Dual-Loop Arrays Fed by Coplanar Parallel Lines for Wideband Circular Polarization

Using the method of moments, we analyze three types of series-fed array antennas for circular polarization. First, we present radiation characteristics of a reference antenna with symmetrical dual loops fed by <formula><tex>$balanced$</tex></formula> parallel lines. Next, we modify the symmetrical dual loops into asymmetrical ones to enhance a circularly polarized (CP) wave bandwidth. It is found that the modified antenna has a bandwidth of 35% for a 3dB gain-drop criterion, where the axial ratio is less than 3 dB. Last, we use <formula><tex>$unbalanced$</tex></formula> parallel lines for feeding the asymmetrical dual loops to simplify the feed system. It is revealed that the antenna shows a CP wave bandwidth of 19%, which is twice as wide as that of the reference antenna.