US2980873A - Waveguide switch device - Google Patents

Description

April 1s, 1961 Filed DeG. 29. 1958 R. M. WALKER ET AL 2,980,873

WAVEGUIDE SWITCH DEVICE 4 Sheets-Sheet 1 [FIGA April 18, 1961 R. M. WALKER ET AL 2,980,873

WAVEGUIDE SWITCH DEVICE 4 Sheets-Sheet 2 Filed Dec. 29, 1958 @Em KWF-E I ODR O AKS-I 4 TWRS ,v All 4 6 N .EMI 4 m 5 EMBBM 6 M VDDAJ. 1 7 M G WMDDHRT A 0 6 .I N 1 f 7 r www@ 5 Mmmm .fn Q .m 0 Y l B I 3 4. M zulil um v UMH. 2 4 h 2 a 2J 2 2 M 51 \V\\ n 8 4 w1 U K w 4 ATT'Ys.

F\ 1 1 IIF April 18, 1961 R. M. WALKER ET AL 2,980,873

WAVEGUIDE SWITCH DEVICE 4 Sheets-Shea?I 5 Filed Dec. 29, 1958 INVENTORS. RICHARD M. WALKER BERNARD D. BERKOWITZ,

ARTHUR A. BLAISDELL 0nd VINCENT J. MSTRETTA BYMQIVOICu/)MAM *Wl AT TYs.

April 18, 1961 R. M. WALKER ETAL 2,980,873

WAVEGUIDE SWITCH DEVICE 4 Sheets-Sheet 4 Filed DeG. 29, 1958 SECTION CLOSED 68 68 69@ @E [FIG] 24 lFIG. I9

INVENTORS. RICHARD M. WALKER,

ATTYS..

WAVEGUIDE SWITCH DEVICE Richard M. Walker, Boston, Bernard D. Berkowitz,

Waltham, Arthur A. Blaisdell, Natick, and Vincent J.

Mistretta, Framingham, Mass., assignors `to Microwave Associates, Inc., Burlington, Mass., a corporation f Massachusetts Vllliled Dec. 29, 1958, Ser. No. 783,520 Claims. (Cl. S33- 98) The tield tof this invention is that of waveguide attenuators and relates, more particularly, to waveguide switches or shutters for opening and closing a waveguide passage with regard to the transmission of microwave energy.

A typical, although by no means the only use of waveguide switches, in that instance commonly referred to as shutters, is in radar duplexer systems employing transmitreceive (TR) or anti-transmit-receive'(ATR) tubes. During normal operation of all systems of this type which employ gas discharge TR tubes, the highly sensitive pointcontact crystal detector of the system is protected by the so-calledkeepalive in the TR tube which continuously supplies electrons in a small resonant gap which, due to these electrons, will fire and electrically shunt the wave'-A Y guide at comparatively low power levels which cannot damage the crystal detector therebehind. Howeven' whenV the installation isV inoperative, with its power turned olf, the keep alive is inoperative and the gap will fire only? at a power level of much higher magnitude'than when the system is operative. In this case the TR tube, beingyuntired, will pass power at levels suiiiciently high to damageV the sensitive detector. Such power may come, for example, from the transmitter of a nearby operating radar set feeding into the antenna of the inoperative set to be protected.

It has been proposed to provide additional protection for the crystal detectors of such systems by mechanically shorting the waveguide transmission line when power is atentf 4 turned off, Veither by way of vanes inserted across the waveguide or by providing the resonant gaps with structures for mechanically bridging them. Such provisions are not satisfactory from the point of view of reliability because they require large linear motion of the shorting structure and because they relay on metallic contacts for their electric performance. Linear motion is objectionable in any equipment which must withstand shock and vibration, and because it requires relatively large operating forces. Furthermore, devices which depend for their operation on linear motion of one component relative to the remainder of the device will undergo changes in operating characteristics when subjected to acceleration at various angles to the direction of the linear motion. VMetallic contacts are objectionable for similar reasons and because they are subject to wear which destroys the electrical characteristics of the device, and because the contact surfaces will acquire deformations causing the device Vto stick in open or closed position.

