We report a photonic crystal-based resonant antenna with a very high directivity and gain. The layer-by-layer dielectric photonic crystal we used in our experiments was designed to have a three dimensional band gap with a mid-gap frequency around 12 GHz. We used the output port of a microwave network analyzer and a monopole antenna to obtain EM waves. The input port of the network analyzer and a standard gain horn antenna were used to receive the radiated EM field from the monopole antenna. The receiver was kept free to rotate around the antenna. We investigated the radiation characteristics of this monopole antenna, which was inserted into the planar defect structures built around a photonic crystal that consisted of 20 layers. The planar defect was formed by separating the 8th and 9th layers of the structure. In order to suppress the radiation in the backward direction, we intentionally chose one of the mirrors of the cavity to have a higher reflectivity (/spl sim/18-20 dB) than the front mirror.