We present modeling of the phase locking of two X-band magnetron oscillators using 1-D and 3-D simulation tools. A 1-D lumped-element circuit model is compared to 3-D particle-in-cell (PIC) simulations in NRL Neptune. The conditions required for phase locking are discussed. We find that both the 1-D and 3-D simulations predict that there are certain connecting waveguide lengths that will support phase locking of the two magnetrons, by bringing the transmission line into the periodic phase resonance condition. The phase locking lengths are around ½ lambda multiples, separated by lengths of waveguide which do not support the phase locking condition.

We present fabrication results and RF cold test of a multiple-electron-beam TWT circuit operating in the millimeter-wave frequency range. Due to the eight beam tunnels and helical waveguide geometry, the circuit is three-dimensional (3D) in nature and requires an additive manufacturing (AM) fabrication technique. The circuit was fabricated in a single piece using direct metal laser melting (DMLM) in Inconel 718 alloy.

We present an overview of additive fabrication methods for upper-millimeter-wave traveling-wave tube (TWT) amplifier slow-wave circuits, including ultraviolet lithography and Cu electroforming (UV-LIGA); 3D-printed mold electroforming (3D-PriME); and direct 3D printing in photopolymer with Cu plating. We describe example fabrication processes for traveling-wave circuits spanning the frequency range 94 GHz to 1 THz and present test data.

We describe the design, development, and initial testing of a very compact, multiple-beam folded-waveguide traveling wave tube (TWT) operating in Ka -band at $\sim $ 6 kV. A proof-of-principle four-beam, $\sim $ 100 mA/beam device has been fabricated and tested, and a 16-beam version of the device has been designed and is predicted to produce an output power up to 1 kW. Here, we describe the design approach we devised and implemented to overcome two fundamental challenges: 1) generating and transporting the tightly spaced beams required to operate in the millimeter-wave regime and 2) developing folded waveguide circuits that can provide high interaction impedance for each of the beams as well as stable operation in a dense high-order-mode environment.

We discuss progress on additive manufacturing (AM) methods for the fabrication of millimeter-wave (mmW) vacuum electronic (VE) devices. Polymer 3D printing is discussed for fabrication of light-weight RF body assemblies with many integrated RF components such as waveguide power couplers and power combiners. Stainless-steel binder-jetting is discussed for fabrication of high-power VE circuits in metal, combined with infiltration of the bulk metal with a filler metal (such as Cu) to increase the electrical and thermal conductivity to the high level needed for mmW circuits.

We present the experimental demonstration of a traveling-wave tube (TWT) power amplifier operating in the ${W}$ -band (75–110 GHz) frequency range. The device is based on a serpentine waveguide (SWG) amplification circuit, a slow wave circuit type capable of high power and broad instantaneous bandwidth in the upper millimeter-wave range. A 20 kV, 140-mA round solenoid-focused electron beam powers the device. At 20 kV, we measure 215 ± 2 W peak RF output power at 93 GHz with 20.1 ± 0.15 dB saturated gain, pulsed at 0.1% duty. We observe 10-GHz instantaneous amplification bandwidth at 100-W minimum output power, covering the range 88–98 GHz. Operating at 20.8 kV, the TWT produces 285 ± 3 W at 91 GHz with 22.4 ± 0.15 dB gain, and 7 GHz, 3-dB bandwidth. The peak electronic efficiency measured is approximately 10%.

We present experimental characterization of a 20-kV, 130-mA thermionic electron gun, which is a component of a W-band traveling-wave tube (TWT) power amplifier. The electron beam is strongly focused by a 6.6-kG permanent magnet solenoid, producing a peak current density up to 800 A/cm 2 . The cathode temperature, focus electrode voltage, and modulating anode voltage are varied to characterize the emitted cathode current and beam transport through the beam tunnel of the TWT RF circuit. We observe the variation of the cathode current from 107 to 155 mA and peak beam transmission of 95% measured at the collector. Experimental results are compared to 2-D simulations with the electron gun and collector design code MICHELLE.

