Bent and Branched Microstrip-Line Antennas for Circular Polarization

We analyze three transmission-line antennas using the moment method. Each line antenna comprises a coplanar feed line, loops, and straight segments connecting the loops and feedline. First, we investigate bent and branched line antennas with loops on one side of the feedline. It is found that the segment length affects both the beam direction and axial ratio for the bent line antenna; in contrast, it only affects the branched line antenna's axial ratio, resulting in a more straightforward design. Subsequently, the branched line antenna is modified with loops on both sides of the feedline to enhance the gain. It is observed that the antenna shows a gain enhancement of 2.0 dB, maintaining the same axial-ratio bandwidth as that of the original branched line antenna. The simulated results are validated by experimental work.