US3560888A - Microwave energy termination device - Google Patents

Abstract

A MATCHED IMPEDANCE TRANSMISSION LINE TERMINATION LOAD HAVING ELECTROMAGNETIC ENERGY ABSORBING MEANS POSITIONED PARALLEL TO THE ELECTRIC FIELD VECTORS OF THE PROPAGATED ENERGY AND EXTENDNG PERPENDICULARLY TO THE LONGITUDINAL AXIS OF THE LINE AT A POINT SPACED A FREQUENCY WALL. COARSE AS WELL AS THE FINE TUNING MEANS ARE PROVIDED FOR REFINEMENT OF THE IMPEDANCE MATCHING. HEAT DISSIPATION MEANS IN COMBINATION WITH THE ABSORPTION MEANS ARE ALSO DISCLOSED.

Description

Feb, 2, 1971 H. w. PERREAULT MICROWAVE ENERGY TERMINATION DEVICE Filed July 31, 1969 2 Sheets-Sheet 1 L BASIC TERMINATION FREQUENCY GHZ FIG: 3

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Feb, 2, 1971 H. w. PERREAULT MICROWAVE ENERGY TERMINATION DEVICE 2 Sheets-Sheet 2 Filed July 51, 1969 30 E.- FIELD 8 w VE/VTOR HENRY m PERREAULT I ATTORNEY United States Patent MICROWAVE ENERGY TERMINATION DEVICE Henry W. Perreault, Chelmsford, Mass., assignor to Raytheon Company, Lexington, Mass, a corporation of Delaware Filed July 31, 1969, Ser. No. 846,397 Int. Cl. H01p 1 /26 US. Cl. 333-22 7 Claims ABSTRACT OF THE DISCLOSURE A matched impedance transmission line termination load having electromagnetic energy absorbing means positioned parallel to the electric field vectors of the propagated energy and extending perpendicularly to the longitudinal axis of the line at a point spaced a frequency dependent distance from an energy reflecting terminal end wall. Coarse as well as fine tuning means are provided for refinement of the impedance matching. Heat dissipation means in combination with the absorption means are also disclosed.

BACKGROUND OF THE INVENTION In the microwave art the termination of transmission lines, particularly at high power levels, presents a continuing problem in view of the energy absorption requirements as well as the necessity for matched impedances to provide substantially reflectionless absorption under varied environmental conditions. Prior art devices have evolved having lengths which may run into several feet, at for example S and L-band frequencies, and combined with the weight of the absorbing material such loads have become objectionably cumbersome and expensive. The high temperatures generated, particularly with the bulky materials involved, have also created problems in life and reproducibility of the electrical parameters. Such devices may also operate under conditions of shock and vibration which further complicates the problems. The considerable quantity of material can hinder impedance matching to provide low voltage standing wave ratio (VSWR) values. Such termination devices for use in waveguide as well as coaxial transmission lines have been commonly provided with long tapered structures to assist in impedance match ing. In this instance length again plays a factor and exceedingly long tapered walls in waveguide or knife-edged tapered bodies are required which are difficult to machine and fabricate of the lossy materials.

Briefly, the ideal termination must be capable of absorbing output power levels which can be as high as hundreds or even thousands of Watts with substantially no reflection of power and with VSWR ratings desirably between 1.01 to 1.10. The impedance matching of the termination to the line must be reasonably independent of temperature as well as be relatively insensitive to other environmental conditions. The bandwidth over which the termination device provides the low VSWR ratings is another important factor to consider in relation to the acceptability of the end product. A need arises, therefore, particularly in present day microwave radar systems, for an improved termination device capable of handling high power levels with low VSWR ratings over substantially broad frequency bands.

SUMMARY OF THE INVENTION The invention provides, in a unitary integral structure, a termination device having a transmission line section with a loaded coaxial section including a coupling element of an energy absorbing means such as a lossy dielectric material extending perpendicularly to the path of the propagated energy. The coupling element penetrates "ice the transmission line in a direction parallel to the electric field vectors of the transmitted electromagnetic energy. The coupling element is extremely compact and a coolant liquid may also be circulated within the energy absorbing means to further increase the power handling capability. In an embodiment for waveguide transmission lines an energy reflecting end member terminal may be provided with tuning means to assist in the refinement of the impedance matching of the device to the line. Such a tuning means may provide a coarse tuning characteristic to assist in compensating for mechanical tolerance deviations during manufacture of the component. Another tuning means may be centrally disposed within the lossy coupling element to provide for fine Vernier tuning adjustment of the impedance matching characteristics. Lossy ceramic materials, as well as combinations of ceramic and plastic, have been utilized for the energy absorbing means. The perpendicular coaxial structure appended to the waveguide structure for, illustratively, C-band frequency in a range of from 4.4 to 6.2 gigahertz will have a height of approximately 1 inch in a directional coupler arrangement to indicate the compactness of the improved termination device relative to prior art devices. The VSWR requirement has also been measured within the required range of 1.01 to 1.10. The termination device is ideally suited for the terminal arms of multiport directional couplers on in-line as well as direct termination components.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the details of construction of a preferred embodiment, will be readily understood after consideration of the following detailed description and reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of an exemplary embodiment of the invention.

