Alan M. Cook

Demonstration of a High Power, Wideband 220-GHz Traveling Wave Amplifier Fabricated by UV-LIGA

We present the first vacuum electronic traveling wave amplifier to incorporate an interaction circuit fabricated by ultraviolet (UV) photolithography and electroforming, demonstrating over 60 W of output power at 214.5 GHz from a 12.1 kV, 118 mA electron beam. The tube also achieved an instantaneous bandwidth of ~15 GHz in G-band in the small signal regime. The all-copper circuit was fabricated in two layers using a UV-transparent polymer monofilament embedded in the photoresist to form the beam tunnel prior to electroforming. Effects arising from fabrication errors and target tolerances are discussed. This microfabrication technique and demonstration paves the way for a new era of vacuum electron devices that could extend into the 1-2 THz range with advances in high-current-density electron guns.

High-Power Copper Gratings for a Sheet-Beam Traveling-Wave Amplifier at G-band

The design, fabrication, and electromagnetic cold testing results of an all-copper grating circuit intended for a G-band sheet-beam traveling-wave amplifier are presented. Fabrication was carried out via ultraviolet photolithography (UV-LIGA) using the SU-8 photoresists. Two cold test methods used to characterize the microfabricated circuits are reported and reveal excellent agreement with simulations. This type of all-copper grating also shows potential for use as a high-average-power sharp-cutoff filter.

Demonstration of a high power, wideband 220 GHz serpentine waveguide amplifier fabricated by UV-LIGA

We present the hot test results of a 220 GHz, serpentine waveguide vacuum electron amplifier showcasing a novel embedded monofilament microfabrication technique based on UV-LIGA. The instantaneous operating bandwidth exceeds 15 GHz and the small signal gain of the circuit is over 14 dB. By varying the voltage slightly, an operating bandwidth of almost 40 GHz is realizable with a minimum circuit gain of 7 dB across the band. A maximum power of just over 60 W was obtained at the output flange of the device, corresponding to a power of almost 80 W generated in the circuit.

Design Methodology and Experimental Verification of Serpentine/Folded-Waveguide TWTs

The general electromagnetic properties and design methodology for serpentine/folded-waveguide (FW) amplifiers are presented. In addition, hybrid-waveguide circuit topologies, which permit greater design flexibility than the basic serpentine/FW topologies, are also introduced, and their dispersion characteristics are discussed. Experimental validation of design methodology and tools is provided via test results of the recently demonstrated wideband 220-GHz serpentine amplifier, which embodies the design methodology described herein. Particular attention will be paid to the comparison between code prediction and experimental data, which are in excellent agreement.

Design of a wideband high-power W-band serpentine TWT

The design of a W-band serpentine TWT with >200 W of power over a 4 GHz bandwidth (>100 W over 7 GHz) is presented. The amplifier is driven by a 122mA, 20 kV electron beam generated by a slightly modified version of the demonstrated 670 GHz beamstick at a reduced magnetic field. The design was performed by both the established MAGIC-3D and the recently validated NRL code Neptune, with good agreement between the two codes. Predicted RF peak power is 245 W, corresponding to 10% electronic efficiency.

Modeling of the NRL G-Band TWT amplifier using the CHRISTINE and TESLA simulation codes

Comparisons between predictions of the NRL large signal codes CHRISTINE and TESLA-FW and measurements of small signal gain of NRLs G-Band serpentine waveguide TWT are presented. Results of a sensitivity study of the effects on gain of the circuit dispersion allow us to identify the most critical physical circuit dimensions for TWT design and to quantify required circuit fabrication tolerances.

Microfabrication and Cold Testing of Copper Circuits for a 50 Watt, 220 GHz Traveling Wave Tube

We present the microfabrication and cold test measurement results of serpentine waveguide amplifier circuits at 220 GHz. The circuits were fabricated using a novel embedded polymer monofilament technique combined with Ultraviolet- LIGA to simultaneously create both the beam tunnel and interaction circuits. We find remarkable characteristic matches between the measurements of the best circuits, illustrating that the process developed is able to create repeatable, highly precise circuits with high yield. It was found that slight beam tunnel misalignment can cause very strong stopbands to appear in the operating band due to bi- or quasi-periodicity. The NRL code TESLA-SW/FW has been used to rapidly simulate the as-built structure under a variety of conditions to accurately predict the performance with an electron beam. The tolerances needed on beam tunnel alignment are studied, with implications extending to the THz range.

Development of a 233 GHz High Gain Traveling Wave Amplifier

We present development plans for a 233 GHz, serpentine waveguide vacuum electron amplifier employing an embedded monofilament microfabrication technique based on UV-LIGA. Output power from the circuit is predicted to exceed 140 W in conjunction with a newly developed electron gun at 20 kV and 124 mA. Design, fabrication and integration progress will be discussed.

Broadband 220-GHz Vacuum Window for a Traveling-Wave Tube Amplifier

We present electromagnetic cold-test measurements of BeO ceramic pillbox vacuum windows for a 220-GHz traveling-wave tube amplifier. Transmission and reflection measurements show better than 20 dB return loss over a 25 GHz bandwidth, with band centers in the range of 212-225 GHz. We observe tuning of the window response as the circular waveguide length is changed. High-power testing is performed at 2.5 W, 100% duty at 218 GHz.

Development of a wideband W-band serpentine waveguide TWT

We are developing a wideband 95-GHz, 200-W TWT powered by a 20-kV, 122-mA electron beam. The serpentine waveguide circuit is fabricated by UV-LIGA using an embedded monofilament, which produces an all-copper structure with beam tunnel. Simulations predict 37 dB small-signal gain and 245 W maximum output power.