US2408420A - Frequency multiplier - Google Patents

Description

Oct. l, 1946. E. u... GINZTON 2,408A2 FREQUENCY MULTIPLIER Filed Jan. 13, 1944 3 Sheets-Shea?, l

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FREQUENCY MULTIPLIER Filed Jan. 13, 1944 3 Sheets-Sheet 2 Patented Oct. l, 1946 UNITED STATES PATENT OFFICE to Sperry Gyroscope Company,

tion of New York Inc., a. corpora- Application January 13, 1944, Serial No. `518,054

21 Claims.

The present application relates to wave transmission apparatus and concerns particularly apparatus suitable for use in microwave systems.

An object of the invention is to provide methods and apparatus for frequency multiplication, particularly arrangements suitable for use in the microwave frequency spectrum.

A specific object of the invention is to provide' a frequency doubler, and another object of the invention is to provide a frequency tripler.

Still another object of the invention is to provide a mixer multiplier.

It is an object of the invention to provide a stable crystal multiplier and to provide a multiplier having high eiciency at high frequency.

A further object of the invention is to provide methods and apparatus for avoiding burn-out of crystal multipliers.

Still another object of the invention is to provide a push-pull arrangement for improving the characteristics of crystals used for frequency multiplication.

Other and further objects and advantages will become apparent as the description proceeds.

In carrying out the invention in its preferred form, a pair of joined transmission lines is employed or a single transmission line is provided with input and output sections designed for different frequencies. Non-linear circuit means such as rectifying crystal means, for example, are interposed in one of the transmission lines designed for the lower frequency and serving as the input transmission line, or transmission line section. The output transmission line, or transmission line section, is coupled to the input transmission line, or transmission line section, and is preferably arranged to cut-olf energy having a wavelength longer than the desired wavelength, in order to insure that the output frequency is substantially a pure harmonic of the input frequency.

A better understanding of the invention will 'be afforded by the following detailed description considered in conjunction with the accompanying drawings, in which Fig. l is a side view, mainly in longitudinal section, of a frequency doubler;

Fig. 2 is another side view of the apparatus of Fig. l turned 90 from the position shown in Fig. 1;

Fig. 3 is a side view, mainly in longitudinal section, of a frequency tripler;

Fig. 4 is a fragmentary view of the apparatus of Fig. 3 including an output end view of the transmission line;

Fig. 5 is a longitudinal sectional view of a mixer multiplier;

Fig. 6 is a bottom view of the apparatus of Fig. 5;

Fig. 7 is a graph illustrating the characteristics of a square-law crystal rectifier of the type which may be employed in the apparatus of Figs. 1 to 6; and

Fig. 8 is a graph illustrating the composite characteristics of push-pull connected crystal rectilers employed in the apparatus of Figs. 3 and 4.

Like reference characters are utilized throughout the drawings to designate like parts.

The frequency multiplier illustrated inthe Figs. 1 and 2, comprises a transmission line II and a lateral transmission line I2 joined to the transmission line II. In the arrangement as illustrated, the transmission line II is designed to receive the input or lower frequency, and the transmission line I2 is designed for supplying the output frequency, e. g. an even harmonic such as double frequency. As shown, the fundamental frequency transmission line II may be of the coaxial or concentric line type assumed to be circular in cross-section and the double frequency or second harmonic transmission line I2 may be of the wave guide type, shown in this case as a rectangular Wave guide. To facilitate making the requisite circuit connections to the transmission line I I, an input transmission line i3 maybe provided for supplying the input energy, for example, ultra high frequency electromagnetic Wave energy having a wavelength of approximately 10 centimeters in case a 5-centimeter wavelength output is desired.

The line II includes outer hollow cylinders I4 and I5 and an inner conducting rod i6. The outer hollow cylinders Il and I5 are joined to and extend laterally above and below the upper and lower surfaces oi the rectangular wave guide i2, which have suitable openings for receiving the hollow cylinders I4 and I5. The inner rod I6 extends through the wave guide I2 and on either side thereof.

