Low-profile circularly polarized radiation elements —loops with balanced and unbalanced feeds

In this paper, the two types of reflector-backed loop antennas have been numerically analyzed. The analyses reveal that a loop with a balanced feed shows a CP wave bandwidth of 15%, which is eight times as wide as that for the other loop with an unbalanced feed, when each loop height above the reflector is 0.25lambda₀. As the loop height decreases to 0.10lambda₀, the difference between the bandwidths is found to disappear. These results (for the loop resonant antennas) are compared to those for previous studies on reflector-backed spiral and curl (non-resonant) antennas. It is found that the difference between the CP wave bandwidths for the resonant and non-resonant antennas also disappears, as their antenna heights decrease to 0.10lambda₀.