US2181871A - Concentric line tuned circuits - Google Patents

Description

Dec. 5, 1939.

70 CA Tl/UD 0F TUBE J. W. CONKLIN CONCENTRIC LINE TUNED CIRCUITS Filed Jan. 50. 1937 ALTER/WW5 r0 GRID DIAHT Q or VAtl/l/M com/5mm r055 INDUCTIVE {i 0I/A/E'CT/0Il .1

r0 (4 mom INVENTOR JAMES W. CONKLIN VBY) [M ATTORNEY Patented Dec. 5, 1939 UNITED STATES CONCENTRIC LINE TUNED CIRCUITS James W. Conklin, Audubon, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 30, 1937, Serial No. 123,096

19 Claims.

The present invention relates to tuned high frequency oscillatory circuits, and more particularly to such of these as are known by the term concentric conductor. resonator or line resonator. By the term concentric conductor resonator is meant a tuned circuit having inner and outer, substantially concentric conductors so coupled together as to form an oscillatory circuit. Examples of these are found in Reissue Patent No. 20,189, granted December 1, 1936, to Hans Otto Roosenstein, and in the article Resonant Lines for Frequency Control by Clarence W. Hansell, published in the A. I. E. E., August, 1935, pages 852 to 857, to which reference is herein made for a more detailed description thereof.

In my United States Patent No. 2,104,554 and 2,124,029, granted January 4, 1938, and July 19, 1938, respectively, and in the above mentioned A. I. E. E. article, are described two types of concentric resonators having inner conductors of double diameter, the resonators being designed to reduce the overall length of the tuned circuit considerably below that of a full quarter-wave counterpart. Essentially these resonators have an inner conductor of two diameters, i. e., a small diameter section which constitutes an effective inductance of minimum length necessary to attain the desired input impedance, and a large diameter section of substantially equal length as said small diameter section, but of a diameter such as to provide a proper effective capacity for resonating at the desired frequency. The entire circuit of inner and outer conductors resonate in the manner of a parallel resonance circuit, in the sense that the inductive reactance of the inductive section and the capacitive reactance of the capacity section will be formed wholly or in part by the correlative functions of the inner and outer conductors or component parts thereof. These concentric resonators having inner conductors of double diameter, as described in the above mentioned patents, are provided with means for maintaining the overall length of inner conductor constant, whereby there is obtained substantial freedom from the effects of variations in .the ambient temperature on the resonant frequency. Although such tuned concentric resonators have proved to be satisfactory, and not objectionably large for use with transmitting equipment, they are still inconveniently large for use with receiving or low power equipment.

The present invention overcomes the foregoing disadvantage and has for its primary object to provide a concentric conductor resonator which is extremely small and compact, and has a mini-- mum overall length commensurate with its associated features.

In my above mentioned United States patents, and in my United States Patent No. 2,103,515, granted December 28, 1937, are shown Various methods of obtaining a fine adjustment of the resonant frequency of the concentric conductor resonators. These are satisfactory for transmitter frequency adjustment, where a sensitivity of adjustment of one part in ten thousand, or alternatively, several hundred cycles is sufiicient. (The expression sensivity of adjustment should not be confused with frequency stability since the former expression refers to the ease with which the system can be adjusted mechanically to a desired frequency, whereas the latter expression concerns the constancy of that frequency once it is set.) However, such methods are not suitable where a finer adjustment of sensitivity is desired, for example, where we wish an adjustment sensitivity of less than one part in five million, as is required in the case of controlling the frequency of two beating high frequency oscillators within several cycles when producing an audio frequency beat.

Accordingly, another object of my invention is to provide a concentric conductor resonator having adjustment means of greater sensitivity and smoothness than heretofore employed.

A further object is to provide adjusting means for a concentric conductor resonator whereby the resulting change in the resonant frequency produced by said adjusting means shall have an approximately logarithmic relation to the movement of the adjusting control.

A still further object is to provide a reduced size of double diameter-inner conductor concentric resonator by greatly increasing the capacity between the larger diameter section of the inner conductor. and the outer conductor.

