US2402625A - Antenna switching device - Google Patents

Description

June 25, I946. R. B. HOFFMAN 2,402,625

ANTENNA SWITCHING DEVICE Filed Nov. 12, 1941 FIG. 1.

ANTENNA 77?.4/V5M/77ER arcs/V52 INVERTER L13 DELAY IMPULSE flack/[V6 c/Rc U/T GENERATOR CIRCUIT FIG. 2. FIG. 3.

HVVENTOR.

ATTORNEY.

Patented June 25, 1946 2,402,625 ANTENNA swrronmo DEVICE Ross B. Hoffman, East Orange, NHL, assignor to Federal Telephone and Radio Corporation, a corporation of Delaware Application November 12, 1941, Serial No. 418,671

12 Claims.

1 This invention relates to improvements in antenna coupling devices, and in particular to such devices as applied to enemy aircraft identiflca tion by friendly aircraft or by antiaircraft stations. A typical system to which the invention is applicable has been disclosed in the copending application of H. G. Busignies, Serial No. 417,151, filed October 30, 194i, and entitled "Aircraft identifier.

Systems have been devised, especially in the police radio field for utilizing one antenna for both transmitting and receiving. Such simultaneous operation can be attained when both transmitting and receiving equipment is operating on slightly different frequencies; and, if only one frequency be used, switch-over from transmitter to receiver may be accomplished by ordinary relayapparatus.

In connection with the use of impulse-energyoperated systems for obstacle identification purposes on the ground or in aircraft, it may be desirable to use only one antenna for transmission and reception on the same frequency with changeover as rapid as a few microseconds, or even a fraction of a microsecond. It is wellknown that impulse systems of the nature referred to involve the transmission of relatively large amounts of power and detection of relatively weak signals. As a result, previous switchover methods and systems may not be satisfactory in impulse sytems of this character.

Accordingly, it is an object of the invention to provide improved'means for enabling concurrent transmission and reception on a common antenna. Another object is to provide improved means for permitting alternate transmission and reception of radiant energy of substantially the same carrier frequency on a single antenna. A further object is to provide improved switching means. It is a more specific object to provide improved means permitting the use of 4a single'antenna for transmission of impulse energy and detection of a reflection thereof.

Other objects and various further features of novelty and invention will hereinafter be pointed out or will occur to those skilled in the art from a reading of the fOllOWing specification in conjunction with the drawing included herewith. In said drawing Fig. 1 is a schematic block diagram illustrating an embodiment of the invention; and

Figs. 2 and 3 show alternative preferred forms of portions of the embodiment shown in Fig. 1.

As above indicated, in systems employing transmission and reception of impulse energy characterized by the same carrier frequency,cer-

. 2 deemed desirable for this purpose to employ permanently coupled transmission lines between the antenna and both the transmitter and receiver, and to make use of additional circuit elements alternately to block each of these trans-- mission lines.

It is known that a resonating section of transmission line, A wave length long, short-circuited at one end, and coupled to another transmission line may introduce substantial voltages into the A preferred embodiment of the invention as thus applied is shown in Fig. 1 where a single antenna i0 is employed for transmission and reception. Antenna l0 may be directly coupled as shown to a transmitter H by a suitable transmission line l2 and'to a receiver l3 by line [4. In order alternately to block transmission lines l2 and i4, short-circuited coupled sections I5 and tain difiiculties may arise in the use of present I6, respectively are provided coupled to each of these lines.

As indicated above it is expressly contemplated that my invention will be applicable to concurrent transmission and reception of impulse energy, re:

ception being operative during intervals between transmission of individual impulses, Due to the extremely rapid rate of switch-over required,

however, mechanical systems for varying the resonance, and hence blocking eflect, of coupled sections l5 and it are deemed inappropriate.

