Hyun-Jun Ha

Theoretical Study for Folded Waveguide Traveling Wave Tube

A wideband folded waveguide traveling-wave tube (TWT) amplifier has advantages of simpler coupling structures and robust structure over the conventional helix TWT. The phase velocity of waves in folded waveguide is slowed down to the velocity of electron beam. Slow-wave interaction with the electron beam in folded waveguide is studied in a linear fashion. For a cold beam, the linear theory predicts a gain of 2 dB/cm and a bandwidth of 37% at the center frequency of 14 GHz. A closed algebraic dispersion relation for the frequency and the axial phase shift per period is obtained using an equivalent circuit model. Numerical solution calculated from the dispersion relation and three-dimensional electromagnetic code, HFSS simulations predict a mode coalescing in the folded waveguide. And a theoretical phase velocity prediction of the electromagnetic wave in this circuit is verified by HFSS simulations.

Wide-band semivane and heavily dielectric loaded helix traveling-wave tubes

Theoretical simulation of the dispersion and interaction impedance characteristics of a semivane loaded negative dispersion helical slow-wave structure, which is a slight variant of a conventional vane-loaded helix of a wide-band traveling-wave tube (TWT), was validated for the nonresonant perturbation measurement. While the experimental and theoretical results agreed well with respect to interaction impedance for both the semivane structure and the structure without vanes, there was disagreement found with respect to the dispersion characteristics of the semivane structure, which was explained quantitatively by the deformation that had taken place in assembling the structure. The output performance of a TWT using the semivane structure fairly agreed with the prediction by an in-house one-dimensional nonlinear Lagrangian code, with respect to saturated output power (/spl sim/50 W), saturated gain (/spl sim/40 dB), and lower-band-edge second harmonic level (/spl sim/-5 dBc), in the operating frequency range of 6-18 GHz, except at the low frequency end of the operating band, where the saturated power was less and the second harmonic level higher than predicted, a finding that may be attributed to the departure of the deformed structure from exhibiting a negative dispersion at the lower band edge.

Three-dimensional particle-in-cell simulation of 10-vane strapped magnetron oscillator

The performance of a 10-vane strapped magnetron oscillator used in microwave ovens was benchmarked using the three-dimensional particle-in-cell (PIC) code MAGIC3D. The formation of the five electron spokes in the oscillation region confirms the /spl pi/-mode oscillation of a 10-vane strapped resonator showing its mode separation with the adjacent mode to be 82%. The measured operating frequency of 2.465 GHz and the saturated output power of 1.04 kW are in good agreement with the simulated values of 2.470 GHz and 1.07 kW, respectively. The magnetron with an efficiency of 75% is operated at the beam voltage of 4.3 kV, the anode current of 0.33 A, and the cathode current of 1.08 A when the external axial magnetic field of 0.19 T is applied. In addition, the measured harmonic components of the radiated output are compared with the simulated one estimated by Fourier transformation of an induced radio-frequency voltage signal, showing good agreement.

Investigation of folded waveguide TWT

The folded waveguide TWT using a linear electron beam is being investigated both theoretically and experimentally. A nonlinear theory is studied. The cold test is performed comparing with the numerical prediction. The experimental work is now underway and will be presented.

EXPERIMENTAL INVESTIGATION OF Ku-BAND FOLDED WAVEGUIDE TWT*

Ku-band (14-14.5 GHz) folded waveguide TWT operated at the beam voltage and current of 6 kV and 0.1 A, respectively, has been studied experimentally. The RF circuit is designed by using a linear theory [1] and its predicted gain for a single stage is 20 dB. The cold test of the assembled RF circuit shows a good agreement with the theoretical prediction [2].

Nonlinear theory of folded waveguide TWT

The authors present a nonlinear theory of folded waveguide travelling wave tubes.

Investigation on wideband tubes

Ku-band folded waveguide type TWT is fabricated. This particular type of TWT draws attention for its robust structure and easier coupling. The linear theory predicts a gain of 2 dB/cm and a bandwidth 37% at the center frequency of 14 GHz when the parameters of the circuit are b=0.469 cm, l=0.746 cm, h=2.017 cm. A dispersion relation is derived using an equivalent circuit model and is compared with HFSS simulation. The electron beam and its diagnostics, solenoid, RF circuit, and other components are discussed.

Focusing of Electron Beam in Double-Gated Field Emitter Arrays

Field emitter arrays (FEAs) draws a great attention in field emission displays and high frequency applications. A good control of electron beam is one of critical issues in many applications. Focusing condition by analytical calculation double-gated FEA is compared with SNU-FEAT code.