A Continuously Tunable Ka-Band Gyrotron

An experimental study was carried out to test the concept of using a gyrotron with a tapered circuit in a uniform magnetic field as a high-power tunable source of millimeter-wave radiation. It was demonstrated that the device can be used as either an oscillator or an amplifier with the operating frequency tunable by varying the magnetic field. In the oscillator mode, the tube produced a peak output power of 500-750 W with the frequency continuously tunable from 30 to 39 GHz. As an amplifier mode, the tube demonstrated an electronic gain of ~23 dB at a magnetically tunable center frequency with an instantaneous bandwidth of ~5 percent. The stability characteristics of the amplifier were also investigated.     

Gyrotron Radiation Affected by a Controlled Modulated Reflector: High Power Experiment

An experiment performed with the gyrotrons of the TJ-II ECRH system has been performed to influence the gyrotron output radiation with a relatively weak wave returned from an external mechanically modulated reflector. An original method is proposed for directly measuring the wavelength of electromagnetic radiation in the free space. The method has been demonstrated in measurements of the wavelength of a high-power gyrotron radiation in the millimeter wavelength range used for plasma ECR heating in the TJ-II stellarator.     

Design of Ka-Band Doubler

This paper describes a Ka-band frequency doubler with balanced structure consisting of Schottky barrier diodes.Input frequency is 1320GHz.Output frequency is 2640GHz and conversion loss 11.2±1.8Db.It can extend microwave signal source to Ka-band.     

Finline Integrated Trans-receiver at Ka-Band

This paper describes the design and development of Integrated Finline Trans-receiver at Ka-Band. Integrated trans-receiver has been designed for Simplex Voice Communication System. The trans-receiver includes a modulator, duplexer and a mixer integrated together on a single substrate RT Duroid 5880. Two Millimeter Wave Gunn sources, one as transmit source and the other one as Local Oscillator source, in Waveguide are connected externally. The system has been realised and tested with the integrated trans-receiver unit for ASK voice Communication System for a range of 2.5 KM LOS. The system is highly useful for short-range communication systems such as Hand-held Millimeter Wave Radio.     

Construction of Ka-Band Preselected Harmonic Mixer

In this paper, a new method to realize pre-selected harmonic mixer is introduced. It includes a harmonic mixer, and a YIG turning filter (YTF) design. A digital driver is used for YTF, which can realize linearization modification and temperature compensation. The spectrum analyzer's out scanning voltage is given an A/D conversion and interface to digital driver.     

Integrated Front-End Radar Receivers at Ka-Band

This paper describes the Integrated Finline Front-end Radar Receivers at Ka-Band. The Front-receivers developed for Radar applications include combining of finline components on a single MIC substrate with various planar transmission lines. The integrated systems so developed have better noise figure and control over phase and gain imbalances as compared to discrete component systems. Two types of Integrated Front-ends Radar receivers are described here. The developed systems are highly compact and reliable.     

The design of attenuation films in Ka-Band

The inherent deviation between measured and theoretical values of attenuation A (db) and rotary angles are caused by using the substrate with attenuation films, depending on the theory of attenuation and transmission property of fundamental mode TE^o ₁₁ in cylindrical waveguides. This paper also discussed the phase problem. According strictly to the wave equation and Poynting's vector, the relation between A (db) and the surface resistance has been deduced. These three main parameters have exact formulas. Some assumptions whose exactitude really exist are based on precise constants and it is thus unnecessary to consider the polarization.We have designd and fabricated Ka-band attenuation films with the method metioned in this paper.The measurement results are very good.The author has not yet found other papers reporting the design of attenuation films.     

Development of Broad Band VCO at Ka-Band

A broad band VCO has been developed at Ka-band for FMCW Radar applications. To achieve a wide range of frequency variation, VCO has been designed in series configuration. Design steps have been presented. VCO exhibits a tuning range of 600 MHz with the power output of 50 mw, when the controlled varactor voltage varies from 7.5 volts to 15 volts. Frequency drift with temperature has been contained within 30 MHz using a proportionally controlled DC heater module over the temperature range of 0°C to +55°C. Phase Noise of the oscillator measured at the mid and extreme frequencies is about -70 dBc/kHz at 10 kHz away from the carrier. The experimental circuit and measured performance is also presented.     

Efficiency Enhancement of the Relativistic Gyrotron

Different numerical models of relativistic gyrotrons are compared. The possibility of optimizing the cavity parameters is considered. Dependences of the efficiency and optimal parameters on the accelerating voltage are obtained. It is shown that an efficiency of 35 to 45% can be achieved in a strongly relativistic gyrotron without energy recovery, and of 60 to 70% in the case of single-stage recovery of the electron beam energy.     

Gyrotron cavity with an optimized profile

A modified gyrotron cavity is proposed. It is shown that an optimized profile of the cavity wall allows decreasing the maximal thermal load on the wall while the electron efficiency stays high, which makes it possible to achieve higher magnitudes of output gyrotron power.     

