# List of cosmic microwave background experiments

This list is a compilation of experiments measuring the cosmic microwave background (CMB) radiation anisotropies and polarization since the first detection of the CMB by Penzias and Wilson in 1964. There have been a variety of experiments to measure the CMB anisotropies and polarization since its first observation in 1964 by Penzias and Wilson. These include a mix of ground-, balloon- and space-based receivers. Some notable experiments in the list are COBE, which first detected the temperature anisotropies of the CMB, and showed that it had a black body spectrum; DASI, which first detected the polarization signal from the CMB; CBI, which made high-resolution observations and obtained the first E-mode polarization spectrum; WMAP; and the Planck spacecraft, which has produced the highest resolution all-sky map to-date of both the temperature anisotropies and polarization signals. Current scientific goals for CMB observation include precise measurement of gravitational lensing, which can constrain the mass of the neutrino; and measurement of B-mode polarization as possible evidence for cosmic inflation.
The design of cosmic microwave background experiments is a very challenging task. The greatest problems are the receivers, the telescope optics and the atmosphere. Many improved microwave amplifier technologies have been designed for microwave background applications. Some technologies used are HEMT, MMIC, SIS and bolometers. Experiments generally use elaborate cryogenic systems to keep the amplifiers cool. Often, experiments are interferometers which only measure the spatial fluctuations in signals on the sky, and are insensitive to the average 2.7 K background.
Another problem is the 1/f noise intrinsic to all detectors. Usually the experimental scan strategy is designed to minimize the effect of such noise. To minimize side lobes, microwave optics usually utilize elaborate lenses and feed horns. Finally, in ground-based (and, to an extent, balloon-based) instruments, water and oxygen in the atmosphere emit and absorb microwave radiation. Even at frequencies where the atmospheric transmission is high, atmospheric emission contributes photon noise that limits the sensitivity of an experiment. CMB research therefore uses of air- and space-borne experiments, as well as dry, high altitude locations such as the Chilean Andes and the South Pole.

## Cosmic microwave background experiments

The list below consists of a partial list of past, current and planned CMB experiments. The name, start and end years of each experiment are given, followed by the basis of the experiment—whether space, balloon or ground based—and the location where appropriate. The frequency and amplifier technologies used are given, as is the main targets of the experiments.
| Name | Start | End | Basis | Location | Frequency (GHz) | Detector technology | Targets |
| Advanced Cosmic Microwave Explorer (ACME) Also HACME: HEMT+ACME | 1988 | 1996 | Ground | South Pole | 26–35; 38–45 | HEMT | Temperature anisotropies |
| Antarctic Plateau Anisotropy Chasing Experiment (APACHE) | 1995 | 1996 | Ground | Antarctic | 100, 150, 250 | Bolometer | Temperature anisotropies |
| Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) | 2001 | 2006 | Balloon | | 3, 5, 7, 10, 30, 90 | HEMT | CMB Spectrum |
| Archeops | 1999 | 2002 | Balloon | | 143, 217, 353, 545 | Bolometer | Measured large and intermediate scale with improved precision at the larger scales. |
| Arcminute Cosmology Bolometer Array Receiver (ACBAR) | 2001 | 2008 | Ground | South Pole | 150, 219, 274 | Bolometer | Temperature anisotropies |
| Arcminute Microkelvin Imager (AMI) | 2005 | — | Ground | UK: Mullard Radio Astronomy Observatory | 12-18 | Interferometer | SZ effect, Temperature anisotropies |
| Q U I JOint TEnerife (QUIJOTE) | 2012 | — | Ground | Tenerife | 11, 13, 17, 19, 30, 40 | Polarizer / OMT | Polarization on degree angular scales |
| ARGO | 1988, 1990, 1993 | 1993 | Balloon | | 150-600 | Bolometer | |
| Array for Microwave Background Anisotropy (AMiBA) | 2007 | — | Ground | Hawaii: Mauna Loa | 86-102 | Interferometer/MMIC | SZ effect; Polarization |
