Coupled Planar Microwave Resonators and Transmission-Line Structures

This chapter presents the fundamental concepts on coupled microwave structures, including coupled resonators, coupled transmission lines and coupled-line structures. Although many concepts and results here presented have a general validity in the microwave field, the chapter focuses on planar coupled structures, which are the building blocks of the sensors described in the book. The chapter introduces the fundamentals of microwave resonators (lumped and distributed) and coupled planar transmission lines, with special emphasis on coupled identical microstrip lines. Coupled resonators are addressed from the field and circuit approaches, introducing the concepts of electric and magnetic coupling, and resonance-frequency splitting. The last section of the chapter presents the coupled-line directional couplers and two-port coupled-line networks.