Wideband Agile Digital Microwave Radiometer

The objectives of this work were to take the initial steps needed to develop a field programmable gate array (FPGA)- based wideband digital radiometer backend (>500 MHz bandwidth) that will enable passive microwave observations with minimal performance degradation in a radiofrequency-interference (RFI)-rich environment. As manmade RF emissions increase over time and fill more of the microwave spectrum, microwave radiometer science applications will be increasingly impacted in a negative way, and the current generation of spaceborne microwave radiometers that use broadband analog back ends will become severely compromised or unusable over an increasing fraction of time on orbit. There is a need to develop a digital radiometer back end that, for each observation period, uses digital signal processing (DSP) algorithms to identify the maximum amount of RFI-free spectrum across the radiometer band to preserve bandwidth to minimize radiometer noise (which is inversely related to the bandwidth). Ultimately, the objective is to incorporate all processing necessary in the back end to take contaminated input spectra and produce a single output value free of manmade signals to minimize data rates for spaceborne radiometer missions. But, to meet these objectives, several intermediate processing algorithms had to be developed, and their performance characterized relative to typical brightness temperature accuracy re quirements for current and future microwave radiometer missions, including those for measuring salinity, soil moisture, and snow pack

The QUIET Instrument

The Q/U Imaging ExperimenT (QUIET) is designed to measure polarization in the Cosmic Microwave Background, targeting the imprint of inflationary gravitational waves at large angular scales ( approx 1 deg.) . Between 2008 October and 2010 December, two independent receiver arrays were deployed sequentially on a 1.4 m side-fed Dragonian telescope. The polarimeters which form the focal planes use a highly compact design based on High Electron Mobility Transistors (HEMTs) that provides simultaneous measurements of the Stokes parameters Q, U, and I in a single module. The 17-element Q-band polarimeter array, with a central frequency of 43.1 GHz, has the best sensitivity (69 micro Ks(exp 1/2)) and the lowest instrumental systematic errors ever achieved in this band, contributing to the tensor-to-scalar ratio at r < 0.1. The 84-element W-band polarimeter array has a sensitivity of 87 micro Ks(exp 1/2) at a central frequency of 94.5 GHz. It has the lowest systematic errors to date, contributing at r < 0.01 (QUIET Collaboration 2012) The two arrays together cover multipoles in the range l approximately equals 25-975 . These are the largest HEMT-ba.sed arrays deployed to date. This article describes the design, calibration, performance of, and sources of systematic error for the instrument

New Measurements of Fine-Scale CMB Polarization Power Spectra from CAPMAP at Both 40 and 90 GHz

We present new measurements of the cosmic microwave background (CMB) polarization from the final season of the Cosmic Anisotropy Polarization MAPper (CAPMAP). The data set was obtained in winter 2004-2005 with the 7 m antenna in Crawford Hill, New Jersey, from 12 W-band (84-100 GHz) and 4 Q-band (36-45 GHz) correlation polarimeters with 3.3' and 6.5' beamsizes, respectively. After selection criteria were applied, 956 (939) hours of data survived for analysis of W-band (Q-band) data. Two independent and complementary pipelines produced results in excellent agreement with each other. A broad suite of null tests as well as extensive simulations showed that systematic errors were minimal, and a comparison of the W-band and Q-band sky maps revealed no contamination from galactic foregrounds. We report the E-mode and B-mode power spectra in 7 bands in the range 200 < l < 3000, extending the range of previous measurements to higher l. The E-mode spectrum, which is detected at 11 sigma significance, is in agreement with cosmological predictions and with previous work at other frequencies and angular resolutions. The BB power spectrum provides one of the best limits to date on B-mode power at 4.8 uK^2 (95% confidence).Comment: 19 pages, 17 figures, 2 tables, submitted to Ap

A Spin Modulated Telescope to Make Two Dimensional CMB Maps

We describe the HEMT Advanced Cosmic Microwave Explorer (HACME), a balloon borne experiment designed to measure sub-degree scale Cosmic Microwave Background anisotropy over hundreds of square degrees, using a unique two dimensional scanning strategy. A spinning flat mirror that is canted relative to its spin axis modulates the direction of beam response in a nearly elliptical path on the sky. The experiment was successfully flown in February of 1996, achieving near laboratory performance for several hours at float altitude. A map free of instrumental systematic effects is produced for a 3.5 hour observation of 630 square degrees, resulting in a flat band power upper limit of (l(l+1)C_l/2 pi)^0.5 < 77 microK at l = 38 (95% confidence). The experiment design, flight operations and data, including atmospheric effects and noise performance, are discussed.Comment: 4 pages, 3 figure

