Active and Passive RF Components for High-Power Systems

Transcription

1 SLAC-PUB-9499 September 22 Actve and Passve RF Components for Hgh-Power Systems Sam G. Tantaw and Chrstopher D. Nantsta Stanford Lnear Accelerator Center, 2575 Sand Hll Rd., Menlo Park, CA 9425 Abstract. In recent years, R&D for pulse compresson and power dstrbuton systems for the Next Lnear Collder has led to the nventon of many novel rf components, some of whch must handle up to 6 MW of pulsed power at X-band. These nclude passve wavegude components, actve swtch desgns, and non-recprocal devces. Among the former s a class of mult-moded, hghly effcent rf components based on planar geometres wth overmoded rectangular ports. Mult-modng allows us, by means of nput phasng, to drect power to dfferent locatons through the same wavegude. Planar symmetry allows the heght to be ncreased to mprove power handlng capacty. Features that nvte breakdown, such as couplng slots, rses and H- plane septa, are avoded. Ths class ncludes hybrds, drectonal couplers, an eght-port superhybrd/dual-mode launcher, a mode-selectve extractor, mode preservng bends, a rectangular mode converter, and mode-mxers. We are able to utlze such rectangular wavegude components n systems ncorporatng low-loss, crcular wavegude delay lnes by means of specally desgned tapers that effcently transform multple rectangular wavegude modes nto ther correspondng crcular wavegude modes, specfcally TE and TE 2 nto crcular TE and TE. These extremely compact tapers can replace well-known mode converters such as the Maré type. Another component, a reflectve TE -TE 2 mode converter n crcular wavegude, allows us to double the delay n reflectve or resonant delay lnes. Ideas for mult-megawatt actve components, such as swtches, have also been pursued. Power-handlng capacty for these s ncreased by makng them also hghly overmoded. We present a desgn methodology for actve rf magnetc components whch are sutable for pulse compresson systems of future X-band lnear collders. We also present an actve swtch based on a PIN dode array. Ths component comprses an array of actve elements arranged so that the electrc felds are reduced and the power handlng capablty s ncreased. Novel desgns allow these components to operate n the low-loss crcular wavegude TE mode. We descrbe the swtchng elements and crcuts. I. INTRODUCTION Because of the requrements of the Next Lnear Collder hgh-power rf systems, passve mcrowave components have developed sgnfcantly durng the last few years [,2]. The power handlng capabltes of these components have ncreased consderably [3]. Ths has been acheved by ncreasng the sze of these components wth respect to the operatng wavelength,.e., by overmodng these components. In partcular a class of mcrowave structures that has complete planar symmetry has been developed. These components carry only TE n modes. Ths makes t possble to make all the manpulatons n the two dmensonal plane. The heght of these components can then be ncreased to reduce the feld and allow for hgh power operaton. Ths class of components s overmoded n both heght and wdth. It allows smultaneous Work supported by the Department of Energy contract DE-AC3-76SF55. Invted talk presented at the Ffth Workshop on Hgh Energy Densty and Hgh Power RF October -5, 2, Snowbrd, Utah.

