Research On Function Extension And Design Method Of Microwave Power Dividers

As a key passive device,the power divider can divide one signal into two or multiple signals and is widely used in power amplifiers,array antenna feeding networks,RF front-ends,and balanced circuits.In addition,with the development of mobile communications,the transmission rate is increasing,and the operating bandwidth is also increasing,thus the environmental noise and the interference between the transmission signals have an increasing impact on the system.To improve the interference immunity of communication systems,balanced to unbalanced(BTU)power dividers can provide an effective solution.Because they not only retain the common-mode suppression characteristics but also provide the flexibility to connect balanced devices to the conventional single-ended devices without additional balun structures.To meet the changing communication system applications,this dissertation is devoted to the function extension and design method of the microwave power dividers,and the main innovations achieved are as follows.(1)A design method of BTU power divider with an arbitrary power division ratio(PDR)is proposed.The method is also extended to the design of BTU branch-line couplers,and two single-ended coupling output BTU branch-line couplers with large PDR are proposed.Based on the theory of PDR being jointly determined by the electrical length and the characteristic impedance of transmission lines,the arbitrary PDR between each branch is accomplished by changing the electrical length.Compared with the conventional design method,the proposed method achieves a large PDR of more than 20 d B without high impedance transmission lines.All the proposed BTU power divider and BTU couplers have good common-mode suppression.In addition,the proposed BTU branch-line coupler with differential through has solved the problem that conventional single-port power detection instruments cannot be used directly to detect the differential circuit and system.(2)A design method of dual-band BTU power divider with independent PDRs is proposed.By taking advantage of the periodicity of the electrical length of the transmission line and the theory of PDR being jointly determined by the electrical length and the characteristic impedance,the PDR at the higher and lower operating frequencies can be designed independently according to the demand.Using network parameters,the design equations for the dual-band BTU power divider are derived.To verify the design method,two dual-band BTU power dividers with the operating frequencies of 1 and 2 GHz are designed and implemented,with the PDRs of-6 d B and 6 d B for the first power divider and 3 d B and-6 d B for the second one.The simulation and measurement results have good agreements.Compared with the existing dual-band BTU power dividers,the proposed method improves the design flexibility of the PDRs at high and low operating frequencies.(3)A BTU power divider/unbalanced-to-balanced(UTB)combiner with reflectionless filtering characteristics is proposed.By loading a novel absorption branch at the input port,the absorption of the reflected waves in the stopband is realized,and the 10-d B return loss band is broadened to avoid signal interference at the source due to the reflected waves in the stopband,thus improving the stability of the system.The frequency selectivity of the power divider/combiner is improved by the combined filtering structure of parallel open and shorted branches.A reflectionless filtering BTU power divider and a reflectionless filtering UTB power combiner are designed and implemented to verify the design method.The measured results show that the-10-d B differential reflected wave absorption bandwidth of the BTU power divider is more than 4 times the passband with the sharp passband edge attenuation;the-10-d B single-ended reflected wave absorption bandwidth of the UTB power combiner is more than 4 times the passband bandwidth with the sharp passband edge attenuation.Broadband reflectionless filtering characteristics and good frequency selectivity are realized.(4)A negative group delay(NGD)Gysel power divider and an NGD BTU power divider are proposed.The NGD characteristics are realized by introducing reflection-type NGD resonant branches at the output ports of the conventional Gysel power divider,and the impedance mismatch problem caused by the reflection-type NGD resonant branch is solved by loading a matching resistor at the input port.The design equations of the NGD Gysel power divider are derived by using the even-and odd-mode analysis method.In order to verify the design equations,an NGD Gysel power divider is designed and implemented.The measured results show that a group delay of-1.97 ns is obtained at 1 GHz.Good impedance matching performance is realized while generating the NGD characteristic.In the NGD BTU power divider,two λ/4 coupled lines with resistor-loaded coupling end and open-circuited isolation end are used to replace the conventional λ/2 inverter,which not only achieves the NGD characteristics but also improves the common-mode suppression performance.The measured results show that the group delay value at the center frequency is-2.06 ns,and the common-mode suppression is 37.3 d B.Compared with the existing NGD BTU power divider,the common-mode suppression performance is significantly improved.