US 2422189 A
Description (OCR text may contain errors)
June 17,1947, M, D, FISKE, 2,422,189
DIELECTRIC WAVE GUIDE SYSTEM Filed Jan. 22, 1944 Inventor: Miiah D. Fiske,
' His Attorney.
Patented June 17, 1947 DIELECTRIC WAVE GUIDE SYSTEM Milan D. Fiske, Schenectady, N. Y.,- assignor to General Electric Company, a corporation of New York Application January 22, 1944, Serial No. 519,267
My invention relates to dielectric wave guides of the hollow pipe type for transmitting electromagnetic waves of ultra high frequency and, more particularly, to structures associated therewith for sectionalizing such a guide to permit operation of adjacent sections under different pressure conditions.
It is known that electromagnetic waves may be propagated through the interior of la hollow pipe type guide constructed of a conductive material-and containing a dielectric medium, such as air or gas, through which the energy of the wave is transmitted. The frequency of the exciting electromagnetic waves, of course, must be greater than the critical minimum frequency established by the dimensions, principally the transverse dimensions, of the guide.
There maybe placed within the interior of a dielectric guide a, metallic wall having an aperture which is tuned to the frequency of the exciting waves to effect a concentration of the potential due to the waves within or across a substantially small dimension of the aperture. If th intensity or magnitude of the exciting electromagnetic waves is increased, the magnitude of the potential diiference appearing between opposing surfaces of the aperture is also increased and, when the magnitude ofthis potential difference increases to a predetermined value established by the configuration of the aperture and dielectric strength of the medium surrounding the aperture, an electric discharge is established across the aperture thereby materially changing the propagation characteristics of the guide. A structure of this nature may be employed, for example, in connection with an ultra high frequency system which is subjected to electromagnetic waves of considerable range of intensity and which utilizes the characteristics of the aperture to effect transmission or attenuation of the Waves within the guide.
It is an object of my invention to provide a new and improved dielectric wave guide of the hollow pipe type in which a transverse metallic wall, having a resonant aperture, is provided with a window to seal said aperture to permit operation of the regions on opposite sides of said wall at diiferent pressures.
It is a further object of my invention to provide a new and improved means for sectionalizing a wave guide.
It is still another object of my invention to provide a new and. improved window for a Wave guide which is substantially reflectionless over a 2 wide frequency band of the electromagnetic waves being propagated along said guide. I
It is a still further object of my invention to provide a new and improved resonant aperture enclosed within or associated with a wave guide of the dielectric type and which is provided with a window having substantially zero phase extension along the guide.
It is a still further object of my invention to provide a new and improved resonant structure associated with the dielectric wave guide which has small frequency sensitivity.
It is still another object of my invention to provide a wave guide of the hollow pipe type with a glass window having a reflection characteristic similar to that of a single tuned parallel circuit.
It is another object of my invention to provide a new and improved window structure associated with a dielectric wave guide which is highly responsive to the magnitude of the exciting electromagnetic waves.
It is a still further object of my invention to provide a, new and improved window for a wave guide having means to prevent sputtering of the glass surface by electrodeless discharge.
One of the features of my invention is the provision in a metallic wall for sectionalizing a wave guide of a resonant aperture, such as a resonant slot, tuned substantially to the frequency of the exciting electromagnetic waves and which is designed toeffect a breakdown of the surrounding medium in the event the intensity of the electromagnetic waves attains or exceeds a predetermined value. The presence of the electric discharge across the slot varies the effective dielectric constant of the dielectric medium through which the electromagnetic waves are propagated thereby changing the Wave guide from a propagator to an attenuator of the electromagnetic waves.
incorporated in a hollow pipe dielectric wave guide; Fig. 2 is a cross-sectional view of the A seal is provided across the resonant aperture and may comprise a vitreous dielectric window structure for the resonant aperture or slot in a wave guide; and Fig. 3 is a view of a modification of the wave guide window of my invention.
It is known that ultra high frequency electromagnetic WaVes may be propagated dielectrically through hollow pipe type guides where the frequency of the exciting electromagnetic waves is greater than a critical minimum frequency which, in turn, is determined principally b the transverse dimensions of the guide. Such guides pref,- erably are constructed of aconductive material, such as copper or brass. of high frequency electromagnetic waves, may be transmitted dielectrically through hollow pipe type guides. Of these waves, the transverse magnetic or TM type waves have both a longitudinal and a transverse component of electric field but only a, transverse component of magnetic field whereas the transverse electric or TE type waves have both a longitudinal and a transverse component of magnetic field but only a transverse component of electric field. Although my invention is applicable to systems for transmitting a great variety of waves, in describing my invention hereinafter reference will be made particularly to the TEM type of wave.
