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.