The term “microwave circuits” is used to identify the electrical circuits used at microwave frequencies for performing signal processing functions like amplification, frequency conversion, mixing, detection, phase shifting, filtering, and power dividing. By “microwave frequencies,” we refer to electromagnetic signals whose wavelength is in centimeters, roughly from 30 cm to 1 mm with the corresponding frequencies ranging from 1GHz (GHz=10
9
Hz) to 300 GHz. band. Microwave frequencies present several interesting and unusual features not found in other portions of the electromagnetic frequency
spectrum. These features make microwaves uniquely suitable for several useful applications in telecommunications, radar, industrial heating and sensors, and so on. The most common consumer application of microwaves is the domestic microwave oven used for food processing.