We report on efforts toward a monolithic Ka-band sheet-beam coupled-cavity TWT circuit. This new circuit serves as a drop-in replacement for a demonstrated device that was originally fabricated using the method of brazing stacked plates.

We present testing of a W-band traveling-wave tube (TWT) based on a serpentine waveguide circuit, powered by a 20 kV, 130mA electron gun. We measure peak output power of 215±2W at 93 GHz with 20.1±0.15dB saturated gain, and>100 W from 88-98 GHz, pulsed at 0.1% duty. Operating at 20.8 kV, the TWT produces 285±3W at 91 GHz with 22.4±0.15dB gain.

We present experimental characterization of a 20 kV, 130 mA thermionic electron gun in a W-band TWT. The gun heater voltage, focus electrode voltage, and modulating anode voltage are swept to characterize the performance of the emitted cathode current and beam transport through the RF circuit. We observe variation of the cathode current from 107 to 155 mA and peak beam transmission of 95% at the collector. Experimental results are compared to 2D MICHELLE simulations.

Millimeter and sub-millimeter wave vacuum electronic devices have been of great interest for a wide variety of applications, but fabrication of the sub-wavelength structures has been a persistent challenge. We present and compare fabrication approaches including CNC micromachining, 3D printed mold electroforming (3D PriME), and UV-photolithography for creating traveling wave tube circuits at 35, 95, 140 and 233 GHz, along with results. To date, CNC micromachining has yielded the best results up to 140 GHz.

We present experimental characterization of W-band serpentine waveguide TWT circuits fabricated by CNC micro-endmill machining. Cold test measurements of S-parameters demonstrate excellent agreement with simulation and precise fabrication repeatability between multiple circuits. The circuit wavelength dispersion was measured in both W- and D-band waveguide bands, covering an octave in frequency, showing agreement with simulation from 85-170 GHz. We discuss details of the fabricated circuits and cold test results.

We report on fabrication techniques for creating vacuum electron (VE) circuits from 30 GHz to 300 GHz. for devices up to 300 GHz, micro-CNC machining appears suitable.

We present fabrication and testing of RF components for a W-band serpentine waveguide TWT. Broadband ceramic RF windows and loads exhibit reflection lower than -20 dB across the TWT operating band, nominally 87-100 GHz. End-to-end cold test of the entire tube assembly, including interaction circuit, shows a clean passband better than -15 dB, in agreement with simulation. We discuss details of the fabricated components and electromagnetic cold test results.

In this paper we present a practical design of Multiple Beam Traveling Wave Tube (MB-TWT) with Folded Waveguide (FW) Slow Wave Structure (SWS) operating at low voltages, 6.2 kV, with output power about 300 Wand central frequency of 29 GHz completed by using NRL large signal design codes [1], [2]. Stability analysis with respect to excitation of high order spurious modes has been done with NRL 3D PIC code Neptune [3].

Folded Waveguide (FW)mini- TWT based on four beams operating at 6.2 kV with total beam power 2.7 kW has been designed by using NRL design codes. The FW slow wave structure (SWS) has been fabricated and "cold" tested. The results of measurements are compared with design. The status of experimental demonstration of the mini- TWT will be presented.

We demonstrate 3D-printed mold electroforming (3D-PriME) fabrication of a W-band serpentine waveguide TWT circuit. The method allows the creation of a solid copper circuit, suitable for a vacuum electron device, beginning with a plastic inverse mold built on a commercial 3D printer. We present details of the fabricated circuit and electromagnetic cold test results.

Initial work is presented on novel monolithic integration of key components for 140 GHz traveling- wave tube arrays.

We present the fabrication and testing of a novel 4 electron beam TWT designed for operation at low voltage (6.2 KV). Presented are cold test and bead pull data from this Ka-band circuit fabricated with micromachining methods.