Accordingly, in accordance with the invention I tion IS in a detuned state,-whereby substantially no blocking of received energy results. A very short instant before the transmission of an impulse,.tube circuit I8 is appropriately energized" as to present such reactance to coupled section l6 that the section 'will resonate and thus prevent any transmitted energy being dissipated in line H. This condition of resonance is preferably maintained for the duration oi. the transmitted impulse and a very short instant thereafter in order to be absolutely sure of blocking reception of impulses as they-are transmitted. 'Since it is desired to make line I: conductivewhile line I4 is not, tube circuit 11 for coupled section I5 is 3 preferable operative in a sense inverse to circuit l8, as will be clear.

The circuit of Fig. 1 shows schematically how the desired relation of blocking and passing effects of coupled sections l5 and I 6 may be obtained. In accordance with known practice an impulse generator l9 may be employed in the generation of impulses to be transmitted and at the same time for energizing an appropriate blocking circuit 20 to assure that the receiver is inoperative as individual impulses are being transmitted. As indicated, blocking circuit 20 may supply a blocking signal of slightly greater duration than that of the transmitted impulses. Suitable means for generating such a signal has been disclosed in the copending application of E. Labin, Ser. No. 386,282, filed April 1, 1941, and entitled "Pulse modulation system. In the form shown, in order to assure that transmitted impulses may fall within the above-mentioned blocking interval, appropriate time delay means 2| may be included in the line energizing transmitter ll.

In accordance with a feature of the invention I employ energy supplied by blocking circuit 20 to control the alternate resonant and nonresonant conditions of coupled sections l5 and I6. As mentioned, the output'of blocking circuit 20 is a series of impulses of slightly greater duration than the transmitted impulses. In the form shown, these blocking impulses may be applied directly to tube circuit l8, and means (not shown) may be provided to control or adjust the magnitude of these impulses to assure resonance in section 16 while such impulses are being supplied. In order to energize tube-circuit l1 appropriately, an inverter circuit 22 of known construction may be employed to feed circuit I1 with blocking-energy inverse to that which is being supplied circuit [8. Thus, coupled section l5 may be maintained normally in a condition of resonance; that is, during intervals between transmission of impulses, to prevent received energy from being dissipated in transmission line I 2, as will be clear.

In Fig. 2 I show a preferred embodiment of a possible tube circuit for performing the functions above mentioned in connection with circuits l1 and I8. In this embodiment a short-circuited quarter-wave length section 23, which may correspond to section l5 or ii in Fig. 1, may be rendered alternately resonant and non-resonant by corresponding alternate substantial application and removal, as the case may be, of a shunt impedance supplied as the output of tube 24. This function of tube 24 is obtained in accordance with blocking signal energy, which may be supplied in the manner above indicated, to the input 25 of the device. In a well-known manner, blocking, or resonance exciting, energy is applied over a coupling condenser 26 and across a resistance, which in the form shown includes a resistor 21 and a portion of a bias-control potentiometer 28.

Turning in more detail to a consideration of tube connections to coupled section 23, output of tube 24, which in the form shown includes a cathode, control grid, screen grid. and anode elements, may be applied to the section at points 3 the voltages at these points being 180 out of phase. Both supply lines include blocking condensers 3|, 32, and one of these lines further includes a resistor 33. Resistor 33 is preferably of such a magnitude that the value of the RC network formed by resistor 33 and the grid-cathode capacitance of tube 24 will-displace the phase of the radio-frequency grid voltage substantially with respect to that at oint 29. Inasmuch as the plate current of tube 24 is in phase with the voltage applied to the control grid, this current leads the voltage at point 30, because voltages at points 29, 30 are out of phase, as will be recalled. It thus becomes clear that radio frequency plate current fed into section 23' through blocking condenser 32 may produce an effective shunt capacity across the section, since voltage and current, as above indicated, are substantially 90 out of phase.