In general, the invention comprises a concentric conductor resonator constructed with two sections of different diameter for the inner conductor, the larger diameter section being conductively connected to but folded back upon the smaller diameter section in such manner that the overall length of line required to tune to a given frequency is greatly reduced. In order to still further reduce the overall length of line of the resonator, there is provided, in accordance with one particular embodiment of the invention, an additional metallic cylinder located within the large diameter section of the inner conductor and conductively connected to the outer conductor of the resonator through the base or end plate thereof for increasing the capacity between the large diameter section of the inner conductor and the outer conductor.

A feature of the invention lies in the arrange ment of the electrically conductive flexible bellows connection which connects with the two different diameter sections of the inner conductor of one embodiment of the invention.

A further feature of the invention resides in the anti-friction thrust bearing mechanism for obtaining micrometer adjustments, together with a coil spring arrangement for eliminating back lash.

Other features reside in the method of and means for obtaining absolute temperature compensation of the resonator at the resonant frequency.

Still further objects and features together with various advantages will appear from a reading of the following description, which is accompanied by a drawing wherein:

Fig. 1 illustrates a cross sectional view of a concentric conductor resonator in accordance with the invention, and

Fig. 2 illustrates a modification thereof.

Referring to Fig. 1 in more detail, there is shown a tuned oscillatory circuit comprising a concentric conductor line resonator having an outer conductor I constituting, in addition, the capacity member as well as the support and shielding for the entire assembly, and an inner conductor having a small diameter section 2 and a larger diameter section 3 folded back over the smaller diameter section. These two sections of different diameters of the inner conductor need not be of the same length but in the practical case will usually be approximately the same length to ffect maximum utilization of space. In general, a section of short circuited transmission line presents an inductive input impedance when less than one-quarter wave long. As the length approaches one-quarter wave, the impedance increases and shifts phase first to a high resistance and then to equivalent capacity reactance as the length increases beyond a quarter wave to a half wave, where the reactance passes through a minimum value and changes to inductive again and repeats the process. In practice, the smaller diameter section 2 of the inner conductor (i. e., inductive section), is preferably less than one-quarter wavelength although it might be desirable in some cases to use a longer conductor, an odd multiple of a quarter wave long. The length would have to be between zero and one-quarter wavelength, between a half and three-quarters wavelength, between one and onequarter wavelengths, etc., and not between multiples of some shorter length. The larger diameter section 3 of the inner conductor is the capacitive section, both sections of inner conductor resonating at the desired frequency in the manner of a parallel resonance circuit. Inner conductor 2, 3 is conductively coupled to the outer conductor I by means of metallic end plate I9, which supports the inner conductor and its associated adjusting equipment. At the opposite end of outer conductor I and fixed thereto by means of screws 2!], 2II, is the end plate II which forms one member of an adjusting capacity comprising plate II and plate I3, and which end plate is removable for convenience in assembling the resonator.

The small diameter section 2 of the inner conductor, which is mounted rigidly to the outer shell I by nut 8, is made of a proper length to develop the desired terminal or input impedance to the resonator. Tuning of the resonator is effected in part by the capacity existing between the cylinder 3 and the outer conductor I. This cylinder 3 is interchangeable for accomplishing major changes in frequency and is aflixed to the inner conductor section 2 by nut I5. A damping ring 4 of suitable insulating material furnishes further lateral support to cylinder 3 and prevents mechanical vibrations due to a bell action of this cylinder. Most of the remaining tuning capacity is formed by the moving plate I3 and the end plate I I. An extensible electrically conducting bellows I4 forms a flexible connection between plate I3 and the main capacity outer cylinder 3. There is some stray capacity between the bellows and the outer cylinder but this is incidental to the operation of the resonator. The primary connection of the capacity cylinder 3 (Fig. 1) to the small diameter inner conductor 2 is through the metallic plate 24 which is adjacent ring I5. An alternative way of visualizing this type of resonator is to consider this plate 24 as the base of a section of line of which cylinder 2 is the inner conductor and cylinder 3 the outer conductor, and inductive reactance thereby constituted tuned to the desired frequency by the capacity formed between cylinders I and 3 plus the capacity between plates II and I3 and the bellows capacity. The range of movement and size of the end plate I3 and bellows I4 is determined by the proportionate capacity required to be variable to cover the desired frequency range and the sensitivity of adjustment, i. e., a given capacity change could be accomplished either with a small spacing and small movement or greater spacing and greater movement. Where it is desired to cover approximately a 5% frequency range, the required sensitivity of adjustment necessitates a large range of movement. This necessitates having approximately 10% of the total capacity variable and a large diameter plate to obtain this capacity with the desired range of movement.

