TE01 Circular Waveguide Research Articles

A novel TM01-TE01 high-power microwave mode converter

This study presents the design and simulation of a novel type of TM01-TE01 mode converter for high-power microwave applications, which efficiently converts the TM01 circular waveguide mode into the TE01 circular waveguide mode. The converter is composed of three sections: power-dividing section, twist-waveguide section and power-combining section. These sections were analyzed and discussed respectively, and the whole converter structure was studied numerically. The results show that at the central frequency 12.5 GHz, the TM01-TE01 conversion loss of the converter made of aluminum is 0.05 dB and the bandwidth for S21 > 0.25 dB is 2.73 GHz. Moreover, the power-handling capacity is over 2 GW.

5-way radial power combiner at W-band by stacked waveguide micromachining

This work presents a 5-way radial power combiner using the very low loss TE01 circular waveguide mode with a performance in the state of art for W-band. The accomplished design shows excellent characteristics: the experimental prototype has a return loss better than 20 dB, with a balance for the amplitudes of (±0.4 dB) and (±3.5o) for the phases, in a 12.8% fractional bandwidth (12 GHz centered at 94 GHz). In order to obtain these specifications, required for instance in plasma diagnosis systems or in power amplifiers, a meticulous step-by-step procedure is developed for both, the design and the challenging manufacture at W-band by stacked waveguide micromachining. The first step involves the design of a mode transducer, from the TE10 mode in the rectangular waveguide to the low-loss TE01 mode in the circular waveguide, with very high purity. In the second step, a 5-way radial power divider is designed. These designs, in order to be successful, have incorporated all the constrains for the manufacturing at W-band, using an E-plane stacked waveguide arrangement for low losses. The power combiner, made up by the transducer and the divider, has been manufactured with great accuracy using a very challenging assembly process, providing experimental results in very good agreement with the theoretical results.

Tunable circularly-polarized turnstile-junction mode converter for high-power microwave applications**Project supported by the National Natural Science Foundation of China (Grant No. 61671457).

Frequency tunability has become a subject of concern in the field of high-power microwave (HPM) source research. However, little information about the corresponding mode converter is available. A tunable circularly-polarized turnstile-junction mode converter (TCTMC) for high-power microwave applications is presented in this paper. The input coaxial TEM mode is transformed into TE10 mode with different phase delays in four rectangular waveguides and then converted into a circularly-polarized TE11 circular waveguide mode. Besides, the rods are added to reduce or even eliminate the reflection. The innovations in this study are as follows. The tunning mechanism is added to the mode converter, which can change the effective length of rectangular waveguide and the distance between the rods installed upstream and the closest edge of the rectangular waveguide, thus improving the conversion efficiency and bandwidth. The conversion efficiency of TCTMC can reach above 98% over the frequency range of 1.42 GHz–2.29 GHz, and the frequency tunning bandwidth is about 47%. Significantly, TCTMC can obtain continuous high conversion efficiency of different frequency points with the change of tuning mechanism.

High-performance 16-way Ku-band radial power combiner based on the TE01-circular waveguide mode.

This work presents a 16-way Ku-band radial power combiner for high power and high frequency applications, using the very low loss TE01 circular waveguide mode. The accomplished design shows an excellent performance: the experimental prototype has a return loss better than 30 dB, with a balance for the amplitudes of (±0.15 dB) and (±2.5°) for the phases, in a 16.7% fractional bandwidth (2 GHz centered at 12 GHz). For obtaining these outstanding specifications, required, for instance, in high-frequency amplification or on plasma systems, a rigorous step-by-step procedure is presented. First, a high-purity mode transducer has been designed, from the TE10 mode in the rectangular waveguide to the TE01 mode in the circular waveguide, with very high attenuation (>50 dB) for the other propagating and evanescent modes in the circular waveguide. This transducer has been manufactured and measured in a back-to-back configuration, validating the design process. Second, an E-plane 16-way radial power divider has been designed, where the power is coupled from the 16 non-reduced-height radial standard waveguides into the TE01 circular waveguide mode, improving the insertion loss response and removing the usual tapered transformers of previous designs limiting the power handling. Finally, both the transducer and the divider have been assembled to make the final radial combiner. The prototype has been carefully manufactured, showing very good agreement between the measurements and the full-wave simulations.

