A Dual-Band Printed Electrically Small Antenna Covered by Two Capacitive Split-Ring Resonators

In this letter, we present a dual-band electrically small antenna (ESA) operating at 934 MHz and 1.55 GHz. The miniaturized radiation structure consists of a small ring and two concentric split-ring resonators on an FR-4 substrate. The resonant response of the proposed radiation structure is characterized by the coupling among two split-ring resonators and the small ring. A weak electric field interaction between two split-ring resonators is observed. This interaction provides an additional capacitance to further reduce the total dimension of the resonant electrical length. The calculated return loss of the proposed structure agrees well with the measured data. Measured radiation patterns are presented. The planar structure is promising for compact wireless devices and may find applications in wireless electrocardiograph sensors, multiband portable MIMO wireless systems, and RF energy-harvesting systems.