In the adjusting mechanism, a fine pitch micrometer screw It operates through an antifriction thrust bearing I having balls I8 bearing against flange It on thrust rod 5 compressing coil spring 5 and moving capacity plate I3. The coil spring removes all backlash from the mechanism. In previous types of adjusting mechanism, without the anti-friction bearing, it was found that a coil spring, to remove backlash, caused high starting friction on the adjusting screw making the action jerky, and a push-pull type of operating screw with unavoidable backlash of the type disclosed in the above mentioned United States patents, was used as the best compromise. Thrust rod 5 also serves to rigidly maintain the alignment of the capacity plate I3 without interfering with freedom of longitudinal movement by virtue of the widely separated bearings at IT and It between which bearings the rod 5 extends as an integral unit. It will also be observed that the hole AI in end plate I3 which accommodates screw I2 is somewhat larger than the screw itself in order to permit lateral alignment in assembling and avoiding lateral pressure on the bearings as far as possible.

It is well known that the capacity between two plates, such as I I and I3, depends in one degree on the spacing between the plates and in general is inversely proportional to the spacing. Thus, a given change in the spacing between the plates will have a large change in the capacity when the total spacing is small and a small change in the capacity when the total spacing is comparatively large. By proper selection of the limits and range of movement, it is possible to approach very closely to a logarithmic change of capacity over a selected range. For small capacity changes, the percentage change in resonant frequency is approximately equal to half the percentage change in capacity. Therefore, it is possible by proper design, and by making the total spacing small compared with the total adjustment movement, to effect an approximately logarithmic rate of change of resonant frequency with movement of the adjusting screw. This characteristic is very desirable in a beat frequency oscillator in order to spread out the low beat frequency range. In case such a characteristic is not desired, by making the total spacing large compared with the total adjustment movement, an approximately linear rate of change of frequency can be obtained with the adjusting screw.

Two types of temperature compensation can be attained with this type of resonator. It may be compensated in such a way that the difference in resonant frequencies of two similar resonators of the invention is unaffected by changes in ambient temperature, or it may be compensated to have the resonant frequency of a single resonator unaffected by changes in ambient temperature at a particular frequency. For beat frequency oscillator application, within limits, the absolute frequency is not important but it is very desirable that the beat frequency should be independent of ambient temperature.

Where two identical resonators of the type of the invention are to be used for independently controlling the frequency of two beating oscillators in a beat frequency oscillator, it is assumed that the two resonators are subjected to the same ambient temperature and the zero beat adjustment will be with the adjusting capacity plates in substantially identical positions. Therefore, for zero beat the two oscillators will have identical temperature characteristics and will hold zero beat with varying ambient temperature. Presuming that the zero beat position is the minimum capacity (maximum spacing) adjustment, it can be shown that the beat frequency will be unaffected by changes in ambient temperature for a particular beat frequency by maintaining the spacing of the capacity plates constant against change by temperature. If the whole resonator were constructed of the same material, the spacing would have the same coefiicient of change as the material. To compensate for this, it is only necessary to select materials or combinations of material for the adjusting screw and thrust rod to have the same overall net linear expansion with changes in temperature as the outer shell of the resonator for a particular spacing. It is thus possible to compensate a beat frequency oscillator for the extreme ranges of the beat frequency and have it fairly well compensated over the entire range.

