US2401353A - Coupled network - Google Patents

Description

June 4, 1946. R. B. HOFFMAN 2,401,353

COUPLED NETWORK Filed July 21, 1942 SOUPCE /2 H/gH FEEQUf/l/C) v EXC/T/NG .S/GIVAL INPUT 4:, I

INVENTOR 055 a l/OFFMAA/ Patented June '4, 1946 COUPLED NETWORK Ross B. Hoffman, East Orange, N. J., assignor to Federal Telephone and Radio Corporation, a

corporation of Delaware Application July 21, 1942, Serial No. 451,721

1 18 Claims.

This invention relates to transmission lines and more particularly to a high frequency controlling network coupled thereto.

In my copending application, Serial No. 418,671 filed November 12, 1941, I disclosed antenna controlling network sections by which concurrent and alternate transmission and reception over a common antenna was made possible. As therein disclosed, I accomplished this by controlling the resonance of quarter wavelength network sections coupled to the transmission lines connecting a common antenna to a transmitter and a receiver. It is known that a, resonating network section one quarter wavelength long, short circuited at one end, and coupled to a. transmission line may introduce substantial voltages at the resonant frequency into the line in the zone of the coupling. If the resistance of the coupled section is negligible, these voltages-may be so large as effectively to block or prevent the passage of power along the transmission line beyond the point where the section is coupled. In my aforesaid application, I utilized this blocking efiect of the quarter wave short circuited coupled sections to effect a switching of the antenna at will from the transmitter circuit to the receiving circuit and vice versa.

This switching was effected by using a control circuit for. two coupled network sections, one for each circuit, whereby the shunt reactance between the open parts of each of the coupled sections could be varied, thus changing the operation of the sections at will between resonance and non-resonance. One of the means for controlling the resonant and non-resonant operation of thesecti'ons included'a vacuum tube circult in which the output of the vacuum tube was applied or removed from across the open part of each section. By this means, the shunt impedance of each section was changed so that when the tube was at cut-oil, the section could be in resonance with the transmission line in one form of the aforesaid invention and when a certain signal or impulse was applied to the grid of the tube, an effective shunt impedance was established thereby detuning or in other words producing a non-resonant condition of the section.

- "l fhe present invention is an improvement of the" coupled controlling network feature of the invention covered in my aforesaid application,

I and one of the objects of the present invention 2 ditions of which may be controlled by variations in very small voltages.

Another object of the invention is to provide a coupled network controllable by a small reactance tube as compared to high power tubes required for controlling the coupled sections heretofore proposed.

Still another object of the invention is to provide a network having vacuum tube control of the tuning thereof wherein the network is'of such a character that effective tuning and/or detuning of the network is possible with but a small tube reactance swing.

A further object of the invention is to provide an improved method for controlling the resonant condition of a network coupled section.

The above objects and others ancillary thereto are accomplished by my invention by usinga doubled coupled network of sections. ferred form, one of the sections is adapted to resonate at a particular wave frequency and the second of the sections, which is slightly dissimilar to the first-mentioned section, is adapted to be tuned to the resonance frequency thereof and thereby alter the resonating condition of the first section. This second section of the network is coupled with the first section and the length thereof is such that when its impedance is changed to a value corresponding to the impedance of the first section, it tends to resonate therewith thereby altering the impedance of the first section. This adverse effect to the resonance condition of the-first section with respect to the transmission line with which it may be coupled reduces the resonant voltages developed in the line thereby unblocking the line to wave transmission at the aforementioned frequency. This variation of the impedance of the second section, so as to bring the impedance thereof in line with the impedanceof the first section, may be made by the use of a vacuum tube circuit in which the variation of impedance may be ef-- fected by variation of the grid voltage of the tube. This methcxi of controlling the resonance and non-resonance of the first section by means of a second section is of great advantage over the application of a tube circuit directly to the vfirst section in that the controlof the resonant condi-' tion can be eil'ected by a vacuum tube having a much smaller reactance. It also permits connection of the tube circuit to-the section further out toward the open end thereof thereby greatly increasing the shunt capacity effect of the tube circuit upon the impedance of the section.

The coupled relation ofthe two network sec- In a pre- For an understanding of these several relationships of the sections and other features of the invention, reference may be had to the following detailed description to be read in connection with v the accompanying drawing in which the sole figure thereof represents schematically a typical form of apparatus by which the aforementioned relations and the method of control of this invention may be performed.

