US3050687A - Gaseous discharge structures - Google Patents

Description

Aug. 21, 1962 J. M. ANDERSON 3,050,687

GASEOUS DISCHARGE STRUCTURES Filed Jan. 2, 1959 2 SheetsSheet 2 E J R lnvenlrer-fl' John MA nder'sorv Fig/0.

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United States Patent 3,050,687 GASEOUS DISCHARGE STRUCTURES John M. Andersou, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Jan. 2, 1959, Ser. No. 784,746 8 Qlaims. ((31. 329-153) I This invention relates to an apparatus for effecting nonlinear interaction between an electromagnetic microwave and a gaseous discharge plasma to produce a resultant output indication having a characteristic related to a characteristic of the microwave.

Non-linear devices are well known for facilitating electron circuit functions such as detection of modulated waves, frequency multiplication and the like and usually comprise unilaterally conducting high vacuum tubes, solid rectifiers or gaseous discharge devices of well known types. Non-linear gaseous discharge devices including those utilizing probes immersed in a discharge plasma possess certain advantages over other non-linear devices, such as high resistance to destruction by burnout in response to excessive applied potential. On the other hand, it has heretofore been the belief that gaseous discharge devices employing probes immersed in the gaseous discharge plasma are responsive and useful at only very low frequencies of the order of a few megacycles per second or less for useful results. This has been based at least partly on the belief that the thickness of the positive ion sheath surrounding the immersed probe must be less than the mean free path of an electron therein and that the time required for an electron to traverse the sheath thickness must be less than the period of the applied wave. Thus, a rather low upper frequency limit was believed to obtain for such devices.

I have discovered, however, that immersed probe, gaseous discharge devices are not so rigidly limited and that the same are operable at least to frequencies of 10,000 megacycles per second. Thus, an immersed probe, gaseous discharge device may possess advantages over other nonlinear devices without being limited in frequency response.

It is therefore a primary object of my invention to exploit the advantageous features of an immersed probe, gaseous discharge device for performing non-linear circuit functions at higher operating frequencies than heretofore achieved.

According to my invention a probe is immersed in a negative glow region of a discharge plasma established in a gas such as one of the noble gases at low pressure of the order of 1 mm. to 50 mm. of mercury. An electromagnetic wave is impressed upon the probe to effect an interaction between the wave and the plasma which takes place at or immediately in the vicinity of the probe surface in contact with the plasma. The non-linearity of such an interaction is useful according to one feature of my invention to detect or demodulate the electromagnetic wave so impressed and according to another feature of my invention such interaction may be employed for the generation of electromagnetic energy at frequencies harmonic to the frequency of the impressed electromagnetic wave.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which I regard as my invention, the invention will be better understood from the following description taken in 3,5@,687 Patented Aug. 21, 1962 ice 2 connection with the accompanying drawings in which:

FIG. 1 is a schema-tic circuit diagram showing a nonlinear device interconnected with external circuit elements and being helpful in explaining my invention;

FIG. 2 is a cross-sectional elevation of one form of my invention showing a non-linear device and a wave guide for introducing electromagnetic wave energy thereto and being useful as a microwave detector;

FIG. 3 is a cross-sectional side elevation of another embodiment of my invention showing the essential elements of a non-linear device and a wave glide for introducing electromagnetic wave energy thereto;

FlG. 4 is a cross-sectional end elevation of the device shown in FIG. 3 and taken along lines 44 thereof;

FIG. 5 is a cross-sectional side elevation of another embodiment of my invention showing a non-linear device together with a wave guide for introducing an electromagnetic wave thereto and useful as a microwave detector;

FIG. 6 is a cross-sectional end elevation of the device shown in PEG. 5 and taken along lines 6-6 thereof;

PEG. 7 is a diagram, partially schematic, illustrating the utilization of a typical crystal cartridge in a non-linear detector system embodying the present invention;

FIG. 8 is a cross-sectional elevation of another embodimerit of my invention illustrating a non-linear device useful as frequency multiplier;

FIG. 9 is a cross-sectional elevation of another embodiment of my invention illustrating a nonlinear device useful as a frequency multiplier; and

FIG. 10 is a cross-sectional elevation of still another embodiment of my invention illustrating a non-linear device useful as a frequency multiplier.

