Zhaojun Zhu

DESIGN OF DIFFERENT SELECTIVITY DUAL-MODE FILTERS WITH E-SHAPED RESONATOR

A novel bandpass fllter design method of achieving difierent selectivity based on E-shaped dual-mode resonator is presented. The characteristic of the E-shaped dual-mode resonator is investigated. The technique of utilizing capacitive and inductive input-output cross-coupling to generate two adjustable transmission zeros at stopband is explored intensively. Advantages of this type of fllter are not only its dual-mode resonator and miniaturization, but also its controllable transmission zeros. The coupling scheme is presented to model the operations of these fllters. Four dual-mode microstrip BPFs have been designed, fabricated, and measured. Both the simulated and measured results are presented. The exemplary fllters verify the feasibility of the new design method.

Application of CAD Simulation Technology in Microwave Tube Research and Fabrication

The application of 3D EM simulation codes and PIC simulation codes, including CST Microwave Studio, Ansoft HFSS, Mafia and Magic, has been investigated in the microwave tube research and fabrication. A S-band helical traveling-wave tube has been fabricated and a X-band magnetron dissected. The simulation results meet the measurements very well. This paper supply with the valuable reference in microwave tube research and fabrication with low cost and high accuracy

Efficiency Improvement of Helix Traveling-Wave Tube

The 2.5-dimensional (2.5-D) particle-in-cell (PIC) simulation code MAGIC and 3-D electromagnetic simulation code HFSS were used to investigate the helix traveling-wave tube (TWT) with positive-negative tapering for efficiency improvement. Some key parameters were analyzed, including high-frequency parameters, non-synchronous parameter, gain parameter, and electron phase. A positively-negatively tapered helix TWT were designed and fabricated. The measured efficiency of the tapered TWT reaches 29%, while that of the non-tapered TWT is 19%. The simulation method of this paper has the averagely relative error of about 5%.

3D Simulation of 18-vane 5.8 GHz Magnetron

An 18-vane 5.8 GHz magnetron simulation model has been fabricated by 3D EM simulation code HFSS and particle in cell (PIC) code Magic3D. The π and π − 1 mode frequency was calculated and the mode segregation was obtained by cold test simulation using HFSS. The performance of the magnetron was benchmarked by hot test simulation using PIC code Magic3D.

High-Selectivity UWB Filters with Adjustable Transmission Zeros

This letter proposes a novel ultra-wideband (UWB) bandpass filter with compact size and high-selectivity performance. The filter has been studied and implemented through multiple-mode resonator (MMR) using new coupling schemes such as capacitive source-load (S-L) coupling/inductive source-load (S-L) coupling. By properly adjusting the length and width of these stubs, its first four resonant modes can be allocated within the 3.1-10.6 GHz passband, whereas its fifth resonant mode is placed above 16.0 GHz. Two transmission zeros (an inherent transmission zero and an additional transmission zero) can be produced. Moreover, the position of the additional zero can be controlled by adjusting the direct coupling inductance/capacitance. Simulated and measured results are in good agreement indicating that the proposed BPF has a passband (3.0-11.0 GHz)/(2.92-10.6 GHz) and a wide stopband width with 23 dB/25 dB attenuation up to 27.0 GHz. The group delay of the filter is relatively constant and less than 0.65 ns/0.52 ns over the operating pass band.

π-Mode Stopband Characteristics Caused by Asymmetries of Support Rod and Loaded Metal in Helix Structures

A fully three-dimensional (3-D) helix traveling-wave tube (TWT) simulation model has been developed using a commercial electromagnetic (EM) finite-element-method (FEM) code. The model is used to simulate the π-mode stopband characteristics caused by asymmetries of support rods and metal loading in helix TWTs. Compared with the previous analytical method, the present simulation method can calculate the natural stopband of the π-mode, the absolute π-mode frequency, and the asymmetric effect of metal loading.

The study of dispersion shaping and harmonic suppression in helix TWT

In the helix traveling-wave tube (TWT), the dispersion shaping and harmonic suppression is studied from theory analysis to simulation investigation in this paper. The negative dispersion is formed to suppress the harmonic content by the loaded slow-wave structure (SWS). After the dispersion shaping, the fundamental output power increases about 40 W and the second harmonic level decreases about 6 dB at the low end of the frequency band.

Calculation of high frequency characteristics for ridge-loaded helical slow-wave structure

Based on the finite number of vanes model, the high frequency characteristics of ridge-loaded helical slow-wave structure (SWS) are analyzed with field match method. This paper presents the sector equivalent method for loaded ridge and support rod, so the process of solution is simplified. The dispersion characteristics, interaction impedance and attenuation are derived for ridge-loaded helical SWS. The calculations are compared with the results of three-dimensional (3-D) electromagnetic (EM) simulation.

Analysis of the Energy Output System for 5.8 GHz Magnetron

In this paper, a kind of microwave energy-output system of the 5.8 GHz 18-vane magnetron was designed and discussed. The QL of the anode was calculated by MAGIC3D. The impact on the energy output system by coaxial impedance converter and short plane of the waveguide was discussed and simulated by CST Microwave Studio. At last we give the structure size of the energy output system for engineering design reference.

Analysis of an inhomogenously ridge-loaded helix SWS used in MPM

In this paper, the ridge-loaded helix slow-wave-structure (SWS) used in microwave power module (MPM) is presented. Based on the finite vane model, the loaded ridge and the support rod in ridge are equalized to the sector waveguides with regard to the helix tape thickness. The dispersion characteristic equation is newly derived. The calculation results meet the measurements very well.