High Efficiency X-band Research Articles

Heterointerfaces via decoration of walnut iron tungstate with bismuth vanadate as high efficiency X-band microwave absorbing materials

The fabrication of FeWO4/BiVO4 composites is a key initial step in the development of effective microwave absorber fillers. Tweaking the loading ratio of composites, complex permittivity and complex permeability of walnut-shaped FeWO4/BiVO4 microspheres is significantly improved. In addition, best sample displays a reasonable minimal reflection loss (RLmini) value, and its effective absorption bandwidth (EAB, with RL -10 dB) value is 3.6 GHz. Moreover, the best samples were evaluated via free-space testing technique too, and comparison is made between the waveguide and free-space measurements. Evidence suggests that the free-space approach can be a valuable additional testing strategy due to its touch-free and non-destructive characteristics. The ability to fabricate high-quality FeWO4/BiVO4 samples with adjustable characteristics and an alternate measurement procedure opens the door to promising novel microwave absorbers. As a result, FeWO4/BiVO4 is predicted to be an exceptionally efficient microwave absorbent material.

Dynamic Dual-Gate Bias Modulation for Linearization of a High-Efficiency Multistage PA

This paper investigates the linearization of high-efficiency multistage PAs through gate bias modulation derived from the envelope of the RF input signal. We show that separate control of the driver- and power-stage gate bias voltages allows for independent linearization of gain and phase. An iterative algorithm determines signal-dependent gate voltage functions that minimize amplitude-to-amplitude (AM/AM) and amplitude-to-phase (AM/PM) distortion, and is demonstrated on a 10-W high-efficiency X-band GaN monolithic microwave integrated circuit (MMIC) PA with a custom-designed hybrid dual-gate bias modulator. The noise power ratio (NPR) of a 5-MHz-wide signal is improved by as much as 9.4 dB compared to the PA with a static bias, without degradation in power-added efficiency (PAE) and gain. The measured average PAE improves from 19.9 % at 9.8-dB backoff by 0.8 points, with a saturated gain increase of 0.2 dB at 9.7 GHz. A long-term evolution (LTE) signal with different envelope statistics and a 10.6-dB peak-to-average power ratio (PAPR) is amplified with an adjacent channel power ratio (ACPR) improvement of up to 7.9 dB.

Theoretical and experimental research on a high efficiency X-band klystron-like RBWO

In this paper, we study an X-band klystron-like relativistic backward wave oscillator (RBWO) with a pre-modulation cavity, modulation ridge, drift tube in the slow wave structure (SWS) and extraction cavity in both theoretical and experiment. PIC simulations show that the conversion efficiency can be up to 62% with output power of 3.0 GW. In experiment, when the diode voltage is 660 kV, and the diode current is 6.4 kA, the output power is 1.9 GW, and the conversion efficiency is 45%(±5%). And we find that the conversion efficiency mainly suffers from the breakdown in the extraction cavity and the plasma from the cylindrical collector. To suppress the breakdown and plasma effect, the breakdown electric field threshold in RF structures(especially in the extraction cavity) had better be larger than 700 kV/cm. Moreover, the distance between the position where the electrons are collected and the end of extraction cavity should be larger than 20 mm in case of the cylindrical collector.

Analysis, Design, and 3-D Simulation of a High-Efficiency Overmoded Nonuniform Relativistic Backward-Wave Oscillator

A high-efficiency X-band overmoded relativistic backward-wave oscillator (RBWO) using a nonuniform slow-wave structure (SWS) and cavity resonant reflector (RR) is designed in order to increase the beam–wave interaction efficiency. The electrodynamic SWS is a sinusoidally corrugated and moderately overmoded (D/ $\lambda$ > 1) structure that decreases the strength of electric field per unit area at its surface and RR. This reduces the probability of occurrence of RF breakdown, hence the pulse shortening. The nonuniform SWS enhances the beam–wave interaction efficiency by providing variable coupling impedance between −1st harmonic of backward fundamental mode and slow space-charge wave associated with the electron beam. The 3-D particle-in-cell simulation of the designed RBWO generated an RF output power of ~700 MW at 9.24 GHz, while driving by a trapezoidal voltage pulse of 600 kV. The axial guiding magnetic field is 2.5 T that restricts the velocity of electron beam in the axial direction only. The output signal has a high mode purity because the higher order modes are cutoff by the structure. The frequency tuning is obtained by varying the distance between RR and SWS.