For a clear understanding of the operation of this invention, reference is had to a schematic representation of a gaseous discharge device in FIG. 1 of the drawings in which 1 designates the discharge device generally having a sealed envelope 2 of glass or other suitable material with an anode 3 disposed at one end of the envelope and a cathode 4- at the other end thereof. For establishing a gaseous discharge within the envelope 2-, it is filled with an ionizable gas at low pressure of the order of 1 to 50 mm. of mercury and a potential gradient within the tube sufficiently large to ionize the gas to preferably a condition of negative glow is produced between the anode and cathode by a direct potential source 5 connected between the anode and cathode through a variable, current limiting resistor 6.

In this structure, interaction between a negative glow region of the ionized plasma and a microwave is produced at a surface of a probe 7 by introducing a microwave in the plasma region on the probe '7 extending into the envelope in the region of the plasma. The electric field intensity in the vicinity of the probe surface is great whereby interaction with the plasma is correspondingly great. Such an interaction is effective to produce a nonlinearity of current flow to the probe and in the device represented in this figure the non-linearity is utilized to detect the modulation of the microwave signal applied.

To this end a potential bias, positive or negative with respect to the anode may be applied to probe 7 from a direct potential source and potentiometer combination 8, through a resistor 9 and the demodulated signal from the probe is applied to the output terminal 19 through a capacitor 11. A de-coupling capacitor 12 is connected between the end of resistor 9 remote from probe 7 and ground.

According tothis structure, detection of a modulated signal is achieved at frequencies considerably greater than thought possible with gaseous discharge devices utilizing probes and the additional feature of my described detector of being highly resistant to destruction by burn out renders the same advantageous over other detectors such as crystals which are highly susceptible to such destruction.

The advantageous features of my invention may be realized in a specific embodiment thereof shown in its entirely at 13 in FIG. 2 and including a casing 14 mounted on a wall 15 of a wave guide 16, for containing a unitary, sealed, gaseous discharge unit 17. Casing 14 is preferably circular in shape and is closed at its open end by cap 18 threadedly engaging the casing end.

According to a feature of my invention, discharge unit 17 includes a sealed enclosure having a metallic cathode 20 which is preferably a hollow cylinder, a ceramic insulator 22 bonded to one end thereof and a ceramic insulator 2'4 bonded to the other end. For imparting strength and rigidity to the structure, metal rings 26 and 28 are bonded to the ceramic insulators at locations opposite to the cathode ends and for centering the entire unit about an opening 30 in the wave guide, the ring 28 fits within a ring 32 securely attached to the Wall 15 of the wave guide.

Each of the ceramic insulators 22 and 24 is apertured to accommodate an electrode extending into the cathode from an end thereof. Aperture 34 accommodates an anode electrode 36 which is supported by a stem 37 welded or otherwise attached to a disc 38 through which is passes. Disc 38 rests against a raised portion 40 of insulator 22 and is preferably bonded thereto to maintain the interior of the cathode 20 sealed. Anode 36 is capacitively coupled to the casing 14 and wave guide 16 through a wafer type of insulator 41 disposed between disc 38 and an interior portion of cap 18. At high frequencies, the anode is, therefore, effectively connected to ground since the wave guide structure is grounded as shown.

Ceramic insulator 24 at the other end of cathode 20 is apertured at 42 to accommodate a conductor 43, reduced at its end portion, to a probe 43a which protrudes into the cathode, axially opposite to anode 36. Conductor 43 extends across wave guide 16 to intercept electromagnetic waves as hereinbelow described in more detail. The conductor 43 is guided by an apertured insulator 44 in which it loosely fits and which is secured in a stub 45 secured to the wave guide. Stem 37, supporting anode 36, is loosely fitted and guided by an apertured insulator 46 secured in a stub on cap 18. Accordingly, the unit 17 including cathode 20, insulators 22 and 24, anode 36, stem 37, conductor 43, disc 38, insulator 41 and rings 26 and 28, is bodily insertable into or removable from the position shown in the drawings by removal of cap 18.

