The millimeter-wave spectrum, generally considered to range from 30 to 300 GHz, is one of the most actively used spectrums today, with applications such as high-data-rate terrestrial and space communications, radar, and electronic warfare. The helix traveling-wave tube (TWT) amplifier has long been a critical component for enabling modern millimeter-wave systems. This paper presents an overview of several recently developed high-power millimeter-wave helix TWTs which have extended the helix TWT performance envelope. In particular, the power-frequency-bandwidth product for these devices has increased by a factor of 4 to over 100 depending upon the application. These helix TWTs operate at power levels up to 1-kW peak power or 500-W average or continuous-wave power and over frequencies from 18 to 46 GHz, with efficiencies up to 60%. The helix TWT performance improvements discussed here have not only kept pace with improvements in rival technologies such as GaN solid-state power amplifiers but also pushed helix TWTs into competition with traditionally higher power and higher frequency vacuum electron devices such as extended-interaction klystrons and coupled-cavity TWTs. Indeed, the modern high-power millimeter-wave helix TWT offers system engineers a singularly attractive amplifier technology with an outstanding combination of small size, light weight, high efficiency, good linearity, high reliability, and large bandwidth.

Latest Advancements in High-Power Millimeter-Wave Helix TWTs

The design of a Ka-band gyrotron traveling wave tube (TWT) amplifier capable of operating over a wide range of peak powers and bandwidths is presented. The amplifier operates in the TE/sub 11/ mode at the fundamental cyclotron harmonic. Instantaneous bandwidths in the range of 2.5 to 3.9 GHz (at 1 dB below saturation) with corresponding peak powers between 92.2 and 57.9 kW can be achieved by simply adjusting the mod-anode voltage of the electron gun. The corresponding gains range from 57.1 to 36.0 dB. The design performance is obtained with a high quality, 6 A, 70 kV electron beam generated with a double-anode magnetron injection gun. This wide range performance capability in the design is achieved via the use of the distributed loss approach in the interacting circuit, which also guarantees zero-drive stability. A diffractive loading scheme is employed in the lossy section of the circuit to ensure high average power operation of the amplifier.

Design of a Ka-band gyro-TWT for radar applications

This is Part I of a two-part report on design and manufacturing methods used at SLAC to produce accelerator klystrons. Chapter 1 begins with the history and applications for klystrons, in both of which Stanford University was extensively involved. The remaining chapters review the theory of klystron operation, derive the principal formulae used in their design, and discuss the assumptions that they involve. These formulae are subsequently used in small-signal calculations of the frequency response of a particular klystron, whose performance is also simulated by two different computer codes. The results of calculations and simulations are compared to the actual performance of the klystron.

/pdf/high-power-klystrons-theory-and-practice-at-the-stanford-4pi6u2u4uw.pdf

High Power Klystrons: Theory and Practice at the Stanford Linear Accelerator CenterPart I

Extending the bandwidth and average power capability of vacuum electron devices for the next generation of millimeter wave radars is a major research goal at the Naval Research Laboratory. Gyro-amplifiers such as the gyroklystron and gyro traveling wave-tube (gyro-TWT) appear to be ideal candidates for this purpose due to their high power handling capability relative to their conventional counterparts, i.e., klystrons and coupled-cavity TWTs. This paper presents the design of a high-average power compatible, Ka-band gyro traveling-wave-tube (gyro-TWT). This amplifier design employs the circular TE/sub 11/ mode and operates at the fundamental cyclotron harmonic. In addition, this design makes use of the distributed loss approach, which has recently been demonstrated to be effective in the suppression of spurious oscillations in gyro-TWTs. The design has been performed using the self-consistent, time-dependent, quasi three-dimensional code MAGY. The code has been successfully used to model gyroklystrons and benchmarked against gyro-TWT linear theory. The code is capable of addressing issues such as absolute instabilities and the effect of reflections, which have also been investigated for this design.

