Four-terminal circularly polarized self-complementary antennas

Circularly-polarized high gain antennas are needed for communication via broadcast or maritime satellites. With a view to developing a wideband circularly-polarized antenna, experimental results are discussed for a structure consisting of a planar four-terminal self-complementary antenna on a core. The four conductors have a toothed shape which improves linear polarizability. The entire antenna structure is such that the sizes of the gaps and conductors are either equal or slightly modified. First, coupling between two opposing plates is qualitatively studied by measurement of the impedance and the radiated electric field. The self-complementary nature of the antenna is confirmed. Next, the directivity, beam width and axial ratio of the circular polarization are studied. When the sizes of the conductors and gaps on the core are identical, the coupling between two orthogonal terminal pairs is small and the self-complementary nature is practically preserved. This antenna has highly constant impedance and excellent directivity. The axial ratio of the antenna system, including the hybrid feed structure, is less than 0.8 dB over a large bandwidth.