Wave guide 16 is effectively short circuited by a conductive plunger 50 movable along a portion thereof for proper positioning and a pair of tuning screws 52 and 54 threaded in wall 14 of wave guide 16 provide for adjustment for proper tuning.

The interior of cathode 20 is filled with an ionizable gas such as one of the noble gases at a low pressure of the order of 1 to 50 mm. of mercury and is sealed from ambient space and from the interior of wave guide 16. The gas within the cathode is ionizable by a potential gradient between the anode 36 and cathode 20. Such a gradient may be established by a direct potential selectable by a movable arm 51, engageable with a potentiometer resistor 52, which in turn is connected across a potential source 53 and applied through a resistor 51a. For selecting a potential bias for probe 43a, another movable arm 54 is engageable with resistor 52 and is connected to the probe through an output load resistor 55. A capacitor 56 is connected between one end of resistor and an output terminal, the other output terminal being grounded. Cathode 20 is preferably connected through a resilient member 57 and a terminal 58 mounted on casing 14 and insulated therefrom by an insulating grommet 59. Suitable switches 60 and 61 are interposed in the cathode line and in the potentiometer energizing line for control of potential application.

In operating the detector 13, an electromagnetic wave is propagated along wave guide 16 from any suitable source with its electric field parallel to conductor 43 and probe 43a. The distance between probe portion 44 and plunger 50 is adjusted to substantially a quarter of a wave length of the frequency of the energy propagated. Thus, standing waves with a maximum intensity in the region of conductor 43 occur in the wave guide and currents are induced in the conductor 43 which create potentials on the probe 43a within cathode 20 which alternate at the frequency of the electromagnetic wave. The probe 43a is configured and located in the ionized region of cathode 20 so that the electric field is of maximum intensity in the immediate vicinity of the probe and produces maximum interaction between the field and the ionized plasma in this vicinity. Insulator 41 establishes an effective capacitive coupling between plate 38 and cap 13 at high frequencies whereby anode 36 is also coupled to the casing at such frequencies. By reason of the non-linear conduction at probe 43a, detection of a modulated incoming signal occurs and the demodulated output may be derived across terminals 62 and 63.

Referring now to FIGS. 3 and 4 of the drawings, represents generally a simplified version of another embodiment of my invention including a hollow wave guide 102 of rectangular cross section and having a bottom wall portion 104 intermediate the sides thereof. As seen in FIG. 4, laterally opposed portions 106 and 107 of bottom wall 104 are inwardly tapered along a length 108 as seen in FIG. 3, to establish an intermediate recess portion 109 between portions 106 and 107. Accordingly, as is shown in these figures, a region 110 of the wave guide, reduced in cross-section, is established wherein it is generally rectangular in cross-section with recess 109 along an intermediate portion of the bottom wall thereof.

In accordance with a feature of my invention, recess 109 accommodates an elongated cathode electrode 114 and a septum-shaped probe 116 is accommodated in a slot 118 longitudinally along an. intermediate portion of the upper wall of the wave guide. Cathode 114 and probe 116 are substantial-1y opposite each other and extend along substantially the same length of the wave guide. Probe 116 is tapered along a portion 117 to minimize reflection of electromagnetic waves propagated toward region 110 :and is supported by a mounting bracket 120 which is capacitively coupled to the upper wall of the wave guide along outer portions of the bracket separated from the wave guide by a continuous insulator 122 disposed between the bracket and the upper wave guide wall.

Region 110 of the wave guide is sealed from ambient space by a window 126 transparent to electromagnetic wave energy but impervious to gas and insulator 122 extends between the probe 116 and adjacent wave guide walls as also shown in FIG. 3 of the drawings. Cathode 114 is provided with :an external terminal 132 extending through an aperture in the bottom wall of the wave guide and is insulated therefrom by an apertured sealing insulator 134 mounted in a tubular support 136 to accommodate the terminal 132.

