Evaluation of the TE12 Mode in Circular Waveguides for Low-Loss High Power Transportation

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Evaluation of the TE12 Mode in Circular
Waveguides for Low-Loss High Power
Transportation Sami G. Tantawi, C. Nantista K.
Fant, G. Bowden, N. Kroll, and A. Vlieks SLAC
Yong Ho Chin, H. Hayano, and Vladimir Vogel
KEK J. Neilson Calabazas Creek, Inc.
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• Outline
• Introduction
• Multi-Moded DLDS
• Mode Analyzer
• TE12 mode launchers
• TE01 mode launchers
• Waveguide Tapers
• Transport line measurements
• Conclusion

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• The high power rf pulse compression techniques
  suggested for the future linear colliders
  involves long runs of low loss transportation
  lines. These runs range from 1000 km to 240 km
  depending on the system.
• These lines are suppose to carry rf pulses with
  power levels up to 600 MW for 1.5 micro-seconds
  at 11.424 GHz. These transportation lines were
  envisioned to be a circular waveguides with
  smooth walls using the low loss TE01 mode.
  Several experimental pulse compression systems
  based on these lines were built and operated at
  power levels up to 500 MW7-8.
• The usage of HE11 mode in corrugated guides were
  deemed impractical because the corrugation depth
  required at X-band is large and that made the
  cost of the waveguide high.
• To reduce the length of the waveguide and
  consequently the cost, a multi-moded rf system
  was suggested. The reduction in cost using this
  technique was analyzed and shown to be
  considerable.

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Delay Lines
Accelerator Structures
Bank of nk of klystrons
Not all the output need to be used. The unused
outputs are terminated by an rf load
A set of hybrids that switches the combined rf to
different outputs
A Unit of a Single-Moded DLDS
A mode launcher which takes nm inputs and
produces nm modes into a single waveguide delay
line
Multi-Moded Delay Lines. The total number of
these lines is np
Accelerator Structures
Bank of klystrons
A set of hybrids that switches the combined rf to
different outputs
A Unit of a Multi-Moded DLDS
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Two banks of power sources each has an nk/2
klystrons
3 dB 90 Degree Hybrid
Single-Moded Delay Lines
Accelerator Structure
Single-moded Binary Pulse Compression
Two banks of power sources each has an nk/2
klystrons
3 dB 90 Degree Hybrid
Short Circuit
Circulator
Single or Multi-Moded Delay Lines
Accelerator Structure
Binary pulse compression can have several
improvements including the use of a circulator
and several modes to reduce the delay line length.
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Relative attenuation of different modes per unit
time in circular waveguide versus the normalized
diameter of the waveguide.
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Multi-Moded DLDS System
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Circular Guide modes Square Guide Modes TE11
(Polarization 1) TE10 TE11(Ploarization
2) TE01 TM01 TM11 TE21 (Polarization 1) TE20
and TE02 (In Phase) TE21 (Polarization
2) TE11 TE01
TE20 and TE02 (out of Phase by 180 degrees) TM11
(Polarization1) TM12 TM11 (Polarization2) TM21
TE31 (Polarization 1) TE12 TE31 (Polarization
2) TE21 TM21 (Polarization 1) TM22 TM21
(Polarization2) TM13 and TM13 (In phase) TE41
(Polarization1) TE22 TE41 (Polarization2) TE31
and TE13 TE12(Polarization1) TE30 TE12(Polariza
tion1) TE03 TM02
TM31 and TM13 (out of phase by 180 degrees)
Modal Connection Between Circular and Square
Waveguides.
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(a) The Circular-to-Rectangular-Tapers TE12 Mode
Transducer. (b) A cut away view of the structure.
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Simulated electric field distribution inside the
TE12 mode transducer. The colors represent the
electric field strength.
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Simulated performance of the TE10 (rectangular)
to TE12 (circular) mode converter. Simulations
are done using HP-HFSS.
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Measured frequency response of two TE12 mode
tranceducers connected back to back.
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The Wrap-Around Mode Converter. The physical
model shown in the picture does not have the back
wall shorting plate, this is done for
illustration purposes only.
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HFSS simulation results for the wrap around mode
converter. The color shades represents the
magnitude of the electrical field. (a) is a cut
plane through the slots, (b) is a cut plane in
the circular guide 2.5 cm away from the slots.
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Measured Transmission coefficient for two
wrap-around mode converters back to back. The
device is optimized at 11.424 GHz.
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TE 12 incident on 2" DSum of Reflected power
-30.0 dBTransmitted power resultsMode
OutputPower (dB)----------------------TE 11
-32.7438TM 11 -24.2549TE 12 -0.0187TE 01
incident on 2" DSum of Reflected power -70
dBTransmitted power results Mode OutputPower
(dB)----------------------TE 01 -0.0128TE 02
-25.3265TE 03 -49.1235TE 04 -67.0160
Simulation
Arc-taper profile, distances are in meters.
Vertical axis is radius and horizontal axis is
axial distance
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Two TE12 mode converters back to back including
up tapers to 4.75 diameter
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Two TE01 mode converters back to back including
up tapers to 4.75 diameter
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Calculated mode amplitude profiles along the mode
rotator, or polarization converter. The
asterisks here indicate cross-polarized modes.
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MAFIA graphic showing electric field arrows for
the WC475 choke resonance. The horizontal axis
is r and the vertical axis is z, both in meters.
The bottom edge of the plot is the symmetry plane
at the gap center.
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The Mode Analyzer
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The scattering of modes due to the step
discontinuity when an incident mode is the TE01
mode
The scattering of modes due to the step
discontinuity when an incident mode is the TE12
mode
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Typical Measurement Setup
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Stability of measurements over time
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Rectangular waveguide calibration measurements
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SLACs TE12 mode launcher
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Measured Mode spectrum of the TE01 mode
transducer.
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Mode Spectrum of the KEK Mode Launcher
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U of Maryland
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Mode Spectrum after the 55 meter of
Waveguide. The mode is Launched using SLACs TE12
mode converter
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Mode Spectrum after the 55 meter of
Waveguide. The mode is Launched using SLACs TE01
mode converter
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Transmission Measurement through a TE12 mode
launcher 55-meter of WC475 Waveguide and a
receiving TE12 Mode Converter. The TE12 was
Launched and received with horizontal
polarization
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Time domain response of the transport line plus
the mode launchers (two mode transducers plus two
arc-tapers). In this figure the two mode
transducers were always aligned with respect to
each other
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The effect of rotating one of the mode TE12 mode
transducer with respect to the other.
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Time domain response of the transport line plus
the mode launchers (two TE01 mode transducers
plus two arc-tapers).
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• Losses Of The TE01 Mode is 1.08 Theory is 1.1
• Losses of the TE12 Mode is 4.5 to 5.1
  (Polarization dependant)Theory is 2.8
• No mode rotation was observed
• None of the mode TE12 converters performed
  satisfactory.

