US3002155A - Microwave broadband crystal holder for cartridge type crystals - Google Patents

Description

Sept. 26, 1961 J. w. DEEs 3,002,155

MICROWAVE BROADBAND CRYSTAL HOLDER FOR CARTRIDGE TYPE CRYSTALS Filed March 2l, 1958 United States Patent O 3,002,155 MICROWAVE BROADBAND CRYSTAL HOLDER FOR CARTRIDGE TYPE CRYSTALS Julian W. Dees, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation Filed Mar. 21, 1958, Ser. No. 722,893 11 Claims. (Cl. 329-162) This invention relates generally to microwave transmission lines, and more particularly to a cartridge type crystal holder for use with a coaxial microwave transmission line.

In certain microwave receiving system, i-t has been customary to mount a cart-ridge type crystal detector concentrically within a coaxial transmission line, i.e., within the outer conductor and serially connected to the inner conductor of the line. Certain of these systems are required to operate over a very wide frequencyrange, i.e., for example 500 megacycles to 12,000 magacycles, however, to the best of the present applicants knowledge, coaxial crystal holders for cartridge type crystals have not been available which were capable of providing good tangential sensitivity over such a frequency range.' Furthermore, many such receiving systems require a direct current return path for the detected signal, i.e., rectified current passed by the crystal detector and to the best of the applicants knowledge, coaxial crystal holders have not been available with an internal direct current return path which would operate satisfactorily from 500 megacycles to 12,000 megacycles.

While various coaxial crystal holders for cartridge type r crystals for use with coaxial microwave transmission lines are presently available, it has been generally necessary to utilize several different holders to cover the range of frequencies from 500 megacycles to 12,000 megacycles in yorder to maintain reasonable sensitivities. Some crystal holders known to the applicant employ padding, or an intentionally introduced lossy network to reduce input VSWR (voltage standing wave ratio). However, in these crystal holders, the frequency range is limited by the characteristics of the lossy network and necessarilyV sacrifices sensitivity for frequency response or band width. In such crystal holders, the padding introduced can, depending upon the type employed, provide a direct current return path, however, in such cases the upper frequency response has been generally limited to about 3 or 4 throusand magacycles and the sensitivity of detection is reduced by the amount of the padding employed. Direct current return paths have also been provided in coaxial crystal holders by other methods, such as the employment of a short-circuited stub both as a tuning device and a direct current return; this method, however, necessarily provides narrow band performance. In addition,kcoaxial crystal holders have been provided with a tine straight wire connected between the center conductor and the outer conductor to provide the direct current return path, however, while this method provides excellent high frequency response, it cannot be used below about 3 or 4 thousand megacycles. f

'Ihere areV available coaxial crystal holders for the tripolar or coaxial type crystalsk which provide broadband operation from about yl0() megacycles to 12,400 megacycles, and with satisfactory sensitivity. Such crystals are, however, far more expensive than the cartridge type crystals and the sensitivity of such crystal holders is attributable to the crystal and not to the crystal holder construction. However, even such coaxial crystal holders for tripolar or coaxial crystals do not have an internal direct current return path; some tripolar crystals are provided with a fine straight wire direct current yreturn path or a coiled wire direct currentreturn, however, these arrangements are limited in operation down to about 1,000

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megacycles. With these exceptions, the direct current return path must be provided externally. v

It is therefore desirable to provide a coaxial crystal holder for cartridge type crystals which will provide broadband operation, i.e., wide band frequency response, for example, from l500 megacycles to.12,000 megacycles, without sacrificing sensitivity. It is of course necessary that such a crystal holder be capable of employment with presently commercially available standard cartridge-type crystals and it is further desirable ,that the arrangement provide good tracking characteristics as well as low crystal spread over the entire frequency band; crystal spread is a measure of the difference in output voltage obtained using a number of unselected crystals of the same type at any specified frequency, input power level and crystal load impedance, while tracking refers to the Vproperty of two or more unselected crystals of the same type to prov-ide the same output Nol-tage characteristic over the entire Ifrequency range. It is additionally desirable that such a broadband crystal holder provide an internal direct current return path which will operate satisfactorily down to at least 500 megacycles thereby eliminating the need to provide an external direct current return path in other circuit elements on the RF or input side of the crystal detector. Such a direct current return path must not interfere with the RF input signal, i.e., it must act as a very high RF shunt impedance, in order not to reflect- RF energygand thereby introduce undesirable signal loss into the system. l n

It is therefore a general object of this invention to provide an improved broadband coaxial microwave crystal holder for cartridge type crystals.

