Dazhen Gu

National Institute of Standards and Technology | NIST · RF Technology Division

We present a study of power spectral density (PSD) estimation from data sampled in the time domain. This work was motivated by our recent development of digital radiometry, where radiation spectra were obtained by processing the digitally sampled signal. The PSD estimation can be generalized by a quadratic estimator and minimization of mean squared...

Main text This report summarizes the results of the measurements performed as a CIPM Key Comparison (CCEM.RF-K27.W) on high frequency power in waveguide among eight National Metrology Institutes (NMIs) of Germany (PTB), UK (NPL), France (LNE), China (NIM), Russia (VINIIFTRI), USA (NIST), Korea (KRISS), Japan (NMIJ). The Pilot Laboratory (PL) is NIM...

This paper describes a metrology instrument designed for detecting noise and interference in digital communications. A quadrature detector downconverts in-phase and quadrature channels, which are each digitized at high speed. This architecture makes the upper and lower signal sidebands separable by digital processing, and has spectral resolution th...

Receiver technology has evolved significantly over the past decades. A variety of receiver architectures have been developed for addressing different applications [1] . In general, more and more analog components have been replaced by their digital counterparts. The recent advance in ultrafast sampling digitizers has even enabled digital front en...

In this work, we show that high antenna frequency selectivity can make it more challenging to accurately measure antenna efficiency in a reverberation chamber (RC) when using the two-antenna method since electronic noise can affect the measured stirred-energy component of the $S$ -parameters. Recognizing whether the measured antenna-efficiency es...

A detailed investigation of the quotient of two independent complex random variables is presented. The numerator has a zero mean, and the denominator has a non-zero mean. A normalization step is taken prior to the theoretical developments in order to simplify the formulation. Next, an indirect approach is taken to derive the statistics of the modul...

We present a general model of noisy scattering-parameter (S-parameter) measurements performed by a vector network analyzer (VNA). The residual error of the S-parameter due to the noise is examined to appear like a complex Gaussian quotient. The statistical analysis of the residual error is given, and relevant statistical quantities are derived and...

Tightly packaged receivers pose a challenge for noise measurements. Their only outputs are often diagnostic or benchmark information—“user data” that result from unknown processing. These include data rate test results, signal-to-noise ratio estimated by the receiver, and so on. Some of these are important gauges of communication viability that may...

To realize microwave power traceability, we apply a newly developed calibration technique for measuring the correction factor of a calorimeter with a vector network analyzer in the WR-15 frequency band. The wave-parameter approach is used to formulate analytic expressions for the correction factor and effective efficiency. This allows us to systema...

We developed a prototype radiometer system to implement a time-domain noise synthesis technique. A solid-state (SS) switch synthesizes noise signals from the outputs of two synchronized electromechanical (EM) switches. The input ports of EM switches are terminated by one unknown noise source, one known cold noise reference, and two known ambient no...

We discuss the analytical derivation of the absolute brightness temperature uncertainty of a hollow conical blackbody source for radiometer calibration. We introduce a Monte Carlo uncertainty propagation analysis method to quantify uncertainty contributions from nonideal emissivity, physical temperature, and antenna pattern, which are the three maj...

We developed a new calibration technique for measuring the correction factor of a calorimeter with a vector network analyzer. Based on a wave-parameter formulation, we developed analytic formulas for the correction-factor (g) and effective-efficiency (η). This allows us to calibrate both the calorimeter and the thermistor mount in a single step. Th...

We present a new measurement technique for quantifying noise temperature based on temperature and time. A single-pole, double-throw (SPDT) ultra-fast switch combines signals from outputs of two synchronized electromechanical (EM) switches. The input ports of EM switches are terminated by one unknown noise source, one known cold noise source, and tw...

Infrared (IR) emissivity is a critical parameter for modeling and predicting heat transfer by radiation. Microwave absorbing materials, having a high emissivity in the microwave spectrum, are crucial in a wide array of applications, such as electromagnetic interference mitigation, stealth technology, and microwave remote sensing and radiometer cali...

