US2431762A - Balanced ultra high frequency generator - Google Patents

Description

Dec. 2, 1947. L, R, MA| |NG I I 2,431,762

BALANCED ULTRA-HIGH-FREQUENGY GENERATOR Filed March 23, 1944 3 0 Lin-lig o Symmmry Fl G@ Fewer Output INVENTOR LEV!) R. my@ BY Patented Dc. 2, 1947 UNITED STATES PATENT OFFICE BALANCED ULTRA mon FREQUENCY GENERATORA Leonard R. Malling, San Diego. Calif., assigner, by mesne assignments, to Hazeltine Research, I nc., Chicago, Ill., a. corporation of Illinois Application March 23, 1944, Serial No. 527,753

11 Claims.

This invention relates to balanced ultrahigh-frequency oscillation generator tunable over tuning the generator over a prescribed range of operating frequencies. A source of space current is applied to the anode electrode of the oscillator tube through one oi the conductors oi the line, being isolated from the controll electrode thereof by means of a suitable blocking condenser which is generally incorporated in the short-circuiting member.

The operating frequency range of such a generator is determined by the allowable travel of the short-circuiting member, the highest obtainable frequency being realized when this member is advanced along the line as tar as possible in the direction of the oscillator tube. The value of this highest obtainable frequency is determined by the distributed parameters of the line and the anode-control electrode capacitance of the oscillator tube which constitutes a loading effect at the electrode terminals of the line. Where a wide operating frequency range is desired, the oscillation generator may also be provided with a second effectively resonant transmission line which is coupled to the oscillator l tube and tunable "in the manner described. In

this case, the lines are tuned together and an increased range of operating frequencies results since the loading eiiect for each line contributed by the interelectrode capacitance ofthe oscillator tube is approximately one-half that of the singleline arrangement. Such oscillation generators,

since they include a single oscillator tube, are

capable of delivering but a limited amount of power. Additionally, it is difoult to construct blockingl condensers which have suitable electrical characteristics at ultra-high frequencies and can electrodes and a second effectively .resonant transmission line coupled between their control electrodes. members for tuning which are 'such that the generator is of the tuned-plate tuned-grid type. While these arrangements provide an increased power output as compared with that of the single-tube oscillation generators mentioned aboveI they have a limited range of operating frequencies due to the loading effect contributed to the electrode-terxninal portions of the transmission lines by the interelectrode.capacitance of the oscillator tubes. Furthermore, in view of the tuning difficulties presented, it has not been considered expedient to double the line arrangement in order to reduce this loading effect, thereby to increase the operating frequency range of such generators.

It is an object of the invention, therefore, to provide an improved balanced ultra-high-frequency oscillation generator which is tunable over a predetermined range of operating frequencies and which avoids one or more of the above-mentioned limitations of prior art arrangements.

It is another object of the invention to provide an improved balanced ultra=high-frequency oscillation generator which is tuiiable over a relatively wide range of operating frequencies. y

It isistill a further object of the invention tio provide a balanced ultra-high-frequencw oscillation generator tunable over a predetermined range of operating frequencies and having an iinproved stability characteristic.

In accordance with the invention, a balanced ultra-high-frequency oscillation generator tunable over a predetermined range of operating frequencies comprises a pair of vacuum tubes individually having anode and control electrodes. The generator includes a i'lrstv balanced transmis? sion line comprising a pair of open conductors individually directly coupled to corresponding electrodes of the vacuum tubes and including adjustable tuning means which constitute therewith i a frequency-adjusting circuit for tuning the generator over the aforesaidrange of operating frequencies. The generator further includes a second balanced transmission line4 comprising a pair of conductors individually directly coupled to the other corresponding electrodes of the vacuum tubes and extending therefrom in the same direction as the rst-mentioned line. The second line has a resonant frequency outside of the range of operating frequencies of the generator and is electrically coupled tothe first lineI for substantially all adjustments oi the tuning means The lines include short-circuitingV for transferring energy from the first to the second line to sustain oscillations.

