Planar Microwave Sensors

In this introductory chapter to planar microwave sensors, the main sensing approaches and working principles are presented, and some representative illustrative prototype examples are reported. Some strategies devoted to sensor performance optimization (manly the sensitivity) are discussed, excluding those strategies based on coupled structures, which are the subject of the subsequent chapters in the book. The chapter also highlights how machine learning can be applied to improve sensor robustness and selectivity. Finally, a section is devoted to outline those aspects of coupled structures that make them useful for sensing.