US2248751A - Transmission modifying network - Google Patents

Transmission modifying network Download PDF

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Publication number
US2248751A
US2248751A US255590A US25559039A US2248751A US 2248751 A US2248751 A US 2248751A US 255590 A US255590 A US 255590A US 25559039 A US25559039 A US 25559039A US 2248751 A US2248751 A US 2248751A
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United States
Prior art keywords
network
transmission line
transmission
conductor
frequency
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Expired - Lifetime
Application number
US255590A
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English (en)
Inventor
Frankel Sidney
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Federal Telegraph Co
Original Assignee
Federal Telegraph Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Federal Telegraph Co filed Critical Federal Telegraph Co
Priority to US255590A priority Critical patent/US2248751A/en
Priority to GB468/40A priority patent/GB534176A/en
Priority to FR863262D priority patent/FR863262A/fr
Application granted granted Critical
Publication of US2248751A publication Critical patent/US2248751A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • 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
    • H03H7/01—Frequency selective two-port networks
    • H03H7/0123—Frequency selective two-port networks comprising distributed impedance elements together with lumped impedance elements

Definitions

  • My invention relates to high frequency transmission systems, and more particularly to transmission modifying or filter networks designed to reject certain high frequency wave components from a transmission line.
  • transmission lines for operating at high frequencies with a balanced load be properly balanced with respect to the earth or ground.
  • These arrangements are particularly useful for connecting a radio frequency receiver or transmitter to its antenna by transmission lines designed to carry voltages which are balanced with respect to ground.
  • unbalanced current may flow in the conductors or feeders of the transmission line.
  • the current in the feeders ar resolvable into two setsof components, the series current, for which the line acts as a loop, and the parallel current, for which the line acts as two halves in parallel.
  • the series current or loop current the component which produces the parallel effect
  • the parallel current in the transmission line represents the degree of unbalance of the line, and when this parallel current is zero the line is balanced.
  • the feeders of the transmission line behave like a single wire, the return circuit being the image conductor in the ground.
  • the impedance of the transmission line to this current may be made very large by the use of a network in accordance with this invention.
  • FIG. 1 represents a diagrammatic embodiment of a network in accordance with my invention
  • Fig. 2 illustrates a network in accordance with my invention applied to a transmission system
  • Figs. 3, 4 and 5 show alternative forms of the network.
  • I0 and II represent two conductors of a transmission line spaced apart a distance d.
  • a short circuited transmission line section I2 having an electrical length equal to a quarter of a Wavelength or odd multiple thereof with respect to the fundamental frequency to be transmitted over the transmission line.
  • Spaced a distance X from the bridging point of transmission line section [2 is another section 13, also electrically a quarter of a wavelength or an odd multiple thereof in length at the operating frequency. Since sections I2 and 13 are electrically a quarter of a wavelength long and are short circuited, they will not effect the loop current in the transmission line, since they will offer substantially infinite impedance at this frequency.
  • a connecting conductor I4 Between the sections I2 and I3 is provided a connecting conductor I4.
  • This conductor is connected between these networks preferably at a point midway of the length of the short circuiting bars on the transmission line section.
  • This network then furnishes a reentrant network in so far as the parallel current in transmission line I 9II is concerned, while offering substantially no impedance to the loop current in the system.
  • This reentrant network may be defined as having one arm 61 equal to X and the other arm 62 equal to i Y-l- Y
  • 62-01 equal to Substituting the values of 01 and 02 given above we have This evaluation is not strictly correct since a quarter wave section such as l2 or [3 is not exactly a quarter wavelength long in physical dimensions because of the so called end effect of the short circuiting bar. It is therefore necessary to make the requisite allowance in the length of the conductor Y to take care of this discrepancy, so that the electrical effective length of sections 12 and I3 and connector IQ for the parallel currents will be 180 different from the distance X.
  • the network will serve as cut-off filter. Accordingly, a parallel wave traveling along the transmission line I illl will be stopped by the blocking filter. There may be small amount of interaction due to the fact that Y differs in length from X and for this reason the network will not be perpendicular to the line. However, if the line spacing is small compared to i, the sections I2--l3 are almost perpendicular to the transmission line Iii-l I and produce little interaction.
  • This device has been set up in a crude form in the field and a very superficial test shows a very great decrease in percentage unbalance.
  • the spacing X between the sections may be chosen as any desired value. If this distance X is chosen equal to and Y is of similar effective length, we get the additional result that l This choice of constants is permissible so far as the filtering action of the section in reducing the fundamental parallel currents is concerned.
  • the wavelength may be designated as and the (is for the second harmonic may be des ignated as 01' and 02', respectively. Thus a multiple of 360.
  • the filter network will thus serve as a sum filter to reduce the second harmonic parallel current as well as a difference filter for the fundamental.
  • 01'+02' 2) ⁇ a multiple of 360 and similarly at each of the other harmonic frequencies the corresponding sum of 01 and Hz is equal to a multiple of 360 so that the arrangement will, under these conditions produce a cut-off not only of the parallel current at the fundamental frequency, but of these parallel currents at all of the harmonic frequencies.
  • the quarter wave sections will also act as a rejection filter for the second harmonic loop current.
  • Fig. 2 The application of this filter network for reduction of parallel currents in a high frequency transmission system is illustrated in Fig. 2.
  • 20 represents a high frequency source connected over a two-conductor transmission line 2
