Investigation on a compact wideband omnidirectional circularly polarized antenna in an indoor propagation channel for 2.4 GHz application

In this paper, for the first time, the capability of a compact low-cost wideband omnidirectional circularly polarized (CP) antenna to suppress multipath fading characteristics in a typical indoor propagation channel for 2.4 GHz applications is investigated. A ray tracing method based on the geometrical optics and uniform theory of diffraction is applied to analyze an indoor propagation channel using the measured radiation patterns of the proposed antenna. The design uses a conventional monopole antenna with a circular ground plane to generate a vertically polarized electric field. Sequentially flag-shaped stubs are then added to the ground plane to produce horizontally polarized electric field and to improve the impedance bandwidth of the proposed antenna. The antenna is designed for 2.4 GHz WLAN application with 10 dB impedance bandwidth of 25.5% and 3 dB axial ratio (AR) bandwidth of 24.5%. The polarization can be readily changed between the left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) by altering the direction of the coaxial probe (monopole) or varying the orientation of the printed bended stubs. Both the LHCP and RHCP prototypes of the proposed antenna are designed, fabricated, and tested, and the similar results are obtained. This paper introduces a cost-effective, wideband circularly polarized antenna for 2.4 GHz applications, addressing multipath fading in indoor channels. Utilizing ray tracing and geometrical optics, the design achieves circular polarization through flag-shaped stubs, enhancing impedance bandwidth. Results show a 10 dB impedance bandwidth of 25.5%, 3 dB axial ratio bandwidth of 24.5%, and switchable LHCP and RHCP with consistent performance between prototypes. The compact design effectively mitigates multipath fading in typical indoor propagation channels.image