US3270280A - Coaxial transmission line termination - Google Patents

Description

Aug. 30. 1966 G, R. TAHARA ETAL 3,270,230

, COAXIAL TRANSMISSION LINE TERMINATION Filed Oct. 18, 1962 Z Sheets-Sheet 1 FIG.

INVENTORS GUY K. PATTERSON and GORO R. TAHARA BY Mix/Q 0m ATTORNEY Aug. 30. 1966 5, R. TAHARA ETAL 3,270,280

COAXIAL TRANSMISSION LINE TERMINATION Sheets-Sheet .2

Filed Oct. 18, 1962 INVENTORS GUY K. PATTERSON and GORO R. TAHARA BY ATTORNEY Aug. 30. 1966 R. TAHARA ETAL 3,270,280

COAXIAL TRANSMISSION LINE TERMINATION Filed Oct. 18. 1962 5 Sheets-Sheet 5 FIG. 3-

lNVENTORS GUY K. PATTERSON and GORO R. TAHARA BY NJNQBQLQW ATTORNEY United States Patent 3,270,280 CUAXHAL TRANM1S1ON LHNE TERMHNATHON Gore R. Tahara, Sunnyvale, and Guy 1i. Patterson, Menlo Park, Calif, assignors to Fhilco Corporation, Philadelphia, Fa, a corporation of Delaware Filed Get. 13, 1962, Ser. No. 231,455 5 Claims. (Cl. 32495) This invention relates to a coaxial transmission line termination, and more particularly to a power absorbing load for the termination of high frequency coaxial transmission lines Often it is desirable to dissipate high frequency energy in a load to prevent the radiation of the energy, the radiant energy being converted to heat energy in the load. Loads for the dissipation of high frequency energy are well known and often include an inner conductor structure comprising an elongated resistor and an outer conductor structure comprising a tapered sleeve surrounding the resistor and connected thereto at one end thereof. When air is used as the dielectric medium between the inner and outer conductor structures, such load devices are capable of dissipating only relatively small amounts of power. When greater radio frequency power must be dissipated, such loads are provided with forced air cooling, or a liquid dielectric is employed to replace the air dielectric. Also, auxiliary refrigerating means are often employed to cool the dielectric liquid when it is desired to handle large radio frequency power. Although numerous schemes have been proposed for cooling such loads, they generally increase in complexity and cost as the amount of energy to be dissipated increases.

A load construction providing good natural convection cooling of the load resistor employed therein is shown in US. Patent 2,901,710 to E. Garthwaite. The load device shown in the patent includes an elongated resistor as the inner conductor and a pair of convergent plates disposed on opposite sides of the resistor as the outer conductor structure. The convergent ends of the plates are connected to one end of the resistor, and means are provided for applying high frequency energy to be dissipated between the other end of the resistor and the divergent ends of the plates. When the load is arranged with the plates positioned vertically, excellent natural convection cooling of the resistor positioned between the plates is provided. In order to handle high power, such units may be built with a large resistor. However, the larger the diameter of the resistor, the greater must be the spacing between the convergent plates of the outer conductor structure, whereby the size of the load is increased.

It is well known that by measuring the voltage across a portion of the resistor included as the inner conductor of a coaxial transmission line termination, an indication of the power dissipated by the termination is obtained. Often, a crystal diode is employed to convert the voltage to DC. for convenient measurement by an indicating instrument having a scale calibrated in watts or power. Crystal diodes, however, have an operating temperature range within which they operate accurately. At operation above the upper temperature limit the diode may burn out or function improperly, and for accurate wattmeter readings this limit must not be exceeded.

An object of this invention is the provision of means for greatly increasing the heat dissipating capability of a coaxial transmission line termination without increasing the over-all dimensions of such a termination.

An object of this invention is the provision of a coaxial transmission line termination of relatively simple construction and having high power hand-ling capabilities.