Referring to the drawing, a source It or high frequency alternating current, such as a. transmitter, is shown for purposes of illustrating the invention, connected by a transmission line ll to a load 12, which may be an antenna. It will be understood, oi. course, that this invention may be used with an antenna which supplies the high frequency current and the part ID may comprise a receiver. I I Coupled to the transmission line I4 is a right angle halt wave network l8, one leg A of which comprises a pair of conductors I8 and I! of the order of or approximately a quarter wavelength and short circuited at one end by a short circuiting conductor l8.- This leg of the network is arranged parallel to the transmission line ll. The other leg B of the network comprises a pair or conductors and 2! connected at one end to the open ends or the conductors I8 and i1 and short circuited at the other end by a short circuiting conductor 22. The two legs, each being in the order of a quarter wavelength, are adapted to resonate with the transmission lines when the transmission lines carry power having the wavelength for which the network coupling is designed. The leg A is parallel to the line H While the leg B is at right angles thereto. At resonance, the voltages built up in the leg A at its end or junction IS with leg B may be such that the voltages effectively block the passage of the power at the point where the network is coupled to the transmission line.

In accordance with my invention, 1 provide a second network 25 comprising parallel conductors 26 and 21 arranged p rallel to the conductors 20 and 2| of the leg B. A short circuiting conductor 28 is provided to short circuit the conductors 28 and 21 at one end of the section. Thesection 25, for the preferred relationship is of an electrical length slightly shorter than a quarter wavelength so that it will not resonate with the network it unless the electrical length of the section 2| is changed by resonance exciting energy to, correspond to the electrical length of the section ii. I accomplish this by providing a vacuum tube circuit along the lines or either of the embodiments disclosed in my oopending application Serial No. 418,671. For purposes 0! illustratio'n, I have chosen a single vacuum tube circuit 30. By means ot-the vacuum tube circuit, the resonant condition or the section II is controlled by controlling the resonance excitin energy applied to the section 2|. This control may be eflected by ignals or other impulse; re-

ceived at the input 43 of the vacuum tube circuit. The resonance exciting signal input may be applied in any well-known manner such as over a coupling condenser 4| and across a resistance which in the iorm, shown includes a resistor 31 and aportion of a bias-control potentiometer 32.

The vacuum tube circuit 30 includes a tube 3|, 3

the output 01 which may include the usual cathode, control grid, second grid, and anode elements, and may be applied to the section 25 at points 32 and 33, the voltages at these points being 180 out of phase. The supply lines to the points 32 and 33 each include a condenser 34 and 35 respectively. Connected to the condenser 34 is a resistor 36 which is preferably of such a magnitude that the value of the R. C. network formed by the resistor 36 and the grid cathode capacitance of tube 3i will displace the phase of the high frequency grid voltage substantially with respect to that at the point 32. Inasmuch as the plate current of the tube 3| is in phase with the voltage applied to the control grid, this current leads the voltage at point 33 because voltages at point 32 and 33 are out of phase. It thus becomes clear that the plate current fed into section 25 through the condenser 35 may produce an eiiective shunt capacity across the section since the voltage and current thereof are substantially 90 out of phase.

Since this effective shunt capacity may vary with the amplification or output of the tube, an appropriate adjustment of the grid bias by means of the potentiometer 38 may control the magnitude of shunt reactance across points 32 and 33 to a desired degree depending on the magnitude of blocking signal applied at the input 40. As desired, high frequency choke 42 and 43 may be provided in the input and output circuits of the tube 3| to isolze the grid and plate supply respectively, and screen grid voltage may then be supplied over a resistor 46, the screen grid being connected to ground through a resistor 41.

The control circuit for the section 25 is preferably normally adjusted so that the section will be detuned when no signal or controlling impulse is received at the input 40. Upon reception of a signal of fixed amplitude. the resultant reactance across the section 25 would be such as to resonate the section, thus decreasing the flow in the network i5 to which the section is coupled.

In operation of the control circuit, assuming that no controlling signal is received at the input 40, the section 25 will have an impedance such that it will not resonate with the leg B of the section Hi. The section I5 is adapted normally to resonate with the high frequency waves transmitted along the transmission lines H. The section H5 at resonance develops a high potential at the open end or junction 19 of the legs A and B thereby setting up correspondingly high voltages in the adjacent transmission lines H, which operate to block and prevent flow of waves beyond the coupling therewith of the section l5. Thus, the propagated waves of the particular frequency for which the section i5 is designed is normally prevented from reaching the load or antenna i2.

