Coaxially fed microstrip antenna for harmonic suppression

A coaxially fed microstrip antenna using a defected ground structure (DGS) for harmonic suppression is proposed, in which the DGS is distributed around the coaxially fed location. The effectiveness of the DGS is discussed for the suppression harmonic frequencies of the antenna. Experimental results show that application of the DGS near to the coaxially fed location of the microstrip antenna can remarkably suppress the harmonic frequencies. Measured radiation patterns indicate that, compared with the reference antenna, the forward radiation of the proposed antenna is suppressed by 20 dB at the second- and the third-harmonic frequency, and the backward radiation is almost not varied.