US2149356A - Wave transmission network - Google Patents

Wave transmission network Download PDF

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Publication number
US2149356A
US2149356A US100400A US10040036A US2149356A US 2149356 A US2149356 A US 2149356A US 100400 A US100400 A US 100400A US 10040036 A US10040036 A US 10040036A US 2149356 A US2149356 A US 2149356A
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United States
Prior art keywords
network
impedance
line
band
sections
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Expired - Lifetime
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US100400A
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English (en)
Inventor
Warren P Mason
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AT&T Corp
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Bell Telephone Laboratories Inc
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Publication date
Priority to NL49003D priority Critical patent/NL49003C/xx
Priority to BE423379D priority patent/BE423379A/xx
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US100400A priority patent/US2149356A/en
Priority to GB21190/37A priority patent/GB498332A/en
Priority to FR826617D priority patent/FR826617A/fr
Priority to CH202644D priority patent/CH202644A/de
Application granted granted Critical
Publication of US2149356A publication Critical patent/US2149356A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/202—Coaxial filters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/38—Impedance-matching networks
    • H03H7/383—Impedance-matching networks comprising distributed impedance elements together with lumped impedance elements

Definitions

  • 'Ihis invention relates to wave transmission networks and more particularly to networks adapted to couple loads having different impedances.
  • An object of the invention is to provide an impedance transforming network suitable for use Yat high frequencies and capable of transmitting a wide band with uniform ratio of transformation.
  • a further object is to provide a network of this type whichk may be very effectively shielded.
  • 15 ⁇ A featurewof the invention is the use of short lengths of transmission line, or transmission lines in, combination with one or more condensers, as component elements in impedance transforming networks of the type set forth above.
  • transmission networks using coils and condensers as reactance elements are diicult to construct and unsatisfactory in operation on account of the small sizes of the elements required and the large effects of the interconnecting windings. Also, if
  • the loss in the transmission band will be excessive due tothe low Qfof the coils, defined as the ratio of reactance to ei'ective f resistance.
  • impedance transforming networks for high frequency use which employ as component elements only short lengths of transmission line, or lengths of line in conjunction with ⁇ condensers.
  • the networks are capable of transmitting comparatively widel bands withy asubstantially uniform ratio of impedance transformation.
  • Such transformers have 40 the advantages of low cost due to the cheapness ⁇ of the component elements, low loss in the transmission band because of the high values of Q obtainable in transmission lines and condensers,
  • Each section of line is preferably uniform throughout its length and should be substantially dissipationless.
  • the line may consist 5 of a balanced pair of parallel wires or rods, or
  • the concentric conductor type in which the outer conductor surrounds the inner one and is coaxial therewith.
  • the former type is preferable for use in balanced structures, and l0 the latter in unbalanced structures.
  • the concentric line has the advantage that it is inherently well shielded.
  • one of the line sections is connected in series with the direction of wave l5 propagation and used as a four-terminal network, with transmission therethrough, and another line section is used as a two-terminal impedance connected either in series or in shunt with the rst-mentioned section.
  • two line sections are used 'as shunt impedances, and in still another embodiment the sections of line are connected in tandem.
  • an L, T or 1r network of condensers is used in combination with the transmission 25 lines.
  • shunt condensers are provided at the ends of the network to absorb distributed capacity associated with the terminal loads.
  • the impedance transforming networks described herein may be used to couple together any two loads having impedances, preferably pure resistances, which differ in magnitude.
  • the networks are especiallyy adapted for use at high 35 frequencies where it is desired to transmit a wide band with a uniform ratio of impedance transformation for the entire band. Examples of such applications are the connection of a transmission line to an antenna, or to a thermi- 4o onic tube, and the coupling of two therrnionic tubes.
  • Fig. 1 represents a ⁇ section of uniform transmission line taken from an innite sequence of such sections
  • Fig. 2 is a diagrammatic representation of one 50 entitled form of the impedance transforming network in accordance with the invention
  • Figs. 3 and 4 represent respectively unbalanced and balanced physical structures for the network of Fig. 2;
  • Fig. 5 shows the equivalent electrical circuit of the network of Fig. 2 and is used in explaining the invention
