US2662937A - Coaxial line resonator electron discharge device arrangement - Google Patents

Description

Patented Dec. 15, 1953 UNITED STATE ATENT OFFICE- COAXIAL LINE RESONATOR ELECTRON DISCHARGE DEVICE ARRANGEMENT Application March 5, 1949, Serial No. 79,867

3 Claims.

This invention relates to coaxial line resonator electron discharge device arrangement and is particularly directed to circuits for amplifiers and/or oscillators operable in the microwave range.

The input and output circuits of electron discharge devices which handle centimeter waves have heretofore been painstakenly isolated to prevent interaction, separate paths for either degenerative or regenerative feed back energy being carefully designed. The frequency of operation of such circuits cannot be easily shifted, and cannot be changed from amplification to oscillation without physical changes in the structure.

An object of this invention is improved circuit apparatus for generation or amplification of high frequency energy.

A more specific object of this invention is circuit apparatus that may be used without structural changes for either generation or amplification of high frequency energy, and that, as a generator or amplifier, may be easily tuned to any frequency over a wide range of frequencies.

In accordance with this invention, a three element vacuum tube with external terminals for each electrode is provided with two tunable transmission lines preferably of the coaxial type, the outer cylindrical conductors of each being joined at an angle at one end and in open internal communication. The joined ends of the cylindrical conductors are coupled at a radio frequencyto one of the electrode terminals, preferably the anode terminal. The internal coaxial conductors of the two lines are connected, respectively, to

the other two electrode terminals and a reciproin cable short-circuiting plunger in each line is moved to a position from the terminals approximately an odd number of quarter wavelengths at the desired operating frequency. Not only may the frequency of operation be selected, but a choice may be made between stable amplification and oscillation, merely by movement of the plungers.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent, and the invention itself will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing wherein:

Fig. 1 is a cross-sectional View of coaxial transmission lines as applied to this invention, and

Fig. 2 is a diagram of the important radio frequency circuits of the apparatus of Fig. l.

The electron discharge device l, is a triode and may be any one of a number of commercial types.

Because the bands of frequencies contemplated for operation of the device of this invention may extend into the centimeter range, the vacuum tube selected should have low interelectrode capacities, short transit time, and low lead impedances. The vacuum tubes commercially known as the 2C39 and 2C37. perform well up to and beyond 3000 megacycles and, structurally, are well adapted to this invention. The anode terminal 2, grid terminal 3; and cathode terminal 4 are annular, are concentric, and are axially spaced, the anode terminal for the particular tube shown, being the largest in diameter. The terminals are hermetically joined by glass cylinders, and the cathode terminal comprises double contacts to receive the low voltage heater current for the cathode.

The high frequency circuits of this invention may be resolved, as shown in Fig. 2, into a cathode-coupled, or so called cathode follower, circuit. The anod is grounded for radio frequency through the capacity 5, the cathode is isolated from ground by the reactance Xe of tank circuit 5, and the grid-to-ground impedance Xg is constituted by a tank circuit, I, so that the cathode potential is free to follow changes in grid potential.

The tank circuits 6 and l comprise tunable transmission lines, as shown in Fig. 1, with coaxial inner and outer conductors. The outer conductors 8 and 9 are straight metal cylinders and g are joined at one end, at right angles the interiors of the cylinders being in open communication.

The tank circuits 6 and l comprise coaxial line resonators isolated from each other electrically by being placed at right angles instead of being isolated as is customary with a metallic shield. This arrangement permits the construction of a plate to grid line togetherwith a plate to cathode line. The diameter of the cylinder 8 is large enough to receive the vacuum tube l with sufficient clearance to accommodate a band 5 of insulating material and. a bracelet ID of spring fingers l i between the wall of the insulating ma terial 5 and the annular anode terminal 2. The centerline of the cylinder 9 is so placed that the end of the inner conductor I2 is opposite the grid terminal ring 3 when the vacuum tube is in place. The inner conductor 13 is aligned and coaxial with the cathode terminal. The cathode terminal contains within its end an additional contact l4 insulated for the low voltage ofthe cathode heater circuit.

To couple the grid for radio frequencies to the center conductor I2, a condenser I5 is installed in the inner end of the conductor. Such a condenser may conveniently comprise a coil of insulated wire or aninsulated metal sleeve dimen- 3 sioned to have the desired capacity with the wall of the inner conductor. Grid biassing potentials may be applied through a high ohmage re sistor It, also located within the inner conductor if desired.

