Wave transmission lines and networks – Resonators – Dielectric type
Utility Patent
1998-12-18
2001-01-02
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Resonators
Dielectric type
C333S222000, C331S096000, C331S1070DP
Utility Patent
active
06169467
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to radio frequency (RF) communications and to resonators used in RF communication equipment. More specifically, the present invention relates to dielectric resonators.
BACKGROUND OF THE INVENTION
Resonators are useful in RF communication equipment in connection with filters, low noise oscillators, and other circuits. When a resonator with a resonant frequency in the UHF-band (i.e.<1.0 GHz) is needed, surface acoustic wave (SAW) technology provides a beneficial solution. In the UHF-band, SAW resonators are relatively small and exhibit a suitably high quality factor (Q). Unfortunately, as frequencies approach the top of the UHF-band, the resulting quality factor for SAW resonators deteriorates, and SAW resonators are usually impractical for resonant frequencies above the UHF-band.
Dielectric resonators may be used to achieve resonant frequencies at the top of the UHF-band and above. Dielectric resonators are smaller than air cavity resonators having equivalent resonant frequencies because wavelength in the dielectric resonator is divided by the square root of the resonator's dielectric constant. In addition, reactive power is not stored strictly inside the dielectric resonator, and fractional modes of resonance are exhibited. As resonant frequencies become higher, the size of the dielectric resonator becomes smaller.
Unfortunately, in the UHF-band, L-band (i.e. 1.0-2.0 GHz) and S-band (i.e. 2.0-4.0 GHz), conventional dielectric resonators are still often undesirably large or exhibit an undesirably low quality factor (Q). This frequency range is used by numerous portable RF communication devices, such as cellular and other telephones. Portable RF communication devices differ from other types of RF communication devices because of a heightened need to consume as little power as possible and to be as small and lightweight as possible. The minimal power consumption need results from portable devices being energized by batteries, and the size and weight are important because such devices are often designed to be carried on the persons of the users of the devices. Unfortunately, a resonator having a low quality factor can cause excessive power consumption, while a resonator that is too large can unnecessarily increase the size and weight of a portable device.
As an example, a conventional cylindrical TE
01&dgr;
mode dielectric resonator, where “&dgr;” indicates a fraction of periodicity in the “Z” direction, having a dielectric constant of around 80 and a lowest resonant frequency of around 1.8 GHz has a diameter of around 2.0 cm and an axial length of around 0.8 cm. The use of a component of such large size and corresponding large weight is highly undesirable in a portable RF communication device. Moreover, even with a conductive cavity surrounding the resonator that further increases size, such a resonator exhibits an undesirably low Q. TM
01&dgr;
mode and other conventional TE and TM mode dielectric resonators tend to be even larger and/or exhibit lower Q.
A conventional practice in connection with dielectric resonators, such as the above-discussed TE
01&dgr;
mode and TM
01&dgr;
dielectric resonators, is to form a small, axially aligned hole through a cylindrical dielectric resonator. The hole serves two functions. It further separates the lowest resonant frequency from the next lowest resonant mode, and it allows the resonator to be mounted using a dielectric screw having a low dielectric constant. The hole has as small a diameter as possible to accommodate a screw large enough to securely mount a given resonator. The use of a hole no larger than necessary to meet mechanical mounting requirements does not significantly influence the performance of the resonator in the lowest resonant frequency mode. Conventionally, a hole less than 0.21 times the resonator's diameter achieves this purpose for resonators having a lowest resonant frequency in the 0.3-6.0 GHz range. However, as the hole size increases relative to the diameter of the resonator, a given resonator risks a deteriorating quality factor and larger overall size.
Another conventional practice in connection with dielectric resonators is to place the resonators within a conductive housing. Conductive walls of the housing influence the performance of the resonator, typically by lowering the resonant frequency and raising the Q as the conductive walls are placed farther from the dielectric resonator. Unfortunately, this practice only makes the resonators that much larger for a given lowest resonant frequency. A conventional TE
01&dgr;
mode resonator that employs a conductive housing has a minimum radius of
0.8&lgr;/{square root over (&egr;
r
)}, where &egr;
r
is the dielectric constant of the dielectric resonator. A conventional TM
01&dgr;
mode resonator that employs a conductive housing has a minimum radius of
0.75&lgr;/{square root over (&egr;
r
)}. Moreover the formation of a small, axially aligned hole through a cylindrical dielectric resonator configured for the TM
01&dgr;
mode forces the resulting structure to be even larger for the same lowest resonant frequency.
SUMMARY OF THE INVENTION
Accordingly, it is an advantage of the present invention that an improved dielectric resonator is provided.
Another advantage of the present invention is that a TE
0&ggr;&dgr;
mode dielectric resonator is provided which achieves suitably high Q in a smaller space than is required by conventional TE
01&dgr;
mode or TM
01&dgr;
mode dielectric resonators.
Another advantage of the present invention is that a relatively large hole in a cylindrical dielectric resonator, preferably greater than 0.21 times the diameter of the resonator, and a conductive wall cause a fractional resonant mode in the radial direction.
Another advantage of the present invention is that a composite dielectric resonator is provided which, given a desired oscillation mode, increases Q while reducing resonator diameter.
The above and other advantages of the present invention are carried out in one form by a resonator configured to resonate in the TE
0&ggr;&dgr;
mode at a lowest resonant frequency having a wavelength &lgr; in empty space. The resonator includes a dielectric resonator disk configured to exhibit an effective dielectric constant &egr;
re
. The disk has first and second opposing ends along an axis of the disk and a closed curve wall surrounding the disk axis and extending between the first and second ends. The disk has a hole penetrating therein from the first disk end and extending toward the second disk end, wherein at least one of the first and second ends serves as a boundary between the disk and a dielectric material having a dielectric constant less than 0.5&egr;
re
. A conductive wall is juxtaposed with the curved wall of the disk and positioned less than
0.75&lgr;/{square root over (&egr;
re
)} from the axis.
The above and other advantages of the present invention are carried out in another form by a resonator having a first dielectric resonator disk and a second dielectric resonator disk. The first dielectric resonator disk has a hole therein and is formed from a first material which exhibits a first dielectric constant and a first quality factor (Q). The second dielectric resonator disk is located inside the hole of the first dielectric resonator disk. The second disk is formed from a second material which exhibits a second dielectric constant and a second quality factor (Q).
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Cheng-Chyi You, Chen-Liang Huang and Chung-Chuang Wei, “Single-Block Ceramic Microwave Bandpass Filters”, The Mi
Gresham Lowell W.
Meschkow Jordan
Meschkow & Gresham, P.L.C
Pascal Robert
Summons Barbara
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