Total Power Radiometer Research Articles

Noise Temperature and Uncertainty Evaluation of a Cryogenic Noise Source by a Sliding Short Method

A cryogenic noise source (CNS) that was cooled by liquid nitrogen was constructed and evaluated in the 8-12 GHz frequency range (the WR-90 waveguide band). A noise temperature of the CNS requires a correction with respect to the boiling point of liquid nitrogen, depending on loss and temperature distributions of a transmission line. We have investigated the transmission line correction factor (TLCF) of the CNS with a sliding short method using a total-power radiometer that is suitable for broadband measurements. The equivalent noise temperature was 79.56-82.90 K, with an uncertainty of 3.89-6.13 K ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> = 2). A comparison of the noise temperature that is obtained by the radiometer with two calibrated noise sources proved the validity of the TLCF.

Research on Modeling of W-band Wide-band Total Power Radiometer Channel

The modeling and analysis of a W-band wide-band radiometer channel is investigated in this paper. In particular, special attention is given to the modeling of wide-band detector. Furthermore, a correction formula of the effective bandwidth of radiometer system is proposed with the influence of the properties of wide-band detector on the radiometer system performances considered. A behavioral model of total power radiometer channel is built, and system analysis is implemented using harmonic balance (HB) method to research the influences of wide-band detector on the radiometer channel.

Applying Millimeter-Wave Correlation Radiometry to the Detection of Self-Luminous Objects at Close Range

The novel application of correlation radiometer theory to the detection of self-luminous objects at close range is presented in the context of human presence detection. Modifications and additions to techniques developed in radio astronomy and remote sensing for close-range terrestrial situations are developed and discussed. To demonstrate the new techniques, a Ka-band correlation radiometer is presented, which detects the presence of a stationary human in an outdoor environment. The correlation radiometer fringe frequency is analyzed in the context of the scanning beam detection system and is estimated using MUSIC and ESPRIT. The visibility, sensitivity, spatial resolution, and dwell time of the system are analyzed. Finally, the correlation response is included in a statistical classifier in conjunction with responses from total power radiometers. Experimental results show improved detection capability over using the total power sensors alone.

Airborne CoSMIR Observations Between 50 and 183 GHz Over Snow-Covered Sierra Mountains

An airborne Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR) was developed recently for calibration/validation of the new-generation DMSP F-series microwave radiometer, the Special Sensor Microwave/Imager/Sounder. The CoSMIR is a total-power radiometer that measures radiation at nine channels over the frequency range of 50-183 GHz. The instrument employs a two-axis gimbaled mechanism to generate the conical scan with periodic calibration. Its scan geometry is software programmable and can be designed to serve the scientific requirements of an experiment. A series of CoSMIR flights was conducted over the coastal regions of California in March and December of 2004, in which the instrument was programmed to acquire both conical and across-track scan data sets simultaneously. Two of these flights on March 25 and December 2 contained segments over the snow-covered Sierra Mountain Range and were selected to demonstrate the novel features of this new instrument

Threshold setting strategies for a quantized total power radiometer

We analyze the impact of a uniform quantizer on the false-alarm probability of a total power radiometer. Different possibilities to set the detection threshold are discussed. The main emphasis is on methods that use the estimated noise level. In particular, we analyze the cell-averaging (CA) constant false-alarm rate threshold setting strategy. The numerical results show that the CA strategy offers the desired false-alarm probability.

Analysis of correlation and total power radiometer front-ends using noise waves

A complete and systematic noise analysis of radiometer front-ends, including both total power and correlation measurements, is presented. The procedure uses the concepts of noise waves and S-parameters, widely used in microwave systems design and takes into account full noise characterization of receivers including mismatch effects. The general formulation is compatible with known total power radiometer analysis and is specially appropriate in correlation radiometers for which the effect of nonideal components, such as input isolators, is analyzed. Along with numerical simulations, simple formulas are given to compute the measured visibility in nonideal conditions. The analysis is validated using experimental results consisting of correlation measurements of four receivers placed inside an anechoic chamber. Good agreement between theoretical predictions and experimental data is observed.

An airborne radiometer for stratospheric water vapor measurements at 183 GHz

The Airborne Millimeter- and Submillimeter Observing System (AMSOS) is a total-power radiometer for observations of the 183.3-GHz water vapor rotational line, operated onboard a Learjet aircraft of the Swiss Air Force. The radiometer is also used to observe the 175.45-GHz ozone line in the other sideband. The neatly designed quasi optics provide a regular and narrow output beam with a half-power beam-width angle of 1.2/spl deg/ and efficient sideband switching. A /spl lambda//4-quasi-optical isolator is used for baseline reduction securing attenuation of internal reflections by more than 30 dB. A low noise temperature of the ambient-temperature-operating system (1900 K) and excellent target pointing (better than 0.1/spl deg/) provide a good duty cycle and reliable calibration. A reliable control over the radiometer's operational parameters, like system stability and system temperatures, and higher automatization were required to come up with high demands of an onboard operation. The measured spectra look typical for the region and time where they were observed.

