Novel antenna for precision cosmology

About 13.8 billion years ago, the universe began as an intensely hot, dense plasma composed of particles like electrons, protons, and light nuclei like helium and lithium. Alongside this matter was radiation, now seen as the Cosmic Microwave Background (CMB). The CMB holds vital clues about historical cosmological and astrophysical processes through subtle distortions in its spectrum.

As the universe expanded and cooled, electrons and protons combined to form the first atoms, predominantly hydrogen and helium, during a period known as the Epoch of Recombination. This process released photons, known as the Cosmological Recombination Radiation (CRR), which manifest as an additive distortion in the CMB spectrum. CRR has never been detected so far. Detecting it would confirm our theoretical understanding of the universe’s thermal and ionisation history. However, its signal strength is a billion times weaker than the CMB radiation, making detection highly challenging and requiring the development of extremely sensitive instruments.

In a new study, researchers from IISc and the Raman Research Institute (RRI) propose a unique fantail-shaped, dual polarised broadband antenna capable of detecting signals as faint as one part in 10,000 in the band of 2.5-4 GHz, where the CRR is expected to be found. The antenna maintains a consistent beam shape across its entire frequency range, and features a smooth return loss that mimics the foreground sky spectrum. These features are crucial for isolating the faint CRR signal from the much stronger galactic foreground signals, something that current antennas are unsuitable for.

The proposed antenna was designed and fabricated on a low-loss dielectric substrate and validated using simulated real-world environmental conditions. Its measured performance demonstrates a sensitivity of 30 milliKelvin across the entire 2.5-4 GHz band, making it the most sensitive antenna proposed for this application so far. In addition to CRR studies, the antenna can also be combined with a radiometer for other applications, such as measuring the absolute temperature of the sky in this frequency band.

Top and bottom view of the antenna

REFERENCE:

Satish K, Rao MS, Sarkar D, Antenna Design for Absolute Sky Measurements at Gigahertz Frequencies—a First Step toward Detecting CMB Spectral Distortions from Recombination. The Astronomical Journal (2024).

https://iopscience.iop.org/article/10.3847/1538-3881/ad4a74