When a single resonator of this type is to be used to rigidly stabilize or control a single oscillator at a given definite frequency, absolute temperature compensation of the resonant frequency is required. It may be assumed that a large capacity spacing will be used compared with the total range of adjustment. It may be shown that under these conditions the resonant frequency will be unaffected by variations in ambient temperature when the coefficient of expansion of the thrust rod and adjusting mechanism is made equal to:

so w) where a is the temperature coefficient of the material forming the inner and outer conductors,

S is the spacing of the adjusting capacity betwen plates II and I3,

L is the total length of the inner conductor assembly,

C is the total capacity of the inner conductor assembly,

and

C is the capacity of the adjusting plates II and Since this coefiicient is less than that of the material of the conductors, it is comparatively easy to obtain by using a composite thrust rod, apportioning its length with materials having two different coefficients to obtain the desired coefiicient. On the other hand, since C is proportional to the area of the plates divided by the spacing S, it is possible, by varying the area or the spacing, or both, to obtain any desired coefficient. Thus, if it is desired to use any particular material for the thrust rod, it is only necessary to design the adjusting capacity so that the quantity is equal to the coefficient of expansion of that material. must always have a lower coefficient than the conductor elements. However, inasmuch as the conductors will generally be made of copper, there are many desirable materials available, such as steel, having a lower coefiicient.

Alternative connections to the inner conductor from electron discharge device equipment have been indicated by dotted lines in Fig. l, as they may be made at any convenient point along the capacity cylinder 3 through a suitable hole or insulating bushing in the outer conductor I.

In Fig. 2 there is illustrated a modification of the circuit of Fig. 1. This figure eliminates the use of the flexible bellows between the two diameter sections 2, 3 of the inner conductor, and provides an additional cylinder 2I within the larger diameter section 3 and conductively coupled to the outer conductor 1 through the base or end plate I9 for increasing the capacity between the large diameter section 3 of the inner conductor and the outer conductor I, with a consequent reduction in the length of the concentric line resonator. The addition of the inner conductor 2| is equivalent, so far as capacity is concerned, to increasing the length of the large diameter section 3, but such an arrangement, it is to be distinctly understood, does not change the effectiveness of temperature compensation which is still proportional to the length of the inner conductor. of the adjusting capacity existing directly between the plate I3 and end plate II, as in Fig. 1, there is now provided an adjusting metallic plate 22 mounted on a screw 23 for providing the adjusting capacity between plate I3 and end plate It will be observed that this material It will be noted that instead is a specific design for use where thermal compensation is considered unnecessary, and consequently the bellows arrangement of Fig. 1 is omitted for simplicity. It will thus be evident that there is no need for a thrust rod as in the case of Fig. 1, all adjustment in Fig. 2 being effected by means of moving plate 22. v

The following advantages are obtained in the concentric conductor resonator of the present invention: (a) Since its diameter is determined by the desired power factor (the considerations in this respect are the same as for a quarter wave line of the same conductor diameters), its overall length is only slightly greater than the minimum required to obtain the desired input impedance on the inner conductor. (1)) As only a small part of the total capacity is adjusted, and that with precision smoothness, high adjustment sensitivity is possible. (0) The adjustment may be made to have a substantially logarithmic adjustment characteristic for such applications as a beat frequency oscillator. (03) It is possible to compensate for variations in the ambient temperature either to hold constant resonant frequency or to hold a constant difference frequency with a similar resonator, such as in a beat frequency oscillater or superheterodyne receiver. (e) Connection to the inner conductor can be made through a very short lead at practically any point throughout the length of the resonator. (f) Its construction and assembly are simple and conveniently adapted to standard material sizes and simple machine operations. (9) Since the ca-- pacity areas are lar e, close spacings are unnecessary and it will be comparatively free from troubles due to mechanical shocks or vibrations.

