US3739305A

US3739305A - Coaxial attenuator assembly having cross-shaped attenuator element

Info

Publication number: US3739305A
Application number: US00190768A
Authority: US
Inventors: H Engelmann
Original assignee: Engelmann Microwave Co
Current assignee: Engelmann Microwave Co
Priority date: 1971-10-20
Filing date: 1971-10-20
Publication date: 1973-06-12
Anticipated expiration: 1990-06-12

Abstract

A low value attenuator for high frequency coaxial applications. The attenuator incorporates a cross-bar attenuator element which includes a pair of resistive bar elements which extend in perpendicular fashion with respect to one another and are electrically connected at their mutual intersection. A pair of spacers support the attenuator element in such fashion in the attenuator assembly that the first bar is coaxial with the axial inner conductor of the assembly and the ends of the second bar electrically contact the outer coaxial conductor. The outer ends of both bars are provided with conductive portions to enable the electrical connections, the connection to the coaxially aligned bar being effected by a pair of coaxial resilient female connectors.

Description

United States Patent Engelmann 1 June 12, 1973' COAXIAL ATTENUATOR ASSEMBLY HAVING CROSS-SHAPED ATTENUATOR ELEMENT Inventor: Herbert F. Engelmann, Kinnelon,

Assignee: Engelmann Microwave Company,

Montville, NJ.

Filed: Oct. 20, 1971 Appl. No.: 190,768

US. Cl 333/81 A, 338/216, 338/333 Int. Cl. 1101p 1/22 Field of Search 338/216; 323/74,

323/81, 94 R; 333/81 R, 81 A References Cited UNITED STATES PATENTS 5/1972 Barth 333/81 A 7/1961 Weinschel 333/81 A 61 055 54? A TTE/VUATOP 'LEME/VT Primary Examiner-Paul L. Gensler Attorney-Popper, Bain, Bobis & Gilfillan [57] ABSTRACT A low value attenuator for high frequency coaxial applications. The attenuator incorporates a cross-bar attenuator element which includes a pair of resistive bar,

elements which extend in perpendicular fashion with respect to one another and are electrically connected at their mutual intersection. A pair of spacers support the attenuator element in such fashion in the attenuator assembly that the first bar is coaxial with the axial inner conductor of the assembly and the ends of the second bar electrically contact the outer coaxial conductor. The outer ends of both bars are provided with conductive portions to enable the electrical connections, the connection to the coaxially aligned bar being effected by a pair of coaxial resilient female connectors.

4 Claims, 8 Drawing Figures 1 COAXIAL ATTENUATOR ASSEMBLY HAVING CROSS-SHAPED ATTENUATOR ELEMENT BACKGROUND OF INVENTION This invention relates generally to attenuators for coaxial conductor systems, and more specifically relates to such an attenuator as is useful in achieving low and relatively constant attenuation over a range of high frequency applications.

In order to achieve broad band performance in a Tee configured attenuator, it is desirable to utilize series and shunt elements which remain purely resistive and of constant value throughout the frequency band. The performance of conventional Tee pad attenuators,

- however, departs markedly from such idealized criteria. Specifically, conventional Tee pad attenuators ordinarily consist of a central resistor assembly in series with a central coaxial conductor, and one or more disctype shunt resistors extending between the central resistor and the outer conductor of the coaxial system. For low attenuation values, the shunt element must be relatively high in resistive value. The disc construction enabling this high resistance thus includes a high resistance film overlying a ceramic or similar dielectric substrate. With such a construction, however, it is found that the resulting R-C combination introduces a capacitive reactance component which results in a severe increase in attenuation with increasing frequency, a result which can be regarded as principally due to the effect of the ceramic disc.

As is also known by those skilled in this art, the effects of impedance change with frequency are most difficult to compensate. Thus, in those instances where conventional Tee pad constructions are utilized for low value attenuation in high frequency applications, it becomes difficult to match the input impedance. This factor limits the utility of such attenuators in that, among other things, such devices are often connected between two circuits of differing impedance and serve as a matching network as well as an attenuator.

In an effort to overcome some of the aforementioned problems, coaxial attenuators have been proposed --such as that disclosed in U. S. Pat. No. 2,994,049 to B. O. Weinschelwhich substitute for the aforementioned discs, shunting elements in the form of radially directed spoke-like members. The advantage of such construction is that the proportion of substrate to resistive film is decreased whereby capacitive effects are reduced. Moreover, the improvement in radial symmetry tends to decrease the likelihood of discontinuities which may produce standing waves and other electrical disturbances. Unfortunately, the Weinschel type of construction is relatively difficult and costly to manufacture in that it consists of a relatively complex shape featuring an apertured hub interjoinedto a coaxial cylinder by the said spokes. Shunting connections to'this assembly are partially effected by conductively coating the hub and cylinder, and the connection and axialsupport for the hub further requires a pair of spring clips screwed together through the hub to provide a pressure contact with the flat ends thereof.