Measurements of Building Construction Materials at Ka-Band

Millimeter waves is expected to be used for indoor broadband wireless access for its rich frequency spectrum resources. To implement the indoor MMW wireless system, it is important to know its propagation characteristics in building, which are governed by the transmission properties of construction materials. This paper focuses on the measurements of reflection characteristics and refractive indices of some interior construction materials (such as glass, brick, plasterboard, silencing board, etc.) at Ka–band. The free–space reflection method was used to measure the reflection and transmission coefficients. Then the complex refractive indices of various materials could be calculated by using the Fresnel's formula.     

Gyrotron based on a superconducting magnet

The replacement of conventional pulsed magnetic field coils previously used to generate the intra-cavity B-field with an 11T superconducting magnet is reported. The resulting more stable mm-wave output pulse is shown and the refurbishment requirements of both the field emission, field-immersed, cold cathode and Marx bank spark gaps demonstrated. This system proved to be tunable, oscillating from 20GHz up to 110GHz, with peak power levels of 450kW and 300kW respectively. Other operating parameters were also examined including mm-wave pulse length as a function of anode-cathode position. The pulse length increased from 87±6ns to 310±10ns with a 2.5 cm horizontal transit of the cathode away from the anode. A similar effect was witnessed with the increase of the intra-cavity B-field from 1.00T to 5.00T resulting in the mm-wave pulse duration increasing from 250±40ns. Second harmonic operation of the cavity resulted in 0.5kW of radiation observed at 96GHz. The pulse-to-pulse mm-wave stability coupled with the mode selectivity of the ohmic-Q-dominated cavity resulted in the identification of several oscillating modes including the TE₁₂, cut-off frequency 21.1 GHz, the TE₀₂, cut-off frequency 29.1 GHz, the TE₃₅ at 74 GHz and the TE_14,2, at 88GHz.     

High-Efficient Mode Converter for ITER Gyrotron

A high-efficiency mode converter of the ITER gyrotron operating mode into the Gaussian wave beam has been developed. It includes an irradiating waveguide with shallow deformation and profiled quasi-optical mirrors to increase the Gaussian content. Low-power tests were carried out with a TE_25.10 mode exciter and a mode converter. A prototype of the short-pulsed 170 GHz gymtmn with the new converter was manufactured and tested. Diffraction losses measured inside the tube were less then 2% at the 1 MW power level. A high Gaussian mode content in the output beam has been also demonstrated.     

Efficiency Enhancement of the Relativistic Gyrotron

The possibilities to increase efficiency of relativistic gyrotrons by optimizing gyrotron parameters have been considered and different calculated models of gyrotrons, compared. Dependencies of the efficiency and optimal parameters on the accelerating voltage have been obtained. It is shown that efficiency of 35-45% can be achieved in a strongly relativistic gyrotron without energy recovery, and 60-70%, in the device with single stage energy recovery of the electron beam.     

Experimental Study of a Ka-Band Cylindrical Open Resonator

A study of the electrodynamical properties of a Ka-band gyrotron open resonator was experimentally conducted. Experiments were accomplished to measure resonant frequencies and their respective loaded quality factors for TE modes in the frequency range from 26 to 40 GHz. In particular, a perturbation technique was used to determine the axial, radial and azimuthal electric field profiles, as an identification method of the TE₀₂₁ mode operating around 35 GHz. In any experimental event, good agreement with the values predicted by theory was found.     

Reflections Influence on the Gyrotron Oscillation Regimes

Influence of some types of reflections on oscillatory processes in gyrotrons has been studied. Estimations of the conditions for oscillation stability in the presence of a reflected signal are given. The processes in a gyrotron with a fixed structure of the RF field have been modeled numerically, and enhancement of the spectrum signal in the presence of reflections has been studied.     

Whispering-Gallery-Mode Gyrotron Operation with a Quasi-Optical Antenna

High-frequency gyrotron operation in the TE611 whispering gallery mode is reported. Powers as high as 112 kW and an efficiency as high as 25.4 percent have been obtained. In addition to the TE611 mode, ten other fundamental modes with frequencies between 133.9 and 216.4 GHz were observed. A quasi-optical antenna for whispering gallery modes has been tested for the TE611 mode. The combination of this antenna and a reflector produces a well-collimated linearly polarized RF beam suitable for electron cyclotron resonance heating (ECRH) or plasma diagnostics. The experimental conversion efficiency was determined to be 89 percent, and the cross polarization was down by 25 dB. A new quasi-optical transmission line employing this antenna has also been tested with the gyrotron. The absence of mode competition for the TE611 mode, as well as the efficient conversion of the output radiation into a linearly polarized Gaussian-like beam, substantiates the arguments for operation in surface modes in high-power gyrotrons. The implications of quasi-optical antennas for megawatt gyrotron window design are discussed.     

Influence of Aftercavity Interaction on Gyrotron Efficiency

We consider theoretically the influence of interaction of a used electron beam with a concurrent wave in the output waveguide transition outside the cavity on the efficiency and energy recovery in a powerful millimeter-wave gyrotron. Without energy recovery, parasitic interaction in the transition reduces the efficiency and output power of a gyrotron by 5–10%. In a gyrotron with energy recovery, losses due to interaction in the transition can become most significant compared with other losses, and the efficiency is reduced by 20–30%. The influence of the transition decreases with decreasing transition length and increasing ratio of the maximum radius to the minimum radius of the transition.