Errors resulting from the reflectivity of calibration targets

For a microwave total-power radiometer, we consider the error introduced by neglecting the difference in the antenna reflection coefficient between when it views a distant scene and when it views a nearby calibration target. An approximate expression is presented for the error, and measurements are described that enable one to estimate the resulting uncertainty in the measured brightness temperature. The measurement results are presented for several combinations of antenna and calibration target. The resulting uncertainty ranges from about 0.1 K to several kelvins for the representative cases considered.

Temperature compensation of total power radiometers

This paper describes a new technique to compensate output variations of total power radiometers due to physical temperature changes of the instrument. This technique performs the correction without the addition of expensive microwave hardware required in Dicke switching or many other widely used methods. A characterization period, over which the input antenna temperature is known, indicates the appropriate output adjustment needed for a change in physical temperature of the radiometer. The method effectively corrects the output in an example radiometer system built with inexpensive commercially available parts. For a 30-K variation in physical temperature, the measured data shows an improvement from 60-K peak-to-peak error to 6.9 K with an average absolute error of 1.1 K.

Calibration procedure of a microwave total-power radiometer

A total-power radiometer built in combination with a beacon receiver is being used for low-level attenuation measurements. This experimental receiver was built to measure atmospheric propagation impairments, using the ITALSAT satellite 50 GHz signal. The radiometer is mainly used to provide the reference level for the beacon measurements. Its precision should be better than /spl plusmn/3 K, for low attenuation levels, in order to have 0.1 dB accuracy in the attenuation measurements. A suitable calibration procedure is described.

Low-cost millimeter-wave beacon receiver including total-power radiometer: design, implementation and measurement calibration

An experimental Earth station has been installed in Madrid, with the aim of studying the propagation characteristics in the Earth-space link at 50 GHz. The station, which consists of a beacon receiver and a radiometer, was constructed in the University at a very reduced cost, compared to commercially available equipment of similar characteristics. The receiver measures the co-polar and cross-polar signal amplitudes and phases for two linear polarizations, with a 30 dB fade margin for the co-polar signals. General descriptions of the various parts of the equipment, as well as some examples of measurements, are presented in the article.

Research for 3mm Band IF-Switch Radiometer

A 3mm band IF-switch Radiometer was proposed in this paper. On the basis of discussing the theory and circuit structure features, the performance of experimental prototype was presented. The research and experiment result shows that not only its stability is better than that of total power radiometer, but also its cost and size are just similar as the latter. In the absence of 3mm band switch it can surely meet the needs of practical use.

ACTS propagation experiment: experiment design, calibration, and data preparation and archival

The National Aeronautics and Space Administration Advanced Communications Technology Satellite (ACTS) propagation experiment was designed to obtain slant-path attenuation statistics for locations within the United States and Canada for use in the design of low-margin Ka-band satellite communication systems. Experimenters at seven different locations have collected propagation data for move than two years. The propagation terminals used for the experiment were identical. A single preprocessing program was used by the experimenters to provide for automatic calibration, generation of attenuation histograms, and data archival. In this paper, the calibration procedures are described mid estimates given for measurement accuracy. ACTS provided beacons at 20.2 and 27.5 GHz for use in making attenuation measurements. In addition to the beacon receivers, each ACTS propagation terminal has two total power radiometers with center frequencies at the beacon frequencies. The radiometers are used to establish the beacon signal reference levels needed for calculating beacon attenuation values. For the combined radiometer and beacon measurement system, the attenuation measurement error was less than a maximum of 1.0 dB and was generally less than 0.3 dB. The dynamic range for attenuation measurement varied from site to site depending on location relative to the peak of the satellite beacon antenna pattern. For locations within the continental United States, the dynamic range was better than 20 dB.

Multistate radiometry: noise de-embedding and "un-terminating"

A noisy one-port device embedded in a noisy two-port, representing a device under test (DUT) and an rf total power radiometer is investigated from the metrology point-of-view. The output noise power, analyzed at different states of either the termination or the two-port, leads to defining relevant issues of noise un-terminating and de-embedding. In consequence, they both form the foundation of a novel noise approach, the multistate radiometry, applicable to simultaneous measurement of the reflection coefficient and the noise temperature of one-port devices. The method features the sole use of noise excitation and techniques of system calibration and accuracy enhancement, and thus is expected to pioneer novel means for automated noise and network analysis of these devices. Some design criteria for building an appropriate instrument, the multistate radiometer, are considered too. Because only noise power detection is employed, the six-port theory can be applied to the analysis of the system.

The multistate radiometer: a novel means for impedance and noise temperature measurement

A novel noise measurement system for the simultaneous determination of the complex impedance and the noise temperature of microwave one-port devices is introduced. Its unique measurement capability is provided by using a specific excitation of the device under test (DUT) from a noise injection circuit at the input of an rf total power radiometer. Due to power measurement of interfering noise waves its operation is like that of a six-port or multistate reflectometer, thus leading to similar techniques for the system calibration and accuracy enhancement. Experimental results show the good measurement accuracy of this new tool.

