Low‐Profile Miniaturized Wideband Circularly Polarized Monopole and MIMO Antennas Using Characteristic Mode Analysis for Wireless Communication

Abstract Low‐profile miniaturized wideband circularly polarized (CP) monopole and multiple‐input‐multiple‐output (MIMO) antennas using characteristic mode analysis (CMA) are presented. The antennas are constructed with a microstrip feeding line, a slot, and a branch, which positions the transmission line perpendicularly to the branch to achieve CP. The CP characteristic is realized through a characteristic angle (CA) difference of approximately 90° at three mode significance (MS) intersections across four modes. CMA provides both theoretical analysis and design guidance for these antennas. The antennas were fabricated and tested, with dimensions of 0.48λ₀ × 0.48λ₀ × 0.03λ₀ and 0.47λ₀ × 0.47λ₀ × 0.03λ₀, where λ₀ represents the free‐space wavelength. Measurements indicate that the monopole antenna achieves a −10 dB impedance bandwidth (IBW) from 3.2 to 8.4 GHz (89.7% relative bandwidth), a 3 dB axial ratio bandwidth (ARBW) from 3.6 to 5.1 GHz (34.5%), and a peak gain of 6.6 dBic. The MIMO antenna has a −10 dB IBW from 3.1 to 8.2 GHz (90.3%), a 3 dB ARBW from 3.2 to 6 GHz (60.9%), and a peak gain of 5.1 dBic. Both antennas feature a low profile, ultra‐wideband IBW, broadband ARBW, and miniaturized design, making them suitable for wideband wireless communication applications.