SOLID-STATE MICROWAVE DEVICES are becoming increasingly widespread in microwave
equipment with new developments almost daily. Most of the currently available solid-state devices are
two-terminal diodes with the capability to generate or amplify microwave energy. Many of the solid-state
devices, such as the TUNNEL DIODE and the BULK-EFFECT DIODE, apply the property of
NEGATIVE RESISTANCE to amplify microwave signals or generate microwave energy. A
characteristic curve illustrating the negative-resistance property of the tunnel diode is shown at the right.
The VARACTOR is a two-terminal diode that acts as a variable capacitance and is the active
element of PARAMETRIC AMPLIFIERS. The parametric amplifier is a low-noise microwave amplifier
that uses variable reactance to amplify microwave signals. The illustration shows an example of a
NONDEGENERATIVE PARAMETRIC AMPLIFIER.