US2945122A - Crystal rectifier tube - Google Patents

Description

July 12, 1960 D. A. LANCIANI 2,945,122

CRYSTAL RECTIFIER TUBE Filed Oct. 11, 1955 INVE DANIEL A. LA .Nl

BY Ha n37, i /w I I, I

ATTORNEYS CRYSTAL RECTIFIER TUBE Daniel A. Lanciani, West Medford, Mass, assignor to Microwave Associates, Inc., Boston, Mass a corporation of Massachusetts Filed on. 1-1, 1955, Ser. No. 539,786 *6 Claims. 01. 250-41 The subject invention relates to a mixer crystal rectifier tube and particularly to a rectifier crystal tube for coupling a rectangular wave guide to a rectifier crystal in the millimeter Wave length region.

Mixer crystal rectifiers designed for thelower microwave frequencies and of a convenient size and shape have been constructed for use with both coaxial and wave guide mounting arrangements. As the Wave length decreases below one centimeter, however, it has been found impractical to scale down the traditional coaxial designs. for example, the 1N53 type of crystal coaxial cartridge for l centimeter use is limited to an inner diameter of .045 inch and an outer conductor diameter of .125 inch in order that the cut-olfwave length of the next higher mode (TE11) in the coaxial section would be substantially less than on the lowest anticipated operating wave length. This provided a resulting cut-off wave length for the cartridge of .635 centimeter which was well below the expected operating range for that design.

However, application of the same considerations in the 4 millimeter region results in inner and outer conductor diameter of .023 inch and .063 inch respectively. These dimensions are obviously too small to be practical. It has therefore proved necessary to design new types of wave guide mounted crystals for rectifier use in the millimeter region. One such device'has been suggested by Dr. G. C. Southworth in-his book, Principles and Applications of Wave Guide Transmission, Van Nostrand Co., New York, 1950 on page 653 (chapter 12). In this design the crystal is mountedin a cylindrical metal housing or cartridge which couples to the rectangular guide through a hole in the side of the cylindrical housing. An adjustable plunger on one side of the cavity in the cylindrical housing carries the crystal and a whisker projects across the opening to the crystal.

It is the object of this invention to provide an improved and more easily manufactured millimeter rectifier tube of convenient size and a construction which may be readily assembled. V

It is a feature of this invention that it utilizes a hollow metallic cylinder or cartridge to house the rectifier, said cartridge being adapted to propagate the TE-ll mode of round wave guide, together with an inner circular to coaxial transition assembly which feeds energy to the whisker silicon junction. 7 A further feature of this invention is the use of a dielectric end seal adjacent the rectangular wave guide to which this assembly is mounted. This dielectric seal functions as a matching transformer between the rectangular guide and the cartridge whereby the position of the remaining RF portions of the rectifier are rendered more or less independent of their distance from the junction. It is a still further feature of this invention that it provides improved and simplified means for RF choking and capacitive bypassing of the IF output lead.

erence to the following figures:

Fig. 1 illustrates a cut-away elevation of the entire rectifier tube assembly.

Fig. 2 is a cross-section through the case and retaining shell showing the poistioning key.

Fig. 3 shows the dominant TEIO mode configuration in a rectangular wave guide.

Fig. 4 shows the dominant TEll mode in a circular wave guide.

Fig. 5 shows the electric field configuration in the vicinity of the converting fin.

As illustrated by reference to Figs. 1 and 2 this invent-ion utilizes a cylindrical case or cartridge 10 appropriately mounted to an opening 11 in a rectangular wave guide section 12 As illustrated the cartridge is mounted coaxially with the rectangular guide but it would also be appropriate to mount the device on the side of a rectangular section having a tuning end plunger. For convenience the case 110 is held by a cylindrical shell 13 having an end flange 15 which is fastened to the end flange of the rectangular guide. The other end of the shell carries a bayonet structure 23 to matewith a standard BNC connector thereby joining a coaxial line to the output end of the crystal tube. Thus the tube is a shielded separable insert which may be easily replaced a if the crystal should burn out. The bayonet connector tends to press the tube into firm contact with the waveguide end. The key 14 projecting from the inside of the shell .fits into the slot 17 in the case thereby aligning the case, including in particular the mode converting fin to be described later, with respect tothe TElO mode in the rectangular guide. I

While direct coupling is shown between the endof the rectangular guide and the end of the case, a quarterwave choke coupling may under some circumstances be desirable. The key and slot structure would tend to interfere with the operation of such a choke joint if located near the center of the top or bottom of the rectangular guide. Therefore this 'structure'may in some cases be located at the side where the electric fieldis at a minimum. To assure proper alignment of the shell and key the pin 19 on the shell is fitted to the hole 21 in the I end flange of the rectangular guide.

