Dielectric resonators are made of
low loss, temperature stable, high
permittivity and high Q ceramic material
in a regular geometric form.
Common examples of the materials
are BaTi4O9 and ZrSnTiO4.6 The material
resonates in various modes determined
by its dimensions and
shielding conditions. TE01δ mode is
used for the optimum temperature
stability and Q. The practical frequency
range for these resonators lies
between 2 and 40
GHz while the Q
factor typically reduces
linearly with
increasing frequency.
A Q of 10,000 at
4 GHz is representative
of commonly
used materials. Because
of its small
size, low price and excellent integrability
in MICs, DRs are very commonly
used in active and passive microwave
components up to mm-wave
frequencies. Development of temperature
stable dielectric resonators
dates back to the late 1970s, soon after
the introduction of three-terminal
devices in the main stream of microwaves.
The marriage between
these two elements has produced a
wide variety of much needed microwave
sources with excellent performance
in terms of phase noise and
temperature stability with desired
compactness and cost. Dielectric resonator
oscillators (DRO) are most
commonly used for fixed tuned or
narrowband tunable configurations to
phase lock or frequency modulate for
numerous applications. A well-known
high volume application for these oscillators
in recent history has been in
the Ku-band DBS applications. Recently,
when there was a large telecom
demand ahead of availability of
fully integrated ICs, these sources
were employed in volume for the 10
Gb/s high speed optical communications
market. With the increased
bandwidth requirements of microwave
communication systems today,
complex modulation schemes using
64QAM or higher are commonly
used. This order of complexity requires
very low close-in phase noise
in order to keep the bit error rate
(BER) in the digital communication
systems under check. Electronically
tunable phase-locked DROs are today
the backbone of the majority of
microwave communication systems
requiring very high performance in a
small size and reasonable cost. DROs
are now commercially available with
better than ±1 ppm/°C and/or with a
phase noise of better than –120
dBc/Hz at 100 kHz at X-band