US2760163A - Radio frequency propagating systems - Google Patents

Description

Aug. 2l, 1956` M. ARDITI RADIO FREQUENCY PROPAGATING SYSTEMS Filed oct. 1`1. 1954 2 Sheets-Sheet l NV E NTO R Ma/cf ARQ/77 BYW Aoav 2 Sheets-Sheet 2 Filed 001.. ll, 1954 INVENTOR MAUR/CE ARD/77 BY /E ATTORNEY RADIO FREQUENCY PROPAGATING SYSTEMS Maurice Arditi, Clifton, N. I., assigner to International Telephone and Telegraph Corporation, Nutley, N. l., a corporation of Maryland Application October 11, 1954, Serial No. 461,390

3 Claims. (Cl. S33-13) This invention relates to radio frequency propagating systems for use in the ultra high frequency range.

It has been proposed heretofore to provide the standard type of hollow rectangular waveguide with a gas discharge tube for attenuation, phase modulation and switching purposes. Such waveguides, however, are characteristically narrow band and in order to cover a wide frequency range, such as 1000 megacyc'les to 10,000 megacycles, for example, six different waveguide sizes are required.

One of the objects of this invention is to provide a novel combination waveguide and gas discharge arrangement suitable for operation over bands of frequency far exceeding that possible with the aforementioned rectangular type of waveguide and gas discharge tube combination.

Another object is to provide a novel structure for direct current isolation of desired portions of a waveguide structure and a further object is to utilize this isolation feature to provide one or more resonant sections along the waveguide for band-pass filtering operation.

An important feature of the invention is the provision of a combination waveguide and gas discharge device capable of operation over an exceptionally broad band of frequencies. The type of waveguide structure employed is that known as Microstrip, which comprises two strip-like conductors disposed in dielectrically spaced parallel relation with one of the strips wider than the other to present thereto a planar conducting surface for propagation of wave energy therealong in a mode approximating the TEM mode. The electric eld in such propagation is distributed in a manner similar to the electric eld distribution between one conductor and the neutral plane of a truly parallel two-conductor line. The positioning of a gas tube between the strips or about the narrower one of the two insures maximum interception of the electric field between the two strips for all frequency signals that can be propagated over the Microstrip line. For example` only one Microstrip and gas-discharge tube arrangement is required for coverage of the frequency range of 1000 megacycles to 10,000 rnegacycles for which six different sizes of the standard rectangular waveguide-tube combination are required. The simplicity of the Microstrip and gas tube structure also makes for economical apparatus in the ultra high frequency range as compared to the high cost of the standard type of expensive waveguide plumbing heretofore believed necessary.

The above mentioned objects and features of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

Fig. l is a view in plan of the combination waveguide and gas discharge device of this invention;

Fig. 2 is a view in side elevation of Fig. l; Fig. 3 is a view in crosssection taken along lines 3 3 of Fig. 2;

`Fig. 4 is a view in plan with the gas tube shown in secparallel relation.

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tion of a modified waveguide and gas tube arrangement; and

Fig. 5 is a longitudinal cross-sectional View taken along lines 5 5 of Fig. 4.

Referring to Figs. l to 3, a section of Microstrip waveguide is shown which includes a lirst or planar conductor 1, a second or strip conductor 2, and a layer of dielectric material 3 which separates the conductors 1 and 2 in The dielectric material may comprise polyethylene, polystyrene, Teon, iiber glass or laminations of ber glass and Teon, or other suitable materia'l of dielectric quality, or if the Microstrip structure permits the dielectric may be air. The dielectric layer 3 is provided with a cutout 4 which 'is slightly wider than the strip conductor 2 and directly underlying the strip 2. ln this cutout is a at elongated glass tube 5 containing a gaseous material, such as neon in a thin strata only a small fraction of a wavelength in thickness. The ends of the glass envelope 5 extend laterally as indicated at 6 and 7 where they terminate about electrodes 8 and 9. The electrodes may be coupled to a source of biasing voltage 10 controlled by a rheostat 11 which is coupled in series with a source of modulating voltage 12. While the cutout 4 may extend to one side edge of the conductor 1, it is preferable to retain or replace the portion of the dielectric indicated at 13 so as to avoid an unbalanced line dielectrically along the tube. If desired, the dielectric material may be removed on both sides of the tube 5. In either case the cutout presents a discontinuity in the line and requires some alteration lin the line or some form of tuning means to overcome the effect of this discontinuity. As shown in Figs. 1 3, small tuning stubs 4a and 4b may be provided at the ends of the cutout 4, the stubs being in the form of small conductive projections soldered to or made integral with the conductor 2. For further information on use of these tuning devices reference may be had to my joint applications with G. A. Deschamps and l. Elefant, Serial Nos. 286,761 and 286,762 led May 8, 1952. If desired the discontinuity of the cutout 4 may be overcome by narrowing the space between conductors 1 and 2 throughout the cutout.

