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ÚCÍ- 8, 1945- A. M. GuREwlTscH FILTERING ARRANGEMENT 2,408,927 Filed July so, 1942 „s _...maè Sì. Inventor; Y Anaiole M. Gur‘ewitsch, Hf?. A‘Ltcarn @n 2,408,927 Patented Oct. 8, 1946 UNITED STATES PATENT OFFICE 2,408,927 FILTERING ARRANGEMENT Anatole M. Gurewitsch, Schenectady, N. Y., as sìgnor to General Electric Company, a corpo ration of New York Application July 30, i942, serial-No. 452,946 5 Claims. (c1. 17a-_44) l This invention relates to an electrical filtering arrangement especially adapted for use at ultra 2 glass cylinders 20 and 2l sealed between them. The part l1 provides a terminal for the grid l2, and a terminal for the anode is provided by a cylindrical enlargement 23 which is welded or soldered against the upper surface of the part the design of radio circuits and like apparatus I6. to provide means for effectively separating the The cathode I3 is provided at its lower extrem direct current and alternating current paths. ity with a flange 25 which parallels the under At the lower frequencies, such as the frequencies surface of the part I8 but which is separated commonly used in radio broadcasting, this sep from that part by an insulating spacer 21 (e. g. aration may be accomplished by the use of choke 10 a mica washer). With this arrangement the coils and condensers, properly arranged. How part I8 has a high frequency connection with the ever,V at higher frequencies, especially at fre cathode through the capacity existing between quencies corresponding to wave lengths on the this part and the flange 25 but is effectively in high frequencies. As is well known, it is frequently necessary in order of a few centimeters, the conventional ar sulated from the cathode as far as direct current rangements fail to produce the desired results 15 is concerned. Separate direct-current connec and it is necessary to resort to more complex ex tions are made to the cathode by means of lead pedients including specially designed ñlters. The present invention is ‘principally concerned with the provision of an improved form of ultra high frequency ñlter which is characterized by simplicity and compactness of structure and which is well adapted for use at even the shortest wave lengths. Briefly, the invention makes use of a multiply in wires 29 secured to the under surface of the part 25 and terminally connected to prongs 3l which depend from the base of the discharge tube. Additional prongs 33 and lead-in wires 34 are provided for the purpose of supplying heat ing current to a coiled filament 35 arranged ' within the cathode cylinder I3 so that the emis sive part of the filament can be maintained at folded coaxial transmission line arrangement 25 an elevated temperature by this means. In the arrangement of Fig. 1 the tube l0 is providing a plurality of quarter wave filter sec seated in a socket or adaptor 31 having acces tions in series. In order to obtain a band-block sible terminals 38 to which appropriate con-fr characteristic the various sections may be made of different lengths so that each corresponds to nections may be made. The socket 31 is itself a quarter wave length at some particular fre 30 >supported by the combination of a ?xed ring 40 and a split locking ring 4l, the ring 40 being quency within the selected frequency range. secured to the inner surface of an elongated The features of the invention desired to be cylinder sleeve 44 having certain further func protected herein are pointed out in the appended tions Which will be explained at a later point. claims. The invention itself, together with its The oscillating circuits employed in connection further objects and advantages, may best be un with the discharge tube l0 are provided by the derstood by reference to the following descrip- y combination oi a series of three concentric tu tion taken in connection with the drawing in which Fig. 1 is a longitudinal sectional view of bular conductors 48, 49 and 58. The outer con ductor 48 has a high frequency connection with a high frequency oscillator embodying one of my improved filter arrangements; Fig. 2 is avpartial section of the discharge tube which is represent ed in less detail in the assembly of Fig. 1, and Fig. 3 is a diagrammatic view useful in explain >ing the operation of the construction of Fig, l. Referring particularly to Fig. 1 there is shown an ultra-high frequency oscillator having a 40 the cathode of the tube l0 through a ring of contact fingers 53 which bear upon the surface of the tube part I8. Similarly, the cylindrical con ductor 48 has a symmetrical connection with the grid of the tube through spring contact fingers 5.5 which bear upon the grid terminal l1. Final ly, a high frequency connection between the in three-electrode discharge tube l0 as its central ner tubular conductor 50 and the anode of the element. As appears more clearly in Fig. 2, this tube l0 is provided by pressing the extremity tube comprises a cylindrical anode ll, a grid l2 of the conductor over a tapered adaptor 51 which 50 and a cylindrical cathode I3 having its emissive is fitted snugly onto the anode terminal and part in the form of a flat disk surface I4 which which bears contact lingers 51’ adapted to en faces the grid |12. The envelope within which gagethe disk I6. The tubular conductor 50 is these