US 3646482 A
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United States Patent 151 3,646,482
Ursenbach Feb. 2 9, 1972  APERIODIC DISPERSIVE LOAD FOR Primary Examiner-Herman KarlSaalbach HIGH-FREQUENCY, HIGH-POWER USE Assistant Examiner-Marvin Nussbaum Attorney-Flynn & Frishauf  Inventor: Francois Ursenbach, Paris, France  Assignee: Thomson-CSF, Paris, France ABSTRACT  Filed; Nov. 12, 1970 The load is formed as a plurality of terminal elements, one being the last and the others being complementary thereto;  Appl' 8850 each one includes an external conductor and an internal conductor, the complementary terminal elements further includ-  F i li i p i m ing a peripheral conductor coaxially surrounding each complementary element and electrically connected to an adjacent NOV. 21, 1969 France ..6940100 peripheral conductor of an adjacent element, the open end of the external conductor of the first terminal element being in- 52 US. Cl. ..333/22 R, 333/22 F, 333/33, terconnected with the adjacent end ofthe peripheral cnduc [51 Int Cl 333/81 gg tor of the next adjacent complementary element, the external d 8 3 3 conductors of two adjacent terminal elements being intercone o m nected by a material transparent to the energy to be dissipated, or directly connected thereto; preferably, a resistive  References Cned element may form the interconnection between an interior UNITED STATES PATENTS conductor and the closed end of an external conductor, and cooling means may be provided (such as by the formation of fletster gaps and making the internal conductor hollow) to addi- Oren) tionall dissi ate a load. 2,853,679 9/1958 Nelson ..333/22 X y p 10 Claims, 6 Drawing Figures l 2 O 9 26 109 111 EN- JIIB PAIENTEUFEB 29 m2 SHEET 1 BF 2 PRIOR ART PAIENTEDFEB 29 I972 sum 2 OF 2 APERIODIC DISPERSIVE LOAD FOR HIGH- FREQUENCY, HIGH-POWER USE The present invention relates to dissipative loads utilized with high-frequency, high-power generators, and more particularly to aperiodic loads of coaxial construction forming dummy antennas for high-power transmitters.
Dummy loads should have the following characteristics:
they should be sufficiently aperiodic so that their normal impedance will remain constant, or within a narrow range within a wide frequency range, at least within the frequency range of the sources to which they are to be connected;
they should present a good match to the maximum power generated by the generators, which may be considerable (several hundreds of kW). This requires external cooling, and they should thus be capable of being used with an external cooling fluid;
the use and the connection of the lines should be simple, and particularly, they should not be of substantial size. They should be as small as possible in view of the lowest frequencies with which they are to be operated.
It is known to make dummy loads by utilizing a resistance in the form of a thin layer as the core, or central conductor of a coaxial structure. Proper choice of the characteristics of such a load can readily provide good aperiodic operation; the energy to be dissipated is, however, small since the volume of the thin layer is small; it is rather fragile and, even if cooled by circulation of a fluid, large power levels cannot be readily dissipated in structures having a reasonable dimension.
It has also been proposed to dissipate energy directly in a cooling fluid, generally water, which is used as a dielectric ofa coaxial structure of the load. Good heat dissipation can be obtained if the volume of the cooling fluid is great and constantly renewed. Such loads usually provide the desired characteristics; yet, the high dielectric constant of water does not permit operation at impedance values less than the impedences usually used with the generators. It has been proposed to interpose a matching transformer between the generator and the load; this expedient however results in a reduction of band width and operational and constructional complications which limit the application of such loads. Increasing the volumetric proportion of water along the load can result in obtaining the desired impedences, but a great portion of the power to be dissipated will be concentrated in a comparatively small volume of water and a good portion of the advantages of this solution and then not obtained.
It is an object of the present invention to provide a dissipative dummy load which has a wide frequency band width, is simple to construct and easy to cool.
