Microstrip-Fed Circular Ring-Slot Antennas With Very Wideband Harmonic Suppression

A microstrip-fed circular ring-slot antenna excited at 2.45 GHz band for wireless local area network (WLAN) 2.4 GHz operation is initially studied to achieve very wideband harmonic suppression between 3 and 20 GHz (7 fc) in which the technique of integrating a stepped impedance resonator that has a low-pass filter characteristic and open stubs that possesses band-stop characteristic into the slot antenna is applied. By further loading two dissimilar slots into the single-band design, a triple-band operation for WLAN 2.4/5.2/5.8 GHz with the harmonic suppression of up to 7.86 fc (2.73-21.9 GHz) is realized.