  • Fig. 6 shows another embodiment of the invention
  • Fig. 7 represents a possible physical structure for the network of Fig. 6;
  • Fig. 8 represents the physical structure of another embodiment of the invention.
  • Fig. 9 shows the network of Fig. 8 used as an interstage coupler between two thermionic tubes
  • Figs. 10 and 12 show alternative circuits for another embodiment of the invention.
  • Figs. l1 and 13 represent possible physical structures for the networks shown respectively in Figs. 10 and 12;
  • Figs. 14 and 15 show respectively the electrical circuit and the physical structure for another embodiment of the invention.
  • FIGs. 16 and 17 are schematic representations of two other embodiments of the invention.
  • Fig. 18 is a perspective View, partly in section, showing the central portion of Fig. 11 on a larger scale.
  • Fig. 2 is a diagrammatic representation of a network comprising only transmission lines and capable of transforming from one impedance to another over a wide range of frequencies.
  • the network consists of two transmission lines each a quarter wave-length long at the mid-frequency of the band to be transformed.
  • the line 2, of length Z1, and characteristic impedance Zul is connected in series between input terminals 3, 4 and output terminals 5, 6.
  • the line l, having a length Z2 and a characteristic impedance Zu2 is short-circuited at one end and at the other end is connected in shunt with the line 2.
  • An input load impedance R1 in series with an electromotive force E is shown connected to the input terminals of the network, and an output load impedance Ro is connected to the output terminals.
  • Fig. 3 'Ihe physicalstructure of the network of Fig. 2 when coaxial transmission lines are used is indicated by Fig. 3, in which 8 and 9 are respectively the inner and outer conductors of line 2 and l0 and Il are respectively the inner and outer conductors of line l.
  • the inner conductor may be separated from the outer conductor in a well-known manner by means of rings or spiders, made of suitable insulating material, not shown G are small.
  • Fig. 4 shows the physical structure when a balanced pair of parallel wires is used for each transmission line.
  • Equations (10) and (11) in terms of transformer theory it will be shown that they are identical in form to the equations applying to a perfect transformer in combination with a symmetrical filter.
  • Fig. 5 shows the equivalent circuit consisting of, two half sections 8, 9 vof a symmetrical lter coupled by a perfect transformer lhaving an impedance step-down 412 to l. The propagation constantof each half section is. and the characteristic impedance K1 of the mst i-sa2 times the characteristic impedance K2 of theJ second. Using the notation for currents and voltages given in Fig.
  • the characteristic impedance K10 of the network on the high impedance side is and therefore the input load impedance R1 should be of this magnitude.
  • the characteristic impedance Kzo at mid-band frequency on the low impedance side is which determines the proper magnitude for the output load impedance Re.
  • the width of the pass band is determined by
  • the cut-off frequencies f1 and f2 of the filter transformer are given by the formula V d, 18)
  • the ratio of the band width to the mean frequency fm is given by the simple formula tion (19).
  • Fig. 2 the structure shown on Fig. 2 is equivalent to a perfect transformer whose ratio is and a filter whose band width is given by Equa- Such a lter will have a flat attenuation loss over about per cent of its theoretical band when it is terminated on each side by re- ⁇ where R1 and Ro are respectively the input and the output resistances that the transformer works between.
  • Y the structure shown on Fig. 2 is equivalent to a perfect transformer whose ratio is and a filter whose band width is given by Equa- Such a lter will have a flat attenuation loss over about per cent of its theoretical band when it is terminated on each side by re- ⁇ where R1 and Ro are respectively the input and the output resistances that the transformer works between.
  • FIG. 6 Another example of a transforming network comprising only transmission lines is the one shown diagrammatically in Fig. 6 which is the inverse of the network of Fig. 2.
  • Fig. 7 A possible physical structure is shown in Fig. 7.
  • the network consists of a section of transmission line Il of length l and characteristic impedance Zo1 in series with an open-circuited line of length Z and characteristic impedance Zo.
  • Y k The band width of the filter for narrow bands is given approximately by y
  • the first transformer discussed is a step-down transformer while the one considered here has a step-up from the input of the line to the output.
  • the rst filter had a mid-shunt impedance characteristic on each end, that is, the impedance of the band is infinity at the two edges whereas the transformer with the series open-circuited iine has a mid-series impedance, since the impedance given by the last expression in Equation (23) goes to zero at the two cut-0H frequencies.
  • the range of transformation is about the same for each and hence one type has. no particular advantage over the other.
  • Fig. 8 shows another impedance transforming network made up only of sections of transmission line which is useful where only a moderate ratio of transformation is required.