The gas within region 110 which, as described in the previous embodiment of the invention, may be one of the noble gases at a pressure of 1 to 50 mm. of mercury, is ionizable to a condition of negative glow by a potential gradient established between cathode 114 and the wave guide walls as an anode. To achieve such ionization, a potential is derived from potentiometer 138 having a direct potential source 140 connected across a potentiometer resistor 142 thereof. A movable arm 144 of the potentiometer, engageable with the resistor 142 along the length thereof, is connected to the wave guide through a variable resistor 146 and terminal 132 is connected to the negative terminal of potential source 140. A positive potential with respect to the cathode is applied to the probe 116 from another arm 148 engageable with resistor 142 along its length and being connected to the probe 116 through an output resistor 150.

In operating the detector 100, a condition of negative glow discharge is established in the region 111' by the application of a suitable potential across the wave guide and cathode 1:14 and an electromagnetic wave is propagated along the wave guide toward the region 110 wherein it is compressed to increase the wave electric field intensity at the surface of the probe 116. Thus, the interaction between the electromagnetic field and the ionized plasma is also increased in the immediate region of the probe 116. The non-linearity of the interaction in the region of contact of the probe 116 with the negative glow plasma is effective to demodulate the microwave signal to produce a demodulated output across resistor 150 and such a demodulated output is applied to the output terminals of the detector, represented at 152, through a capacitor 154. A decoupling capacitor 156, between arm 148 and ground, is provided.

Referring now to FIGS. 5 and 6 illustrating another embodiment of my invention, 166 represents generally the detector in its entirety shown in these figures. Detector 160 includes a conductive closed-end hollow wave guide 162, preferably of rectangular cross-section, and having a conductive box 164 with edges of an open side thereof secured to one wall 166 of the wave guide to cover a portion of that side. An opening 168 is formed in wall 166 to establish communication between box 164 and wave guide 162 and a conductive wire grid 169 is disposed over the opening to form an effective wave guide wall to electromagnetic wave energy of appropriate frequencres.

According to a feature of this embodiment of my invention an elongated cathode 170 is located longitudinally along box 164 above opening 168 as seen in FIGS. 5 and 6 and a septum-type of probe 172 is disposed along wave guide 162 beneath opening 168 and cathode 170 as seen in these figures. Insulation, such as mica shown at 173, is disposed between closely adjacent surfaces of the probe and wave guide to establish capacitive coupling therebetween at high frequencies. External electrical connections to cathode 170 are facilitated by a lead 174 extending through an insulator 176 which is bonded in a tubular support 178 opening into a wall of box 164. External electrical connections to probe 172 are facilitated by a pair of terminals 180 and 18-2 extending through openings in a wall of wave guide 162 and being mounted in insulators 184 and 186 secured to the interiors of the supports.

A confined region 188 within the wave guide 162 is established by a window 191 of material such as mica disposed in the wave guide and being transparent to electromagnetic wave energy while being impervious to gas. The region 138 is filled with 'ionizable gas at low pressure and ionization thereof is achieved by applying a potential between cathode electrode 170 and wave guide 162 by a potential source 192. To derive such a potential, a potentiometer resistor 194 is connected across the source 192 and a pair of moveable arms 196 and 198 adjustably engageable with the resistor, are connected, respectively, to the wave guide 162 and to the probe 172, while cathode 170 is connected to the negative terminal of source 192. A current limiting resistor 20% is interposed in the line connection to wave guide 162 and an output resistor 202 is interposed in a line connection from arm 198 to probe 172.

Electromagnetic wave energy is propagated along wave guide 162 into the region 188 wherein the electric field thereof is intense in the region of the upper surface of 6 the probe adjacent to grid 169. The applied potential across cathode and wave guide 162 establishes a region of negative glow ionization within the wave guide 162 and the electric field intensity of the electromagnetic wave being greatest along the surface of the probe nearest grid 169, produces an interaction between the electromagnetic wave and negative glow plasma which is non linear in character to detect the modulation of the impressed electromagnetic waves. A demodulated output produced across resistor 202, may be applied to output terminal 294 through a capacitor 206. A second output terminal 267 is grounded and a decoupling capacitor 208 etween arm 198 and ground is provided.