We present a waveguide-to-stripline transition for full D-band operation from 110 to 170 GHz. An E-plane probe in parallel with the waveguide main axis is configured to effectively couple the signal in the primary TE₁₀ mode from the waveguide into the quasi-TEM mode on the chip. Stripline is chosen to minimize the propagation loss, which in turn fa...

A conical cavity has been designed and fabricated for use as a broadband passive microwave calibration source, or blackbody, at the National Institute of Standards and Technology. The blackbody will be used as a national primary standard for brightness temperature and will allow for the prelaunch calibration of spaceborne radiometers and calibratio...

We present a new method for two-port vector network analyzer (VNA) calibration, which uses multiple offset-reflect standards and a flush thru connection. Offset-reflect standards consist of sections of the same uniform transmission line with different lengths, which are terminated with the same highly reflective load. The unknown propagation consta...

A modified measurement technique and nonlinear least-squares solution method is introduced for determining complex permittivity and permeability in transmission lines. In addition to a two-port S-parameter measurement, a one-port measurement of the shorted sample is employed. For low-loss samples, material property determination using the tradition...

This paper describes the development of a waveguide radiometer to measure noise from millimeter wave electronic components from 75 GHz to 110 GHz. The radiometer will estimate the noise temperature of a device under test (DUT) based on comparison with room temperature and 77K noise standards. This is a standard physical approach in other NIST micro...

We outline the theoretical formulation of radiometry of the free-space radiation emitted by a blackbody target. Simulation shows a much smaller drop of radiation intensity of a Lambertian source than that of an incoherent source in the near-field region, indicative of a powerful influence produced by the coherence property of the blackbody source....

We apply coherence-propagation theory to model the radiation generated by a planar passive thermal source of any state of coherence. Of our particular interest is the blackbody calibration source with partially coherent characteristic that produces the radiant intensity with its angular distribution following Lambert’s cosine law in the far field....

Microwave brightness temperature (T b ) observations by satellite sounders represent some of the most important input data for numerical weather prediction (NWP) models as well as providing vital records for climate trend detection. Each flight instrument, even if built to nominally identical specifications, has a unique calibration, typically base...

We present a geometric error model associated with calibration-target misalignment in passive microwave remote-sensing systems. The developed analytic formulation is universally applicable to both lateral and rotational misalignment conditions. Numerical simulations are performed on two practical blackbody targets of different sizes used as radiati...

[1] We report measurements and uncertainty analysis on a cryogenic low-noise amplifier (LNA) with a very low noise temperature (NT), among the lowest noise performances reported at microwave frequencies. The LNA consists of three stages of InP high electron mobility transistors with a gate length of 130 nm. It exhibits about 44 dB gain and less tha...

We report our recent progress toward the development of microwave brightness-temperature (BT) standards. As one of the crucial parameters, the target illumination efficiency (IE) was traditionally determined from the relative antenna pattern. We propose a measurement technique to extract the target IE solely by the use of passive radiometric measur...

We present detailed on-wafer scattering-parameter measurements and equivalent circuit modeling of a metal semiconductor field-effect transistor (MESFET) that incorporates a GaN nanowire (NW). A systematic procedure is established to extract intrinsic model parameters by removing extrinsic parameters of the NW under different bias conditions. All pa...

We report a verification method for noise-temperature (NT) measurements on cryogenic low-noise amplifiers (LNAs) at liquid helium temperature. The method uses a comparison between the individual measurements of the LNA and an attenuator and the joint measurements of the tandem of the two. As a first step, we were able to determine the loss and the...

We compare three methods of quantifying illumination efficiency (IE). The ratio IE describes the contribution of energy emitted from a blackbody target to the total energy measured at an antenna aperture in a free-space microwave calibration target radiometric measurement. Measurements are compared at three frequencies: 18 GHz, 22.5 GHz, and 26 GHz...

We describe and demonstrate a standard radiometer for making microwave brightness-temperature measurements that are traceable to fundamental noise standards. The standard radiometer is based on a National Institute of Standards and Technology (NIST) waveguide radiometer for 18-26.5 GHz, fitted with an antenna to measure radiated power. The fraction...

We propose and implement verification methods for measurements of the noise parameters of amplifiers and transis- tors. Because the verification rests on the comparison of different measurement results, it also serves as a test of the uncertainties. The verification process consists of first measuring separately both a passive two-port device and t...