In this embodiment the gas tube provides for several possible functions. It may be used for attenuating the propagation of wave energy along the line or it may be used as a phase shifter, amplitude or phase modulator, or as a switch. The tube 5 in the position shown intercepts substantially all or at least a very high percentage of the electric field which exists between the conductors 1 and 2. When the gaseous medium is ionized, the gas plasma absorbs the radio frequency energy and, depending upon the pressure of the gas and the degree of ionization, substantially complete absorption can be had, thus operating as a switch. The bias 10 may be controlled by rheostat 11 to place the gas in partial ionization and the source 12 which may be a signal wave or pulse source, may be utilized to modulate the wave energy by varying the degree of ionization of the gas.

Referring to Figs. 4 and 5, the strip conductor is divided into two portions 2a and 2b to which is secured a gas discharge device 14 which comprises an envelope 15 into which projects two strip sections 16 and 17. The inner ends of the sections 16 and 17 are shaped to provide a V gap 18 corresponding to the V-shaped gaps disclosed in my copending application, Serial No. 324,545, filed December 6, 1952. This form of gap is particularly adapted for the propagation of radio frequency energy while operating to isolate the two strip sections electrically. The strip portions 16 and 17 may be disposed in overlapping relation to the ends of strip sections 2a and 2b to which they may be secured as by soldering, as indicated at 19.

While separate electrodes may be provided within the envelope 15, I prefer to utilize the strip sections 16 and 17 to effect ionization of the gas. This is done by providing two coaxial couplers 20 and 21 which are coupled at opposite ends of thedevice. The planar conductor 1a is provided with an opening 22 about which the outer conductor 23 of the coupler 20 is secured. The inner conductor 24 of the coupler unit extends through the opening 22 and is connected directly to the strip con` ductor 1a, as indicated at 25. The coupler 20 is provided with a movable plunger 26 which has an annular sleeve of dielectric material 27 to electrically insulate the inner conductor from the outer conductor. By adjusting the plunger 26 with respect to the junction 2S, a susceptance is provided in the Microstrip line which presents in conjunction with the gap 18 a resonant section having a band pass characteristic. The position of the plunger 26 determines the value of the susceptance. The spacing of the junction with respect to the gap 18 is selected to approximate a half wavelength. The coupler 21 which is likewise coupled to the strip 2b at 28 is provided with adjustable plunger 29 which operates as a short between the inner and outer conductors 30 and 31. By adjusting plunger 29 approximately a quarter wavelength from the strip 2b allowing for the dielectric constant of material 3a, this provides a minimum of reflection of the radio frequency flowing along the Microstrip line. This coupling 21 provides for a direct current return circuit between the strip portion 17 and ground and the source of biasing potential 33. By applying a bias on the portions 16 and 17 the gaseous medium of tube 14 is ionized as may be required. In the provision of the direct current return circuit through coupler 21, it should be noted that the Microstrip conductor 2a and other circuitry to which it may be coupled are maintained isolated with respect to ground or the planar conductor 1a.

In order to overcome the discontinuity provided by the cutout 34, tuning stubs and 36 may be provided adjacent the ends of the cutout 34 similarly as provided in connection with the cutout 4 in Figs. l, 2 and 3.