For producing the desired second harmonic in the output, a. non-linear circuit element I1 is interposed in the transmission line II, for example, in series with the inner conductor rod I6.`

In order to facilitate the mounting and replacement of the non-linear element Il, the hollow cylinder I4 and the rod I6 may be jointed so as to have physically separable portions I8 and I9,`= respectively. A conventional threaded coupling 21 is provided for joining the hollow cylindrical of a crystal rectier unit of the type employed in v microwave and other ultra high frequency radio receiving systemator rectifyfing, detecting, or demodulating ultra, high frequency energy. It

is shown as a standard unit incased in a cylinder 22 with a downwardly extending pin terminal 28 and an upper flat contact terminal 2d. The rod it is provided with a socket at the upper end to receive the pin terminal 28 and the rod i 9 is provided with the contact button 25 at the lower end to make contact with the crystal terminal 2Q.

The input line i3 may also be a conventional coaxial line, including an outer cylinder 2G elec trically and mechanically joined to the cylinder i8, and an inner conducting rod 2l electrically and mechanically connect/ed to the inner cona battery di? may be provided which is electrically connected in series with the nonlinear crystal element ill. For example, the battery 2@ may be provided with conductors 3i electrically connected to the inner rod it and the outer cylinder i 5, the later being electrically connected, in turn, to the wave guide i2, the outer cylinder ifi, the outer cylinder id and the inner conducting rod i 9. The coupling 2i serves to connect the h'ollow cylinders ill and it electrically aswell as mechanically, and the rod i@ and the cylinder it are electrically connected at their upper ends.

For the purpose of tuning the transmission line li and preventing reflections resulting in a high 'standing wave ratio, adjustable high frequency snorting plugs. or tuning elements 32 and 823 are provided. The tuning element 32 comprises an adjusting knob or handle 8G to which is secured a plug or annulus 35 of suitable conducting material, such as brass, which' makes electrical contact with both the outer cylinder i@ and the inner rod i9. Pins 3b may be provided which are rigidly secured to the plug 85 and are slidably retained within an annular slot 3l yin the knob 8d. The knob 3Q may be formed as a hurled ringnut and the outer surface ofthe cylinder i8 may be threaded for engagement by the nut 3G. The cylinder it is provided with slots 38 on both sides to receive th'e pins 80.

The lower tuning element 88 maybe similarly constructed except that it includes a snorting plug 35' having an inner part ii making electrical contact with the rod it, an outer part l2 making electrical contact with the hollow cylinder ib, and a thin insulating band i3 oi' suitable low loss material, such as polystyrene tape, separating the parts (Si and l2 so as to form a condenser, the plates of which are the confronting surfaces of the members @i and ft2. Such' a condenser serves as a high frequency short with' respect to the alternating current input, but serves to insulate the rod i@ from the outer conductor i in order to provide a direct current circuit.

for the biasing battery 29 and the crystal rectifier Il.

Suitable means are also provided for tuning the portion 4G of the wave guide i2, shown to the left oi the transmission line ii position plug 45, uijustably mounted by means of a screw t6 having a supporting block el and formed as a quarter-wave trap spaced from the inner surfaces of th'e wave guide i2.

A Such means ,may take the form of a conventional adjustable The portion d8 of the wave guide i2 extending f to the right of the transmission line ii is broken away in Fig. 1 to simplify the drawings, but it will be understood that suitable connections by conventional choke couplings or the like, may be made between the output end is of the wave guide i2 and apparatus to which second harB monic wave energy is to be supplied.

The conversion of the fundamental frequency energy supplied through the transmission line i3 to thedouble frequency or second harmonic wave energy leaving the wave guide from the output end i8 results from the lacls of linearity between voltage input and current output of the crystal rectifier il.

The characteristic curve of such a crystal rectier of the square-law type is shown in Fig. '7 in which current is measured along the vertical axis and voltage is measured along the horizontal axis. The magnitude of the biasing voltage in the battery 2@ is so chosen as to accentuate th'e second harmonic. The exact amount of bias required will depend upon the individual crystal employed, and the type of crystal, lit is known, for example, that silicon crystal rectiers and germanium crystal rectiiiers have opposite types of characteristic curves, one being of the type which bends upward as shown in Fig. 7, so that the crystal is operated near the heel of the curve, and the other being of the type which droops or bends downwardly so that the crystal is operated near the mee of the curve.

