Design And Implementation Of Ultra Wideband Directional Quadrature Coupler

Directional coupler is a kind of RF component which can distribute power. It issuitable for many occasions. The operating frequency range of the directional couplerresearched in this paper is from30MHz to512MHz. According to the definition of bandratio and relative bandwidth, this component is an UWB(Ultra Wide Band) RF compo-nent. At present there is no stripline coupler can work normally in such a wide band andat so low frequency. Hence the research of this paper has been an innovation. ThisUWB directional quadrature coupler has four ports as follows, input port, direct port,couple port and isolation port. It can distribute power equally and at the same time keepthe phase difference at90°between direct port and couple port. By using this relation-ship, the directional coupler researched in this paper can be used for quadrature vectorsynthesis of the VHF/UHF adaptive interference canceller.The couple mode of directional coupler are forward couple and back couple.According to the stripline model of the simulation instrument, back couple is discussedin detail in this paper. At first the structure and application of directional coupler hasbeen explained. And second, directional coupler is analysed by using microwavenetwork and odd-even mode analysis. Then constraint condition is obtained. On thebasis of above analysis, odd mode characteristic impedance and even mode character-ristic impedance are obtained from the research of the directional coupler by usingmicrowave equivalent circuit and interpolation polynomial. The physical parameter ofstripline can be obtained from the relationship with odd mode characteristic impedanceand even mode characteristic impedance. For decrease of component size and practicalapplication, the research on miniaturization has been done and correction measures hasbeen acquired. Asimulation instrument,named ADS, a product of Agilent company, canbe used for schematic simulation and PCB simulation of this directional coupler. Thenthe product can be produced and tested after designing the PCB of this coupler. At last,for future research, a method which can reduce the reflection of input port has beenresearched and verified.