Referring now to Fig; 1 of the accompanying drawings, my invention is there illustrated as applied to a system including a hollow pipe type wave guide of the dielectric type. The dielectric wave guide may be ofrectangular cross section formed by conductive material, such as copper or brass, having a height a and a base dimension D. Electromagnetic waves are established within the guide by suitable exciting electrodes which may have variousconfiguratioris depending upon the nature 'of the excitation required or desired. One form which the input electrode or exciting means may assume is that of a concentric line including tubular outer conductor 1 and an inner conductor 2, the former of which is conductively connected to the bottom of the waveguide and the latter of which may be conductively connected to the top. There is positioned within the wave uide a metal wall 3 which may be constructed of a suitable alloy, such as an iron-nickel-cobalt alloy. The wall 3 is provided with an aperture 4 having an appreciable dimension transverse to the direction of propagation of electromagnetic waves within the guide. Where the wave guide is excited by electromagnetic waves of the TEm type, for example, the slot affords a principal dimension transverse to the electric component of the electromagnetic field and effects a concentration of the potential due to the wave across the upper and lower edges of the slot. This accentuation or concentration of the potential due to the wave is effected by virtue of the fact that the slot is tuned to the frequency of the exciting waves, i. e., causes little reflection of electromagnetic waves of this frequency. If desired, the resonant aperture may be of the configuration .illustrated wherein the slot 4 is rectangular in shape. A resonant slot of this type is described ingreater detail and claimed in my copendin application. Serial No. 458,422, filed September 15, 1942, and assigned to the assignee of the present invention.
In ultra high frequency transmission systems which employ dielectric wave guides of th hollowpipe type, it is desirable frequently to operate adjacent sections of a, wave guide at different pressures. atmospheric pressure while the adjacent section is either evacuated or filledwith a suitable gas at 4 a pressure other than atmospheric. To this end, in the system'illustrated in Fig. 1, the complete opening or aperture 4 is sealed by means of a dielectric window 5 constructed of a suitable vitreous material, such as a boron-silicate glass, having substantially the same coefiicient of linear expansion as the alloy material of which the transverse wall3 is constituted.
The wall 3 and the associated dielectric window constitute one end of a sealed chambe or section of the dielectric wave guide, the longitudinal end of such section being provided by the end wall Moreover, many types Thus, one section may be operated at beyond the concentric electrode means I and 2.
It is to be understood that the concentric line may glass is hermetically sealed in place, the window may be ground on both sides to obtain precise dimensions so that the surfaces of the glass 5 are coplanar with the surfaces of the wall 3. So constructed, the window 5 lies nearly in a single electrical plane, that is, it has very little phase extension along the guide. Hence, the effect of the window 5 and the resonant slot 4 can be compared to a single resonant circuit in a transmission line so far as their reflection properties are concerned. The thin element constituted by the window 5 and the resonant slot 4 behaves as a parallel resonant circuit shunted across the line, this circuit having negligible resistance because of the high conductivity of the metal wall 3 and low dielectric loss in the glass 5. It has been found that such an element can be made almost completely refiectionless over a wide band of frequencies. Theeffect, therefore, of such a thin element is considerably different from an element having a substantial phase extension along the wave guide, for such an element would be represented by two or more circuits of finite phase separation and, in general,'reflection from sucha combination would not vanish at any frequency.
For a thin composite element comprising the metal wall 3 and a glass window 5 sealed across the gap 4, it has been found that the reflection versus frequency curve of an incident electromagnetic wave is almost identical with the ordinary tent the exact resonance frequency, et gen-u erally speaking, as the effective dimensions of the aperture transverse to the electric component of the field is increased, the frequency to which the aperture is resonant is decreased. At the same time, the phase extension of the composite window structure increases with the height of the resonant slot 4.
.The voltage Or Potential difference appearing between the upper and lower edges of the aperture 4 is eifected by the resonant characteristics of the aperture and the magnitude of this voltage difference increases as the magnitude of the exciting waves increases. Upon reaching a predetermined value, the dielectric material or medium adjacent to the window 5 across the aperture breaks down, that is, the voltage difference is sufficient to cause ionization of the medium and an electric discharge takes place across the aperture 4. Upon occurrence of such an electric discharge the wave transmitting characteristics of the guide are radically changed causing rapid attenuation of the electromagnetic waves within the vicinity of the wall 3. The presence of the charged particles within the vicinity of the resonant aperture during the electric discharge effectively changes the dielectric constant of the medium through which the waves are being propagated thereby substantially increasing the critical minimum frequency for the particular guide employed so that the waves are not propagated an appreciable distance beyond the wall 3. I
The voltage or potential difference appearing between the upper and lower edges of slot 4 effects a concentration of electric field across the slot and across the window 5. Where the window is used to separate two wave guide sections having different pressure conditions, it has been found that as the potential diiference across the slot 4 increases, an electrodeless discharge, i. e., an electric discharge which takes place by virtue of the electric field strength being suificient to produce ionization without the presence of any electrodes, occurs across the window 5 on its lower pressure side. In Fig. 3 there is shown a modification of my invention wherein means is provided to reduce or eliminate sputtering onto the glass window 5 produced by this electrodeless discharge. This sputtering arises whenever the discharge, the area of which varies with the strength of the incident electromagnetic energy, becomes great enough that it extends over the entire window 5 and touches any portion of the metallic wall 3. layer of glass 1 connected to the glass window 5 and extending over the portion of the metal wall 3 adjacent to the aperture 4. The layer 1 has a minimum thickness and extends a substantial distance over the outer surfaces of wall 3 toward the walls of the wave guide.
