A Novel Near-Field Resonant Parasitic Electrically Small Antenna With a Wide Tuning Range

An electrically small antenna (ESA), designed on the near-field resonant parasitic (NFRP) technology and with a wide tuning range, is proposed. It utilizes a capacitively loaded loop (CLL) as its NFRP element, and tunes its resonant frequency by adjusting CLL's capacitance. Quite different from normal NFRP antennas using one ESA such as a semiloop antenna (SLA) as the driven element, the proposed antenna employs a composite driven element (CDE), which combines a monopole and a SLA. Analyses reveal the CDE is able to realize good tuning impedance matching and effectively excite the CLL over a wide frequency range. A prototype is designed, fabricated, and measured. Results show it achieves a 10 dB tuning bandwidth up to 107.9% (36–117 MHz) with a dimension of only 0.036
$\lambda \times {\text {0.030}}\lambda \times {\text {0.018}}\lambda$
(
ka
= 0.18), where
$\lambda$
is the wavelength corresponding to the start tuning frequency of 36 MHz.