In this paper, we designed the power detector with the capacitor to decrease the estimation error and directional coupler which are used in 2.45GHz ISM band, also compared and analyzed the characteristics of the power sensitivity to estimate the performance of detector, the bandwidth and the printed circuit board size. As the results, their volatage sensitivity is constant from -50dBm to -25dBm wich is the input power, but the detector composed by the directional coupler is superior about 3mV/㎼ than by the single diode from -25dBm to -10dBm and its bandwidth is wider about 63MHz than the directorinal coupling power detector with he capacitor. Therefore when the output level of transmitter is below -20dBm, the power detector with the capacitor had better be selected as the detector for the power ontrol to reduce the area because of the similar characteristics, and above -20dBm or in the wide hand system, the estimation error can be eliminated by the selection of directional coupler considered the voltage sensitivity for the power detector.