We report on the characterization of blackbody target reflections as part of the recent progress on the development of brightness temperature standards for microwave remote sensing at the National Institute of Standards and Technology. The very low reflections from the blackbody targets used in airborne or satellite remote sensing systems present c...

Contact resistance and conductivity of individual platinum (Pt) nanowires (NWs) embedded in coplanar waveguide structures are investigated at high frequencies. Two approaches to extract the NW conductivity and contact resistance from two-port S-parameters are developed. The first approach is based on transmission-line theory, while the second appro...

The electrical response of two-port photoconductive GaN nanowire devices was measured from 50 MHz to 33 GHz. The admittance of the nanowire devices showed an increase on the order of 10% throughout the measured frequency range after exposure to steady ultraviolet illumination. Two different two-port microwave network models were used to extract mic...

We report on the characterization of blackbody target reflections as part of the recent progress on the development of brightness temperature standards for microwave remote sensing at the National Institute of Standards and Technology. The very low reflections from the blackbody targets used in airborne or satellite remote-sensing systems present c...

We present a de-embedding roadmap for extracting parasitic elements of a nanowire (NW) metal semiconductor field effect transistor (MESFET) from full two-port scattering-parameter measurements in 0.1–25 GHz range. The NW MESFET is integrated in a microwave coplanar waveguide structure. A conventional MESFET circuit model is modified to include capa...

Three all-electrical detection techniques—differential resistance (dV/dI), rf/microwave transmission, and spin rectification measurements—were used to measure the magnetic response of individual patterned Permalloy structures. The investigated techniques enable the identification of distinctive magnetization states, such as vortex nucleation and ex...

We present a broadband on-wafer calibration from 45 MHz to 40 GHz for variable temperature measurements, which requires three standards: a thru, reflect, and series resistor. At room temperature, the maximum error of this technique, compared to a benchmark nine-standard multiline thru-reflect-line (TRL) method, is comparable to the repeatability of...

The magnetization response of single, patterned, thin-film Permalloy (Ni_80Fe_20, Py) elements embedded in a coplanar waveguide (CPW) is investigated. The anisotropic magnetoresistance (AMR) effect serves as the detection mechanism in current-modulated differential resistance (dV/ dI) and rectification effect measurements, which reveal magnetizatio...

In the above titled paper (ibid., vol. 58, no. 5, pp. 1140-1150, May 10), some errors have been detected. The corrections are presented here.

We report a miniaturized phase shifter operating in the frequency range from 5 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 mechanical counterparts. It provides adequate impedance coverage, ultra-fast response, as well as...

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 embedded in the same plane within a serrated conductor. Broadband measurements and full-wave finite...

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 radiometric T_B measurements, all of which must be calibrated against physi...

We report on 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 temperatures used for airborne and/or satellite systems along with an aluminum plate were me...

Patterned permalloy films embedded in a coplanar waveguide (CPW) were fabricated, and the magnetization dynamics of such structures were investigated. Anisotropic magneto-resistance (AMR) effect was utilized as the detection mechanism to study the dynamics of such device structures. The introduced approach is suitable for investigation of magnetiza...

A two-port GaN nanowire (NW) device with one Schottky contact and one Ohmic contact was characterized up to 10 GHz using on-wafer microwave measurements. In addition to the measurement of the broadband response, two additional applications of microwave measurements are introduced: (1) the capability to distinguish a Schottky-type contact from an Oh...

This paper presents a detailed study of the IF properties of phonon-cooled NbN hot electron bolometer (HEB) terahertz mixers and receivers, performed over the widest intermediate frequency range reported so far. First, a broadband technique is used to obtain the IF small-signal output impedance of HEB mixers using network analyzer measurements. The...

We report a coplanar waveguide notch filter with an integrated air-bridge, designed for operation at submillimeter wave frequencies and cryogenic temperatures. The filter is built with a planar slot-ring antenna, which is in turn loaded with a superconducting mixer detector. The filter is designed to have a narrow-band response with 40 dB of attenu...