2 manpulaton of multple TE n modes;.e. multmodng. Because of ths these components can perform several functons at the same tme, resultng n compact and effcent system ntegraton. To make a connecton between these modes and crcular wavegudes needed to transfer rf power over long dstances, we ve developed a specal type of multmoded crcular-to-rectangular taper. We present the desgn of these components and show ther applcaton to some rf systems. Another class of multmoded components that depends on the azmuthal symmetry of crcular wavegude carryng the TE n modes has been developed. Ths class s used to reduce the length of rf storage lnes. We present the desgn methodology and expermental data for ths type of component. We also extend the sprt of overmoded wavegude structures to actve and nonrecprocal devces. We present the theory for a nonrecprocal devce that operates n the coaxal crcular wavegude mode TE. Ths devce has the potental of handlng tens of megawatts at X-band. It could be used as a crculator or as a swtch. Smlar attempts have been made to ncrease the power handlng capabltes of bulk effect semconductor components. Reports have been made on optcally controlled semconductor swtches operatng n overmoded wavegude [4]. Here we report the development of a swtch made from a PIN dode array operatng n an overmoded wavegude carryng the TE mode. The PIN dode rf swtch was nvented n the mddle of the twenteth century [5,6]. PIN dode swtches have wde applcatons at the low to medum power levels. Varous packaged PIN dodes are commercally avalable. However, due to ther small sze, packaged PIN dodes cannot be used for swtchng very hgh power rf sgnals. At the end of 96 s, a rectangular wavegude swtch [7,8] was developed to handle hgher power rf sgnals than packaged PIN dodes. The wndow swtch was tested up to kw at X-band wthout problem. Thus, the power handlng capablty of a semconductor rf swtch has been at the level of kw; ths s stll low for applcaton to actve pulse compresson systems for future lnear collders. A hgh power devce can comprse an array of actve elements arranged so that the electrc felds are reduced and the power handlng capablty s ncreased. In ths paper, we wll dscuss hgh power rf swtches, whch consst of the actve swtchng elements. The basc dea s to dstrbute the power nto several elements so that the amount of the power to be handled by each element s reduced, n addton to mprovng the maxmum power of each element by desgnng t n an over moded structure. II. PLANAR COMPONENTS The dea for planar components has started by the need for a 3dB hybrd capable of handlng hundreds of megawatts of rf power at X-band for a SLED-II pulse compresson system [9]. A satsfactory devce was desgned based on the R.H. Dcke s crcut synthess of a 3dB hybrd [] (see Fg. ). Then t was realzed that the two nterconnectng gudes could be combned nto one sngle gude carryng two modes [] as shown n Fgure. Ths resulted n the so-called magc-h hybrd. The devce

3 has full planar symmetry, and the heght can be adjusted to any value requred to reduce surface feld and ncrease power handlng capacty. FIGURE. Schematc of the h-planar geometres of the a) two-rung ladder and b) "magc H" hybrd desgns. Power-flow arrows ndcate output ports for the ndcated nput port. By puttng two of these hybrds together, sde-by-sde, a dual moded wavegude wth smlar dmensons as the connectng gude could be produced (see Fg. 2). Addng the remanng parts of the hybrd to ths devce resulted nto the nventon of the so-called cross potent superhybrd [2] (see Fg. 2) FIGURE 2. Combnng four H-plane hybrds resulted n the nventon of the Cross Potent Superhybrd Ths superhybrd can be used to combne power from four rf sources nto any one of four outputs. The choce of the output port depends on the phases of the nputs. The scatterng matrx of the devce s gven by:

4 = 2 S cp One varaton on ths devce s acheved by elmnatng two of the output ports n exchange for a sngle port carryng two modes. Fgure 3 shows such a devce that can launch ether the TE or the TE 2 modes n one sngle port dependng on the phases of the nput devces. Dealng wth two modes at once, TE and TE 2, s possble. For example Fgure 4 shows bends that transfer these two modes perfectly at the same tme. For the theory for these bends the reader s referred to [3]. π/2 π/2 TE out a) π/2 π -π/2 TE 2 out b) FIGURE 3. Cross Potent Launcher wth smulated electrc feld plots llustratng launchng a) TE and b) TE 2 n the rght overmoded rectangular port wth the ndcated relatve phases for four equal ampltude nputs. Alternate phasngs of the nputs send the power to ether of the left ports. a) b) FIGURE 4. Overmoded H-plane bend wavegude wth smulated electrc feld plots llustratng a) TE mode transmsson and b) TE 2 mode transmsson. One can also mx those two modes by makng an H-plane bend n these planar wavegudes (see Fg. 5). Usng ths and the center part of the cross potent superhybrd,