The processing of hexagonally sampled signals with standard rectangular techniques: application to 2-D large aperture synthesis interferometric radiometers

In Earth observation programs there is a need of passive low frequency (L-band) measurements to monitor soil moisture and ocean salinity with high spatial resolution 10-20 km, a radiometric resolution of 1 K and a revisit time of 1-3 days. Compared to total power radiometers aperture synthesis interferometric radiometers are technologically attractive because of their reduced mass and hardware requirements. In this field it should be mentioned the one-dimensional (1D) linear interferometer ESTAR developed by NASA and MIRAS a two-dimensional (2D) Y-shaped interferometer currently under study by European Space Agency (ESA). Interferometer radiometers measure the correlation between pairs of nondirective antennas. Each complex correlation is a sample of the "visibility" function which, in the ideal case, is the spatial Fourier transform of the brightness temperature distribution. Since most receiver phase and amplitude errors can be hardware calibrated, Fourier based iterative inversion methods will be useful when antenna errors are small, their radiation voltage patterns are not too different, and mutual coupling is small. In order to minimize on-board hardware requirements-antennas, receivers and correlators-the choice of the interferometer array shape is of great importance since it determines the (u,v) sampling strategy and the minimum number of visibility samples required for a determined aliasing level. In this sense, Y-shaped and triangular-shaped arrays with equally spaced antennas are optimal. The main contribution of this paper is a technique that allows the authors to process the visibility samples over the hexagonal sampling grids given by Y-shaped and triangular-shaped arrays with standard rectangular FFT routines. Since no interpolation processes are involved, the risk of induced artifacts in the recovered brightness temperature over the wide held of view required in Earth observation missions is minimized and signal to noise ratio (SNR) is preserved.

Optimization of a Total Power Radiometer Based on the Systems Analysis Approach

Optimization of a Total Power Radiometer Based on the Systems Analysis Approach

An Absolute Measurement of the Cosmic Microwave Background Radiation Temperature at 10.7 GH[CLC]z[/CLC

A balloon-borne experiment has measured the absolute temperature of the cosmic microwave background radiation (CMBR) at 10.7 GHz to be Tcmbr = 2.730 +- .014 K. The error is the quadratic sum of several systematic errors, with statistical error of less than 0.1 mK. The instrument comprises a cooled corrugated horn antenna coupled to a total-power radiometer. A cryogenic mechanical waveguide switch alternately connects the radiometer to the horn and to an internal reference load. The small measured temperature difference (<= 20 mK) between the sky signal and the reference load in conjunction with the use of a cold front end keeps systematic instrumental corrections small. Atmospheric and window emission are minimized by flying the instrument at 24 km altitude. A large outer ground screen and smaller inner screen shield the instrument from stray radiation from the ground and the balloon. In-flight tests constrain the magnitude of ground radiation contamination, and low level interference is monitored through observations in several narrow frequency bands.

FDTD analysis of the radiometric temperature measurement of a bilayered biological tissue using a body-contacting waveguide probe

Radiometric signal received by an open-ended rectangular waveguide probe in direct contact with a bilayered biological tissue is analyzed by the FDTD method. A two-layer tissue model consists of an outer thin skin layer over a semi-infinite fat layer is analyzed for a X-band total power radiometer. A spherical tumor with same permittivity as, but slightly higher temperature than, the surrounding normal fat tissue is assumed to exist inside the fat tissue. Active probe characteristics are analyzed first using the FDTD method for a propagating, sinusoidally time-varying, TE/sub 10/ type of excitation source. For the same waveguide probe operated as the radiometer antenna, radiometric weighting factors associated with individual tissue cells are then derived from the FDTD calculated field values. Near field radiating characteristics of the probe and radiometric signals determined for tumors of various size and depth are discussed. The presence of the skin is found to result in a lower power transmission coefficient across the probe aperture and significantly lower absorbed powers by fat; both of these contribute to the much lower radiometric signals observed. >

Detection of the Josephson self-radiation from YBCO step-edge junctions in millimeter-wave

We have investigated both DC and AC Josephson effects of the YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) thin film step-edge junctions; single step-edge junction on LaAlO/sub 3/ substrate with the step angle about 50-60/spl deg/ and biepitaxial double step-edge junction made on MgO substrate with a CeO/sub 2/ seed layer. The Josephson self-radiation was directly detected using the total power radiometer receiver systems with receiving frequencies of K band (21-23 GHz) and millimeter-wave (46-48 GHz and 71-73 GHz) range, respectively. For single step-edge junctions, the Josephson self-radiation peaks exhibited at the voltages corresponding to the basic Josephson voltage-frequency relation. The maximum first-harmonic self-radiation power at receiving frequency f/sub REC/=72 GHz and Josephson linewidth were P(I)=2.0/spl times/10/sup -3/W and /spl Delta/f=3.62 GHz at 4.2 K, respectively. For microwave irradiation, the harmonic Shapiro steps and additional half integer steps with their quasi-periodic variation satisfying the Josephson equation V=(n/m)(hf/2e) were clearly observed. For double step-edge junctions, we also observed the steps corresponding to the two junction boundaries on the two steep steps. These behaviors described with different current-phase relations corresponding to the crystal orientation relationship between the two junction boundaries. >