The tuned concentric lines of l and 2 can be coupled to a vacuum tube in any desired manner by direct, inductive, or capacitive connec tions. Both figures show one way of directly coupling the folded back, larger diameter section 3 of the inner conductor to the grid of a vacuum tube, when such a tuned concentric line is to be used as the frequency controlling element of an oscillator. It will be noted that these direct connections extend through a suitable hole in the outer conductor to the large diameter section of the inner conductor. Where, however, it is desired that a lower impedance tap be used, the direct connection may be made through holes in both the outer conductor and the large diameter or capacity section of the inner conductor whereby connection may be made to the small diameter section of the inner conductor. Such an arrangement is shown in dotted lines in Fig. 1. It will be understood, of course, that where desired other types of connection may be employed, such as an inductive connection in the manner also shown in dotted lines in Fig. 1, and that the tuned concentric line is not limited sole- 1y for use as a frequency controlling element of an oscillator since it can be employed as an impedance coupling element bet Jeen stages of a radio transmitter or receiver. or as a substitute for a tuned oscillatory circuit wherever such an oscillatory circuit can be use What is claimed is: i 1. An oscillatory circuit comprising a concentric line resonator having an inner and an outer conductor, said inner conductor having two sections of different diameters, the larger diameter section being folded back over the smaller diameter section for approximately the entire length of said smaller diameter section, said sections being conductively connected together at only one of their adjacent ends.

2. An oscillatory circuit comprising a concentric line resonator having inner and outer conductors conductively coupled together at one end,

section being folded back over the 3. An oscillatory circuit comprising a concentric line resonator having inner and outer conductors coupled together at one end, said inner conductor having two sections of different diameter, a flexible conductive bellows comprising an extension of the larger diameter section of the inner conductor to increase the length thereof, the smaller diameter section being coaxial with said outer conductor and supported at one of its ends by said outer conductor, the larger diameter section being folded back over the smaller diameter section for approximately the entire length of said smaller diameter section, said sections being connected together at only the other end of said smaller diameter section.

4. An oscillatory circuit comprising a concentric line resonator having an inner and an outer cylindrical conductor, means for conductivcly coupling said two conductors together at one end to constitute a tuned circuit, said inner conductor of said tuned circuit having two sections oi different diameter conductively coupled together end to end, the larger diameter section being folded back over the smaller diameter section, and a cylindrical conductor located between the two diameter sections of inner conductor and coupled to said outer conductor at said one end for increasing the capacity between said inner and outer conductors.

5. An oscillatory circuit comprising a concentric line resonator having an inner and an outer tubular conductor rigidly connected together at one end, said inner conductor having two sections of different diameters conductively coupled together, the larger diameter section being folded back over the smaller diameter section and held in position by a metallic plate extending substantially the width of the larger diameter section, adjusting mechanism for adjusting the effective length of said inner conductor comprising a thrust rod within the smaller diameter section extending from said one end of the resonator to said metallic plate, a bearing at each end of said thrust rod, a compressed coil spring located between one of said bearings and a flange on said rod, and a line pitch micrometer screw engaging said other bearing.

6. An oscillatory circuit comprising a concentric line resonator having aninner and an outer tubular conductor rigidly connected together at one end, said inner conductor having two sections of different diameters, the larger section being folded back over the smaller diameter section, a first end plate having a width substantially the width of said larger diameter section conduc tively coupling said two diameter sections to gather at the end of said smaller diameter sec tion remote from said one end, a second plate conductively connected to the other end of said outer conductor and forming with said first end plate a capacity, adjusting mechanism at said rigidly connected end including a thrust rod located within said smaller diameter section extending from said rigidly connected end to said first end plate, the coefiicient of expansion of said thrust rod and adjusting mechanism being equal to H a LC Where a is the temperature coefficient of the material forming the inner and outer conductors, S is the spacing between said two plates, L is the total length of the inner and outer conductor assembly, C is the total capacity between the inner conductor assembly and the outer conductor, and C is the capacity of the two plates.

7. A tuned circuit comprising inner and outer conductors, said inner conductor having two sections, an inductive and a capacitive section, the whole tuned circuit resonating at the desired frequency in the manner of a parallel resonance circuit, said capacitive section extending over substantially the entire length of said inductive section.

8. A tuned circuit comprising inner and outer conductors, said inner conductor having two sections, an inductive and a capacity section, said inductive section consisting of a relatively short conductor less than one-quarter wavelength in length, and said capacitive section consisting of a conducting surface in close proximity with the outer conductor and forming a capacity therewith, the Whole tuned circuit resonating at the desired frequency in the manner of a parallel resonance circuit, said capacitive section extending over substantially the entire length of said inductive section.