This effective shunt capacity may varywith the amplification or output of the tube. Accordingly, appropriate adjustment, say of grid bias by means of potentiometer 28, may control the magnitude of shunt reactance across points 29, 30 to a desired degree, depending on the ma nitude of blocking signal applied at input 25. As desired, radio frequency chokes 34. 35 may be provided in the input and output circuits of tube 24 to isolate grid and plate supply respectively, and a screen grid voltage may then be supplied over a resistor 36.

The unit shown in Fig. 2 would preferably normally be adjusted so that coupled section 23 would be detuned when no signal is supplied to input 25. Upon application of the signal of fixed amplitude, the resultant reactance across the section would be such as to resonate the section, thus preventing flow of current in the transmission line to which the section is coupled, as will be clear.

It is further clear that in an alternative embodiment the physical length of section 23 may be so designed that the large effective shunt capacity due to the circuit of Fig. 2 when a si nal is applied will detune rather than resonate the section, and so that the normal efl'ective shunt reactance ofiered by the circuit when no signal is applied will permit section 23 to resonate. Thus, when a blocking impulse is impressed at input 25, section 23 may be detuned to permit passage of energy along the line to which it is coupled; and when the blocking impulse is removed, a blocking effect results on the line. Thus, the identical blocking impulse, which served in the first-discussed case to produce a blocking action on the line to which the section was coupled, may also serve in this alternative embodiment to pass energy along a line; and, during the interval no blocking signal is applied, the former section may be detuned to pass energy, whereas the latter may resonate and block. It would, therefore, be clearly possible in an alternative embodiment of the circuit of Fig. l to employ a coupled-section circuit of the former nature coupled say to line l4, and one of the latter nature coupled to line l2. In such case, the blocking signal obtained fromv circuit 20 could be supplied directly to tube circuits i7 and I8, and there would be no need for inverter 22.

In Fig. 3 I show a further preferred embodiment of possible circuits I! or IS. The circuit employed makes use of the property of a A; wavelength line to present an impedance varying in phase at one end of the line when a shunt resistance at the other end is varied.

In the form shown a wave-length line 31 may be connected to a coupled section 23'- between points 29', 30" in a manner which may be similar to corresponding connections shown in Fig. 2. Line 31 is shown terminated by a shunt inductance 38 and by the respective outputs of ably so selected as to have a value permitting resonance with the internal capacities of tubes 39 and 40, for a purpose that will readily be understood.

As in the case of Fig, 2 the gain of tubes 39 and 40 may be controlled by appropriate adjustment of a bias-control potentiometer 29'. It will be clear that as bias of tubes 39 and 40 isthus varied, these tubes may be made to operate within a range from cut-off to saturation, and that concurrently the eil'ective shunt impedance offered by the plate circuits of these tubes may vary from a resistive value of Q/wC as a maximum to a value approximately equal to l l m39 m40 as a minimum, where Gm39 and Gmm are the mutual conductance values of tubes 39 and 49, re-' spectively. It is considered that such a, variation will be sufilcient to produce 1. large enough phase variation at the 29', 39' end of line 31 to tune and detune coupled section 23' completely.

The efiective shunt impedance presented by the plates of tubes 39 and 40 may be varied by varying the voltage applied to the grids, as introduced across resistor 21' nd a portion of potentiometer 29'; and the exact point of operation, as aboveindicated, may be determined by adjustment of potentiometer 29'. I prefer to .make such adjustment so that plate current Will flow in tubes 39 and 40 when no signal is applied. Under this condition section 23' would be non-resonant or detuned, and no blocking effect would be obtained in the transmission line to which section 23' is coupled. Since section 23' is thus detuned, substantially no current will be induced therein from the line to which it is coupled, and consequently no loss will ensue, due to the low resistance introduced by tubes 39 and 40 being coupled to line 31.