FIG. 2 is a plan view of the embodiment shown in FIG. 1;

FIG. 3 is a graph illustrating the VSWR measurements of an illustrative embodiment;

FIG. 4 is a detailed cross-sectional view of an alternative embodiment of the invention; and

FIG. 5 is a plan view of another alternative embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2 an embodiment of a waveguide termination device utilizing the invention is shown and indicated generally by the numeral 10. A section of hollow pipe type waveguide transmission line 12 is enclosed at one end by a terminal short-circuited end wall 14 which may be fixed or movable as preferred for the particular application. The opposing end of waveguide section 12 supports a coupling flange member 16 for mounting the device in a transmission line. The flange members may have conventional choke arrangements and are selected along with the waveguide section in accordance with standard microwave art for the propagation of electromagnetic energy at a particular frequency of operation. The flanged waveguide section is shown for illustrative purposes only and the invention may be mounted in any transmission line arrangement such as a terminal load component for use in a multiported directional coupler. In such an arrangement the termination device is mounted in an auxiliary transmission line which is coupled to the main transmission line by means of a coupling aperture in a common wall.

The embodiment of the invention comprises a coaxial energy absorbing coupling element 18 which is disposed perpendicularly to the longitudinal axis of the waveguide transmission line and supported by the broad wall 20 of waveguide section 12. The coupling element includes the energy absorbing member 22 of a lossy dielectric material such as for example a ceramic material having lossy dielectric properties. One such material is available under the trade name Radite manufactured by the Radar Design Corporation, New York. The lossy energy absorbing member 22 is enclosed and supported by housing member 24 which is terminated by a conductive plate 26. The inner end of the absorbing member 22 is provided with tapered walls 28 to match the impedance of the termination device to the transmission line. The tapered lossy energy absorbing member penetrates the hollow transmission line and is substantially centrally oriented with respect to a point approximately one-quarter of a wavelength from the short-circuited end wall 14. The length of the tapered portion as well as the overall height and the depth of insertion of the member 28 may be determined by wellknown microwave techniques upon ascertaining the frequency of operation and the approximate amount of the power to be absorbed.

The orientation of the lossy energy absorbing member 22 is noted to be parallel to the E-field vector of the transrnitted electromagnetic energy as indicated by the arrow 30. Since impedance matching is a critical parameter in termination devices of the type under consideration, particularly directional couplers and low power devices, it may be desirable to incorporate tuning adjustment means. A conductive tuning member 32 is illustrated within the short-circuited terminal end wall 14 for example coarse tuning of the device. An auxiliary or final fine tuning member 34 may be provided within a central passageway 36 in absorbing member 22. The tuning member 34 is threadably engaged within plate member 26 to be axially moved within the passageway 36.

Referring now to FIG. 3 the VSWR measurements of an exemplary embodiment are shown. This embodiment was utilized as a termination of a secondary arm of a crossed-guide type directional coupler and operated over a frequency range in C-band of from 4.4 to 6.2 gigahertz. Curve 38 represents the readings across the band of the termination device without the provision of any tuning matching means. Over the range shown of from 4.4 to 5.4 gigahertz the device had VSWR ratings of 1.10 or less. Curve 40 indicates the enhancement of the low VSWR characteristics over substantially the entire bandwidth by means of adjustment of the coarse tuning member 32. Curve 42 illustrates a further refinement of the operating characteristics and a further extension of the low VSWR upon actuation of the fine tuning member 34 for impedance matching. It will be noted that readings as low as 1.01 may be obtained with this embodiment of the invention.

Referring next to FIG. 4 an alternative embodiment of the invention incorporating the circulation of a dielectric coolant is shown. In this device the waveguide section 44 is terminated by a short-circuited end wall 46. In view of the higher power handling capabilities for the subject device and perhaps less critical impedance matching the tuning members have been omitted. Cylindrical housing member 48 is secured to waveguide section 44 by metallurgically joining flange 50 to the top broad wall 52. Coupling flange 54 is secured adjacent to the open end of the waveguide section.