Another object of this invention is to provide an improved broadband coaxial crystal holder for cartridge type crystals incorporating an internal Vdirect current return path which will opera-te in a satisfactory manner down to at least 500 megacycles.

A further object of this invention is to provide an im proved broadband microwave crystal holder for cartridge type crystals in which the tracking properties and crystal spread rcharacteristics are improved rover those heretofore provided by prior crystal holders over a wide frequency range.

It is a specific object of my invention to provide an improved broadband crystal -holder for use with cartridge type crystals which will provide a tangential sensitivity in excess of -40 dbm` `from 500 megacycles to 12,000 megacycles and an output voltage in excess of ten vmillivolts atan input power level of -20 dbm using a crystal load impedance of from 5,000 to 10,000 ohms and a forward bias current of from ten to seventy microamperes over Vthe entire frequency range and using any number of unselected crystals of the same type. r

My invention, in its broader aspects, therefore, provides a coaxial microwave crystal holder for cartridge type crystals adapted to be connected to a coaxial microwave transmission line and having concentric inner and outer conductors with a crystal concentrically disposed within the outer conductor and serially connected with the inner conductor. The portion of the transmission line of which the crystal holder effectively forms a part has a first portion on the RF (radiofrequency) side of the crystal having a iirst characteristicimpedance and a second portion adjacent the crystal having a second characteristic impedance higher than the first characteristic impedance; I haveV found that increasing the characteristicv impedance adjacent the crystal increases the sensitivity of the device over the `desired wide frequency range which in turn improves'the crystal spread and the tracking characteristics. In the preferred" embodimentrof my invention, the outer conductor has a step for-med in its inner surface in general alignment `v`vith the RF terminal of the crystal cartridge, the step effectively dividing the outer conductor into a rst portion extending on the RF side of the crystal cartridge with a rst inside diameter thereby providing a first characteristic impedance, and a second portion ex tending in the opposite direction from the tirst portion and generally coextensive with the crystal cartridge, with its second inside diameter greater than the first inside diameter thereby providing a second characteristic impedance greater than the lirst characteristic impedance. An annular conductive member extends inwardly from the second portion of the outer conductor adjacent the step and having its center opening surrounding and spaced from the RF terminal of the crystal cartridge thereby providing a capacitive iris therewith.

In order to provide the direct current return path, in accordance with the broader aspects of my invention, I provide a at spiral conductor surrounding the inner conductor and having its inner end connected to the inner conductor on the RF side of the crystal and having its outer end connected to the outer conductor thereby providing high RF impedance and low direct current resistance. lIn the preferred embodiment of my invention, an annular member of insulating material is provided surrounding the portion of the inner conductor connected to the RF terminal of the crystal cartridge and extending outwardly to the rst portion ofthe outer conductor. A spiral conductor is supported on one side of the annular insulating material surrounding the inner conductor with its inner end connected thereto and its outer end connected to` the outer conductor.

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 drawings, wherein:

FIG. 1 is a side-elevational view, partly in section and partly broken away, illustrating a coaxial microwave crystal holder incorporating my invention;

FIG. 2 is an end view of the spiral direct current return path incorporated in FIG. 1;

FIG. 3 is a cross-sectional view of the spiral return path of FIG. 2 taken along the line 3-3;

FIG. 4 shows a simplified equivalent circuit for the device of FIG. l useful in explaining my invention;

FIG. 5 shows a plot of tangential sensitivity against frequency obtained with a crystal holder incorporating my invention; and

FIG. 6 is a plot showing voltage output against frequency obtained vtuth a crystal holder incorporating my invention.