`When the triple harmonic of the fundamental frequency is desired, a crystal multiplier may also be employed and the dimensions of the output transmission line may be so chosen as to cut o' the undesired lower frequencies, such as the fundamental frequency and the second harmonic, passing only the thirdl harmonic. However, in order to increase the eiiciency of the apparatus and avoid wearing out the crystal, when an odd harmonic is desired I prefer to employ a pushpull connection with two oppositely connected crystals, by means of which the second harmonic is inherently suppressed. For example, as illus trated in Fig. 3, a transmission line iii vmay be employed having an input end 52 to which iundamental frequency energy is supplied, and an' output end at which an harmonic output is obtained.

The input portion of the line 5i is arranged as a double concentric circular transmission line with an inner concentric line 56 and an outer hollow'cylindrical conductor 55, concentric with the line et. The latter is adapted to be cone .nected by conventional couplings to a similar type of concentric line (not shown) from which the input energy is received. The coaxial line Ed in- 'cludes a hollow cylinder Et and 'an inner conducting rod el. The outer hollow cylinder t5 is tapered, as shown at 58, toward a point 59 at sions oi which are so chosen that its cut on? wavelength is slightly longer than the desired harmonic, for instance, the third harmonic of the energy supplied through the input concentric line il. For example, the line 54 may be designed for 10 centimeter input and the wave guide output section 63 may be designed for 3.5 centimeters cut-ofi. For tuning the input end of the concentric line 5I, a conventional slidable shorting plug 6| is provided, which includes an annulus 62 of conducting material making electrical contact with both the outer hollowfcylinder 55 and the hollow cylinder 56.

For introducing the odd harmonic, a pair of nonlinear elements, such as crystal rectiiiers 63 is provided/ For supporting the crystal rectifiers 63 and enabling direct current bias connections to be made thereto, a pair of lateral coaxial lines 6I is provided, extending above and below the transmission line 5i. The lines 64 may be similar in construction, each including an outer hollow cylindrical conductor 65 and an inner conducting rod 66. In order to provide for removability f the crystal rectifier 63, the outer cylinder 65 is removably attached to the outer conductor 55 of the transmission line 5i. For example, a hollow projection 61 may be formed in the surface of the conductor 55 with the inside threaded to receive the lower exteriorly threaded end 68 of the hollow cylinder 65. For; tuning the line 64, a short-ing plug 33 may be provided similar to that described in connection with Fig, 1, or the shorting plug may include a single conducting hollow annulus 35 with a thin cylinder 69 of non-conducting material insulating the inner surface of the annulus 35 from the rod 66, so as to form a high frequency short, but preserve direct current insulation.

For making direct current connections the outer end of the line 64 is formed as a pin and socket connector including an outer screw threaded contact 14 electrically connected to the outer oonductor I8 and a concentric pin contact 12 electrically connected to the conducting rod B6. For supporting the pin 12 in the outer end of the rod 66, an insulating bushing 13 is provided, and the annulus plug 35 serves to support the intermediate portion of the rod 66.

For supporting the crystals 63 laterally, insulating bushings 14 are provided, and for coupling the input end of the transmission line i to the transmission lines 64, a transverse internal conductor rod 15 is provided which is concentric with the transmission lines 64 forming a continuation of the inner rods 66, that is electrically and mechanically connected to the inner rod 51 of the transmission lines 54 and 5i. The upper and lower ends of the rod 1'5 are drilled to form sockets for receiving the pin contacts of the crystal rectilers 63 and the inner ends of the rod 66 are provided with contact buttons, as previously described, to make electrical contact with the crystal rectifier 63.

It will be understood that the portion of the lower transmission line 6E, which has been broken away, is shown as turned 90 in Fig. 3, in order to show the slot 38 for receiving the pins 36.

The crystal rectifier 63 may be of the same type as represented by the crystal rectifier I1 of Fig. i, except that one of the crystal rectifiers 63 is mounted in a non-standard position; that is, with reversed polarity. Biasing batteries (not shown) are connected to the upper and lower direct current contacts 1i and 12 for biasing the rectiers 63 and the polarities of the biasing voltage are made oppositely with respect to the inner conlductor-s 86, so that each rectifier is biased in the same manner with respect to its own polarity.

