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The 1990 Microwave Power Tube Conference.

The 1990 Microwave Power Tube Conference

Plenary Session

The conference theme, Tubes for the 21st Century, underlined the continuing vitality of a technology which, though born in the 1940s, is expected to provide high power microwave sources well into the next century. However, the long evolution of tubes has resulted in neglect of sponsored R&D by the largest customer, the US government. Also, recent reductions in military spending have caused serious problems of production overcapacity in the tube industry. On the first day of the conference the Plenary Session was held and these issues were highlighted by highly qualified leaders from the government, the industry and the academia.

The keynote speaker, Joseph Saloom, of M/A-COM, reviewed problems of the entire microwave component industry, which has seen a sales decline in the last three years, while R&D has not kept up with inflation for the last decade. This industry, so essential for many defense systems, has serious problems. (The substantial texts of Saloom's speech and George Caryotakis' luncheon speech were published in Microwave Journal Sept. 1990, p. 47.)

Captain James Polk, US Navy, the first government speaker, had good news about the AEGIS ship system. AEGIS, the most microwave-tube-intensive system in the US arsenal, is slated for steady growth well beyond the end of this century. With tube activities coordinated by the Naval Weapons Supply Center at Crane, Indiana, MTBF continues to improve by 25 percent each year, while operating costs from tubes have decreased. These results matched or bettered the Navy's requirements. The Navy, through the AEGIS program, also has sponsored some basic tube development, such as a low noise CFA program.

Horst Wittmann, of AFOSR, commented on the depth and diversity of current research in vacuum electronics and the recent shift of research from industry to government laboratories and universities. However, this research seems to lack coordination and leadership. To improve this, he suggested setting up an industrial working group to set policy and strategy vis a vis DoD and foreign competition. "Do not expect DoD to solve all the problems," was the ending note.

Robert Parker, of NRL, who is now playing a lead DoD role in revitalizing the vacuum electronics technology base, noted "20 years of benign neglect" of the field. This has resulted in a dangerous shrinkage of the talent pool, of ready on-shore production capability and even of the ability to provide the enhanced performance required by currently known threats. Research and development activity has not kept pace with the growing usage of tubes. Parker was spearheading an initiative to provide substantial support in four technological areas, including the microwave power module, computational techniques, mm-wave amplifiers and vacuum microelectronics.

Neville Luhmann, of UCLA, reported on the joint DoD, industry and university advanced thermionic research initiative (ATRI). The ATRI program at UCLA provides a unique source of next generation engineers and scientists for vacuum electronics through a structured two-year course curriculum, supported by a teaching staff of 10 people.

Stan Kaisel dealt with the subject of reliability. He noted that reliability in systems, for some kinds of tubes, has doubled in just the past two years. However, the obsolete reference MIL-HDBK-217E still promulgates ancient reliability data that generally shows only one-tenth of the MTBFs seen today. Industry and government should undertake an urgent initiative to revise HDBK-217E.

The radar industry users' standpoint was represented by David Lynch, of Hughes Aircraft Company. He expressed his belief that tubes and solid-state devices will coexist in systems for a very long time. To assure this, the tube community must provide continued performance improvements in noise, power, bandwidth, efficiency, weight and reliability. Richard Marinaccio, of Westinghouse, representing the ECM industry, presented the view that there is a strong trend from single-tube, high power systems toward systems with a multitude of smaller mini tubes in agile arrays.

During the late afternoon, the tube industry presented its views. Ronald Forbess, of Hughes Electron Dynamics Division, described tubes as a maturing technology that still has unlimited challenges to fulfill for DoD that now are seriously underfunded. Capacity must be reduced or used for new products. He quoted some achievements, including the increase of space-tube efficiencies from 38 to 60 percent in the last decade. While the industry must get its own house in order, it will not be able to continue to provide the needed national defense base without government help. James Munger, of Litton Electron Devices, gave another industry view. With yearly domestic sales of about one-half billion and worldwide sales of one billion, the tube industry is about the same size as the golf cart rental business and is almost entirely dominated by a single customer, the government. As military requirements trend downward, sales are declining and profits even more so. Competing wavelength devices, optical and IR, will not eliminate the need for tubes and it behooves us all to keep the industry healthy. To accomplish this, the industry must operate more efficiently, and a more enlightened approach from the government is needed. The required investment should be made mostly by the companies, but they can only do this if their single customer, the government, allows them to make an adequate profit. This is difficult to achieve in today's shrinking market-place. He suggested the creation of a working group at the OSD level to channel more development funds into the tube industry, giving clearer direction to industry and amend the needlessly adversarial procurement practices. The tube industry can and will do its share, but its sole customer must do its part as well.

