Wave transmission lines and networks – Resonators – With tuning
Reexamination Certificate
2000-09-27
2003-03-25
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Resonators
With tuning
C333S219100, C331S1070DP
Reexamination Certificate
active
06538536
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to dielectric resonator oscillators (DROs) and methods of their assembly and, more specifically, to DROs having dielectric resonators that are attached to the DRO housing in such a manner that the DRO operation is not substantially affected by mechanical vibration.
BACKGROUND OF THE INVENTION
Dielectric resonator oscillators (DROs) are commonly used in high-precision RF and microwave systems to generate high-frequency signals of extremely good spectral purity. For example, DROs have been used in radars, transponders, and communication systems, among other systems, to generate microwave signals with extremely low phase noise and good temperature stability. Generally, in these systems, the DRO is used to generate a frequency that is locked to a reference oscillator within a phase-locked loop circuit.
FIG. 1
illustrates a cross-sectional, side view of a DRO
100
in accordance with the prior art. DRO
100
includes dielectric resonator
102
, housing
104
, housing lid
106
, dielectric pedestal
108
, printed wiring board substrate
110
, microstrips
112
, tuning screw
114
, and wall mounted electric tuner
116
. Dielectric resonator
102
is used as a frequency determining circuit element. Dielectric resonator
102
is made of a rigid ceramic material, having a very high dielectric value.
Housing
104
and housing lid
106
are made of a metallic material. Housing
104
is a structure having a bottom
118
and sides
120
. When assembled, housing
104
and housing lid
106
create a resonant cavity
122
.
During operation, electromagnetic energy is coupled into cavity
122
and resonator
102
at the resonant frequency via microstrips
112
located on substrate
110
, which is located on the housing bottom
114
. Likewise, energy at the resonant frequency can be extracted from cavity
122
via microstrips
112
.
The relative position of dielectric resonator
102
within resonant cavity
122
affects the frequency characteristics and the Q of the DRO. The position of resonator
102
is defined by the height of pedestal
108
and the horizontal placement of dielectric resonator
102
on pedestal
108
. Pedestal
108
is made of a solid, low-loss, low-dielectric constant material.
During a typical assembly process, substrate
110
and microstrips
112
are first attached to the housing bottom
118
. Then, pedestal
108
is attached to the substrate
110
using an epoxy material, which requires a high-temperature, heat-curing process. In some prior art processes, pedestal
108
is attached directly to housing bottom
118
using an epoxy, after substrate
110
is attached to the housing bottom
118
.
After pedestal
108
is attached to housing
104
(or substrate
110
) and heat-cured, resonator
102
is placed on pedestal
108
, and an iterative position adjustment process is performed. This is necessary because the oscillator circuit will oscillate only over a fairly narrow range of resonator positions on pedestal
108
. The position adjustment process involves assembling housing lid
106
to housing
104
, and testing the frequency. The lid
106
is then removed, and if the frequency is not accurate enough, the resonator position on pedestal
108
is adjusted along the horizontal plane. This testing and position adjustment process is repeated until the desired performance is attained. Resonator
102
is then carefully removed, applied with epoxy, and re-positioned on pedestal
108
. The assembly is again heat-cured and tested for performance. Coarse frequency adjustments are then performed using tuning screw
114
, as is described below.
As the above description indicates, the entire DRO
100
is heated at least twice during assembly. This double-heating process decreases the yield of acceptable DROs, because the circuitry within DRO
100
is cumulatively affected by the heating processes. In addition, it can be difficult and time consuming to accurately adjust the position of resonator
102
on pedestal
108
, and to accurately re-position resonator
102
on pedestal
108
after application of the epoxy to resonator
102
.
The dimensions of resonator
102
define the resonant frequency of resonator
102
. This frequency can be varied by a small percentage using tuning screw
114
and/or electric tuner
116
, both of which capacitively load resonator
102
. Tuning screw
114
is used to coarsely tune resonator
102
(e.g., within about one percent of the resonant frequency), and wall mounted electric tuner
116
is used to finely tune resonator
102
(e.g., by tenths of a percent).
The frequency characteristics of resonator
102
are adversely affected if tuning screw
114
makes contact with resonator
102
. Accordingly, an air gap
128
must exist between the bottom of tuning screw
114
and the top of resonator
102
in prior art systems.
In this prior art configuration, resonator
102
is held in position only by pedestal
108
. Accordingly, when DRO
100
is subject to mechanical vibration, pedestal
108
and resonator
102
can sway. When the vibration is sufficient, the movement of resonator
102
within cavity
122
can be enough to adversely affect the frequency characteristics of the DRO
100
. In some cases, the movement can be severe enough to cause frequency fluctuations in the megahertz range, which can cause a DRO that is used in conjunction with a phase-locked loop circuit to lose lock with the reference oscillator. If the vibration is more than momentary, the circuit will continue to lose lock. Because prior art DROs are so sensitive to resonator position, prior art DROs are unsuitable, in many cases, for use in mobile apparatus, or other apparatus that may experience vibration conditions.
What are needed are DROs and methods of their assembly that simplify the process of positioning the dielectric resonator within the DRO cavity. In addition, what are needed are methods of assembling a DRO that eliminate the need to subject the DRO circuitry to multiple heating processes. Finally, what are needed are DROs that have resonators mounted in a manner that the DRO operation is not substantially affected by mechanical vibration.
REFERENCES:
patent: 5027090 (1991-06-01), Gueble et al.
patent: 5233319 (1993-08-01), Mizan et al.
patent: 5323129 (1994-06-01), Harris
patent: 5608363 (1997-03-01), Cameron et al.
patent: 5612655 (1997-03-01), Stronks et al.
patent: 5714920 (1998-02-01), Ivanov et al.
patent: 6002311 (1999-12-01), Wey et al.
Goodman Charles J.
Seely Warren L.
Ingrassia Fisher & Lorenz
Jones Stephen E.
Motorola Inc.
Pascal Robert
LandOfFree
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