Jishi Ren

A new improved slow wave structure for broadband millimeter wave traveling wave tubes

There continues to be increasing demands for high performance broadband traveling wave tubes (TWTs) at millimeter waves (MMW) for communications applications. The high performance requirements for these TWTs include relatively high power, efficiency, and good linearity. The smaller size and the associated effects of the small size on the manufacture of these MMW TWTs, together with the relatively high power requirements, provide motivation for innovative improvements in slow wave structures (SWSs) for high performance, high power MMW TWTs.

Characterizations of crystal-grid filter in quasi-optical circuits using 3-D anisotropic FDTD formulation and Floquet boundary condition

An analysis of anisotropic crystal grid-plate used in quasi-optical circuits is presented in this paper. The 3-D anisotropy FDTD formulation using permeability tensor is directly implemented with necessary treatments on the local fields specified by the relationship between the electric displacement and field, as well as on the air-anisotropy interface. Floquet boundary condition using one unit cell and a pulse excitation are employed for analysis of the large grid-anisotropy plate. The simulated results of field rotation, transmittance, reflectance, as well as the effects of the grid on the anisotropy plate are obtained and show excellent agreement with experiments.

Ku band, 100 kW traveling wave tube based on large quasi-optical spatial power combining array

We report here further development of the novel quasi-optical spatial power combining array for high power millimeter wave (MMW) traveling wave tubes (TWTs) by demonstrating a Ku-band high power TWT which covers 12-15 GHz and with 100 kilowatt (kW) output power. Specifically, a Ku-band high power TWT which consists of a quasi-optical spatial power combining array of fifteen beam-wave interaction circuit slow wave structures and, as a result, beam width/height aspect ratio of close to 85 was developed to achieve a combined output power of over 100 kW at Ku-band. The 15 individual beam-wave interaction structures in the quasi-optical spatial power combining array are arranged into a linear array. Instead of a single cathode, fifteen cathodes, each with its own focus electrode or, in other words, a total of 15 focus electrodes are also used to create a required large sheet of beam for the large quasi-optical spatial power combining array of 15 channels of individual beam-wave interaction structure. Although a single stage collector was initially designed, however, a multi-stage depressed collector will also be designed and implemented to improve the efficiency of this K-band high power TWT. The overall size of the Ku-band high power TWT is relatively small since the same vacuum envelope and electron beam focus optics are shared among the five beam-wave interaction structures. Design and fabrication of this Ku-band high power TWT will be presented to demonstrate the large quasi optical spatial power combining array for very high power MMW TWTs and with reasonable broad bandwidth.

Nonlinear FDTD analysis of back-to-back varactor diode frequency tripler

A quasi-optical diode-grid frequency tripler array was analyzed by the Finite-Difference Time-Domain (FDTD) method in this paper. A nonlinear algorithm was successfully developed in order to deal with the nonlinear characteristic of a varactor. The results obtained for a test case showed excellent agreement between the FDTD and a direct mathematical method. The detailed analysis of a frequency tripler array employing back-to-back AlGaAs/GaAs heterojunction varactor was given.

FDTD simulations of quasi-optical MESFET oscillator arrays

A method for the FDTD analysis of quasi-optical MESFET arrays is presented in this paper. To analyze active devices such as MESFETs, this method creates a set of field-state central finite difference equations; and all the field and state variables are solved simultaneously at the same FDTD time step. It will be shown in this paper that this formulation is simple and straightforward. The analysis of quasi-optical MESFET oscillator arrays have been performed to show the application of this method. Excellent agreements have been obtained between the results from this simulation method, from commercial softwares, and from experimental measurements to show the validity of this method.

Quasi-optical spatial power combining millimeter wave high power traveling wave tubes

A quasi optical spatial power combining traveling wave tube has been successfully developed and used to increase the output power from solid state devices (as the driver). We report here the development of novel quasi optical spatial power combining for vacuum electronic devices and, more specifically, for traveling wave tubes (TWTs) to increase output power at millimeter waves (MMW) and higher frequencies. A quasi optical spatial power combining array of five complete plus two half slow wave structures (SWSs) was developed at W-band (center frequency 95 GHz) to achieve a combined output power of over 1000 Watts. These SWSs are arranged into a linear array. A sheet beam electron gun and a single stage collector were designed and implemented to mate to the SWSs for this W-band high power TWT.

Microfabrication manufacturable vacuum triodes

The development effort of a microfabrication manufacturable vacuum triodes for base station power amplifier application. This work is based on InnoSys proprietary solid state vacuum device (SSVD) technology to enable conventional vacuum tubes to have IC form factors, to be low-cost, and to utilize microelectronic design, microfabrication, and manufacturing technologies. Emission properties, current-voltage curves, linearity performance of microfabricated vacuum triodes are studied by finite element and finite difference time domain methods.

Development of software package for the design of high-performance vacuum devices

This paper reports on our work and progress in the simulation and design of the high-performance vacuum devices. Miniaturization and easy manufacturing of vacuum devices have been of interest to the research community of vacuum electronics. The goal of this work is both to explore the performance limits of and to develop necessary design tool for the high-performance vacuum devices that utilize advanced manufacturing techniques. As a result, our simulation and modeling package for the design of the high-performance vacuum devices consists of all three of electromagnetic, structural, and thermal analyses. In this paper, we report on the findings and results of our development of the simulation and modeling package for the design of the high-performance vacuum devices. Electrical characteristics and performance of the vacuum devices are highly geometry dependent. The electromagnetic analysis of these devices is accompanied by mechanical, i.e., structural and thermal, analyses in our simulation and modeling package.

Development of three-dimensional monolithic microwave integrated circuit components

FDTD applications in 3D monolithic microwave integrated circuit (MMIC) design are introduced in this paper. The source implementation for active device modeling, device grid-characterization, a novel spiral component simulations are presented. Our research in this area have shown that FDTD is a very effective tool for the design of 3D MMICs.

An Efficient Surface Impedance Boundary Condition for the FDTD Modeling of Surface-Emitting Lasers with Bragg Stacks

A surface impedance boundary condition (SIBC) is presented for the finite-difference time-domain (FDTD) simulation of surface-emitting lasers with Bragg stacks. This method eliminates the need to directly implement the actual Bragg stack structure in the FDTD code and enables three-dimensional FDTD modeling of surface emitting lasers such as vertical cavity surface-emitting lasers (VCSELs). The SIBC is derived from the equivalent surface impedance properties at the interface between the cavity and Bragg stack. The three-dimensional finite-difference formula tions of the SIBC are given in this paper. Simulations of VCSELs are performed with both the SIBC and the actual Bragg stack structure. The excellent agreement obtained between these two simulations shows the validity of the SIBC developed in this work.A surface impedance boundary condition (SIBC) is presented for the finite-difference time-domain (FDTD) simulation of surface-emitting lasers with Bragg stacks. This method eliminates the need to directly implement the actual Bragg stack structure in the FDTD code and enables three-dimensional FDTD modeling of surface emitting lasers such as vertical cavity surface-emitting lasers (VCSELs). The SIBC is derived from the equivalent surface impedance properties at the interface between the cavity and Bragg stack. The three-dimensional finite-difference formula tions of the SIBC are given in this paper. Simulations of VCSELs are performed with both the SIBC and the actual Bragg stack structure. The excellent agreement obtained between these two simulations shows the validity of the SIBC developed in this work.