In operation of the embodiment illustrated in Figs. 4 and 5, let it be assumed that the embodiment is to be utilized as a band pass filter. In this case, the tube 1d is maintained in an rin-ionized condition so that the susceptance value of the gap 13 is utilized to provide the desired resonant circuit. When it is desirable to block the band pass frequencies, the tube 14 is ionized by applying a positive bias from source 33 thus ionizing the gaseous medium to attenuate the flow of wave energy along the Microst-rip. The gas plasma thus formed absorbs the wave energy thereby blocking its passage. This switching function may act as a complete blocking of wave energy or it may be so controlled as to change the band pass characteristic of the filter in addition to its function as an attenuator. For example, if the gap 1S is relatively wide the gas plasma may function to change the susceptance value thereof thus changing the band pass characteristics of the lter. However, if the gap 18 is relatively small, the gas plasma may have relatively small de-tuning effect on the gap susceptance and would in that case function only as an attenuator to the band pass frequencies.

While I have shown only one filtering section in the embodiment of Figs. 4 and 5, it will be readily apparent to those skilled in the art that the unit may be multiplied to form a series of filtering or resonant sections, each of which may be controlled independently with regard to the ionization of the gaseous medium surrounding the gap 18. In this way the overall band pass characteristics could be varied by ionizing the gaseous medium at one or more of the gaps.

Gases other than neon may be used in tubes 5 and 14. The gas or gas mixture used should be light with a high ionization potential for rapid diffusion and high breakdown power. Helium and hydrogen either alone or mixed at an appropriate pressure are particularly satisfactory for this purpose. For further information on the gas and gas pressure that may be used reference may be had to copending application of L. Goldstein and P. E. Dorney, erial No. 307,874 led September 4, 1952.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

l. In apparatus of the character described, a rst conductor, a second conductor, means disposing said conductors in dielectrically spaced, substantially parallel relation, said rst conductor being wider than said second conductor to present thereto a planar surface whereby the electric eld distribution of radio frequency waves propagated therealong is in a mode approximating the TEM mode thus enabling propagation of wave energy over a wide band of frequencies, said second conductor having a gap therein for direct current isolation of one part of said second conductor from the other, said gap being shaped for spaced overlapping relation to enable wave propagation thereacross, a tube containing a gaseous medium surrounding the section of said second conductor containing said gap, a source of voltage, said first conductor having an opening therein, a coaxial coupler with the outer conductor connected to said iirst conductor about said opening, and the inner conductor thereof extending through said opening and connected to said second conductor on one side of said gap, means coupling one side of said source of voltage to said inner conductor, an insulated plunger disposed in said coaxial coupler, means for adjusting the position of said plunger to determine the susceptance of said coupling with respect to wave energy propagated along said first and second conductors and means connecting the other side of said source of voltage to the second conductor on the other side of said gap.

2. The apparatus according to claim 1, wherein the gap in said second conductor comprises a susceptance with respect to propagation of wave energy along said rst and second conductors, said coaxial coupler being disposed a selected distance from said gap to present a second susceptance and thereby produce in conjunction therewith `a resonant section for band-pass filtering of wave energy propagated along said rst and second conductors.

3. In apparatus of the character described, a first conductor, a second conductor, means disposing said conductors in dielectrically spaced, substantially parallel relation, said rst conductor being wider than said second conductor to present thereto a planar surface whereby the electric field distribution of radio frequency -waves propagated therealong is in a mode approximating the TEM mode thus enabling propagation of wave energy over a wide band of frequencies, said second conductor having a V-shaped gap therein whereby portions of said V-shaped gap overlap to enhance propagation of wave energy therealong while isolating the conductor parts with respect to direct current flow, a tube containing a gaseous medium surrounding the section of' said second conductor containing said gap whereby ionization of said gaseous medium renders said gap conductive with respect to direct current flow, said first conductor having openings therethrough, one on each side of said gap, a first coaxial coupling unit with the outer conductor thereof coupled about one of said openings, and the inner conductor thereof extending through said opening in coupled relation `to said second conductor, an insulating plunger contained in said first coupling unit, means to adjust the position of said plunger for tuning purposes, a source of voltage coupled to said inner conductor and .to said first conductor, a second coaxial coupling unit having the outer conductor thereof coupled to said rst con- References Cited in the file of this patent UNITED STATES PATENTS 2,532,157 Evans Nov. 28, 1950 6 Fiske June 19, 1951 Cohen et al. June 9, 1953 Goldstein et al. June 23, 1953 Varela July 21, 1953 OTHER REFERENCES Convention Record of the 1953 I. R. E. National Convention, part l0, Microwaves, pages 27-37; copy received July 30, 1953, in Scientific Library.

10 Electrical Communication, December 1953; pp.

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