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Several electrically small antenna systems that utilize the magnetic couplings between a coaxially-fed semi-loop antenna and capacitively-loaded loop (CLL)-based near-field resonant parasitic (NFRP) elements are presented. Both one and two gap CLL elements are considered; their impact on the system performance, particularly their effects of the resonance frequencies and the corresponding Q values, is evaluated. By integrating multiple NFRP CLL elements with the coaxially-fed semi-circular loop antenna, electrically small multi-band systems are achieved. They can be designed for a broad range of frequencies by tuning the NFRP elements separately. Dual band designs are reported that achieve operation at the GPS LI (1.5754 GHz) and L2 (1.2276 GHz) frequencies. Their operational modes and performance characteristics are studied. These lead to additional electrically small antenna designs, which feature only one driven loop antenna and two NFRP CLL elements and which achieve circularly polarized (CP) operation. A CP antenna whose electrical size is ka = 0.495 at the GPS LI frequency is presented in detail. Its simulated bandwidth and beamwidth, for which the axial ratio (AR) is less than 3 dB, are, respectively, 7.8 MHz and 76°.
Date of Publication: March 2011