We explore the frequency-dependent relative permittivity of Ruddlesden-Popper series Srn+1TinO3n+1 (n=1,2,3) thin films as a function of temperature and dc electric field. Interdigitated capacitors and coplanar waveguides were used to extract the frequency response from 500 Hz to 40 GHz. At room temperature, the in-plane relative permittivities (ε1...

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 parameters of amplifiers. We present measured results for noise parameters of a low noise ampli...

We report on 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 of 0.5-5 THz. Terahertz imagers based on HEB technology have sufficient sensitivity to opera...

This letter describes the design of highly packaged heterodyne receivers for terahertz applications. The 3-D integration of a terahertz mixer with a low-noise intermediate frequency amplifier is implemented for the first time using off-the-shelf components. Thereby, an-order-of-magnitude volume and weight reduction are accomplished. We validate our...

We are developing hot electron bolometer (HEB) mixer receivers for heterodyne detection at terahertz frequencies. HEB detectors provide unprecedented sensitivity and spectral resolution at terahertz frequencies. Terahertz imagers based on HEB technology have sufficient sensitivity to operate in a passive imaging mode, thus eliminating the need for...

Superconducting hot-electron-bolometer (HEB) receivers, integrated on multichip modules, allow coherent detection of terahertz radiation. Terahertz sensors are being increasingly used for implementation of multielement focal-plane arrays (FPA), which are a two-dimensional array of detectors placed at the focal plane of a reflector (or lens) and use...

We report a remarkable progress in the develop- ment of highly packaged heterodyne receivers using NbN HEB mixers and MMIC IF amplifiers. We are presenting a record IF noise bandwidth of 8 GHz (measured for a »700 GHz LO) using a lumped element matching network for the input of the IF pre- amplifier. Further, we describe the first three-dimensional...

Imaging and spectroscopy at terahertz frequencies (defined roughly as 300 GHz - 3 THz) have great potential for both healthcare and homeland security applications. Terahertz frequencies correspond to energy level transitions of important molecules in biology and astrophysics. Terahertz radiation (T-rays) can penetrate clothing and, to some extent,...

We are proposing a general approach to find the optimal coupling conditions between a NbN HEB mixer and its corresponding HEMT IF amplifier. We present our progress towards the development of suitable models for the analysis of the mixer/LNA sub-system in HEB terahertz down-converters. Our modeling approach takes into account parasitic reactances f...

We report precision measurements of the effective input noise temperature of a cryogenic (liquid-helium temperature) monolithic-microwave integrated-circuit amplifier at the amplifier reference planes within the cryostat. A method is given for characterizing and removing the effect of the transmission lines between the amplifier reference planes an...

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 hot electron bolometric (HEB) mixer integrated with an InP MMIC IF low-noise amplifier (LNA). A harmonic multiplier with an output power of about 250 p...

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 monolithic microwave integrated circuit (MMIC) IF amplifiers in a single block. HEB technology is becoming the basis for advanced terahertz imaging and spectroscopic techn...

We have achieved the first demonstration of a low-noise heterodyne array operating at a frequency above 1 THz (1.6 THz). The prototype array has three elements, consisting of NbN hot electron bolometer (HEB) detectors on silicon substrates. We use a quasi-optical design to couple the signal and local oscillator (LO) power to the detector. We also d...

In order to develop multi-pixel focal plane arrays at terahertz frequencies based on hot electron bolometer (HEB) technology, special consideration must be given to the power coupling configuration. Tunable terahertz local oscillator (LO) sources have insufficient power to bias large arrays of HEB mixers. We are developing a new quasi-optical coupl...

Interest in alternative imaging, with an emphasis on medical and security applications, is increasing. The terahertz spectrum is beginning to be explored for these applications. A prototype scanning imaging system is described here. This system currently operates at 1.6 THz and uses a HEB as a heterodyne detection element. Object scanning is accomp...

Abstract— Phonon-cooled NbN HEB mixers have been suc- cessfully integrated with InP MMIC IF amplifiers to produce low-noise HEB-MMIC receivers. Noise temperatures of less than 1,600 K and receiver noise temperature bandwidths of at least 4 GHz (measured at 1.6 THz) have earlier been demonstrated for this type of integrated receivers. Our configurat...