'In the specific application of the, invention to be described hereinafter, a balanced ultra-highfrequency oscillation generator including a frequency-determining circuit and a pair of vacuum tubes individually having anode, cathode and control electrodes comprises a pair of short-circuited transmission lines. Each of the lines has an effective electrical length substantially equal to an integral multiple of a quarter-wave length at a predetermined operating frequency of the generator and each line comprises a pair of open conductors individually coupled to corresponding electrodes of the vacuum tubes. The frequencydetermining circuit has at the aforementioned operating frequency a desired mode of resonance in which the currents in vcorresponding portions of the conductors of each of the lines are in phase opposition and the lines are included in an additional circuit whichhas an undesired Inode of resonance in which the currents in corresponding portions of the conductors are in phase. The generator includes means for so loading the lastnamed circuit that the undesired mode of resonance occurs at a predetermined frequency substantially. different from the aforementioned operating frequency of the generator.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection .with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a schematic circuit diagram of a balanced ultra-high-frequency oscillation generator embodying the present invention; Fig. 2 is a schematic circuit diagram which is electrically equivalent to the circuit of Fig. 1; Figs. 3a and 3b are additional schematic circuit diagrams utilized in describing an operating characteristic of the Fig. 1 arrangement; while Fig. 4 comprises a graph representing the power output-frequency characteristic of the oscillation generator represented in Fig. 1.

Referring now more particularly' to Fig. 1 of the drawing, there is represented a balanced ultra-high-frequency oscillation generator tunable over a prescribed wide range of operating frequencies and embodying the present invention. The generator includes a pair of vacuum tubes I and `II individually having anode, cathode and control electrodes. The generator also includes a first plurality of balanced transmission lines individually directly coupled to corresponding electrodes of each of the vacuum tubes. Specifically, one transmission line vcomprising a pair of open parallel conductors I2, I3 is directly coupled to the anode electrodes of tubes I0 and II, respectively, while another transmission line comprising a pair of open parallel conductors I4, I5 is similarly coupled to the anode electrodes of the vacuum tubes. The conductors of each such line have uniformly distributed inductance and capacitance and the lines are symmetrically disposed with reference to the vacuum tubes, extending therefrom in opposite directions, as represented in the drawing. This relationship of lines I2, I3 and I4, I5 may be described as a feed-through arrangement since conductors I4 Aand I5 may be considered effectively to comprise extensions of conductors I2 and I3, respectively. Adjustable short-circuiting elements .I6 and I1 are included, respectively, in lines I2, I3 and I4. I5 andare arranged to frequencies.

The generator further includes a second plurality of balanced transmission lines corresponding in number with the first-described plurality and individually directly coupled to other corresponding electrodes of tubes I0, II. In particular, one transmission line comprising a; pair of open conductors I8, I9 is directly coupled to the control electrodes of the vacuum tubes, While another transmission line comprising a pair of open conductors 20, 2l is similarly coupled to the control electrodes of the tubes. The con ductors of lines I8, I9 and 20, 2I have uniformly distributed inductance and capacitance and their physical arrangement with reference to tubes I0 and II is substantially the same as that described in connection with lines I2, I3 and I4, I5. In other Words, as represented in the drawing, corresponding ones of the described first and second plurality of lines extend from the tubes in the same direction. Each of lines I8, I9 and 20, 2I'is proportioned to have an effective electrical length equal to an integral multiple of a quarter-wave length at a predetermined operating frequency outside of, and preferably above, the range of operating frequencies of the generator. That is to say, each such line has a resonant frequency which lies above the range of operating frequencies of the generator. This proportioning of the electrical lengths of lines I8, I9 and ZIl, 2|, as well as their physical relationship with reference to lines I2, I3 and I4, I5, is effective electrically to couple corresponding ones of v.I'l of line I4, I5.

the rst and second pluralities of lines for substantially all adjustments of the tuning means I 6, I'i for transferring energy from the first to the second plurality of lines in order to sustain oscillations. 'As an aid to this coupling, line I8, I9 includes an inverted or reversed loop portion 22 which is magnetically coupled to short-circuiting element I8 of line I2, I3 for substantially all adjustments. of the short-circuiting element, while line 2li, 2I includes a reversed loop portion 23 magnetically coupled to short-circuiting element These loop portions are inverted so that the energy transferred between the lines has the proper polarity for sustaining oscillations.