Referring now to FIGS. 1, 2 and 3, my improved broadband crystal holder, generally identified as -1, includes at its RF or input end, a generally conventional type N connector 2 adapted to be connected to a coaxial transmission line. The connector 2 comprises an outer metallic sleeve portion 3 having internal threads 4 formed therein for securing the device to mating external threads on the connector of the associated coaxial transmission line. Sleeve portion 3 of connector 2 is rotatably connected to body portion 5 formed of any suitable conductive metal, such as silver plated brass. Body portion 5 has a cylindrical part 6 extending Within sleeve member 3 of connector 2 which terminates in a plurality of resilient segments 7 adapted to be inserted in a conventional type N connector, as is well known in the art. Body portion 5 has an enlarged cavity 8 formed therein communicating with the bore 23 of its cylindrical part 6 and a block of suitable insulating material such as polytetraflucroethylene (known by the Du Pont ltrademark Teflon) 9 is positioned in the cavity 8 and supports center pin I10 concentrically within the cylindricalfpart'.. The center pin 10, which may be made ofA any suitable conductive material, Such as beryllium cpper has an end portion 11 adapted to mate with a corresponding fem-ale 4 i portion of the center conductor of a type N connector; it will now be seen that the cylindrical part 6 of the body portion S and the coaxial center pin 10 respectively form the outer and inner conductors of a segment of coaxial transmission line. y

An essentially tubular member 12, likewise formed of any suitable conductive material, such as silver plated brass, is provided with body portion 5 being removably secured thereto, as by threaded connection 13 on the exterior surface of the tubular member 12. Center pin 10 has a portion 14 extending coaxially into tubular member 12 with suitable resilient fingers 15 formed on its end for engaging the pin terminal 16 of a suitable cartridgetype crystal detector 17.

Cartridge type crystal detector 17 conventionally has a generally cylindrical body portion @18, generally formed of ceramic material, with a metal sleeve portion 19 forming the other terminal. The metal sleeve portion 19 of the cartridge crystal 17 is supported coaxially Within the tubular member 12 by means of an annular insert member 2t) seated in a machined recess 21 in the bore of tubular member 12 with an annular sleeve 22 of suitable insulating material, such as nylon, separating the metal sleeve 19' and the annular insert member 20; the annular insert member 20, together with the insulating sleeve 22 and the metallic terminal 19, on the crystal detector 17, cooperate to form a capacitive connection between the terminal 19 and the tubular member 12, as will be hereinafter more fully described.

The inner surface of the tubular member 12 has a step 24 formed therein in general alignment with thc pin terminal 16 of crystal 17 and thus dividing the tubular member l12 into a rst section 25 and a second section 26.

It Will readily be seen that the section 25 of the tubular member 12 extends toward the RF end of the assembly and has a smaller inside diameter than does the other section 26 which extends generally coextensively with the crystal 17 and has a larger inside diameter thank the section 25. An annular conductive iris member 27 is provided seated within the section 26 of the tubular member 12 and preferably abutting the step 24. Annular member 27 has its central opening 28 coaxially surrounding and spaced from the resilient fingers 15 on the end 14 of the center pin 10, thus forming a capacitive connection therewith, which will be hereinafter more fully described. In assembling the tubular member 12 and the annular iris member 27 and annular insert member 20, which are all preferably formed of brass, the annular iris member 27 is rst inserted into the section y26 of the tubular member 12 and soldered into position abutting the step 24, the annular insert member 20' is then inserted into the recessed portion 21 and soldered in place, and theresulting assembly is then preferably silver plated as a unit.

Referring now to FIGS. 2 and 3 in addition to FIG. 1, my improved direct current return path comprises a flat annular or washer-shaped member 29 formed of suitable insulating material, such as an epoxy resin-glass laminate. Conductive rings 30 and 31 are respectively supported on one face of the member 29 adjacent the central opening 32 and outer periphery 33, these conductive rings 30 and 31 being interconnected by a spiral conductor 34 also supported on the face of the member 29, i.e., the spiral conductor 34 surrounds the central opening 32 and cou ductive ring 30` with its inner end connected thereto and with its outer end connected to the cuter conductive ring 31. The member 29 with the conductive lings 3GP and 31 and the spiral conductor 34 supported thereon may be yformed by one of the Well known printed circuit techniques. For example, the epoxy-glass laminated member 29 may be initially copper clad on one side, i.e., having a layer of copper deposited on one side. A photosensitive acid resist material is then applied to the copper surface and the same is then exposed to light, lgenerally ultraviolet, through a photographic negative ofthe deing, which hardens the portions of the photoresist mate-r rial which have been yexposed to light and the unexposed portions are then etched away, for example in a ferrie chloride bath, thereby leaving the desired conductive pattern on the surface of the member 29 as shown in FIGS. 2 and 3. Insulating member 29 with conductive rings 30 and 31 and the spiral conductor 34 supported thereon is positioned with center pin extending through the central opening 32 and with its portion 14 abutting the center conductive ring 30 and thus in electrical contact therewith, and with the end of tubular member 12v likewise vabutting the outer conductive ring 31 and therefore also in electrical contact therewith. While I have employed the photoetching process for producing the direct current return members described above, it will be readily understood that other printed circuit techniques well known in the art may be employed. It will be further understood that while in the particular embodiment shown, a spiral conductor 34 of about three turns was found to provide the desired high RF impedance and satisfactory operation down to at least 500 megacycles, satisfactory functioning at lower frequencies may beobtained by a suitable variation of the number of spiral vturns and the size of the spiral line.