5 one can make a devce that separates these modes nto dfferent wavegudes (see Fg. 5). Indeed, these desgns are not unque. For example, another desgn that can separate these two modes s shown n Fgure 6. Jog Converter wth HFSS smulated electrc felds llustratng converson from TE to TE 2 (left to rght) or from TE 2 to TE (rght to left). Mode Mxer wth HFSS smulated electrc felds llustratng converson from TE 2 to an equal mxture of TE and TE 2. TE n TE 2 n FIGURE 5. Mode mxers and some of ther use n mode separators or mode extractors TE n TE 2 n FIGURE 6. Mode-Selectve Extractor To connect these devces wth crcular wavegudes, whch s beng used for lowloss energy transfer and storage, we use a specal type of crcular-to-rectangular taper [4]. Ths taper converts the rectangular gude TE mode nto the TE mode of

6 crcular gude and the rectangular TE 2 nto the low-loss TE mode of the crcular gude (see Fg. 7) mm TE 2 TE 39.8 mm TE mm mm TE Smulated electrc felds (HFSS)of the mult-moded crcular to rectangular taper Taper Geometry (Operatng Frequency=.424 GHz) FIGURE 7. Dual-Moded Rectangular/Crcular Converter/Taper Based on these components, t s possble to desgn several hgh power rf pulse compresson systems. For example, the Delay Lne Dstrbuton System (DLDS) [5] could be greatly smplfed usng these components (see [3]). III. MULTIMODED DELAY LINES All pulse compresson systems consdered for the NLC use very long runs of low loss overmoded crcular wavegude [6]. The SLED-II system [9] s of partcular nterest because t mnmzes these runs. Yet, even an rf pulse compresson system based on SLED-II may use hundreds of klometers of wavegude for the full nstallaton. Here we show a method for reducng these long runs of wavegudes by makng them multmoded. Consder the delay lne shown n Fgure 8. TE TE 2 TE 2 TE FIGURE 8. Dual-moded delay lne The rf sgnal s njected nto the delay lne wavegude n the TE mode. Ths s the only azmuthally symmetrc TE mode supported at the nput port. The wavegude s then tapered up to a dameter that supports several TE n modes. The TE mode travels

7 all the way to the end of the delay lne and then gets reflected and converted nto the TE 2 mode. The TE 2 mode travels back to the begnnng of ths lne and, snce the nput of the lne cuts off ths mode, gets reflected. If the nput taper s desgned carefully, TE 2 can be reflected perfectly. Then, because of recprocty, the TE 2 wave gets converted back to TE at the end of the lne. Ths mode then travels back and exts the lne. The total delay n the delay lne s twce that seen by a sngle moded lne. Hence, one can cut the length of delay lne by a factor of two. The End Mode Converter The mode converter at the end of the delay lne s shown n Fgure 9. It s bascally a step n the crcular wavegude. If the bg wavegude supports only the TE and the TE 2 mode among all TE n modes and the small wavegude supports only the TE mode, then the devce could be vewed as a three-port network. One can choose the dameter of the small gude such that the couplngs between each mode n the large gude and the sngle mode n the small gude are equal. In ths case, t s a symmetrcal three-port network. A theory for such a devce s presented n [7]. It shows that there exsts a poston for placng a short crcut n the mddle arm of ths three-port network (the small gude n ths case) that makes t possble to transfer the power perfectly between the remanng two arms, or n ths case between the TE and the TE 2 modes n the large gude FIGURE 9. TE -TE 2 reflectve mode converter. The dmensons shown are for an operatng frequency of.424 GHz. The feld pattern shown from fnte element smulatons predcts a peak electrc feld of 26.6 MV/m for 3 MW of nput power. The only step left n the desgn of ths end mode converter s a careful taper desgn that reduces the dameter of the delay lne nto the dameter of a wavegude that can support only TE and TE 2 modes. The taper needs to transfer both modes perfectly. Expermental Results Fgure a shows the delay through a 75 ns delay lne wth a short crcut at the end for a total delay of 5 ns. Fgure b shows the delay after placng the mode converter at the end of ths lne. The delay was doubled at the expense of ncreased loss. The loss can be brought back down by usng larger dameter wavegude for the delay lne.