.Objects of this invention are to provide a waveguide shutter which essentially eliminates the above defects by minimizing the force required to operate the device and the possibility of wear, to provide such a device which due to its very small motion permits fast operation and also minimizes force, impact and wear, to provide such a device which eliminates the use of metallic contacts for establishing its electrical function, and to provide a waveguide shutter whose characteristics are not appreciably affected by acceleration in any direction, such as, for example, might be caused by shock and vibration.

Other objects are to provide waveguide shutters, which when in closed position, will eifect substantially complete reflection of microwave energy and will allow only negligible lealrage of the microwave energy through the waveguide, and which, when in open position, will permit transmission of microwave energy through the switch with minimum insertion loss,.to provide a shutter whose characteristics are not adversely affected by shock or vibration; which is fast-acting, not subject to excessive wear,V

and which requires a minimum of power for its actuation, and to provide a shutter system which is simple, compact, fully `reliable and efcient, and which can be easily adapted forinsertion in various types of waveguide transmission lines.

A brief summary of the nature and substance of theinvention and of some of its main aspects is as follows:

`Systems according to the invention comprise, for attachment within a waveguide section of a transmission line: a vane, means forrotatably mounting the vane In theherein described preferred embodiment of-this invention the actuating means are electromagnetic and, in a specific, particularly practical aspect, comprise, a permanent magnet rotatable with the shutter, and an electromagnet disposed adjacent to the walls of the waveguide section such as to align the shutter magnet with the field of the electromagnet when the electromagnet is energized, causing the shutter to rotate between closed and open positions, a permanent biasing force such as spring means being utilized for returning the shutter to normal position when the electromagnetic eld is withdrawnf In the preferred embodiment of this invention, the-shutter `comprises a thin vane of a configuration similar to but slightly smaller then the cross-section of the waveguide passage and has axial pivots integral therewith for rotatably mounting the shutter in low friction bearings disposed in the center of opposite waveguide walls. In alternative embodiments, the vane is provided with one or more irises resonant with the capacitive or inductive gaps existing between the vane and the waveguide when the switch is in closed position, these gaps providing mechanical clearance for rotation of the vane' within the waveguide section passage, thereby increasing the microwave attenuation elected by the switch. In other alternative embodiments, the vane edges are provided with dielectrically-lled slots to provide a filter section in the gaps between'the vane and the waveguide when the switch is in closed position; these lter sections also increase the microwave attenuation effected by the switch. y

In another aspect of the invention, lumped impedances are provided near opposite vane edges in'the form of metallic bodies or buttons adjacent the pivots of the vane at the guide walls, these buttons constituting matching reactances for eliminating the reactive mismatch resulting from the vane in open position. 'Y

These and other objects, aspects of novelty, and details of construction will appear from the following description of a practical embodiment with several modifications thereof. A

The description of theseyembodiments refers to drawings in which n Fig. 1 is an exploded isometric view of the waveguide switch according to thisV invention;

Fig. 2 is a side view of awaveguide shutter according` Fig. 5 is a section on line 5 5 of Fig. 3;

Y "agesozs t j Figs. 6, 10, 14 and 18` are partial views of alternative embodiments of the shutter vane according to the invention shown as they would appear in closed position` lookinginto-a waveguide; l Figs. 7', 11, 15 and 19` are sections on the correspondingly numberedlines' of Figs. 6, 10, 14 and 1'8;

Figs. 8, 12, l6`andr 20 are partial views of the shutter i of Figs. 6, 1'0, 14 and l8trespectively, shown as theyy would appear in openposition looking into a waveguide; and' Figs.' 9`, 13,Y 17 anclJ 21 are equivalent electric circuitl The shutter'is connected in the transmission line in conventional manner, here by the liange connectors, 4 and 6, as shown. The arrow w indicates the direction of flow of microwave energy through the waveguide. v y

The shutter assembly includes a rectangular waveguide section 7 comprising the broad webs 8 Vand 9, which correspond to the broad walls of the waveguide sections 2` and 3, and the narrow webs, 11 and 12, which correspond to the narrow walls of the waveguide sections 2 and 3. The waveguide section 7 is constructed of the usual waveguide'material such as brass or aluminum.