In order to complete the assembly, another body portion 36 is provided formed of suitable conductive material, such as silver plated brass, and having a threading engagement, as at 37 with the tubular member 12. Body portion 36 defines a cavity 38 which is closed by a conductive member 39 threadingly engaged with corresponding internal threads at the end of the body portion 36, as at 40, and which has a cylindrical extension portion 41 forming a part of a conventional BNC connector. A center pin 42 is provided formed of suitable conductive material, such as beryllium copper, pin 42 being supported by suitable insulating material 43, such as polytetrofiuoroethelenewhich in turn is supported by means of the plug member 39 as shown. Center pin member 42 has, conventional resilient segments 44 formed at its end for engagement with a complementary center pin of a type BNC connector as is well known in the art. The electrical connection between the center pin 42 and the terminal19 of the crystal 17 is formed by a contact member 45 which is urged against terminal 19 of crystal cartridge 17 by means of a suitable coil spring 46, likewise formed of lsuitable conductive material such as beryllium copper; one end of spring 46 embraces a portion 47 of the contact member 45 and the other end embraces end 48 of the center pin 42, all within cavity 38 formed by body portion 36. A suitable annular or washer shaped member 49 formed of suitable insulating material, such as Teon, surrounds portion 47 of the contact member 45`and serves as a guide for the contact member 45 within the cavity 38.

In prior untuned arrangements of coaxial crystal holdes" for cartridge type crystals known to the applicant, it was found that the sensitivity fell off very rapidly above about 7,000 megacycles. The provision of the step 24 in the tubular member 12 thereby increasing the characteristic impedance of the coaxial line in the region of the crystal y cartridge, together with the provision of the capacitive mum improvement insensitivity is obtained by locating the step 24 adjacent the RF end of the crystal cartridge 17 and with the inside diameter of the portion 26 of the `tubular member 12 being on the order of ten percent greater than the insidek diameter of the portion 25. The

optimum position of the iris 27 and the diameter of its central opening 28 likewise was emperically determined since again, the applicant is unaware of any satisfactory method of calculation, however, it was yfound that the optimum position of the iris was at the same point along the coaxial input line as the step 24 and it is the applicants belief that an aperture 28 therein having a diameter approximately one-half the inside diameter of the portion 26 of tubular member 12 will provide generally satisfactory results. f

It will be understood that the stepped impedance providedby the step 24 is of such a nature that a higher coaxial line characteristicimpedance exists along the line `toward or closer to the crystal. In FIG. 4 there is showna simplified equivalent circuit for the device of FIG. 1, it being understood that FIG. 4 is not intended to portray an accurate equivalent circuit which could be freely subst-ituted for the device of FIG. 1. It will bev recalled that #lumped impedances, i.e., series inductance and shunt capacitance can generally be substituted for a coaxial transmission line and thus, in FIG. 4, the series induc tance identified as XL1 indicates the distributed inductance of the coaxial line to which the crystal'holder 1 is connected, XL2 identifies the distributed inductance of the portion of the line to the left of the step 24, i.e., that defined .by the portion 25 of the tubular member 12, and Xm identifies the higherdistributed inductance of the increased inside diameter portion 26. Likewise, the shunt capacitance identified as X61 indicates the distributed capacitance of the coaxial transmission line to the left of the step 24, the shunt capacitance identified as XZ indicates the shunt capacitance introduced by virtue of the step 24, andthe shunt capacitance XC3 indicates the shunt capacitance introduced by the iris member 27. It will also be seen that the shunt inductance XM in the spiral conductor 34 connected between the tubular member 12 and the center pin 10 provides a high RF impedance, vand a low direct current resistance return path' for the rectifiedy or detected current passed by the crystal 17. It will now be seen that the capacitor formed by the insulating sleeve 22 separating the terminal 19 of crystal cartridge 17 and the annular conductive member 20 forms an RF by-pass capacitor for by-passing any RF energy (or signal) which is passed by the crystal 17 to ground. It will be readily understood that the center pin 42 may be connected to the grid 50 of a suitable amplifier 51 with grid resistance 52 constituting the load impedance for the crystal 17. It will be further readily understood that employment of ya different type of crystal cartridge will introduce different geometry into the system and may necessitate suitable adjustment in the positioning of the step 24, the relative inside diameters of'the lsections 25 and 26, the location of the capacitive iris 27 and the proportioning of the center opening 28 therein. f