Simulational Investigation of a High-Efficiency X-Band Magnetically Insulated Line Oscillator**supported by National Natural Science Foundation of China (No. 11075210) and the Special Financial Grant from the China Postdoctoral Science Foundation (No. 201104761)

The magnetically insulated line oscillator (MILO) is a gigawatt-class, coaxial crossed-field microwave tube, which is at present a major hotspot in the field of high-power microwaves (HPM) research. In order to improve the power conversion efficiency and eliminate or at least minimize anode plasma formation in the load region and radio frequency (RF) breakdown in the slow wave structure (SWS) section, an X-band MILO is presented and investigated numerically with KARAT code. The design idea is briefly presented and the simulation results are given and discussed. In the simulation, HPM is generated with peak power of 3.4 GW, maximum electric field of about 1 MV/cm, and peak power conversion efficiency of 14.0%, when the voltage is 559.1 kV and the current is 43.2 kA. The microwave frequency is pure and falls in the X-band of 9.0 GHz. The theoretical investigation and the simulation results are given to prove that the anode plasma formation and the RF breakdown can be effectively avoided or at least minimized, respectively.

Waveform Evidence of Gate Harmonic Short Circuit Benefits for High Efficiency X-Band Power Amplifiers

An active load pull waveform measurement system has been utilized to investigate, by drain current waveform analysis, the effect of short circuits at the second and higher harmonics on the gate of a 750 μm Gallium Arsenide transistor. It is confirmed that the half wave rectified sinusoidal current waveform necessary for modes of operation such as class B, J and F is not optimally generated at X-Band frequencies for transistors controlled purely by bias. The disrupting effect of the nonlinear device gate capacitance must be accounted for to take full advantage of these high efficiency modes. The addition of a simple wide band filter circuit at the input of a MMIC test cell to “short” the gate higher harmonics is shown to force the drain current waveform towards the ideal case and hence yield a significant increase in drain efficiency of up to 10 percent.

High efficiency X-band relativistic backward wave oscillator with non-uniform slow wave structures

Backward wave oscillators (BWOs) driven by intense relativistic electron beams are very efficient means of producing high-power microwaves. However, the efficiency of conventional BWO is lower than 30%. An X-band oversized BWO with non-uniform slow wave structure is designed to improve RF output characteristics. In particle-in-cell simulation, a high power microwave with a power of 8.0 GW and efficiency of 40% is obtained, compared with that of 30% obtained in a conventional relativistic BWO.

High efficiency X-band magnetically insulated line oscillator with a separate cathode

An X-band magnetically insulated line oscillator (MILO) with a separate cathode has been proposed in order to improve microwave output characteristics. The separate cathode consists of three parts with gradually decreased radii, which are divided by two deep grooves, and only partial cathode surfaces are allowed to emit electrons. In particle-in-cell simulation, high-power microwave with a power of 6.9 GW, frequency of 9.26 GHz, and efficiency of 20.6% is generated, compared with that of 12.2% obtained in a conventional cathode X-band MILO, and the power ratio of the output transverse-electromagnetic mode to transverse-magnetic (TM01) mode is increased from 4 to 27.

High-power high-efficiency X-band AlGaAs/GaAs heterojunction bipolar transistors with undercut collectors

We report on the power performance of X-band AlGaAs/GaAs heterojunction bipolar transistors with undercut collectors for reduced base-collector capacitance. A 10×(2.8×50) μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> HBT unit cell exhibited 2.09 W continuous wave (CW) output power (4.18 W/mm power density), 62.2% power-added efficiency, and 7.13 dB associated gain at 10 GHz at a collector bias voltage of 10 V. When tuned for maximum efficiency, the same transistor delivered a CW output power of 1.36 W, a power-added efficiency of 74.2%, and an associated gain of 7.32 dB at the same frequency and collector bias voltage. To our knowledge, this is the first demonstration of high-power (>1.3 W), high-efficiency (>74%) AlGaAs/GaAs HBT's using a simple collector undercut technique without the need for significant modifications of baseline HBT process.

High efficiency X-band Gunn oscillators

Experimental results are reported for X-band Gunn devices operated in the hybrid mode of Huang and MacKenzie. The high efficiency observed on one diode (22 percent at 19.15 W of peak power) is, to the best of our knowledge, the highest reported in this frequency range. Comparison of our results with theoretical calculations by Huang and MacKenzie is made.