The cathodes of tubes I0 and II are of the directly-heated type and have a pair of cathode leads which connect to a source of heater voltage, as indicated by the arrows. The mid-point of the cathode of tube I0 is coupled to ground through a radio-frequency choke 30. Condensers 3| and 32 are provided to maintain substantially the same radio-frequency potential at both cath- A trol electrodes of the vacuum tubes are grounded through a radio-frequency choke 4I and a grid resistor 42. an adjustable condenser 43 is coupled between the short-circuited terminals of transmission line I4, I5 and ground for a purpose to be described fully hereinafter. An output signal is obtained from the generator by means of a pick-up loop 5I) which is electrically coupled to transmission line I4, I5. This output signal may be supplied to a suitable utilizing circuit, such as an antenna system 5I, by way of a coaxial cable 52 which couples the antenna to pick-up loop 50. The antenna circuit is tunable through an adjustable condenser 53.

In considering the operation of the described arrangement, it will be understood that shortcircuit-ing elements I E and i 'I are adjusted to have substantially identical positions with reference to their associated transmission lines. For any given adjustment of these short-circuiting elements, transmission lines I2, I3 and I4, I5 individually comprise an effectively resonant Vtransmission line having an effective electrical length which is preferably equal to a quarter-wave length corresponding to a predetermined operating frequency of the oscillation generator. As is well known from transmission-line theory, any effectively resonant transmission line having such an effective electrical length exhibits the impedance characteristics of a parallel resonant circuit. Therefore, each short-circuiting element with its associated transmission line provides a frequency-adjusting circuit for the generator, the frequency-adjusting circuit provided by each such line and its short-circuiting element having the same operating or resonant frequency. The particular value of this operating frequency is determined by: (1) the position of the short-circuiting element which determines the effective .electrical length of the line; (2) the distributed parameters of the line; and (3) the terminating impedance of the line which, for the case under consideration, comprises substantially one-haiil the interelectrode capacitance of the anode and cathode electrodes of vacuum tubes I and II since lines I2, I3 and I4, I5 are arranged in a parallel relationship with reference to these electrodes. Additionally, for any given adjustment of the short-circuiting elements IB and I'I, transmission lines I8, I9 and 2U, 2| have a resonant frequency which is above the operating frequency of the generator. For this reason, lines I3, I3 and 2li, 2l effectively comprise inductive reactances which are electrically coupled to lines I2, I3 and I4, I5 to provide the requisite feed-back voltage for sustaining oscillations. 'Ihe coupling between these lines utilized for transferring feed-back lenergy is contributed largely by the loop portions 22 and 23 since these loop portions are magnetically coupled with the short-circuiting elements of transmission lines I2, I3 and I4, I5 where there is a current maximum under stabilized oscillating conditions.

From the foregoing discussion it will be evident that the schematic circuit diagram of Fig. 2 is the electrical equivalent of the Fig. 1 arrangement. In this equivalent circuit the distributed inductance of transmission lines I2, I3-and I4, I5 is represented by the lumped inductance L, while the distributed capacitance thereof and the anode-cathode interelectrode capacitance of tubes i0- and II are represented by the lumped capacitance C. Transmission lines I8, I 9 and 20, 2|, which have been described as presenting an inductive reactance for any given adjustment of the short-circuiting elements I6 and I1, are represented by the inductance L1 having a mutual coupling M with the inductance L. The circuit arrangement of Fig. 2 will be recognized as a conventional push-pull type oscillation generator, the operation of which is well understood in the art so that a description thereof is unnecessary. For tuning the oscillation generator over its range of operating frequencies, the inductance and capacitance of its frequency-adjusting circuit are simultaneously adjustable, as indicated in Fig. 2, through short-circuiting elements I6 and I'I which are effective, respectively, to adjust the effective electrical lengths of transmission lines I2, I3 and I4, I5 to integral multiples of a quarter-wave length corresponding to a desired operating frequency.

Willie a balanced oscillation generator of the type under consideration has satisfactory stability characteristics when constructed of lumped parameters, an unstable operating condition is possible when the generator employs transmission lines arranged in a feed-through manner, as represented in Fig. 1'. This unstable operating condition may be attributed to a parasitic mode of resonance of the transmission lines which comprise the frequency-adjusting circultof the gcnerator and will be described with particular reference to the sketches of Figs. 3a and 3b.