| Atacama B-Mode Search (ABS) | 2012 | 2014 | Ground | Chile: Atacama Desert | 145 | Bolometer | Polarization |
| Atacama Cosmology Telescope (ACT) | 2008 | 2022 | Ground | Chile: Atacama Desert | 148, 218, 277 | Bolometer | Small-scale temperature and polarization anisotropies |
| Atacama Pathfinder Experiment (APEX) | 2007 | — | Ground | Chile: Atacama Desert | 150, 217 | Bolometer | Temperature anisotropies; SZ effect |
| Australia Telescope Compact Array (ATCA) | 1991 | 1997 | Ground | Paul Wild Observatory, New South Wales, Australia | 8.7 | HEMT | |
| Background Emission Anisotropy Scanning Telescope (BEAST) | 2000 | — | Balloon, Ground | | 25–35; 38-45 | HEMT | A ground single dish CMB observatory at the University of California's White Mountain Peak Research station. |
| Background Imaging of Cosmic Extragalactic Polarization (BICEP1) | 2006 | 2008 | Ground | South Pole | 100, 150, 220 | Bolometer | Measured degree-scale polarization with improved precision. |
| BICEP2 | 2009 | 2012 | Ground | South Pole | 150 | Bolometer | Degree-scale B-mode polarization. |
| Keck Array | 2010 | | Ground | South Pole | 95, 150, 220 | Bolometer | Degree-scale B-mode polarization. |
| Balloon-borne Anisotropy Measurement (BAM) | 1995 | 1998 | Balloon | University of British Columbia and Brown University balloon experiment | 110-250 | Spectrometer | Used differential Fourier Transform Spectrometer to measure degree scale anisotropy |
| Balloon-borne Radiometers for Sky Polarisation Observations (BaR-SPoRT) | Cancelled | — | Balloon | | 32, 90 | Polarizer / OMT | |
| Berkeley-Illinois-Maryland Association (BIMA) | 1986 | 2004 | Ground | Hat Creek Radio Observatory, California, USA | 70–116; 210-270 | SIS | |
| BOOMERanG experiment | 1997 | 2003 | Balloon | Long-duration balloon above Antarctica | 90-420 | Bolometer | Intermediate scale fluctuations |
| B-mode RAdiation INterferometer (BRAIN) | Never | — | Ground | Dome-C, Antarctica | | | |
| Clover | Cancelled | — | Ground | | 97, 150, 230 | Bolometer | Cancelled experiment to measure the small scale fluctuations and to search for B-mode polarization. |
| Cobra | 1982 | 1990 | Sounding Rocket | University of British Columbia | 27-900 | Bolometers/ FTS | Frequency spectrum of CMB |
| Cosmic Anisotropy Polarization Mapper (CAPMAP) | 2002 | 2008 | Ground | Crawford Hill Telescope, New Jersey | 40, 90 | MMIC/HEMT | |
| Cosmic Anisotropy Telescope (CAT) | 1994 | 1997 | Ground | Mullard Radio Astronomy Observatory | 13-17 | Interferometer / HEMT | Very small scale fluctuations in small regions of the sky. |
| Cosmic Background Imager (CBI) | 2000 | 2008 | Ground | Llano de Chajnantor Observatory, Chile | 26-36 | HEMT | Very small scale temperature and polarization anisotropies in a small patch of sky. |
| Cosmology Large Angular Scale Surveyor (CLASS) | 2015 | — | Ground | Llano de Chajnantor Observatory, Chile | 40, 90, 150, 220 | TES Bolometer | B-mode polarization signal at multipoles from 2 to 100 |
| Primordial Inflation Polarization Explorer (PIPER) | Future | — | Balloon | | 200, 270, 350, 800 | TES bolometers | B-mode polarization signal |
| COSMOSOMAS | 1998 | 2007 | Ground | Teide Observatory, Tenerife, Spain | 10-18 | HEMT | Circular scanning experiments for CMB and foregrounds |
| Cosmic Background Explorer (COBE) | 1989 | 1993 | Space | Earth orbit | 31.5, 53, 90 (DMR) | | Temperature anisotropies; frequency power spectrum; solar system and galactic dust foregrounds. |
| Cosmic Background Explorer (COBE) | 1989 | 1990 | Space | Earth orbit | 68-3000 200 frequencies (FIRAS) | Bolometers | CMB Spectrum; CMB Temperature; CIB spectrum; Temperature anisotropies; frequency power spectrum; solar system and galactic dust foregrounds. |
| TRIS | 1994 | 2001 | Ground | Campo Imperatore | 0.6, 0.82, 2.5 | | CMB frequency power spectrum |
| COMPASS | 2001 | 2001 | Ground | Pine Bluff, Wisconsin | 26 to 36 | HEMT | Polarization on degree angular scales |
| Cosmological Gene (CG) | 1999 | 2009 | Ground | RATAN-600, Caucasus, Russia | 0.6 to 32 | HEMT | |