  • a network 23 of the type similar to that illustrated in Fig. 1.
  • the high frequency voltages impressed upon the line from the source 20 are conducted over the line 2
  • are not impeded by the presence of network 23.
  • network 23 is designed as outlined above, so that the parallel currents at the fundamental frequency are filtered out, as pointed out above.
  • the network 23 may be so designed, as outlined above, as to act as a rejection filter for the various harmonic frequencies.
  • the high frequency source 23, may be, for example, a radio transmitter in which case the load 22 may be represented as an antenna.
  • the high frequency source 20 may be a receiving antenna which is connected over a balanced line 2
  • the filter network in accordance with my invention need not be applied only to radio transmitting and receiving arrangements, but may be used in any circuit in which a high frequency balanced line is desired.
  • the network may have various forms other than that shown in Figs. 1 and 2, if desired.
  • the preferred form of Fig. 1 is easier to adjust since the short circuiting bar may be moved to vary the tuning.
  • Fig. 3 is shown an arrangement where the networks 32 and 33 corresponding to 2 and 13 of Fig. 1 are made triangular in shape. These networks or sections are bridged across transmission line 30 and are interconnected by conductor. Sections 32 and 33 may be adjusted in a known manner so as to present to series currents in line 30 substantially infinite impedance. The other adjustments may then be made in accordance with the teaching of this application so the completed network circuit operates as a cut-off filter.
  • Fig. 4 an arrangement similar to Fig. 3 is shown except that the sections 42 and 43 are directly connected together at 44, instead of using a separate connecting conductor.
  • This network may be properly adjusted to operate as a rejection filter.
  • the effect of their reaction on the line must be considered but this is not of any great importance if the angle made with the line is maintained greater than 45.
  • FIG. 5 A still further alternative structure is shown in Fig. 5.
  • each of the sections 42, 43 are two conductor parallel transmission lines similar to those shown in Fig. 1. These lines are brought together so that a common short circuiting bar 44 may be used and no additional conductor for interconnecting them is required.
  • the variation from perpendicular relationship must be taken into consideration in designing the network.
  • the sections will have to be electrically an odd multiple of quarter wavelengths long instead of simply one quarter wavelength in order that the other dimensions for the cut-off filter may be realized.
  • any of the known means for avoiding such trouble may be provided.
  • the network may be provided with a shield, the network may be folded to cancel out radiation, or known compensating means may be used.
  • a high frequency transmission network for reducing parallel currents in a two-conductor transmission line while permitting free passage of balanced loop current, comprising impedance means offering substantially infinite impedance to the working frequency bridged across said conductors, a second impedance means of similar characteristics to said first impedance means bridged across said transmission line at a point spaced from said first section, and a conductor connecting together said impedance means, the overall electrical length of said impedance means and said connecting conductor differing from said spacing by a quarter wavelength or odd multiple of said working frequency, and the sum of overall length and said spacing being equal to one wavelength or an integral multiple of the wavelength of said working frequency.
  • a high frequency transmission net work for reducing parallel currents in a two-conductor transmission line while permitting free passage of balanced loop current comprising impedance means offering substantially infinite impedance to the working frequency bridged across said conductors, a second impedance means of similar characteristics to said first impedance means bridged across said transmission line at a point spaced from said first section, and a conductor connecting together said impedance means, the overall electrical length of said impedance means and said connecting conductor differing from said spacing by a quarter wavelength or odd multiple of said working frequency.
  • a high frequency transmission network for reducing parallel currents in a two-conductor transmission line while permitting free passage of balanced loop current, comprising impedance means offering substantially infinite impedance to the Working frequency bridged across said conductors, a second impedance means of similar characteristics to said first impedance means bridged across said transmission line at a point spaced from said first section, and a conductor connecting together said impedance means, the overall electrical length of said impedance means, said connecting conductor, and said spacing being equal to one wavelength or an integral multiple of a wavelength at said working frequency.
  • a high frequency transmission system comprising a two-conductor transmission line, a high frequency energy source coupled to said line, and means for reducing parallel currents in the conductors of said transmission line comprising impedance elements effectively equal to a short circuited transmission line an odd number of quarter wavelengths long bridged across said transmission line conductors at spaced points and a conductive connection intermediate the ends of said impedance elements.
  • a high frequency transmission network for reducing parallel currents in a two-conductor transmission line while permitting free passage of balanced loop current comprising a short circuited quarter wavelength section of transmission line bridged across said conductors, a second short circuited quarter wavelength section bridged across said transmission line at a point spaced from said first section, and a conductive connection intermediate the ends of said short circuited sections.
  • a high frequency transmission network designed to pass the fundamental frequency loop current and to act as a blocking filter for the second harmonic frequency loop current and the fundamental and harmonic frequency parallel currents, comprising a first short circuited section of transmission line a quarter wavelength or an odd multiple of said fundamental frequency in length, bridged across said transmission line, a second short circuited section of transmission line, a quarter wavelength or an odd multiple of said fundamental frequency long, bridged across said transmission line at a point spaced substantially a quarter wavelength or an odd multiple at said fundamental frequency from said first named section, and a conductor approximately a quarter of a wavelength or an odd multiple thereof long interconnecting said short circuited sections.

