US2483818A - Variable reactive microwave device - Google Patents

Description

0dr. 4, 1949. J. EVANS EACTIVE MICROWAVE DEVICE VARIABLE R Original Filed Oct. 3l, 1944 Patented Oct. 4, 1949 l 2,483,818 VARIABLE REAc'rIvE MICROWAVE DEVICE John Evans, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Dela- Ware Original application October 31, 1944, Serial No. 561,277. Divided and this application July 18, 1947, Serial No. 761,969

claims. (c1. 332-29) This application is a division of my copending application Serial No. 561,277, filed October 31, 1944, entitled Variable reactive microwave device, and assigned to the same assignee as the instant invention.

This invention relates generally to microwave transmission systems and more particularly to an improved method of and means for adjusting reactance or attenuation in a microwave communication system.

It has been found that the effective dielectric constant of certain gases, liquids and solids varies as a function of the electric or magnetic field to which the dielectric is subjected. This effect is believed to be caused by the orientation of molecular or cystalline dipoles of the particular material in planes which are parallel to the direction of the applied field. In dielectrics wherein the molecular dipoles are of substantially insulating material, the orientation of the molecular dipoles may be produced by means of an applied electrostatic eld. In materials which include comminuted or molecular conducting particles, Such, for example, as comminuted iron, the orientation of the particles may beproduced by means of an applied magnetic field.

Inthe absence of an applied field, the molecular dipoles of the dielectric material have random oientation. However, in the presence of a biasing field, the orientation of the molecular dipoles in plaries parallel to the eld producesa secondary field which will oppose the propagation of microwaves through the dielectric material. Hence, a dielectric of any of the types described vmay be enclosed within a conventional waveguide transmission system to provide a waveguide section having reactance, phase rotation, or attenuation which Vary as a function of an applied biasing electrostatic or magnetic field, depending upon the dielectric material employed.

A variable reactive lwaveguide section of the type described may be employed for controlling the phase, amplitude or frequency of microwaves transmitted through an otherwise conventional waveguide system.

Among the objects of the invention are to provide an improved method of and means for varying reactance in a waveguide transmission system. Another object of the inventionis to provide an improved method of and means for adjusting attenuation in a waveguide transmission system. A further object of the invention is to provide an improved method of and means for phase modulating microwave energy. An additional object is to provide an improved method 2 of and means for amplitude modulating microwave energy. Another object of the invention if to provide an improved method of and means for frequency modulating microwave energy.

A still further object of the invention is to provide an improved method of and means for adjusting the dielectric constant of a dielectric enclosed within a section of a waveguide transmission system. Another object of the invention is to provide an improved microwave variable reactance comprising a section of waveguide enclosing a material of which the dielectric constant may be varied as a function of an applied field. Other objects of the invention will become apparent in view of the more detailed description which follows, considered in .combination with the appended claims.

The invention will be described in greater detail by reference to the accompanying drawing of which Figure 1 is a perspective view of one embodiment of the invention; Figure 2 is an elevational cross-sectional view, taken along the section line II-II, of the device illustrated in. Figure 1; Figure 3 is a cross-sectional elevational view of an optional cross-sectional structure for the device illustrated in Figure 1; Figure 4 is a schematic circuit diagram of one system embodiment of the invention; Figure 5 is a schematic circuit diagram of a second system embodiment-of the invention; and Figure 6 is a schematic circuit diagram of a third system embodiment of the invention. Similar reference characters are applied to similar elements throughout the drawing.

Referring to Figures 1 and 2 of the drawing, a preferred embodiment of the invention comprises a pair of U-shaped insulating channel members 3, 5 of polystyrene or other insulating material, joined together on the lines-1. 9 toprovide a waveguide of rectangular cross-section. The inner surfaces of the insulating dielectric channels 3, 5 are coated with conductive layers II, I3 except in the immediate vicinity of the joints 1, 9. A conductive coating may be applied to the polystyrene walls by employing an ethylene dichlorlde and styrol cement in combination with powdered silver to provide a continuous silver coating having high electrical conductivity. Since the conductive layers I I, I3 on the insulating waveguide walls 3, 5 are insulating from each other by the gaps adjacent the joints 1, 9, the opposing conductive elements may be employed for establishing a dielectric eld in a vertical plane within the waveguide. Contacts I5, IT, extending through the dielectric waveguide walls, 3, 5, respectively, and electrically connected to the conductive layers I I, I3, respectively, may be connected. for example, through a biasing battery I9 to the secondary winding I9 of a pulse transformer 2l, to the primary winding 23 of which may be applied keying pulses or other modulation signals from a source not shown. If the use: of a modulation transformer is not practicable, the modulation signals may be applied directly or through any other known means to the contacts I5, I1.

