arXiv subjects

Oisin Creaner

Publications and source records attributed to Oisin Creaner.

4 recordsLinked to original sources

arXiv2026

Characterising the response of an International LOFAR Station

Phased-array radio interferometers with fixed antennas are a highly scalable design which can achieve a large gain. However they are complex systems and challenging to calibrate. Here we examine the response of an International LOFAR Station, the high-band antennas of the Irish LOFAR station. In modelling our measured responses, we account for projection effects, the frequency-dependence of the aperture efficiency and pulsar spectra, as well as sky and instrumental noise contributions. We perform long-track observations of 11 bright pulsars as they move across the sky, apply RFI mitigation and determine the signal-to-noise ratio response as a function of time, elevation and azimuth. We use the DreamBeam software to model the beam response of the station to compare with what is observed. The sensitivity map so obtained was validated using observations of PSR B0329+54 on the Swedish LOFAR station. As expected, the sensitivity is higher near the zenith. However, an asymmetry with respect to the zenith point is detected. Characterising the instrumental response in azimuth reveals a better performance as the targets rise, as compared to when they set. This trend is seen for all pulsars and is consistent with other International Stations. The magnitude of the effect can exceed 20%. We consider variations in the beam model and noise level, both frequency- and time- dependent, to try to account for this. A possible explanation for the hysteresis-like response in elevation could be an imbalanced signal weighting of the polarisation components. This work addresses the importance of accurate beam modelling and noise evaluation for the LOFAR 2.0 system upgrade as well as being relevant to the under-construction SKA-Low facility.

astro-ph.IM↗

arXiv2024

Automation of MKID Simulations for Array Building with AEM (Automated Electromagnetic MKID Simulations)

Microwave Kinetic Inductance Detectors (MKIDs) are photon detectors comprised of superconducting LC resonators with unique resonant frequencies corresponding to their geometrical structure. As each pixel has its own geometry, electromagnetic simulations by hand of every pixel in a kilo-pixel array are impractical. Simulating fewer pixels and interpolating in between risks reduced pixel yield in arrays due to overlapping resonant frequencies. We introduce a new software called AEM (Automated Electromagnetic MKID simulations) that automates the constructions and simulations of every simulated MKID pixel in an array according to specified resonant frequencies and a Qc range. We show automated designs to have an increased pixel yield (avoiding loses due to interpolation completely), increased accuracy in resonance frequency and Qc values when compared to interpolated structures. We also demonstrate a simulated trial of AEM for 100 MKIDs between 4 & 8 GHz to produce MKIDs with accuracies of +-0.2 MHz with a runtime of 10 hrs 45 mins.

astro-ph.IM↗

arXiv2024

Limitations to the energy resolution of single-photon sensitive Microwave Kinetic Inductance Detectors

This paper describes the energy resolution of Microwave Kinetic Inductance Detectors (MKIDs), and models some limiting factors to it. Energy resolution is a measure of the smallest possible difference in energy of the impinging photons, Delta E, that the detector can identify and is of critical importance for many applications. Limits to the energy resolution cause by the Fano effect, amplifier noise, current inhomogeneities, and readout sampling frequency are taken into consideration for this model. This paper describes an approach to combine all of these limitations and predict a wavelength dependency of the upper limit to the resolving power.

physics.ins-det↗

arXiv2023

Frequency Domain Multiplexing for MKIDs: Comparing the Xilinx ZCU111 RFSoC with their new 2x2 RFSoC board

The Xilinx ZCU111 Radio Frequency System on Chip (RFSoC) is a promising solution for reading out large arrays of microwave kinetic inductance detectors (MKIDs). The board boasts eight on-chip 12-bit / 4.096 GSPS analogue-to-digital converters (ADCs) and eight 14-bit / 6.554 GSPS digital-to-analogue converters (DACs), as well as field programmable gate array (FPGA) resources of 930,000 logic cells and 4,272 digital signal processing (DSP) slices. While this is sufficient data converter bandwidth for the readout of 8,000 MKIDs, with a 2 MHz channel-spacing, and a 1 MHz sampling rate (per channel), additional FPGA resources are needed to perform the DSP needed to process this large number of MKIDs. A solution to this problem is the new Xilinx RFSoC 2x2 board. This board costs only one fifth of the ZCU111 while still providing the same logic resources as the ZCU111, albeit with only a quarter of the data converter resources. Thus, using multiple RFSoC 2x2 boards would provide a better balance between FPGA resources and data converters, allowing the full utilization of the RF bandwidth provided by the data converters, while also lowering the cost per pixel value of the readout system, from approximately EUR2.50 per pixel with the ZCU111, to EUR1 per pixel.

astro-ph.IM↗