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  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)
US255590A 1939-02-10 1939-02-10 Transmission modifying network Expired - Lifetime US2248751A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US255590A US2248751A (en) 1939-02-10 1939-02-10 Transmission modifying network
GB468/40A GB534176A (en) 1939-02-10 1940-01-09 Modifying networks for the transmission of high frequency currents
FR863262D FR863262A (fr) 1939-02-10 1940-02-03 Systèmes de transmission à fréquences élevées

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US255590A US2248751A (en) 1939-02-10 1939-02-10 Transmission modifying network

Publications (1)

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US2248751A true US2248751A (en) 1941-07-08

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Application Number Title Priority Date Filing Date
US255590A Expired - Lifetime US2248751A (en) 1939-02-10 1939-02-10 Transmission modifying network

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Country Link
US (1) US2248751A (fr)
FR (1) FR863262A (fr)
GB (1) GB534176A (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2435618A (en) * 1944-07-05 1948-02-10 Raytheon Mfg Co Coaxial transmission line
US2474277A (en) * 1945-03-19 1949-06-28 Standard Telephones Cables Ltd Transmission line
US2708238A (en) * 1954-04-09 1955-05-10 Silverman Emanuel Television wave trap and the like
US3747030A (en) * 1971-06-07 1973-07-17 Oak Electro Netics Corp Band pass filter with transmission line section
US4455540A (en) * 1981-07-24 1984-06-19 Thomson-Csf Band pass filter with linear resonators open at both their extremities

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2435618A (en) * 1944-07-05 1948-02-10 Raytheon Mfg Co Coaxial transmission line
US2474277A (en) * 1945-03-19 1949-06-28 Standard Telephones Cables Ltd Transmission line
US2708238A (en) * 1954-04-09 1955-05-10 Silverman Emanuel Television wave trap and the like
US3747030A (en) * 1971-06-07 1973-07-17 Oak Electro Netics Corp Band pass filter with transmission line section
US4455540A (en) * 1981-07-24 1984-06-19 Thomson-Csf Band pass filter with linear resonators open at both their extremities

Also Published As

Publication number Publication date
FR863262A (fr) 1941-03-28
GB534176A (en) 1941-02-28

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