An Electrically Small Antenna Using Defected Ground Structure for RFID, GPS and IEEE 802.11 a/b/g/s Applications

A compact size (20 x 21 mm(2)) planar tri-band electrically small antenna is presented for Wireless ISM, RFID application resonating at 1.57 GHz, 2.47 GHz and 926 MHz. The Proposed structure consists of a dual-slot radiating patch and two split ring structures made using combination of L and U shapes forming a defected ground structure (DGS). Length and width of the planar slot is optimized to get the required frequency bands whereas incorporation of DGS leads to increase in impedance bandwidth. The simulated and measured return losses (S-11) of all three frequency bands are greater than 10 dB. Impedance bandwidths of 20 MHz (913-934 MHz), 90 MHz (1.5-1.59 GHz) and 70 MHz (2.43-2.50 GHz) are achieved for the proposed range. The electrically small antenna radiation pattern is omnidirectional, and gains of 0.32 dBi, 1.2 dBi and 1.5 dBi are achieved which make the antenna suitable for RFID, GPS and WLAN applications.