In accordance with the foregoing it may be regarded as an object of the present invention, to provide alow value attenuator for high frequency coaxial applications which provides relatively constant attenuation over a wide frequency range.

It is a further object of the invention, to provide a coaxial attenuator for high frequency applications which is constructed to introduce relatively low capacitive reactance as a function of increasing frequencies in the system in which the unit is employed.

It is an additional object of the present invention to provide a coaxial attenuator for high frequency applications, which employs radially directed elements to reduce undesirable capacitive effects, but which nevertheless is of very simple, economical, and sturdy construction.

SUMMARY OF INVENTION The foregoing objects, and-others as will become apparent in the course of the ensuing specification, are achieved in an attenuator according to the present invention incorporating an attenuator element which includes a pair of resistive bar elements which symmetrically intersect and extend perpendicularly with respect to one another. The said bars may comprise one or more pieces and are electrically connected at their mutual intersection. A pair of spacers sandwich the attenuator element and support the element in such fashion in the attenuator assembly that the first bar is coaxial with the axial inner conductive elements of the assembly and the ends of the second bar electrically contact the coaxial outer conductor. The outer ends of both bars are provided with conductive termination coverings to enable the electrical connections, the connection to the coaxially aligned bar beingsimply effected via a paid of conventional female resilient connectors.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the present invention may be had from the following detailed description, particularly when read in the light of the accompanying drawings, wherein:

FIG. 1 is a longitudinal cross-sectional view through an attenuator such in accordance with the present invention;

FIGS. 2A, 2B and 2C comprise a view similar to FIG. 1 but showing the three basic elements of the attenuator according to the invention as being axially separated;

FIGS. 3A and 3B are, respectively, plan and elevational views of the attenuator element support and spacer utilized in the structure according to the invention; and

FIGS. 4A and 4B are, respectively, plan and end view of the cross-bar attenuator element according to the present invention.

DETAILED DESCRIPTION a first threaded portion 17 on one end for connection to a coaxial conductor fitting (notshown) and a second threaded portion 18 (FIG. 28) adjacent the other end for threadedly securing connector 11 within attenuator element mounting section 14. Disposed within cylindrical member 16 is a longitudinally axially extending cylindrical conductor 20 having a plurality of longitudinally extending slits disposed adjacent each end to define resilient sections within which to receive the male connector portions of axial conductors as is described below in detail. Conductor 20 is mounted within and electrically isolated from cylindrical member 16 by a cylindrical insulator sleeve 21 which may be any of many suitable dielectric materials known to those skilled in this art.

Female connector 12 (FIG. 2A) comprises a first cylindrical section 23 and a second cylindrical section 24 which are slidably interlocked by a tongue and groove joint 26. The tongue and groove joint 26 permits relative rotation of first and second

cylindrical sections

23, 24 but precludes relative axial movement therebetween.

The inner surface of first cylindrical section 23 is provided adjacent one end with a threaded portion 26 (FIG. 2A) for threadedly engaging one end of attenuator mounting section 14 as is discussed below in detail. Similarly, the inner surface of second cylindrical section 24 is provided with a threaded portion 28 for connection to a coaxial conductor fitting (not shown). Rigidly disposed within first cylinder section 23 is a support washer 30 on which is mounted a conventional coaxial conductor including an axially disposed longitudinally extending conductor having a male end 32 and a female end 34. Also mounted on support washer 30 is a cylindrical conductor 36 which is in electrical contact with washer 30 and spaced from the axial conductor by insulator sleeve 38.

Attenuator element mounting section 14 (FIG. 2C) includes a cylindrical element 40 having a relieved portion of its outer surface in which are formed threads 42. The inner surface of cylindrical element 40 is relieved adjacent one end to define an annular channel 43 in which are formed internal threads 44. Disposed within the inner surface of element 40 are a pair of positioning and

spacer washers

46, 47 the outside diameters of which are substantially equal to the inside diameters of element 40. As is discussed below in detail,

spacer washers

46, 47 are provided with diametrically extending grooves 48 (FIGS. 3A and 3B) for positioning an attenuator element 50 therein.