An object of this invention is the provision of a watt- 3,27%,230 atented August 30, 1966 meter which includes a heat dissipating termination and crystal diode, said diode being located at a relatively cool location on the termination whereby large power measurements may be made without overheating the diode.

These and other objects and advantages of the invention are achieved by means of a load construction including a pair of convergent plates as the outer conductor structure and a plurality of parallel connected elongated resistors as the inner conductor structure. The resistors are located one above the other and, when the load is used as a wattmeter, a diode holder is secured to the lower-most resistor. Since the heat from the resistors rises by convection of cooling fluid, such as air, the heat from the resistors above the lower-most resistor contribute little to the temperature rise of the diode. Further, by mounting the resistors in a divergent manner, a maximum physical separation of the diode from the upper resistors is obtained.

In the drawings, wherein like reference characters refer to the same parts in the several views:

FIGURE 1 is a top view of a termination embodying this invention;

FIGURE 2 is a side elevational view of the termination shown in FIGURE 1, with parts shown broken away for clarity; and

FIGURE 3 is an enlarged fragmentary sectional view through the diode holder showing the manner in which it is mounted on the termination.

Referring to FIGURES 1 and 2 of the drawings, the termination of this invention comprises a pair of elongated tubular film-type load resistors of identical construction, It) and 11, disposed between a pair of convergent plates, or slab lines 13 and 14, also of identical construction. Resistors 10 and 11 comprise the inner conductor structure of the load, and plates 13 and 14 comprise the outer conductor structure thereof. The convergent ends of the plates 13 and 14 are connected to terminals of resistors 10 and 11 by means of rear contact plate assemblies 16 and 16' of identical construction. When the termination is used in a Wattmeter arrangement a diode holder 15 is secured to the lower contact plate assembly 16' in a manner shown in FIGURE 3 and described in detail hereinbelow.

The divergent front ends of plates 13 and 14 are secured by screw fastening means 17 to the vertical side walls of a front end connector body 18. A line connector member 19 engages the tapped portion of a through hole 21 formed in the connector body, and together with the connector body provides an electrical connection between an attaching collar of a coaxial line, not shown, and the outer conductor structure 13, 14 of the termination.

A tapered inner connector 22, coaxially disposed within the connector member 19 and electrically insulated therefrom by a suitable dielectric sleeve, conductively connects to a generally cylindrical brass pin 23 formed with an integral axial flange 241 which extends over the inner connector 22 in good electrical connection therewith. A dielectric bushing 26 is positioned in the space between the pin 23 and the connector body 18 and extends inwardly from the connector body 18. A setscrew 27 (FIG. 1) fixedly secures the bushing within the connector body 18.

The rear end of bushing 26 is preferably formed with a vertical recess 28 which extends the entire height thereof and within which is positioned a contact mounting plate 2%. The reduced diameter rear end of the pin 23 extends into a hole formed in the center of the contact mounting plate 29 and is suitably connected thereto by soft soldering or the like.

The rear end of the contact mounting plate is provided with a pair of intersecting surfaces extending at an angle of slightly less than 90 with the axis 31 of the load device. A pair of identically constructed input connector contacts 32, 33 are secured to said contact mounting plate, the input connector contacts being provided with generally forwardly extending pins 34 and 36 which engage suitable holes formed in the rearward walls of the contact mounting plate and which are fixedly secured thereto by soft soldering or the like.

The tubular film-type load resistors and ill each may comprise a glazed cylindrical ceramic tube 41 with a resistor film 42 disposed on the external surface thereof. Said film may comprise an alloy including a highly stable tin oxide deposited on the external surface of the glazed ceramic tube which is then fired at a high temperature to disperse the resistance film throughout the body of the glaze. Bands 44 and 44' of conductive metal, such as silver, are applied to the ends of the resistors and extend over the resistance film in good electrical contact therewith. It will here be understood that, for purposes of illustration and clarity, the showing of the resistance film 42 and conductive bands 44 and 44' is greatly exaggerated dimensionally in the drawing. The input connector contacts 32 and 33 are provided with axially extending slotted flanges which extend over the conductive bands 44 and are secured thereto by soldering or other suitable means not shown.