A coolant liquid-containing shell member 56 is provided with a tapered section 58. A material such as quartz glass or plastic materials such as those available under the trade names Vicor or Rexolite may be utilized for member 56. The length and incline of the tapered section 58 again follows microwave art techniques. Member 56 is supported within housing member 48 and maintained liquid tight by plural O- ring members 50 and 62 sandwiched o neither side of flanged lip 64 abutting shoulder 66. A top plate member 68 supports an inlet and outlet conduit means 70 and 72, respectively. A threaded cap screw arrangement 74 having a clearance aperture 76 engages the outer threaded portion of housing member 48 to create a pressure bearing on the under-lying plate member 68 and O- ring members 60 and 62. Any suitable coolant having lossy dielectric properties can be circulated within the shell member 56 to absorb the electromagnetic energy. The use of a coolant medium will facilitate operation at higher power levels.

In FIG. 5 another alternative arrangement is shown. In this embodiment a common flange 78 is joined to the end of dual waveguide sections 80 and 82 having a common narrow wall 84. Compact termination devices 86 and 88 similar to those shown either in FIGS. 1 and 2 or FIG. 4 are mounted in each waveguide section and spaced from the closed end wall members 90 and 92. Again as in the previous examples coarse as well as fine tuning ad justment means may be provided where desired. Such dual waveguide arrangements will be adapted for use with hybrid junctions in numerous microwave system arrangements.

Numerous modifications, alterations and variations in structure as well as lossy materials employed will readily occur to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims. It is intended, therefore, that the embodiments shown and described herein be considered as illustrative only and not in a limiting sense.

What is claimed is:

1. An electromagnetic energy termination device comprising:

waveguide transmission means for propagating said energy;

said waveguide means being terminated in an energy reflecting end member;

coaxial coupling means comprising an element of an energy absorbing medium extending perpendicularly to the longitudinal axis of said waveguide means and parallel to the electric field vectors of said energy at a point spaced from said end member;

said energy absorbing element extending within said waveguide and having an inner tapered end portion of reducing cross-sectional dimensions;

and means for adjustment of the impedance matching characteristics of said absorbing element to said transmission means.

2. An etlectromagnetic energy termination device according to claim 1 wherein said adjustment means comprise a tuning conductive member provided in said end member.

3. An electromagnetic energy termination device according to claim 1 wherein a movable conductive member is disposed axially within said energy absorbing element to provide said impedance matching refinement means.

4. An electromagnetic energy termination device according to claim 1 wherein said energy absorbing means comprise a fluid coolant.

5. An electromagnetic energy termination device comprising:

waveguide transmission means for propagating said energy;

said waveguide means being terminated in an energy reflecting end member; means for absorbing said energy extending perpendicularly to the longitudinal axis of said waveguide means and parallel to the electric field vectors of said energy at a point spaced from said end member;

said absorbing means including a substantially hollow element of a lossy dielectric medium;

means for circulation of a fluid coolant within said hollow element; and

means for substantially matching the impedance of said transmission path to said absorbing means.

6. An electromagnetic energy termination device according to claim 5 wherein the inner end portion of said hollow element disposed within said transmission means is tapered by a dimension suflicient to match the impedance of said transmission path to said absorbing means.

7. An electromagnetic energy termination device commovably secured in said end wall member and a prising: centrally disposed axially movable conductive memwaveguide transmission means having broad and narber disposed within said absorbing element.

row walls for propagating said energy; said Waveguide means being enclosed at one end by a 5 References Cited conductive wall member;

UNITED STATES PATENTS coaxial coupling means comprlsing an element of an energy absorbing medium extending parallel to said 3: 12:

gzlrrow walls at a po1nt spaced from said end mern- 2194423 4 7/1960 Ronde an encircling conductive housing member secured to 10 FOREIGN PATENTS one of said broad walls and supporting said abs0rb- 105,148 9/1938 Australia 333 22 ing element whereby the inner end portion extends 1,221,073 5/1960 France 333 22 within said waveguide means;

said inner end portion being tapered inwardly in the 15 HERMAN KARL AA AC p i Examiner direction of the opposing broad wall;

and means for the adjustment of the impedance match- NUSSBAUM Asslstant Examiner ing characteristics of said absorbing element to said U 8 C1 X R transmission means;

said adjustment means including a conductive member 0

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