8 Reflected Pulse Input Pulse Input Pulse Mag.2.2 Magntude Magntude Tme [ns] Tme [ns] (a) (b) REPLACE THIS TEXT WITH THE FIGURE GRAPHIC FIGURE. (a) Measured delay through 75 feet of WC475 wavegude termnated wth a flat plate. The round trp delay tme s 54 ns. (b) Measured delay through 75 feet of WC475 wavegude termnated wth the TE -TE 2 mode converter. The round trp delay tme s 32 ns. The operatng frequency s.424 GHz. IV. ACTIVE SEMICONDUCTOR DEVICES A new actve wndow, PIN/NIP dode array actve wndow, whch s operated at TE mode n the crcular wavegude was proposed and developed [8]. Our actve wndow s desgned and bult to avod the dffcultes of the TE mode rectangular wavegude wndow swtch and to handle X-band rf sgnals at mult-megawatt levels. Ths s acheved by usng an overmoded structure, thus ncreasng the cross sectonal area and reducng the power densty. usng the TE mode n crcular wavegude, whch has no electrc feld at the wavegude wall, thus avodng edge effects, for a more robust desgn. In ths secton, we descrbe the desgn of our PIN/NIP dode array actve wndow. The Slcon Wndow The conceptual vew of our actve wndow s llustrated n Fgure. The base materal of the wndow s hghly pure slcon. Ths wndow s located n a crcular wavegude, whch s operated at the TE mode. As shown n the fgure, the PIN/NIP dode structure s a set of radal lnes. Each lne s heavly doped by P-type and N-type mpurtes on the topsde and backsde surfaces, respectvely. Each dode lne s covered by a metal lne, whch supples bas voltage and current to the dode lne. The TE electrc feld orentaton s also ndcated n Fgure. All electrc feld lnes are n the azmuthal drecton;.e. the dode lnes are perpendcular to the electrc feld of the rf sgnal. Ths means that the reflecton caused by the dode structure and the metal

9 lnes s very small when the actve wndow s reverse or zero based; the rf sgnal only sees the delectrc contrbuton of the bulk slcon materal. Ths s the off status of the actve wndow. To mnmze the reflecton from the lnes, the coverage factor, whch s defned as the rato of the area of the dode structure to that of the whole actve regon of the wndow, s chosen to be %. The P lnes on the front and the N lnes on the back are arranged to alternate wth each other (see Fgure ). A sde-cut vew of the actve wndow llustrates the dea (see Fgure 2). When forward bas s appled, a massve number of njected carrers goes across the I regon. Snce the P and N lnes are alternatng, the njected carrers fll the I regon, and the ncdent rf sgnal s reflected. Ths s the on status of the actve wndow. The thckness of the actve wndow, whch s the same as the I regon wdth n ths desgn, must be small enough so that the carrers njected from the heavly doped P and N lnes by the forward bas can dffuse through the hgh receptvty I regon to the heavly doped lnes on the other sde. Ths s a very mportant pont to acheve good rf solaton at the on status. The carrer lfetme n the hgh resstvty slcon materal s closely related to the dffuson length of the carrers. It s gven by L ( ) / 2 D = τd AP, where L D s the dffuson length of the carrers, τ s the carrer lfetme n the slcon materal, and D AP s the dffuson coeffcent. The dffuson coeffcent n slcon s D AP = 5.6 cm 2 /s, gvng / 2 L D 4( τ ( µ sec) ) µ m. Hence, the base materal of the actve wndow must be very pure slcon and must have long carrer lfetme to acheve good conductvty modulaton wth forward bas. Whle ths puts an upper lmt on the wndow thckness, there s a lower lmt for ths thckness. If the wndow s much thnner than the skn depth, good solaton of the rf sgnal would not be obtaned. If we assume the carrer densty to be 7 cm -3 n the I regon wth forward bas, then the skn depth δ s can be calculated wth knowledge of the carrer motlty n slcon. At a frequency of.424 GHz, δs µm. FIGURE. Conceptual vew of PIN/NIP dode actve wndow.

