The Develop Of The Broadband Directional Coupler In The L-band With High Directivity High Precision And High Power

The directional couplers are widely used in microwave technology as a microwavecomponents.The microwave signal can be coupled in accordance with a predetermineddirection. Generally, we use the coupling power to regulation or monitor the signal. It isa device with four ports, and every port has mathed characteristics.So it can be appliedto the microwave circuit or its subsystem easily.Firstly, we introduced the concept and the basic technical parameters and thedevelopment of the directional coupler, and described the qualitative characteristics ofthe coupler and the main work of this paper.Secondly, we introduced and analysis the theory of the directional coupler. Theodd-even-mode method which described in detail in this paper is one of the mostcommonly used method in analysising the parallel-coupled transmission line directionalcoupler. Either a single or multi-element coupled transmission lines can be equivalent toa single or multi-element stepped-impedance filter. Thus, the four-port network isequivalent to a two-port network. Then we combined the odd-even-mode method withthe characteristics of microwave network, and analysed the equivalent ABCD matrixand the scattering matrix of the directional coupler in detail.Then we introduced thecoupler’s important characteristics, stripline and coupled stripline. and derived themethod of how to calculate the various technical parameters.Thirdly, the single, symmetric multi-element coupled transmission lines andasymmetric multi-element coupled transmission lines were analysed and synthetized byodd-even-mode analysis theory and microwave network theory.The analysis andsynthesis of directional coupler with single coupled line is relatively easy. The analysisof directional coupler with multi-element coupled transmission lines bases on theodd-even-mode method.The synthesis of symmetric directional coupler use the sinepolynomial approximation,and the synthesis of asymmetric directional coupler use theChebyshev polynomial approximation. These complicated synthesis can also beimplemented by computer software.Finally, the directional coupler which meet the technical requirements were achieved through symmetric and asymmetric two structures.We got the size of thecoupled transmission lines of the directional coupler by the systhesis and calculationdescribed previously, and simulated and optimized by ADS2009, then made the coupleraccording to the results of the simulation and optimization, of course need further debugand modify.The directional coupler is working in the L-band with good directional and highprecision.It can work in the high-power (continuous wave500W, pulse power5kW)environment, Its Operating frequency is between0.95GHz-2GHz,direction is greater than orequal to25dB, the degree coupling is30dB, and change in the range of0.5%.Test thecoupler with a vector network analyzer,we can see between the specified band itsperformance can achieve the technical demand.