The web 11 yhas a central aperture 14 to receive' the bearing 16, preferably a ball bearing as shown, a' shoulder 17 being provided for properly positioning the bearing. The web 12 has a similar aperture 18 and shoulder 19 for receiving and positioning the bearing 21.'

The shutter proper 22, as shownin Figs. 1 and 3, is formed by a thin, rectangular, metallic vane 23 of slightly smaller dimensions than the waveguide passage 13. Cylindrical buttons, 24 and 26 are coaxially mounted on the vane on its longitudinal vaxis and have axially threaded bores 30. An axial pivot screw 27 is locked in threaded engagement with the button 24, and a second axial pivot screw 28 is similarlyk locked in threaded engagement with the button 26. Sleeves 29 and 31 areY fitted over the screws 27 and 28 respectively, for properly positioning the vane 23 between the bearings 16 and 21, equally spaced from 4the waveguide webs 11 and 12.

The second pivot screw holds a permanent magnetV 32, in fixed relation to the shutter vane 23, by the screw head 33, for rotation as a unit. The magnet has a flattened side 34 and is positioned on the screw 28 so that its pole axis as indicated in Fig. 2,-normally extends parallel to the. direction of flow of microwave energy through the shutter; assembly and transversely of the broad faces of the vane 23. A stop intheV form of a pin 36 projecting above `the bearing 16, is so positioned and dimensioned that. rotational movement of the magnet 32 is confined with a 90 arc. The spiral spring 37 engages the web 12 and the axial pivot screw 27y for biasing the vane 23 to the position shown in Fig. 3 whereby the magnet 32 will abut the stop 36 as shown in Fig. 2. The vane 23 will then be disposed within the passage 13 transversely ofthe direction of ow of the microwave energy therethrough. It will be evident that the magnet can be rotated away from the stop 36 until the opposite end of the magnet face 34 abuts the stop and that such motion corresponds to a 90 rotation of the vane 23 moving it to a position within the passage 13 parallel to the flow of microwave energyy therethrough. The plate 37.1 and the screw 37.2 serve to hold the bearing 21 in place'A and the screw 37.2 at the. same time anchorsoneend' of the spring 37. The other end of 'the spring.' is staked to theY spring collar 37.3, which in turn is heldY against the sleeve 29 by the head of the pivot screw 27.

At either end ,ofY the waveguide passage 1'3 the webs 8, 9, 11, and 12,. which define the passage .13, meet in laterally extending flanges 38 and 39 which form a rectilinearly peripheral groove 41 as shownV in Figs. 2, 3, 4 and 5. The core piece 42, notched as at 43 to fit over the web 12 and grooved as Yat 44 to provide clearance for the-spring 37, is fixed within the rectilinear groove 41 adjacent. the web` 12. SeriesV connected field coils 46.1v and: 46.2"'wound on cylindrical` coreV pieces 47: are

., mounted within the rectilinear groove 41, one` adjacent each ofv the webs 81 and 9respectively, and are fixed to the corepie'ce42v by the screws 48; ' I'hercoreA pieces 49 and 51, notched as at 52 and 53, respectively,to fitl the web 11, are mounted within the rectilinear groove 41 adjacent the web 111` to provide the gap 54 therebetween, and arejoined' each toV alcore piece 47 by a screw 56. Bores` 57 extending through the waveguide anges 38 and 39 and through the. core'. pieces 42, 49 and 51, are provided for fastening the waveguide switchy 1 within a waveguide transmission line.