Following industry, a timely DoD view was given by Rear Admiral James Greene, Jr., currently in the office of the Under Secretary of Defense for Acquisition, in his presentation, "DoD Acquisition: Changes and Challenges." He stated that DoD is now listening as never before, and industry should take advantage of this. DoD is committed to living by the tenets of TQM and improving the acquisition process by increased stability, accountability and mutual trust. The new direction also points to empowered program managers and less influence from staff functions that should play mainly supporting roles. While specifics of the changes are just now jelling, Greene asked the industry to speak up for the changes that are needed.

Technical session began on the second day of the conference. The morning was occupied with parallel sessions on crossed-field devices and helix traveling-wave tubes.

Crossed-Field Devices

The major topic of the first session on crossed-field amplifiers, chaired by Robert Symons, of Litton, was the Navy-sponsored effort to lower the intrapulse noise levels of crossed-field amplifiers. In the first paper, Richard Abrams and Robert Parker, of the Naval Research Laboratory, stated Navy goals of -70 dBc/MHz intrapulse noise and one ns root-mean-square jitter. NRL has reinforced the experimental effort with a computer code development and computational program at SAIC, in McLean, VA.

In separate papers, McDowell, of Varian, Chris Wheeland, of Litton, and Norm Dionne, of Raytheon, reported interesting results from tubes in which the secondary emission from a portion of cathode, at the output end of the tube, was reduced by using a cathode material of lower secondary ratio, slotting or coating. McDowell also used beam scrapers mounted on the cathode in the drift space. Dionne reported on the effect of barreling or anti-barreling of the magnetic field. Useful increases in the power output of controlled-emission tubes was obtained in this manner. Raytheon also is investigating the effect of circuit length on noise. Rodney Vaughan, of Litton, reported on an experiment in which a thermionic filament was placed in a groove in the secondary emission cathode of a CFA. At very low filament heating power, nanoampere level currents stopped jitter completely.

Thomas and Jenkins, of Varian, reported on observations of noise as a function of frequency, in which they noticed a periodicity related to the periodicity of the measured return loss of the slow-wave circuit. Singhal, Marks and Johnson, of Raytheon; Jones, of NWSC; and Dahlgren and Unger, of NWSC, Crane, concluded the first part of the crossed-field session with a description of the noise measurement for power tubes.

The second part of the crossed-field device session was chaired by Grant St. John, of Raytheon. This session began with A. MacMullen, of TSC, who described a developmental system that extends the performance of the system described by Singhal. Broadband digitized signals from an S-band CFA were used as an example showing cycle-by-cycle waveforms.

Treado, of Varian, presented a paper on a high power, rising-sun magnetron with a relatively low operating voltage and high efficiency. Power combining without circulators was demonstrated. 7 MW output, limited by arcing, was in reasonable agreement with calculation.

Gregory, of Litton, showed promising initial results on an injection-locked magnetron pair with wide-locking bandwidth and high duty cycle. Rick Smith, of Mission Research, covered efforts to measure electron space charge in operating CFAs by detecting the modulation space charge imposes on an injected laser beam. Chernin, of SAIC, reported on a program to examine prior computer simulations of CFAs and to extend their usefulness by the addition of a guiding center approximation. Mackie, of Georgia Tech Research Institute, described analyses of shelf-life data. The results support the concepts that an infant mortality (Weibull) model fits the data better than the commonly used exponential failure model. The session was wrapped up by Snow, of NWSC, Crane, who showed an application of the Taguchi technique to assess quality of vendors by measuring acceptance test variations. Objections were raised to the technique because it omitted important life data from the decision-making process.

Helix TWTs and Reliability

Paul Puri, of Raytheon, chaired the first part of the helix session. The opening paper dealt with a microwave power module (MPM), which will result from a Navy program described by Abrams and Parker. The objective is to combine the advantages of solid-state and vacuum electronics for high reliability, high power and low cost into modules to make advanced phased-array systems more affordable.

