Antenna Temperature Research Articles

Patch antenna quasioptical mixers

AbstractTwo novel quasioptical mixers using patch antennas and compact local oscillator (LO) ports are described: a fundamentally pumped mixer with a waveguide LO and a subharmonically pumped mixer with a planar LO. The angular dependence of the antenna patterns, the isotropic conversion loss, and the mixer noise figure are presented. A 7.5‐dB noise figure has been measured at 35 GHz for the subharmonically pumped design. The importance of the effective antenna temperature and its effect on the mixer noise figure are discussed.

Distance Determination of Mass Losing Carbon Stars from CO and HCN Radio Observations

AbstractA method of distance determination of evolved carbon stars is proposed and applied to six stars for which the terminal velocity of expansion and the angular size are obtained from the CO and HCN radio observations made at the Nobeyama Radio Observatory. The method assumes the radiation driven wind in spherical geometry. Within those small samples, however, two types of mass losing stars that are systematically different in the antenna temperature ratio TA (CO)/TA(HCN) ≷1, in the velocity ratio υ(CO)/υ(HCN)≶1, and in the angular size ratio θ(CO)/θ(HCN)≷1 seem to be present, suggesting nonspherical geometry of the outflow.

Design of Chinese Second 25-m VLBI Antenna

The first Chinese 25-m VLBI antenna has just been completed at the She-Shan Station of the Shanghai Observatory. In accordance with the plan of the Chinese VLBI Network, the second 25-m VLBI antenna will be established at the Urumqi VLBI Station. It is a shaped symmetric dual reflector Cassegrain antenna and will be equipped with nine feeds from 0.3 GHz to 23 GHz. The surface accuracy of the main reflector is 0.65 mm, and the 14-m central part has a better surface accuracy (0.42 mm) to provide the possibility of making VLBI observations at 44 GHz. This antenna has a semihomology design, and its subreflector has a mechanism to focus it in three dimensions. Crossed dipole feeds for the 0.32 and 0.61 GHz bands are located in the middle of the subreflector, and the focussing mechanism will retract it to bring the dipoles to the prime focus. For other frequencies, a corrugated horn will be mounted at the Cassegrain focus. To obtain dual frequency operation at X and S bands, a flat dichroic reflector and an elliptical reflector will be mounted over the on-axis S band horn and off-axis X band horn, respectively. The antenna has a wheel and track mounting, and the pointing will be controlled by an IBM PC/XT microcomputer. The pointing and tracking accuracy is 16 arcsecond. The estimated aperture efficiencies are in the range of 45–65%. The estimated antenna temperatures are in the range of 35–100 K.

A total power radiometer in the 3-mm wavelength range

It is well known [i] that the application of the modulation method in radiometers decreases the potential senstivity of the receiver, but is justified by the fact that it ensures high stability and dependable performance. For some tasks, for example, in measurements of moderate duration or in other instances when a long, continuous observation time is not required, there is reason to consider the possible use of the total power radiometer. Theoretically, the sensitivity f a total power radiometer is twice as high as that of a modulation radiometer. In addition, realization of the total power method of reception can provide a gain in sensitivity but at the expense of simplification of the input receiver channel. Practical application of total power radiometers is limited for a number of reasons, the most significant of which are fluctuations of the gain coefficient (GC) and fluctuations of the level of internal noise of the receiver [2]. In the millimeter range fluctuations of the radio emission of the atmosphere and instability of radiation reference standards become apreciable [3]. Progress in radioelectronic engineering has led to the appearance of new basic components. At the present time, there are many commercial state-of-the-art microwave devices, distinguished by small overall dimensions and weight, low-voltage power supply, high mechanical strength, and operational dependability, implementation of which has led to an increase in the stability of the parameters of the radio reception of the apparatus. Therefore, it has become advisable to carry out a new analysis of the possibilities of radiometric receivers. The present paper is devoted to problems of the practical construction of a total power radiometer in the millimeter range. In this paper the dependence of the sensitivity of the total power radiometer on measurement time and on the time constant of the output cascade are considered, practical steps towards increasing the stability of performance of the radiometer are described, and experimental results are presented. ~ Sensitivity of the Total Power Radiometer. Problems in the calculation and measurement of the sensitivity of radiometers and of the influence on the sensitivity of various factors have been covered quite broadly in the literature [I-4]. Typically, the sensitivity is determined by the magnitude of the internal noise sources of the radiometer which add onto the input where &p is the growth of the spectral density of the power of the measured signal or a quantity proportional to it, e.g., antenna temperature, D[u(t)] is the variance of the output noise u(t) of the radiometer, and $ is a quantity which is proportional to the gain coefficient of the radiometer. We will consider the output noise u(t) over the observation time interval t o . We will assume that u(t) is a stationary random function. After the time interval t o we will determine the mean-square deviation of u(t) from u(t), its average over this same interval t o . Then, after the statistical averaging (we will denote this operation by a straight line above), we write