electrodes are enclosed comprises a series insulated from the adaptor 51 with respect to of three circular metal parts I6, l1 and I8 which 55 direct currents by the interposition between are supported in mutually spaced relation by 2,408,927 3 their juxtaposed surfaces of a mica sleeve 58. It will be seen, however, that the capacity which exists through the mica assures that the con ductive parts in question are effectively directly connected as far as high frequency currents are concerned. With the arrangement speciñed, the space be tween the conductors 4B and 49 forms in effect a transmission line section which may be ad justed as to length to provide a resonant tank having a resonant frequency appropriately re lated to the desired frequency of operation of the oscillator. This adjustment may be accom plished by the use of an annular plug orcontact ring 6G having two sets of contact ñngers El and 62 which respectively bear upon the opposed surfaces of the tubular conductors `llß‘and Q9. Actuating rods 54 which extend out through a to the main structure of the oscillator and is operated at ground potential, so that no diñiculty exists with reference to the D.-C. connections to this element. On the other hand, mutually insulated connections must be made to both the anode l! and the cathode I3. The anode terminal is insulated from the grounded structure by the mica spacer 58, and positive potential is applied to it by the use of a conductor l2 connecting with the adaptor 51 and extending outwardly through an insulating block '5... at the end of the oscillator structure. an ex ternaily accessible terminal for this arrange ment being indicated at l5. Due to the gap pro vided‘between the tubular conductor 50 and the adaptor 5l by the spacer 58 there is some tend Yency for coupling to exist between the otherwise compietely enclosed high frequency system and the direct current conductor T2 and its associ ated circuits. In _order to avoid objectionable effects attributable to this cause, it is expedient to provide filtering means in the formrof hollow A similar tunable transmission line section iS ` provided between the grid and anode by the com metal sîeeves i8 and 78 ñtted on the conductor l2 bination of the tubular conductors 49 and 50. The resonant frequency of the tank circuit thus and each providing a reentrant discontinuity with respect to currents ilowing along this conductor~ provided between‘the grid and anode is adjust able, as in the case of the grid-to-'cathode cir Filtering means of the type specified are known `er se and are not intended to be claimed herein except as embodied in an improved arrangement to be described at a later point. Their usefulness cuit, by means of a slidable contact ring or plunger l(53,' having Vexternally accessible actuating rods 69. Assuming the application of appropriate’direot ‘ l'J depends in part upon'the consideration that the current potentials to the various electrodes of the‘turbe iii-_, oscillations may be obtained by conductor "i2 and the surrounding tube 5i) form a coaxial transmission line to which the propagation provided‘and by arranging for a properfeed back The passage of such energy along the line may properly adjusting 4the two tunable tank circuits of high frequency energy is necessarily conñned. coupling between thesencircuits. The principles be alternatively viewed as attributable to high which govern the operation of an` oscillator of this kind arel fully described in frequency currents flowing over` the opposed sur faces of the coaxial conductors orto the propaga tion of waves in the space between the conduc ` rial No. 448,205, nieu of Richard C. Jensen assigned to _the General Electric Company, a corporation of New York. In 40 tors. Taking the latter viewpoint, it may be'said that the discontinuities provided by the sleeves 'I8 and l@ tend to block the propagated waves quired that the inner and> outer lines betuned by reflecting them operating frequency, such tuning being obtained For complete blocking or reflection‘to 'occur at a particular frequency, the optimum condi tion is that in which the length of the blocking by adjusting each` line so that its length corre sponds approximately to an odd number (e. g. l, 3, 5, etc.) of quarter wave lengths at the> fre quency to which it is being tuned. Feedback may in some instances be provided Asolely’by the inter-electrode capacity of the tube l i) butin most >`cases it is found preferable to employ a probe o1* loop (not shown in Fig. l) extending betweenj the inner and outer transmission line sections for pro viding more positive coupling between them. , jOn the assumption that the concentric con sleeve is a quartel` wave length (or an odd num ber of quarter wave lengths) at `such, frequency and in which the impedance “seen”l at the right hand end of the sleeve is infinite. The latter con dition is fulfilled `by the reentrant'sleeve con struction illustrated in Fig. 1 since the resonant quarter wave section enclosed by each sleeve actu ally represents an inñnite impedance (at ‘ the resonant frequency) in series withy the section 55 formed between the outer surface of the sleeve ductors ¿58, 49, 5G and the connectedmetallic parts` provide a Vcomplete conductive enclosure, it would appear that high frequency energy de andthe surrounding conductor. It is also de sirable that the difference in diameter between each sleeve and the conductor 'l2 be relatively veloped within the enclosure `should be great and that the spacing between the sleeve confined and that no high frequency coupling 60 and the surrounding conductor 5l be small. By between the oscillating system and external making the sleeves 78 and 'I9 of different lengths agencies should exist. However, such an as sumption ignores the presence of the insulating spacers 2l (Fig. 2) and 58 (Fig. l). These spacers, which are required to permit the establishment of D.