Compact circular waveguide TM 02 ‐TE 11 mode converter

Using the concept of a metallic cylinder and a linearly tapered metallic baffle loaded in a circular waveguide to convert TM02 circular waveguide mode into TE11 circular waveguide mode, a novel and compact circular waveguide TM02-TE11 mode converter is designed, fabricated, and measured. The detailed design methods, experimental setups and results are presented in this study. Simulation results show that the purity of output fundamental TE11 mode of the converter exceeds 99.6% for an operating frequency of 9.4 GHz and the power capability is as high as 1.66 GW, the mode conversion efficiency is more than 90% from 9.23 to 9.83 GHz band and the relative bandwidth is about 6.38%. A good agreement between measurements and simulations is observed. The circular waveguide TM02-TE11 mode converter has many advantages, such as the simple structure, coaxial input and output, high conversion efficiency, proper bandwidth and high power-handling capability. When used in the field of high power microwave transmission and radiation, the proposed converter could significantly enhance the compactness of all the radiation systems.

Analysis of the multipactor effect in circular waveguides excited by two orthogonal polarization waves

Circular waveguides, either employed as resonant cavities or as irises connecting adjacent guides, are widely present in many passive components used in different applications (i.e., particle accelerators and satellite subsystems). In this paper, we present the study of the multipactor effect in circular waveguides considering the coexistence of the two polarizations of the fundamental TE11 circular waveguide mode. For a better understanding of the problem, only low multipactor orders have been explored as a function of the polarization ellipse eccentricity. Special attention has been paid to the linear and circular polarizations, but other more general configurations have also been explored.

Relativistic Fermi-Ulam map: Application to WEGA stellarator lower hybrid power operation

Analytical and numerical support is here provided in support of the explanation [Laqua et al., Plasma Phys. Controlled Fusion 56, 075022 (2014)] for the observation of ∼MeV electrons during Lower Hybrid (LH) operation in EC pre-heated plasma at the WEGA stellarator [Otte et al., Nukleonika, 57, 171 (2012)]. In the quoted experiments, LH power from the WEGA TE11 circular waveguide, 9 cm diameter, un-phased, 2.45 GHz antenna, is radiated into a B ≅ 0.5 T, n¯e ≅ 5 × 1017 1/m3 plasma at Te ≅ 10 eV bulk temperature with an EC-generated 50 keV population of electrons. In response, the fast electrons travel around flux or drift surfaces essentially without collisions, repeatedly interacting with the rf field close to the antenna mouth, and gaining energy in the process. Our WEGA antenna calculations indicate a predominantly standing electric field pattern at the antenna mouth. From a simple approximation of the corresponding Hamiltonian equations of motion, we derive here a relativistic generalization of the simplified area-preserving Fermi-Ulam (F-U) map [M. A. Lieberman and A. J. Lichtenberg, Phys. Rev. A 5, 1852 (1972), Lichtenberg et al., Physica D 1, 291 (1980)], allowing phase-space global stochasticity analysis. At typical WEGA plasma and antenna conditions, and with correlated phases between electron–antenna electric field interaction events, the F-U map and supporting numerical simulations predict an absolute energy barrier in the range of 300 keV. In contrast, with random phases intervening between interaction events, the electron energy can reach ∼MeV values, compatible with the measurements on WEGA [Laqua et al., Plasma Phys. Controlled Fusion 56, 075022 (2014)].

A mode converter to generate a Gaussian-like mode for injection into the VENUS electron cyclotron resonance ion source

A number of superconducting electron cyclotron resonance (ECR) ion sources use gyrotrons at either 24 or 28 GHz for ECR heating. In these systems, the microwave power is launched into the plasma using the TE01 circular waveguide mode. This is fundamentally different and may be less efficient than the typical rectangular, linearly polarized TE10 mode used for launching waves at lower frequencies. To improve the 28 GHz microwave coupling in VENUS, a TE01-HE11 mode conversion system has been built to test launching HE11 microwave power into the plasma chamber. The HE11 mode is a quasi-Gaussian, linearly polarized mode, which should couple strongly to the plasma electrons. The mode conversion is done in two steps. First, a 0.66 m long "snake" converts the TE01 mode to the TE11 mode. Second, a corrugated circular waveguide excites the HE11 mode, which is launched directly into the plasma chamber. The design concept draws on the development of similar devices used in tokamaks and stellerators. The first tests of the new coupling system are described below.

