Dynamic Modulation Yields One-Way Beam Splitting

This article demonstrates the realization of an extraordinary beam splitter based on nonreciprocal and synchronized photonic transitions in obliquely illuminated space-time-modulated (STM) slabs which impart the coherent temporal frequency and spatial frequency shifts. As a consequence of such unusual photonic transitions, a one-way beam splitting and amplification is exhibited by the STM slab. Beam splitting is a vital operation for various optical and photonic systems, ranging from quantum computation to fluorescence spectroscopy and microscopy. Despite the beam splitting is conceptually a simple operation, the performance characteristics of beam splitters significantly influence the repeatability and accuracy of the entire optical system. As of today, there has been no approach exhibiting a nonreciprocal beam splitting accompanied with transmission gain and an arbitrary splitting angle. Here, we show that oblique illumination of a periodic and semi-coherent dynamically-modulated slab results in coherent photonic transitions between the incident light beam and its counterpart space-time harmonic (STH). Such photonic transitions introduce a unidirectional synchronization and momentum exchange between two STHs with same temporal frequencies, but opposite spatial frequencies. Such a beam splitting technique offers high isolation, transmission gain and zero beam tilting, and is expected to drastically decrease the resource and isolation requirements in optical and photonic systems. In addition to the analytical solution, we provide a closed-form solution for the electromagnetic fields in STM structures, and accordingly, investigate the properties of the wave isolation and amplification in subluminal, superluminal and luminal ST modulations

Theory and Applications of Infinitesimal Dipole Models for Computational Electromagnetics

The recently introduced quantum particle swarm optimization (QPSO) algorithm is employed to find infinitesimal dipole models (IDM) for antennas with known near-fields (measured or computed). The IDM can predict accurately both the near-fields and the far- fields of the antenna. A theory is developed to explain the mechanism behind the IDM using the multipole expansion method. The IDM obtained from single frequency solutions is extrapolated over a frequency range around the design frequency. The method is demonstrated by analyzing conductingand dielectric- type antennas. A calibration procedure is proposed to systematically implement infinitesimal dipoles within existing MOM codes. The interaction of the IDM with passive and active objects is studied through several examples. The IDM proved to predict the interaction efficiently. A closed-form expression for the mutual admittance between similar or dissimilar antennas, with arbitrary orientations and/or locations, is derived using the reaction theorem

On the 3-D Placement of Airborne Base Stations Using Tethered UAVs

One of the main challenges slowing the deployment of airborne base stations (BSs) using unmanned aerial vehicles (UAVs) is the limited on-board energy and flight time. One potential solution to such problem, is to provide the UAV with power supply through a tether that connects the UAV to the ground. In this paper, we study the optimal placement of tethered UAVs (TUAVs) to minimize the average path-loss between the TUAV and a receiver located on the ground. Given that the tether has a maximum length, and the launching point of the TUAV (the starting point of the tether) is placed on a rooftop, the TUAV is only allowed to hover within a specific hovering region. Beside the maximum tether length, this hovering region also depends on the heights of the buildings surrounding the rooftop, which requires the inclination angle of the tether not to be below a given minimum value, in order to avoid tangling and ensure safety. We first formulate the optimization problem for such setup and provide some useful insights on its solution. Next, we derive upper and lower bounds for the optimal values of the tether length and inclination angle. We also propose a suboptimal closed-form solution for the tether length and its inclination angle that is based on maximizing the line-of-sight probability. Finally, we derive the probability distribution of the minimum inclination angle of the tether length. We show that its mean value varies depending on the environment from 10 degrees in suburban environments to 31 degrees in high rise urban environments. Our numerical results show that the derived upper and lower bounds on the optimal values of the tether length and inclination angle lead to tight suboptimal values of the average path-loss that are only 0-3 dBs above the minimum value

Ultra-Wideband Transient Arrays: Focusing and Defocusing

Abstract-Some focusing properties of the ultra-wideband time-domain focused array antennas were presented. Large current radiators are considered as the elements of the antenna array. Several antenna arrays with different sizes and number of elements are modeled. It is shown that similar to narrow band antennas, the actual maximum field region shifts from the intended focus region towards the antenna aperture

Design of integrated diplexer-power divider

A new configuration is introduced to integrate diplexers and power dividers. The proposed configuration is based on coupling matrix. The design of the lumped element network is based on addition of an extra term to the conventional error function of the coupling matrix to decouple the two ports of the power divider. An optimized lumped element network is implemented successfully on an EBG based guiding technology known as ridge gap waveguide. The optimization of the physical structure is done efficiently by dividing the diplexer-power divider into many sub-circuits and analyzing the corrected delay response of them

Low-Profile Low-Cost High Gain 60 GHz Antenna

A new design perspective that utilizes the diffracted fields from planar metallic sheets to implement high gain, low profile, and low-cost antenna at 60 GHz is presented. The proposed antenna is matched over the 60-GHz ISM band (57–64 GHz). The proposed antenna can be employed in a linear antenna array with one wavelength distance between the array elements without generating grating lobes. The proposed antenna structure is suitable for short range, low power applications. The proposed antenna is vialess planar structure. The simplicity of the structure is advantageous in relaxing the fabrication process requirements