The dielectric plug 16 is fitted to the end of the case or cartridge 10 adjacent the junction with the rectangular wave guide 12. It is the function of this plug to act as a moisture-sealing window and at the same time to serve as a junction matching device. If this dielectric plug were made to have an eifective length of one-half wave length, the window would be refiectioiiless within the circular wave guide portion of the case 10 adjacent the rectangular guard. However, the RF impedance mismatch created by the junction would then have'to be compensated with proper dimensioning of the remaining whisker silicon geometry. This would have the critical disadvantage'of requiring these rectifying elements to be precisely located a specified distance from the junction and in addition the relatively large distance between the junction reflection and the compensating reflection of the whisker would tend to make the unit frequency sensithe TE-ll mode in the circular guide 10. V In the 4 millimeter region this dimension should be accurate to within .001". In addition the plug element 16 is designed to have a characteristic impedance which is the geometric mean between the impedance of the rectangular wave T1118 invention will be more easily understood by refguide 112 and the circular wave guide element or section 10. Described mathematically where Z is the impedance of the filled circular guide V 3 and Z and Z; the impedances of the air filled rectangular and circular guides respectively. The wave length of dielectric filled circular guide may be closely approximated bymultiplying the wave length in air filled circular guide where K is the dielectric constant. For use inthe. millimeter wave region, it has been found that Teflon having a dielectric constant of approximately 2.15 is an ap-.

propriate material to lower the impedance of the circular- -To connect the circular wave guide section to the silicon junction an additional transition element 18 in the form of a circular to coaxial transition fin is utilized. This fin is mounted for ease of assembly in a cylindrical conductive section 2%) which may be press-fitted into the cylindrical interior of case 10 to appropriately position the fin 18 with respect to the plug 16. To provide a compact design, the fin is positioned adjacent to the plug 16 and the conductive cylinder 20 is rotated in position about the axis of the tube 10 to appropriately align fin 18 with respect to the TElO mode propagating in the rectangular guide 12. Since the cartridge is a separable unit the fin is actually oriented with respect to the aligning element 14 on the exterior of the case 10 so that upon assembly with the rectangular wave guide the fin will be appropriately oriented.

slab having parallel sides, a front face sloping upward away from the front of the cartridge at an angle of approximately with the axis and having a substantially vertical rear face in the same plane as the end of the cylindrical supporting section 20. The pure silicon wafer is mounted on a raised boss projecting on the order of ,52" from the rear face of the fin 18 on the axis of the tube 10. It has been found that a circular to ooaxial transition of this type is substantially more efficient 7 11 from the silicondiode, particularly during assembly. h

This spacer is preferably of thin material to avoid interfering with the coupling between the whisker and the cavity surrounding it. 'The spacer may be of metal .provided that it is not thick enough to short out the plunger 28 to the case 10.

4 of theinsulating material 26. The capacitance between the surface of the plunger and the inner wall of the case is designed to be approximately seven microfarads for 4 millimeter operation.

The plunger 28 is cylindrical and has a cylindrical internally threaded opening 34. A metal pin preferably in the form of two sections 36 and 38 are threaded to fit this opening. The threaded pin 36 carries on its forward end the whisker 40 having a sharpened point which makes contact with the silicon wafer. The whisker 4-0 has a bent center section in the form of a helical spring which prevents the pressure on the upper point against the wafer to beadjusted without any tendency for the point to slide ofi its location on the axis of the case 10. The pressure of this contact is adjusted by rotating the pin 36 to screw it into the cavity 34 the required distance. A slot 42 is provided in the back of this pin to facilitate this adjustment. When this adjustment has been made the second section of the pin 38 is screwed into the cavity and serves to lock the first pin in position. This second pin 38 projects backward into the rear section of the cylindrical housing pin to provide a suitable IF output connection.

In operation the above described millimeter wave rectifier operates as follows. Microwave power propagating in the rectangular wave guide 12 in the form of energy in the dominant TElO mode as illustrated in Fig. 3 is efiiciently transformed with the aid of the dielectric matching window 16 into the TEll mode operating the forward part of the circular cartridge 10, as illustrated by reference to Fig. 4. This circular TEll mode is thereafter intensified in the center of the case by the coupling loop in the form of a triangular fin 18.

The electric field intensity and distribution is shown approximately in Fig. 5. Coupling between the RF field and the junction is accomplished in the cavity surr0unding the whisker. The intense field in the region of the p f fin tends to bend parallel to the whisker after passing The fin 18 is preferably in the form of a triangular away from the transition fin. While the mode configuration is complex and the mode is not purely coaxial in form it is similar to coaxial propagation and the fin may be convenientlydesignated asa circular to coaxial transition fin. The propagation of RF power into the IF output section is blocked by theoperation of the flangechokingelement 28 which isformed as an integral part of the IF output.

While the presently preferred embodiment utilizes the above-described coupling loop in which the silicon wafer is mounted to thetransition fin and the whisker to the pin, it would he obviously possible to' reverse this arrangement and mount the whisker to the fin and the silicon' wafer on the pin. Such an arrangement would in crease the'displacement of the silicon from the trailing edge of the transition fin and this displacement has already proven effective in improving performance at some frequencies. The entire device may be easily assembled since all of the parts are in the form of cylindrical elements which may be fitted to the inside of the cylindrical Adjacent and abutting this spacer is the cylindrical intween the front face of the first flanges and the inner.

cylindrical surface ofthe groove iseifectivelyone-half wave lehg'th; taking into account the dielectric constant case and the case 10 in turn is groovedto permit appropriate alignment of the fin 18 with respect to the rectangular wave guide 12. a

While this invention has been described with respect to a single embodiment it will be understood that the exact construction, of the invention may be varied by those skilled in the art Without departing from the scope of this invention as described in the following claims.