The rear contact plate assemblies 16 and 16', as shown in the drawings, each include a slotted axial flange 47 secured to the silver conducting bands 44' of the resistors 1i) and 11 by a plurality of retaining rings 46. Screws 43, extending through holes formed in the outer conductor plates, fixedly secure the rear contact plate assemblies 16 and 16 to the plates. The outer conductor plates 13 and 14 are spaced apart by metal spacers 49 of brass or the like secured to the plates by screw fastening means 51. The spacers 49 are of different lengths to provide the proper curvature of the outer conductor plates 13 and 14, and for good matching of the load to the transmission line the plates are provided with a substantially exponential curvature.

Resistors 10 and 11 are electrically connected in parallel in the novel arrangement of this invention, the energy from a power source, not shown, entering the device through the line connector 19 and dividing substantially equally at said resistors. The two resistors in parallel provide an increased power dissipating surface over single resistor constructions for increased power handling capabilities.

The coaxial line termination described in detail above is particularly well suited for use in making radio frequency power measurements. Reference is now also made to FIGURE 3 of the drawings wherein the connection of microwave diode holder to the novel coaxial line termination is shown in detail. Although the diode holder forms no part of the invention, a suitable construction includes a housing 51 having an axial flange 52 secured by retaining rings 46 to flange 47 on lower rear contact plate assembly 16'. The housing is capped by a ferrule 53 secured thereto by a captive threaded collar 54. A cartridge-type diode 56 is coaxially supported in housing 51 by a bushing 57.

A metallic ring or band 58 of silver or the like is applied to resistor 11 a spaced distance from the rear end thereof and electrical connection is made between said band and diode 56; the connection including a metallic band 59 inside the resistor Ill connected to band 53 by conductors 61 extending through axial holes in the resistor. A metallic spider, or disc, 62 engages band 59 and supports one terminal of a harmonic suppression resistor 63. The other terminal of resistor 63 is connected to a contact pin 64 of diode 56 by means of a sleeve 66. The other diode. terminal 67 is connected to a radio frequency bypass capacitor 68 of the disc type and through electrical components, not shown, to a DC. output conductor 69. As is well understood by those skilled in this art, the DC. output is directly proportional to the voltage across the portion of resistor 11 between bands 44' and 58 which, in turn, is directly proportional to the power dissipated by the termination. A flow of cooling fluid such as air through the tubular resistors is made possible by radial holes 71 formed in the flanges of the input connector contacts 32 and 33. The rear end of resistor 10 is left open and radial holes 72 are formed in housing 51 for accommodation of the fiow of air through resistors It) and 11, respectively.

As is well understood, crystal diodes such as diode 56 have a temperature operating range within which they must operate. If the temperature exceeds the maximum temperature rating the diode either burns out or fails to function as predicted. In either case, the accuracy of the wattmeter is impaired. With the novel termination construction of this invention, the diode is not only mounted adjacent the inner conductor of the termination, but is also mounted at a relatively cool position. A substantial portion of the heat from upper resistor it) rises by convection of the cooling fluid and thereby contributes little to the rise in temperature of the diode. Since substantially one-half of the total power dissipated by the termination is dissipated by resistor Jill, it will be apparent that the termination is capable of handling more power without damaging the diode than would a termination of similar construction but employing only a single resistor. In accordance with this invention, the parallel connected resistors extend in a divergent manner from the front end of the load to the rear end thereof. By placing the resistors close together at the front end a minimum mismatch of impedance is experienced at the input to the resistors. A good impedance match at the input to the resistors would be diflicult to obtain if the resistors were spread apart a substantial distance thereat, and for this reason, the resistors are physically located close together adjacent the input ends. By spacing the other ends of the resistors apart as illustrated, the diode 56 is located a maximum distance from the heat-producing resistor iii, and consequently, the wattmeter is capable of high power measurements without damage to the diode. Although the divergent arrangement of resistors 10 and 11 is not essential to the proper operation of the load device, the large power handling capability is made possible by locating the diode 56 below resistor lltl adjacent the end of lower resistor 11.