The diagram of. Fig. 3a represents the frequency-adjusting circuit of the generator provided by the short-circuited effectively resonant transmission lines I2, I3 and I4, I5 for a particular operating condition. This circuit is repre-"" sented as having, at the particular operating frequency of the generator, a desired mode of resonance in which voltage r. *.xima occur at the anode electrodes. as represented by the polarity indications, and in which current maxima occur at the short-circuited terminals of each transmission line. The current distribution along the lines is such that the current in corresponding portions of the conductors of each line is in phase opposition. This current relationship is indicated by the arrows. In this, the desired mode of resonance, the frequency-adjusting circuit has an axis of electrical symmetry which corresponds to that of the generator and the resonant frequency varies with adjustments of short-circuiting elements I6 and I'I.

The condition represented in Fig. 3b is an unde-.

sponding portions of the conductors of each line are in phase. For this mode of resonance the circuit is symmetrical about an axis which is pei'- pendicular to the axis of electrical symmetry of the generator. When this undesired mode of resonance occurs, conductors I2 and I4 are effectively in parallel with conductors I3 and I5 in a circuit which is completed through ground by way of the condensers C', shown in broken-line construction since they comprise the inherent capacitance to ground at the short-circuited terminals oi.' the transmission lines. It may be shown to a rst .approximation that the frequency of this undesiredmode of resonance is independent of the position of short-circuiting elements I6 and I 1.

Where the desired and the undesired mode of resonance appear at the same operating frequency of the generator, the power output is seriously reduced because the circuit exhibiting the unde-- sired mode of resonance acts as a load on the generator and absorbs a large portion of the power. In accordance with the invention, condenser 43 is coupled to transmission line I4, I5

' as well as the described geometrical relationship for the purpose of so loading the circuit arrangement represented by the diagram of Fig.. b that the undesired mode of resonance occurs at a predetermined frequency which is substantially different from any desired operating frequency of the generator. The frequency-adjusting circuit has a voltage minima at the short-circuited terminals of the transmission lines so that coupling the loading condenser 43 at this point has substantially no effect on the operating frequency of the frequency-adjusting circuit.

The power output-frequency characteristic of the oscillation generator of Fig. 1 is represented by the full-line curve of Fig. 4. In this figure, the frequency designations f1 and f2 represent the lower and upper limits, respectively, of the desired operating frequency range of the oscillation generator. Over this range the power output has a substantially constant value. The loading effect of condenser 43 causes the reduced power output, resulting from the aforedescribed undesired mode resonance, to occur at a frequency f4 outside of the desired range. In absence of this loading feature, a reduced power output may occur at some frequency fa within the desired operating frequency range.

A balanced ultra-high frequency oscillation generator in accordance with the present invention will be seen to have a relatively wide range of operating frequencies by virtue of the feedthrough line arrangement utilized as the frequency-'adjusting circuit. Furthermore, the arrangement is characterized by an improved n stability and produces a substantially constant power output at all operating frequencies within4 the desired Wide range.

Where an unusually wide operating range is not required, it will be apparent that a single balanced transmission linemay be coupled to the anode electrodes of tubes I0 and and a single balanced transmission line may likewise be coupled to the control electrodes thereof. In any case, the transmission lines may have any of a variety of shapes. It is only necessary that the lines be so shaped and arranged that there is an electrical coupling between the lines connected to the anode electrodes and those connected to the control electrodes of the vacuum tubes for the purpose of providing a voltage feed-back path.

Oscillation generators constructed in accordance with the invention and arranged for operation at very high frequencies may include transmission lines of relatively short physical lengths. In particular, lines I8, I9 and 20, 2| have progressively shorter physical lengths for higher operating frequencies of the generator. In the extreme case, these lines have the physical appearance of a single-turn inductor and, in such a. case, the inductor leads may be considered to comprise the open conductors of a transmission line. Furthermore, while lines I8, I9 and 20, 2| include In this alternative form of the invention, the

described effective electrical length of these lines with reference to that of lines I2, I3 and I4, I5,

of such lines, aords sufiicient feedback to sustain oscillations.

