US1985042A - Wave transmission network - Google Patents

Description

INVEN70R .C. E. LANE ATTORAEK WAVE TRANSMISSION NETWORK mw O F Dec. 18, 1934.

Patented Dec. 18, 1934 e 1,985,042 .35 i :wavarmlis m W RK? j A N a r ClarenceELLane, West Orange, N. J.,-as signor. to Q ice f J g Bell-TelephoneLaboratories, Incorporated, New

. York,-;N. Y., acorporationotj New York A This inventionre ates to ,wave transmission networks and more: particularly to shielding arm n sfor use in su h-n o v The principal object of; ,the-invention is to im- 5 prove the transmission;characteristics ofv wave transmission networks designed; for use at high :frequencies w51;; v

-Another object is tov provide adequate electrostatic and electromagnetic shielding for the component impedance elements used in transmission networks; 1 I 1 j j 2 Another objectis to make the impedance of a network element independent of its surround- -fuff 1:? "1.?

A further object 111 13118 inventionis to take account of the stray admittancesassociated with the component.- impedance branches comprising suchanetwork. 1 a j 5 1 A feature of the lIlVGIltlOIljS-fi. radio vire-- -quency filter the branches .of which have double shielding, withthe; capacitance between shields utilized as, part of 1 the lumped impedances requiredinthe'filter design. In waveitransmission networks, as ordinarily built, there are always present certain stray admittances between the component elements, and also mutual impedances ,1-resulting from stray -magnetio .fields,-1These-couplings impair the transmission characteristicsof the network by changing the .valuesof.- the lumped impedance elements, and: also byintroducing additional paths-.efor the currentsm: These harmful efiects .are'especially noticeable inenetworks-udesigned for: usewat high frequencies, These couplings ,35 may be decreased-in magnitude, to; a certain extent, :by'ma;physical-'separation of the elements, but thereare-obvious limitsto the extent to -which; this method can be employed-practically. Inthe case of electrostatic coupling to ground, 40. it is scarcelyof any .-value,,iand in any case ex- "cessive'separation ofthe; parts of a circuit introduces-other errors'due to the length 0f the wiring 'sinvolved. In accordance with the present inventionfth'ese'difliculties are overcome by the use ofindividually-shielded elements and, where necessary, by resorting to double shielding for the elements. A single shield, if made from material fof highconductivity and "properly spaced from the inductors, will gensiany reduce the stray fmagl ieti'c 'fields' to a tolerable magnitude and; will alsofmake definite the impedance effective between the terminalsof the element. Vari- I able elements may be used in combination .and 55 adjusted within their shield to have the required elements. These secondaryshields. are, usually to operate'at high frequencies, and maylresult appl'ie tion Julyes,lsssgserial No. 6 82,5 86

11 Claims.. (Cl."17s;44)f

frequencies of "resonance and antiresonance. When the individually shielded elements or com.- binations are, assembled in a complete network,

however, there will be introduced capacitances between each shield and every othershield, and 5 also betweenfthe shields'and. ground. In order to localize ,thesestray 'capacitances and make definite theirv magnitudes, ,a secondjor outer shield is placed around certain of the impedance all connectedto ground 'or'otherwise fixed at the samepotential, and shielded wiring is used to connect the individual elements. Additional capacitances between .-the outer and innershields will thus be introduced, but these are taken into account by connecting them in parallel with the lumped capacitances 'calld'lfor in the network design andby makingproper allowance therefor.

, The nature or the invention will be morefully understoodfrom the followingidetailed descrip- 20 tion and by reference to the accompanying drawing 'the single figure of which shows an enrlbodiment. of the invention in a wave transmission network. I I

The figure illustrates schematically theapplication of the invention to an unbalanced composite wave filter comprising sections of the type illustrated anddescribed in the United States patents to George A. Campbell, 1,227,113 issued May 22, 1917' and,1,493,600 issued May 11s, .1924, and'Patentf1,559,638 t William H.

Martin issued November 3, 1925. The filter is of the series-shunt type, comprising lumped'impedance branches in series with the direction of wave propagation andin alternation therewith 3 impedances connected in shunt-with the line.

"The network has a pairof' input terminals 11, 12 and a'pair of output terminals 13,-.14 by means of which it may be'connected between two sections offiatransmissio'n line or other apparatus-.1 One side of the filter, the path betweenterminals 12-and 14, maybe ground or otherwise fixedrin potential, as shown at .G.

Fora detailed explanation of-how such a filter .may be designed, reference is made tothe above.

and electrostatic couplings will exist when the physical elements are assembled into'the composite structure, thus impairing" thei transmission characteristics or thefilter. hese undesired effects are. most apparent in networks" designed in a shifting of the transmission band, an increase of attenuation in the band, a decrease of attenuation in the attenuating regions or a change in the characteristic impedance. In accordance with the invention, the stray fields are confined, and the capacitative couplings are localized and made definite, by enclosing each impedance'branch of the filter ina -separate conductive shield. Thus, as shown in the figure, the series impedances Z1, Z3, Z5, Z7 and Z9 are surrounded, respectively, by the shields 15, 16, 17, 18 and 19. In like manner, the shunt impedance branches Z2, Z4, Z6 and Z8 are enclosed, respectively, in the individual shields 20, 21, 22 and 23. The shields are mod-- erately thick, made of material of high conductivity as, for example, copper and are suitably spaced from the enclosed elements. Each shield is electrically connected to one terminal of the impedance branch which it surrounds, as shown at 24, 25 and 26. The inductors and capacitors may be made variable, as indicated schematically by the arrows shown in the figure, so that the'branch impedances may be 'adjusted within their individual shields to have the grounded side of the enclosed impedance, as

shown at 26. In accordance with the invention, the stray capacitances associated with the series branches are localized and made definite in magnitude by surrounding each series impedance with an outer or secondary shield, shownin the figure asparts 2'7, 28, 29, 30' and 31. These outer shields are electrically connected to the grounded side of the filter, as shown at 32, 33.