To permit the waves to pass, a signal of small voltage may be applied at the input 40 thereby establishing by means of the tube circuit 30 a shunt reactance across the section 25 at the points 32 and 33. This shunt reactance eil'ect changes the electrical length of the section 25 to correspond closely to the electrical length or the leg B of section ii. The mutual inductance relationship oi the leg B and the section 25 under this condition alters the electrical length of the, leg A of the section IS with respect to the irequency of the current of the transmission line.

This results in a decrease in the resonance rela- 5. tween the two sections II and 25. The voltages in the section It decrease immediately upon the establishment of near resonance between the two sections, and this decrease limits the building up.

of voltages in the section 25. That is to say,

the voltages built up in the section 25 will be considerably less than the voltages in the section l since the voltages of the section l5 are decreasing as the voltages in section 25 are building up I are relatively small, it follows that the tube 3|, for control operation, need have only a small reactance value. This is an important advantage over controlling coupled networks heretofore shunt capacity would be in the nature of a trimming action only. At resonance the voltages across the' open end of the section 25 are maximum, but since this maximum is relatively low for the section 25 of the network system of my invention, the maximum voltages are not so great as to produce deleterious or undesirable efiects on even a low reactance tube even when the connections 32 and 33 are located relatively near the open end of the-section. The advantage of locating the connecting points 32 and 33 more closely adjacent the open end than the short circuit end 28 is that the shunt reactance of thetub circuit produces greater effect and, therefore, more sensitive control.

In addition to the above-described resonance controlling relationship between the coupled network sections l5 and 25 of my invention, severalother controlling relationships are contemplated. Assume,- for example, that the section I5 is normally resonant at the frequency of the transmitted current when the section 25 is tuned to resonance at the same frequency. This resonant relation may e detunedto permit current flow in the transmission line by applyin an impedance across the section 25. For another controlling relationship, assume that the section I! is normally detuned with respect to the frequency of the transmitted current when the section 28 is tuned. This resonance condition will permit current fiow. Then when the section 25 is detuned, it has the effect of tuning the section I! thereby preventing current flow. For still another controlling relationship, assume that the section I! is normally detuned with respect to the frequency of the transmitted current when section 26 is detuned. This condition also permits current fiow. Then when section 25 is tuned, it will have the efiect of tuning the section l5 thereby preventing current flow. v Thus, while I have shown but one embodiment of the invention, I recognize that many changes and variations are possible in the construction and method of control thereof without departing from the invention. It is to be understood, therefore, that the embodiment as herein shown and described is to be regarded as illustrative of the invention only and not as restricting the appended claims.

What I claim is:

ince the voltages produced in the section 25 1. In a high frequency transmission system having a transmission. line and means for propa- I gating high frequency energy waves therealong; means including a network to control the transmission of said energy waves along said line, said network comprising a first transmission line section so coupled to said line that resonance of. the section at the frequency of said energy waves is operable to substantially block the fiow of said energy waves past the point of such coupling, a

second transmission line section coupled to the first mentioned section, and means to control the resonance of said first section by controlling the resonant relationship between said first and said section sections.

2. In a high frequency transmission system having a. transmission line and means for propagating high ,frequency energy waves therealong; means including a network to control the transmission of said energy-waves along said line, said network comprising a firstsection coupled to said line, said section being resonatable at the frequency of said energy waves to build up voltages operable to substantially block the fiow of said energy waves past the point of such coupling, a second section coupled to the first section. the resonance tuning and detuning of said second section controlling the resonance condition of said 7 first section, and means responsive to input signals to apply a. shunt reactance across said second section to control the tuning and detuning of said second section.

