Abstract: This paper designs a kind of passive device – directional coupler used for power detection and extraction.At first, analyses and abtains the theory formulas contacting each component and performence target, by using the equivalent of transmission line (TL) couplers and lumped element (LE) couplers.Then for the high frequency (VHF) bands, TL couplers are hard to carry out to be tight structures, and lumped elements have the limits of transmission power, considering the design targets of loose coupling and high directionality as well, this paper proposes a solution method consisting of lumped elements and microstrip inductors, and designs a coupler model.Furthermore, according to the real requests as 100 MHz centre frequency and 300 W transmission power of the developed RF system, the validation of model correctness is given, and the schematic and momentum simulation are implemented by ADS software in this paper.The measured performance curves of real circuit and measured results analysis are presented at last.