By Amit Malewar 4 Dec, 2024
Collected at: https://www.techexplorist.com/novel-antenna-design-measure-faint-cosmological-radio-frequency-signals/93978/
The Universe is approximately 13.8 billion years old. Shortly after the Big Bang, it was hot and dense, preventing the existence of atoms and prompting matter formation in the form of electrons, protons, and light nuclei like helium and lithium.
Radiation also coexisted with matter, which we now observe as the Cosmic Microwave Background (CMB). The CMB’s distortions in its spectrum carry vital information about the early Universe.
One such distortion occurred during the Epoch of Recombination when the Universe cooled and expanded. This led to the transition of matter from a fully ionized plasma to neutral hydrogen and helium atoms. As this happened, photons were emitted in a process known as Cosmological Recombination Radiation (CRR), adding a distortion to the CMB spectrum.
It is a significant challenge to detect Cosmic Recombination Radiation (CRR), which is nine orders of magnitude fainter than the CMB. The CMB is measured at about 3 degrees Kelvin, equivalent to -270°C.
CRR’s detection would provide crucial confirmation of our understanding of the Universe’s thermal and ionization history. It would also offer a unique opportunity to measure the abundance of helium in the Universe before it started forming in the cores of stars. However, due to CRR’s extraordinarily faint and elusive nature, the scientific community faces the challenge of developing susceptible instruments to detect this radiation.
Scientists at the Raman Research Institute in Bangalore have developed a novel antenna design to perform sky measurements in the 2.5 – 4 Gigahertz (GHz) frequency range. This frequency range is considered optimal for detecting faint cosmic recombination radiation (CRR) signals, which have never been detected before. These elusive signals contain crucial information that could enhance our understanding of the Universe’s thermal and ionization history.
This unique ground-based broadband antenna can detect as faint as one part in 10,000.
Keerthipriya Sathish, lead author of the paper and Research Scientist at RRI, said, “For the sky measurements we plan to perform, the broadband antenna offered us the highest sensitivity compared to other antennas designed for the same bandwidth. The metric of being frequency-independent over the wideband and ensuring smooth frequency performance is unconventional, something only a custom design, such as ours, could achieve. An off-the-shelf wideband antenna won’t work.”
A fantail antenna has been proposed for detecting Cosmological Recombination Radiation (CRR) due to its unique design and stable frequency performance. This antenna features a dual-polarized dipole design with four arms, each shaped like a fantail. Its key advantage is that it maintains the same radiation pattern across frequencies, with only a +/- 1% variation in characteristics. This allows it to consistently target the same patch of the sky across its full operational bandwidth of 1.5 GHz (2.5 to 4 GHz), which is crucial for distinguishing spectral distortions from galactic foregrounds.
The antenna weighs 150 grams and measures 14 cm x 14 cm in a square box shape. It consists of a flat, low-loss dielectric substrate with the antenna etched in copper on top and an aluminum ground plate on the bottom. A thick foam layer, radio-transparent and housing the antenna’s connectors, sits between these plates, ensuring the antenna is lightweight yet robust for its purpose.
Mayuri Rao, faculty, RRI, said, “The antenna has a sensitivity of around 30 millikelvins (mK) across the 2.5-4 GHz frequency range, enabling it to detect tiny temperature variations in the sky. Even before scaling it to an array, this antenna will enable exciting first-science results once integrated with its custom receiver.”
“We plan to study a reported excess radiation in the sky from a previous experiment at 3.3 GHz, attributed to exotic physics, including Dark Matter annihilation. Such experiments with this antenna will help inform improvements in the antenna and experiment design to go all the way to the sensitivity needed for a CRR detection.”
The authors noted, “An antenna array will be deployed in radio-quiet locations, where there is minimal or no radio frequency interference. The design of this planar antenna is such that it is easily fabricated using methods similar to those used in Printed Circuit Board (PCB) printing. Thus, this design offers high machining accuracy and consistency during replication for multiple-element arrays, is portable and easily deployable.”
Journal Reference:
- Keerthipriya Sathish, Mayuri Sathyanarayana Rao, and Debdeep Sarkar. Antenna Design for Absolute Sky Measurements at Gigahertz Frequencies—a First Step toward Detecting CMB Spectral Distortions from Recombination. The Astronomical Journal. DOI 10.3847/1538-3881/ad4a74
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