Low Q electrically small linear and elliptical polarized spherical dipole antennas

• Published in: IEEE transactions on antennas and propagation Vol. 53; no. 3; pp. 1047 - 1053
• Main Author: Best, S.R.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-03-2005; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antenna feeds; Antennas; Applied sciences; Bandwidth; Dipole antennas; Efficiency; Electric resistance; electrically small antennas; Exact sciences and technology; Frequency; Helical antennas; Impedance; Magnetic resonance; Polarization; Q factor; Radiocommunications; Telecommunications; Telecommunications and information theory; Performance evaluation; Rectilinear polarization; Wire antenna; Dipole antennas; High Q factor; Q factor; Elliptic polarization; helical antennas; Spherical antenna; Dipole antenna; Mismatching; Helical antenna; electrically small antennas; Impedance matching; Radiation pattern; Axial ratio; Electric dipole; Magnetic dipole
• ISSN: 0018-926X; 1558-2221
• DOI: 10.1109/TAP.2004.842600

Electrically small antennas are generally presumed to exhibit high impedance mismatch (high VSWR), low efficiency, high quality factor (Q); and, therefore, narrow operating bandwidth. For an electric or magnetic dipole antenna, there is a fundamental lower bound for the quality factor that is determined as a function of the antenna's occupied physical volume. In this paper, the quality factor of a resonant, electrically small electric dipole is minimized by allowing the antenna geometry to utilize the occupied spherical volume to the greatest extent possible. A self-resonant, electrically small electric dipole antenna is presented that exhibits an impedance near 50 Ohms, an efficiency in excess of 95% and a quality factor that is within 1.5 times the fundamental lower bound at a value of ka less than 0.27. Through an arrangement of the antenna's wire geometry, the electrically small dipole's polarization is converted from linear to elliptical (with an axial ratio of 3 dB), resulting in a further reduction in the quality factor. The elliptically polarized, electrically small antenna exhibits an impedance near 50 Ohms, an efficiency in excess of 95% and it has an omnidirectional, figure-eight radiation pattern.