SUBJECT MATTER OF THE PRESENT INVENTION Briefly, a first terminal element is provided having a dielectric loss liquid filling the element. The element itself has an external and an internal conductor. The external conductor has an open end and a closed end. n, in which n is at least 1, complementary terminal elements are interposed between the first terminal element and the supply of the power to be dissipated, typically a coaxial line. The interior conductors of these complementary elements are interconnected, preferably aligned. The external conductors of the adjacent terminal elements are simply interconnected together if their closed ends are located face to face; but, if their closed ends are remote from each other, they are interconnected by means of ajoint ofa material transparent to the energy to be dissipated, but tight with respect to the liquid. Each complementary element is coaxially surrounded by a peripheral conductor. Each of the peripheral conductors is electrically connected to an adjacent peripheral conductor, the open end of the exterior conductor of the first terminal element being connected to the peripheral conductor of an adjacent terminal element. The assembly of all these peripheral conductors and of the complementary elements forms, respectively, the outer, and the inner conductor of the dissipative load, the other end of the load forming input terminal (adapted for connection to the coaxial line). The sections of the peripheral conductors are so designed that" the characteristic impedance, as seen from the coaxial line, is equal to the sum of the characteristic impedances of each one of the elements.
The invention will be described by way of example with reference to the accompanying drawings, wherein:
FIG. 1 is a cross-sectional schematic illustration of a load in accordance with the prior art and forming a portion of the combination element of the present invention;
FIG. 2 is a transverse schematic view of the load in accordance with the present invention;
FIG. 3 is a different embodiment of the load of FIG. 2;
FIG. 4 is a four-element load of the type of FIG. 2;
FIG. 5 is a four-element load of the type of FIG. 3; and
FIG. 6 illustrates, in schematic cross section, a different embodiment for the structure of one of the elements.
A coaxial supply cable C has an inner conductor 1 andan outer conductor 2, respectively extended by inner conductor 5 and outer conductor 4 of the load. The outer conductor 4 of the load is closed off by a disk 6 connected at 10 to the inner conductor 5. The assembly forms a coaxial line' 7 which is filled with a dielectric loss liquid, such as water-and, as well known, energy is dissipated therein. The length of that load is so selected that, for all frequencies within the band to be transmitted, the wave reflected by disk 6 arrives at window 3 sufficiently attenuated such that the standing wave ratio caused by the power supply device with which the load is associated, is matched. It is possible to decrease the standing wave ratio, for a given wavelength, by substituting for short circuit 10 a resistance which absorbs part of the energy to be dissipated at that point; all the energy may be so dissipated if the value of the resistance approaches that of the characteristic impedance of the line.
The dissipating element of FIG. 1, and known, is a coaxial line section, open at one end and closed at the other, and forms a basis for the resistive load in accordance with the present invention.
The characteristic impedance which is obtained is low, and even if conductor 5 is reduced in diameter, it remains below the resistances generally desired. The lower limit of conductor 5 is rapidly approached due to mechanical considerations.
FIG. 2 illustrates the load in accordance with the present invention; the interior conductor 12 is common to two basic or base terminal elements, similar to the element of FIG. 1. The outer cylindrical conductors ll, 22 have the same diameter and the same length. Their adjacent ends are open, and separated by a cylindrical joint 9, made of material which is transparent to radioelectric waves but tight with respect to water. The other ends are short circuited to the interior conductor 12 by respective disks 15, 16. The coaxial line 8 thus formed can have water circulating therein, supplied for example by means of openings 13, 14 in the short circuit l5,the return being through the conductor 12 which, in this case, is made hollow and in tubular form. Openings pierced into conductor 12 to provide for fluid circulation are not shown to simplify the drawing. Line 8 is supplied by a coaxial supply cable D, having an inner conductor 27 terminating at the short circuit 16, and an external conductor 21 which extends over the load element and terminates at a step formed by a circular ring 23 adjacent the open end of conductor 11.