When, thereafter, a blocking signal characterized by a negative impulse is applied, tubes 39 and 60 will be cut oil, thus permitting section 23' to resonate with the reactance presented by the A; wave-length line terminated by the parallel shunt combination of inductance 33 and the internal capacities of tubes 39 and 49. Under this condition no flow of current will take place in the transmission line to which section 23' is coupled, but a high circulating current will be present in the circuit comprising section 23', line 31, and the tuned circuit made up of inductance 6 and the tube capacities.

It will be recalled from the discussionof Fig. 2 that the physical length of section 23 may be designed to resonate when the efiect of the tube circuit across points 29, 30 is substantially open circuit and to detune when the eifective shunt capacity is large. An analogous variation may be made in the circuit of Fig. 3 by also appropriately designing the length of the section (23'). In the thus modified form of Fig. 3 section 23' could be made to resonate normally, that is, while no blocking signal is applied to the input, and to detune when a negative blocking impulse is applied. In such case, then, it would be possible to use say the first-described embodiment of Fig. 3 to block and open line I4, and the latter to perform the inverse function with regard to line 12, as will be clear. It thus appears that coupled sections l5 and I6 could be made alternately to operate in inverse senses upon application of the same negative blocking signals simultaneously to both tube circuits |'I,. l8. Naturally, of

course in this proposal, as-in the case of the corresponding proposalin connection with Fig. 2, there would be no need for inverter 22.

Although I have described the embodiment shown in Fig. 3 as operative upon application of a negative blocking impulse, it is clear that it may also operate upon application of positive impulses. In this case, tubes 39, 40 would normally be biassed below cut-oif, and application of blocking impulses of correct magnitude could be made either to resonate or detune section 23', depending upon the designed physical length thereof in view of the foregoing discussion.

I have purposely omitted any reference in this disclosure as to what point along the section the tube circuit should be inserted, inasmuch as the particular connection point is considered relatively unimportant. I prefer, however, to employ some point along the section generallyintermediate the open and shorted ends. The reason for such preference is clear. 1 capacity were inserted near the shorted end the voltage shunted would be relatively low and pracsion systems." On the other hand, at resonance,

voltages across the open end are a maximum and may be so great as to produce deleteriousor undesirable effects on the tube circuits. Accordingly, as indicated, some intermediate position is preferred.

Although I have described my invention in particular detail in connection with transmission and reception on a common antenna, it is clear that the antenna is merely illustrative, for it may be considered representative, for example, of a transmission line or other network in conjunction with which concurrent transmission and reception are desired. It is also clear that many modifications. additions, and omissions may be made within the scope of the invention.

What I claim is:

1. A radio system including impulse transmitter means, antenna means, receiver means responsive to reflections of impulse energy transmitted by said transmitter means, a firstv transmission line connecting said transmitter means to said antenna means, a second transmission line connecting said receiver means to said .an-

tenna means, impedance varying means'spaced from each of said transmission lines and respectively coupled thereto and means controlled by said impulse transmitter means alternately rendering said impedancevarying means effective ontheir respective transmission lines to render said first and then said second transmission lines ineffective to pass such impulse energy.

2..A radio system including transmitter means transmitting periodically recurrent impulse ener y, antenna means. receiver means responsive If the efiective shunt 7 alternately rendering said first and said secondmentioned connecting means ineffective to pass such impulse energy in accordance with said pefi'odic recurrence.

3. An impulse energy transmission and reception system including an impulse transmitter, a receiver, an antenna, connecting means connecting said transmitter and said receiver to said antenna, and control means rendering said connecting means inefl'ective alternately to connect said transmitter and said receiver to said antenna, said control means including a relatively short section of transmission line coupled to said connecting m ans and short-circuited at one end of said section, and means controlled by said transmitter periodically varying the effective shunt reactance between points on each side of said section. v

4. An impulse energy system according to claim 3, in which said connecting means includes a transmission line coupling said transmitter and said antenna, and a transmission line connectin said receiver and said antenna, and in which said control means includes one said section coupled to said first transmission line and another said section coupled to said second transmission line.