Palmer, Dayton, Force, Raquet and Lee, of NASA Lewis, proposed a novel, miniature helical traveling-wave tube as an output amplifier for each element of an electronically steered transmit phased array. A multistage depressed collector and low power cathode heater enhance efficiency to 50 percent.

Wada, of Hughes, described efficiency improvement of 50 W satellite TWTs. A new taper, changed from a linear to a linear combined with uniform velocity section as a result of computer optimization, increased efficiency from 53 to 58 percent. Jacquez, Campbell and Cascone, of Varian, described a TWT, built with conventional construction techniques, which demonstrated a peak output power of 20 to 30 W over 50 to 56 GHz. It operates with a cathode voltage of 14.7 kV and a current of 55.5 mA.

Features of a 2 kW, 7.5 percent duty, 6 to 18 GHz pulse TWT were presented in a paper by Carignan, Davis, and Puri, of Raytheon. Designed to meet performance requirements of upgraded airborned ECM systems, it requires a prime power of 100 W per percent cycle of duty.

Molinelli, of ITT Avionics, discussed experience gained on the implementation of a field performance warranty program on the AN/ALQ-172 system.

CW output power limitations of helix TWTs were considered by A. Schram, of Varian. Results support classic tungsten helix construction. Test results on X-band and I-and J-band multi-kW level helix TWTs, using direct helix-to-waveguide connections were presented.

The second helix TWT session was chaired by Phil Lally, of Teledyne MEC. It included several papers on TWT reliability as well as papers on other aspects of helix TWTs.

Webb, of Teledyne MEC, described the reliability and producibility enhancement program (RPE) carried out on the TWTs for the ALQ-165. "The TWT Reliability Initiative," by Daniszewski, Jones and Bivens, of RADC, and McRee, of WRLC, described steps to improve the reliability of the ALQ-99 Band 7 output TWT. Major Schnoll of the ASPJ Joint Program Office, and Geimer and Benson, of ITT Avionics, described a program to incorporate improvements in the ASPJ TWT that had been developed on the industrial modernization, mantech, techmod, and reliability producibility enhancement programs.

Thompson and Broder, of Westinghouse, and Robertson and Grant, of Varian, described increases in both the reliability and efficiency of a pulsed S-band TWT and a CWI-and J-band TWT. Sauseng, of Hughes, reviewed the properties of ring-bar, contrawound helix, and strap-loaded bifilar helix circuits. These circuits are useful for high voltage (>20 kV), modest-bandwith application. Durkin, of General Instruments, described the application of a TWT in a compact air-dropped decoy buoy. The application imposed severe packaging constraints. The solution was to make the tube package part of the system.

The session concluded with Hulley, of COMSAT, who discussed switchoffs in space TWTs. Switchoffs are the automatic turn-off of the power supply by protective circuitry because of a high voltage breakdown and consequent excessive current.

Poster Session

A number of interesting papers were presented at the poster session. Computer programs that were demonstrated included the IBC code by Morey and Birdsall, of the University of California, Berkeley. The program simulates the time evolution of the fields of a TWT following a change in the input signal level as well as the steady-state solution. In addition, Doniger, Friedlander and Nordquist, of Varian, demonstrated an integrated set of klystron design programs that turn a PC-AT into a klystron engineering workstation.

Robertson, of Varian, described a particle-in-cell code being developed for the simulation of crossed-field devices using parallel processing. Aster, of Varian, described analytic modeling techniques for microwave circuit design. Application of finite element analysis to power tube reliability problems was described in separate papers by Rocci, of RADC, and Sabbagh et al., of Sabbagh Associates, and Johnson, of NWSC.

Papers on measurements included one by Sims, of Varian, on a computer-aided vision system for complex TWT parts; one by Appling, of Teledyne MEC, on a computerized 3-D grid measuring device; and one by Dohler, Groshart and Stolz, of Northrop DSD, which also described computer-aided optical inspection means. Treado et al., of Varian, and Doggett, of North Carolina State University, described sophisticated methods of measuring phase and amplitude of electric fields in crossed-field devices using a computer-controlled network analyzer and subminiature probes. Harper, of Raytheon, devised a miniature smooth-bore magnetron that can be used to make measurements of static magnetic fields in high temperature environments.

