Electromagnetically coupled microstrip antennas with circular polarization

Recently, electromagnetically coupled microstrip antennas have been studied extensively. This paper proposes a new microstrip circularly polarized antenna in which an orthogonal mode with a phase difference of 90° is generated on a radiating element via the path length difference of the traveling wave currents on the strip transmission line coupled electromagnetically at two points with the radiating element. By experiments and numerical calculations, the operations of the circular loop and square patch circularly polarized antennas based on the present principle are confirmed. The radiation pattern, input impedance and current distribution are studied. The proposed circularly polarized antenna employing electromagnetic coupling has less spurious radiation from the transmission line than the direct coupled two‐point fed structure and is enabled to provide an excellent circular polarization with a simple construction. Circular polarization can be obtained in a wide angle. If the input and load terminals are interchanged, the direction of the circular polarization can be switched easily.