developed geometries

Rapid developments in this field took place in the USA during the Second World War, when specialized laboratories were set up at MIT (Massachusetts Institute of Technology) and Columbia University to apply microwave techniques to radar problems. At that time, two basic guidance structures were frequently employed: the metal waveguide and the TEM coaxial line. Waveguides enabled high-power, low-loss energy transmission. Coaxial lines, born with the submarine cable, provided wider-band transmissions thanks to the absence of dispersion. But as frequency increased, so did losses, particularly in the dielectric, setting a boundary beyond which the coaxial line was replaced by the waveguide, whose dominant mode was exploited. However, the waveguide was a cumbersome structure, with transverse dimensions of the order of magnitude of the wavelength. The two-wire line, on the other hand, was hardly...