Design and Analysis of a Low-Profile Dual-Band Circularly Polarized Monopole Antenna Based on Characteristic Mode Analysis

This paper presents the design of a simple dual-band circularly polarized monopole antenna using characteristic mode analysis. First, a dual-band elliptically polarized "L"-shaped monopole antenna with a partial ground is designed; then, a rectangular stub and a parasitic structure on the ground plane are implemented to achieve dual-band CP operation. To enhance impedance bandwidth and generate circular polarization in the upper band, the rectangular stub is attached to the "L"-shaped strip. The parasitic structure is employed for simultaneous dual-band CP radiation. Characteristic mode analysis is undertaken to predict the performance of the antenna before excitation. The modal analysis which is undertaken before excitation shows the natural modes that can be excited by the antenna structure to generate a dual-band CP response. The analysis gives approximate bandwidths that can be achieved by the antenna even before excitation. The overall dimension of the antenna is 0.379 lambda 0x0.379 lambda 0x0.015 lambda 0, where lambda 0 is the corresponding free-space wavelength at 5.7 GHz. The measured -10 dB impedance bandwidth (ZBW) is realized to be 75.9% (4.5 GHz-10 GHz). The measured 3 dB axial ratio bandwidths (ARBW) at the lower and upper bands are 6% (5.6 GHz-5.95 GHz) and 28% (6.65 GHz-8.82 GHz), respectively. The proposed antenna features a simple and compact structure for Wi-Fi, WLAN, WiMAX, and C band applications.