Innovative augmentation of impedance transformation in the design of highly flexible multi-functional RF/microwave circuits and components

Abstract

The burgeoning of a multi-standard wireless communication system (WCS) with the multitude of emerging applications has been permeating the design and development of radio frequency (RF) circuits and components of the front-end subsystem. To support multiple standards, the design and development of the multi-band RF and Microwave circuits and components are highly desirable. This is due to the fact that these wireless standards are operating at multiple frequencies, and therefore, the multi-band architectures reduce system size, cost, power consumption, etc., rather than the conventional approach of using individual subsystems for the individual frequencies. Furthermore, the multi-functional RF components eliminate the redundant uni-functional components and associated interconnections between the uni-functional components of a communication system by exhibiting all the features inherently. This further reduces the system size/volume, power consumption, insertion loss, etc. However, it should be noted that the design and development of such multi-band multifunctional components are found to be very challenging. The key constraints are the achievable frequency ratios, achievable impedance transformation ratios, and increased design complexities. For example, the literature is replete with the dual-band impedance transformers, but the range of frequency ratios and impedance transformation ratios is limited. More importantly, the concurrent operation of high impedance transformation ratios at high frequency ratios is much limited. One of the possible reasons is the limited design flexibility at the expense of increased functionality. Subsequently, the requirement of multi-functional characteristics affects the design flexibility further. Furthermore, the development on the domain of multi-band multi-functional components is not explored much in the literature. Therefore, this thesis aims to investigate and address the existing lacunae on the design and development of multi-band multi-functional components. Firstly, the challenges associated with the impedance transformers for high impedance transformation ratios at high frequency ratios are discussed and addressed. Also, the concurrent high frequency ratios and high impedance ratios are accomplished. Secondly, the RF and Microwave components exhibiting multiple inherent features like impedance transformation, DC blocking, differential phase shifts, balanced-to-unbalanced signal conversion, etc., are investigated. In addition, the multi-functional architectures, inherently exhibiting more than one feature, with dual-band operations are addressed. More specifically, the developed architectures for operation at high impedance transformation ratios and high frequency ratios, even concurrently, are accomplished. Thirdly, this thesis addresses the challenges associated with the arbitrary impedance environments, varying with the design frequencies. The architectures for dual-band impedance transforming power divider with frequency-dependent complex port impedances at two arbitrary design frequencies are presented. No such feature from a dual-band power divider or combiner is presented in the literature. Finally, it should also be noted that the reported design architectures are simplified and uni-planar and are supported by sound and systematic analytical design solutions, which is rare in the literature. The closed-form equations with innovative design strategies make the designs re-configurable for the wide range of design specifications, and thus the enhanced micro strip compatibility is attained. The closed-form design equations not only make it easy to calculate the design parameters but also enables the quick prototyping of the circuits and components. Overall, the contributions are within the realm of simplifying the design strategies and rapid prototyping backed by the closed-form design equations for multi-frequency communication circuits and systems. In brief, this research work has the potential to significantly advance the current state-of-the-art that may eventually lead to a paradigm shift in the way such systems are designed. This thesis also paves a new dimension of the applications of multi-functional components, which leads to a unified PCB solution for the RF front end of a communication system. The future directions and possible improvements are also reported.