-C. potential differences between the vari ous electrodes of the tube lû, represent leakage gaps in an otherwise continuous metallic struc and by using as many such sleeves as are needed, a considerable band of frequencies may be blocked so that unwanted coupling is prevented regard oscillator is operated. . , A generally Vsimilarproblem with respectto high frequency coupling exists in connection with the means employed'for supplying heating _cur high frequency energy and other disadvantageous 70 rent (either D.-C. or 6o cycle'A.-C.) tothe cath effects. For this reason it is necessary to provide ode of the tube iin These means include the ture and may permit uncontrolled radiation of socket terminal 38', which. is assumed to be con filtering means in association with the D.-,C. and low frequency A.-C. connections’of the tube.Y nected to the cathode filament, and a conductor The grid i4 of the tube is connected directly 75 85 having a connection with this terminal (the other cathode connections do not appear in Fig. 4desired to operate the oscillator at one frequency _,only, all the filter sections may be made of identi cal length, that is to'say, of a length correspond >1,_but are indicated diagrammatically in Fig. 3). .The `conductor 88 extends through an opening 81 formed in a transverse wall part> 88 which other wise4 completely encloses the space within which >ing to a quarter wave length at the frequency in question. On the other hand. where a range of operating frequencies is to be employed, the various iiltering sections are preferably made of different lengths as shown, so that the arrange the socket end of the tube 4|) is positioned. At one vend it is supported in an insulating bushingv >90,' and at vthe other end is provided with an ex ternally accessible terminal 9| mounted in an insulating wall part‘92. Objectionable high fre quency coupling is to be anticipated in connec tion with this arrangement becausev of the pos sible- propagation of high frequency- energy through the gap provided by the cathode spacer 21 (Fig. 2), through the glass seals of the tube ment as a whole provides a band-stop filter. The operation of the invention may be 4further lo explained by reference to the diagrammatic rep resentation of Fig. 3 in which elements which can be readily identified with parts previously de scribed in connection with Figs. 1 and 2 are des ignated by similar numerals differentiated by „ |íJ,.through the opening Si' and along the con priming. l yAs has been previously explained, the oscil ductor 86. VThis problem may, of course, be dealt with by a filtering arrangement identical with that em lating system is made up of the discharge tube I8’ and the two resonant circuits which are re ployed inV connection with the anode, that is, by spectively provided between thenconduct’orsrl'ß' the use of several reentrant quarter wave iilters arranged sequentially in axial alignment. How ever, while the use of such an arrangement in connection with the anode does not tend ma terially to increase the space requirements of the oscillator, the same consideration does not apply in connection with the cathode; that is to say, the use of two or more quarter wave ñlters arranged in end-to-end relation in connection with the cathode terminal would obviously greatly extend the length of the structure as a whole. In accordanceV with my invention this dif ficulty is avoided by the use of a folded conductor arrangement in which a number of quarter wave filter sections are provided in a concentric rela and 49’ and the conductors 49’ and 50’. Feed back is provided (in part) by means of a conduc tive probe ||8 which is mounted on the tuning ring 6G' and which extends through an axial slot cut in the tubular conductor A9'. An output ar 25 rangement for the high frequency energy de veloped is illustrated as comprising a coupling loop H6 which extends into the space between the conductors 49’ and 50’ and which is made externally accessible by means of a concentric 30 conductor transmission line comprising a metal tube H8 and a coaxial wire |20. Direct current terminal connections for the electrodes of the tube I8’ are indicated at 12’ and 86', cathode bias being provided by a resistor | |5 tionship. This arrangement includes in the first 35 connected in series with the cathode. The con instance a conductive element 93 which surrounds siderations which require the use of filtering ar the conductor 86 and which for a short portion rangements in association with these connections of its length forms with the conductor a coaxial arise from the presence of the condensers |2| and transmission line along which high frequency |22, the first set representing the by-pass capac energy passing through the opening 8l