Referring to Fig. 7, a third harmonic compo- 5 nent of relatively great strength may be obtained from a square law crystal rectifier by a sufficiently large biasing voltage in the reverse (negative) direction so that the natural boundary layer is brlgn down and current flows in the reverse directior along the curve 11. The magnitude of the bias is such that the crystal operates around a voltage, represented by the vertical dotted line 18. The crystal is then forced to operate along the reversed portion 11 of its characteristic curve which has a relatively large third degree curvature. In order to avoid the necessity for care in preventing the crystal from being burned out and to increase stability two opposed crystals may be employed.

By employing two crystals of opposite polarity connected in push-pull, a stable third harmonic component of considerable strength is obtained. The composite push-pull characteristic curve is shown in Fig. 8. By selecting biasing voltages equalling the distances between the vertical axis I and the vertical lines 18 and 19, an inner portion of the characteristic curve between the lines 18 and 19 is effectively eliminated, and each crystal tends to operate with respect to one or the other of the lines 18 and 19 and the combination operates as if it had a characteristic curve represented by the curve lines 6I and 82, joined at the points 83 and 8l.

If it is desired to mix or heterodyne one input circuit with another of a harmonic frequency, this may be done by employing a combination mixer multiplier, as illustrated in Fig. 5, for example. In this case, the fundamental frequency of a high frequency circuit, such as a three centimeter circuit, may be heterodyned With the third harmonic of a lower frequency input such as a 9 centimeter circuit. To this end, as shown in Fig. 5, an input wave guide 85, an input adjustable coaxial transmission line 86, and a coupling transmission line 81 may be employed, including a crystal rectifier element 88 for generating the third harmonic of the wave supplied through the coaxial line 86. For supplying the heterodyned output, a coaxial transmission line output coupling 89 may be provided.

The interconnecting transmission line 81 includes an. outer hollow conductor 9i, an inner cylindrical conductor 92, a suita-ble adjustable snorting `stub device 93 for tuning, a contact de vice 94 for making an electrical connection with the upper or ilat 'contact of the crystal rectifier 88. As shown, the inner conductor 92 is of relatively large diameter in comparison with the outer cylinder 9i and a narrow rod 95 is provided for joining the lower end of the conductor 92 to the crystal contact Sii. The input coaxial transmission line 86 includes an outer hollow cylindricai conductor 91 and an inner conductor 98. For tuning purposes the outer conductor 91 may bc in the form of a telescoping tube. For coupling' the transmission line 86 to the transmission line 81 a lV-probe 99 mounted within the cylinder 9i may be connected to the end of the inner conductor 96. The outer conductor 9i is removably 7o joined to the top surface of the wave guide 85.

by means of a suitatble threaded extension 6? such as described in connection with Fig. 3.

The output transmission line connection 89 includes a hollow cylindrical member lili electrically and mechanically joined to the lower surface of the wave guide 85, an insulating bushing |02 supporting a connector socket |03 and an internally flanged tubular or cup-shaped member |04, threaded into the member I| for supporting the insulator |02. The termina1 |03 has a drilled opening |05 at the upper end serving as a socketl contact for the lower pin terminal of the crystal rectifier 88 and has a connecting pin |06 extending downwardly through the insulator |02 and a suitable opening in the member |04. The member |0| is provided with flanges |01, thus forming with the pin or conductor rod |06, a suitable coupling of the type used for making connections with concentric transmission lines.

In order to avoid discontinuities in the wave guide 85, a. quarter-wave trap may be mounted around the socket terminal |05, spaced therefrom. Likewise, the contact mem-ber 94 may be provided with a tubular extension H2 forming a quarter-wave trap.