10 FIGURE 2. Sde vew of PIN/NIP dode actve wndow. In the actual desgn of our prototype actve wndow, the dode structure conssts of 4 radal lnes each on the front and back. The wdth of the radal lnes s tapered from 25 µm near the wavegude surface to 2 µm near center of the wndow. The lne wdth and the number of lnes are chosen so that the coverage factor s %. The thckness of the wndow s 225 µm. If the carrer densty acheved 7 cm -3,ths thckness s more than the skn depth of the ntrnsc regon for X-band rf sgnals. At ths carrer densty, the surface resstance R s 4.8 ohms at our operatng frequency of.424 GHz. The dameter of actve regon and wavegude s.299 nches, so that the wavegude mpedance s 4.6 tmes the mpedance of vacuum. Hence, the loss dsspated n the wndow when the wndow s on s gven by Rs L Pl ( total) / Pn = 4.23%. Z RF Structure and Wndow Support The rf structure to support the wndow s shown n Fgure 3. It conssts of two alumnum crcular wavegudes wth steps, a ceramc rng, and metal sprngs. The actve wndow s located between the two wavegudes. The ceramc rng fxes the actve wndow at the desgn poston. The TE mode rf sgnal s launched by a compact wrap-around mode converter (see [3]). The dameter of the wavegudes changes from.5 nches to.3 nches at the center by steps desgned so that the whole rf structure s matched wthout the wndow. Snce slcon has a large delectrc constant, the mpedance msmatch at the surface of the actve wndow s large, causng non-neglgble reflecton. Because we are nterested n the pure characterstcs of the actve wndow, the structure was desgned wthout matchng sectons to compensate for the msmatch at the wndow surfaces. g

11 FIGURE 3. Actve wndow and rf structure. The two wavegudes are DC separated. The ceramc rng works as the DC voltage gap. There are metal sprngs between the actve wndow and the wavegudes. The wavegudes are connected to a basng crcut. The basng voltage s suppled to the actve wndow through the wavegudes and the sprngs, and the wavegudes are DC solated from the TE mode converters by mylar nsulators. There s a gap between the two wavegudes, but no choke structure. Snce the surface currents of TE mode n crcular wavegudes are azmuthal, the gap does not cut any surface currents and there s no rf leakage through the gap. Indeed, ths a bg advantage of ths structure over TE mode rectangular wndow swtches; we can avod the complex choke geometry necessary n the rf structures of ths later type. Fnally, vacuum seals necessary for hgh power operaton under vacuum are made wth Vton rubber gaskets for DC solaton. Expermental Results The hgh power experment was performed wth an X-band klystron (XL-2) and a SLED-II rf pulse compresson system at SLAC. A hgh power rf sgnal of 9 ns pulse

12 duraton at.424 GHz was generated by the klystron, compressed by the SLED-II system, and fed to the actve wavegude wndow. The SLED-II system allowed us to operate the klystron at a relatvely low power level and acted as a buffer between the klystron and the unmatched wndow. The power level output to the actve wndow was up to 5 MW. For our experments, ths was hgh enough. The compressed rf pulse duraton was 5ns. The repetton rate was lmted to 5 Hz, snce the actve wndow dd not have coolng. The ncdent, reflected, and transmtted rf sgnals were measured by power meters and rf dode detectors through drectonal couplers. The TE mode converters have vew-ports to watch the surfaces of the wndow so that the vdeo camera could detect flashes of lght f arcs occur on the surface of the actve wndow. Two types of slcon wndows were prepared for ths hgh power experment. Frst one s an actve wndow, whch has a full PIN/NIP dode array structure on both the front and back. Ths actve wndow s the 7 cm -3 dopng densty verson. The resstvty of the base materal s 5 ohm-cm. The wndow thckness s 225 µm. The second one had only the metal lne structure on one sde and no dopng lne structure; the other sde had no structure (metal-only verson). Ths verson of the wndow was prepared for nvestgatng the breakdown propertes of the thn metal structure. The resstvty of ts base materal s ohm-cm and ts thckness s 35 µm. FIGURE 4. Input versus transmsson and reflecton power. In Fgure 4, the reflected and transmtted powers from the actve wndow wth full dode structure are plotted. As shown n the fgure, the reflected and transmtted powers were proportonal to the nput power. Hence, the reflecton coeffcent dd not change and the loss dsspated nto the actve wndow dd not ncrease wth ncreasng the nput power up to 5.2MW. Ths means that avalanche breakdowns dd not occur at

