Multi-mode coupling wave theory for helically corrugated waveguide

Helically corrugated waveguide has been used in various applications such as gyro-backward wave oscillators, gyro-traveling wave amplifier and microwave pulse compressor. A fast prediction of the dispersion characteristic of the operating eigenwave is very important when designing a helically corrugated waveguide. In this paper, multi-mode coupling wave equations were developed based on the perturbation method. This method was then used to analyze a five-fold helically corrugated waveguide used for X-band microwave compression. The calculated result from this analysis was found to be in excellent agreement with the results from numerical simulation using CST Microwave Studio and vector network analyzer measurements

Low loss transmission line for a 3.4-kW, 93-GHz gyro-traveling-wave amplifier

In this article, a transmission line system for the propagation of millimeter-wave radiation is presented. The full system includes a TE11-to-TE01 mode converter, waveguide tapers, miter bends, and many straight sections. The design of each of these components is described, and the optimized simulation results are given. The mode converter shows a greater than 96% mode conversion efficiency that can be achieved over a 2% bandwidth at the ${W}$ -band. The miter bends demonstrate a transmission loss of 0.04 dB each over the same bandwidth when they are configured to introduce a mixture of higher order waveguide modes before the reflecting surface. An example transmission line system with a propagation length of 20 m, inclusive of four 90° bends with an oxygen-free high conductivity (OFHC) copper waveguide material, was studied over a 90-96-GHz frequency range and showed a 0.84-dB transmission loss at 93 GHz

Status and ongoing development of a KW-level broadband W-band gyro-TWA

A broadband, kW-level gyrotron traveling wave amplifier (gyro-TWA) in W-band was developed based on a helically corrugated interaction region and a cusp electron gun. Experiments were carried out to demonstrate the versatility of the gyro-TWA and to investigate its broad instantaneous amplification bandwidth. Following the successful prototyping, research is being carried out to improve the stability of the amplifier and widen its capability for continuous wave operation for long-range high-data-rate communication applications

Feedhorn synthesis using a parameterized aperture field distribution

In this letter, we present an improved method for synthesizing smooth-profiled horns. A direct connection between the mode compositions and far-field parameters was established by utilizing a parameterized aperture field distribution and the field decomposition method. It speeds up the optimization process by a factor of 5. The requirements for the aperture field to maintain a constant directivity were studied based on the method. A feedhorn was optimized for a W-band gyro-TWA with a 0.7 dB variation of the directivity within a bandwidth of 10%

A high-power Ka-band free electron maser, defined by a 2D – 1D Bragg lasing cavity

One of the on-going research programs, at the University of Strathclyde, involves the development of high-power, pulsed, Free-Electron Masers (FEMs) with the lasing cavity defined using periodic corrugations on the drift-tube walls 1-4 . These corrugations form 1D and 2D Bragg resonators, whose reflection bands determine the dominant resonance of the maser 5 . Proper selection of the FEM undulator magnetic field strength, allows for efficient extraction of energy from a mildly relativistic (400 - 500 keV) electron beam at the resonant frequency of the lasing cavity, leading to monochromatic output at power levels of several tens of megawatts and pulse durations of ~150ns (determined primarily by the pulse duration of the driving power supply of ~250ns)

Numerical and Experimental Validation of the Passive Performance of a Co-Harmonic Gyro-Multiplier Interaction Region

The azimuthally rippled cavity for a large orbit, co-harmonic gyro-multiplier, designed to operate at the 2nd and 4th harmonics, at frequencies of 37.5 GHz and 75 GHz, respectively, has been numerically and experimentally confirmed to be insensitive to the polarization of quadrupole, TE2,n-like modes, including the 2nd harmonic operating mode of the multiplier, a cylindrical TE2,2-like waveguide mode. To test the cavity with this mode required the design, construction and measurement of ripple wall mode converters, converting the cylindrical TE2,1 mode to the TE2,2 mode. These were designed to operate at a central frequency of ~37.9 GHz, with predicted mode purity of better than 85%, and 3 dB bandwidth of 161 MHz. The constructed converter had a central operating frequency of 37.7 GHz, with S-parameter measurements used to infer suitable mode purity, and an operational 3 dB bandwidth of 50 MHz. This has allowed farfield phase measurements of the corrugated cavity to be conducted, where the orientation of the geometry to the polarization of both the TE2,1 and TE2,2 modes was shown to have no effect on the dispersion

Microwave undulator to generate short-wavelength FEL radiation

This paper presents the design and the measurement of a short section of a 36 GHz microwave undulator, as well as the electron beam dynamic and the spectrum of the FEL radiation based on the microwave undulator. The operation of the microwave undulator at a higher frequency of 94 GHz is also discussed

Experimental study of microwave pulse compression using a five-fold helically corrugated waveguide

This paper presents the experimental study of microwave pulse compression using a five-fold helically corrugated waveguide. In the experiment, the maximum power compression ratio of 25.2 was achieved by compressing an input microwave pulse of 80 ns duration and 9.65 GHz to 9.05 GHz frequency swept range into a 1.6 ns Gaussian-envelope pulse. For an average input power of 5.8 kW generated by a conventional traveling wave tube, a peak pulse output power of 144.8 kW was measured corresponding to an energy efficiency of 66.3%

Beam dynamic study of a Ka-band microwave undulator and its potential drive sources

Microwave undulators (MUs) have great potential to be an alternative solution to permanent magnet undulators in a free electron laser (FEL) when shorter undulator periods are required. In this paper, the factors that affect the choice of the high-power drive sources were studied via a Ka-band cavity-type MU with a corrugated waveguide proposed for the CompactLight X-ray FEL. They include the technology of the high-power vacuum electronic devices, the quality factor of the MU cavity that was demonstrated by prototyping a short section of the MU structure, and the beam dynamic study of the electrons’ trajectories inside the MU. It showed that at high beam energy, a high-power oscillator is feasible to be used as the drive source. At low beam energy, the maximum transverse drift distance becomes larger therefore an amplifier has to be used to minimize the drift distance of the electrons by controlling the injection phase

Design and experiments of a five-fold helically corrugated waveguide for microwave pulse compression

Metal waveguide can be used as a dispersive medium to convert long duration, lower power pulses into short, higher peak power pulses. This provides an advanced method to generate radiation with gigawatts power in the millimeter and sub-millimeter wavelength range by compressing a megawatt level long duration pulse. In this paper, a five-fold helically corrugated waveguide operating in X-band was designed and constructed. The experiments conducted show that a 5.75 kW average power microwave pulse with a 6% bandwidth and duration of 80 ns can be compressed into a 144.8 kW, 1.6 ns pulse with a power compression factor of 25.2