  • the network consists of two portions of line I3, I4 having characteristic impedances Zo1 and Zn3 respectively,
  • Equation (30) reduces to the simple form 4 ⁇ or for narrow bands and f1: Y V.
  • Fig. 8 acts as a narrow band coupling unit which introduces a transformation from input to output.
  • the design equations for this transforming filter are Y
  • the network of Fig. 8 is useful as an interstage coupler between the plate of one screen grid or pentode tube and the grid of the next one.
  • Such an application is illustrated by Fig. 9 where the v network 25 is used to couple the plate of tube I6 to the kgrid of tube.
  • a high'frequency pentode such as
  • the shunt line I5 is effectively short-circuited at high frequencies by means of the condenser 30 of large capacitance connected between the inner and outer conductors near the outer end of the line. A dire'ct metallic connection cannot be made here because the B-battery 3
  • the condenser 32 also has a large capacitance and is used to keep the voltage of the battery 3
  • the width of the band passed can be accurately controlled and a atter gain characteristic is obtained.
  • distributed capacity in the plate and grid of the vacuum tube can be absorbed in the iilter by making the line length Z1 shorter. Since only half of the total distributed capacity has to be absorbed on each end of the filter, a higher impedance can be built up in the filter for the same band width, and hence more gain per section can be obtained than with a tuned circuit.
  • Condensers can'be constructed which have little dissipation at radio frequencies and therefore may be used in the networksiwithout unduly increasing' the'los's in the transmission band.
  • Combinations of lines with condensers have the advantages that much more isolatedbands can be obtained, in general narrower pass bands can vbe obtained, and at the lower frequencies shortersectons of lines can be -employed if they are4 resonated vby capacities.
  • Fig. shows one type of network using transmission lines and condensers.
  • the network consists of a transmission line I8 of length Z and characteristic impedance Zul and a second line I9 of length l and characteristic impedance Zon connected in tandem, with a vT network made up of condensers C1, C2 and C3 interposed between the two line sections.
  • the physical construction of the network of Fig. 10 is shown in the perspective view of Fig. 11, and the central portion is shown in more detail in Fig. 18, which is a Aperspective View partly in section.
  • the inner conductor 30 terminates in a metallic disc 3
  • the flanged disc 34 Between these two discs but separated therefrom is the flanged disc 34, the flange 35 of which is separated from the outer conductor 36 by the insulating ring 4
  • is shown in Fig. 18, but is not shown in Fig. 11 due to the small The capacity C1 capacity betweenthe discs 33 and 34.
  • the capacity between the flange 35 and the outer conductor 36 constitutes C2.
  • Equations (36) and (37) simplify to sin -il v Cri-Cz-l-Ca Comparing these equations With Equations (12) and (13)
  • Equations (12) and (13) We have for the image parameters tion ratio (38)
  • Equations (12) and (13) We have for the image parameters tion ratio (38)
  • the condenser C3 For narrow transmission bands it is necessary for the condenser C3 to have a iinite value. Also, for. this case, the formulas give afairly large value for the shunt condenser C2.
  • a more practical arrangement is to replace the two series condensers C1 and C3 and the shunt condenser Cz by a 1r network consisting of two shunt condensers CA and Cc separated by a series condenser These condensers will s between the partition and the disc 40.
  • the capacity CB is that effective between the two discs 39 and 40, through the hole 2
  • the transformer just discussed is suitable for transforming from line impedances down to very low impedances, but cannot be used to transform from line impedances up to very high impedances such as the impedance of a vacuum tube.
  • One such transformer is shown in Fig. 14 and the physical structure in Fig. 15. It consists of two short-circuited shunt lines 23 and 24 of length Z and having characteristic impedances Z01 and Zo2 respectively, connected together by av T or 1r network of capacities.
  • the capacities C1' C2 and C3 are furnished by a physical structure similar to that shown in Figs. 11 and 18, described above.
  • FIG. 16 Another type of transformer of some interest is one which will transform from very high impedances to very low impedances.
  • a transformer is shown on Fig. 16. It has a short-circuited shunt line 26 of length Z1 and characteristic impedance Zo1 on the high impedance end and a series line 21 of length Z2 and characteristic impedance Zo2 on the low impedance end.
  • Such a transformer does not have a constant transformation ratioy over the whole band but for about per cent of the theoretical band with the transformation ratio is approximately constant.
  • the design equations for this transformer are 'I'he transformer is especially useful since it will give the widest transmission band for a given transformation ratio of any of the transformers discussed.
  • the capacitance of the condenser C'z can be adjusted to compensate for the reactive component of the input load impedance.