It will be understood that the loading reactance, consisting of condenser 43, may be distributed and applied to the short-circuited terminals of each of transmission lines I2, I3 and I4, I5 instead of being coupled to a single line in the manner represented in Fig. 1.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modications may be made therein without departing from the invention, and itis, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A balanced ultra-high-frequency oscillation generation tunable over a predetermined range of operating frequencies comprising, a pair of vacuum tubes individually having anode and control electrodes, a first balanced transmission line' comprising a pair of open conductors individually directly coupled to correspondence electrodes of said tubes, adjustable tuning means included in said line and constituting therewith a frequencyadjusting circuit for tuning said generator over said range of operating frequencies, and a second balanced transmission line comprising a pair of conductors individually directly coupled to the other corresponding electrodes of said tubes and extending therefrom in the same direction as said first line, said second line having a resonant frequency outside of said range of operating frequencies and being electrically coupled to said first line for substantially all adjustments of said tuning means for transferring energy from said first to said second line to sustain oscillations.

2. A balanced ultra-high-frequency oscillation generator tunable over a predetermined range of operating frequencies comprising, a pair of vacuum tubes individually having anode and controlelectrodes, a first balanced transmission line comprising a pair of open parallel conductors individually directly coupled to corresponding electrodes of said tubes, adjustable tuning means included in said line and constituting therewith a frequency-adjusting circuit for tuning said generator over said range of operating frequencies, and a second balanced transmission line comprising a pair of conductors individually directly coupled to the other corresponding electrodes of said tubes and extending therefrom in the same direction as said first line, said second line having a resonant frequency outside of said range of operating frequencies and being electrically coupled to said rst line for substantially all adjustments of said tuning means for transferring energy from said first to said second line to sustain oscillations.

3. A balanced ultra-high-frequency oscillation generator tunable over a predetermined range of operating frequencies comprising, a pair of vacuum tubes individually having anode and control electrodes, a first balanced transmission line comprising a Pair of open conductors individually directly coupled to said anode electrodes of said tubes, adjustable tuning means included in said line and constituting therewith a frequencyadjusting circuit for tuning said generator over said range of operating frequencies, and av second balanced transmission line comprising a pair of conductors individually directly coupled to said control electrodes of said tubes and extending therefrom in the same direction as said first line, said second line having a resonant frequency outside of said range of operating frequencies and being electrically coupled to said first line for substantially all adjustments of said tuning means for transferring energy from said first to said second line to sustain oscillations.

4. A balanced ultra-high-frequency oscillation generator tunable over a predetermined fange of operating frequencies comprising, a pair of vacuum tubes individually having anode and coni trol electrodes, a rst balanced transmission line said range of operating frequencies, and a second comprising a pair of open conductors individually directly coupled to corresponding electrodes ,of said tubes, adjustable shortcircuiting means included in said line and constituting therewith a frequency-adjusting circuit fortuning said generator over said range of operating frequencies, and a'second balanced transmission line compris-e ing a pair of conductors individually directly coupled to the other corresponding electrodes of l said tubes and extending therefrom in the same direction as said rst line, said second line having a resonant frequency outside of said range of operating frequencies and being electrically coupled to saidrst line Afor substantially all adjustments of said short-circuiting means for transferring energy from said rst to said second line to sustain oscillations.

5. A balanced ultra-high-frequency oscillation generator tunable over a predetermined range of operating frequencies comprising, a pair of vacuum tubes individually having anode and control electrodes, a first balanced transmission line comprising a pair of open conductors individually directly coupled to corresponding electrodes of said tubes, adjustable tuning means included in said line and constituting therewith a frequencyadjusting circuit for tuning said generator over balanced transmission line comprising a pair of conductors individuallydirectly coupled to the other corresponding electrodes of said tubes Aand extending therefrom in the same direction as vsaid first line, said second line having an effective of operating frequencies comprising, a pair of vacuum tubes individually having anode and control electrodes, a first balanced transmission line comprising a pair of open conductors individually directly coupled to corresponding electrodes of said tubes, adjustable tuning means included in -said line and constituting therewith a frequencyadjusting circuit for tuning said generator over said range of operating frequencies, anda second balanced transmission line comprising a pair of conductors individually directly coupled to the other corresponding electrodes of said tubes and extending therefrom in the same direction as said `llrst line, said second line having an effective electrical length equal to an integral multiple of a quarter-Wave length at a predetermined frequency'above said range of operating frequencies and being electrically coupled to said rst line for substantially all adjustments of said tuning l0 means for transferring energy from said rst to said second line to sustain oscillations.