The length of the lines enclosed by the inner and outer conductors of each transmission line is adjusted by the sliding short circuiting pistons l1 and [B so that the resonant frequency of the lines may be adjusted by reciprocation of the piston rods shown. Since the transmission line conductors are insulated from the direct current potentials of the anode and grid, the radio-freouency short-circuiting pistons need not be insulated for direct current in the conductors. High frequency energy may be removed from the line of line 6 by a loop I9 connected as shown to a coaxial line 20. The loop is part of the shortcircuiting piston i1 where the R. F. current is high. This position of the loop is desirable so that for a given settingo! the piston, maximum output current may beselected. This arrange ment of the loops provides the plungers with unrestricted travel while maintaining input and output loops at optimum coupling points. Where the device is to be used as an amplifier, the input 100p 2| is added to the grid cavity.

Operation may best be understood by reference again to Fig. 2. The reactances Xg and X represent the combined parallel canacitances and inductances in the grid and cathode circuits offered, respectively, by the coaxial transm ssion lines I and 6. For simplicity the interelectrode capacities between the grid and plate, and between the cathode and plate are considered combined in parallel with the capacities of the lines. It is understood of course that the reactances of a transmission line, unlike condensers and coils, cannot be represented in circuit diagrams by lumped capacities and inductances because the sign of impedance presented at the end of the line depends on the frequency of energy in the line. The impedance may, for example, be an effective capacitance, inductance, or resistance merely by tuning the line to a frequency above, below, or equal to the frequency of applied energy.

These facts contribute importantly to this invention, as will appear. Since the impedance Xe of the cathode circuit is common to both the input and output circuits of the vacuum tube. energy is fed back into the grid circuit from the plate circuit. Now, whether this feedback energy is degenerative or regenerative, and whether the tube will function as an amplifier or an oscillator, will depend on whether reactance Xe is negative or positive, or more precisely, whether Xe is capacitive or inductive. Selection of capacitive or inductive reactance at X0 is conveniently determined by tuning the transmission line 6 to a frequency above or below the applied frequency. If, for example, transmission line 6 is tuned by moving the shortcircuiting plunger to a position slightly less than wavelength, the line will appear as a condenser in the cathode circuit and the tube will oscillate. If, however, the plunger is moved out slightly beyond wavelength, the line will appear as inductance and the tube will function only as a stable amplifier. In either case the grid-anode circuit 1 including the reactance X;

and the input capacities of the tube must. resonate at the desired frequency. :Tuning the input to resonance is but a matter of slidin plunger l8 to the proper position. High impeddevices to prevent oscillations.

the case with which the output may be ad The output is taken from a broad band low imance may be obtained at the input end of any short-circuited transmission line when the length of the line is any odd number of quarter wavelengths. The 2, wavelength is mentioned because of the convenient size of apparatus in the 10 centimeter band. Similar results may be obtained with an open circuited. line an even number quarter wavelengths long.

As an oscillator, an important advantage of this invention is the complete absence of any special feedback provision. The transmission lines are easily constructed and in a short time can be adjusted to oscillate at any desired frequency. The usual cut-and-try method of adjusting amplitude and phase of feedback energy involving time and considerable expense is entirely obviated. Similarly, as an amplifier the principal advantage of the device of this invention is the absence of any added neutralizing An added advantage in both oscillator and amplifier use is JStECl.

pedance circuit instead of the usual high impedance circuit which requires a large and critical impedance stepdown.

While there has been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of this invention.

What is claimed is:

1. An electron discharge device arrangement comprising a pair of coaxial line resonators opening into each other and extending at right angles to each other so that their electrical fields at said opening are at right angles and do not interact, each of said resonators including an inner and outer conductor and each resonator being closed at its outer end, means for injecting R. F. energy into one of said resonators and means for taking out R. F. energy from the other of said resonators, an electron discharge device extending into one of said line resonators within its outer conductor at the point where said resonators open into each other without closing the opening therebetween, said electron discharge device having at least three electrodes one of which is coupled to the outer conductors of both resonators, the other two electrodes being separately coupled to different ones of the inner conductors.

2. An arrangement according to claim 1 wherein said electrodes comprise an anode, cathode and grid, said grid being coupled to one of said inner conductors and one of the other electrodes being coupled to the other of said inner conductors, the remaining electrode being coupled to both outer conductors of said resonators.

3. An arrangement according to claim 2 where in said anode is coupled to the outer conductors and the cathode is coupled to said other inner conductor.

ALEXANDER. HORVATH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,223,835 Smith Dec. 3, 1940 2,283,568 Ohl May 19, 1942 2,421,591 Bailey June 3, 1947 2,451,825 Guarrera Oct. 19, 194-3 2,535,039 Charchian Dec. 26, 1950

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