13 ths power level. If the avalanche breakdown occurred, there would be copous carrers n the ntrnsc regon, and the reflecton coeffcent would have changed. However, arcng started at an nput power level of around 4 MW. When arcng occurred, the vacuum n the system went from -8 Torr at normal operaton to above -5 Torr, and nterlocks stopped the klystron. After the onset of arcng, the reflected power ncreased and the transmtted power slowly decreased. Ths arcng was very vacuum dependent. We had to process slowly from the lower power levels after the trps. Flashng lghts were observed by the vdeo camera from both sdes when the arcng occurred. These characterstcs, vacuum dependency and flashng lghts, are typcal characterstcs of the vacuum breakdowns, not of avalanche breakdowns. FIGURE 5.Waveform wth zero bas and 3V forward bas. After achevng the maxmum nput power of 5.2 MW, the arcng occurred more and more frequently, and also at lower power levels. We could not rase the nput power further. Thus, the hgh power operaton was lmted by arcng. The maxmum feld at the surface of the wndow s calculated as 3.8 MV/m at 5.2 MW.

14 The waveforms of the transmtted and reflected rf sgnal wth and wthout the forward bas voltage are shown n Fgure 5. Wth the forward bas voltage at 3 volts, the reflecton ncreased and the transmsson decreased. The reflected rf sgnal was modulated from. MW to.68 MW, and the transmtted rf sgnal was modulated from.63 MW to 6 kw. A db of transmsson modulaton was thus acheved. Wth the forward bas, no arcng on the surface of the actve wndow was observed, whch s reasonable because the actve wndow s a conductor, and the electrc feld of rf sgnal s mnmum near the wndow surface. V. ACTIVE MAGNETIC DEVICES The mplementaton of a crculator or a swtch can be acheved usng a two-port nonrecprocal network plus a 3dB hybrd and a spltter (see Fg. 6). The smplest mplementaton of the nonrecprocal element n an overmoded wavegude usng the TE mode s shown n Fgure 7. Ths mplementaton also depends on the so-called wrap-around mode converter [3]. In ths system the mode converter launches the TE mode, whch has both axal and radal magnetc felds, n a coaxal structure. At the ends of the structure, the coaxal gude becomes narrow and only the coaxal TEM mode can propagate (see Fg. 2). A pulsed current sgnal could be launched from that narrow port (port-a n Fg. 2) Ths pulse would have only azmuthal magnetce feld. Ths feld s used to bas a pece of garnet wrapped around the center conductor of the coaxal structure. Ths structure has several advantges for handlng hgh power rf sgnals: - Operatng n an overmoded wavegude, wth a large cross sectonal area for a gven wavelength, should gve the devce a hgh power handlng capacty. 2- All rf electrc feld lnes are parallel to the nterface between the garnet materal and vacuum (see the theory secton below). 3- The center conductor could be used to cool the garnet materal; t could be made as a tube wth water flowng through the center. Spltter Port Nonrecprocal Element 3dB Hybrd Port 2 Port 3 FIGURE 6. Ths three-port network wll work as a crculator f the phase shft through the two-port nonrecprocal element dffers by 8 degrees for dfferent propagaton drecton. The system could work as a swtch f one can control the phase shft through the element.