'I'he righthand end 0f the wave guide 85 is closed by a suitable plug |08 which may be made adjustable, if desired, but which need not be adjusted if initially properly positioned to terminate the wave guide for the frequency of its input. For matching the apparatus to the waveguide input, in order to avoid reflections and in order to obtain,minimum standing wave ratio, adjustable tuning probes |09 may be provided which consist of rods with a suitable axially adjustable circuit of a conventional type for fixing the extent to which the rod extends into the wave guide 85.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein forl the purpose of explaining its principle of operation and showing its application, but it will be obvious to those skilled in the art that many modifications and variations are possible, and Iv aim, therefore, to cover all such modifications and variations as fall within the scope of my invention which is'defined in the appended claims.

What is claimed is:

1. A microwave multiplier, comprising in combination a wave guide, a coaxial transmission line `joined transversely to said wave guide, but having an inner conductor extending through said wave guide, a crystal rectifier in series with said i inner conductor, and a connection for supplying fundamental frequency energy to said coaxial transmission line whereby a harmonic thereof is supplied to said Wave guide.

2. Apparatus as in claim 1 including a source of direct current bias in series with said crystal.

3. A frequency multiplier comprising in cbmbination, a transmission line with a fundamental frequency energy input connection and a harmonic energy output connection, transverse transmission lines joined to said first-mentioned transmission line, said last-mentioned transmission lines being of the coaxial type, each including a nonlinear circuit element and being coupled to the first-mentioned transmission line input.

4. A frequency multiplier comprising an electrically conducting member having a longitudinally extending conductor therein to form a coaxial input transmission line, and having an open portion forming a wave guide output transmission line, a pair of transverse transmission lines of coaxial type having inner conductors joined and extending through the first-mentioned conducting member, and electrically connected to the inner conductor of the input c0- axial transmission line, and non-linear circuit elements included in the inner conductors of the transverse transmission lines.

5. Apparatus as in the preceding claim including tuning adjustments for the coaxial 5 transmission lines.

6. A mixer multiplier, comprising in combination a high frequency input transmission line,

' a low frequency input transmission line, a transmission line connecting the two, and a hetero- 10 dyne output connection from said connecting transmission line, one ,of said lines including a nonlinear circuit element for introducing a harmonic of the input energy of the low frequency input transmission line.

7. A frequency tripler, comprising in combination an input transmission line designed for fundamental frequency input, an output transmission line coupled thereto, an interposed nonlinear circuit means for introducing harmonics, the output transmission line having such dimensions as to cut off wavelengths longer than the third harmonic of the fundamental frequency input.

8. A frequency'multiplier, comprising a hollow electrically conducting member having a longitudinally extending conductor therein to form a coaxial input transmission line, and having an /open portion forming a wave guide output transmission line, transverse transmission line means coupled to the input transmission line and nonlinear circuit means in said transverse transmission line means.

9. A mixer multiplier, comprising in combination a high frequency input transmission line, a low frequency input transmission line, interconnecting means extending therebetween, and nonlinear means in said interconnecting means for producing a, harmonic of the frequency supplied through the-low frequency input transmission line.

1 0. Apparatus as in the preceding claim, further including a heterodyne output connection for extracting heterodyne energy from said nonlinear means.

11. A microwave frequency multiplier comprising, in combination, a hollow pipe wave guide, a tubular conductor opening into said wave guide, a further conductor within said tubular conductor forming a coaxial transmission line therewith and extending transversely across said hollow pipe wave guide, a crystal rectifier connected y in series with said further conductor, means for supplying ultra high frequency energy to said crystal rectifier, and means for tuning said coaxial line to control the current distribution along the portion of said further conductor extending across said wave guide.

12. A microwave frequency multiplier comprising, in combination, a hollow pipe wave guide, 60 first and second tubular conductors connected to Vsaid wave guide and extending in opposite directions therefrom, a further conductor extending through said first tubular conductor, said wave guide and said second tubular conductor and forming with said tubular conductors, first and second coaxial transmission lines coupled to said.

wave guide, a crystal rectifier in series with said further conductor, means for applying to' said crystal rectifier ultra high frequency energy of a wavelength longer than the cut-off wavelength of said wave guide, movable means within said first coaxial line for providing an adjustable ultra high frequency energy conducting path between said first tubular conductor and said further conductor, and movable means within said second coaxial line for providing an adjustable ultra high frequency energy conducting path between said second tubular conductor and said further conductor.