5. An impulse energy system according to claim 3, in which said connecting means include a transmission line coupling said transmitter and said, antenna, and a transmission line connecting said receiver and said antenna, and in which said control means includes one said section coupled to said first transmission line and another said section coupled to said second transmission line, and wherein said periodically varying means is connected between points on each side of each said section and periodically varies the effective shunt reactance between said points on said one section in a sense inverse to such periodic variation between said points on said other section.

6. The method of varying the resonant condition of a /4 wave-length transmission line having one end short-circuited, which comprises connecting one end of a wave-length line between points on each side of said transmission line and varying a resistance connected across the other end of said A; wave-length line.

7. The method of transmitting impulse ene y and receiving reflections thereof on a single antenna connected to an impulse transmitter and a receiver, there being'a section of transmission line inductively coupled to the line connecting the transmitter and antenna-and another such section inductively coupled to the line connecting the,antenna and receiver, which method comprises resonating the section of transmission line inductively coupled to the' line connecting the receiver and antenna during transmission of impulse energy, and resonating the section of transmission line inductively coupled to the line connecting the transmitter and antenna during intervals between said transmission of impulse energy.

8. The method of transmitting impulse energy and receiving reflections thereof on a Single antenna connected to an impulse transmitter and a receiver, there being a section of transmission line inductively coupled to the line connecting the transmitter and antenna and anothersuch section inductively coupled to the line connecting the antenna and receiver, which method comprises resonating the section of transmission line inductively coupled to the line connecting the receiver and antenna during transmission of im- 8 pulse energy while detuning the section of transmission line inductively coupled to the line connecting the transmitter and antenna; and resonating said second-mentioned section while detiming said first-mentioned section during intervals between said transmission of impulse energy.

9. In a system for controllingener y flow alon a transmission line, a short circuited quarter wave-length section inductively coupled to said line, means including vacuum tube controlmeans connected across said section and forming a variable efi'ective shunt reactance across said section for alternately tuning and detuning said section in accordance with signals applied to said vacuum tube control means, said control means including a vacuum tube having a cathode, a control grid, and an anode, means connecting said grid to one side or said section, and means connecting said anode to the other side of said section, said first-mentioned and said second-mentioned connecting means each including means eifecting substantially a relative phase displacement between current in each said connecting means.

10. In a system for controlling energy flow along a transmission line, a short-circuited quarter wave-length section inductively coupled to said line, means including vacuum tube control means connected across said section and forming a variable effective shunt reactance across said section for alternately tuning and detuning said section in accordance with signals applied to said vacuum tube control means, said control means including a pair of vacuum tubes, each of said vacuum tubes including a cathode, a control grid, and an anode, a wave-length line having one end connected across said section and each side of the other end connected to the anode of one of said vacuum tubes, means connecting the grids of said tubes, and an impedance bridging said other end or said 3 8 wavelength line, said impedance beingsuch as to form with internal impedances of said tubes a resonant circuit.

11. In a system for controlling radio frequency energy flow along a transmission line, a shortcircuited line section inductively coupled to said transmission line, and control mean connected across said section and forming a variably reactive shunt impedance across said-section for tuning and detuning said section in accordance with variation of said control means, said control means including a A; wave-length line having one end connected across said section, and means producing a variable resistance effect across the other end oi. said wave-length line.

12. A radio system including transmitter means for transmission at a given carrier frequency, antenna means, receiver means responsive to said given carrier frequency, a first transmission line connecting said transmitter vmeans to said antenna means, a second transmission line connecting said receiver means to said ant a means, impedance varying means spaced m each of said transmission lines and respecti ely coupled thereto, and means responsive to energy from said transmitter for alternately rendering said impedance varying means effective on their respective transmission lines to render said first and the said second transmission lines ineffective to pass energy of said given carrier frequency.

- ROSS B. HOFFMAN.

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