Magnetic materials and their application Seldon et al., of Varian, and Falce, of Ceradyne, Semicon, described improvements in manufacturing techniques for high energy samarium-cobalt magnets. Leupold, of the US Army LABCOM, described novel configurations of magnetic materials. Baird, of the University of Utah, and Phillips and Snyder, of M-square Microtek, discussed the stability of long-period-focused (LPG) electron beams. These same authors, and Baum, of Utah, did a field analysis of the LPF magnetic circuit.

During this session, novel cathodes were described. Falce, of Semicon, described new forms of reservoir cathodes that can achieve 30 [A/cm.sup.2] at as low as [1050 degrees C] brightness temperature. Kirkpatrick et al., of NRL, discussed ways of fabricating field-emission cathodes with many points using biological and eutectic-composite microstructures.

Reports on vacuum tube materials included an investigation of fluctuating body current in TWTs using boron nitride rods by Groshart and Stolz, of Northrop DSD. Evidence of delamination in the BN seems to correlate with the amount of fluctuation observed. Schieuer, Grow, Baird and Barnett, of Utah, measured and found ways of maximizing the RF conductivity of thin aluminum films on diamond substrates at mm-and submm-wavelengths. This work should lead to improved backward-wave oscillators in the 600 to 1800 GHz frequency range. Smith, Hirooka and Luhmann, of UCLA, and Jensen and Curren, of NASA Lewis, reported on investigations of a plasma-etched isotropic graphite collector surface for secondary emission control.

Cain and Grow, of Utah, reported results on the dielectric and metallic loading of contrawound helix circuits. Christensen, Goebel, Schumacher and Watkins, of Hughes, described a production model of the crossatron, a grid-controlled crossed-field plasma on-off switch of considerable capability.

The paper that outlined the most ambitious goals was presented by Matt Allen and Caryotakis, of the Stanford Linear Accelerator Center. It described possible approaches to the generation of pulses with peak powers of hundreds of MWs for use in the next generation of high energy physics research accelerators.

Cathodes, Guns and Optics

The technical session on cathodes, guns and optics was chaired by Paul Fischer of ET&DL, US Army LABCOM. The present state of the art of thermionic cathodes and the potential for future advances was examined in a paper presented by Longo, of Hughes Aircraft. Some of the ongoing research on the scandate cathode, which shows great promise for higher current density and longer life, was discussed.

Wintucky reviewed the 1990 Tri-Service/NASA Cathode Workshop in a paper co-authored by B. Smith (LABCOM), Gibson (NRL), Ryan (RADC) and Dayton (NASA). The 1990 Cathode Workshop was co-sponsored by NASA Lewis Research Center and the Advisory Group on Electron Devices, with the support of DoD.

"Fast and Superfast Warmup Cathodes Using Novel APG/APBN Heaters" was co-authored by Cattelino and Miram, of Varian, and B. Smith, of the US Army LABCOM. The authors described fast warmup designs with cathode diameters ranging from 0.16" to 2.33."

True, of Litton, discussed a fully relativistic deformable mesh optics code useful in the solution of beam optics problems, and the use of potential grading electrodes for MV guns. Carignan, Assil and Puri, of Raytheon, told how electron beam performance for a 200 W, CW TWT for airborne ECM was improved significantly through the use of a three-dimensional computer code for modeling electron guns with radial vane grids.

Focusing and Thermal Design

The technical session on focusing thermal design was chaired by Ed Daniszewski, of RADC. Bartos, of NASA Lewis Research Center, described recent development of a 3-D finite element thermal and mechanical computer model for use with helix slow-wave structures by HEDD. The program provided a full temperature distribution of a cold-compression, diamond-rod supported helix model.

Altoz, of Westinghouse, discussed a methodology for thermal design of high heat density collector tubes. Both turbulent and laminar flow conditions were considered. Snyder, of M-Square Microtek, reported experimental results achieved by employing a long period focusing (LPF) permanent magnet stack. LPF is based on the successive addition of odd harmonics of the magnetic field. Employing LPF circuits with magnetic periods from 2 to 7 times the normal PPM spacing, 99.9 percent beam transmission was obtained.