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• Conclusion
• We have demonstrated the possibility of using the
  TE12 mode in highly over-moded circular
  waveguides as a means of low-loss transport of rf
  signals. The over all losses were small and
  compared relatively well with theory.
• The waveguide used in the experiments were
  extruded oxygen-free high-conductivity copper. It
  was shown that these waveguides could be
  manufactured good enough to eliminate all cross
  polarization mode mixing. Nonetheless, we
  observed some conversion to the virtually
  degenerate mode, TE41. However, the conversion
  levels were small.
• We also compared our results for TE12 with those
  of the low loss TE01. In this process we showed
  that connecting flanges and waveguides could be
  used to propagate either modes. This paves the
  way to developing a multi-moded system were
  different signals could be loaded over different
  modes.
• We reported a novel technique for measuring the
  modal content of a highly over-moded waveguides.
  We also, reported a technique for efficiently
  exiting the TE12 mode and the TE01 mode. Finally,
  we showed how to design and implement a
  polarization rotator for the TE12 mode.
• Over the 55 meter of WC475 losses of The TE01
  Mode is 1.08 Theory is 1.1. Losses of the TE12
  Mode is 4.5 to 5.1 theory is 2.8

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The Mode analyzer being Aligned
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The Mode Analyzer System
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TE12 Mode Launcher, a spacer for the mode
rotator, nonlinear taper and, transport line
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The end of the mode analyzer and transport line
is terminated by a multi-moded load
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The Wrap-Around Mode Converter, The Arc-Taper,
and the Mode Analyzer