In constructing a wave guide system embodying my invention, the section In may be provided at its end with a shoulder ll, against which the transverse wall 3 abuts. guide, at its end connecting with section l0 may be provided with an integral sleeve I 3 which slips over the outer surface of section In so that wall 3 is held firmly between adjacent edges of sections l0 and I2.
From the foregoing description, it is thus seen that my invention provides a new and improved window for sealing adjacent sections of a wave guide having differential pressures therebetween, the window having a small phase extension and causing a minimum reflection of the electromagnetic wave being propagated along the guide. At the same time, the composite structure has a low frequency sensitivity, that is, provides efficient transmission ove a substantial band of frequencies of the electromagnetic wave. The window, furthermore, may be employed as a breakdawn element if the medium on one side thereof is readily ionizable. When electromagnetic waves of sufficient intensity imping on the window the This means comprises a glaze or thin The section I2 of the F medium, which may be a low-pressure gas, breaks down and causes a very considerable attenuation of the waves passing through the window.
While I have shown and described my invention as applied to one particular embodiment thereof, it will be obvious to those skilled in the art that changes and modifications may be made withoutdeparting from my invention, and I therefore intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. A combination, a dielectric wave guide of the hollow-pipe type and comprising a pair of adjacent sections having differential pressures therein, exciting means for establishing electromagnetic waves within said guide, and means for transmitting said waves between said sectionssubstantially without reflection, said means comprising a metallic wall associated with said guide and lying between said sections within a plane substantially transverse to the direction of wave propagation through said guide, said wall being provided with an aperture having an appreciable dimension perpendicular to the electric component of field incident to the propagation of waves through said guide, and vitreous means sealed across said aperture and substantially co planar with said wall, said aperture and said vitreous means being tuned to the frequency of said exciting means and having substantially zero phase extension along said guide.
2. In a dielectric wave guide of the hollowpipe type and including a substantially closed section, exciting means for establishing electromagnetic waves Within said section, and means for facilitating transmission of said waves from said section substantially without reflection, said means comprising a metallic wall defining a boundary of said section and lying in a plane substantially transverse to the direction of wave propagation through said guide, said wall being provided with an aperture having an appreciable dimension perpendicular to the electric component of the field incident to the propagation of waves through said guide and tuned to the frequency of said exciting means, and a glass window hermetically sealed across said aperture and substantially coplanar with said wall, said window and said aperture having a minimum phase extension along said wave guide.
3. In combination, a dielectric wave guide of the hollow-pipe type, excitin means for establishing electromagnetic waves within said guide, a metallic wall associated with said guide and lying in a plane substantially transverse to the direction of wave propagation therethrough provided with an aperture having an appreciable dimension perpendicular to the electric component of the field incident to the propagation of waves through said guide, and a vitreous member sealed across said aperture, said vitreous member having a portion extending over the surface of said wall adjacent said aperture to pre- Vent injury to said member produced by an electric discharge established across said aperture in the presence of electromagnetic waves of substantial intensity.
4. In combination, a dielectric wave guide of the hollow-pipe type, exciting means for establishing electromagnetic waves within said guide, a metallic wall associated with said guide and lying in a plane substantially transverse to the direction of Wave propagation through said guide mans by $1 6 am; aimrwradu t6 elegs of S ibSt'afitiaI i tegifslti}, sa d I mgle; thihlay r ofrilf sulaitlin 'g t'e'rilaovgfiigg sa'i djwall adjacent samfajpe tui e.
inatidfija di lect ic wa e i dewf theiiblldw p pe; 1331p? inq'comppismg p51; oi qqljace nfi 's ect'ibhs' having difie feritji l prgsures thel 'ebtwen, exitirig mea 'r is fo i' Establishing elgdigiqr'ngpetic waves within said guidg, and f0: tfgtmxpitbing said waves bgtwegp said s eict'i ris 'subs taht ially Without reflectipn, said me "risfcombri'si'x ig metallic wall associated with ,sg d; guide andlyingbetwgen said sgc'tion s within afplan e s i 1btaliitia11y transverse to the direcjqign 6f. wav b pgtion through aid guideysa id wan q roviq q w th 'an a rtu e 'avin fan a r ia dim nsi qnz IK QQiQ W 't the e e REFEK NQE TE? V lThe following references are of record in th e file of this patent:
STATES PAT NTS umb? Name t 7 2,129,713 Southworth Sept; 13; 19318: 2,200,023 Dallenbach :May'7., 1940;