| Microwaves are generally considered to be a specific part of the wide radio
frequency spectrum. The band from 300 MHz to 30 GHz is typically considered
to be “microwaves,” for example by the Institute of Electrical end
Electronics Engineers (IEEE), although many of us prefer to set the lower
limit somewhat higher—perhaps at 1 or even 3 GHz. Above 30 GHz, the
term “millimeter waves” is used. High school physics suggests that we are
talking about wavelengths ranging from about 30 cm down to 10 mm.
The tremendous growth in mobile communications during the past
10 years has particularly caused a respective increase in the need for microwave
and millimeter wave components, devices, and systems. Besides this
well-known application area, microwave frequencies are widely in use, for
example, in satellite networks, radar and navigation systems, remote sensing,
and industrial measurements. Two common features are seen in the latest
developments. First, the number of individual units (components or devices)
is increasing exponentially, so their production costs should be minimal. At
the same time, many of the technical requirements, especially those related to
microwave performance, are becoming more and more strict. Higher power
levels and lower noise figures should be available, and systems should withstand
considerable amounts of mutual interference without noticeable degradation
in service quality. In addition to this, weight and size constraints are
becoming severe. |
