Slot microstrip antenna with harmonic control

With the introduction of the circularly symmetrical slot near the coaxial feed location of the square microstrip antenna patch, harmonic suppression performance can be realized in the antenna. Effectiveness of the circularly symmetrical slot for harmonic suppression is studied. Experimental results show that application of the circularly symmetrical slot near the coaxial feed location of the microstrip antenna patch can remarkably suppress the harmonic frequencies. Measured radiation patterns indicate that the forward radiation is suppressed by more than 20～25dB at the second and the third harmonic frequencies compared with the reference antenna, while both the forward radiation gain and the backward radiation at the fundamental mode resonant frequency remains basically unchanged.