PO ? Prospects in interstellar medium

Proton transfer and condensation reactions followed by dissociative electron recombination and charge transfer processes may yield a significant concentration of PO in interstellar clouds. Relevant terrestrial PO lines in the ultraviolet, infrared and microwave regions are listed in order to aid the detection of PO in interstellar clouds. Within the framework of Klein-Dunham potential, spontaneous emission rates and oscillator strengths of strong (Δv=0 sequence) beta bands of the PO molecule are estimated. For SgrB2 source, under optically thin case, each of the two strongest2π1/2,J=2.5−1.5 rotational transitions (108.998 GHz and 109.206 GHz) of PO would have antenna temperature less than 125 mk for beam efficiency∼0.6 and μ=0.7D (electric dipole moment of PO in thev″=0 level of theX2 π state). For Orion molecular cloud, PO (4, 4.5, 5-3, 3.5, 4) (e, f) lines are excitable at 196.305 and 196.500 GHz and each line would have antenna temperature less than 110 mK.

A Simplified Microwave Model and Its Application to the Determination of Some Oceanic Environmental Parametric Values, Using Multichannel Microwave Radiometric Observations

This paper proposes a simplified microwave model, linerized by Taylor expansion and incorporating observed fundamental microwave emissive properties, and discusses its application along with the least square method for determining some oceanic environmental parametric values from multichannel observation data. As a case study, microwave radiometric observations were made in vertical and horizontal polarizations at 6.7 and 18.6 GHz at incidence angles from 200 to 700 at steps of 100, and sea-surface temperature, wind speed, and sky brightness temperatures at the above dual frequencies at zenith angles from 200 to 700 were determined from a set of observed data at each incidence angle. The algorithm-derived results were compared with observed ones and showed good agreements within 10 percent of errors at incidence angles from 200 to 600; however, no good agreement was attained at large incidence angles such as 70°, except sky brightness temperature at 6.7 GHz. This disagreement may be attributed mainly to the difficulty and incompleteness in corrections such as estimation of reflected sky radiation and antenna characteristics, both for retrieval of the antenna temperature averaged over the main lobe and observation errors. This fact, however, may also suggest that observations at such larger incidence angles are of less utility.

New measurements of the cosmic background radiation temperature at 3.3 millimeter wavelength

view Abstract Citations (14) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New Measurements of the Cosmic Background Radiation Temperature at 3.3 Millimeter Wavelength Witebsky, Chris ; Smoot, George ; de Amici, Giovanni ; Friedman, Scott D. Abstract The results of measurements of the cosmic background radiation (CBR) at 3.3 mm are reported, and the instrument, system operation, and data analysis procedures are described in detail. A CBR brightness temperature of 2.57 K with a 1 sigma uncertainty of + or - 0.12 K is obtained. The results are compared with measurements by other authors, and the cold-load antenna temperature and atmospheric model used in the study are discussed in appendices. Publication: The Astrophysical Journal Pub Date: November 1986 DOI: 10.1086/164671 Bibcode: 1986ApJ...310..145W Keywords: Background Radiation; Radiation Measurement; Radiation Spectra; Radio Astronomy; Relic Radiation; Temperature Measurement; Antenna Arrays; Atmospheric Models; Calibrating; Instrument Errors; Millimeter Waves; Radiometers; Space Radiation; COSMIC BACKGROUND RADIATION; INSTRUMENTS full text sources ADS |