In accordance with the present invention, the attenuator element is seen to comprise a cross-bar resistor member which may be best seen in FIGS. 4A and 4B. As is evident from the Figures, attenuator element 50 comprises a first longitudinally axially extending resistor bar 52 and a transversely extending second resistor bar 53. From a geometric point of view, bars 52 and 53 are shown as a pair of linearly extending elements intersecting at the respective mid-point thereof. In practice, however, although the member 50 can be constructed as a monolithic unit, it may be simpler for one of the bars to be of unit construction with the alternate bar comprising two or more sections adjoining the first bar at the said mid-point. Thus, in FIG. 4A, it can be seen that longitudinally extending bar52 is defined by two sections 52a and 52b, which sections adjoin the midpoint of transversely extending second bar 53.

Bars

52 and 53 consist of a cylindrical dielectric substrate, e.g., ceramic,glass, quartz or similar refractory insulation material, upon which is deposited a thin resistive film 60. As is recognized by those skilled in these arts, film 60 may be of a noble metal or noble metal alloy deposited on the substrate by the firing of a suitable salt of one of said metals, or alternatively the film may comprise a vacuum deposited layer of chromium, nickel, or similar known resistive film compositions. At the end of each bar there are formed a plurality of terminations or conductive end portions 62 which may be highly conductive materials deposited such as by vacuum depositing, plating or like procedures. Similarly, electrical connection between the

bars

52 and 53 is achieved by the provision of a conductive film at the intersection of the two bar elements or, as shown in FIG. 4A, by providing a conductive sleeve 67 of material which engages the inner end of bar sections 52a and 52b and also the central portion of bar 53. This electrical connection can be augmented by the provision of a deposit of conductive material such as material 68 shown in FIG. 4A.

As may be seen in FIG. 4A, longitudinal bar 52 is somewhat longer than transversely extending bar 53 and adapted for connection with the axial conductor of male connector section 11 and female connector section 12. In assembling attenuator element mounting section 14, attenuator element 50 is positioned within cylindrical element 40 such that bar 52 extends coaxially of cylindrical element 40 and bar 53 extends transversely diametrically of cylindrical element 40. Member 50 is maintained in position with cylindrical element 40 by positioning

washers

46 and 47 which, may be best seen in FIGS. 3A and 3B. Specifically, positioning

members

46 and 47 are generally circular having a central longitudinally axially extending bore 70 and a axially longitudinally extending counterbore 73. That portion of positioning washer 46 which is radially outward of counterbore 73 defines an annular shoulder in which is formed a pair of diametrically disposed radially extending annular channels 48. Annular channels 48 are semi-circular in cross-sectional configuration and sized to receive transversely extending cross-bar 53 therein. Thus, when the

positioning washers

46 and 47 are disposed opposed to one another with their annular channels in alignment, the transversely extending cross-bar 53 of attenuator element 50 may be rigidly received therebetween and basically supported thereby. With the attenuator element so assembled, the conductive end portions 62 of transversely extending cross bar 53 are in electrical connection with

positioning washers

46 and 47. Further, positioning washer 47 is in electrical contact with a spacer washer 77 which provides for electrical contact with the coaxial conductive portion of male connector 11. With attenuator element mounting section so assembled, the transversely extending cross-bar 53 acts as a shunting element between the axial conductor of the attenuator assembly and the coaxial conductor of the attenuator assembly. In this regard, it can be seen from FIGS. 1 and 2 that the axial conductive path through attenuator 10 includes

conductors

20, 52, 34 and 32. Similarly, the coaxial conductive path through attenuator 10 includes

conductors

16, 77, 47, 53, 46, 30 and 36.

To assemble the attenuator, second threaded portion 18 of male connector 11 is advanced inwardly of attenuator element mounting section 14 and threadedly engaged with the internal threads 44 of annular channel 43. When these elements are in full threaded engagement, the split end of axially extending cylindrical conductor 20 of male connector 11 is positioned over the terminated end 62 of attenuator element 50 and in electrical engagement therewith.

Thereafter, the complete assembly of attenuator can be achieved by advancing the relieved portion of the outer surface of attenuator element mounting section 14 into the first cylindrical section 23 of female connector element 12 and engaging the threaded portion 42 of element 14 with the internally threaded portion 26 of first cylindrical section 23 of female connector 12. When full threaded connection is made between these two elements, the terminated end of longitudinally axially extending bar 52 of attenuator element 50 is received within the female end 34 of the longitudinally axially extending conductor 31 of female connector 12. With these elements so assembled, the attenuator 10 is fully assembled and ready for use.

The attenuator such as in accordance with the teaching of this invention has been found to provide relatively constant attenuation over a useful frequency range of operation, particularly in the high frequency ranges.

Although the attenuator according to the invention has been described only with respect to a single embodiment thereof, it is considered to be manifest that many modifications and variations to this structure can be made without departing from the spirit of this invention.