A crystal holder in accordance with FIG. l has been constructed for use with type MA-408A and 1N23C cartridge crystals. In this device, the tubular member 12 had a length of .955 inch with section 25 being .250 inch long and having an inside diameter of .375 inch and with portion 14 of center pin 10 having an outside diameter of .156 inch, thereby to provide an input characteristic impedancev of approximately 50'ohms. Portion 26 of the tubular member 12 was .505 inch long and had an n- `side diameter of .437 inch; iris 27 was .050 inch long with an inside diameter of .221 inch. The direct current return pathpmember 29 was photoetched on copper clad epoxy laminate .004 inch thick with the copper layer being .0014 inch thick, conductive rings 30 and 31 being respectively A020 and .095 inch wide and the spiral conductor 34 having approximately three turns .005 inch wide.

Referring' now to FIG. 5, there is shown a plot Voff' the tangential sensitivity characteristic of the coaxial microwave crystal holder described above, employing an MA-408A type crystal feeding a video amplifier having a bandwidth of,3.5 megacycles, the load resistor 52 having 10,000 ohms :and a bias of 50 microamperes being provided. It will be seen that in the frequency range from 500 to 12,000 megacycles, the tangential sensitivity is at fall times 'in excess of -40 dbm, actually varying between about 42.5 and -57 dbm. Likewise referring to FIG. .6 which is a plot of the voltage output of the same crystal lholder against lfrequency with a power input level of .20 dbm, it is seen that the voltage output is at all times in .excess of lmillivolts over the range from 500 to 12,000 megacycles.

It will now be seen that I have provided a broadband -coaxial crystal holder for cartridge type crystals for use .with a coaxial transmission line at microwave frequencies which .provides s atisfactory sensitivity and voltage out- ,put over an extremely wide range of frequencies, `i.e., `500 to 12,000 megacycles, and which also incorporates van internal direct current return path, which operates satisfactorily down to the lower frequency, i.e., 500 -megacycles While I have described above the principles of my 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 my invention.

What is claimed is:

1. For use with a coaxial microwave transmission line having concentric inner and outer conductors, a crystal holder vfor cartridge type crystals comprising: an outer .generally tubular member for-med of conductive material and adapted to be connected to said outer conductor of said transmission line; a crystal coaxially disposed with- `:in said tubular member and having one terminal .adapted to be connected to said inner conductor of said transmission line; said tubular member having a first portion toward said transmission line providing a first characteristic impedance for said holder, said tubular member having ,a second `portion remote from said transmission line profv-iding a second characteristicimpedance greater than said first characteristic impedance; said crystal beingconcenftrically and axially disposed inside said second portion; capacitor means 4between said tubular member and said one crystal termi-nal; capacitor means between said tubular member and the other terminal of said crystal; and a spiral conductor having `its inner end connected to said .one terminal of said crystal and its other end connected to -said :tubular member for providing a high radio frequency impedance return `path for rectified current passed 'by said crystal.

2. In combination: a section of coaxial microwave transmission line having concentric inner and outer coniductors; a cartridge type crystal connectrically disposed within said outer conductor and serially connected .with

said inner conductor; said ltransmission Vline having a first portion on the radio frequency side of said crystal having a first characteristic impedance and asecond portion adjacent said crystal `having a second characteristic impedance .higher than said first characteristic impedance; said second portion b eingzaxially coextensivewith said crystal; .and capacitor means 'between said outer conductor and said inner conductor on the radio frequency iside of said crystal.

