Yu Xinhua

Phase rematch on overmoded waveguide mode converter for BWO

The overmoded transmission line is often adopted by high-power millimeter wave system, so the influence of various distortion has to be evaluated. The distortion of waveguide can be utilized if we know its influence to the modes. So, the questions of mode coupling should be studied which arising from waveguide distortion. For the output mode of Backward wave oscillator and Virtual cathode oscillator is often TM01 mode and TM0n mixed modes. The TM0n-TM01 mode converter can adopt gradual radius changes of the waveguide, and TM01 mode radiate outside only converter to TE11 mode, so the thorough study of the structure and characteristic of TM01-TE11 mode converter is needed. The size of a waveguide is large under a high-power situation, thus it is necessary to take account more waves and their mutual coupling as well as the attenuation of circular waveguide and the option of coupling mode etc. Heavy considerations have been given to the influence of multimode factor, backward wave, ohmic losses carried from metal wall, modes choice and phase rematch.

High power bend mode converter in overmoded waveguide for gyroklystron

The output mode of gyroklystron TE₀₁ and TE₀₂ are very inconvenient for direct use, so it must be taken a mode conversion, especially high power mode conversion. And its mode converter adopt mostly the following sequence: 1. TE_on (gyrotron) -TE₀₁-TE₁₁-HE₁₁ (antenna) 2. TE_on (gyrotron) -TE₀₁-TM₁₁-HE₁₁ (antenna) The first sequence has been employed here, adopting perturbation of axis curved, and arriving at an efficient circular waveguide converter with conversion efficiency reaching 98% and bandwidth exceeding 5%, while its overlength(881.6mm) confines its practice to a limited field with inconvenient machining. Thus the second sequence is chosen to for better usage, with TM₁₁ as the intermediate polarized mode, HE₁₁ the latter one, to radiate outside, during the process of which TE₀₁-TM₁₁ conversion is the most important. The same phase velocity of TE₀₁ and TM₁₁ made a proper selection of a part of the single-curvature circular waveguide fit the realization of their conversion well.

35 GHz widebandTE01-HE11 mode converter for Gyroklystron applications

Future plans call for increasing the uplink and downlink frequencies used for communication with deep space probes from the present 2 GHz and 8 GHz bands into the millimeter band, 33-35GHz. High power transmitters, on the order of several hundred kilowatts will thus be required in the millimeter band. The only sources presently capable of producing this power level are Gyro devices, such as Gyroklystron, Gryo-TWT and Gyrotron. In order to produce these power levels Gyro devices employ unconventional interaction cavities. These cavities resonate in higher order waveguide modes, and typically deliver the output signal into an oversize circular waveguide in a higher order waveguide mode, such as a TEoη mode. If the power is to be used constructively, for example to illuminate a reflector antenna, a Gaussian beam is typically required. Transformation of the TEoη mode into a Gaussian beam is achieved through the use of several mode converters. One possible system of mode converters is depicted in Figure 1. Here the TEoi mode is emitted by the Gyroklystron into highly overmoded circular waveguide. The TEoi mode then enters the TEoi-TMn mode converter, which consists of circular waveguide sinusoidal bend. The TMn mode then enters a corrugated TMn -HEn mode converter, and finally exits into space through a corrugated horn section.

Design of a novel 30.5GHz transition for gyro-TWT

A novel 30.5GHz transition section used to transmit TE01 mode efficiently is designed. The calculations indicate that the section can transmit TE01 mode with efficiency over 0.989 within a bandwidth of 1.7GHz. Comparison between the section and linear one shows that the former is much shorter than the latter, and is very helpful for construction of a compact microwave device.

Study of complex mode converter for 3mm-wave complex cavity Gyrotron

A complex mode converter consisting of waveguide and quasi-optical mode converters is proposed to utilize high mode-transforming efficiency of the former and compact size of the latter. Radiation patterns of quasi-optical mode converter with TE0n modes as its feeds are got by numerical calculation method based on the theory of vector diffraction integral. These patterns show that the radiation pattern is more similar to the wanted Gauss pattern when the feed takes the mode TE01. So the conclusion is that the complex mode converter, transforming TE0n mode to TE01 mode by waveguide converter and then TE01 mode to good Gauss pattern, is helpful to hold higher converting efficiency and smaller size than waveguide or quasi-optical one alone.

Analysis and simulation of pseudospark discharge

Pseudospark discharges are sources of intense electron beams. Reported in this paper are theoretical studies of the pseudospark discharges. We have developed a theoretical and computational model to study the initiation phase of pseudospark discharges via PIC-MCC method. From the numerical results,we have identified a sequence of physical events. In spite of the approximation in this model, the picture which has emerged provides insight into the virtual anode moving which were observed by previous experiments.