Innovative Vacuum Electronics. University of Wisconsin 22 June, 2001

Transcription

1 Innovative Vacuum Electronics University of Wisconsin 22 June, 2001

2 UW Colleagues and Support UW collaborators J. Scharer, I. Dobson, B. VanVeen, S. Hagness, D. van der Weide, K. Jain A. Choffrut, M. Converse, S. Gallagher, W.-J. Lee, M. McNeely, M. Neumann, J. Wohlbier, M. Wirth Financial Support DoD MURI AFOSR UW

3 UW Emphasis Linear Beam vacuum electron devices Klystron amplifiers Traveling Wave Tubes 1 GHz - 1 THz

4 General Objectives Improve understanding of VED nonlinearities Impact communications, ECM, surveillance, remote sensing Increase linearity, efficiency Enable new technologies Emphasis on compact devices and moderate powers ( W)

5 Projects and collaborations Multitoned Klystron Amplifier (1,7) Impulse Response (1) (4,6) Multitone Theory (2,8,9) (2-5) (6) mm- & submm-wave s Basic studies Saturated, Linearized s Collaborators & Contributors 1 University of Michigan 2 Northrop Grumman (& Litton) 3 NASA Glenn 4 NRL, U Maryland, SAIC (CHRISTINE support) 5 Teledyne 6 Boeing 7 CPI 8 Analex, Inc 9 Argonne National Lab

6 Multitoned Klystron Amplifier Objectives: intermodulation physics and suppression Impact: communications, basic science f f 1 f 2 f New theoretical model (U. Michigan)* Experimental evaluation Varian (4K3SL) 4-cavity KLA 2-tone excitation eventual experiments to examine IMP suppression *Lau, et al, IEEE T.P.S. 28 [3], (2001)

7 Multitoned Klystron Amplifier First results Calibration Case: P in = 5dBm 40 Measurement Simulation Normalized simulation f 1 f 2 Pout (db) rd, 5 th, & 7 th IMPs Frequency (GHz) Preliminary comparison of theory and experiment Illustrative spectrum at the second cavity

8 Basic studies Objectives: advanced linear & spent beam physics, nonlinear distortion and control Impact: communications, ECM, basic science experimental WIsconsin Northrop Grumman (XWING) (pulsed) cathode flux shield cathode e-beam anode input (output tap) V - + beam final µ wave output µ multiple wave output taps sever capacitive differential current fluctuation probe (to scope) to vacuum pump valve I current detector RFE or ExB analyzer V bias Teledyne (CW)

9 Basic studies Novel features and capabilities of the XWING Large C, high space charge (MPM-relevant) Wideband (working f ~ GHz) Multiple taps enable studies of: Wave evolution Hot phase velocity of drive, harmonic, and IM tones Direct growth rate measurements Can study transient pulse amplification Can examine spent beam during all studies

10 Basic studies Gain [db] Gain vs. Frequency New Results G - td sim G - Chris G - exp Frequency [GHz] Evolution of multitone spectra f 1 f 2 2 & 2.1 GHz drive, 15dBm port 1! ~ 2f ~ 3f port 4 5 linear growth rate growth rate (db/cm) expt Pierce Chris. 1D frequency (GHz) z! port 6

11 Impulse Response Objective: impulse response (UWB transient) of s Impact: single-msmt characterization, impulse radar, impulse radio, basic science t t Use as time-domain characterization tool? Dispersion, nonlinear, and transient physics

12 Impulse Response Results 1D, dispersive, time-domain (transient) models developed linear (with U. Michigan) nonlinear Experiment designed and configured using XWING Goal: establish use and limits of multi-tone, frequencydomain models for ultrawideband transients

13 Multitone Theory Objective: modeling nonlinear multitone dynamics Impact: communications, ECM, basic science MUlti-tone Spectral Eulerian (MUSE) model Basic Research Tool: Physics very accessible Allows analytic solution for distortion product growth rates Improved computational efficiency ~ 1/10 time (vs. standard disk model) for dispersionless, low gain ( small C ), space-charge-free version of model Recently added dispersion, space charge, & high gain (large C) physics Issues Prior formulation: limited to - 5 db backoff (unsaturated), New formulation: includes saturation physics Accuracy? Speed? Retains propensity for clear physics and analytic solutions

14 Multitone Theory Illustrative Results Disk MUSE 10 Input No effects Add dispersion Add space charge GHz 0.1 V V* (Volts 2 ) 1E-4 1E-8 1E-12 1E GHz Pierce Parameters C 1.6GHz = 0.11 C 3.2GHz = QC 1.6GHz = 0.15 QC 3.2GHz = 0.37 b 1.6GHz = 0.95 b 3.2GHz = 4.09 V V* (Volts 2 ) E-3 1E-4 1E-5 1E-6 1E z (cm) 1E Frequency (GHz) Comparison of MUSE and conventional Lagrangian (disk) predictions exact agreement except for saturation Spectrally dense excitation - spectral regrowth & NPR - effects of dispersion - effects of space charge

15 Saturated Linearized s Objective: linear amplification at high efficiency Impact: Communications, ECM LInearization using Nonlinear Components (LINC) Previous application: low frequency solid state amplifiers Novel to high frequency VEDs Converts arbitrary AM-and-PM signal to two quadrature, PM, constant-amplitude signals. Amplify with 2 s and combine. Baseband input s(t) s i,1 (t) SCS QMOD s m,1 (t) s o,1 (t) s out (t) Signal component separator s i,2 (t) QMOD Frequency up-conversion s m,2 (t) amplifiers s o,2 (t) Power combiner

16 Saturated Linearized s Preliminary Results OBO = 0.2 db π/4-shifted differential QPSK similar results with offset 4QAM Future studies will also investigate linearization of saturated single- configurations

17 mm- & submm-wave s Objective: compact, low-cost, efficient sources of mmwave and THz regime coherent radiation Impact: Very-high high-data-rate wireless comm, remote sensing (environment, industrial, security scans), covert space-space & space-earth earth comm, astrophysical research, high-res radar, and...??.new THz applications! Strong motivation for compact sources that are: frequency agile powerful (vs. solid state) efficient reliable cheap Micro-VEDs: micromachined Vacuum Electron Devices Current technology: BWO s suboptimal size, efficiency, weight.

18 mm- & submm-wave s Micromachining Micromachined s µm-scale 3D structures from 2D substrates lithography based methods DRIE, LIGA, SU-8, microplasma, microedm UW: THz regime s (w/ Analex, NGC, Argonne) Micrograph of silicon trenches 80 microns deep, 4.5 µm space widths/2 µm line widths. Aspect ratio=18:1, SiO2 mask, etch rate >2.2 µm/min, Anisotropy > Courtesy of Surface Technology Systems plc η electronic ~1%

19 Summary Research frontier in linear beam VEDs: linearity with efficiency multitone & spectrally dense excitations high-data-rate digital impulse excitation multi-carrier New compact sources in mm-wave and submm-wave (THz) regimes