  • Fig. 1'7 ⁇ shows a modification of the network of Fig. 2 in which a shunt condenser appears at each end of the network.
  • a shunt condenser appears at each end of the network.
  • Such a structure is useful where it is desired to absorb capacity associated with one or both of the load impedances. This may be done by adjusting the values of the condensers C1 and C2.
  • a network in accordance with claim 1 in which said two sections of line are short-circuited at their distant ends and at their other ends are connected in shunt at the ends of said network.
  • interposed connecting means comprise a third section of uniform transmission line connected in shunt between said two sections of line.
  • a four-terminal wave transmission network adapted to transmit freely a selected band of frequencies with a substantially uniform ratio of impedance transformation for coupling two loads having unequal impedances comprising two sections of uniform transmission line having equal lengths but different characteristic imwhich said interposed connecting means comprise a series-shunt arrangement of, condensers.
  • said interposed connecting means comprise a network of condensers having an impedance transformation ratio equal to the ratio of the characteristic impedances of said sections of line.
  • a four-terminal wave transmission network adapted to transmit freely a selected band of frequencies with a substantially uniform ratio of impedance transformation for coupling two loads having unequal impedances, said network comprising two sections of uniform transmission line and a series-shunt arrangement of condensers interconnecting said sections, the lengths of said sections being equal and each being not substantially greater than a quarter of the wavelength corresponding to the mean frequency of said band, the ratio of the characteristic impedances of said sections being equal to the ratiov of the impedances of said loads, and the capacitances of said condensers being proportional so that said arrangement of condensers provides an impedance transformation equal to the ratio of the impedances of said sections of line.
  • a network in accordance with claim '7 in which said two sections of line are short-circuited at their distant ends and at their other ends are connected in shunt at the two ends respectively of said arrangement of condensers.
  • a network for transmitting with a substantially uniform ratio of impedance transformation a selected band of frequencies between two loads having unequal impedances comprising two sections of uniform transmission line connected in tandem between said loads, and a third section of uniform line shortcircuited at one end and at its other end connected in shunt between said two sections, the length of each of said first-mentioned two sections being substantially equal to a. quarter of the wave-length corresponding to the upper cutoi frequency of said band, and the ratio of the characteristic impedances of said two sections being equal to the ratio of the impedances of said loads.
  • a network for transmitting with la substantially uniformratio of impedance transformation a selected band of frequencies between two loads having unequal impedances comprising two sections of uniform transmission line connected in tandem between said loads, and a series-shunt arrangement of condensers interposed between said two sections, the length of eachy of said sections beingknot substantially greater than a quarter of the wavelength corresponding to the mean frequency of said band, the ratio of the characteristic impedances of said sections being equal to the ratio of the impedances of said loads, and the capacitances of said condensers being so proportional that said sections of line are connected without impedance mismatch.
  • a network for transmitting with a substantially uniform ratio of impedance transformation a selected band of frequencies between two loads having unequal impedances said network comprising a series-shunt arrangement of condensers and two sections of uniform transmission line, said sections being short-circuited at their distant ends and connected at their other ends in shunt at the two ends respectively of said arrangement of condensers, the length of each of said sections being not substantially greater than a quarter of the wave-length corresponding to the mean frequency of said band, the ratio of the characteristic impedances of said sections being equal to the ratio of the impedances of said loads, and the capacitances of said condensers being so proportional that said arrangement of condensers has an impedance transformation ratio equal to the ratio of the characteristic impedances of said sections of line.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
  • Communication Cables (AREA)
US100400A 1936-09-12 1936-09-12 Wave transmission network Expired - Lifetime US2149356A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
NL49003D NL49003C (en(2012)) 1936-09-12
BE423379D BE423379A (en(2012)) 1936-09-12
US100400A US2149356A (en) 1936-09-12 1936-09-12 Wave transmission network
GB21190/37A GB498332A (en) 1936-09-12 1937-07-30 Improvements in or relating to electrical wave transmission networks
FR826617D FR826617A (fr) 1936-09-12 1937-09-11 Réseaux de transmission d'ondes électriques
CH202644D CH202644A (de) 1936-09-12 1937-09-11 Vierpoliges Übertragungsnetzwerk zwischen zwei zu koppelnden Anordnungen mit verschiedenen Wellenwiderständen.