Polystyrene windows 25, 21 extending across the entire inner cross-section of the waveguide section adjacent the ends thereof, provide a sealedl chamber 39 in which a predetermined gas, liquid, or solid dielectric material having a variable dielectric constant may be enclosed. The length of the enclosed chamber within the waveguide section may be selected to be of the order of 1/4 or l/2 wavelength as desired. However, the length of the adjustably reactive chamber may be otherwise selected to conform with the reactive requirements of the particular associated microwave circuit. In order to minimize microwave reflections due to the discontinuities provided by the polystyrene windows 25, 21, one or more reactive tuning plugs 29, 3| may be provided inthe connecting waveguide adjacent each end of the variably reactive waveguide section. Both ends of the variably reactive waveguide section may include conductive flanges 33, 35 for connection to adjacent conventional rectangular waveguides as, for example, the waveguide 31 including the tuning plugs 29 and 3I.

The enclosed chamber 39 between the polystyrene windows 25, 21 may be filled either with a gaseous, liquid or solid dielectric in which the dielectric constant varies with the strength of an applied field. A typical liquid having these characteristics comprises nitrobenzol having quinine crystals emulsied therewith. Under the stress of an applied electrostatic field, the quinine crystals are oriented in planesparallel to the applied eld. Various other materials may be employed either singly or in combination with neutral supporting liquids such as nitrobenzol.

A typical solid in which the molecular dipolesA may be oriented by the application of a dielectric field is titanium dioxide (T102). In the case of both the liquids and the solids enumerated heretofore, the dielectric eld may be modulated directly by means of the modulating potentials to provide a section of waveguide having variable reactive or attenuating characteristics to microwaves propagated therethrough. It should be understood that the variations in dielectric constant, in the liquid or solid mediums employed, provides a corresponding variation in the propagation velocity of microwaves transmitted therethrough.

Certain gases such, for example, as ammonia, also may be employed as variable microwave absorptive dielectric materials since these gases absorb microwave energy within predetermined frequency ranges. For example, ammonia gas absorbs microwave energy at wavelengths in the region of 3.2 centimeters and 1.1 centimeter. Thus, the modulation applied to the control cell termz'nals I5, I1 may comprise 3.2 centimeter wavelength which are modulated by means of the desired low frequency keying or modulating signals. The variable dielectric constant or loss characteristics of the gas due to phase rotationthence may be employed to modulate microwaves having a wavelength, for example, of the order of two centimeters which are propagated through the waveguide system. Thus, it is seen that the variable dielectric constant or loss characteristics of various gases, liquids, or solids may be modified in accordance with the modulating potentials to vary the reactance, or attenuation, of a waveguide section forming a control cell portion of a microwave waveguide system. Insofar as liquid dielectrics are concerned, the speed of response to applied modulation signals is a function of the viscosity of the liquid. This effect has not been fully investigated with gases or solid dielectrics.

Figure 2 illustrates schematically the parallel orientation of the molecular dipoles 4I of an insulating material in response to an applied electrostatic field established between the conductive waveguide surfaces II, I3.

Figure 3 illustrates a modification of the device described in Figures 1 and 2 wherein the waveguide section includes conventional conductive walls 43 closed at each end by a polystyrene window as illustrated at 25. A portion of the window 25 is shown broken away to illustrate the use of a magnetically sensitive dielectric 45 within the space between the dielectric windows 25, 21. A pair of magnetic pole pieces 41, 4S, including serially-connected windings 5 I, 53, respectively, connected to the secondary winding I9 of the modulation transformer 2I, provide a inagnetic field transversely of the waveguide section which may be employed to vary the dielectric constant of the enclosed material 45.

A dielectric 'in which the dielectric constant may be varied in response to an applied magnetic field may, for example, comprise nitrobenzol having finely comminuted iron dust in emulsiontherewith. Application of a transverse magnetic field between thevpole pieces 41, 49 causes the comminuted iron particles to arrange themselves in planes parallel to the magnetic field, thereby changing the effective dielectric constant of the emulsion in the same manner as described heretofore 4for the embodiment of the invention employing a modulating dielectric eld. It should be understood that the use of nitrobenzol as a support for the comminuted iron particles is purely illustrative, and that various other neutral supporting liquids may be employed in a. similar manner.

Also, it should be understood that other magnetic materials, such as comminuted nickel, may be substituted for the comminuted iron in the magnetically sensitive emulsion. The modification of the invention illustrated in Figure 3 has the advantage that a conventional section of waveguide, having continuous metallic walls. may be employed for the variable reactance control cell device.

