Omnidirectional Circularly Polarized Antenna Based on Dual Zeroth-Order Resonances

This paper presents an omnidirectional circularly polarized (CP) antenna utilizing two orthogonal zeroth-order resonance (ZOR) modes. One of the two ZOR modes is based on a round mushroom construction while the other one is based on the artificial mu-negative transmission line (MNG-TL) devised by using periodical capacitor-loaded lines. The mushroom structure offers a vertical polarization while the periodical capacitor-loaded lines is featured by a horizontally polarized radiation. The proposed antenna is easy to fabricate for a low profile design. The measured axial ratio is less than 3 dB inside the range of 2.35-2.47 GHz. The measured| S
₁₁
| is better than -10 dB across the range of 2.21 to 2.61 GHz. Acceptable agreement has been observed between simulation and measurement.