I claim:

1. An attenuator for a high frequency coaxial conductor system, comprising:

a first coaxial connector fitting, said first coaxial connector fitting having a first inner axial conductor and a first outer conductor coaxial with said first inner axial conductor;

asecond coaxial connector fitting, said second coaxial connector fitting having a second inner axial conductor and a second outer conductor coaxial with said second inner axial conductor;

an attenuator element mounting section disposed between and secured to said first and second coaxial connector fittings, said attenuator element mounting section comprising an outer cylindrical section and a third outer conductor disposed within said outer cylindrical section, said third outer conductor extending longitudinally and being coaxial with the longitudinal axes of said first and second inner axial conductors, and said third outer conductor being in electrical engagement with said first and second outer conductors;

an attenuator element secured within and supported by said attenuator element mounting section, said attenuator element comprising a single longitudinally axially extending resistive bar element and a transversely extending resistive bar element crossing said longitudinally axially extending resistive bar element to define a cross-shape, said longitudinally extending and transversely extending resistive bar elements cooperating to define a longitudinally extending plane containing the entire cross-shaped structure of said attenuator element, said longitudinally and transversely extending bar elements being in electrical connection at their point of intersection; and

said longitudinally axially extending resistive bar ele- I ment being in electrical engagement at one end with the first axial conductor of said first coaxial connector fitting and the other end of said longitudinally axially extending bar element being in electrical connection with the second axial conductor of said second coaxial connector fitting, and wherein said transversely extending bar element of said attenuator element is rigidly received by and in electrical engagement with said third outer conductor of said attenuator element mounting section.

2. An attenuator according to claim 1 wherein said bar members of said attenuatorelement are cylindrical in cross-section and include a dielectric substrate overcoated with a resistive film, the ends of said bars and the point of intersection of said bars being provided with conductor material.

3. An attenuator element according to claim 1 wherein said third outer conductor of said attenuator element mounting section comprises a first positioning washer disposed within said outer cylindrical section and a second positioning washer longitudinally spaced from said first positioning washer and disposed within said outer cylindrical section, and first and second positioning washers being disposed longitudinally on opposite sides of said transversely extending resistive bar element, each said positioning washers being in electrical engagement with the outer ends of said transversely extending resistive bar element.

4. An attenuator according to claim 3 wherein said positioning washers include generally semi-circular radially extending channels formed in at least one radially extending surface of each said washers, said semicircular radially extending channels for receiving the outer ends of said transversely extending resistive bar elements in rigidly engaged relationship.

Claims

1. An attenuator for a high frequency coaxial conductor system, comprising: a first coaxial connector fitting, said first coaxial connector fitting having a first inner axial conductor and a first outer conductor coaxial with said first inner axial conductor; a second coaxial connector fitting, said second coaxial connector fitting having a second inner axial conductor and a second outer conductor coaxial with said second inner axial conductor; an attenuator element mounting section disposed between and secured to said first and second coaxial connector fittings, said attenuator element mounting section comprising an outer cylindrical section and a third outer conductor disposed within said outer cylindrical section, said third outer conductor extending longitudinally and being coaxial with the longitudinal axes of said first and second inner axial conductors, and said third outer conductor being in electrical engagement with said first and second outer conductors; an attenuator element secured within and supported by said attenuator element mounting section, said attenuator element comprising a single longitudinally axially extending resistive bar element and a transversely extending resistive bar element crossing said longitudinally axially extending resistive bar element to define a cross-shape, said longitudinally extending and transversely extending resistive bar elements cooperating to define a longitudinally extending plane containing the entire cross-shaped structure of said attenuator element, said longitudinally and transversely extending bar elements being in electrical connection at their point of intersection; and said longitudinally axially extending resistive bar element being in electrical engagement at one end with the first axial conductor of said first coaxial connector fitting and the other end of said longitudinally axially extending bar element being in electrical connection with the second axial conductor of said second coaxial connector fitting, and wherein said transversely extending bar element of said attenuator element is rigidly received by and in electrical engagement with said third outer conductor of said attenuator element mounting section.

2. An attenuator according to claim 1 wherein said bar members of said attenuator element are cylindrical in cross-section and include a dielectric substrate overcoated with a resistive film, the ends of said bars and the point of intersection of said bars being provided with conductor material.

4. An attenuator according to claim 3 wherein said positioning washers include generally semi-circular radially extending channels formed in at least one radially extending surface of each said washers, said semi-circular radially extending channels for receiving the outer ends of said transversely extending resistive bar elements in rigidly engaged relationship.