Design of multi-band, broadband passive circuits and their application in RF power amplifiers

Abstract

The last two years have shown a different life scenario when the pandemic hit every part of the world. It reshaped the life of humans rapidly by forcing work from home, online education, online shopping and more. The pandemic has put brakes on this constantly fast-moving world. However, technology bridged the gap of physical distancing by providing everything online, from medical assistance to non-essential items, from family video-calling to online schooling and many more. The internet has played a preeminent role in the last two years, and technology in the hand of every human, from kids to adults, assists in overcoming stressful situations. The technologies that will formulate the next-generation wireless systems are being defined today. The primary motivation of this research was the increased complexity of mobile devices, resulting in more significant challenges and stringent requirements in the design of all front-end components, including filters, power dividers, matching networks and power amplifiers (PAs). Inevitably, RF front-end solutions for different applications, including telecommunication, aerospace, military and others, have moved from the discrete solution with one or more single-band circuits, including PA modules, matching networks etc., towards the ultimate multi-band solutions. In this approach, one module will support all existing standards while covering different frequency bands of operation. This doctoral dissertation focused on the challenges and considerations in designing different components in any RF front-end module. The main contribution of this thesis is to develop dual-band/broadband architectures for passive devices, including matching networks and power dividers, as well as their applications in active devices such as harmonically tuned power amplifiers. Various design methods have been discussed and analyzed to provide different architectures with practical solutions. Design and analysis of distinct matching networks are proposed. The theoretical basis for designing the dual-band matching networks, closed-form equations, analysis, additional case studies and fabrication of prototypes for validation purposes is contributed. Different scenarios discussed include real-to-real matching, real-to-complex matching and complex-to-complex matching, depending on the nature of the source and load type. Also, broadband power dividers have been studied rigorously to operate over a wide range of frequencies with DC blocking capability, which is a primary demand in any RF front end. Two different broadband power dividers operating over a wide range of frequencies, including their design and analysis, are proposed. Other methods are presented with inherent DC-blocking capabilities that are useful in many practical applications. Along with passive circuits, the multi-band matching network is utilized to design power amplifiers that can provide desirable performance in terms of efficiency and gain. Two methodologies are proposed, which are simple and supported by closed-form equations that maintain easy fabrication and are pragmatic in implementation. It considers the application of multi-band matching networks in designing high-efficiency RF power amplifiers. Thus the key findings of this thesis include different multi-band/broadband passive devices, including matching networks and power dividers which are accompanied by closed-form equations to obtain mathematical formulations for easy designing and prototyping. The application of matching networks in active devices, i.e. power amplifiers, is explored. The harmonically tuned power amplifier, accompanied by formulations and design procedures to obtain optimum performance, is verified with design examples and case studies.