3. In combination: a section of coaxial microwave transmission line having concentric inner and outer conductors; a cartridge type crystal concentrically disposed within said -outer conductor and serially connected with said inner conductor; said transmission line having a first portion -on :the radio frequency side of said crystal having a first characteristic impedance and a second portion adjacent said crystal having a second characteristie impedance higher than said first characteristic pedance; said Vsecond portion being substantially axially coextensive with said crystal; and an annular conductive member ,extending inwardly from said outer conductor and Ahaving ,its center opening surrounding and spaced from said inner conductor on the radio frequency side of said crystal thereby forming a capacitive iris therewith.

4. In combination: a section of coaxial microwave transmission line having concentric inner Iand outer con.- ,ductorsg a generally tubular crystal cartridge concen- .trically disposed Within said outer conductor and hav.- ing its terminals serially connected with said inner conductor; said outer conductor having a step formed in its inner surface in kgeneral alignment with the vradio frequency terminal of said crystal cartridge, said step dividing said outer conductor into a first portion extending on the radio frequency side of crystal cartridge with a first inside diameter thereby providing a first characteristic impedance and a second portion extending in the opposite direction from said first portion with .a second inside diameter greater than said first inside diameter thereby providing a second characteristic impedance greater than said first characteristic impedance; and an annular conductive member extending inwardly from said second portion of said outer conductor adjacent said step and having it center opening surrounding and spaced from said radio frequency terminal of said crystal cartridge thereby forming a capacitive iris there with.

5. In combination: a section of coaxial microwave transmission line having concentric inner and outer conductors; a generally tubular crystal cartridge concentrically disposed within said outer conductor and having its terminals serially connected with said inner conductor; said outer conductor having a step formed ,in its inner surface in general alignment with the radio frequency terminal of said crystal cartridge, said step dividing said outer conductor into Va first portion extending on the radio frequency side of crystal cartridge with a first inside diameter thereby providing a first characteristic impedance and a second portion extending in the opposite direction from said first portion witha second inside diameter greater than said first inside diameter thereby providing a second characteristic impedance greater ,than said first characteristic impedance, said second inside diameter being approximately 10% greater than said rst inside diameter; and an annular conductive member extending inwardly from said second portion of s aid outer conductor adjacent said step and having its center opening surrounding and spaced from said radio frequency terminal of said crystal cartridge thereby forming a capacitive kiris therewith, the inside diameter of said annular member being approximately one-half of the inside diameter of said second portion of said outer conductor.

6. In combination: a section of coaxial microwave transmission line having concentric inner and outer oo nductors; a cartridge type crystal concentrically disposed within said outer conductor and serially connected with said inner conductor; said transmission line having a rst portion o n .the radio frequency side of said crystal having a first characteristic :impedance and second portion adjacent said crystal having la second Vcharacteristic 'impedance higher than said first characteristic impedance; an iris capacitively coupling the radio frequency side of said crystal to said outer conductor; and a fiat spiral conductor surrounding said inner conductor having its inner end connected to said inner conductor `on said radio Yfrequency side of said crystal and `having its outer end connected to said outer conductor thereby providing a high radio `frequency impedance return path for rectified current passed by said crystal.

7. In combination: a section of coaxial microwave transmission line having concentric inner and outer conductors; a cartridge type crystal concentrically disposed within said outer conductor and serially connected with said inner conductor; said transmission yline having a first portion on the radio frequency side of said crystal having a first characteristic impedance and a second portion adjacent said crystal having a second characteristic mfpedance higher `than said lfirst characteristic impedance; an iris capacitively coupling the radio frequency side of said crystal to said outer conductor; an annular member of insulating material surrounding said inner conductor on the radio frequency side of said crystal and extending outwardly to said outer conductor; and a spiral conductor supported on said annular insulating member surrounding said inner conductor with its inner end contacting t-he same and its outer end contacting said outer conductor thereby providing a high radio frequency impedance return path for rectified current passed by said crystal.