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US100400A US2149356A (en) 1936-09-12 1936-09-12 Wave transmission network

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US2149356A true US2149356A (en) 1939-03-07

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BE (1) BE423379A (en(2012))
CH (1) CH202644A (en(2012))
FR (1) FR826617A (en(2012))
GB (1) GB498332A (en(2012))
NL (1) NL49003C (en(2012))

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2446982A (en) * 1943-02-08 1948-08-10 Us Navy Apparatus for broad-band radio transmission
US2516529A (en) * 1946-03-04 1950-07-25 Richard C Raymond Capacitive connection for coaxial lines
US2524821A (en) * 1943-12-28 1950-10-10 Int Standard Electric Corp Wide frequency band amplifier
US2526846A (en) * 1947-03-12 1950-10-24 David F Bowman Impedance-transforming arrangement
US2528367A (en) * 1946-03-09 1950-10-31 Rca Corp Radio wave conducting device
US2563591A (en) * 1951-08-07 Microwave converter
US2931992A (en) * 1956-07-02 1960-04-05 Bell Telephone Labor Inc Microwave impedance branch
US2968772A (en) * 1958-11-14 1961-01-17 Bell Telephone Labor Inc Wave filter
US3167729A (en) * 1962-10-29 1965-01-26 Sylvania Electric Prod Microwave filter insertable within outer wall of coaxial line

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2563591A (en) * 1951-08-07 Microwave converter
US2446982A (en) * 1943-02-08 1948-08-10 Us Navy Apparatus for broad-band radio transmission
US2524821A (en) * 1943-12-28 1950-10-10 Int Standard Electric Corp Wide frequency band amplifier
US2516529A (en) * 1946-03-04 1950-07-25 Richard C Raymond Capacitive connection for coaxial lines
US2528367A (en) * 1946-03-09 1950-10-31 Rca Corp Radio wave conducting device
US2526846A (en) * 1947-03-12 1950-10-24 David F Bowman Impedance-transforming arrangement
US2931992A (en) * 1956-07-02 1960-04-05 Bell Telephone Labor Inc Microwave impedance branch
US2968772A (en) * 1958-11-14 1961-01-17 Bell Telephone Labor Inc Wave filter
US3167729A (en) * 1962-10-29 1965-01-26 Sylvania Electric Prod Microwave filter insertable within outer wall of coaxial line

Also Published As

Publication number Publication date
NL49003C (en(2012))
FR826617A (fr) 1938-04-06
GB498332A (en) 1939-01-06
BE423379A (en(2012))
CH202644A (de) 1939-01-31

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