Low-Q, Electrically Small, Efficient Near-Field Resonant Parasitic Antennas

Metamaterial-inspired electrically small Z, stub and canopy antennas are reported. They are near-field, resonant parasitic designs. Different Z and stub antenna configurations and the effect on their Q values are studied. Their behavior led to the canopy antenna design. At the size of ka ~ 0.046, the canopy antenna is an electric-based antenna with high overall efficiency (over 90%) and low Q-ratio value and whose input resistance is almost completely matched to a 50 Omega source. The resonant frequency, ~300 MHz, in the UHF band is selected for the designs. The canopy antenna is studied extensively to explore the lowest achievable Q values. Various coupling configurations, canopy shapes, and metal-air ratios are investigated. Circuit models are also introduced to explain the radiation mechanism. Numerical simulation results are analyzed and compared with previously derived Q value limits for electrically small antennas that are based on the standard circuit models of spherical wave multipoles. The Q value of the canopy antenna for the lowest order, single electric resonance is shown to reach a fundamental limit of approximately 1.75 times the Chu value.