Experimental Study of Reactively Loaded Parasitic Microstrip Array Antenna for Circular Polarization

This paper describes the experimental study of a parasitic microstrip array antenna operated in circular polarization (CP). This antenna applies a microstrip antenna with dual-orthogonal feed as an antenna element for excitation of the CP wave from both fed and parasitic elements. A new switched reactance circuit using an SP3T switch taking three reactance states is connected to two ports on each parasitic element. The radiation pattern is controlled by switching the reactance state. The measured radiation pattern and the axial ratio of the two-element array (one fed and one parasite) indicated that the main beam was switched depending on the reactance state (capacitive, short, and inductive) with an axial ratio below 3 dB. The capability of 360deg beam-switching in the azimuth direction was verified by measurement of the five-element two-dimensional array (one fed and four parasites). By setting proper reactance values, the main beam was tilted in the elevation plane at the azimuth of every 45deg interval, and the axial ratio was acceptable. The measured results agreed with the calculated ones. From these experimental observations we concluded that the antenna works as a switched-beam antenna operated in CP wave.