ULTRA-BROADBAND HIGH EFFICIENCY MODE CONVERTER

In this paper, we develop a small-sized mode converter with high performance, high conversion e-ciency and instantaneous bandwidth as high as 55%. This mode converter transforms energy from the TM01 flrst high-order mode towards the fundamental TE11 circular waveguide mode The proposed structure increases the free spurious operating bandwidth in comparison with the existing results in literature. An X/Ku-bands experiment prototype unit was designed, ensuring practical return losses better than 28dB and insertion losses less than 0.1dB (conversion e-ciency > 98:8%) within the entire frequency bandwidth ranging from 9.25GHz to 16.25GHz The presented architecture ofiers useful features such as very wide bandwidth, small size, easy achievement as well as excellent performance, which makes it very suitable for High-power microwave (HPM) sources that generate the TM01 circular waveguide mode. In these cases, the TE11 mode is needed since it has a convergent radiation pattern able to drive conventional antennas. Moreover, this compact concept is fully scalable to any millimeter frequency band.

A Dual-Band Coaxial Waveguide Mode Converter for High-Power Microwave Applications

A dual-band coaxial waveguide mode converter is investigated. In the converter, the TEM mode (Coa.TEM) and TM01 circular waveguide (Cir.TM01) mode are transformed simultaneously into TE11 coaxial waveguide (Coa.TE11) mode and TE11 circular waveguide (Cir.TE11) mode, respectively. The optimized geometrical dimensions are achieved by employing the mode coupling theory. A mode converter at 1.3 GHz and 5.0 GHz is designed, and conversion efficiencies of Coa.TEM-to-Coa.TE11 and Cir.TM01-to-Cir.TE11 are 99.88% and 99.70% at central frequency, respectively. Over the frequency ranges 1.15–1.51 GHz and 4.87–5.19 GHz, the conversion efficiency exceeds 90%. A good agreement between theoretical calculations and computer simulations is observed, demonstrating the feasibility of the dual-band mode converter.

A Mode Converter with Multi-waveguide Output from the TE01 Circular Waveguide Mode to the TE10 Rectangular Mode for Millimeter Wave Gyro-device Applications

A mode converter with multi-waveguide output for millimeter wave gyro-device applications is proposed in this article, which is used to convert the TE01 circular waveguide mode into the TE10 rectangular waveguide mode. Computer simulations with Ansoft HFSS code show that the energy transmission coefficient of larger than 95.96% may be reached in the frequency range from 34.094 GHz to 35.8 GHz (a bandwidth of 1.706 GHz) at a VSWR of lower than 1.5 for the input operating mode.

Effects of high‐frequency electromagnetic fields on DNA strand breaks using comet assay method

AbstractWe investigated whether exposure to high‐frequency electromagnetic fields causes DNA damage in cells, using the alkaline comet assay. The exposure device made for this study used a TE01 circular waveguide operating at a frequency of 2.45 GHz. Cells of the human brain tumor‐derived MO54 cell line were exposed to an electromagnetic field (input power: 7.8 W, average SAR in the middle well of an annular culture plate: CW 50 W/kg) for 2 hours and the tail moments of the cells in the inner, middle, and outer wells of the plate were compared with those of sham‐exposed cells. There was no significant difference between the high‐frequency electromagnetic field‐exposed groups and the sham‐exposed groups. Three studies performed under the same conditions gave similar results. Next, cells were exposed to a stronger electromagnetic field (input power: 13 W, average SAR in the middle well: CW 100 W/kg) for 2 hours and compared with sham‐exposed cells. There was also no significant difference in the tail moments of cells in the inner, middle, and outer wells of the plate in the high‐frequency electromagnetic field‐exposed groups and the sham‐exposed groups. These findings suggest that a high‐frequency electromagnetic field does not cause direct DNA damage, and does not induce DNA strand breaks, even at a SAR of 100 W/kg. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 9–15, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10075

