Oscillators – With outer casing or housing
Reexamination Certificate
2000-06-22
2001-12-04
Grimm, Siegfried H. (Department: 2817)
Oscillators
With outer casing or housing
C331S074000, C331S096000, C331S1170FE
Reexamination Certificate
active
06326856
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to YIG oscillators, and more specifically to a YIG oscillator having a low Vibration Sensitivity.
TECHNICAL BACKGROUND
YIG oscillators are a favored form of fundamental electromagnetic energy generators at frequencies in the spectrum of about 1 GHz to about 100 GHz. A YIG oscillator is an oscillator comprising an yttrium iron garnet crystal, which when placed in saturating magnetic field oscillates to generate electromagnetic energy at frequencies related to the strength of the magnetic field. More particularly, the output of a YIG oscillator is linearly dependent on the magnetic flux density in an air gap of a magnetic structure where the YIG crystal is positioned. The magnetic flux density, in turn, is inversely proportional to the length of the air gap, provided that the rest of the parameters of the magnetic circuit are constant.
For example, a 10 GHz YIG oscillator having an air gap length of 1 mm will exhibit a 1 kHz frequency deviation for an air gap length displacement of 1 Angstrom (1E-10 m).
A YIG oscillator structure comprises a metal enclosure enclosing and carrying the electric and magnetic circuitry. The enclosure serves as electrical as well as mechanical interface. Consequently, an external mechanical vibration will propagate into the magnetic structure and affect the length of the air gap, and thus the frequency of the oscillator. Hence, YIG oscillators are sensitive to mechanical vibration and the vibration frequency will appear as a frequency modulation of the YIG oscillator frequency. The modulation frequency is equal to the vibration frequency and the frequency deviation is proportional to the vibration level in terms of g's [m/s
2
] and the Vibration Sensitivity in terms of frequency deviation vs. vibration level [Hz/g]. Usually the vibration sensitivity is constant vs. vibration frequency superimposed by mechanical resonance peaks.
The YIG oscillator is a low phase-noise device tunable over wide frequency ranges. In applications where the YIG oscillator is used as a low phase-noise source in an environment where mechanical vibrations are present, low Vibration Sensitivity performance is crucial at least for a part of the vibration spectrum. Therefore, attempts have been made to reduce the Vibration Sensitivity of the YIG oscillator by providing different external resilient structures supporting the enclosure. The resilient structures are arranged so as to embody a mechanical filter between the external mechanic structure and the very YIG oscillator.
Hitherto this has typically been taken care of by the purchaser of the YIG oscillator, who has had to make an application specific solution. This, more or less inevitably, has resulted in comparatively large resilient structures. Consequently it is desirable to provide a complete YIG oscillator relieving the purchaser of his problem of resiliently supporting the YIG oscillator.
Additionally, the arrangement of an external resilient structure between the enclosure of the YIG oscillator and the external mechanical structure, gives rise to another problem. The problem relates to how to resiliently transmit the microwave output signal from the YIG oscillator to an external microwave circuit, which is supported by the external mechanic structure.
Another prior art solution to the problem of mechanical vibrations is disclosed in U.S. Pat. No. 5,652,550, where the YIG oscillator is enclosed and supported by an aerogel structure. A second outer enclosure is provided in order to hold the aerogel. Also this solution leads to an undesired size of the resulting device. Additionally, like the above described known resilient structures the solution according to U.S. Pat. No. 5,652,550 suffers from the lack of a resilient arrangement for transmitting the microwave output signal from the YIG oscillator to the external circuitry.
SUMMARY OF THE INVENTION
One object of this invention is to provide a YIG oscillator supported by a resilient structure reducing the Vibration Sensitivity yet being significantly smaller than the prior art arrangements and providing a solution to the problem of the transmission of the microwave output signal.
The object is achieved by a YIG oscillator according to the appended claims.
The YIG oscillator according to the invention, in a first aspect thereof, thus comprises a magnetic structure; an oscillator circuit board attached to said magnetic structure and carrying a YIG resonator positioned in an air gap of said magnetic structure; and an interface circuit board comprising terminals for external connections, said interface circuit board supporting said magnetic structure by means of a resilient means attached to said interface circuit board; and a flexible circuit connected at one end to the oscillator circuit board and connected at the other end to the interface circuit board.
In a second aspect of the invention, the YIG oscillator comprises an enclosure, a magnetic structure; an oscillator circuit board attached to said magnetic structure and carrying a YIG resonator positioned in an air gap of said magnetic structure; and an interface circuit board comprising terminals for external connections; said magnetic structure and said oscillator circuit board being enclosed by said enclosure, said interface circuit board supporting said enclosure, wherein said YIG oscillator further comprises a flexible circuit, extending through said enclosure and interconnecting said oscillator circuit board with said interface circuit board; and a resilient means comprising a resilient element enclosed by and attached to said enclosure and supporting said magnetic structure.
According to the present invention the YIG oscillator advantageously comprises an individual interface circuit board to which the external connections are made, a flexible circuit connecting the interface circuit board with the oscillator circuit board, and a resilient means supporting the magnetic structure and thus providing a suspension for the magnetic structure and thereby the YIG oscillator. In accordance with the invention the resilient support is provided between the interface circuit board and the magnetic structure, either as a direct link therebetween or indirectly, such as via an enclosure as defined in the second aspect of the invention. In either case the invention provides for mechanically connecting the interface circuit board in a rigid relation to an external mechanical structure, while achieving an arrangement for the magnetic structure, which is less sensitive to vibrations since it is resiliently rather than rigidly connected to the external mechanical structure.
The magnetic structure and the resilient means in conjunction forms a mechanical filter. The characteristics of such a filter can be chosen as required for a specific application.
In an advantageous embodiment, the resilient means comprises at least one resilient element consisting of a polymer, thereby being easily given appropriate characteristics in terms of elasticity modulus and absorption (hysteresis) defining the mechanical low pass filter resonant frequency (cut-off frequency).
In another advantageous embodiment of said polymer the Coefficient of Thermal Conductivity of the polymer of choice will relax thermal tensions and decrease thermal gradients in the magnet structure thus reducing or eliminating so called phase-pops, sudden mechanical relaxation phenomena due to thermal gradients and TCE (temperature coefficient) mismatch.
In another advantageous embodiment the polymer embeds at least a portion of said flexible circuit contributing to the characteristic impedance of a transmission line on the flexible circuit. The transmission line can be made a coplanar waveguide (CPW). In this case the width of the conductor spacing in the coplanar structure is made larger, less critical and easier to manufacture when the CPW transmission line is covered by the polymer, in particular if the polymer has a low microwave absorption and a relative dielectric constant higher than e
r
=1.
F
Christie Parker & Hale LLP
Grimm Siegfried H.
Sivers Ima AB
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