In this manner an electromagnet is provided for establishingl a magnetic circuit comprising the core pieces,

42', 47, 49 and 51, directed across the gap 54, and capable of rotating the permanent magnet 32 therein to the extentV permitted by the stop 36.

yA. non-magnetic cover 59, held to core pieces 49 and S1 by-the screws 61 and having a sealing gasket 62, closes the gap 54. The coils, 46.1 and 46.2 are confined in potting compound 63 which lillsthe groove 41 adjacent Y the webs 8 and 9, the nuts 70 being encased in said potf ting of coil' 46.1 kto'receive the screws 66. Terminals 64 for theleads 65 .from the coils 46.2 as shown in Fig.

Y3,V are fastened to the switch device by the screws 66.

The nuts- 70 are electrically connected internally to the ends of the windings of 46.1. For 4the sake of simplicity this is not illustrated in the drawings. The core piece 42 is provided with an external groove 67 for receiving and protecting the leads 65.

. The operation of devices according to the invention as exemplified bythe above-described embodiment is as follows.

It will be readily understood that a waveguide switch according to this invention, within a waveguide transmission line as shown in Fig. 2,V for example within the transmission line to the receiver crystal in conventional radar equipment, will have its vane 22 normally biased into the position transversely of the waveguide passage 13 by the spring '37 as shown in Figs. 3 and 4 and will therefore reflect substantially all microwave energy directed towards it within the waveguide section 2. Thus the shutter `will protect the receiver crystal of the radar set, while it isin power-off condition, from injurious exposure to random high-power R.F. signals such as might be emitted by other radar equipment operating in the vicinity.

r When/the radar set incorporating the shutter is placed in operative condition with the TRv tube keep alive on, thek shutter is rendered ineffective by connecting the terminals l64. to a D.C. source withV suitable switching apparatus. The coils. 46l will thus be excited and will establish a magneticv field across the gap 54 which will rotate the magnet 32 into alignment therewith against the bias of the spring 37 to the extent permitted by the stop 36, thereby rotating the shutter 22 to a position parallel to the wave-guide passage 13. In this position, the shutter will permitv normal operation vof the radar set. TheA following'favorable mechanical conditions will prevail at closed and open kpositions and during movement from one to the other.

` The` shutter according to the invention has a very short and positive motion and is therefore fast-acting, and it will not be subject to injury or disalignment when exposed to shockl or vibration; It willialso be noted that its operation inball bearings minimizes the possibility of Vwear and the force required foroperation.` Furthermore-the shutter operation?v is `not dependent upon' the making and breaking of metallic electrical contacts within the switch, thevane being always spaced from the waveguide walls. This feature also eliminates-possibilities ofwear and furaesdsvs 4 will retain its operating characteristics even when the switch device isaccelerated in any direction.` u nlike shutter devices which are not so balanced, this 'dev1ce 1sV particularly useful Ain high -speed aircraft and missiles.

Withregard tofelectrical operating conditions, the leakage inlclosed'position and the insertion loss inopen positionare of primaryimportance; these conditions are optimally favorablerin devices constructed according tothe present4 invention forthe following reasons. i i i When in closed position as shownin Figs. 3 and 4, the shutter vanepresents a short circuit across thewaveguide, reflecting essentially all the power. As indicated above, this `is the `normal position of a shutter used for the protection of crystal detectors in inoperative radar systems. In anidealconstructiom the leakage of the closed shutter should be zero. Theleakage in structures such as shown in Figs. 3 and 4 is determined by the capacitance between the vane edges and the broad waveguide walls. This capacitance can'be made larger with a resulting decrease in leakage by making the gap indicated at g of Fig. 3 smaller, or by increasing the vane thickness indicated at ft of Fig. 4. The possible increase in capacitance `is controlled by` practical manufacturing conditions and assembly tolerances. In previous practice, lleakage has been controlledfby metallic contacts and has been dependent upon cleaness, wear and humidity. In the present invention, negligible leakage is permitted but this leakage does not vary with age or change in environmental conditions. The leakage value is less than 1% in power over the entire yfrequency range of the waveguide system in which the shutterv is installed.` Lower leakage values may be obtained over 4a narrower frequency range with shutter embodiments to be described below.