Referring now to FIG. 7 of the drawings illustrating a detector according to another embodiment of my invention 211 represents generally the detector in its entirety mounted in a closed end wave guide 212 along which modulated electromagnetic wave energy is propagated to be impressed on the detector.

According to a feature of this embodiment of the invention a detector unit 213 having a size and shape the same as present-1y conventional crystal detectors includes a hollow cathode tube 214 filled with an ionizable gas at low pressure for forming a hollow cathode discharge by a potential gradient between the cathode and an anode 216 mounted at one end of the cathode on a ceramic plate 21% closing off the cathode interior. External connections to the anode are enabled by a rivet 22!] integral with the anode and passing through ceramic plate 218 and being also useful to secure the anode in place. Interaction between the electromagnetic wave and the ionized gas is achieved by placing a conductor 222 in the path of the electromagnetic wave to have such energy induced therein and positioning a thin probe portion 224 at the end of the probe in the region of the hollow cathode discharge. For supporting conductor 222, a flange 226 is provided near one end thereof for engagement with one end of a hollow ceramic insulator 228 having the other end apertured at 230 and being in contact with the end of cathode 214. The engaging surfaces between cathode 214 and plate 218, between the cathode and the end of insulator 228 and between insulator 228 and flange 226 are preferably bonded and sealed to maintain the interior of the detector 210 free from contaminous ambient air or other foreign matter.

Detector 210 is preferably mounted in wave guide 212 through cylindrical sleeve 231 in the Wall of the wave guide and an opening 232 in an opposite wave guide wall accommodates the flange 226 of probe 222. Insulators 233 and 235 effectively bypass microwave currents between the metal surfaces which contact them and the microwaves are then contained to exist only within the wave guide 212.

An ionizing potential gradient between the anode 216 and cathode 214 is established by a direct potential source connected across a resistor 236, one end of which is connected to the cathode and an intermediate point of which is connected to the anode. For potential. control, an arm 23 8, adjustable to contact resistor 236 at any point along its length, is connected to probe 222 through a load resistor 240 and for bypassing high frequencies, a pair of by- pass capacitors 242 and 244 are connected between arm 23S and anode 216 and between the am 238 and ground respectively. An output is produced across terminals 246 and direct potential is blocked by a blocking capacitor 247 connected between the probe 222 and an output terminal of a pair 246, the other terminal of which is connected to ground. A further by-pass capacitor 239 is disposed between one end of load resistor 240 and ground.

In the operation of the detector 210, it is disposed in a wave guide as shown in FIG. 7 and electromagnetic wave energy is propagated along the wave guide toward the de tector. The distance between the end wall 237 of the wave guide and conductor 222 is established at substantially a quarter wave length of the incoming wave whereby standing waves of maximum intensity in the region of the conductor are established in the Wave guide. Thus, the electromagnetic Wave energy induces current to flow in the conductor 222 and alternating potentials at the microwave frequency are created on the probe 224. As explained hereinabove, the electric field is of maximum intensity in the region of the probe end 224 and the interaction between the electromagnetic field and the ionized gas is also of maximum intensity in this region. This effects a non-linear current conduction or rectification of the electromagnetic wave to demodulate the wave and the demodulated signal thereof is produced across load resistor 240 and appears at output terminals 246. According to this embodiment of the invention, commercially available crystal detector mounts are readily modified and adapted for detection according to the principles of my invention. It is further to be noted that the unit 213 shown in FIG. 7 is readily adaptable not only in wave guide crystal mounts but also in crystal mounts for coaxial and other lines and is useful from zero frequency or direct current to frequencies of the order of 10,000 megacycles per second.