PPM focused immersed cathode TWTs were discussed by AI Theiss, of Litton. He considered idealized, constant-density, parabolic-temperature profile beams propagating in fields corresponding to stable flow. He showed that available magnetic field, circuit thermal capability and required RF power output restrict the thermal content, space-charge density and cathode immersion of the electron beam.

Amboss, of Hughes, presented a study of the origins and magnitudes of the transverse magnetic fields produced during solenoid winding. Employing the results of this work, a 44 GHz, 1 kW solenoid focused TWT achieved 98 percent beam transmission with RF applied.

Gyrotrons

The technical session on gyrotrons was chaired by Richard Temkin, of MIT. Jory, of Varian, presented a paper describing research observed during an October 1989 visit to the Institute of Applied Physics, Gorky, USSR. Major advances at Gorky include a 500 kW, 167 GHz, 20 ms pulsed gyrotron and a 500 MW, 10 GHz, 20 ns pulsed relativistic BWO.

Advances in whispering-gallery-mode gyrotron research at Varian were presented by Felch. A 140 GHz gyrotron has been built and tested. It operates in the [TE.sub.15,2,1] mode and produces 940 kW at 35 percent efficiency in short pulse tests. The goal is to achieve 400 kW in CW operation.

A 149 GHz gyrotron oscillator with a novel cavity operating in the [TE.sub.16,2,1] mode in short [mu] pulses was described by K.Y. Xu and co-workers at MIT. 1.2 MW was obtained with an 89 kV, 48 A electron.

Advances in the quasi-optical gyrotron experiment at the NRL were described by Manheimer. A peak power of 425 kW in a 13 [mu.s] pulse at 120 GHz was obtained with a 100 kV, 40 A electron beam.

The design and test of an 8 GHz, 500 kW gyrotron oscillator was reported by Lawrence Ives, of Varian. Up to 565 kW has been achieved at 42.5 percent efficiency in 1 to 10 ms pulses.

Research on a quasi-optical coupler for high frequency gyrotrons was presented by Huey, of Varian. The coupler is needed to transform the power from a whispering-gallery-mode gyrotron into a free space, Gaussian mode for long distance transmission.

Gyro Devices and Ubitrons

In this session, chaired by Robert K. Parker, of NRL, the first paper, by Danly, Pendergast, Temkin and Wurtele, of MIT, described the potential of the cyclotron autoresonance maser as a high power mm-wave device. They outlined current and proposed experiments at MIT, LLNL, NRL and UCLA. The MIT experiments are designed for 17 and 35 GHz using electron beams from a 1 MeV, 500 A induction LINAC and a 700 kV, 780 A modulator.

Wang, Lin, Luhmann and McDermott, of UCLA, proposed the high power CARM amplifier as an RF source for extending the center of mass energy of the Stanford Linear Accelerator Center linear collider. The proposed device is a 160 MW, 17 GHz, 1 MeV amplifier with a design efficiency of 40 percent.

Caplan and Kulke, of LLNL, and McDermott and Luhmann, of UCLA, described the design of a 250 GHz CARM oscillator experiment at LLNL. The device uses a 2 MeV, 1 kA electron beam from an induction linac. The design of the CARM was presented along with cold test data from the Bragg reflectors that form the ends of the resonant cavity.

The design of harmonic gyroklystron amplifiers for 35 and 94 GHz were described by Scheitrum, Symons and True, of Litton. A magnetic field reversal is used to generate an axis encircling electron beam. Cyclotron harmonic operation reduces the required magnetic field to normal solenoid values. Electron beam simulations have shown very low velocity spreads.

Broadband operation of a low voltage Ka-band gyro-TWT was described by S. and G. Park, of Omega P; Kyser, of B.K. Systems; and Armstrong, Ahn and Ganguly, of NRL.A small signal bandwidth of 33 percent is reported for this Ka-band reflection amplifier.

The last paper on ubitron amplifier research at NRL was authored by Jackson, of NRL; Pershing, of Mission Research Corporation; Bluem and Granatstein, of the University of Maryland; and Freund, of SAIC. Operation of the ubitron in fundamental mode has yielded instantaneous bandwidth of 25 percent and a peak gain of 19 dB at mid Ku-band. The output power of hundreds of kW was limited by the available input power.