15 Garnet Materal Port A (Bas) Port B (Bas) Wraparound Mode converter Port (rf) Coaxal TE mode propagate n ths coaxal structure Port 2 (rf) FIGURE 7. Nonrecprocal two-port devce employng the TE mode. Several varatons on ths devce are possble. An elegant mplementaton of the system shown schematcally n Fgure 6 s llustrated n Fgure 8. In ths geometry the spltter s realzed by dvdng the power between the TE and the TE 2 modes. These two modes nteract wth the garnet coated secton n dfferent manners. To mplement the crculator, one could desgn the system to make the phase dfference between these two modes n the forward drecton dffer from that of the backward drecton by π. To mplement a swtch, one could control that phase dfference by varyng the current n the center conductor. For a proof of prncple numercal experment we consdered the propertes of calcum vanadum doped garnet [9]. We chose ths materal because of ts narrow lne wdth. The calculated values for µ and k of ts permeablty tensor are shown n Fgures 5 and 6. The operatng frequency used to generate these curves s.424 GHz. The delectrc constant of ths materal s about 4. The basng magnetc feld was chosen so that the materal would operate below the resonance frequency. Garnet Materal Port A (Bas) Port 3 (rf) Wrap-around Mode converter Coaxal TE and TE 2 mode propagate n ths coaxal structure Port 2 (rf) Port (rf) FIGURE 8. Implementaton of the overmoded crculator/swtch. Fgure 9 shows the requred garnet thckness and length for a π phase dfference between forward and backward TE mode waves. For the optmum thckness, the rf losses are less than one percent. Ths s a manageable loss level whose heat can be removed by coolng through the center conductor.

16 FIGURE 9. The requred dmensons of the garnet materal for a π phase shft between forward and backward waves for the TE. VI. CONCLUSIONS In ths paper, we have presented an overvew of some developments made over the past few years n the area of hgh power mcrowave components. Ths work has been motvated by the requrements of an rf system for a next generaton electron-postron lnear collder, whch must handle X-band power levels up to hundreds of megawatts. These components are thus all overmoded to amelorate breakdown problems assocated wth hgh felds. They nclude several passve wavegude devces that make use of mult-modng for drectng power through phasng of combned sources. These take advantage of planar symmetry for ease of mode manpulaton and heght-ndependence of the desgns. They also nclude mode converters between rectangular wavegude modes, between rectangular and crcular wavegude modes, and between crcular wavegude modes. The latter devce can be used to double the storage tme n a reflectve delay lne. Some novel actve components, actvated by pulsed voltage or current, have also been descrbed. These nclude a PIN dode array on a slcon wafer operatng as an rf wndow and a garnet based nonrecprocal wavegude structure. Some expermental results for the former at mult-megawatt operaton have been presented. Both take advantage of the TE mode feld pattern n crcular wavegude. Ether of these devces, although they requre further development, have the potental of provdng the bass for a hgh power mcrowave swtch. ACKNOWLEDGMENTS The authors would lke to thank Professors Ronald Ruth, Perry Wlson, Norman Kroll and Roger Mller for many useful dscussons. We would lke to thank Gordon Bowden for hs help n constructng the rf structure. The semconductor swtch work was done n collaboraton wth Fumhko Tamura. We are also grateful for the help and effort of Chuck Yoneda and the vacuum group at the Klystron Department at SLAC. Ths work was supported the US Department of Energy contract DEAC3-76SF55.