Referring now to FIG. 8 of the drawings illustrating another embodiment of my invention according to which the interaction between an electromagnetic wave and an ionized plasma is exploited to achieve frequency multiplication, 248 designates the multiplier generally which includes a conductive ground plane 250 above which and perpendicular to which a conductive probe 252 is disposed. The probe is located within an enclosure 254 which may be of glass or any other material transparent to electromagnetic waves. The region within enclosure 254 is filled with an ionizable gas at low pressure and for establishing a region of negative glow discharge 256 within the enclosure, a pair of cathode leectrodes 258 and 260 are disposed at opposite sides of the enclosure and have applied thereto a direct potential from a direct potential source 261 through a current limiting resistor 262 and a current controlling switch 264, the other positive side of the source 261 being connected to the base electrode 250.

In operating the multiplier 248, a microwave of any predetermined frequency fis propagated over the ground plane 250 with its electric vector parallel to the probe 252'. It is assumed under the circumstances that the microwave is propagated in a direction essentially perpendicular to and into the face of the paper in FIG. 8. A portion of the microwave is intercepted by the probe whereby currents are induced therein which alternate at the microwave frequency. The microwave currents induced in the probe are basically non-sinusoidal by virtue of the physical processes involved at the probe surface, and hereinabove described with respect to other embodiments of the invention, and flow into the ground plane surrounding the probe. If probe 252 is constructed so as to be a quarter wave length monopole above the ground plane 250 at some frequency higher than the frequency 1, preferably some multiple thereof, re-radiation from the probe within the enclosure 354- is enhanced at this higher frequency multiple. To further enhance the effect of frequency multiplication, many probes erected above the plane 250 may be provided in the form of a multi-element array with appropriate spacing to concentrate re-radiation in the particular direction where it may be picked up by a horn or other appropriate means. Under the circumstances the plasma electron density can be adjusted so that no appreciable direct interaction occurs between the plasma and the microwave at either the fundamental or multiple frequency of the microwave. In a practical embodiment of this form of invention, the ground plane 250 may be the inside lower surface of a conventional hollow wave guide of such size and dimensions as to support propagation of electromagnetic wave energy at the frequency f.

In accordance with another embodiment of my invena CB tion a frequency multiplier disclosed in FIG. 9 of the drawings may be established by a conductive ground plane 266 above which is formed a region 268 of ionized gas 270 in which the gas is contained in an electromagnetic wave transparent and gas impelvious enclosure 272. Below the ground plane 266 is provided an electromagnetic wave guide 27 4' having as one wall thereof the ground plane 266 and across which is disposed a probe 276. The probe is mounted in a stub 278- in one wall of the wave guide and extends therefrom through an aperture 230 in the ground plane and into the region of enclosure 272. Wave guide 27 4 is of such size and dimensions as to support such propagation of electromagnetic wave energy at a frequency f and in which the electric vector of the propagated Wave is parallel to the probe 276 whereby currents at the frequency f are induced in the probe 276. Thus currents at the frequency f are propagated along the coaxial wave guide formed by the probe 276 passing through the ground plane 266 and are introduced into the region within the enclosure 272. The end of probe 276 protruding into the region above the ground plane is of a length equal to a quarter wave length at some multiple of frequency f and re-radiation at such multiple occurs within the region above the ground plane and within the enclosure 272 by reason of the non-linear conduction at the surface of the probe resulting from the interaction with the ionized plasma. In this embodiment of the invention currents at the harmonic frequency are prevented from being transferred into the wave guide 27 4 by a choke structure 282 within the surface of the ground plane 266. A removable plate 233 secured in position on ground plane 266 facilitates access to the choke. With proper account of microwave phases, a number of probes similar to probe 276 may be disposed "along the wave guide 274 and protruding into the region of ionized plasma.