I claim:

1. A crystal millimeter rectifier mounting device for use witha rectangular waveguide comprising a cartridge having a cylindrical central opening adjacent the rectangular guideand in sequence thereafter, a cylindrical ,di electric sealing element matching the circular wave guide impedanceto that-of the rectangular guide, a circular to coaxial tfansforming fin conductively mounted to said cartridge, an axially mounted crystal-whisker assembly,

, one element of which is conductively mounted to said fin and the other element of which is electrically isolated from the cartridge, and connecting means for the IF crystal output.

2. A crystal rectifier mounting comprising a rectangular wave guide having an opening, a sealed cylindrical case having a dielectric sealing window adjacentthe rectangular wave guide opening to establish a circular mode of propagation in the cylindrical case, a circular mode to coaxial mode transition fin conductively mounted to said case adjacent the dielectric window, a rectifying crystal mounted to the trailing edge of said fin, a cylindrical insulating sleeve supported on said case facing said trailing edge of the fin, a pin mounted in said sleeve, a whisker mounted on the forward end of said pin and in contact with the crystal, and keying means for mounting the cylindrical case to the rectangular guide whereby the fin is oriented with respect to the dominant mode in the rectangular guide.

. 3. A crystal wave guide rectifier cartridge for use with a rectangular wave guide having an aperture and propagating the TElO mode comprising a cylindrical case having an open end in which the related circular TEll mode will propagate, means for mounting the open end of said case in the aperture, a sealing cylindrical dielectric plug in the case adjacent the aperture having an effective length of substantially one-fourth wave length and having a characteristic impedance adapted to match the impedance of the two wave guides, a circular to coaxial coupling loop conductively attached to said case and oriented parallel to the dominantelectrical mode in the cylindrical case, a silicon-whisker assembly mounted along the axis of the case one element of which is mounted in the coupling loop and the other of which is mounted on a conductive pin displaced from said loop and insulated from the case.

4. A very high frequency crystal rectifier mounting for use with rectangular waveguides comprising a conductive circular case, means adapted for mounting said circular case on a rectangular wave guide, a dielectric sealing window adjacent the rectangular guide having a characteristic impedance between that of the rectangular and circular guides whereby the end seal acts as a matching transformer, a circular to coaxial transformer fin of substantially triangular shape mounted in the case parallel to the short sides of the rectangular guide and having a forward face slanting backward from the side of the case and a substantially vertical rear face, a crystal mounted on said rear face at the axis of said circular case, an insulating sleeve supported on said case facing said rear face of said transformer fin, a conductive choke element mounted in said sleeve, a pin movably mounted in said choke for adjustment along the axis and projecting backward into the open end of the case to provide a coaxial output connector, and a whisker connecting the end of said pin and the crystal.

5. A wave guide mounted rectifier cartridge comprising a cylindrical case, a dielectric sealing impedance matching cylindrical plug effectively one-fourth wave length long in the end of said case, a substantially triangular circular to coaxial transforming fin adjacentsaid dielectric plug, a rectifying crystal mounted to said fin, a cylindrical insulating sleeve supported on said case facing said fin on the side opposite of said plug, a cylindrically conductive choke element mounted in said sleeve, a first pin threaded to said choke for adjustment along the axis of the case, a whisker on said pin in contact with the crystal across a cavity to the rear of the fin and a second pin threaded to said choke projecting backward into the open end of said case whereby rotation of the second pin will lock the first pin in position.

6. A millimeter wave crystal rectifier for use with a rectangular wave guide having an opening comprising a circular cartridge having a diameter at least equal to the largest diagonal dimension of the rectangular wave guide, means for mounting said cartridge over the opening in the rectangular wave guide, a moisture sealing transformer coupling dielectric window in the cartridge adjacent the rectangular wave guide having an effective length of approximately one quarter the wave length of the dominant mode in the dielectric filled cartridge and having an impedance characteristic approximating the geometric mean of the impedances of the rectangular wave guide and the circular cartridge whereby the remaining RF portions of the rectifier mounting are rendered substantially independent of their distances from the junc tion between the rectangular guide and the cartridge, a silicon rectifier element, a circular wave guide to coaxial wave guide transition element for coupling microwave energy from the circular wave guide in the form of a triangular fin having parallel sides, a front edge slanting a move the whisker along the axis, said choke section having appropriately dimensional flanges, and a cylindrical dielectric sealing spacer to insulate the choke and the pin from the cartridge wall.

References Cited in the file of this patent UNITED STATES PATENTS 2,734,170 Engelmann et al. Feb. 7, 1956

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