| Degree Angular Scale Interferometer (DASI) | 1999 | 2003 | Ground | South Pole | 26-36 | HEMT | Temperature and polarization anisotropy on degree angular scales |
| The E and B Experiment (EBEX) | 2012 | 2013 | Balloon | Antarctica | 150-450 | Bolometer | Inflationary gravitational-wave background (IGB) signal in B-mode polarization |
| Far Infra-Red Survey (FIRS) | 1989 | 1989 | Balloon | National Scientific Balloon Facility, Fort Sumner, New Mexico | 170-680 | Bolometer | Temperature anisotropy on large angular scales. |
| KU-band Polarization IDentifier (KUPID) | 2003 | — | Ground | Crawford Hill Telescope, New Jersey | 12-18 | HEMT | |
| Medium Scale Anisotropy Measurement (MSAM) | 1992 | 1997 | Balloon | | 150-650 | Bolometer | |
| Millimeter Anisotropy eXperiment IMaging Array (MAXIMA) | 1995, 1998, 1999 | 1999 | Balloon | Near Palestine, Texas | 150-420 | Bolometer | Intermediate scale temperature fluctuations. |
| Millimeter Interferometer (MINT) | 2001 | 2002 | Ground | Cerro Toco, Chile | 145 | SIS | Temperature anisotropies around multipole 1500 |
| Millimeter-Wave Bolometric Interferometer (MBI-B) | Future | — | Ground | | 90 | Bolometer | |
| Mobile Anisotropy Telescope (MAT) | 1997, 1998 | 1998 | Ground | Cerro Toco, Chile | 30-140 | HEMT / SIS | |
| Polarization Observations of Large Angular Regions (POLAR) | 2000 | 2000 | Ground | Pine Bluff, Wisconsin, USA | 26-46 | HEMT | Polarization at large angular scales |
| POLARBEAR | 2012 | — | Ground | Chajnantor plateau (Chile) | 150 | Antenna-coupled TES | CMB Polarization. Primordial and lensed B-modes. |
| Polatron | Never | — | Ground | | 100 | Bolometer | |
| Princeton I, Q, and U Experiment (PIQUE) | 2002 | 2002 | Ground | Princeton University | 90 | Bolometer | |
| Python | 1992 | 1997 | Ground | South Pole | 30-90 | HEMT / Bolometer | Temperature anisotropy on intermediate angular scales |
| QMAP | 1996 | 1996 | Balloon | | 30-140 | HEMT / SIS | |
| QUaD | 2005 | 2007 | Ground | South Pole | 100, 150 | Bolometer | Polarization at intermediate angular scale |
| QUBIC | Future | — | Ground | | 150, 220 | Bolometer | B-mode polarization on intermediate angular scale. |
| Q/U Imaging ExperimenT (QUIET) | 2008 | 2010 | Ground | Llano de Chajnantor Observatory, Chile | 40, 90 | HEMT | |
| RELIKT-1 | 1983 | 1984 | Space | Earth orbit | 37 | | Temperature anisotropies |
| Saskatoon experiment | 1993 | 1995 | Ground | Saskatchewan | 26-46 | HEMT | |
| Simons Observatory | 2021 | - | Ground | Atacama | 27/39, 93/145, 225/280 GHz | Bolometers | B-mode polarization, SZE galaxy clusters, sources |
| Sky Polarization Observatory (SPOrt) | Cancelled | — | Space | International Space Station | 22-90 | | Polarization |
| South Pole Telescope | 2006 | | Ground | South Pole | | | Small scale temperature and polarization. |
| SPIDER | 2015 | | Balloon | Antarctica | 90, 150, 220 | Bolometer | Large scale polarization. |
| Sunyaev-Zeldovich Array (SZA) | 2004 | 2008 | Ground | Owens Valley Radio Observatory | 26–36; 85-115 | Interferometer | Produced sensitive CMB anisotropy constraints at l ~ 4000, measured the SZ effect in hundreds of galaxy clusters. Now part of CARMA |
| MUltiplexed Squid/Tes Array for Ninety Gigahertz (MUSTANG/MUSTANG2) | 2007 | — | Ground | Green Bank Telescope (West Virginia, USA) | 90 | TES bolometers | Sunyaev-Zeldovich effect (also used for non-CMB work) |
| Sunyaev-Zeldovich Infrared Experiment (SuZIE) | 1996 | — | Ground | Caltech Submillimeter Observatory, Mauna Kea, Hawaii | 150, 220, 350 | Bolometer | SZ effect |
| Tenerife Experiment | 1984 | 2000 | Ground | Tenerife | 10, 15, 33 | HEMT | Temperature anisotropies from degree to arcminute angular scales |
| TopHat | 2001 | 2001 | Balloon | Antarctica | 150-720 | Bolometer | |
| Very Small Array | 2002 | 2008 | Ground | Tenerife | 26-36 | Interferometer / HEMT | Intermediate and small scale fluctuations in small regions of the sky. |
| Wilkinson Microwave Anisotropy Probe (WMAP) | 2001 | 2010 | Space | Lagrange 2 | 23-94 | HEMT | Temperature anisotropies; Polarization |
| Planck | 2009 | 2013 | Space | Lagrange 2 | 30-857 | HEMT / Bolometer | Temperature and polarization anisotropies; foregrounds |