Zi-Cheng Wang

Predistortion Linearization of an X-Band TWTA for Communications Applications

Using a predistortion linearizer is an important way to improve traveling-wave tube amplifier (TWTA) linearity. However, predistortion linearizers cannot usually control amplitude modulation (AM)/AM and AM/phase modulation (PM) conversion separately, so it is difficult to satisfy linearization requirements for AM/AM and AM/PM conversion simultaneously. This paper proposes a predistortion linearizer with a relatively simple circuit structure, which provides good control of gain expansion over the input power dynamic range while keeping the amount of phase expansion small. Good linearity improvement has been obtained for a 45-W X-band TWTA with this predistortion linearizer.

A THz Backward-Wave Oscillator Based on a Double-Grating Rectangular Waveguide

A double-grating rectangular waveguide system with a round beam channel is proposed as the slow-wave interaction structure of a terahertz (THz) backward-wave oscillator (BWO). Applying the latest microfabrication techniques, the interaction structure is fully realizable and easily assembled. The basic design principle including the beam-wave dispersion relation, interaction impedance, and the system configuration is presented. A detailed sensitivity analysis of this THz BWO circuit is carried out to investigate the structure errors caused by fabrication and brazing. Both upstream and downstream ends are loaded with step tapers to improve the voltage standing wave ratio. The downstream reflection is absorbed by a linear attenuator. The round electron beam is generated by a pierce gun with compression ratio of 15. A 3-D particle-in-cell simulation demonstrates a broad electronic tunable bandwidth, a 3-dB bandwidth exceeding 28 GHz with highest output power 16 W, and interaction efficiency 3.57%.

Theory and Simulation of Arbitrarily Shaped Groove Staggered Double Grating Array Waveguide

A theoretical model for the arbitrarily shaped groove staggered double grating array waveguide (SDGAW) slow-wave structure is proposed in this paper. The boundary of the groove was approximately replaced by a series of steps and the formulas of dispersion and interaction impedance were obtained utilizing the field matching method combined with the continuity of transverse admittance. Considering the traditional single mode approximation (SMA) model is not so accurate for describing the high frequency (HF) characteristics, a multiple modes approximation (MMA) model is established, which takes account for the higher order terms in the grooves, thus greatly improves the accuracy of the numerical calculations. As an example, the HF characteristics of a cosine groove SDGAW for a 0.22-THz traveling wave tube were calculated utilizing the SMA model, the MMA model, and HFSS code, the results were compared and discussed. Comparison of the HF characteristics among several kinds of groove shaped SDGAWs has been made by numerical calculation.

Three dimensional nonlinear analysis of a single-grating rectangular waveguide Cerenkov maser

A three dimensional (3-D) nonlinear model for illustrating the beam-wave interaction in a single-grating rectangular waveguide sheet-beam Cerenkov maser is presented. The dynamical equations and the equations of motion are solved self-consistently to predict the device performance. Space-charge effects and Ohmic losses are considered in the model. A 1.03 THz backward wave oscillator and a 0.65 THz traveling wave tube are discussed as two illustrative examples.

THE RESEARCH AND APPLICATION OF COMBINING LUT AND MEMORY COMPENSATION FOR TWTA LINEARIZATION WITH RELATIVELY LOW SAMPLING FREQUENCY

If sampling frequency is not high enough, the efiect of adaptive memory polynomial predistortion linearizer is not very good for TWTA linearization. In order to keep the adaptive memory polynomial predistortion linearizer valid, usually the output power level of the TWTA must be reduced, which corresponds to a reduced e-ciency of the TWTA. In this paper, we present a digital predistortion linearizer by combining LUT (Look-Up-Table) and memory-efiect compensation technique, which may provide good linear performance with less reduction of the output power and relatively low sampling frequency. The results of simulations and experiments show that good linearity improvement can be reached for an X-band TWTA with this predistortion linearizer.

A diode-based predistortion linearizer for traveling wave tube amplifiers

The simulation and design of a predistortion linearizer based on schottky and varactor diodes are presented. The linearizer is capable of providing different combinations of the amplitude and phase characteristics for the use of the different traveling wave tube amplifiers (TWTAs). About 4–6dB gain expansion and 30–60 degrees phase shift can be compensated for the TWTAs saturation response over input power dynamic range with the linearizer.

Investigation of Circular Comb Slow-Wave Structure of THz Backward-Wave Oscillators: Investigation of Circular Comb Slow-Wave Structure of THz Backward-Wave Oscillators

Investigation of Circular Comb Slow-Wave Structure of THz Backward-Wave Oscillators Wang Zi-cheng1 Lu De-jian12 Wang Li1 Li Hai-qiang1 Zhang Shi-jie1 Xu An-yu1 Hao Bao-liang1 Song Pei-de1 Dai Zhi-hao1 1(Institute of Electronics, Chinese Academy of Science, Beijing 100190, China) 2(Graduate University of Chinese Academy of Science, Beijing 100039, China) Abstract: 3-D electromagnetic simulation software is used to calculate the dispersion and interaction impedance of circular comb Slow-Wave Structure (SWS) which works for Terahertz (THz) Backward-wave Oscillators (BWO). The results show that the inner radius of SWS is 0.175mm in the band of 430-570GHz, and the inner radius of SWS is 0.1mm in the band of 760-940GHz. The large radius of SWS is a great help for improving beam transmission. The interaction impedance of fundamental backward wave of the SWS is smaller than 1 Ω is a good explain to the truth that the electronic efficiency of THz BWO is smaller than 0.01%.

A wideband input/output structure for the staggered double grating sheet beam travelling wave tube

A wideband input/output structure for the staggered double grating sheet beam traveling wave tube (SBTWT) is designed, which has the merits of simple structure, low reflection and high isolation in a wide frequency band. A design example is given for a 94GHz sheet beam travelling wave tube, the CST-MWS simulation results show the S parameters are satisfactory.

A three dimensional large signal model for sheet beam travelling wave tubes

A three-dimensional (3-D) frequency domain large signal code called SBTWT3D for illustrating the beam-wave interaction in the sheet beam traveling-wave tube (SBTWT) is presented. A 3-D nonlinear beam-wave interaction analysis for a W band SBTWT is performed and the calculation results are compared with those obtained from time-domain 3-D particle-in-cell simulations.

Structural design for power probe of W-band power meter

A structure for power probe of W-band power meter is designed under the premise of ensuring absorption rate and steady working of materials at high temperature. Basing on heat analysis ANSYS code, the temperature distribution of the probe has been simulated with 0-50mW input power. The designed probe meets the requirements of calibration and measurement according to the simulation results for temperature difference, heat-balance time and heat-withstanding capability of the material.