The hypersonic flight regime is conventionally defined for Mach > 5; in these conditions, the flying object becomes enveloped in a plasma. This plasma is densest in thin surface layers, but, in typical situations of interest, it impacts electromagnetic wave propagation in an electrically large volume. We address this problem with a hybrid approach. We employ the equivalence theorem to separate the inhomogeneous plasma region from the surrounding free space via an equivalent (Huygens) surface and the Eikonal approximation to Maxwell equations in the large inhomogeneous region for obtaining equivalent currents on the separating surface. Then, we obtain the scattered field via (exact) free-space radiation of these surface equivalent currents. The method is extensively tested against reference results and then applied to a real-life reentry vehicle with full 3-D plasma computed via computational fluid dynamic (CFD) simulations. We address both scattering [radar cross section (RCS)] from the entire vehicle and radiation from the onboard antennas. From our results, significant radio link path losses can be associated with plasma spatial variations (gradients) and collisional losses to an extent that matches well the usually perceived blackout in crossing layers in the cutoff. Furthermore, we find good agreement with existing literature concerning significant alterations of the radar response (RCS) due to the plasma envelope.

This paper presents an investigation of a new technique for the accurate determination of the full sphere pattern of an antenna from truncated spherical near field measurements. The approach was first described and is based on determining a set of equivalent currents that radiate the same pattern in the known area and thus extrapolate the unknown fields in the truncated area. The study is performed on actual measured near-field data to investigate the effectiveness of the technique in realistic spherical near field antenna measurement scenarios.

Nonlinear effects in the radio front-end can degrade communication quality and system performance. In this paper we present a new design technique for reconfigurable antennas that minimizes the nonlinear distortion and maximizes power efficiency through the minimization of the coupling between the internal switching ports and the external feeding ports. As a nonlinear design and validation instance, we present the nonlinear characterization up to 50 GHz of a PIN diode commonly used as a switch for reconfigurable devices in the microwave band. Nonlinear models are extracted through X-parameter measurements supported by accurate calibration and de-embedding procedures. Nonlinear switch models are validated by S-parameter measurements in the low power signal regime and by harmonic measurements in the large-signal regime and are further used to predict the measured nonlinearities of a reconfigurable antenna. These models have the desired particularity of being integrated straightforwardly in the internal multi-port method formulation, which is used and extended to account for the power induced on the switching elements. A new figure of merit for the design of reconfigurable antennas is introduced—the power margin, that is, the power difference between the fed port and the switching elements, which combined with the nonlinear load models directly translates into nonlinearities and power-efficiency-related metrics. Therefore, beyond traditional antenna aspects such as port match, gain, and beam orientation, switch power criteria are included in the design methodology. Guidelines for the design of reconfigurable antennas and parasitic layers of minimum nonlinearity are provided as well as the inherent trade-offs. A particular antenna design suitable for 5G communications in the 3.5 GHz band is presented according to these guidelines, in which the specific switching states for a set of target performance metrics are obtained via a balancing of the available figures of merit with multi-objective separation criteria, which enables good control of the various design trade-offs. Average Error Vector Magnitude (EVM) and power efficiency improvement of 12 and 6 dB, respectively, are obtained with the application of this design approach. In summary, this paper introduces a new framework for the nonlinear modeling and design of reconfigurable antennas and provides a set of general-purpose tools applicable in cases beyond those used as examples and validation in this work. Additionally, the use of these models and guidelines is presented, demonstrating one of the most appealing advantages of the reconfigurable parasitic layer approach, their low nonlinearity.

We present the multi-physical analysis of the induction-corrosion process undergone by a buried pipe subject to electromagnetic induction from a nearby High Voltage Transmission Line (HVTL). The scenario analyzed models a typical situation found in Colombia by using realistic characteristics of the pipe, the HVTL, and environmental parameters such as soil resistivity. The results presented provide a quantitative view of the corrosion process and constitute a useful tool for the analysis and design of the increasingly common situation of pipelines running near HVTLs.

This paper describes the design and validation by simulation of compact dual-port reconfigurable antennas (via switches) providing antenna diversity or port duplexing, which in turn are useful in advanced techniques such as cognitive radio (CR) and Multiple-Input Multiple-Output (MIMO). The design results from optimization of an initial structure using the Genetic Algorithm (GA) and evaluated via Method of Moments (MoM) electromagnetic simulation. The optimization process determines concurrently: antenna geometry, location, number and state of the switching devices. The starting point is a simple planar antenna that offers robustness, compactness and allows for an easy fabrication. The resulting devices operate over a band of 0.6 octaves and possess dimensions under 0.25λ0 × 0.25λ0 for the lowest frequency of operation.

Solar flares and Coronal Mass Ejections (CMEs) are two examples of solar explosive and transient phenomena. Both phenomena give rise to characteristic signals in the radio band in decametric and hectometric ranges, with more associated phenomena such as Type III and IV radio bursts. Additionally, in the Quiet Sun emission, we can observe radio signatures in these ranges, coming from the low Corona. In this article we describe the design process, validation in simulation, implementation and results of a multi-element radio interferometer for solar observations at 1.42 GHz. The development of the instrument was divided in two phases. An initial phase with the design of a 2-element drift interferometer, where each of the antenna elements is a $2\times 2$ 2 × 2 printed Yagi-Uda element array with an eight meter baseline. For the second phase, a 4-element radio interferometer was designed. For each element we use the same printed Yagi-Uda antennas in the focus of a parabolic reflector dish, and a fully-steerable pier. The signals correlation are performed electronically using a R econfigurable O pen A rchitecture C omputer H ardware ( ROACH ) unit, with a downconversion stage for each element, and the pipeline for data acquisition, processing and visualization is done entirely on Python. We also show the obtained results for testing in each phase, as well as the First Light of the full interferometer.