Compact Crossed-Dipole Antennas Loaded with Near-Field Resonant Parasitic Elements

Two compact planar crossed-dipole antennas loaded with near-field resonant parasitic (NFRP) elements are reported. The NFRP and crossed-dipole elements are designed for the desired circularly polarized (CP) radiation. By placing the NFRP element over the driven element at angles of 0° and 45°, respectively, dual-band and broadband CP antennas are realized. All radiating elements of antennas are 35 mm × 35 mm × 0.508 mm (0.187 λ₀ × 0.187 λ₀ × 0.0027 λ₀ at 1.6 GHz) in size. The dual-band CP antenna has a measured S₁₁ <-10-dB bandwidth of 226 MHz (1.473-1.699 GHz) and measured 3-dB axial ratio (AR) bandwidths of 12 MHz (1.530-1.542 GHz) and 35 MHz (1.580-1.615 GHz) with minimum AR CP frequencies of 1.535 GHz (AR = 0.26 dB) and 1.595 GHz (AR = 2.08 dB), respectively. The broadband CP antenna has a measured S₁₁ <-10-dB bandwidth of 218 MHz (1.491-1.709 GHz) and a 3-dB AR bandwidth of 145 MHz (1.490-1.635 GHz). These compact antennas yield bidirectional electromagnetic fields with high radiation efficiency across their operational bandwidths.