S. Limbach

Folded waveguide traveling-wave tube sources for terahertz radiation

Microfabricated folded waveguide traveling-wave tubes (TWTs) are potential compact sources of wide-band, high-power terahertz radiation. We present feasibility studies of an oscillator concept using an amplifier with delayed feedback. Simulations of a 560-GHz oscillator and experimental evaluation of the concept at 50 GHz are presented. Additionally, results from various fabrication methods that are under investigation, such as X-ray lithography, electroforming, and molding (LIGA), UV LIGA, and deep reactive ion etching are presented. Observations and measurements are reported on the generation of stable single-frequency oscillation states. On varying the feedback level, the oscillation changes from a stable single-frequency state at the threshold to multifrequency spectra in the overdriven state. Simulation and experimental results on amplifier characterization and dynamics of the regenerative TWT oscillator include spectral evolution and phase stability of the generated frequencies. The results of the experiment are in good agreement with the simulations.

Novel TWT interaction circuits for high frequency applications

Summary form only given. The initial focus of this program is on the development of Ka-band TWTs producing 10 W of RF power. These devices would potentially be used as RF sources for phased array antennas. This requires innovative TWT designs, which result in improved repeatability, increased yield and reliability, and reduced cost over existing Ka-band devices. To do this, the batch nature of micro-electro-mechanical systems (MEMS) fabrication techniques is ideal. However, many TWT interaction circuits, such as the conventional helix, are not compatible with MEMS techniques. Thus, Calabazas Creek Research, Inc. (CCR) has computationally investigated several innovative TWT interaction circuits based on MEMS fabrication. These include the square helix, planar helix and modified folded waveguide circuits.

Terahertz-regime, micro-VEDs: evaluation of micromachined TWT conceptual designs

Summary form only given. The Terahertz (THz) region of the electromagnetic spectrum (/spl sim/300-3000 GHz) has enormous potential for high-data-rate communications, spectroscopy, astronomy, space research, medicine, biology, surveillance, remote sensing, industrial process control, etc. The most critical roadblock to full exploitation of the THz band is lack of coherent radiation sources that are powerful (0.01-10.0 W continuous wave), efficient (>1%), frequency agile (instantaneously tunable over 1% bandwidths or more), reliable, and relatively inexpensive. Micro-machined Vacuum Electron Devices (micro-VEDs) represent a promising solution. We describe prospects for miniature, THz-regime TWTs fabricated using micromachining techniques. Several /spl sim/600 GHz conceptual designs are compared. Their expected performance has been analyzed using 1D, 2.5D, and 3D TWT codes. A folded waveguide (FWG) TWT forward-wave amplifier design is presented based on a Northrop Grumman (NGC) optimized design procedure. This conceptual device is compared to the simulated performance of a novel, micro-VED helix TWT. Conceptual FWG TWT backward-wave amplifiers and oscillators are also discussed. A scaled (100 GHz) FWG TWT operating at a relatively low voltage (/spl sim/12 kV) is under development at NGC. Also, actual-size micromachining experiments are planned to evaluate the feasibility of arrays of micro-VED TWTs. Progress and results of these efforts are described. This work was supported, in part by AFOSR, ONR, and NSF.

Comprehensive simulations of compact THz radiation sources using microfabricated, folded waveguide TWTs

Microfabricated folded waveguide traveling wave tubes (FWG-TWT) are potential compact sources of wideband (/spl sim/20% instantaneous bandwidth), high power (0.01 - 1 W) THz radiation. We present numerical simulations indicating that a 560 GHz, 56 mW, 1% (intrinsic) efficiency oscillator is realistically achievable, and a 400 GHz amplifier with gains between 10 and 30 dB are feasible with circuit lengths of a few centimeters. We also discuss a scale-model experiment at 50 GHz to investigate an oscillator concept using a recirculated power feedback approach.

THz radiation using compact folded waveguide TWT oscillators

Microfabricated folded waveguide traveling wave tubes are a promising solution to the generation of compact, wideband, high power terahertz radiation. We present feasibility studies of an oscillator concept using an amplifier with recirculated feedback. Simulations of a 560 GHz oscillator and experimental verification of the principle at 50 GHz are presented. Observation and measurements are reported on the generation of stable single frequency oscillation states. On varying the feedback level, the oscillation changes from a single frequency state at threshold to multifrequency spectra in overdriven state. Investigations on dynamics of the regenerative TWT oscillator will be presented. Additionally, preliminary results of experiments to fabricate 100-400 GHz folded waveguide TWT circuits will be reported.

W-band MEMS-based TWT development

Summary form only given. Calabazas Creek Research, Inc. is funded by the U.S. Air Force to develop advanced, wideband, high frequency, micro-electro-mechanical systems (MEMS)-based traveling wave tubes (TWTs) for the transformational communications architecture. Specifically, the program is developing an 83.5 GHz TWT. Full power testing of the TWT in a solenoid magnetic field by Boeing Satellite System, Inc. is planned in 2004. Following successful completion, PPM focusing will be implemented and development of a device for space qualification will begin. The program is scheduled for completion in April 2005. Successful completion of this program will increase the operating range and applications for vacuum-based RF devices.

THz radiation using high power, microfabricated, wideband TWTs

Microfabricated, miniature, folded waveguide traveling wave tube (FWG-TWT) devices are potential compact sources of wideband (/spl sim/20% instantaneous bandwidth), high power (0.01-1 W) THz radiation. We present theoretical analyses and numerical simulations indicating that a 560 GHz, 56 mW, 1% (intrinsic) efficiency oscillator is realistically achievable, and amplifiers with gains between 10 and 30 dB are feasible with circuit lengths of a few centimeters. We also discuss a scale-model experiment at 50 GHz to investigate an oscillator concept using a recirculated power feedback approach, and a 400 GHz proof-of-concept amplifier.

MEMS-microfabricated components for millimeter-wave and THz TWTs

Summary form only given. Microfabrication techniques used for MEMS offer promising advantages for fabrication of mm-wave and THz vacuum electronic devices (/spl mu/VEDs). This paper describes results of an exploratory investigation of several microfabrication methods considered candidates for production of circuits or circuit components for mm-wave and THz TWTs. The processes investigated have included LIGA, hot embossing (polymer micromolding), and deep reactive ion etching (DRIE). The circuits and circuit components investigated have included folded waveguides (FWGs), gratings, resistive wall amplifiers, and novel attenuators for FWG TWTs. We present and discuss the results of the microfabrication experiments, the design analyses, and their implications for advanced mm-wave and THz /spl mu/VEDs.

Generation of Terahertz Regime Radiation by Microfabricated Folded Waveguide Traveling Wave Tubes

The fabrication of a terahertz regime folded waveguide traveling wave tube (FWTWT) using MEMS microfabrication techniques is currently underway. Recent developments in the design, fabrication method, and measured data are presented

Investigations of folded waveguide TWT oscillators for THz radiation

In this paper we are investigating folded waveguide traveling wave tubes (FWGTWT). These FWGTWTs combine the power density and high frequency advantages of vacuum microelectronics with the powerful microfabrication methods of MEMS and solid state electronics. Experimental, theoretical and computer simulation investigations of a FWGTWT oscillator have been performed, including microfabrication tests of a variety of methods.