Phase control of circularly polarized waves from a parasitic dipole mounted above a slot

A combination of a slot and a parasitic dipole is a well known element for circular polarization. The authors adopted these elements and proposed a single-layer linear-to-circular polarization converter consisting of a dipole array to be mounted on an existing narrow-wall slotted waveguide array. Unfortunately, the slots on the narrow wall in an existing array are inclined alternatively with respect to the waveguide axis. It results in an alternating phase error of the array illumination and serious grating lobes appear in the array pattern. The authors have suppressed these lobes by changing only the dipole angle at the cost of the axial ratio of the element pattern. They discuss and extract the mechanism of this novel finding. By using the simple approximation for the induced currents on the dipole, they express the amplitude and the phase of circular polarization in analytical forms. This expression clearly explains the behavior of the circular polarization. An important result is that the phase of the circular polarization is determined only by the dipole angle and is independent of that of the slot. These relations are also confirmed by experiments.