Wave transmission lines and networks – Resonators – With tuning
Reexamination Certificate
1999-02-17
2001-01-30
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Resonators
With tuning
C333S204000, C333S205000
Reexamination Certificate
active
06181225
ABSTRACT:
BACKGROUND OF THE INVENTION
Many radio frequency oscillators today depend on the use of high dielectric coaxial resonators to establish the frequency of oscillation. These resonators are generally available off the shelf or can be customized to a particular frequency. The resonators are small, but relatively expensive, e.g. more than 20 times, in comparison with common surface mount parts such as resistors and capacitors. However, where high performance and stability are needed there are few alternatives.
In the case of a variable frequency oscillator, the frequency of the resonator needs to be pulled above or below the natural frequency of oscillation. This is normally done by shunting the resonator with a varactor diode, which changes in capacitance depending on the DC voltage at its terminals. Adding this component unfortunately lowers the performance, as the varactor is subject to more loss than the resonator. As the tuning range is made wider, the loading by the varactor becomes more significant, reducing the benefit of the original resonator in terms of its high performance and good phase noise performance. In short, the use of an expensive dielectric resonator becomes difficult to justify in a circuit where the quality factor, Q, is impaired by other components connected to it.
In these cases where the resonator Q of the oscillator becomes heavily dominated by the varactor or other tuning components, the use of a high Q resonator has little effect on the overall loaded Q.
In an attempt to overcome some of these problems, various alternative resonators have been proposed. For instance, U.S. Pat. No. 5,420,554 discloses a method and apparatus for adjusting a resonant frequency of a transmission line resonator assembly. The '554 patent uses laser tuning to center the resonant frequency. The tuning is accomplished by deflecting a metallized plastic assembly that is located directly atop a resonator electrode. However, the '554 patent does not make clear how deflection, and thus tuning, is made permanent. Further, the '554 device is fabricated on a printed circuit board rather than using thick film technology, which would allow for surface mounting in numerous applications.
In view of the above, there is a need for a low cost resonator that can offer performance that is nearly equivalent to the performance offered by a high Q coaxial dielectric design.
SUMMARY OF THE INVENTION
The problems addressed above are in large part solved by a resonator of the present invention. The resonator structure is made of low cost alumina offering performance in a variable frequency oscillator application that is nearly equivalent to that of a high Q dielectric design. The resonator structure is tunable over a wide range with substantially no effect on oscillator phase noise or signal amplitude. The resonator utilizes a unique geometric structure which employs a transmission line preferably on alumina, conducting via holes (called castellations) and a topside ground pattern formed with a thick film of silver and/or palladium. A plurality of resonators may be formed by a step and repeat pattern then snapped apart for low cost, high volume manufacture. The resonator may be tuned in both a vertical and horizontal direction by removing topside metal from the resonator, to raise and lower the frequency, until the desired frequency is met. Low phase noise is preferably achieved by using a slab resonator that is short in length in combination with a fairly large loading capacitor to optimally match the impedance of the oscillator active device (transistor).
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Itron, Inc.
Lee Benny
Nguyen Patricia T.
Patterson Thuente Skaar & Christensen P.A.
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