13. A microwave frequency multiplier as dened in claim 12, further including means for applying direct bias voltage to said crystal rec'- tier for varying the operating characteristics thereof whereby the frequency multiplication efficiency of said frequency multiplier may be enhanced.

14. A microwavev frequency multiplier comprising a hollow pipe wave guide, first and second tubular conductors connected to said wave guide and extending in opposite directions therefrom, 'a further conductor extending through said first tubular conductor, said wave guide and said second tubular conductor and forming with said first and second tubular conductors, first and second coaxial transmission lines coupled to said wave guide, a first crystal rectifier positioned within said first tubular conductor and connected in series with said further conductor, a second crystal rectifier positioned within said second tubular conductor and connected in series with said further conductor, means for applying to said further conductor intermediate said first and second crystal rectifiers ultra high frequency energy of a wavelength longer than the cut-off wavelength of said wave guide, movable means in said first tubular conductor for providing an ultra high Vfrequency current path between said first tubular conductor and said further conductor, and movable means in said second tubular conductor for providing an ultra high frequency current path between said second tubular conductor and said further conductor.

15. A microwave frequency multiplier as defined in claim 14, further including means connected to said further conductor for applying direct bias potential to said crystal rectiiiers.

16. A microwave frequency multiplier comprising, in combination, a wave guide, a tubular conductor opening into said wave guide, a further conductor within said tubular wave guide forming a coaxial transmission line therewith and extending transversely across said wave guide, a crystal rectifier connected in series with said further conductor, means for supplying to said crystal rectifier ultra high frequency energy of a wavelength longer than the cut-off wavelength of said wave guide to produce harmonic currents in said transmission line, meansfor tuning said coaxial transmission line to regulate `the harmonic currents therein, and means for applying a'direct bias potential to said crystal rectifier for enhancing the harmonic operation thereof.

y 17. Apparatus as recited in claim 16, further including movable ultra high frequency current conducting means positioned within said coaxial transmissibn line for varying the ultra high frequency current distribution along said further conductor, whereby high intensity har- 10 monic energy coupling is provided between said further conductor and said wave guide.

18. A microwave frequency multiplier comprising a hollow pipe wave guide, a conductor extending transversely through said wave guide, tubular conducting means connected to said wave guide and forming an outer conductor for cooperation with said first conductor as a coaxial .transmission line, means for applying to said rst conductor ultra high frequency energy of a wavelength longer than the cut-off wavelength of said wave guide, a first crystal rectier connected in series with said conductor in a first current-carrying orientation, and` a second crystal rectifier connected in series with said conductor in an opposite current-carrying orientation for conduction of Acurrent during opposed half cycles of the applied ultra high frequency energy.

19. Ultra high frequency apparatus comprising first and second coaxial line elements connected together at a junction point, means for producing an ultra-high frequency potential difference between the inner conductors of said coaxial line elements and the outer conductors thereof at said junction point, and an energy utilization device coupled to said coaxial line elements at said junction point and responsive to ultra-high frequency currents in the inner conductors of said first and second coaxial line elements.

20. Ultra high frequency apparatus comprising first and second coaxial line elements connected together at a junction point, a third coaxial line joining said first and second coaxial line elements at said junction point, the inner conductor of said third coaxial line being connected to the inner conductors of said first and second coaxial line elements at said junction point, and a wave guide adjoining said first and second coaxial line elements at said junction point and coupled to the inner conductors thereof, whereby said wave guide is coupled to said third coaxial line through electromagnetic cou.

pling between said wave guide and the inner conductors of said rst and second coaxial line elements.

2l. Ultra high frequency apparatus comprising a hollow pipe wave guide having first and second openings therethrough, first and second tubular conductors connected to said wave guide vat said openings, a third conductor extending through said first tubular conductor, said wave guide and said second tubular conductor and forming first and second transmission lines with said first and second tubular conductors, and a fourth conductor connected to said third conductor at a point between said first and second transmission lines, whereby said fourth conductor is coupled to electromagnetic energy guided through said hollow pipe wave guide in accordance with the difference of impedance to current flow through said first and second transmission lines.

EDWARD L. GINZTON.

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