In accordance with still another embodiment of my invention a frequency multiplier 284 as shown in FIG. 10 of the drawings may be provided in a ridge wave guide 286 adaptable for propagating electromagnetic wave energy at a frequency f and having disposed in opposite side walls thereof a pair of electrodes 288 and 290 and supported by respective insulators 292 and 294 in tubes 296 and 298 communicating with respective sides of the wave guide. The cathode electrodes 288 and 290 have impressed thereon a direct potential negative with respect to wave guide 286, derived from source 300 connected to the respective electrodes through a current limiting resistor 362 and a controlling switch 303. The region within wave guide 286 is filled with an ionizable gas at low pressure whereby the potential on electrodes 288 and 290 establishes a region of negative glow discharge 305 within the wave guide. A second wave guide 304 is formed within one of the ridges of wave guide 286 and is provided with an apertured wall 306 through which a probe 308 extending from the wall opposite to the aperture into the region of wave guide 286 between the ridges thereof. In the operation of the multiplier 2'84, electromagnetic wave energy is propagated along the wave guide 286 at a frequency f and with the electric field vector in a direction parallel to the probe 308. Such energy induces cur rents in the probe 308 and by reason of the non-linearity of such conduction the currents so induced are effective to re-radiate an electromagnetic 'wave energy in the wave guide 304 at some multiple of frequency 1. Wave guide 304 is so sized and proportioned as to sustain propagation of electromagnetic wave radiation at this multiple frequency to be applied to further circuitry.

While the embodiments of invention shown in FIGS. 8, 9 and 10 are in principle effective and workable in virtually any frequency range, it is noted that as a practical matter the same are believed to have greatest utility at impressed frequencies in excess of megacycles per second since at frequencies less than this, probe lengths and the size of other components necessanily become very large.

While the present invention has been described by referonce to particular embodiments thereof, it will be under stood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An apparatus comprising a wave guide having an aperture in a wall thereof, an enclosure mounted on said wave guide and having an aperture in alignment with the aperture in the wall of said wave guide, a probe extending across said wave guide and through said apertures into the region of said enclosure and being insulated from said wave guide and said enclosure, an anode extending into the region of said enclosure and being insulated there-i from, said anode being spaced from said probe, means for applying a direct potential to said anode positive with respect to said enclosure and including a potential source and lead connections to said probe and to said anode and a load resistor interposed in series with said probe, means for shorting a portion of said wave guide at a location spaced from said probe and means for propagating electromagnetic wave energy along said wave guide having a wave length substantially four times the distance between said probe and said short whereby a potential is induced in said probe, an ioniza-ble gas in said enclosure and being in a condition of negative glow discharge, the electromagnetic wave energy at the surface of said probe interacting with the negative glow plasma whereby a demodulation effect occurs in the vicinity of said probe in said enclosure to produce an output signal across said load resistor.

2. An apparatus comprising a wave guide having an aperture in one wall thereof, a closed chamber having an aperture in alignment with the aperture in said wave guide, said chamber being filled with an ionizable gas, an anode in said chamber being insulated therefrom and means applying direct potential across said chamber and said anode to cause said gas to be ionized in a condition of negative glow discharge, a conductor in a portion of said wave guide and extending through said apertures and terminating in a probe within the region of negative glow in said chamber, means shorting said wave guide at a location spaced from said probe, and means for propagating electromagnetic wave energy along said wave guide having a wave length substantially four times the spacing between said probe and said short, means applying a positive potential on said pro-be with respect to said chamber and including a connection having a serially connected resistor and means for deriving a potential across said resistor indicative of the modulation on the electromagnetic wave propagated along said wave guide.

3. An apparatus comprising means providing an enclosed volume containing an ionizable gas at low pressure, means including anode and cathode electrode means having spaced and mutually insulated electrode surfaces exposed to the interior of said first mentioned means for establishing a potential gradient in a portion of said volume sufficiently great to establish a region of negative glow discharge therein, an elongated conductive probe projecting in a predetermined direction into said region and having a portion with a small surface area therein, means for directing an electromagnetic wave having an electric vector with a component parallel to said direction to impinge on said probe and induce electrical currents therein and impedance means connected in series with said probe for deriving an output resulting from the interaction between the potential produced at the surface of said probe within said region and the negative glow plasma immediately adjacent thereto dependent upon the electromagnetic wave intensity impinging on said probe.