8. In combination: a section of coaxial microwave transmission line having concentric inner and outer conductors; a generally tubular crystal cartridge concentrically disposed within said outer conductor and having its terminals serially connected with said inner conductor; said outer conductor having a step formed in its inner surface in general alignment with the radio frequency terminal of said crystal cartridge, said step dividing said outer conductor into a first portion extending on the radio frequency side of crystal cartridge with a first inside diameter thereby providing a first characteristic impedance and a second portion extending in the opposite direction axially coextensive with said crystal from said first portion with a second inside diameter greater than said Ifirst inside diameter thereby providing a second characteristic impedance greater than said first characteristic impedance; an annular member of insulating material removably positioned within said outer conductor surrounding the portion of said inner conductor connected to said radio frequency terminal of said crystal cartridge and extending outwardly to said first portion of said outer conductor; and a spiral conductor supported on one sde of said annular insulating member surrounding said inner conductor portion with its inner end contacting the same and its outer end contacting said outer conductor thereby providing a high radio frequency impedance return path for rectified current passed by said crystal cartridge.

9. In combination: a section of coaxial microwave transmission line having concentric inner and outer conductors; a cartridge type crystal concentrically disposed within said outer conductor and serially connected with said inner conductor; saidrtransmission line having a first portion on the radio frequency side of said crystal having a first characteristic impedance and. a second'portion adjacent said crystal having a second characteristic impedance higher than said first characteristic impedance; said second portion being `axially coextensive with said crystal; capacitor means between said outer conductor and said inner conductor on the radio frequency side of said crystal; and a fiat spiral conductor surrounding said inner conductor having its inner end connected to said f inner conductor on said radio frequency side of Said crystal and having its outer end connected to saidk outer conductor thereby providing a high radio frequency impedance return path for rectified current passed by said crystal.

10. In combination: a section of coaxial microwave transmission line having concentric inner and outer conductors; a generally tubular crystal cartridge concentrically disposed within said outer conductor and having its terminals serially connected with said inner conductor; said outer conductor having a step formed in its inner surface in general alignment with the radio frequency terminal of said crystal cartridge, said step dividing said outer conductor into a first portion extending on the radio frequency side of crystal cartridge with a first inside diameter thereby providing a rst characteristic impedance and a second portion extending in the opposite direction from said first portion with a second inside diameter greater than said first inside diameter thereby providing a second characteristic impedance greater than said first characteristic impedance; an annular conductive member extending inwardly from said second portion of said outer conductor adjacent said step and having its center opening surrounding and spaced from said radio frequency terminal of `said crystal cartridge thereby forming a capacitive iris therewith; an annular member of insulating material removably positioned within said outer conductor surrounding the portion of said inner conductor connected to said radio lfrequency terminal of said crystal cartridge and extending outwardly to said first portion of said outer conductor; and a spiral conductor suported on one side of said annular insulating member surrounding said inner conductor portion with its inner end contacting the same and its outer end contacting said outer conductor thereby providing a radio frequency impedance return path for rectified current passed by said crystal cartridge.

11. In combination: a section of coaxial microwave transmission line having concentric inner and outer conductors; a generally tubular crystal cartridge concentrically disposed within said outer conductor and having yits terminals serially connected with said inner conductor;

said outer conductor having a step formed in its inner surface in general alignment with the radio frequency terminal of said crystal cartridge, said step dividing said outer conductor into a first portion extending on the radio frequency side of crystal cartridge with a first inside diameter thereby providing a first characteristic impedance and a second portion extending in the opposite direction from said first portion with a second inside diameter greater than said first inside diameter thereby providing a second characteristic impedance greater than said first characteristic impedance; an annular conductive member yextending inwardly from said second portion of said outer conductor adjacent said step and having its center opening surrounding and spaced from said radio frequency terminal of said crystal cartridge thereby forming a capacitive iris therewith; an `annular member of insulating material removably positioned within said outer conductor surrounding the portion of Said inner conductor connected to said radio frequency terminal of said crystal cartridge and extending outwardly to said first portion Yof said outer conductor; a spiral conductor supported on one side of said annular insulating member surrounding said inner conductor portion with its inner end contacting the same and its outer end contacting to said outer conductor thereby providing a high radio frequency impedance return path for rectified current passed by said crystal cartridge; another annular conductive member extending inwardly from said second portion ofl said outer conductor and embracing the other terminal of said crystal cartridge; and an annular member formed of insulating material spacing said other crystal cartridge terminal from the opening in said other annular conductive member thereby forming a capacitive connection therewith.

References Cited in the file of this patent l UNITED STATES PATENTS 2,498,335 Hunt Feb. 2l, 1950 2,527,979 Woodyard Oct. 31, 1950 2,810,829 Schrock Oct. 22, 1957 2,816,270 Lewis Dec. 10, 1957 2,840,710 Levy June 24, 1958

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