Harmonics suppression of microstrip patch antenna using defected ground structure

Active micro strip patch antennas radiate harmonic frequencies and Suppression of Harmonics is an important factor for MPA. In this paper suppression of higher order modes upto third harmonics of the fundamental operating frequency of microstrip patch antenna has been discussed. The design will reduce higher order harmonics without affecting fundamental frequency. A stub with defected ground structure (DGS) is integrated to a microstrip transmission line of patch antenna to reject the harmonics. The DGS pattern used here is simple and can easily be etched on ground plane. Here compact low pass filter (LPF) with circular head dumbell shaped DGS and circular headed open stub have been designed. Wide stop band and high filter selectivity have been achieved by this design. The designed low pass filter is integrated with microstrip line feed of the square patch antenna. The addition of the circular headed stub with feed line improves the suppression of higher order harmonics of fundamental operating frequency. The equivalent circuit is also discussed here. The fundamental operating frequency passes through the pass band and the higher order harmonics got rejected by the stop band of the low pass filter.