9. A tuned circuit comprising inner and outer conductors, said inner conductor having two sections, an inductive and a capacity section, said inductive section consisting of a relatively short conductor less than one quarter wavelength in length, and said capacitive section consisting of a conducting surface directly connected at one end to said inductive section and surrounding the same for substantially its entire effective length, said conducting surface being in close proximity with the outer conductor and forming a capacity therewith, the Whole tuned circuit resonating at the desired frequency in the manner of a parallel resonance circuit, and a metallic plate conductively connected to said outer conductor and cooperating with said capacity section for enabling adjustment of the capacity of the capacity section of said inner conductor with respect to the outer conductor.

10. An oscillatory circuit comprising a concentric line resonator having an inner and an outer conductor, said inner conductor having two sections of diiferent diameters and of approximately the same length conductively coupled together at only one of their adjacent ends, the larger diameter section being folded back over the smaller diameter section, and a metallic bellows at the conductively coupled end of said larger diameter section, said bellows being directly connected to and effectively increasing the length of said larger diameter section.

11. A tuned circuit comprising inner and outer conductors, said inner conductor having two sections, an inductive and a capacitive section, the whole tuned circuit resonating at the desired frequency in the manner of a parallel resonance circuit, said capacitive section extending over substantially the entire length of said inductive section, said inner conductor being short and having only such length as is necessary to provide an input impedance to match the impedance of an associated input circuit.

12. A folded, concentric resonant line comprising an outer cylindrical conductor and a central conductor, a mechanical and electrical connection between said conductors at one of their adjacent ends, and an intermediate cylindrical conductor constructed and arranged to be mechanically and electrically coupled to the other end of said central conductor, said intermediate conductor being so constructed and arranged as to surround substantially the entire length of said central conductor and extending substantially parallel to said central conductor.

13. A resonant line comprising an outer conductor and a concentric central conductor electrically coupled together at one end, an intermediate concentric conductor electrically coupled to one of said first two conductors at its other end, said intermediate conductor being so constructed and arranged as to surround the greater part of the length of said central conductor, and means for magnetically coupling a utilization circuit to a conductor of said line at a place of greatest current flow in said conductor.

14. An oscillatory circuit comprising a coaxial line resonator having an inner and an outer conductor, means for coupling said two conductors together at one end to constitute a tuned circuit, said inner conductor of said tuned circuit having two sections of different diameters conductively coupled together end to end, the larger diameter section being folded back over the smaller diameter section, and a coaxial conductor located between the two diameter sections of inner conductor and coupled to said outer conductor at said one end for increasing the capacity between said inner and outer conductors.

15. A tuning device comprising a pair of condoctors disposed one within the other, the inner conductor of said pair having two sections of different diameters and of substantially equal length, the larger diameter section being secured to the smaller diameter section and folded back over said smaller diameter section.

16. A tuning device comprising a pair of conductors disposed one within the other, the inner conductor of said pair having two sections of difierent diameters and of substantially equal length, the larger diameter section being secured to the smaller diameter section and folded back over said smaller diameter section, and a hollow conductor located between said two sections of inner conductor and coupled at one end to said outer conductor of said pair.

17. A resonant line comprising an outer conductor and a concentric central conductor electrically coupled together at one end, and an intermediate concentric conductor electrically coupled to one of said first two conductors at its other end, said intermediate conductor being so constructed and arranged as to surround substantially the entire length of said central conductor, and means for coupling a utilization cirtially the major portion of the length of the inner conductor of said pair.

19. A concentric resonant line comprising an outer cylindrical conductor and a central conductor, a mechanical and electrical connection between said conductors at one of their adjacent ends, and an intermediate cylindrical conductor constructed and arranged to be mechanically and electrically coupled to the other end of said central conductor, said intermediate conductor being so constructed and arranged as to surround substantially the entire length of said central conductor and extending substantially parallel to said central conductor, and frequency adjusting means connected to the other end of said outer conductor.

JAMES W. CONKLIN.

Images