Abstract: This paper experimentally studies the coupling coefficient of microwaves into apertures with different shapes and sizes. The apertures used in the experiment mainly include elliptic aperture, circle, square loop, crossed rectangular slots, circular aperture, square aperture, equilateral triangular aperture, and parelleloriented rectangular slots. The coupling coefficients for these apertures in the frequency range from 2 to 18GHz are presented and compared with that for the rectangular slot.