The invention now having been described in detail in accordance with the requirements of the patent statutes, various changes and modifications will suggest themselves to those skilled in this art. For example, the invention is not limited to the use of a pair of resistors, more than two resistors may be employed in parallel in accordance with this invention, It will be apparent when more resistors are employed, more surface will be available for the dissipation of heat. With the outer conductor plates, or slab lines, in a generally vertical position as illustrated, air easily circulates by convention past the load resistors to cool them. If desired, the termination may be supported in a casing containing a liquid dielectric as is well understood by those skilled in this art. -In such an arrangement the flow of fluid such as transformer or mineral oil past the resistors provides for increased cooling action. However, by employing a plurality of resistors, the increased power handling capability of the load is made possible without resort to liquid dielectric in many instances. The disadvantages of the use of liquid dielectric, including the possibility of leakage of the dielectric from the casing or housing is thereby eliminated. It is intended that these and other such changes and modifications shall fall within the spirit and scope of the invention as recited in the following claims.

We claim:

1. A microwave load for use in energy dissipating or measuring apparatus including an inner conductor structure comprising a pair of elongated resistors electrically connected in parallel, an outer conductor structure comprising a pair of convergent slab lines disposed on opposite sides of said resistors, said resistors extending in a divergent manner from the divergent to the convergent ends of the slab lines, means connecting the convergent ends of said slab lines to one interconnection of the said resistors, and means at the divergent ends of said slab lines for connection of a source of microwave energy between said slab lines and the other interconnection of said resistors.

2. The invention as recited in claim 1 including a diode and terminal means therefor to which measuring means may be connected, said diode connected adjacent one end of one of said resistors.

3. A microwave load for use in energy dissipating or measuring apparatus, comprising: a pair of convergent plates to be positioned substantially vertically; a pair of elongate resistors between said plates, said resistors being one above the other When said plates are disposed vertically and extending divergently from the divergent to the convergent ends of said plates; means for connecting the divergent ends of said plates to the outer conductor of a coaxial line; means for connecting the convergent ends of said resistors to the inner conductor of a coaxial line; and means connecting the divergent ends of said resistors to the convergent ends of said plates.

4. Apparatus according to claim 3, further including a diode and terminal means therefor to which measuring means may be connected, said diode connected to the lower resistor at the divergent end thereof.

5. Apparatus according to claim 3, wherein the divergent ends of said plates are secured and electrically connected to a connector body, and the convergent ends of said resistors are supported by said body but are insulated therefrom.

References Cited by the Examiner UNITED STATES PATENTS 2,399,930 5/1946 Keister 333-22 2,524,183 10/1950 Wheeler 324 2,565,900 8/1951 Wiley 32495 2,901,710 8/1959 Garthwaite 333-22 3,027,514 3/1962 Bird 324--95 WALTER L. CARLSON, Primary Examiner.

R. V. ROLINEC, Assistant Examiner.

Claims (1)

1. A MICROWAVE LOAD FOR USE IN ENERGY DISSIPATING OR MEASUREMENT APPARATUS INCLUDING AN INNER CONDUCTOR STRUCTURE COMPRISING A PAIR OF ELONGATED RESISTORS ELECTRICALLY CONNECTED IN PARALLEL, AN OUTER CONDUCTOR STRUCTURE COMPRISING A PAIR OF CONVERGENT SLAB LINES DISPOSED ON OPPOSITE SIDES OF SAID RESISTORS, SAID RESISTOR EXTENDING IN A DIVERGENT MANNER FROM THE DIVERGENT TO THE CONVERGENT ENDS OF THE SLAB LINES, MEANS CONNECTING THE CONVERGENT

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