In open position, the vane is essentially -reectionless and therefore the R.F. signalI passes freely through the shutter device to the receiver, without appreciable insertion loss. This favorable operation is materially aided by the provision of the abovedescribed buttons 24 and 26 for the following reason. In open position, the vane divides vane 23. `This iris is selected to be resonant -at a frequency considerably higher than'operating frequency. vIn this case, the equivalent circuit, as shown in Fig. 9, includes iris inductance`69a and iris capacitance 69b as well as the gap capacitance 68a resulting from the gap required for mechanical clearance between the Vclosed vane 68 and the broad waveguide web 8. The iris represents an inductive parallelcircuit land at operating frequency this inductanceis series Yresonant with the fgap capacitance 68a thereby presentinga complete short circuitV across the waveguide. This type of`vane` effects substantially complete attenuation, tests indicating leakage of less than 0.1% of the incident power over a 12% frequency range. in the open position, vane 68 causes insertion losses similar to those measured for the simple vane 23 according to Fig. 3.

` The vane 71 as shown in Figs. 10 to l2 is provided with slots 72.1, 72.2 lled with dielectric material 73. Each/ slot represents a short choke section to provideva Ifilter in'each gap as shown by the equivalent circuit Fig. 13 wherein 72a are the gap impedances between the vane impedance 71 and the broad waveguide walls 8 and-9. The effective depth of the slots determines whether these impedances yaire inductive or capacitive and this effective depth and hence the type of impedance can be controlled by varying the dielectric constant of the material which yfills the slots. Tests indicate that a slot of a depth approximately equal to 1A; of a guide wavelength has an inductive effect and that a slot of a depth approximately equal to 3/3 of a guide wavelength has a capacitive effect; in either case, the electrical characteristics of this vane `over Va 12% frequency range are similar to that of the vane 68 according to Figs. 6 to 9.

The vane 74 shown in Figs. 14 to 16 has a single slot 76 filled with a dielectric material 77. Tests indicate that in this instance a slot depth slightly less than 1A! of a guide Wavelength has a capacitive elect and increases the attenuating effect of the closed vane over a' 12% frequency range to approximately that of the vane 68 of Figs. 6 to 8. Fig. 17 shows the reduced capacitances 76a existing in the gap between the vane Y74v and the broad waveguide the waveguide into two equal guides each nearly half the full waveguide cross section.k The open vane inevitably introduces a certain amount of capacitive and resistive .mismatch The capacitive reactance is largely matched .ently be shown below by actual'performance data. The

major contribution to the insertion loss of components of this type is reflected power which can be determined by VSWR measurements. The matching buttons' are very effective in providing a very low VSWR over a wide frequency range, indicatingpractically zero insertion loss. One of the first models constructed according to the present invention,lwith- buttons 24, 26 according to Figs. 3, 4-and 5, had the negligible insertion loss Aof less than 0.1 dbover a 12%A frequency range. The VSWRv over the 12% frequency range was less than 1.06.

The above-described construction with the vane normally closed transversely across the waveguide, assumes a normally tie-energized controlling magnetic motor. This manner of operation can be reversed .by rotating the magnetic armature 32 on its shaft 28 to put it parallel to the vane. The shutter is then normally open'with` the motor de-energiied which,"when energized, will rotate the vane in opposite direction into closed position.

The alternative embodiments according to Figs. 6 to 2l illustrate vane constructions which can be used with shutters such as shown in Fig. 3, these alternative embodiments effecting even greater attenuation of microwave en ergy when the switch is in closed position,'as compared tothe simple vane of Fig. 3.

