The Decoupled Potential Integral Equation for Time-Harmonic Electromagnetic Scattering

We present a new formulation for the problem of electromagnetic scattering from perfect electric conductors. While our representation for the electric and magnetic fields is based on the standard vector and scalar potentials ${\bf A},\phi$ in the Lorenz gauge, we establish boundary conditions on the potentials themselves, rather than on the field quantities. This permits the development of a well-conditioned second kind Fredholm integral equation which has no spurious resonances, avoids low frequency breakdown, and is insensitive to the genus of the scatterer. The equations for the vector and scalar potentials are decoupled. That is, the unknown scalar potential defining the scattered field, $\phi^{Sc}$, is determined entirely by the incident scalar potential $\phi^{In}$. Likewise, the unknown vector potential defining the scattered field, ${\bf A}^{Sc}$, is determined entirely by the incident vector potential ${\bf A}^{In}$. This decoupled formulation is valid not only in the static limit but for arbitrary $\omega\ge 0$.Comment: 33 pages, 7 figure

A Gap Waveguide-Based 2x2 Circularly-polarized Monopulse Antenna Array

Paper submitted to The European Conference on Antennas and Propagation 2022 (EuCAP), 27 March - 1 April 2022, Madrid (Spain).This paper presents a circular-polarized gap-waveguide-based compact monopulse array antenna for millimeter-wave tracking applications at Ka-band (29 to 31 GHz). The gap waveguide planar monopulse comparator network is integrated in a single layer with a 2x2 corporate-fed network combining ridge gap and groove gap waveguides. Radiating cavities consist of cubes with chamfered corners. Preliminary results show a bandwidth of 2 GHz with input reflection coefficients better than -20 dB for both ports of the antenna. In addition, the isolation between ports is greater than 50 dB. The design allows for scalability to build higher gain arrays from the antenna presented in this communication.This work is part of the projects PID2019-107688RB-C22 and PID2019-103982RB-C43 funded by the Spanish Ministry of Science and Innovation MCIN/AEI/10.13039/501100011033

Mecanismo para conmutar el sentido de la polarización circular en antenas ranuradas en la banda Ka

This paper presents two slotted array antennas working in the Ka-band with switchable circular polarization capability. The first prototype is a series-fed slotted-waveguide linear array composed of ten T-shaped slots. The second antenna is a two-dimensional array with 2x2 T-shaped slots fed by a corporate distribution network. In both cases, a reflection coefficient below -10 dB has been experimentally observed within the targeted frequency band between 29.5 and 30.5 GHz. Good polarization purity is achieved for both polarization senses and in both prototypes. The fundamental contribution of the paper is to propose a simple mechanism to switch the circular polarization sense in a low-cost, low-profile and high-efficient antenna. The design and experimental results confirm that the solution is suitable for both one- and two-dimensional arrays in the millimeter-wave band

The key role of off-axis singularities in free-space vortex transmutation

We experimentally demonstrate the generation of off-axis phase singularities in a vortex transmutation process induced by the breaking of rotational symmetry. The process takes place in free space by launching a highly-charged vortex, owning full rotational symmetry, into a linear thin diffractive element presenting discrete rotational symmetry. It is shown that off-axis phase singularities follow straight dark rays bifurcating from the symmetry axis. This phenomenon may provide new routes towards the spatial control of multiple phase singularities for applications in atom trapping and particle manipulation.Comment: 4 pages, 4 figures, to appear in Applied Physics B: Lasers and Optic

Antennas and Propagation Lab. Annual Research Report 2019

The Antennas and Propagation Laboratory (APL) focuses its research activities on various areas related to the analysis and design of antennas, as well as to the analysis of different propagation environments. The operating frequency bands under study range from UHF to the V band, thereby covering a wide range of applications, from mobile terminals, to satellite antennas. This report details some of its projects up to 2019

Symmetry, winding number and topological charge of vortex solitons in discrete-symmetry media

We determine the functional behavior near the discrete rotational symmetry axis of discrete vortices of the nonlinear Schr\"odinger equation. We show that these solutions present a central phase singularity whose charge is restricted by symmetry arguments. Consequently, we demonstrate that the existence of high-charged discrete vortices is related to the presence of other off-axis phase singularities, whose positions and charges are also restricted by symmetry arguments. To illustrate our theoretical results, we offer two numerical examples of high-charged discrete vortices in photonic crystal fibers showing hexagonal discrete rotational invariance.Comment: 6 pages, 2 figure

PIFA antenna for smart watch application in the 2.4 GHz band

[EN] This paper presents a Planar Inverted-F Antenna (PIFA) design for a smartwatch application, optimized to operate on the 2.4 GHz Bluetooth frequency band, on the proximity of the human forearm. The PIFA antenna is mounted on the watchstrap that is used as the antenna substrate. The antenna is fed in a singular way, since a coplanar wave-guide (CPW) transmission line is used to excite the antenna. The antenna is integrated in the watchstrap, curved over the phantom forearm and simulated along with the watchcase. A return loss of ¿20 dB is obtained at 2.4 GHz, and an efficiency of ¿5 dB, which represents a good efficiency taking into account the effect of the human forearm.This work has been supported by the Spanish Ministry of Science and Innovation (Ministerio Ciencia e Innovación) under project PID2019-107885GB-C32.Abdelhakim, A.; Cabedo Fabres, M.; Ferrando Bataller, M. (2021). PIFA antenna for smart watch application in the 2.4 GHz band. IEEE. 703-704. https://doi.org/10.1109/APS/URSI47566.2021.970448070370