A cavity resonator, usually used in reference
to electromagnetic resonators, is one in which the waves exist
in a hollow space inside the device. Acoustic cavity resonators,
in which sound is produced by air vibrating in a cavity with one
opening, are known as Helmholtz resonators. Cavity Resonators In
ordinary electronic equipment a resonant circuit consists of a
coil and a capacitor that are connected either in series or in
parallel. The resonant frequency of the circuit is increased by
reducing the capacitance, the inductance, or both. A point is
eventually reached where the inductance and the capacitance can
be reduced no further. This is the highest frequency at which a
conventional circuit can oscillate. The upper limit for a
conventional resonant circuit is between 2000 and 3000
megahertz. At these frequencies, the inductance may consist of a
coil of one-half turn, and the capacitance may simply be the
stray capacitance of the coil. Tuning a one-half turn coil is
very difficult and tuning stray capacitance is even more
difficult. In addition, such a circuit will handle only very
small amounts of current. NEETS, Module 10, Introduction to Wave
Propagation explained that a 1/4! section of transmission line
can act as a resonant circuit. The same is true of a 1/4!
section of waveguide. Since a waveguide is hollow, it can also
be considered as a RESONANT CAVITY. By definition, a resonant
cavity is any space completely enclosed by conducting walls that
can contain oscillating electromagnetic fields and possess
resonant properties.