Absolute measurements of brightness temperature of distributed cosmic radio radiation in the meter-wavelength range

UDC 532.164.4 Results of measurements of absolute brightness temperatures of distributed cosmic radio radiation in the wavelength range 0.8-1.5 m from regions with coordinates = ~.5 ~ and ~ = 17h-20 h are presented. Measurements were performed by the "null" method involving substitution of a "black" disk, which produced uncertainties from 9 to 12% in the brightness temperature measurements, significantly superior to uncertainties provided by existing radio-isophote mapsor those recalculated to the frequencies studied herein (z15-30%). The standardized "null" regions can be used as references in performing relative measurements. One of the major problems in the study of distributed cosmic radio radiation is the comparison of radio-isophotes, i.e., the spatial distribution of brightness temperature of such radiation. The greatest difficulties occur in establishing an absolute temperature scale, i.e., absolute values of brightness temperatures in reference regions, relative to which brightness temperatures can be calculated in relative measurements. The uncertainties of absolute measurements presented in available radio-isophote maps range from 15 to 30%. These uncertainties are produced mainly by the contribution of radiation received by side and back lobes of the radiotelescope antenna, which is difficult to calculate, as well as uncertainties in the antenna parameter values and the thermal calibration of the receiving apparatus. Relative temperature values indicated on the isophotes are known tomuch greater accuracy, since in relative measurements it is possible to create conditions under which the contribution to antenna temperature of interfering radio radiation entering the side and rear lobes remains constant during the measurement process and can be eliminated. The brightness temperatures of "reference" regions T~ ef should then be close to minimal so that uncertainties in their absolute measurement will have less effect on uncertainties in brightness temperature values measured relative to T~ of. In the meter wavelength range minimum brightness temperatures are about 300~ The possibility then arises (see [i]) of measuring such temperatures by the null method of substituting a "black" disk, the brightness temperature of which is close to that of the surrounding medium, i.e., 300~ The "black" disk method [2] is widely used in radio astronomy and antenna technology. The essence of the method may be described as follows. A disk coated with an "absolute" absorbing material at temperature T o is used as a radio radiation brightness temperature reference. The radiation from the disk is first measured (plane of the disk perpendicular to the antenna pattern), and then the disk is removed from the pattern in a manner such that no construction elements are added or disappear. The antenna remains fixed during the measurements, only the disk appearing and disappearing in the direction of the'main lobe. The temperature increment of the antenna is then [2]

Simultaneous measurements of atmospheric emissions at 10, 33, and 90 GHz

As part of a larger experiment to measure the cosmic microwave background radiation spectrum, frequent simultaneous measurements of microwave thermal emissions from the earth's atmosphere have been made at 10, 33, and 90 GHz. We have performed these measurements at two separate locations, Berkeley, California, and the White Mountain Research Station located near Bishop, California, which differ greatly in altitude and climatic conditions. Typical values of the atmospheric antenna temperature measured in Berkeley (250‐m elevation) during good weather are 2.54±0.29, 12.4±0.3, and 34.3±0.5 K for 10, 33, and 90 GHz, respectively. Corresponding values measured at White Mountain (3800 m) are 1.11± 0.04, 4.48±0.18, and 11.0±0.1 K. Because the measurements are simultaneous in nature, correlations between the measurements taken at the various frequencies provide constraints on models of the microwave emission of the earth's atmosphere, especially models describing atmospheric emission as a function of precipitable water content.

Recommended Rest Frequencies for Observed Interstellar Molecular Microwave Transitions—1985 Revision

Accurate transition frequencies for the transitions of the molecular species detected in interstellar clouds are presented. These are recommended for reference in future astronomical observations in the radio and microwave regions. The transition frequencies have been selected through critical examination and analysis of the spectroscopic data in the literature. The species identity, quantum number labels, and probable error limits (2σ) are presented for each transition. Representative line antenna temperatures are also given for a typical source as a convenience to users. References are cited to both the astronomical and laboratory literature.