The impedance of the load, as seen from the cable D is twice the characteristic impedance which is common to the two elements forming the line 8.
Let it be assumed that at any instant, along conductor 21, a current exists in the direction of the arrows a. This current will propagate in the direction of the arrows b (along 11), arrows 0 (along 12), arrows d (along the interior face of 22) arrow e (along the exterior face of 22); looked at from the point of view of impedance, the two terminal consecutive elements are placed in series with respect to cable D. The dimensions of these elements are thus given thereby. The energy transmitted by the cable is dissipated in water circulating in cavity 8. Correct operation is insured however only it the length of the terminal elements, that is the length of the corresponding conductors l1 and 22 is sufficient such that the energy reflected by their respective short circuits 15, 16 is sufficiently attenuated, considering the quality of the match which is desired.
The linear attenuation of the elements of the line increases with frequency. For a low utilization frequency, the reflection coefficient must be greater. A substantial improvement of match is obtained if two consecutive elements are given a length having a difference equal to a quarter wavelength of the wave propagating in the element at the minimum frequency; the reflected voltages at the input with respect to each other are thus placed in opposition.
FIG. 3 illustrates a different embodiment of the load in which the two terminal elements forming the load are dif ferently connected. A hollow, tubular interior conductor 112 is common to the first terminal element, and to the second element. The external cylindrical conductor 111 and short circuit 115 are identical to elements 11 and in FIG. 2. The second terminal element had its position inverted with respect to the corresponding one in FIG. 2. Thus, short circuit 215 is placed to face the open end of conductor 111, and is separated therefrom by a joint 109, watertight but transparent to radioelectric energy, and identical to joint 9 of FIG. 2. The open end of conductor 211 is separated by means of a joint 209 identical to joint 109 from the short circuit plane 28 closing off the interior conductor 122 with respect to a coaxial supply cable E.
Line 108, thus formed, may have water circulating therein up to short circuit 28 if openings are provided in the short circuit 215. These openings are preferably radial to conserve the electrical separation between the elements. The water inputs are respectively seen at 113, 114, the return flow being through the hollow tube 112.
The exterior conductor 121 of cable E is connected to the open end of conductor 111 across a cylindrical peripheral conductor 26, coaxially surrounding conductor 211. Two step connections are formed by circular rings 25, 24.
Conductors 211 and 26 form a coaxial line section each. Their radius is selected such that the characteristic impedance is equal to that of one of the elements of line 108. The entire load thus provides, at the level of joint 209, an impedance which is the sum of the impedances of the line and one element radially placed in series therewith.
Analogous ways to compensate for frequency dependence can be used in the line of FIG. 3 similar to that of PEG. 2; complementary compensation can be obtained by varying the characteristics of the line section formed by the conductors 211 and 26.
Any number n of terminal elements may be interconnected, and it is not necessary that the number is limited to two.
FIG. 4 illustrates, at the right side of line AA,, a load similar to that illustrated in FIG. 2, and the various elements thereof have been given the same reference numerals. At the left of the line AA,,, a coaxial supply cable F has an inner conductor 43, connected to line 8 across an identical line 48 and an outer conductor 44 connected to a peripheral conductor 21 over a conductor 45 identical to conductor 21. A discontinuity 46, in form of a ring is provided. The coaxial line 48 has an interior conductor 47 and two outer conductors 42 and 41, a joint 49, identical, respectively, to elements 12, 22, and 11 and 9 ofline 8.
The impedance presented at separation AA,, between the conductors 21 and 22 is double that of the terminal elements, and adds to the sum of the two other terminal elements of the cavity 48, so that the impedance between conductors 43 and 44 will be four times the impedance of a single terminal element.
in general, the overall impedance obtained by placing n pairs of elements, each having a separate impedance R in series will be 2 NR.
The elements described in connection with P16. 3 may likewise be associated in any desired number.