/pdf/design-of-a-ka-band-gyro-twt-for-radar-applications-57h8wbz44n.pdf

This paper reports the research work of an X-band sheet beam klystron with the aim of principle verification, which is fulfilled at the Institute of Electronics, Chinese Academy of Sciences. This paper includes two phases. The first phase is planned to build the sheet beam electron optics prototype tube using the closed periodically cusped magnetic focusing. The measured data shows that the rectangular beam with the cross section of 50 mm × 4 mm can propagate through ~ 300 mm from the cathode surface to the collector with the transmission of 92.4% at the voltage of 110 kV. This foregoing work successfully solves the beam formation and transportation and becomes the basis for developing the sheet beam klystron. In the second phase, the high-frequency interaction structure is designed and cold tested. The X-band sheet beam klystron is constructed and hot tested in the full voltage. The amplification characteristic can be observed near the voltage of 125 kV. For the drive power of 0.71 kW and the working frequency of 11.69 GHz, the output power of 2.8 MW is achieved with the 3 dB bandwidth of 30 MHz, and, correspondingly, the gain and the efficiency are 35.96 dB and 32.52%, respectively. At the same time, the beam transmission is 73.3%. An over 93% transmission is realized at the voltage of 135 kV, whereas the oscillation occurs in the tube. This research exhibits that the sheet beam klystron is a promising device for the high-power applications, whereas seeking the measures to overcome the oscillation is still an arduous task in the future.

Researches on an $X$ -Band Sheet Beam Klystron

Summary form only given. Results are reported for a 1.3 GHz, 10 MW multiple beam klystron that is being developed for the TESLA linear accelerator facility. It features six off-axis electron beams which are contained in a common enclosure, common and higher-order-mode input and output cavities, conventional klystron intermediate cavities with external tuners, dual waveguide and window outputs and six isolated collectors for the measurement of intercepted beam current on each beam line. The design parameters for the device are 10 MW peak RF output power with 150 kW average power, 1.5 ms pulse length, 65% efficiency, 50 dB gain, 4 MHz 1 dB bandwidth, 114 kV beam voltage, 131 A total beam current (emitted by the six cathodes) and 2.0 A/cm/sup 2/ maximum cathode loading.

Operation of a 1.3 GHz, 10 MW multiple beam klystron

A high efficiency multiple beam klystron, designated the VKL-8301, is being developed for the DESY superconducting linear accelerator TESLA in Hamburg, Germany. The accelerator will require 572 klystrons each producing up to 10 MW of rf output power at 1300 MHz. A multiple beam klystron will be used due to its ability to produce large rf output powers using moderate electron beam energies.

Development of a 10 MW, L-band multiple beam klystron for TESLA

2The SLAC XL5 klystron, which produces 50 MW at 12 GHz, is being used in several high gradient accelerators and test stands. The design has been transferred to industry and is currently being modified for ease of assembly and for cost reduction. Two klystrons of the new design will be manufactured and fully characterized.

Industrialization effort of the SLAC XL5 klystron

A new line of high-efficiency multi-stage depressed collector (MSDC) klystron amplifiers has been developed by Communications and Power Industries Microwave Power Products (CPI/MPP) for use in satellite communications and scientific applications market. These klystrons are air-cooled with permanent magnet focusing. The first products are designed to service the satellite uplink and terrestrial repeater markets. MSDC technology for these applications can reduce power consumption by as much as 60%. A general discussion about the benefits of MSDC technology for these applications, as well as two examples of their use, are presented. CPI/MPP has developed the VKU-8891M series klystrons which provide 2.4 kW CW tunable in the frequency range from 17.3 to 18.4 GHz with instantaneous bandwidths up to 85 MHz. The klystron is designed with a 4-stage MSDC which has increased the saturated efficiency of the device from 24% to 40% A detailed discussion of the design, as well as a comparison between simulation and experiment, is presented. CPI/MPP is also developing the VKS-7964M klystron in the frequency range from 2.1 to 2.4 GHz, with instantaneous bandwidths up to 8 MHz. This klystron has a 4-stage MSDC. The simulated efficiency of this klystron approaches 60%. We predict the measured efficiency. A detailed discussion of the design, as well as a comparison between simulation and experiment, is presented.

Permanent magnet focused, multi-stage depressed collector klystron amplifiers for satellite communications

PPM focusing has been used in a 2.5 MW, 9300 MHz klystron. The design will be discussed and test results for three klystrons presented.

Design and operation of a 2.5 MW, PPM focused X-band klystron

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