Use of the method of parametric estimation in the problem of determining antenna beam patterns from weak radio sources

UDC 621.317.743.7 A means of treating measurement data consisting in the direct estimation of the numerical parameters characterizing the main lobe of the pattern by the method of least squares is analyzed in application to the radio-astronomical method of antenna measurements. The errors in determining the gain, the direction of maximum reception, etc. are found from the information matrix. The results of a test of the method on a 7-m reflecting antenna at a wavelength of 6 cm are presented. One of the limitations of the radio-astronomical method of determining antenna beam patterns (BP) [i] is the smallness of the increment AT a of antenna temperature from the source in comparison with the fluctuation threshold Tfl of the measurement receiver. In determining the parameters characterizing the main lobe of a BP it is possible, however, to lower the demands on the ratio ATa/Tfl through optimum methods of treatment of the measurement results. For this purpose one usually uses linear filtration (convolution of the measured BP cross section with a patternlike function: see [2], for example), which increases the signal/noise ratioat each point of the "smoothed" BP cross section, keeping its shape unchanged under certain conditions. At the same time, in practice one is often required not to reconstruct the shape of the main lobe of the BP, which is usually known, but to determine numerical parameters such as the gain, proportional to ATa, the direction 9 m of maximum reception, and the width Ag0. s of the main lobe at the 0.5 level, and with an error not exceeding an assigned value. These parameters are usually found graphically from the "smoothed" BP, but in this case one cannot always give precisely the error of their determination; in addition, such a procedure is not optimal. In this paper we propose to find the required values of the parameters directly from the measurement data using suitable optimal procedures of parameteric estimation; an advantage of such an approach is, in particular, the possibility of finding the errors of determination of the unknown parameters in explicit form (see below).

Tricarbon monoxide in TMC-1.

We report the measurement of three new lines of C3O in TMC-1. The observed peak antenna temperatures, appropriately corrected for atmospheric and telescope losses, are found to be consistent with a large velocity gradient radiative transfer model whose parameters span the range of standard values for this cloud. The derived fractional abundance for C3O is 1.4 x 10(-10), comparable with the results predicted from a model calculation based on a gas-phase ion-molecule reaction scheme. The results of negative searches for C3O in six other sources are not inconsistent with expected conditions in these clouds.

Quantitative Measurements of Path-Integrated Rain Rate by an Airborne Microwave Radiometer over the Ocean

Data on the airborne microwave radiometer, which is one of the sensors of the airborne microwave rain-scatterometer/radiometer (AMRS) system, are analyzed to infer path-integrated rain rate measured from topside. The equation of radiative transfer is used to relate quantitatively the antenna temperature to the rain rate profile inferred by the scatterometer. The influence of the ocean surface temperature on the radiometer measurements of rain is evaluated by a model computation. The theoretical prediction agrees excellently with the measurements. The effect of nonuniform rain along the propagation path is also evaluated by using the experimental data. It is shown that the excess antenna temperature (difference between the antenna temperature under raining and no-rain conditions) in the 10 GHz band is proportional to the path-integrated rain rate, and a method for determining the reference temperature (antenna temperature under a no-rain condition) is suggested.

Microwave antenna temperature of the earth from geostationary orbit

The microwave antenna temperature of the earth has been computed for the case of a communication satellite antenna viewing the earth from geostationary orbit. An earth‐coverage beam is assumed and detailed computations are performed to account for varying land‐ocean fractions within the field of view. Emission characteristics of the earth's atmosphere and surface are used with an accurate radiative transfer program to compute observed brightness temperatures. Values of 250 to 290 K commonly used for antenna temperature in satellite communication noise calculations are found to be over conservative estimates, with more realistic values lying in the 60–240 K range depending on frequency and subsatellite longitude. These values also depend on assumptions concerning antenna beam coverage. Variations in atmospheric and surface conditions, and variations in antenna beam shape (as distinct from coverage), affect the computed results by less than ≃ 10 K.

