César Briso Rodríguez

Propagation Mechanism Modeling in the Near-Region of Arbitrary Cross-Sectional Tunnels

Along with the increase of the use of working frequencies in advanced radio communication systems, the near-region inside tunnels lengthens considerably and even occupies the whole propagation cell or the entire length of some short tunnels. This paper analytically models the propagation mechanisms and their dividing point in the near-region of arbitrary cross-sectional tunnels for the first time. To begin with, the propagation losses owing to the free space mechanism and the multimode waveguide mechanism are modeled, respectively. Then, by conjunctively employing the propagation theory and the three-dimensional solid geometry, the paper presents a general model for the dividing point between two propagation mechanisms. It is worthy to mention that this model can be applied in arbitrary cross-sectional tunnels. Furthermore, the general dividing point model is specified in rectangular, circular, and arched tunnels, respectively. Five groups of measurements are used to justify the model in different tunnels at different frequencies. Finally, in order to facilitate the use of the model, simplified analytical solutions for the dividing point in five specific application situations are derived. The results in this paper could help deepen the insight into the propagation mechanisms in tunnels.

Planar Ultrawideband Antenna with Photonically Controlled Notched Bands

A design of a planar microstrip-fed ultrawideband (UWB) printed circular monopole antenna with optically controlled notched bands is presented. The proposed antenna is composed of a circular ultrawideband patch, with an etched T-shaped slot controlled by an integrated silicon switch. The slot modifies the frequency response of the antenna suppressing 3.5–5 GHz band when the switch is in open state. The optical switch is controlled by a low-power near-infrared (808 nm) laser diode, which causes the change in the frequency response of the antenna generating a frequency notch. This solution could be expanded to include several notches in the antenna frequency response achieving a fully reconfigurable UWB antenna. The antenna could be remotely controlled at large distances using optical fiber. The prototype antenna has been fully characterized to verify these design concepts.

Wideband channel measurements and analysis in High-Speed Railway environments

In the past few years, there has been an increasing interest of wideband wireless communications of High-Speed Railways (HSRs), which have plenty of specific propagation scenarios. Wideband channel modeling of HSR is important for system design of the next generation of HSR communications. However, there is a lack of deep understanding regarding the characteristics of wideband channels in the complex environments such as railway cuttings and stations.

Gbps data transmission in biomedical and communications instruments

The paper proposes a distribution network for Gbps data transmission over. The study is based on a real design made for data communications of an aerospace instrument. This type of transmissions presents problems based principally on crosstalk and attenuation, therefore a careful design of distribution network and an adjustment of terminal loads are very important. A frequency scaled prototype at 20Mbps has been designed and tested, obtaining models of the complete circuit, crosstalk and interferences between near buses. Then a new design has been proposed to be used up to 8Gbps. On this design, the wired distribution network is based on the use of broadband couplers and low-loss transmission lines. Finally, possible aspects will be analyzed, as it was done in the Transmission/Reception System, such as the crosstalk or interferences between near buses and the possible introduction of some mechanism of protection.

High-resolution radar calibration system

In this work, we present a study of the frequency calibration system used to characterize the precision of the current and future radars. First, a general vision of the system is given. Moreover, basic procedures are explained to calibrate Doppler radars. Later, different architectures are presented, depending on the estimated parameters: speed and distance. Finally, a practical calibration system is presented, where the system precision is the most important factor. This system is able to simulate objects that move away at high speed (targets reach several Mach numbers).