Microwave electronics, such as radars, and radio and other communication devices are made of many electronic parts called “circuits” or “components.” These are designed and constructed to manipulate electromagnetic phenomena into carrying out different microwave signal processing functions such as generating, modulating, controlling, and amplifying signals. They are also used in frequency translation.
Early Microwave Circuits
In the early development of microwave circuits and systems (during and just after World War II) heavy and bulky microwave circuits in the form of voluminous, hollow metallic pipes and tubes were used. These large, three-dimensional waveguides are still in use today for certain high-power applications. However, since the 1960s, planar transmission line circuits have been the more popular choice.
Introduction of MICs
Also in the 1960s, the concept of microwave integrated circuits (MICs) was introduced. Instead of building individual microwave components separately and then connecting them on a piece-by-piece basis, it was thought it would be more cost effective and mass-producible to laminate or “print” an entire circuit on a single planar dielectric substrate (that looks like a small, flat chocolate chip) with various components connected to each other (usually by soldering) in a continuous integrated fashion.
What are Planar Circuits
A planar circuit always consists of a number of specific, but carefully dimensioned, very thin, metallic line and/or slot patterns that are formed on or between planar dielectric substrates. These metal lines or patterns connect components of microwave electronics such as transistors, resistors, and capacitors, and may perform other circuit functions. Typically, the thickness of those conducting patterns is around 0.5 micrometer through 50 micrometers.
What is a Hybrid MIC
If a MIC is fabricated on a non-semiconductor substrate such as ceramic, microwave diodes and transistors as well as other “active” and “passive” components may be mounted on the substrate to realize a specific application. Such a resulting circuit is usually referred to as a hybrid MIC. Integrated parts on the substrate only deal with passive functions such as filter and power divider, which process the microwave signal in their own ways without additional electric intervening.
MICs Today
Now there are many new techniques used for making more and more small, compact, and complex circuits. One well-known example is to design three-dimensional high-density MICs in which many layers of circuits are vertically stacked. It is hoped that in the future it will be possible to fabricate a complete and very cheap microwave electronics system on a single planar-layered chip.