Detection of the CO (J = 7 = 6) rotational transition at lambda = 0.37 millimeters toward Orion

The J = 7→6 rotational transition of carbon monoxide has been detected toward the Kleinmann-Low nebula. The peak antenna temperature is 110±35K centered at V<SUB>LSR</SUB> = +5 km s<SUP>-1</SUP>; the FWHM line width is 35±5 km s<SUP>-1</SUP>, and its optical depth ≤0.3. The integrated intensity of the line between -20 and +30 km s<SUP>-1</SUP> leads to a total flux density of (2.5±0.5)×10<SUP>-14</SUP>W m<SUP>-2</SUP> in the beam of 35arcsec±5arcsec.

Catalog of CO observations of galaxies

A series of tables summarizes all observations of CO isotopes in external galaxies up to spring 1984. Entries include the morphological type, apparent magnitude, diameter, recession velocity, and H I content of the galaxies, and lists for the CO observations the telescope used, the features examined, the portion of the galaxy observed, the antenna temperatures of detections and their upper limits, the detected and extrapolated integrated emission, the uncertainties in the data, and the distribution of emission in mapped galaxies. Differences in the calibration convention employed by observers and notations appearing in the literature are explained, and conversion factors are derived.

New maser lines of methanol

We found that the 4/sub -//sub 1/--3/sub 0/ E line (36.169 GHz) of methanol (CH/sub 3/OH) is a maser in Sgr B2, with an antenna temperature of up to 60 K and a velocity width of approx.10 km s/sup -1/. This maser is spatially extended with angular size of up to 90'', is distributed along the edge of H II regions, and apparently is not directly attached to star forming regions. Components with a narrow velocity width also exist. They are unresolved by our beam and have a velocity width of <1.5 km s/sup -1/.

The millimeter spectrum of Titan: Detectability of HCN, HC3N, and CH3CN and the CO abundance

The flux emitted by Titan's disk in millimeter lines of HCN, HC3N, CH3CN, and CO is calculated by means of a radiative transfer formulation which takes into account the sphericity of the atmosphere. It is demonstrated that the plane-parallel approximation for radiative transfer is no longer valid, especially in the core of emission lines, when Titan is not spatially resolved. The antenna temperatures which would be measured by large radiotelescopes observing Titan at frequencies of (1−0) and (2−1) transitions of CO, of (1−0), (2−1), and (3−2) transitions of HCN, and of selected transitions of HC3N and CH3CN in the range 80–300 GHz are calculated. The observability of these transitions is investigated. It is concluded that there is the possibility of inferring the vertical stratospheric distribution of these species from line shape measurements to be achieved with existing or forthcoming radioastronomical instrumentation. The determination of the CO abundance by D. O. Muhleman, G. L. Berge, and R. T. Clancy (1984, (Science (Washington, D.C.), 223, 393–396) from measurements at 115.3 GHz in two 200 MHz bands, is reinterpreted by means of this radiative transfer formulation. A CO mixing ratio between 3 × 10−5 and 18 × 10−5, with a most plausible value of 7.5 × 10−5, is found.

A low density molecular cloud in the vicinity of the Pleiades

The central region of a small, low density molecular cloud, which lies to the south of the Pleiades cluster, has been studied through the use of molecular line observations. Column densities for CH, OH, /sup 12/CO, and /sup 13/CO are derived from the radio data. The CH and OH data yield a visual extinction through the center of the cloud of about 3 mag. The ratio of the antenna temperatures for the OH main lines is consistent with optically thin emission; therefore, the OH results are a good indication of the total extinction through the optically thin emission; therefore, the OH results are a good indication of the total extinction through the cloud. The analysis of the carbon monoxide data produces a relatively high kinetic temperature of at least 20 K, a low total gas density of approx.300-500 cm/sup -3/, and a column density of approx.4 x 10/sup 17/ cm/sup -2/ for /sup 12/CO. Thus this small molecular cloud is not typical of the molecular material generally studied in Taurus.

On the interpretation of the broad-band millimeter-wave flux from Orion

Spectral observations of the core of Orion A at wavelengths around 1.3 mm show a high density of strong, broad emission lines. The combined flux in lines with peak antenna temperatures stronger than 0.2 K accounts for approximately 40 percent of the broad-band millimeter-wave flux from the region. Thus the broad-band flux from Orion A is in large part due to sources other than dust emission.