US 3358248 A
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Description (OCR text may contain errors)
Dec. 12, 1967 T. s. SAAD 3,358,248
MICROWAVE COUPLED LINE, DEVICE HAVING INSULATED COUPLED INNER CONDUCTORS WITHIN A COMMON OUTER CONDUCTOR Filed July 22, 1964 //VVEN7U/?.' THEODORE S. SAAD ATTORNEYS United States Patent 3,358,248 MICROWAVE COUPLED LINE DEVICE HAVING INSULATED COUPLED INNER CONDUCTORS WITHIN A COMMON OUTER CONDUCTGR Theodore S. Saad, Westwood, Mass., assignor to Sage Laboratories, Inc, East Natick, Mass., a corporation of Massachusetts Filed July 22, 1964, Ser. No. 334,455 3 Claims. (Cl. 333-) ABSTRACT OF THE DISCLOSURE A microwave coupled line device includes a pair of insulated inner conductors, each having inulation bonded thereto and separated by the thickness of the insulation therebetween for a distance corresponding substantially to a quarter wavelength at the center operating frequency, the thickness of the insulation being comparable to and typically less than the thickness of each conductor. A common outer conductor surrounds and is insulatedly separated by an annular bead from the inner conductors by a radial distance greater than the radial distance spanned by the assembly of the inner conductors and the insulation therebetween and many times greater than the thickness of the insulation therebetween. In a specific form, there are four terminal pairs outside the cavity enclosed by the outer conductor with each terminal pair having its inner terminal coupled to a respective end of the inner conductors and its outer terminal intercoupled with the other outer terminals by the common outer conductor.
The present invention relates in general to coupled line devices and more particularly concerns a novel hybrid of high electrical performance, small physical form and easy and inexpensive to fabricate in large and small quantities while maintaining a high degree of repeatability in electrical performance and facilitating the convenient location of external terminals.
One well known type of four terminal pair hybrid comprises a pair of conductors centered in an outer conductor with precision supports that maintain quarter-wavelength segments of the two conductors in precise fixed relationship. Each end of the two conductors is brought out to the inner terminal of a coaxial terminal pair so that when the terminal pairs are properly terminated, energy applied to one terminal pair divides equally and in phase quadrature to the nearest two terminal pairs while substantially no energy is delivered to the farthest terminal pair. While these hybrids perform satisfactorily, precise machining and assembling procedures are required to achieve satisfactory level of performance. Moreover, relatively large conductors have been employed with the result that the size of these hybrids is not infrequently greater than that desired. Moreover, relatively large sized conductors react with a surrounding outer conductor so as to alter the electrical properties and frequently require the introduction of special compensating elements within the cavity. And the geometry of the specific structure frequently limits the available locations for output terminals.
Accordingly, it is an important object of this invention to provide a high performance miniaturized coupled line device that is relatively easy and inexpensive to fabricate.
It is another object of the invention to provide a hybrid in accordance with the preceding object that facilitates convenient location of terminals for connection to external apparatus.
According to the invention, first and second inner conductors with insulation bonded thereto are arranged within an insulatedly separated outer conductor side-by-side for a quarter wavelength, separated by the insulation thickness therebetween. The ends of the inner conductors are coupled to a respective signal terminal of a terminal pair, the other terminal of each pair being a reference terminal intercoupled by the outer conductor with the other reference terminals.
Numerous other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawing in which:
FIG. 1 is a longitudinal sectional view, and
HG. 2 is a central diametrical sectional view of an embodiment of this invention comprising two insulated Wires contiguous for a quarter wavelength in a circular cylinder.