3. The coupled network in a high frequency transmission system as defined in claim 2 wherein said first section is normally resonance tuned at the frequency of the energy waves and said sec- 0nd section is normally resonance detuned at said frequency and said control means is operable to resonance tune said second section and thereby diminish the resonance relationship betweensaid resonance detunesaid second section and thereby diminish the resonance relationship between said first section and said line. n

5. The coupled network in a high frequency transmission system as defined in claim 2 wherein said first section is normally resonance detunedat the frequency of the energy waves and said second section is normally resonance tuned at said frequency and said control means is operable to resonance detune said second section and thereby tune said first section to resonance at said frequency to block the flow of energy waves along the line. 1

6. In a high frequency transmission system having a transmission line and means for propagating high frequency energy waves therealong; means'including a network to control the transmission of said energywaves along said line, said network comprisinga first section coupled to said line, said section being resonatable at the fre quency of said energy waves to build up voltages operable to substantially block the fiow of said energy waves past the point of such coupling, a part of said first section being disposed at right angles to said line, a second section coupled to said part, and means to apply a shunt reactance across saidsecond section to control the tuning anddetuning oi'ssid second section to resonance a second section coupled to said other leg, and

means to apply a shunt impedance to said second section to control the tuning and detuning of said second section to resonance at said frequency to thereby control the resonance tuning of said first section.

8. In a high frequency transmission system having a transmission line and means for propa gating high frequency energy waves therealong; means including a network to control the transmission of said energy waves along said line, said network comprising a first section having two legs each in the order of a quarter wavelength,

I other leg being disposed at right angles thereto,

another section coupled to said other leg, and a resonance exciting input circuit having a tube responsive to input signals to apply a shunt reactance across said second section to control the tuning and detuning of said second section 'to resonance at said frequency to thereby control the resonance tuning of said first section.

9. A network for use in controlling the flow of high frequency energy waves along a transmission line comprising a plurality of sections, one of said sections being of an effective electrical length in the order of a quarter length of the energy waves-to be controlled, a second of said sections being coupled with said one section but of a length dissimilar thereto, and said second section having means operable to effect change of the electrical length thereof to correspond to the electrical length of said one section.

10. A network for use in controlling the flow of high frequency energy waves along a transmission line comprising a plurality of sections, one of said sections having two legs disposed at right angles to each other, each leg being of an electrical length in the order of a quarter length of the energy waves to be controlled. a second of said sections being coupled with one of said legs, and said second section having a resonance exciting input connection having means responsive to input signals to effect change of the electrical length thereof to correspond to the electrical length of said one leg.

11. A network for use in controlling the flow of high frequency energy waves along a transmission line comprising a plurality of sections, one of said sections having two legs disposed at right angles to each other, each leg being of an effective electrical length in the order of a quarter wavelength of the energy waves to be controlled,

-a second of said sections being coupled with one of said legs, and said second section having means operable to effect change of the electrical length thereof to correspond to the electrical length of said one leg.

12. The method of controlling the flow of high frequency energy waves along a transmission line having coupled thereto a network including two transmission line sections, comprising so coupling one'of said sections to said line that resonance of said one section at the frequency of said energy waves is operable to substantially block the flow of said energy waves past the point of coupling,

and controlling this resonance relationship of said one section by controlling the resonance relationship between said two sections.

13. The method of controlling the flow of high frequency energy waves along a transmission line having coupled thereto a network including two transmission line sections, comprising so coupling one of said sections to said line that resonance of said one section at the frequency of said energy waves is operable to substantially block the flow of said energy waves past the point of coupling. controlling the other of said sections independently of the flow of said energy waves, and controlling the resonance relationship between said one section and said transmission line by controlling the resonance relationship between said two sections.

14. The method as defined in claim 13 wherein the controlof the resonance relationship between the two network sections comprises applying at will a shunt reactance across the second of the two sections.

15. The method as defined in claim 13 wherein said one section is normally resonance. tuned at the frequency of the energy waves. the second of said two sections is normally resonance detuned at said frequency, and the normal resonance condition of said one section is detuned by tuning said second section to said frequency.

16. The method as defined in claim 13 wherein said one section is normally resonance detuned at the frequency of the energy waves, the second of said two sections is normally resonance tuned at aid frequency, and the normal resonance condition of said one section is detuned by detuning said second section.

17. The method as defined in claim 13 wherein the two network sections are normally resonance tuned at the frequency of the energy waves, and the normal resonance condition of said one section thereof is altered by detuning the second of the two sections.

18. In a high frequency transmission system having a transmission line and means for propagating high frequency energy waves therealong, means including a network to control the transmission of said energy waves along said line, said network comprising a first transmission line section so coupled to said line that resonance of the section at the frequency of said energy waves is operable to substantially block the flow of said energy waves past the point of such. coupling, a second transmission line section coupled to the first mentioned section, and means energized independently of the electrical status of said transmission line for controlling the resonance of said second section to thereby control the resonance of said first section. 1

- ROSS B. HOFFMAN.

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