Multi-Frequency/Wideband Impedance Transform Methods Based On Modified Small Reflection Theory And Its Applications

With the rapid development of modern wireless communication,various communication applications emerge in endlessly.In order to fulfill the increasing requirement of multi-function and high-data-rate communication,the corresponding system usually operates at multiple bands or a single band with wide bandwidth.On one hand,although multi-band communication sys-tem can be realized by single-band components,power dividers/combiners,and radio-frequency switches,it usually has the disadvantage of bulk-size,high-cost,and poor-performance.Obvi-ously,it is difficult to fulfill the requirements of multi-mode communication as well as porta-bility.Therefore,a practical multi-band communication system usually comprises multi-band components.Up to now,the design of multi-frequency components and their key part of trans-former are usually based on transmission line theory,impedance matrix,admittance matrix,or ABCD matrix,their complexity increases with their bands in an exponential manner.There-fore,these methods are difficult to be extended to the design with triple and more bands.On the other hand,the method for the wideband transformation is limited to the matching net-work with real source and load.In view of the above,a further research on the approach of multi-frequency/wideband impedance transformation(with real/complex source and load)and its application is carried out.The main content and major contributions of this thesis are as follows:Firstly,the conventional small reflection theory is modified,and its scope is then broadened.The modified small reflection theory(MSRT)is applicable not only to the wideband transfor-mation,but also to the multi-frequency transformation.Meanwhile,the source and the load of transformations are no longer limited to real impedances.Moreover,compared to other methods such as transmission line theory,ABCD matrix,impedance/admittance matrix,its dominated equations can be reduced to a single matrix equation.In addition,the size of transformer can be directly controlled by the introduced reference frequency.Secondly,based on the MSRT,an approach for the multi-frequency real-to-real transforma-tion(a fixed real source impedance is transformed to a fixed real load impedance)is proposed.By introducing a mapping with regard to the modified small reflection coefficients,the complex-ity of dominated equations is almost unchanged after the introduction of additional transmission lines.In addition,the number of matching frequencies,the frequency ratio,and the impedance transform ratio of transformation can be arbitrary.Thirdly,based on the MSRT,by introducing two equivalent transformations and sufficient sub-transformers with equal impedance transform ratio,an approach for the multi-frequency complex-to-complex transformation(a complex frequency-dependent source impedance is transformed to a complex frequency-dependent load impedance)is proposed.When it is ap-plied to the design of multi-frequency power amplifiers in cascade,both the complexity and size are nearly half of the conventional methods.Fourthly,a design approach for the wideband real-to-complex transformation is proposed.Based on the above multi-frequency real-to-complex transformation,by directly constructing a pair of conjugated complex impedances based on the least-square method,a closed-form design formula for the wideband real-to-complex transformation is deduced.The proposed wideband real-to-complex transformation in this paper features simple structure and easy design.Fifthly,a new multi-frequency/wideband power divider/combiner is proposed.By applying the above multi-frequency/wideband real-to-complex and real-to-real transformations to its odd-and even-mode equivalent circuits,the design of multi-frequency/wideband power divider/com-biner is simplified.In addition,due to the adopted structure of two-stage circuit and stepped-impedance coupled lines,the multi-frequency/wideband power divider/combiner features only one isolation resistor and compact size.Finally,a triple-frequency class-F^-1high-efficiency power amplifier is designed by uti-lizing the multi-frequency real-to-complex transformation.It features easy design and can be readily extended to the design of power amplifier with arbitrary operating frequencies.More-over,a new 22-element equivalent circuit applied to Ga N power amplifier with gate leakage current and self-heating is proposed,and the parameter extraction is simplified by using the least square method.