Design Of New Microwave Directional Couplers And Gysel Power Dividers

With the rapid development of the modern wireless communication systems,radio frequency circuit requires microwave components with increasingly high performance.Microwave components which work in multiple frequency bands or integrate diversified functions can simplify circuit structure,reduce loss and become hot in research.The couplers and power dividers,as the key components of the passive microwave circuit,are widely used in designing due to their functions of power splitting and power synthesis.The directional coupler is a lossless and reciprocal network and is matching at all ports.It is used not only in feed networks o f phased arrays,but also in power combining amplifiers to have the matched reflection coefficients on inputs and outputs and to allow an important degree of freedom.The Gysel structure which is a modified version of the Wilkinson structure,provides a so lution of thermal problem and is suitable for high power applications.According to the trend of the microwave designing,the optimized structures of coupler and power divider are explored and the new technologies are studied.Also,couplers and power dividers with superior performances are proposed.Major works and contributions of this dissertation are outlined as follows:1.A new branch-line coupler for dual-band operation and size reduction is proposed.Also,a coupler with both harmonic suppression a nd unequal dividing ratio is realized.Firstly,both the dual band response of ?-shaped transmission lines and the principle of the quarter-wavelength transmission line substituted by a compact dual transmission lines are studied.By combining ?-shaped transmission lines and dual transmission lines model,a novel topology of ?-shaped dual transmission lines is proposed and applied to present a dual band coupler with compact size.Secondly,the transmission zero introd uced by a parallel open circuited stub is studied.By combining the T-shaped network and the double side parallel striplines,a coupler aimed at harmonic suppression,large power dividing ratio and compact size are presented.Finally,two types of couplers are simulated,fabricated and tested to verify the good performances.2.A dual-band Gysel power divider with large power dividing ratio and a quad-band Gysel power divider are presented.O n the basis of the conventional two-way Gysel power divider,three parallel open circuit stubs are applied to the transmission line between two load ports.The new Gysel structure is p roved to acquire the dual-band response by using the circuit theory.Due to the higher effective permittivity and characteristic impedance provided by the etched defects on the ground plane,a dual-band Gysel power divider with large power dividing ratio is presented.Also,the characteristics of the image impedance and insert phase of a coupled line ended by a short circuit are analyzed.According to the even-odd mode analysis method,four solutions of the electrical length are derived.A ?-shaped network,which is composed of three pairs of coupled lines,is proposed to adjust the output phase difference to ±90 degree and to realize impedance matching at three arbitrary frequencies and a related frequency.By applying the new impedance tra nsformer to the traditional Gysel structure,a quad-band Gysel power divider is designed.Finally,two kinds of Gysel power dividers are simulated,fabricated and tested to verify the design theory.3.A generalized Gysel power divider with arbitrary power dividing ratio is proposed.Based on the conventional Gysel structure,a single-band Gysel power divider consisting of transmission lines with flexible electrical lengths and characteristic impedances is presented.Explicit closed-form design equations are derived based on the modified even-odd-mode analysis.Detailed discussions show that the design equations in some previous works are special cases of our equations.In this sense,the proposed Gysel power divider can be viewed as a generalized structure.Since more parameters are introduced,the realization of the Gysel power divider with high power dividing ratio becomes flexible and much easier.Also,it is more suitable for high power applications when compared to the structures composed of complicated transmission lines.Two Gysel power dividers with different power dividing ratios are designed and fabricated to show the superior performance.4.A dual-band Gysel power divider with frequency ratio larger than 3 is presented.According to the transmission matrix theory,a ? shaped structure is equivalent to an transmission line with arbitrary electrical length.By applying the ? shaped topology,the generalized single-band Gysel structure is extended to dual-band response.Theoretical derivation and parameters analysis show that the dual-band Gysel power divider with frequency ratio larger than 3 and large power dividing ratio can be successfully achieved,which is hard to realize by conventional methods.Finally,two prototypes with different power dividing ratios and frequency ratios are fabricated,the measured results show superior performance of the structure.