4. An apparatus comprising a closed chamber containing an ionizable gas and means establishing a region of negative glow discharge in said chamber including a generally cylindrical cathode and an anode electrode having an electrode surface exposed to the interior of said cathode and insulated therefrom, an elongated conductive probe of small transverse dimension having a portion protruding into said region of negative glow discharge and means for inducing a current at microwave frequency in said probe whereby interaction between microwave energy and the negative glow plasma occurs at the probe surface and means responsive to current conducted by said probe for producing an output potential dependent upon said interaction.

5. An apparatus comprising a Wave guide having outer, spaced, portions of one wall thereof tapered inwardly along a length thereof to form an internal recess therebetween, a cathode elect-rode disposed along a portion of said recess, a probe supported on a wall of said wave guide and being insulated therefrom, said probe being substantially opposite to said cathode electrode and spaced therefrom, the region between said cathode electrode and said probe being filled with an ionizable gas and means for applying a potential to said wave guide positive with respect to said cathode to ionize said gas into a negative glow condition, a portion of said probe having a small surface area projecting into said region and means for applying a potential to said probe positive with respect to said cathode, said last mentioned means including a line connection having a resistor serially interposed therein, means for propagating electromagnetic wave energy along said wave guide and means for deriving an output potential across said resistor indicative of the modulation on said electromagnetic wave.

6. An apparatus comprising a wave guide having an internal recess along one wall thereof, a cathode electrode insulated from said wave guide and extending along a portion of said recess, an elongated, thin, conductive probe projecting into said wave guide and having a portion coextensive with said cathode, said probe being insulated from said wave guide, the region between said probe and said cathode being filled with an io-nizable gas at low pressure, means applying a potential to said probe positive with respect to said cathode through a load resistor and means applying a potential to said wave guide positive with respect to said cathode to ionize said gas into a condition of negative glow whereby modulated electromagnetic waves propagated along said wave guide are demodulated by the interaction of the electromagnetic wave energy with the ionized gas at the surface of said probe.

7. An apparatus comprising a wave guide having an internal recess along one wall thereof, a cathode insulated from said wave guide and extending along a portion of said recess, a thin, conductive probe projecting into said wave guide from another wall thereof and having a portion coextensive with said cathode, said probe being capacitively coupled to said wave guide, the region between said probe and said cathode being filled with an ionizable gas at low pressure, means applying a potential to said probe, positive with respect to said cathode through a load resistor, and means for applying a potential to said wave guide positive with respect to said cathode to ionize said gas to a condition of negative glow whereby modulated electromagnetic waves propagated along said wave guide induce high frequency currents in said probe and an interaction between the electromagnetic wave energy and the ionized gas at the surface of said probe occurs to produce the modulating potential across said load resistor.

8. An apparatus comprising a Wave guide having an elongated opening along one wall thereof, an enclosure having its open side in communication with said opening, an elongated cathode disposed in said enclosure and being substantially coextensive with said opening, a conductive grid across said opening presenting an effective wall for the propagation of electromagnetic waves of predetermined frequency along said Wave guide, an elongated, thin, conductive probe mounted in said wave guide on a 1 1 wall remote from said opening and being insulated from and capacitively coupled to said wave guide, said probe being spaced from said opening and the region between said opening and said probe being filled with an ionizable gas at low pressure, means applying a potential to said probe positive with respect to said cathode through a load resistor, and means applying a potential to said Wave guide positive with respect to said cathode to ionize the gas in said region into a condition of negative glow whereby modulated electromagnetic Waves propagated along said Wave guide are demodulated by the interaction between the electromagnetic wave energy and the ionized gas at the surface of said probe.

References Cited in the file of this patent UNITED STATES PATENTS 2,765,445 Zaleski Oct. 2, 1956 2,768,320 Hagen Oct. 23, 1956 2,848,649 Byrant Aug. 19, 1958 2,877,417 White Mar. 10, 1959 10 2,928,000 White Mar. 8, 1960

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