Klystrons

The klystron session, chaired by Ed Lawson, of Westinghouse, began with a paper by G.A. Westenskow, of the Lawrence Livermore National Laboratory, on behalf of the LLN/SLAC/LBL collaboration to develop high power, short-wave-length (2.6 cm) relativistic klystrons. The main effort was the design of klystrons with a 1.2 MV, 1 kA beam and a 50 ns RF duration. Using traveling-wave output structures, peak RF power of 330 MW was achieved without RF pulse shortening.

Dr. George Ewell and Robert Kerr, of the Georgia Tech Research Institute, discussed the impact of phase noise on overall radar performance and methods for measuring the required phase noise.

Shpock, Litton, and Donald Seers, of the US Army, ARDEC, SMCAR-ESW-D at Rock Island, reported on improvements in the pulsed klystron amplifier tube for the Vulcan Air Defense System radar.

Allen, of Varian, addressed the state of the art in medium power klystrons. Examples cited included a high reliability design for uplink systems at Ku-band with 3 kW CW power; multi-mode klystrons operating over a wide range of power levels; long pulse klystrons (up to one second), including tubes at 250 kW CW at C- and X-band; tubes with tuners that can change channels within 3 seconds or less; PPM focusing at 600 kW at X-band; a mm-wave design for high reproducible manufacture; and klystrons with MTBFs of over 50,000 hours. Allen also presented a paper by Albert Mizuhara, of Varian, describing the features of a 250 kW CW klystron operating at 8510 MHz that was developed for the deep space radar of the Jet Propulsion Laboratory.

Symons, Kirshner, Laycock and of Litton, discussed Clustered-Cavity klystron development. The fourth experimental klystron has met most of its goals. The tube produces 3 to 4 MW from 2.9 to 3.3 GHz. Lower-than-predicted cavity Qs gave smooth small signal gain curves. Symons theorized that the accepted small-signal beam-loading models are not correct. Analytic work shows that velocity modulation on the beam, at the input to each cavity gap, is important, but has been neglected in the past. He also reported on results obtained using a new synthesis method for multi-cavity extended-interaction output circuits.

Coupled Cavity

Traveling-Wave Tubes

The coupled cavity session, chaired by Ronald LeBorgne, of Hughes Aircraft, concentrated on recent advances in high power and mm-wave tubes. Vaszari, of Hughes Aircraft, reported on three folded-waveguide tubes fabricated using computer-controlled electrical discharge machining (EDM). The tubes described included a 1 kW CW, 45 GHz integral solenoid focused tube, a 200 W, CW 60 GHz PPM focused tube and a 100 W, 94 GHz PPM focused tube.

Wilson, of NASA Lewis, presented design and experimental results on a new type of velocity taper called the phase-adjusted taper (PAT). Results obtained on a Ka-band tube showed that the 17 step PAT increased the power from 420 W to 1000 W and efficiency from 9.6 percent to 22.6 percent.

The Millitron ladder circuit used in applications at lower than mm-wave frequencies was discussed by Shepard, of Varian. The reentrant double-staggered ladder (RDSL) was described and shown to have improved thermal bandwidth and impedance capabilities.

Tancredi, of Hughes, described a new 2.25 kW CW, PPM-focused SATCOM-terminal TWT, which featured an air-cooled, two-stage collector to achieve an overall efficiency of 37 percent and extremely low distortion characteristics.

A mono-constructed folded helix for mm-wave applications was described by Dave Gallagher, of Northrop DSD. Cold test data was presented for the 40 to 55 GHz frequency band. Because of match-related complications, the goal of 100 W was demonstrated only at midband.

The final paper in the coupled-cavity session, which was presented by Harper, of Raytheon, described an EDM technique for fabricating a double-ladder delay line from a single block of copper. Cold test results indicate that a wider bandwidth can be achieved with this technique than with other known methods.

Millimeter and Submillimeter Wave

Devices

The session on mm-and submm-wave devices was chaired by J. Dayton, of NASA Lewis. The first paper, "The Grating-Coupled Oscillator," was presented by Walsh, of Dart-mouth; Price, Fisch, Jackson and Xu; Marshall, of Creare; and Kimmet, of the University of Essex. Data were presented showing voltage tuning of the oscillation of the grating-coupled oscillator or oratron over 80 to 145 GHz.

