Microstrip-Fed Ring Slot Antenna Design With Wideband Harmonic Suppression

A microstrip-fed circular ring slot antenna (CRSA) with a fundamental mode at 2.45 GHz is initially studied. To suppress the additional harmonic modes excited by the ring slot, a single inverted U-shaped slot (or defected ground structure, DGS) is integrated into the CRSA. Through this, harmonic suppression over a wide bandwidth (approximately between 3 and 9 GHz) is achieved. This DGS can also be applied to other microstrip-fed ring slot antennas, such as square and triangular ring slot antennas.