`Thevane 68 shown in Figs. 6 to 8 s provided with a Yrectangular iris 69 but is otherwise the same as the shutter webs `8 and 9. i

The vane 78 shown in Figs.` 18 to 20 is provided with diaphragms '79 and 81 forming the inductive irises 82 and 83. 'Il-lese inductances 82u and 83a are adjusted to resonate with the capacitances 78a and 79a and` 81a as indicated in Fig. 2l, existing in the gaps between the vane 78 and the diaphragms 79V and 81 respectively, and the broad waveguide webs. The vane 78 as provided withthe diaphragms 79 and 81 has an atenuating effect approximately equal to that of the vane 68 of Figs. 6 to 8.

From the above practical test results it will be evident that devices according to the invention provide substantially complete microwave attenuation when in closed position and Vpermit substantially complete microwave transmission when in open position. It will also be evident that this device is suitable for use with Vvarious types of Awaveguide apparatus, such as for example the so-called short-slot hybrid or the folded magic tee, to perform functions such as that of an attenuator or of a rotary switch from one antenna to another', or of a variable power divider.

It .will be further evident that certain features of the invention-such as the central suspension of the vane, the clearance between vane and guide section, and the mismatch eliminating buttons between vane and guide wall positions-did not necessarily have to be used with rectangular guides but have more general application.

It should be understood that `the present disclosure is for the purpose of ilustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

i l. Waveguide switch apparatus comprising: a straight rectangular waveguide section of substantially uniform internal cross section -fthrougheutits length; a substane tially flat rectangular metallic shutter lvane having a thicknesjs'which is -a-minor fractionof any internalcross-V sectional .dimension of saidwaveguide section, said vane being dimensioned in the length and-width directions perpendicular to its thickness dimension evectively to ll theinternal transverse cross section of said waveguide without touching any of the walls thereof; means for mounting the shutter v ane for rotation within said `guide section, about an axis of symmetry of the guide section and the vane, to eachoftwo fixed positions, one of which is a closed position transversely of the guide sectionand the other of which is Van open position parallel to the guide section axis; and metallic bodies of substantially cylindrical cross section permanently aixed to each nart row side edge of said vane concentric with the rotational axis thereof, each of said bodies presenting a substantially circular surface adjacent and spaced from the confronting narrow wall portions, respectively, of the waveguide section, said bodies being dimensioned and located to constitute axially symmetrical lumped inductance elements for matching the capacitive reactance across the Waveguide section introduced by the vane in the open position.

2. Waveguide switch apparatuscomprising: a straight rectangular waveguide section of substantially uniform internal cross section throughout its length; a substantially at rectangular metallic shutter vane having a thickness which is a minor fraction o f any internal lcross-sectional dimension of said waveguide section, said .vane being dimensioned in the length and width directions perpendicular to its thickness dimension elfectively -to lill the internal cross sectionof said waveguide Vwithout touch-V an axis of symmetry of -the guide sectionl and the vane,

to each of two ixed positions, one of'which is aclosed position transversely of the guide section and the other of which is an open position parallel to the guide section axis; and metallic bodies of substantially cylindrical cross section, each having a diameter which is of the order of half the dimension of said vane in said width ldimension, permanently affixed to each narrow side edge of said vane concentric with the rotational axis thereof, eachof said bodies presenting a substantially circular surface adjacent and spaced from the confronting narrow Wall por-v tions, respectively, of the waveguide section, said bodies being dimensioned Aand located to constitute axially sym# metrical lumped inductance elements for matching the capacitive reactance -across the waveguide section introduced by the vane in the openposition. I