Stankiewicz, Heinen, Ebihara and Dayton, of NASA, Lewis; Barnett, of Analex Corp; Geis and Efremow, of MIT, Lincoln Lab; and Grow, of the University of Utah, summarized work on a novel backward-wave oscillator. Oscillations have been observed at 311 GHz with voltage tunability of more than an octave. An output of 21.5 mW was measured at 270 GHz.

"High Frequency Phase Locked Sources," by D. Sprehn, Rettig, Peebles and Luhmann, of UCLA, described experiments in phase locking a 280 GHz backward-wave oscillator and a 140 GHz reflex klystron to a 35 GHz reference. Baird, R. Freudenberg and R. Grow, of the University of Utah, described the theory and design of a high-Q open-ring cavity resonator as applied to a high efficiency forward-wave auto-resonant peniotron. An efficiency of 80 percent at 95 GHz was predicted.

"Peniotron-Like Free Electron Laser" by G. Dohler and D. Gallagher, of Northrop, predicted a power of several hundred watts at 90 GHz with a 10 percent instantaneous bandwidth by operating a free electron laser in a resonant mode that has some similarities to peniotron operation.

The final paper, "Nonlinear Analysis of the Cerenkov Maser," by H. Freund and A. Ganguly, of NRL, described numerical investigations of an electron beam passing through a dielectric-lined waveguide. The computation is in good agreement with experimental results obtained by General Dynamics at 8.9 GHz.

Novel Devices

The novel devices session, chaired by Kevin Felch, of Varian, covered a wide range of interesting new concepts. Manheimer, of NRL, reviewed available data on the gyrocon and the magnicon. Both were conceived in the Soviet Union for particle accelerators applications. Soviet gyrocons have achieved efficiencies of 80 percent with peak output of 40 MW at 430 MHz. Magnicons have been operated at 7 GHz. Manheimer outlined his own magnicon design. He expects 50 MW at 10 to 20 GHz, with 50 to 70 percent efficiency.

Kodis, of NRL, described density-modulated microwave devices with high power capabilities at UHF and L-band. An experiment at the NRL will use a gridded thermionic cathode to produce 100 percent density modulation of the electron beam, prior to extracting the microwave power using a tape helix circuit.

Warren, of UCLA and Johnson, of Varian, in separate papers, discussed vacuum FETs. Warren discussed a proposed vacuum field-emission-triode distributed amplifier that might produce a gain of 9 dB over a frequency range of 1 to 24 GHz. Johnson wants to produce 1 to 50 W at frequencies in excess of 60 GHz. He speculated that at 1 THz similar power levels may be attainable.

Igor Alexeff, of Tennesee, reviewed work carried out over the past 10 years on the orbitron, a novel device that consists of a positively-charged wire in a cavity resonator. A negative-mass instability that results in microwave emission can occur in such a device. 1 W has been produced at 1 THz and 1 kW at lower frequencies.

Puri, of Raytheon, discussed a new type of combiner that adds the outputs of mini-TWTs to obtain 0.5 to 1.5 kW for electronic warfare applications. This approach allows graceful degradation of an amplifier system, and has cost, reliability, and power supply advantages.

Armand Staprans received his PhD in electrical engineering at the University of California, Berkeley in 1959. Since then, he has worked at Varian Associates as an individual contributor, project engineer and eventually as chief engineer of the Microwave Tube Division. Currently, Staprans is VP and GM of the Coupled Cavity Tubes Products Division. He is an IEEE fellow. His interests include the development of very high power klystrons, twystrons, TWTs and gyrotrons. Staprans has been active in IEEE affairs and in conference and publications work and has served two terms on the administrative committee of the Electron Devices Society.

Robert S. Symons received his BS degree with distinction and his MS degree, both in electrical engineering, from Stanford University. He has worked for Varian Associates Inc. for 32 years in various capacities, including management of radar and accelerator tube engineering and manufacturing. Since 1983, Symons has been technical director at Litton's Electron Devices Division. From 1980 to 1983, he was associate editor of the IEEE's "Transactions on Electron Devices." Symons has been issued 22 US patents. He is a member of Phi Beta Kappa, Tau Beta Pi and is a fellow of the IEEE.
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Author:Staprans, A.; Symons, R.S.
Publication:Microwave Journal
Date:Dec 1, 1990
Words:5230
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