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Mehdi, Imran

Publications and source records attributed to Mehdi, Imran.

88 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

THz Local Oscillator Technology

The last decade has seen a number of technological advancements that have now made it possible to implement fully solid state local oscillator chains up to 2 THz. These chains are composed of cascaded planar multiplier stages that are pumped with W-band high power sources. The high power W-band sources are achieved by power combining MMIC amplifiers and can provide in access of 150 mW with about 10% bandwidth. Planar diode technology has also enabled novel circuit topologies that can take advantage of the high input power and demonstrate significant efficiencies well into the THz range. Cascaded chains to 1.9 THz have now been demonstrated with enough output power to successfully pump hot-electron bolometer mixers in this frequency range. An overview of the current State-of-the-Art of the local oscillator technology will be presented along with highlighting future trends and challenges.

multipliers↗
NASA NTRS2004

Reliability of Cascaded THz Frequency Chains with Planar GaAs Circuits

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.

reliability on Schottky diode multipliers↗
NASA NTRS2004

Tunable All-Solid-State Local Oscillators to 1900 GHz

We present a status report of an ongoing effort to develop robust tunable all-solid-state sources up to 1900 GHz for the Heterodyne Instrument for the Far Infrared (HIFI) on the Herschel Space Observatory. GaAs based multi-chip power amplifier modules at W-band are used to drive cascaded chains of multipliers. We have demonstrated performance from chains comprised of four doublers up to 1600 GHz as well as from a x2x3x3 chain to 1900 GHz. Measured peak output power of 23 (micro)W at 1782 GHz and 2.6 (micro)W at 1900 GHz has been achieved when the multipliers are cooled to 120K. The 1900 GHz tripler was pumped with a four anode tripler that produces a peak of 4 mW at 630 GHz when cooled to 120 K. We believe that these sources can now be used to pump hot electron bolometer (HEB) heterodyne mixers.ter (HEB) heterodyne mixers.

local oscillator↗
NASA NTRS2003

LO sources for 1-3 THz: present status and future prospective

This talk will present an overview of the current technologies that are available for implementing local oscillator sources for 1-3 THz applications. Progress to date on specific components will be discussed in some detail. Outstanding issues and concerns regarding practical implementation of these new technologies will also be discussed.

Schottky diode multipliers↗
NASA NTRS2003

Design and Varactors: Operational Considerations. A Reliability Study for Robust Planar GaAs

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

THz frequencies↗
NASA NTRS2001

Proceedings of the Twelfth International Symposium on Space Terahertz Technology

The Twelfth International Symposium on Space Terahertz Technology was held February 14-16, 2001 in San Diego, California, USA. This symposium was jointly sponsored by the National Aeronautics and Space Administration (NASA) and the Jet Propulsion Laboratory, California Institute of Technology. The symposium featured sixty nine presentations covering a wide variety of technical topics relevant to Terahertz Technology. The presentations can be divided into five broad technology areas: Hot Electron Bolometers, superconductor insulator superconductor (SIS) technology, local oscillator (LO) technology, Antennas and Measurements, and Direct Detectors. The symposium provides scientists, engineers, and researchers working in the terahertz technology and science fields to engineers their work and exchange ideas with colleagues.

Mehdi, Imran↗
NASA NTRS2001

Temperature Effects in Varactors and Multipliers

Varactor diode multipliers are a critical part of many THz measurement systems. The power and efficiencies of these devices limit the available power for THz sources. Varactor operation is determined by the physics of the varactor device and a careful doping profile design is needed to optimize the performance. Higher doped devices are limited by junction breakdown and lower doped structures are limited by current saturation. Higher doped structures typically have higher efficiencies and lower doped structures typically have higher powers at the same operating frequency and impedance level. However, the device material properties are also a function of the operating temperature. Recent experimental evidence has shown that the power output of a multiplier can be improved by cooling the device. We have used a particle Monte Carlo simulation to investigate the temperature dependent velocity vs. electric field in GaAs. This information was then included in a nonlinear device circuit simulator to predict multiplier performance for various temperatures and device designs. This paper will describe the results of this analysis of temperature dependent multiplier operation.

East, J.↗
NASA NTRS1995

Millimeter And Submillimeter-Wave Integrated Circuits On Quartz

Proposed Quartz substrate Upside-down Integrated Device (QUID) relies on UV-curable adhesive to bond semiconductor with quartz. Integrated circuits including planar GaAs Schottky diodes and passive circuit elements (such as bandpass filters) fabricated on quartz substrates. Circuits designed to operate as mixers in waveguide circuit at millimeter and submillimeter wavelengths. Integrated circuits mechanically more robust, larger, and easier to handle than planar Schottky diode chips. Quartz substrate more suitable for waveguide circuits than GaAs substrate.

Mehdi, Imran↗
NASA NTRS1994

Microwave GaAs Integrated Circuits On Quartz Substrates

Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

Siegel, Peter H.↗
NASA NTRS1991

Improved millimeter-wave mixer performance analysis at cryogenic temperatures

The results of a 600-GHz mixer performance analysis using an improved model for computing the Schottky diode capacitance-voltage (C-V) relationship are presented. The computed C-V data for a realistic submillimeter-waver mixer diode are given as a function of physical temperature and compared to the standard analytic expression based on a solution of Poisson's equation. Both C-V relationships are used to predict the performance of an ideally terminated 600 GHz mixer operating at 300, 140, 80, and 30 K. It is shown that the drift-diffusion model more accurately describes the mixer performance when the physical temperature is reduced below roughly 100 K.

Siegel, Peter H.↗