tends to ity provided by the insulating washer 21 (Fig. 2) be propagated. To block the ñow of such energy and the second set representing the capacity pro a reentrant quarter wave discontinuity is pro vided by the mica insert 58 (Fig. 1). As has vided by mounting upon the conductor 86 a me been previously indicated, these spacers repre tallic sleeve 94 which is open at one end and sent gaps through which undesirable high fre which is of materially larger diameter than the quency coupling may occur. As far as the anode conductor. The length of the sleeve 94 is made conductor 12' is concerned such coupling is pre such as to correspond closely to one or more vented by the inclusion of the filtering elements odd quarter wave lengths at a selected frequency 18’ and 19’. In connection with the cathode Within the expected operating range of the oscil supply conductor 86’ a similar function is per 50 lator. In series with this "arrangement there is formed by the concentrically arranged ñlters 96’ provided a second reentrant quarter wave filter to 10|’. Accordingly, no substantial coupling be ing section provided by a tubular conductor 91, tween the high frequency oscillator and the ex which may be looked upon as a reversely bent ternal circuits is permitted. extension of the conductor 93. This is surround While the invention has been described by ref 55 ed by a tubular conductor 98 which bears a re erence to a particular embodiment it will be un versely bent part |08 adapted to provide a still derstood that numerous modifications may be further reentrant discontinuity in the path of made by those skilled in the art without depart wave propagation. A sleeve |0| fitted into the ing from the invention. I, therefore, aim in the cylinder 44 decreases the dimensions of the free appended claims to cover all such equivalent var 60 space about the conductive part lüû. A metallic iations as come Within the true spirit and scope washer |03 which closely surrounds the extrem of the foregoing disclosure. In the claims, wher ity of the conductor 86 serves to support the as ever the term “quarter wave” is employed it is sociated tubular elements 98 and |80 and closes to be understood as applying either to a single one end of the inner conductor. For supporting quarter wave or to any odd number of quarter 65 this structure and for securing it to the remain waves. ing structure of the oscillator, use is made of a clamping ring ||0 which abuts against a narrow flange I|| provided on the outer surface of the part d4 and which has a screw-threaded engage ment with the part 43 as indicated at ||2. As a result of the Aarrangement described, the What I claim as new and desire to secure by Letters Patent of the United States is: 1. A filter comprising a plurality of successively telescoped coaxial conductors connected to pro vide a plurality of quarter wave discontinuities in series,` adjacent ones of said conductors being only possible path for the escape of high fre insulated from each other for unidirectional quency energy through the left hand extremity currents. of the apparatus of Fig. 1 is by series passage 2. A band-stop filter for frequencies within a through the various filter sections. Where it is 75 7 @A085927 given- range comprising a plurality of successively telescoped concentric conductors *connected to provide a number of filtering sections in lseries, 'adjacent ones of said conductors being insulated from each other for unidirectional currentsy each of said sections having a length corresponding to a quarter wave length at some frequency within the given range, and the various sections being of diiîerent diameters whereby each represents a comprising, a high frequency ñlter including a plurality of telescoped conductors arranged to provide ‘a multiple reversed path for‘electromag netic waves tending to pass through the ñlter, each reversed section of the filter comprising a reentrant discontinuity effective to block passage of waves of a particular wave length, and adja cent ones of said conductors being insulated from each other for unidirectional currents. 5. In combination, a high frequency system, a 3. In» an- arrangement for decoupling the power 10 conductor for supplying current to a. pait of said leads to an ultra high frequency space resonant system, and a high frequency filter associated system, a high frequency ñlter including a plu with said conductor, said ñlter comprising a con rality of telescoped conductors of varying diam ductive tube surrounding said conductor and de eters connected to provide a number of filtering sections in series, each of said sections comprising 16 fining with it a'coaxial transmission line, means on said conductor for providing a quarter wave a reentrant quarter wave discontinuity in the discontinuity with respect'to the others. l path of propagation of the waves desired to be discontinuity in saidrline, and further conductive filtered, and adjacent ones of said conductors being insulated from each other for unidirectional means concentrically surrounding said tube and insulated therefrom at the frequency of `said cur currents. 4. A device for decoupling the power leads to an ultra high frequency space resonant system 20 rent for providing a, second quarter wave discon tinuity serially related to the first. ANATOLE M. GUREWITS CH.