Using the method of moments, we investigate two types of circularly polarized loop array antennas with and without a coplanar feedline (CF). The loops and the CF are located above a ground plane at a height of a quarter-wavelength. First, we analyze decoupling two-element array antennas. It is found that the antennas with and without the CF show reduced cross-polarization levels of -15 and -16 dB, respectively, when compared with that (-8 dB) of a conventional two-element array antenna without a CF. Next, we analyze sequential two-element array antennas. It is revealed that the antennas with and without a CF have bandwidths of 23% for a 3 dB axial-ratio criterion and 49% for a 3 dB gain-drop criterion, respectively. The analysis results are validated by an experimental work.
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