Engineering topics
Publications and source records attributed to Lin, Robert.
Broadband electronically tunable sources in the terahertz range are a critical technology for enabling space-borne as well as ground-based applications. By power-combining MMIC amplifier and frequency tripler chips, we have recently demonstrated >1 mW of output power at 900 GHz. This source provides a stepping stone to enable sources in the 2-3 THz range than can sufficiently pump multi-pixel imaging arrays.
This design starts with commercial 85- to 115-GHz sources that are amplified to as much as 250 mW using power amplifiers developed for the Herschel Space Observatory. The frequency is then tripled using a novel waveguide GaAs Schottky diode frequency tripler. This planar diode produces 26 mW at 318 GHz. Peak conversion efficiency is over 15 percent, and the measured bandwidth of about 265 - 30 GHz is limited more by the driving source than by the tripler itself. This innovation is based on an integrated circuit designed originally for a single-chip 260- to 340-GHz balanced tripler. The power-combined version has two mirror-image tripler chips that are power-combined in-phase in a single waveguide block using a compact Y-junction divider at the input waveguide, and a Y-junction combiner at the output waveguide. The tripler uses a split-block waveguide design with two independent DC bias lines.
We report on the design and performance of a novel broadband, biased, subharmonic 520-590 GHz fix-tuned frequency mixer that utilizes planar Schottky diodes. The suspended stripline circuit is fabricated on a GaAs membrane mounted in a split waveguide block. The chip is supported by thick beam leads that are also used to provide precise radio frequency (RF) grounding, RF coupling and dc/intermediate frequency connections. At room temperature, the mixer has a measured double sideband noise temperature of 3000 to 4000 K across the design band.
Planar GaAs Schottky diodes will be utilized for all of the LO chains on the HIPI instrument for the Herschel Space Observatory. A better understanding of device degradation mechanisms is desirable in order to specify environmental and operational conditions that do not reduce device life times. Failures and degradation associated with ESD (Electrostatic Discharge), high temperatures, DC currents and RF induced current and heating have been investigated. The goal is to establish a procedure to obtain the safe operating range for a given frequency multiplier.
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Preliminary conclusions include: Limits for reverse currents cannot be set. Based on current data we want to avoid any reverse bias current. We know 1 micro-A is too high. Leakage current gets suppressed when operated at 120K. Migration and verification: a) Reverse Bias Voltage will be limited; b) Health check with I/V curve: 1) Minimal reverse voltage shall be x0.75 of the calculated voltage breakdown Vbr; 2) Degradation of the Reverse Bias voltage at given current will be used as indication of ESD incidents or other Damages (high RF power, heat); 3) Calculation of diodes parameter to verify initial health check result in forward direction. RF output power starts to degrade when diode I/V curve is very strongly degraded only. Experienced on 400GHz doubler and 200GHz doubler
This paper will describe on-going investigations into the effects of excessive reverse currents in Schottky diodes along with presenting a methodology for determining safe bias conditions for a given multiplier.
The High Energy Solar Physics mission offers the opportunity for major breakthroughs in the understanding of the fundamental energy release and particle acceleration processes at the core of the solar flare problem. The following subject areas are covered: the scientific objectives of HESP; what we can expect from the HESP observations; the high energy imaging spectrometer (HEISPEC); the HESP spacecraft; and budget and schedule.
To address the central scientific questions surrounding solar flares, coordinated observations of electromagnetic radiation and energetic particles must be made from spacecraft, balloons, rockets, and ground-based observatories. A program to enhance capabilities in these areas in preparation for the next solar maximum in 1991 is recommended. The major scientific issues are described, and required observations and coordination of observations and analyses are detailed. A program plan and conceptual budgets are provided.