U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Search Publications by: Dazhen Gu (Fed)

Search Title, Abstract, Conference, Citation, Keyword or Author
Displaying 51 - 72 of 72

A Compact Variable-Temperature Broadband Series-Resistor Calibration

January 1, 2011
Author(s)
Nathan D. Orloff, Jordi Mateu, Arkadiusz C. Lewandowski, Eduard Rocas, Joshua P. King, Dazhen Gu, Juan C. Collado Gomez, Ichiro Takeuchi, Xiaoli Lu, James C. Booth
We present a method to obtain a broadband on wafer calibration from 45 MHz to 40 GHz for variable temperature, which requires three standards: a thru-reflect, and series-resistor. The maximum error of this technique compared to a benchmark 9 standard

Noise-Parameter Measurements with a Reflection Type Phase Shifter

November 1, 2010
Author(s)
Dazhen Gu, Dave K. Walker, James P. Randa
We report a miniaturized phase shifter operating in the frequency range from 5 GHz to 7 GHz for noise-parameter extraction. Such a tunable solid-state unit represents a significant reduction in the size and mass as a source-pull component, compared to its

Contactless Approaches for RF Characterization of Metallic Nanowires

September 28, 2010
Author(s)
Kichul Kim, Paul Rice, Thomas M. Wallis, SangHyun S. Lim, Dazhen Gu, Atif A. Imtiaz, Pavel Kabos, Dejan Filipovic
Two approaches for microwave characterization of nanowire (NW) conductivity are described in this paper. To remove the uncertainty associated with contacts, the NWs are either suspended above the center conductor of a coplanar waveguide (CPW) host or

Comparison of Microwave Black-Body Target Radiometric Measurements

July 30, 2010
Author(s)
Dave K. Walker, Dazhen Gu, Katherine MacReynolds, Randy Direen, James P. Randa, Amanda Cox, Derek A. Houtz, Robert L. Billinger
Accurate characterization of the brightness temperature (T_B) of black-body targets used for calibrating microwave remote-sensing radiometers includes many inputs: antenna pattern and loss, target temperature, target emissivity, mechanical alignment, and

Metrology of Microstructured Waveguides for Spintronic Applications

July 30, 2010
Author(s)
SangHyun S. Lim, Atif A. Imtiaz, Dazhen Gu, Pavel Kabos, Thomas Mitchell (Mitch) Wallis
Patterned permallay films as a part of a coplanar waveguide (CPW) were fabricated, and the magnetization dynamics of such structures was investigated as fundamental building blocks for magnetic spintronic devices. Anisotropic magneto-resistance (AMR)

REFLECTIVITY STUDIES OF PASSIVE MICROWAVE CALIBRATION TARGETS AND ABSORPTIVE MATERIALS

July 30, 2010
Author(s)
Dazhen Gu, Amanda Cox, Derek A. Houtz, Dave K. Walker, James P. Randa, Robert L. Billinger
We report the characterization of blackbody reflections as a part of the recent progress on the development of brightness standards for microwave remote sensing at National Institute of Standards and Technology (NIST).Three blackbody targets at variable

High frequency characterization of a Schottky contact to a GaN nanowire bundle

June 16, 2010
Author(s)
Chin J. Chiang, Thomas M. Wallis, Dazhen Gu, Atif A. Imtiaz, Pavel Kabos, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford, Kichul Kim, Dejan Filipovic
A GaN nanowire (NW) Schottky contact was characterized up to 10 GHz. Using a calibration procedure and circuit model a capacitance-voltage (CV) curve was obtained, from which a carrier concentration was calculated for the first time. These results

AIR-BRIDGE INTEGRATED STUB FILTER FOR SUB-MILLIMETER WAVE APPLICATIONS

June 1, 2009
Author(s)
Dazhen Gu, Fernando Rodriquez-Morales, Sigfrid Yngvesson
We report a coplanar waveguide notch filter with an integrated air-bridge, designed for operation at sub-millimeter wave frequencies and cryogenic temperatures. The filter is built with a planar slot- ring antenna, which is in turn loaded with a su