7. A balanced ultra-high-frequency oscillation generator tunable over a predetermined range of operating frequencies comprising, a. pair of vacuum tubes individually having anode and control electrodes, a first balanced transmission line comprising a, pair of open conductors individually directly coupled to corresponding electrodes of said tubes', adjustable tuning means included in said line and constituting therewith a frequency-adjusting circuit for tuning said generator over said range of operating frequencies, and a second balanced transmission line comprising a pair of conductors individually directly coupled to the other corresponding electrodes of said tubes and ex..

` tending therefrom in the same direction as said first line, said second line having a resonant fre- `quency outside of said range of operating frequencies and including a loop portionl which is electrically coupled to said rst line for substantially" all adjustments of said tuning means for transferring energy from said rst to said second line to sustain oscillations.

8. A balanced ultra-high-frequency oscillation generator tunable over a predetermined range of operating frequencies comprising, a pair of vacuum tubes individually having anode and control electrodes, a rst balanced transmission line comprising a pair of open conductors individually directly coupled to corresponding electrodes of said tubes, adjustable short-circuiting means included in said line and constituting therewith a frequency-adjusting circuit for tuning said gener- 'ator over said range of operating frequencies, and

a second balanced transmission line comprising a pair of conductors individually directly coupled to the other corresponding electrodes of said tubes and extending therefrom in the same direc-v generator tunable over a predetermined range of operating frequencies comprising, a pair of vacuum tubes individually having anode and control electrodes, a first balanced transmission line comprising a pair of open'conductprs individually directly coupled to corresponding electrodes of said tubes, adjustable tuning means including in said line and constituting therewith a frequency-adjusting circuit for tuning said generator over said range of operating frequencies, and a second balanced transmission line comprising a pair of conductors individually directly coupled to the other corresponding electrodes of said tubes and extending therefrom in the same direction as said first line, said second line having a resonant frequency outside of said range of operating frequencies and including a reversed loop portion which is electrically coupled to said rst line for substantially all adjustments of said tuning means for transferring energy from said first to said second line to sustain oscillations.

10. A balanced ultra-highffrequency oscillation generator tunable over a predetermined range of operating frequencies comprising, a pair of vacuum tubes individually having anode and control electrodes, a first plurality of balanced transmission lines each comprising a pair of open conductors individually directly coupled to corresponding electrodes of said tubes, adjustable tuning means included in said rst plurality of lines and constituting therewith a frequency-ad justing circuit for tuning said generator over said range of operating frequencies, and a second plurality of balanced transmission lines corresponding in number with said first-named plurality and each extending therefrom in th`e same direction as a corresponding one of said first-named plurality of lines and each comprising a pair of conductors individually directly coupled to the other corresponding electrodes of said tubes. said second plurality of lines individually having a resonant frequency outside of said range of operating frequencies and being electrically coupled to a corresponding one of said rst plurality of linesfor substantially all adjustments of said tuning means for transferring energy from said first to said second plurality of lines to sustain oscillations.

11. A balanced ultra-high-frequency oscillation generator tunable over a predetermined range of operating frequencies comprising, a pair of vacuum tubes individually having anode and control electrodes, a` ilrst pair of balanced transmission lines each comprising a pair of open conductors individually directly coupled to correspending electrodes of said tubes, adjustable tunoperating frequencies, and a second pair ofbalanced transmission lines each comprising a pair of conductors individually directly coupled to the other corresponding electrodes of said tubes and each extending therefrom in the same direction as respective ones of said rst-named pair ci lines, said second pair of lines individually having a resonant frequency outside of said range of operating frequencies and each being electrically coupled to a corresponding one of said first pair of lines for substantially all adjustments of said tuning means for transferring energy from said first to said second pair of lines to sustain oscillations.

LEONARD R. MALLING.

REFERENCES CITED The following references are of record in the file of this patent:

Switzerland Mar. 16, 1937

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