FIG. 5 illustrates, at the right side of separating line BB., a load of that of FIG. 3, the individual components of which have been given the same reference numerals. At the left of separating line BB,,, coaxial cable G has its inner conductor 53 connected to conductor 112 over two basic elements 51 and 52, which are identical to those of line 108; and its outer conductor 54 connected to step ring 24 across peripheral conductors 55 and 56 and the step rings 57, 58. On following the increase of impedance from the short circuit terminal 115 towards the other end of the load, the impedance present at a level of a cylindrical peripheral conductor is equal to that of the level of the preceding conductor increased by R, which is the impedance of one of the basic terminal elements.
In general, the overall impedance obtained by placing n elements in series will be nR.
in general, the lines may be compensated as described in FlGS. 2, and 3.
in the above-described examples, the conductors utilized are cylindrical and coaxial, which is their usual form. it is, of course, obvious that it is possible to use conductors in which the axes are not congruent, but rather, parallel. Calculation of their characteristic impedance is well known. Likewise, the conductor sections may have other shapes than circular. It is likewise not necessary that all elements of the coaxial lines have the same impedance; the dimensions of the conductors will then, only, have to be readjusted. It is possible to apply to the load resistances, known devices and attachments to increase their characteristic impedance, or to modify the elements accordingly. FIG. 6 illustrates a base element in which the reference numerals which are similar to those of FIG. 1 represent the same elements. The inner conductor 5 is, however, replaced by a helical, or spiral conductor 65. This increases the linear inductance, and thus the characteristic impedance of the element. The impedance may further be increased by use of an electrically resistive metallic element.
The loads in accordance with the invention can be prepared to provide impedance values which are customary in use, for example 50 ohms with greatly reduced space requirements, and which have a wide band width. The lines are simple to construct and do not require any delicate or fragile components. Their power dissipation is high.
Various changes and modifications may be made within the inventive concept.
1. A periodic dissipative load for high-frequency high power use comprising a first terminal element and a dielectric loss liquid filling said terminal element, said terminal element including an external conductor having a closed end and an open end,
and an internal conductor;
n (wherein n is at least 1) complementary terminal elements, also filled with said liquid, interposed between said first terminal element and the supply of power to be dissipated, each of said complementary terminal elements having an internal conductor and an external conductor, the internal conductors of said first and complementary terminal elements being interconnected;
a material transparent to energy to be dissipated forming joints at said open ends of said external conductors of said first and complementary elements;
n peripheral conductors respectively coaxially surrounding said n complementary elements and being serially electrically connected with the open end of the external conductor of the first terminal element, said n peripheral conductors and said n complementary elements forming respectively outer and inner conductors having ends, opposite to said first terminal element, forming the input to the load, adapted to be connected to the source of power to be dissipated;
and the dimensions of said peripheral conductors being predetermined to provide a characteristic input impedance equal to the sum of the characteristic impedances of said terminal elements.
2. Load according to claim 1 wherein n is at least equal to 2 and wherein the external conductors of at least two complementary elements are electrically interconnected at their closed end.
3. Load according to claim 1 wherein each of said first and complementary elements comprises an electrical connection between its internal conductor and the closed end of its external conductor.
4. Load according to claim 3 wherein said electrical connection comprises a resistive element.
5. Load according to claim 1 wherein n+1 is an even number, and said first and complementary elements are associated with each other in pairs, the open ends of the two external conductors ofa pair being mounted face to face, and interconnected by one of said joints.
6. Load according to claim 1 wherein each of the n complementary elements is arranged such that the closed end of its external conductor be contiguous with the open end of an adjacent element and interconnected therewith by one of said joints.
7. Load according to claim 1 wherein the lengths of the elements are difierent to provide for compensation of waves reflected at closed ends of the external conductors of said first and complementary terminal elements.
8. Load according to claim 1 wherein said first and complementary elements are all of equal characteristic impedances