Development of high powerX-band semiconductor microwave switch for pulse compression systems of future linear colliders

We describe development of semiconductor X-band high-power RF switches. The target applications are high-power RF pulse compression systems for future linear colliders. We describe the design methodology of the architecture of the whole switch systems. We present the scaling law that governs the relation between power handling capability and number of elements. We designed and built several active waveguide windows for the active element. The waveguide window is a silicon wafer with an array of four hundred PIN/NIP diodes covering the surface of the window. This waveguide window is located in an over-moded TE01 circular waveguide. The results of high power RF measurements of the active waveguide window are presented. The experiment is performed at power levels of a few megawatts at X-band.

Fundamental-mode amplifier performance of the NRL ubitron

An experimental and theoretical research program to study the ubitron-FEL interaction is in progress at the Naval Research Laboratory, including both fundamental and harmonic modes of operation. Operation of a ubitron-FEL amplifier using the fundamental wiggler harmonic interaction with the TE11 circular-waveguide mode is reported here. The experiment employs a 190–250 keV electron beam with currents up to 37 A, using a helical wiggler/axial guide-field configuration. Small-signal gains as high as 17–19 dB have been observed in the 13–18 GHz frequency band, corresponding to a gain per free-space wavelength approaching 1.5 dB/λ. These results were obtained using a modified SLAC klystron gun. Improved performance is expected using a higher-current (100 A), higher-quality electron gun currently being installed. The theoretical program includes a nonlinear analysis of the rf and electron beam interaction while propagating through a cylindrical waveguide with a helical-wiggler field and an axial guide field. The analysis includes beam injection into the wiggler, wiggler inhomogenieties, efficiency enhancement by means of tapered wigglers, beam thermal effects and harmonic interactions. The experimental results presented in this paper are in reasonable agreement with the nonlinear simulation of the interaction in the Raman regime.

Mutual admittance between circular apertures on a large conducting sphere

Explicit expressions for the self admittance and the mutual admittance Yij between two arbitrarily polarized circular apertures are presented. The aperture field distribution is that of TE11 circular waveguide mode. The analysis makes use of a spherical mode expansion and of the addition theorem for tesseral harmonics. Numerical results show Yij as a function of angular separation θ. The E‐plane coupling exhibits asymptotic (large θ) behavior consistent with the lowest “hard” surface ray order results. The slope of the H‐plane coupling for large values of θ does not correspond to the lowest‐order “soft” surface ray attenuation, but rather to that of the lowest‐order “hard” ray. This behavior is explained.

An electron synchrotron maser based on an intense relativistic electron beam

An electron cyclotron maser has been operated with an output of ∼50 MW of coherent radiation at a frequency ∼8 GHz. A magnetic field configuration is described which effectively converts streaming electron energy into energy transverse to the streaming direction. The redistribution of beam energy makes available a source of free energy to be converted, via an instability, into radiation at the Doppler-shifted relativistic electron cyclotron frequency. A nonlinear theoretical analysis shows that the coherent synchrotron radiation is a relativistic negative mass type instability reflecting the fact that the cyclotron frequency is a function of the electron energy. The emission was narrow band with a coherence time ≳50 nsec, and was also spatially coherent being primarily radiated into the TE01 circular waveguide mode. The potential for making a frequency tunable maser by employing a tapered drift tube has also been demonstrated.

Room-Temperature Faraday Rotation in n-Type InSb Films at 23.4 GHz

Measurements were made of Faraday rotation on ∼1 μ thick evaporated and recrystallized polycrystalline InSb films. The experiments were carried out at room temperature using TE11 circular waveguide with dc magnetic fields up to 7 kOe. Rotations on the order of 50 deg were observed. The experimental results are in reasonable agreement with a theoretical model based on free-carrier Faraday rotation, including multiple reflections, using the mobilities and carrier concentrations found by separate dc measurements.