Loop and spiral line antennas at microstrip substrate surface

Radiation elements printed on a dielectric material have not been fully addressed due to difficulties in determining the current distributions on the radiation elements. The authors describe some new aspects of the radiation characteristics of a loop antenna. Special attention is paid to generation of a circularly polarised wave with a single voltage source. The numerical results show that a loop antenna fed by a single source can radiate an axial beam of circular polarisation, when perturbation elements are added to the loop proper. The addition of the perturbation elements generates a travelling wave type current distribution along the loop. Finally the authors analyse a printed spiral antenna on a grounded dielectric substrate. Many linear filaments are consecutively connected to form spiral antenna arms. It is found that the spiral antenna can be used over more than a 20% bandwidth, despite the fact that the spiral is backed by a grounded substrate