The capacitance between each inner shield and its associated outer shield is now fixed in magnitude and I may be represented by the dotted capacitances Ca, CeQCe, Cd and Ce shown'in the figure. In accordancelwith the invention these capacitances are taken into account and allowed for by adjusting the values of certain of the lumped capacitances called forin the filter design. For example, if the inner shields 15, 16

of the series impedances Z1, Z2 are connected to the .terminals adjacent the common shunt branch Z2, as shown at 24, 25, the capacitances (3a, Cb will be placed ,efiectively in parallel with the capacitance C1 of the Z2. branch, and may 'be' allowed for by an adjustment in the value of (31. If the value of the required capacitance in the shunt branch Z2 is C1, then the proper magnitude of C1 is found by subtracting from C1 the sum of Ca and Ge. In equation form,

Likewise, with the inner shield '17 of the series impedance branch Z5 connected to the terminal 34, as shown in the figure, the capacitance. Cc

is placed efiectively in parallel with the capacitance C2 of the shunt impedance Z4. If C? is the design capacitance required for the shunt individualv where C3' is, the, required design capacitance.

I balanced structure.

' another of said branches.

impedance Z4, the value of C2 is given by the following equation:

Also, when the inner shields 18 and 19 are tied, respectively, to the terminals 35, 36 the capacitances Cd and Ce will be effectively in shunt with the capacitance C3, the correctvaluevor which is given by 1:

"The component impedance branches of the filter are connected. together by shielded conductorslsuchyfor example, as the concentric conductor cable shown schematically in the figure at 37, 38, andthe shield of eachconnector is tied to ground, as indicated at 39, 40. Or, if desired, the connecting shields may be made integral with the other shields, as indicated at 41.

In some instances, if the wiring is'suiilci'ently short, the shielded connectors may be dispensed with and open wiring employedin its stead.

If the shields arearranged as described above,

and the capacitances in the shunt impedance branches are adjusted as" explained, the assembled filter will operate satisfactorily in any surroundings- Networks shielded-in this manner maybe designed to provide desired transmission characteristics which, without the use of such shielding, could not be realized.

The invention-has been'described inconnection with an unbalanced filter but it is apparent that the same principles may be applied to a Also, the invention is applicable to other types of transmission networks such, for example, as equalizers, phase correctors, delay networks and balancing networks.-

" What is claimed is: i

1. In a wave transmission network comprising a plurality of impedance branches, an impedance branch enclosed in a shield of conductive material, and a separate outer shield'of conductive material surrounding said first mentioned shield,

the capacitance between said two shields being utilized as a part of the lumped impedance-of 2. In a wave transmission-network, means for electrostatically and electromagnetic-ally shielding a component "branch impedance comprising a metalliclshield completely surrounding said impedance, and a separate metallic shield completely' enclosing said first mentioned shield, the capacitance between said two shieldsbeing utilizedas a part of the lumped impedance of a different impedance branch of said network.

ternately disposed in shunt therewith, an indi-' vidual shield. around each oi said branches, and

outer shields enclosing certain of said branches, the capacitance between said outershields and their respectively associated inner shields being 7 utilized as a part of the lumped impedances of said filter.

4.,In a'wave transmission network comprising impedancein series with the direction of wave propagation, and in alternation therewith impedances. connected in shunt with the line, two

separate shields surrounding each of said series impedances, the capacitance between ,said two shields forming a 'partof said shunt impedances.

5. Aplurality of impedance branches disposed between a pair of input terminals and a pair each of said series branches forming a part of the shunt impedances of said filter.

'7, In a wave transmission network having a I plurality of impedance branches, an electropletely shielded branch comprising a lumped,

impedance, an inner shield madeof conductive material surrounding said impedance, .and a separate outer shieldof conductive material enclosing said inner shield, said outer shield being at ground potential, whereby the stray magnetic fields from said impedance are effectively confined and the stray admittances between said inner shield and ground are localizedbetween said two shields, the capacitance between said two shields being utilized asa part of one of the lumped impedances of said network.

9. In a wave filter comprising a plurality of impedance branches connected between a pair of input terminals and a pair of output terminals, double shielding for certain of said impedance branches, said double shielding comprising an inner shield of conductive material and a separate outer shield completely surrounding said inner shield, the capacitance between said inner and said outer shields being utilized as a part of the lumped impedances of said filter,

10. A wave transmission network having a pair of input terminals and a pair of output terminals, said network comprising an electrical path between each input terminal and a corresponding output terminal, two impedances connected in series in one of. said paths, a'third impedance connected between the junction point of said two series-impedances and a point in the other of said paths, a separateinner shield surrounding each of said series impedances, said shields being electrically connected to said junction point, and individual outer shields surrounding each of said inner shields, the capacitance between each of said inner shields and its associated outer shield being, so connected into the circuit as to form a part of said third impedance.

11. A wave transmission network having a pair of input terminals and a pair of output terminals, said network comprising an electrical path between each input terminal and its associated output terminal, one of said paths being grounded, a plurality of impedances in series in the other of said paths, a shunt impedance branch connected between each junction point formed by said series impedances and the grounded side of said network, an individual shield surrounding each of said series impedances and making electrical connection with one terminal thereof, a separate shield enclosing each of said shunt impedance branches, said last mentioned shields being conductively connected with the grounded side of said network, and an outer shield surrounding each of said series impedances, said outer shields being electrically connected to the grounded side of said network.

CLARENCE E. LANE.

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