17 REFERENCES. Sam G. Tantaw, New Development n RF Pulse Compresson, Proc. of the XX Internatonal Lnac Conference, Monterey, Calforna, USA, August 2-25, 2, p , and the references cted theren. 2. Chrstopher D. Nantsta and Sam G. Tantaw, "A Planar Rectangular Wavegude Launcher and Extractor for a Dual-Moded RF Power Dstrbuton System," Proc. of the XX Internatonal Lnac Conference, Monterey, Calforna, USA, August 2-25, S.G. Tantaw, et al., "The Generaton of 4-MW RF Pulses at X Band Usng Resonant Delay Lnes," IEEE Trans. Mcrowave Theory Tech., vol. 47, no. 2, pp , Dec. 999; SLAC- PUB Sam G. Tantaw, Ronald D. Ruth, Arnold E. Vleks, and Max Zolotorev, Actve hgh-power RF pulse compresson usng optcally swtched resonant delay lnes, IEEE Transactons on Mcrowave Theory and Technques, MTT-45(8), August 997, p S. M. Sze, Physcs of Semconductor Devces, John Wley & Sons, second edton, Joseph F. Whte, Mcrowave Semconductor Engneerng, Van Nostrand Renhold Company, New York, Kenneth E. Mortenson, Jose M. Borrego, Paul Bakeman, E. Jr., and Ronald J. Gutmann, Mcrowave slcon wndows for hgh-power broad-band swtchng applcatons, IEEE Journal of Sold-State Crcuts, SC-4(6), December 969, p Kenneth E. Mortenson, Albert L. Armstrong, Jose M. Borrego, and Joseph F. Whte, A Revew of Bulk Semconductor Mcrowave Control Components, Proceedngs of the IEEE, 59(8), August 97, p P. B. Wlson, Z. D. Farkas, and R. D. Ruth, "SLED II: A New Method of RF Pulse Compresson," Lnear Accl. Conf., Albuquerque, NM, September 99; SLAC-PUB Montgomery, Dcke, and Purcell, Prncples of Mcrowave Crcuts, Rad. Lab. Seres, 948, p C.D. Nantsta, W.R. Fowkes, N.M. Kroll, and S.G. Tantaw, Planar Wavegude Hybrds for Very Hgh Power RF, proc. Of the 999 IEEE Partcle Accelerator Conference, New York, N.Y., March 29-Aprl 2, Chrstopher D. Nantsta and Sam G. Tantaw, "A Compact, Planar, Eght-Port Wavegude Power Dvder/Combner: The Cross Potent Superhybrd," IEEE Mcrowave Guded Wave Lett., vol., no. 2, pp , December 2; SLAC-PUB Chrstopher D. Nantsta and Sam G. Tantaw, "Mult-Moded Passve RF Pulse Compresson Development at SLAC," proc. of Advanced Accelerator Concepts Workshop, Santa Fe, NM, June -6, S.G. Tantaw, N.M. Kroll, and K. Fant, RF Components Usng Over-moded Rectangular Wavegudes for the Next Lnear Collder Mult-Moded Delay Lne RF Dstrbuton System, Proc. Of The IEEE Partcle Accelerator Conference, New York Cty, March 29th - Aprl 2nd, 999, p H. Mzuno, Y. Otake, A New Rf Power Dstrbuton System For X Band Lnac Equvalent To An Rf Pulse Compresson Scheme Of Factor 2**N, 7th Internatonal Lnac Conference (LINAC94), Tsukuba, Japan, Aug 2-26, S.G. Tantaw, R.D. Ruth, and P.B. Wlson, A Comparson Between Pulse Compresson Optons for NLC, proc. of IEEE Partcle Accelerator Conference (PAC 99), New York, 29 Mar - 2 Apr 999. Publshed n *New York 999, Partcle accelerator, vol. * Sam G. Tantaw and Mkhal I. Peteln, The Desgn and Analyss of Mult-Megawatt Dstrbuted Sngle Pole Double Throw (SPDT) Mcrowave Swtches, n IEEE MTT-S Dgest, 998, pp Fumhko Tamura and Sam G. Tantaw, Development of Hgh Power X-band Semconductor RF Swtches for Pulse Compresson Systems of Future Lnear Collders, proceedngs of the XX Internatonal Lnac Conference, Monterey, Calforna, USA, August 2-25,