Traveling wave tubes are rapidly evolving to provide unprecedented power level in comparison to solid state devices in the millimeter waves region of the spectrum (80–300 GHz) thus enabling a wide ...

https://www.tandfonline.com/doi/pdf/10.1080/09205071.2020.1848643

Millimeter wave traveling wave tubes for the 21st Century

The development of a G-band traveling wave tube for wireless communications and airborne radars is described. The maximum output power of this device is over 20 W. This device provides a saturation output power over 15 W and a saturation gain over 32 dB with a bandwidth of 7.6 GHz. A folded waveguide circuit with modified circular bends is utilized to eliminate the band-edge instability caused by the high beam voltage of 20 kV. A pencil beam of 50 mA with a transmission ratio over 95 % is realized, making the device capable of operating in continuous wave mode. Periodic permanent magnets are employed for compactness. Chemical vapor deposition diamond disc is used in the input and output RF windows to minimize the loss and voltage standing wave ratios of the traveling wave tube. The weight and the size of the device are 2 kg and 300 mm $\times70$ mm $\times70$ mm, respectively. The efficiency of the device is over 5 %.

A G-Band Traveling Wave Tube With 20 W Continuous Wave Output Power

This letter presents the research progress of a pulsed G-band 50 W traveling wave tube (TWT) with pencil beam focused by periodic permanent magnet (PPM). Three approaches have been combined to improve the tube’s operation performances including setting the operating point near the cutoff frequency, using the folded waveguide (FWG) slow wave structure (SWS) with modified circular bends (MCBs), and adopting phase velocity tapering (PVT) technique. The measured output power can be over 50 W at 5% duty cycle with a bandwidth of 3.6 GHz when the beam voltage is 24.25 kV and the beam current is 59 mA. Corresponding electronic efficiency and gain are higher than 3.5% and 35 dB, respectively. The results provide a demonstration of a compact terahertz amplifier with high power, high electronic efficiency and significant bandwidth.

Demonstration of a Pulsed G-Band 50-W Traveling Wave Tube

We propose and experimentally demonstrate a high-power and wide-bandwidth terahertz travelling wave tube (TWT), which is with two cascade amplification sections: the output wave of the first TWT is used as the input of the second one. Using a 17 kV, 71 mA electron beam, the measured peak power is over 60 watt and the average output power is over 12 watts with 20% duty cycle at the frequency around 0.22 THz. The gain is about 30 dB and the bandwidth is over 6 GHz. The average power-bandwidth-gain product reaches record high in the designed spectral range. We envisage that this new developed terahertz TWT will have broad application prospects, such as in long-range radar and communication systems.

Demonstration of a High-Power and Wide-Bandwidth G-Band Traveling Wave Tube With Cascade Amplification

The interaction between a linear electron beam and a guided electromagnetic wave is studied in the contest of exceptional points of degeneracy (EPD) supported by such an interactive system. The study focuses on the case of a linear beam traveling wave tube (TWT) with a realistic helix waveguide slow-wave structure (SWS). The interaction is formulated by an analytical model that is a generalization of the Pierce model, assuming a one-dimensional electron flow along a dispersive single-mode guiding SWS and taking into account space-charge effects in the system. The augmented model using phase velocity and characteristic impedance obtained via full-wave simulations is validated by calculating gain versus frequency and comparing it with that from more complex electron beam simulators. This comparison also shows the accuracy of our new model compared with respect to the non-dispersive Pierce model. EPDs are then investigated using the augmented model, observing the coalescence of complex-valued wavenumbers and the system's eigenvectors. The point in the complex dispersion diagram at which the TWT-system starts/ceases to exhibit a convection instability, i.e., a mode starts/ceases to grow exponentially along the TWT, is the EPD. We also demonstrate the EPD existence by showing that the Puiseux fractional power series expansion well approximates the bifurcation of the dispersion diagram at the EPD. This latter concept also explains the "exceptional" sensitivity of the TWT-system to changes in the beam's electron velocity when operating near an EPD.

Exceptional Degeneracies in Traveling Wave Tubes with Dispersive Slow-Wave Structure Including Space-Charge Effect

The development of a compact radio frequency (RF) vacuum power amplifier for high-resolution airborne radar is described. The amplifier, a microwave power module (MPM), operates in the upper millimeter-wave frequency band of 231.5–235 GHz providing a peak output power of 32 W. Common with previous extremely high frequency MPM development at Electron Devices, the ${G}$ -band MPM consists of a periodic permanent magnet focused serpentine waveguide traveling wave tube (TWT) and a miniaturized 20-kV electronic power conditioner. Input drive to the MPM for saturation is around 10 mW. Low-loss chemical vapor deposition diamond WR-4.3 windows serve as the input and output ports of the TWT. Due to the high duty of the radar application, a four-stage TWT collector is employed for beam energy recovery. The MPM operates from a 270- $\text{V}_{\sf {dc}}$ power source. Two MPM configurations have been constructed: a single integrated unit for laboratory testing and a split-package configuration for integration in a standard electro-optical/infrared gimbal. The split-package flight test unit has a maximum prime power requirement of 176 W, corresponding to an overall amplifier efficiency of 9%. The radar sensor has been flown on a modified DC-3 test bed with high-resolution real-time video imagery obtained under cloud-obscured operating conditions.

Robert Tobin

Papers

A Compact Extremely High Frequency MPM Power Amplifier