With reference now to the drawing and more particularly FIG. 1 thereof, there is shown a longitudinal sectional view of the embodiment of the invention in which the four terminal pairs A, B, C and D of the hybrid are diagrammatically represented. When these terminal pairs are terminated in their respective characteristic impedances, energy applied to one terminal pair divides equally between the nearest two terminal pairs While negligible energy is delivered to the farthest terminal pair. Thus, energy applied to terminal pair A divides equally between terminal pairs B and C in phase quadrature while virtually no energy is delivered to terminal pair D. Conductor 11 intercouples signal terminal 12 of terminal pair A and signal terminal 13 of terminal pair C. Conductor 13 intercouples signal terminal 14 of terminal pair B and signal terminal 15 of terminal pair D. Thin layers of insulation 16 and 17 are bonded to conductors 11 and 13, respectively. These insulating portions are in contact along the line 21 for a quarter wavelength at center frequency so that the conductors 11 and 13 are separated by the insulation thicknesses. An annular insulating Wafer 22 supports the insulated conductors 11 and 13 symmetrically within the conducting cylindrical casing 23 defining the outer conductor. Casing 23 also intercoupled the interference terminals 24, 25, 26 and 27 of terminal pairs A, B, C and D, respectively.
FIG. 2 is a diametrical sectional view through the embodiment of FIG. 1 illustrating how the insulating wafer 22 keeps conductors 11 and 13 centered within the cavity defined by the conductive casing 23.
In a specific embodiment of the invention No. 20 wire with a Teflon coating .004 inch thick was placed in a cylindrical cavity 1.460 inches long, .234 inch in diameter, and the ends of each wire brought out to type TNC coaxial terminals to provide a coupling of 3 db 0.4 db and an isolation of 29 db minimum over a frequency range of l to 2 gigacycles. The annular supporting head was made of Teflon and had an inner diameter of .067 inch.
An important feature of the invention is the adaptability of the structure to accommodating terminal pairs at different locations. FIG. 1 shows terminal pairs being brought out at diametrically opposed points in the cylindrical outer conductor. But the invention operates equally well with the terminal pairs in space quadrature. Alternatively, terminal pairs could be brought out through the end caps of the cavity. Also, the wires can be internally twisted up to without affecting performance.
The invention is illustrated with separate circular wires in a circular cavity. The cavity could be rectangular or of other shape. The wires could be rectangular and might be bonded to a common separating insulating strip.
Other modifications and uses of and departures from the specific embodiments described herein may be practiced by those skilled in the art without departing from the inventive concepts. Consequently, the invention is to be construed as limited solely by the spirit and scope of the appended claims.
What is claimed is:
1. High frequency apparatus operative over a frequency range embracing a predetermined center frequency comprising,
first and second insulated inner conductors, each having insulation bonded thereto and separated by the thickness of said insulation therebetween for a distance corresponding substantially to a quarter wavelength at said center frequency and separated by a greater distance. elsewhere,
the thicknes of said separating insulation being less than the thickness of each conductor,
means including an outer conductor defining a cavity surrounding and insulateally separated from said inner conductors and maintained in fixed relationship, with the radial distance between said outer conductor and said inner conductors being greater than the combined thickness of said inner conductors with said separating insulation and being many times greater than the distance between said inner conductors, established by said separating insulation,
means defining four terminal pairs outside said cavity,
each terminal pair having a signal terminal coupled to a respective end of said conductors and a reference terminal intercoupled with the other reference terminals by said outer conductor.
2. High frequency apparatus in accordance with claim 1 and further comprising,
means for supporting said first and second inner conductors symmetrical about the axis of said outer conductor for at least said quarter wavelength, said inner conductors being much closer to said axis than to said outer conductor along said quarter wavelength. 3. High frequency apparatus in accordance with claim 2 wherein said inner conductors and said outer conductor are of substantially circular cross section and said means for maintaining comprises an insulating annular bead of inner diameter corresponding substantially to the radial distance spanned by said first and second'insulated inner conductors, of outer diameter corresponding substantially to the inner diameter of said outer conductor and of length corresponding substantially to said common length and snugly surrounds said first and second insulated inner conductors.
References Cited UNITED STATES PATENTS 2,679,632 5/1954 Bellows 333-10 3,105,207 9/1963 Ca pewell et al. 333 10 3,237,130 2/1966 COhn 333 10 FOREIGN PATENTS 1,197,584 12/1959 France.
1,146,559 4/1963 Germany.
HERMAN KARL SAALBACH, Primary Examiner.
RONALD D. COHN, SAXFIELD CHATMON, 1a., Assistant Examiners.