Oscillators – Automatic frequency stabilization using a phase or frequency... – With reference oscillator or source
Reexamination Certificate
2002-06-06
2003-12-30
Tokar, Michael (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
With reference oscillator or source
C333S116000, C333S134000, C333S206000
Reexamination Certificate
active
06670856
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to coupled transmission lines for electromagnetic waves and, in particular to coupled transmission lines that are tunable and/or tolerant of manufacturing variations.
BACKGROUND OF THE INVENTION
Coupled transmission lines are used to make a variety of high frequency electromagnetic wave devices (RF and microwave) including frequency selective filters, signal splitters, and combiners, and delay lines. A typical coupled transmission line comprises a pair of elongated conductive strips separated by an intervening layer of dielectric material.
FIG. 1
, which is prior art, illustrates a transverse cross section of a common form of a coupled transmission line
10
wherein a pair of conductive strips
11
A and
11
B are separated by a gap of spacing G on a dielectric substrate
12
having a dielectric constant E. This form of the transmission line where the strips
11
A and
11
B overlap across at least a portion of the gap is referred to as a broadside coupled line.
FIG. 2
, also conventional, illustrates an alternative coupled transmission line
20
wherein the conductive strips
11
A and
11
B are partially offset across the gap G. The amount overlap between
11
A and
11
B is designated L. This type of transmission line is called an off-set broadside coupled transmission line.
In each form, the degree of coupling C between the two strips
11
A and
11
B is a key parameter in the function of the transmission lines and devices using them. C is inversely proportional to the gap spacing G, and jointly proportional to the square root of the dielectric constant E and the overlap L.
In the fabrication of coupled transmission lines, it is difficult to control with desired precision the degree of coupling C. Common methods for manufacturing broadside coupled lines include thin film and thick film circuit technology, laminated printed circuit board technology, low temperature cofired ceramic (LTCC) technology and high temperature cofired ceramic (HTCC) technology. In these technologies, the degree of coupling is affected by manufacturing variations in dielectric constant, conductor width, conductor-to-conductor misalignment and dielectric thickness. Accordingly, there is a need for a broadside coupled transmission line structure that is tolerant of normal manufacturing variation and/or can be readily tuned.
SUMMARY OF THE INVENTION
In accordance with the invention, coupled transmission lines are fabricated in forms that are tolerant of manufacturing variation or can be readily tuned. In accordance with a first embodiment, the transmission line is formed with alternating overlapping edges for enhanced manufacturing tolerance. In a second embodiment, the line is provided one or more overlapping adjustment regions to permit tuning. A third embodiment has both alternating overlapping edges and one or more tuning regions.
REFERENCES:
patent: 3769617 (1973-10-01), West
patent: 4891612 (1990-01-01), Gleason et al.
patent: 5767753 (1998-06-01), Ruelke
patent: 5825263 (1998-10-01), Falt
Lamina Ceramics
Lowenstein & Sandler PC
Mai Lam T.
Tokar Michael
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