Low-Profile Wideband Circularly Polarized Microstrip Antenna with Conical Radiation Pattern
A low-profile wideband circularly polarized (CP) microstrip antenna with conical radiation pattern is designed in this paper. Based on the center-fed circular microstrip patch structure, the proposed antenna symmetrically employs 5 shorting vias connecting the patch and the ground plane to provide the θ-polarization and 11 slant sector branches at the edge of circular patch to generate the φ-polarization. With the phase difference of 90° between the two orthogonal polarizations, the design radiates right-handed circularly polarized (RHCP) waves. The proposed antenna works at three resonant modes. To realize broad operating bandwidth, the slant sector branches should be carefully adjusted to make the second resonant mode couple the first mode (TM01 mode) and third mode (TM02 mode) together. The measured results show that the proposed antenna has a low profile of 0.025λ, impedance bandwidth of 35.4% (3.74-5.35 GHz), and axial ratio (AR) bandwidth of 38% (3.7-5.45 GHz). To further verify the characteristics of the proposed antenna, the studies on several important parameters are carried out by HFSS simulation, and a simple design guideline is provided.