Variable Termination Unit for Noise-Parameter Measurements

April 1, 2009
Author(s)
Dazhen Gu, Dave K. Walker, James P. Randa
NIST has upgraded its measurement capability of noise parameters on low-noise amplifiers with a variable termination unit (VTU) in the 1 to 12.4 GHz frequency range. Such a unit allows improved time efficiency and accuracy in the noise-temperature

Broadband Dielectric Spectroscopy of Ruddlesden-Popper Sr(n+1)Ti(n)O(3n+1) (n= 1, 2, 3) Thin Films

January 29, 2009
Author(s)
Nathan D. Orloff, Ichiro Takeuchi, James C. Booth, Dazhen Gu, Jordi Mateu, C. J. Fennie, K. M. Rabe, W Tian, D.G. Schlom
We explore the frequency dependent permittivity of Ruddlesden-Popper series Sr(n+1)Ti(n)O(3n+1) (n= 1, 2, 3) thin films as a function of temperature and dc electric-field. Interdigitated capacitors and coplanar waveguides are used to extract the frequency

Noise-parameter measurement with automated variable terminations

June 8, 2008
Author(s)
Dazhen Gu, Dave K. Walker, James P. Randa
NIST has upgraded its measurement capability of noise parameters on low-noise amplifiers with a variable termination unit in the 1 to 12.4 GHz range. Such a unit allows improved time efficiency in the noise-temperature measurements used to de-embed noise

A Passive Heterodyne HEB Imager Operating at 850 GHz

May 15, 2008
Author(s)
Eyal Gerecht, Dazhen Gu, Lixing You, Sigfrid Yngvessen
We report the development and characterization of a passive heterodyne hot electron bolometer (HEB) imager operating at 850 GHz. HEB detectors provide unprecedented sensitivity and spectral resolution at terahertz frequencies covering the frequency range

STANDARDS DEVELOPMENT FOR REMOTE SENSING AT MICROWAVE AND TERAHERTZ FREQUENCIES

September 7, 2007
Author(s)
James P. Randa, Eyal Gerecht, Dave K. Walker, Amanda Cox, Dazhen Gu, Lixing You, Robert L. Billinger
The Noise Project in the Electromagnetics Division of the National Institute of Standards and Technology (NIST) has proposed the development of standards for microwave brightness temperature, for use in remote-sensing applications such as satellite-based

Terahertz radiometer design for traceable noise-temperature measurements

July 14, 2006
Author(s)
Eyal Gerecht, Dazhen Gu, James P. Randa, Dave K. Walker, Robert L. Billinger
We report on design of a radiometer for traceable noise-temperature measurements at terahertz frequencies, including noise measurements on cryogenic IF components, development and test of quasi-optical adapter technology, development of black body

A Two-Dimensional Terahertz Imaging System Using Hot Electron Bolometer

May 10, 2006
Author(s)
Dazhen Gu, Eyal Gerecht, Fernando Rodriquez Morales, Sigfrid Yngvesson
We present first results with a two-dimensional(2D)scanning, terahertz passive heterodyne imaging system currently under development. The imager is based on a phonon-cooled quasi-optically coupled HEB mixer integrated with an InP MMIC IF low-noise

Precision Measurement Method for Cryogenic Amplifier Noise Temperatures Below 5 K

March 1, 2006
Author(s)
James P. Randa, Eyal Gerecht, Dazhen Gu, Robert L. Billinger
We report precision measurements of the effective input noise temperature of a cryogenic (liquid helium temperature) MMIC amplifier at the amplifier reference planes within the cryostat. A method is given for characterizing and removing the effect of the

HEB FPA Imaging Technology for Security and Biomedical Applications

September 19, 2005
Author(s)
Eyal Gerecht, Dazhen Gu, Sigfrid Yngvesson, Fernando Rodriguez-Morales, Ric Zannoni, John Nicholson
We have demonstrated a low-noise heterodyne three-element focal plane array (FPA) at 1.6 THz consisting of NbN Hot Electron Bolometric (HEB) detectors, intimately integrated with MMIC IF amplifiers in a single block. HEB technology is becoming the basis