Instrumental and Analytic Methods for Bolometric Polarimetry

We discuss instrumental and analytic methods that have been developed for the first generation of bolometric cosmic microwave background (CMB) polarimeters. The design, characterization, and analysis of data obtained using Polarization Sensitive Bolometers (PSBs) are described in detail. This is followed by a brief study of the effect of various polarization modulation techniques on the recovery of sky polarization from scanning polarimeter data. Having been successfully implemented on the sub-orbital Boomerang experiment, PSBs are currently operational in two terrestrial CMB polarization experiments (QUaD and the Robinson Telescope). We investigate two approaches to the analysis of data from these experiments, using realistic simulations of time ordered data to illustrate the impact of instrumental effects on the fidelity of the recovered polarization signal. We find that the analysis of difference time streams takes full advantage of the high degree of common mode rejection afforded by the PSB design. In addition to the observational efforts currently underway, this discussion is directly applicable to the PSBs that constitute the polarized capability of the Planck HFI instrument.Comment: 23 pages, 11 figures. for submission to A&

MMIC power amplifiers as local oscillator drivers for FIRST

The Heterodyne Instrument for the Far-Infrared and Sub- millimeter Telescope requires local oscillators well into the terahertz frequency range. The mechanism to realize the local oscillators will involve synthesizers, active multiplier chains (AMC's) with output frequencies from 71 - 112.5 GHz, power amplifiers to amplify the AMC signals, and chains of Schottky diode multipliers to achieve terahertz frequencies. We will present the latest state-of-the-art results on 70 - 115 GHz Monolithic Millimeter-wave Integrated Circuit power amplifier technology

First measurements of the polarization of the cosmic microwave background radiation at small angular scales from CAPMAP

Polarization results from the Cosmic Anisotropy Polarization MAPper (CAPMAP) experiment are reported. These are based upon 433 hours, after cuts, observing a 2 square degree patch around the North Celestial Pole (NCP) with four 90 GHz correlation polarimeters coupled to optics defining 4\arcmin beams. The E-mode flat bandpower anisotropy within $\ell=940^{+330}_{-300}$ is measured as 66$^{+69}_{-29} \mu$K$^2$; the 95% Confidence level upper limit for B-mode power within $\ell=1050^{+590}_{-520}$ is measured as 38 $\mu$K$^2$.Comment: 4 pages, 2 figures; corrected formatting and comments of second version, identical in substance. In the first version the wrong concordance model was used, results (fit to multiplier to concordance model) and figures have been updated to the proper one. In the first version the central 68% regions were quoted, while now the 68% confidence intervals of highest posterior density are give

Temporal Experiment for Storms and Tropical Systems Technology Demonstration (TEMPEST-D) Mission: Enabling Time-Resolved Cloud and Precipitation Observations from 6U-Class Satellite Constellations

The Temporal Experiment for Storms and Tropical Systems Technology Demonstration (TEMPEST-D) mission is to demonstrate the capability of 6U-Class satellite constellations to perform repeat-pass radiometry to measure clouds and precipitation with high temporal resolution on a global basis. The TEMPEST mission concept is to improve understanding of clouds and precipitation by providing critical information on their time evolution in different climatic regimes. Measuring at five frequencies from 89 to 182 GHz, TEMPEST-D millimeter-wave radiometers are capable of penetrating into the cloud to observe changes as precipitation begins or ice accumulates inside the storm. The TEMPEST-D flight model radiometer instrument has been completed, passed functional testing, vibration testing and self-compatibility testing with the XB1 spacecraft bus. The next steps for the TEMPEST-D millimeter-wave radiometer are thermal vacuum testing and antenna pattern measurements. The complete TEMPEST-D flight system will be delivered to NanoRacks for launch integration in the autumn of 2017, in preparation for launch to the ISS in the second quarter of 2018, with deployment shortly thereafter into a nominal orbit at 400-km altitude and 51.6° inclination