A Novel Quad-band Electrically Small Antenna

Multi-band Electrically Small (ES) antennas are promising candidates for wireless sensing nodes and wearable devices. However, designing ES antennas for multi-band operation is challenging. In this paper, a novel method to design a quad-band completely ES antenna is presented. The proposed method is based on the even and odd modes of a split-ring antenna (SRA) and uses RF trap loading to get dual-band operation for each mode. The proposed antenna is ES for all bands, and at each band, the radiating structure uses almost the whole available volume, so a good bandwidth is obtained for all four bands. The proposed antenna is fabricated, and the performance at each band is measured in a proper ES antenna setup. The measured results validate the proposed method, with Qs only roughly 3 to 8 times of Chu's limit among four bands, given that the proposed antenna is cylindrical rather than spherical.