TRAVELLING WAVE MECHANISM AND NOVEL ANALYSIS OF THE PLANAR ARCHIMEDEAN SPIRAL ANTENNA IN FREE SPACE

While Archimedean spiral antennas were invented a half-century ago, only self- complementary impedance can be evaluated directly from the Babinet's principle. This paper examines the efiects of metal width and arm spacing on printed spiral's input impedance. A model is proposed based on examination by decomposition of planar spiral. A closed-form expression for the input impedance of Archimedean spiral antenna is obtained by evaluating the proposed model with conformal mapping techniques. Full-wave numerical simulations, Babinet's principle, and a fabricated antenna demonstrate the accuracy of the proposed model. The expression in this work can be used to flnd the impedance of a variety of spiral complementary structures analytically. The examination and discussion on the efiects of other parameters and features in addition to the spiral itself are also provided through numerical simulation.