3. Waveguide switch apparatus comprising: a straight rectangular" waveguide section of substantially uniform internal cross vsection throughout its length;,a substantially hat rectangular metallic shutter Vane having a thickness which isa minor ifraction of any internal :crosssectional dimension of said waveguide section, saidvane being dimensioned in the-length and width directions perpendicular to its thickness dimension elfectively to ll the internal `transverse cross-section of said waveguide without touching any ofthe walls thereofymeans for mounting the shutter Ivane for rotation within said guide section, about an axis of symmetry of the guide section and the vane, to each of two fixed positions, one of which is a closed Vposition transverselyot the guide section -and thev other of whichis an open-position parallel ,to the guide section axis; metallicbodies of substantially `cylindrical cross section permanently aixed to each narrow side edgeofsaid yaneconcentric with the-rotational axis thereof, each of said bodies presenting .e ,substantially circular surface adjacent and spaced from the con- -fronting narrow wall portions,'respectivelof the wave-V guide section, said bodies-being dimeusioned and klQCited to constitute axially symmetrical lumped induetanceelermeritsy for matching the capacitive reactance l across the waveguide section introduced by the vane vin the open pastion;y thelength--of-.said wavesuidesection being only slightlygreaterthan lthe dimensione; said vane in said width direction, said `waveguide section being -itted at each' ,6nd, lWith tranSveIsely Yontwardly extending ange means forzattachingrsaid waveguide section insaO waveguide transmission line; 'andsactuatingf means contained substantially entirely withinvtheannular space outside said waveguide section bounded by vsaid ;ange :means for rotating said vane between .each .o f said two xedpositions. e i,

4. Waveguide switch apparatus according to Vclaim .3 in whichthe actuatingrmeans', comprises a lshaft extending from the -vanelthrough the waveguide section; ,magnet core means arranged around theperipheryofsaid .waveguide `section` and having an .airqgap therein; coil means on said core means adapted to establishamagnetic eld in said core means; permanent magnet armaturemeans aixed to said shaft withinsaid ,air:gap; and .biasing means connected between said waveguide .sectiontandsaid shaft urging the vane torotate in lone direction v.Opposed to the direction in which said-.armature means liis .urged vby said magneticeld when said-.core meansisgenergized; whereby thevane can be rotated betweensaid two positions by establishing andgremoving the eld.

5. Vwaveguide switch -apparatus comprising: astraight rectangular ywaveguide section `of substantially `uniform internal vcross section .thronghout itsalengthya substantially Ailat Irectangular metallieshutter .vaneghaving substantially flat edges and-,agthicleuessiwhich isaminor fraction `of any internal crossesectional dimension Aof said waveguide section, said ,vane :being dimensioned-.in the length'and width directions perpendicular.toits-,thickness dimension Aeffectively to ,lill the v internal transverse cross section of 'said .waveguide withouttouching any of the 1 walls, thereof; means for vmounting:theshutter.vanefor rotation within fsaidguide section, `about :an ,of symmerry` ofthe guide section and the fvane/,vtoeach of two xed positions, one .of whichtisacl'osedpositiontransversely-of the guide Vrsection f and theother offwhich is .an open position parallel :lo the guide section axis; vmetallic bodies of Asubstantially cylindrical cross section Apermanently axed to Yeach narrowside edge .ofjsaid vane concentric with ,1t-he rotational ,axis thereof, -each of said bodiesfpresenting asubstantially ,circular surface adjacent and spaced -from .the L confronting narrow .wall portions, respectively, of the waveguide-section, said bodies -being dimensioned Vand located to :CQnStituIeiaXially asymmetrical lumped inductance elements for matching the capacitive reactance .-across the waveguide isecton :introduced `by the vane intheopen position; andren iris opening in said vane,resonan t .at 'afirequency `vwhieh'is high relative to the intendedoperating frequeneyof ,the Awaveguide, said in's inductance gbeing z.resonant substantially at said operating frequeney with theoapacitance existing between ,the c-at edges :of `the .shutter vane and ,the adj acent wide walls of. said waveguide section when the vane is in Isaid closed position, -wl1erebvssaid vane nsaid closed position provides asubstantially complete short circuit across said waveguide section at '4s-aid operating frequency. y

. References Cited y inthe'iile ofy this patent 'UNITED -STATES 'PATENTS 2,175,046 Warner v O ct. 3, 1939 2,480,189 I-rving,.. Ang. 30, 1949 2,573,713 Kannenbergy Nov. '6, 1 951 2,814,782 z neski `Nov. 26, 1957 2,816,272 Braden Dec. 10, 1957

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