3.1 Introduction

It is the extensive use of passive components that makes MMIC design so different to conventional integrated circuit design and layout. In MMIC design, passive components are used for impedance matching, DC biasing, phase-shifting, filtering and many other functions. This chapter describes the key passive components that are used in MMIC design. These components include not only the basic lumped inductors, capacitors and resistors, but also a wide range of distributed transmission-line components. These transmission-line components include microstrip lines and elements such as bends and T-junctions, as well as standard building blocks like couplers and power splitters/combiners. Most often, these building blocks are realised in the microstrip transmission-line medium. However, other types of transmission line such as coplanar waveguide (CPW), slotline, and 'thin-film microstrip' are being used more and more. The principal advantages to be gained from using CPW are increased packing density of circuits and reduced dispersion for millimetre-wave operation. Transitions between the different transmission-line media can be used to realise components such as baluns. At the lower microwave frequencies transmission-line components are often too large to be practical. To overcome this, the standard microstrip components such as couplers and power splitters can be realised with lumped-element equivalent networks or by using the lumped-distributed miniaturisation technique. These approaches are an interesting example of how the precisely defined passive components available on MMICs can be used to develop new circuit techniques which overcome the fundamental size limitation not encountered with...