arXiv subjects

David González-Ovejero

Publications and source records attributed to David González-Ovejero.

5 recordsLinked to original sources

arXiv2026

Status and future development of the COSMOCal Project for absolute CMB polarization calibration

Cosmic Microwave Background (CMB) polarization measurements are pushing instrumental sensitivities to levels where calibration systematics become a dominant limitation. The large dynamic range between cosmological and Galactic emission prevents future experiments from relying only on diffuse sky measurements or standard celestial calibrators. To address this challenge, the COSmological Microwave Observations Calibrator (COSMOCal) project proposes an artificial calibration source deployed as a guest payload on a geostationary satellite, scheduled for launch by the Eutelsat group by 2030. This source will provide stable, well-characterized polarized microwave signals accessible to multiple ground-based observatories. In this work, we present the status of the project, the updated development timeline, and the refined scientific and technical requirements, defined with the observatories that plan to use this calibration source. Furthermore, we investigate the interplay between instrumental systematics and component separation in the presence of complex models of interstellar dust emission. We discuss in this paper how this can impact the recovery of the primordial signal, and whether residual calibration errors can degrade the performance of foreground cleaning algorithms.

astro-ph.IM↗

arXiv2026

Plane-Wave Excitation of Multi-Beam Modulated Metasurface Antennas

This paper explores the design of multibeam metasurface (MTS) antennas excited by multi-directional plane-wave launchers. First, we solve the fundamental yet open problem of a plane surface wave (SW) that propagates obliquely to the modulation direction of a sinusoidally modulated MTS. Closed-form expressions are provided to accurately predict the beam pointing angles for any propagation direction of the illuminating plane SW and for any Floquet harmonic. Then, the proposed formulation is used to design a highly directive multibeam MTS antenna at K-band with linear polarization. The designed antenna combines an MTS and a pillbox quasi-optical beamformer arranged in a very compact space. A pillbox is a double-layer structure that embeds a reflector coupled to multiple primary feeds in the lower layer. The beams launched by the primary feeds are thus transformed into plane waves with different directions in the upper layer. Printing a modulated MTS in the upper layer results in a low-profile, multibeam antenna suitable for PCB fabrication. Experimental results validate the proposed formulation. The fabricated MTS antenna exhibits a maximum directivity of 30.5 dB and a 17.5% fractional -3 dB directivity bandwidth over the 19.7-21.7 GHz band. By switching feeds and modifying the operating frequency, the scanning range is [$3^o$,$35^o$] in elevation and [$-76^o$,$+76^o$] in azimuth. Additionally, different antenna designs are included that demonstrate the validity and generality of the derived formulation. The proposed multibeam concept can be exploited in satellite communications and 5G/6G networks.

physics.app-ph↗

arXiv2026

Leaky-Wave Antenna Analysis using Multi-Modal Network Theory with Open Periodic Boundaries

This paper introduces two methods for analyzing periodic leaky-wave antennas (LWAs) within a new framework denoted as multi-modal network theory (MNT) with open periodic boundaries (OPBs). The approach is hybrid, combining analytical techniques with a commercial full-wave solver. The first method computes the dispersion diagram of periodic LWAs. It is iterative and relies on the full-wave simulation of a single unit-cell of a LWA, coupled with the analytical solution of an eigenvalue problem. This method effectively captures both the phase and attenuation constants of periodic LWAs while using fewer modes than previous methods with commercial frequency-domain solvers. The method is validated by computing the dispersion of classic LWA unit-cells and comparing them to those obtained through full-wave simulations of the full-length antenna and other state-of-the-art methods. The second, also based on OPB-MNT, focuses on LWA analysis in reception. Specifically, it determines the response of a unit-cell to an incident plane wave. To validate this method, we compute the response of LWA with different unit-cell designs. By comparing these results with the corresponding dispersion analysis, we show that the receiving case and the eigenvalue problem are related but not simply time-reversed versions of each other.

physics.optics↗

arXiv2026

Expressivity of Programmable-Metasurface-Based Physical Neural Networks: Encoding Non-Linearity, Structural Non-Linearity, and Depth

Wave-based signal processing conventionally encodes input data into the input wavefront, making it challenging to implement non-linear operations. Programmable wave systems enable an alternative approach: encoding the input data into the scattering properties of tunable components. With such structural input encoding, two potentially non-linear mappings are involved: first, from the input data to the tunable components' scattering characteristics, and, second, from these scattering characteristics to the output wavefront. In this paper, we systematically examine the expressivity of a wave-based physical neural network (WPNN) with structural input encoding. Our analysis is based on a physics-consistent multiport-network model of a compact D-band rich-scattering cavity parametrized by a 100-element programmable metasurface. We separately control encoding non-linearity, structural non-linearity, and network depth in order to examine their interplay, considering a controlled scalar regression task. With phase encoding and strong inter-element mutual coupling (MC), both aforementioned mappings are strongly non-linear and the WPNN performs very well even with a single layer. We further observe that additional layers can partially compensate for weak inter-element MC. In addition, we demonstrate that WPNN depth can improve expressivity even when it is not associated with an increase in trainable weights. Altogether, our results provide a physics-consistent picture of how encoding choice, MC strength, and depth jointly govern the expressive power of PM-based WPNNs, informing design choices for future experimental implementations of WPNNs.

eess.SP↗

arXiv2022

First-principles analysis of energy exchange in time-varying capacitors for energy trapping applications

Time-varying networks, consisting of lumped elements, such as resistors, capacitors, and inductors, actively modulated in time, have introduced a host of novel wave phenomena and witnessed a remarkable development during recent years. This paper investigates the scattering from a time varying capacitor and how such a load can be fully reflectionless when the capacitance is suitably modulated in time. We analytically derive the required temporal dependence of the capacitance and show how in contrast to other techniques it avoids extreme and negative values and, as a result, can be implemented in a feasible way, when the capacitor is charged with a DC voltage source. We also derive from first principles the energy balance of such a time-varying capacitor, proving that the energy of an incoming pulse is transferred to the modulation source. Our findings clarify scattering of waves from time-varying capacitors and open up a new way to matching of broadband pulses.

physics.app-ph↗