Since the reactance or attenuation of the devices thus described may be varied within wide limits, they are ideally adapted to provide modulating elements for conventional microwave transmission systems. For example, as illustrated in Figure 4, the control cell comprising the invention may be interposed between a microwave receiver and a microwave antenna in a waveguide coupling system wherein a microwave transmitter is connected through an auxiliary waveguide to the same microwave antenna. A transmitter 6I is connected through a waveguide 63 to a microwave antenna. Similarly, a microwave receiver 65 Iis connected through a receiver waveguide 61 to the same antenna as, for example. in radar systems. The control cell 69 may be interposed in the receiver waveguide 61 at a point, for example, A wavelength from the junction with the transmitter waveguide 63. The

. mitter 6i, as indicated by the dash line 13, also may be connected to the control cell 69 to block signals in the receiver waveguide 61 when the transmitter 6I is keyed on. The keying pulses from the keying pulse source 1| thus may provide an effective short circuit across the control cell 69 when the transmitter is keyed on, thereby providing a relatively high impedance looking into the receiver waveguide 61 at the point where it joins the transmitter waveguide 63. In the absence of transmitter keying pulses, the control cell eillciently transmits to the receiver the signals derived from the antenna.

Figure 5 illustrates schematically the manner in which the control cell 69l may be serially interposed ina waveguide transmission system 63 connecting a microwave transmitter 6| to a load 15. Since the control cell provides variable delay of microwave signals applied therethrough to the load due to the variations in microwave propagation velocity, the modulation voltage source 1l' may be connected to the control cell to vary the phase of signals applied to the load 1l. The effective length of the control cell and/or the magnitude of the modulating signals may be selected to providethe desired phase shift in response to modulation potentials.

Figure 6 schematically illustrates the manner in which the control cell 69 may be employed for frequency-modulating a source of microwave oscillatlons. In this modification of the invention, the control cell may comprise, for example, all

'or a portion of a cavity resonator forming the tank circuit of the oscillation source. The effective reactance oi the control cell 69 may be varied by means of the modulation voltage source 1|' in the same manner as described heretofo thereby providing correspondingvariations in the frequency of the microwave oscillations generated by the oscillator tube 11. The output of the oscillator 11 is applied directly, or through suitable coupling circuits, to the load 15. It should be understood that the structure and conformation of the control cell may be varied in any manner known in the microwave art to provide the desired type of oscillator tube tankV circuit. The rectangular waveguide structure described and specically illustrated herein is intended purely for the purpose of illustration. since the control electrostatic or electromagnetic fields may be applied to an enclosed field-responsive dielectric in any other structure or manner known in the art. s

Thus the invention described comprises animproved method o! and means fori varying reactance-or attenuation in a microwavetransmission system wherein predetermined dielectrics. havingldielectric constants dependent upon an applied ileld, are employed to provide variable reactance, delay, or loss characteristics in a waveguide transmission system.

I claim as my invention:

l. In a modulation system including a source of microwave oscillations, a load, a transmission line interconnecting said oscillation source and said load and a source of modulation potentials, the improvement comprising a variable reactive device operable upon said oscillation "source and comprising a section of waveguide containing a pliant dielectric, comminuted particles of solid material mixed .with said dielectric, means for establishing a eld transversely of said waveguide section for orienting said particles, and means for varyingsaid field in response to said modulation potentials to modulate said oscillations.

, 2. In a phase modulation system including a source of microwave oscillations, a load, a waveguide transmission line interconnecting said oscillation source and said load and a source of modulating potentials, the improvement com prising a variable reactive device interposed in said line between said oscillation source and said load and comprising a section of waveguide containing a pliant dielectric, comminuted particles of solidmaterial mixed with said dielectric, means for establishing a field transversely of said waveguide section for orienting said particles, and means for varying said field in response to said modulation potentials to phase-modulate said oscillations.

3. In a frequency modulation system including a source of microwave oscillations, a load, a transmission line interconnecting said oscillation source and said load and a source of modulation potentials, the improvement comprising a variable reactive device forming a portion of the frequency determining circuit of said oscillation source and vcomprising a section of waveguide containing a pliant dielectric, comminuted particles of solid material mixed with said dielectric, means forestablishing a field transversely of said waveguide section for orienting said particles, and means for varying said eld in response to said modulation potentials to frequency-modulate said oscillation. y 4. Apparatus according to claim l wherein said comminuted particles comprise a dielectric responsive to the transverse electric iield within said waveguide section.

5. Apparatus according to claim 1 wherein said comminuted particles comprise magnetic material responsive to the transverse magnetic field within said waveguide section.

' JOHN EVANS.

REFERENCES CITED The following references are of record Ain the ille of this patent:

UNITED STATES PATENTS

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