Survey on Mitigating the Problems of Parabolic Reflectors for Efficient Communication

In this paper, various problems associated with parabolic reflectors, its causes and the approach to mitigate these problems are discussed. The problems include; side lobe radiations, edge diffraction, aperture blockage, cross polarisation, feed spill over, feed illumination taper, pointing error, surface error and phase error. These problems have adverse effect on the overall gain, efficiency and directivity of the antenna thereby inhibiting efficient communication process. The result of the survey reveals that, phase error tends to be the most difficult of the aforementioned problems due to the challenges associated with locating the phase centre at reflector’s focus. The aperture blockage seems to have the least method of solution, because the problem can be solved by changing the centre feed to an offset feed. Detailed investigation of these problems and the relevant solutions are necessary, since parabolic reflectors are among the most common antennas with diverse application.

The Performance of a Low Berm in Reducing Traffic Noise

Traffic noise measurements were made behind a low, earth berm and in an adjacent open field to estimate insertion loss. The traffic was comprised of a mix of light vehicles, heavy trucks, and some medium trucks. The berm had a height of 1.65 meters above the roadway and began at the outside shoulder of a four-lane highway along U.S. Highway 101 in Northern California. Two microphone positions were located on the far side of the berm at distances of 28 and 40 meters from the center of the near lane of vehicular traffic. Away from the berm, a microphone was placed in an open field at 28 meters from the highway at a site upstream of the berm. The difference between the open location and those behind the berm were 11.6 and 9.9 dB for the 28- and 40-meter locations, respectively. The reductions obtained with the berm are compared to double edge diffraction theory and acoustic scale model results from the literature. The results of this study are reviewed in this paper and a comparison to FHWA Traffic Noise Model results is presented.

Experimental observation of asymmetrical microwave jets and far-field distribution generated by a dual-material system

In this paper, we report the experimental and numerical investigation of plane wave diffraction by an all-dielectric dual-material cuboid. Edge diffraction by a cuboid leads to the generation of a narrow, high intensity beam in the near-field region called a photonic jet. We examine the dependence of the jet behavior and orientation on the materials and dimensions of constitutive parts in the microwave frequency domain. The possibility to shift and deviate the resultant microwave jet in the near-field region of such a structure depending on the size of constitutive parts is demonstrated numerically. Experimentally, we observe a shift in the spatial position of the jet. The experimental asymmetric electric field profile observed in the far-field region is attributed to the input of multiple edge waves generated by the dual-material cuboid. The presented results may be scaled at different frequency bands such as optical frequencies for designing nanostructures enabling the focusing and deviation functionality and creation of new optical devices which would satisfy the needs of emerging nanophotonic applications.

Detection of subsurface lineaments using edge diffraction

Detection and imaging of sub-wavelength features in the subsurface using diffracted waves are rapidly gaining momentum in the oil and gas industry as well as in the fields of engineering, archeology, and homeland security. Most of the proposed methods include coherent summation of the recorded wavefield along diffraction traveltime surfaces from point scatterers. The summation focuses energy onto point-like diffractors which appear at the resulting images as prominent anomalies. However, in cases when the target is an elongated object such as a fault plane, fracture, tunnel, or elongated cave, a more efficient imaging method can be constructed. We present an algorithm for detecting and characterizing linear subsurface elements using a linear diffractor operator. The proposed algorithm is based on the coherent summation of the edge diffraction generated by the entire lineament and on the analysis of the calculated coherence measure (semblance). The advantages and limitations of the proposed method are demonstrated, and the results are compared to the conventional point-diffractor-based techniques. Synthetic and real data examples demonstrate that using a linear-diffractor-based algorithm can dramatically improve the detection of linear objects.

A Simple Propagation Model to Characterize the Effects of Multiple Human Bodies Blocking Indoor Short-Range Links at 28 GHz

This study aims to provide a simple approach to characterize the effects of scattering by human bodies in the vicinity of a short-range indoor link at 28 GHz while the link is fully blocked by another body. In the study, a street canyon propagation characterized by a four-ray model is incorporated to consider the human bodies. For this model, the received signal is assumed to be composed of a direct component that is exposed to shadowing due to a human body blocking the link and a multipath component due to reflections from human bodies around the link. In order to predict the attenuation due to shadowing, the double knife-edge diffraction (DKED) model is employed. Moreover, to predict the attenuation due to multipath, the reflected fields from the human bodies around the link are used. The measurements are compared with the simulations in order to evaluate the prediction accuracy of the model. The acceptable results achieved in this study suggest that this simple model might work correctly for short-range indoor links at millimeter-wave (mmWave) frequencies.

Comparative study of hard X-ray undulator beamline performance in the Korean 4GSR and the PLS-II

A new light source based on the electron storage ring, dubbed the “diffraction-limited storage ring” (DLSR) to keep the full intrinsic wave nature of X-rays had been proposed since the early stage of storage ring history and has finally been developed successfully, and an upgrade and a new construction programs have now chosen in the worldwide synchrotron facilities. The construction of the so-called “4th generation storage ring” (4GSR), which is a newly-coined term aiming in the same direction, was decided in Korea. The Korean 4GSR is expected to be 10–100 times brighter than the Pohang Light Source-II (PLS-II). Hard X-ray undulator beamlines will benefit from the 4GSR due to its low emittance approaching the diffraction limit. In the PLS-II, more than 10 hard X-ray undulator beamlines are currently in operation. We present a comparative study of the representative hard X-ray undulator beamlines by using the cutting-edge diffraction-spectroscopy techniques in the PLS-II and the 4GSR for better understanding the upcoming light source in Korea. The figures-of-merit of the two specific experimental techniques, resonant inelastic X-ray scattering (RIXS) and resonant X-ray emission spectroscopy (RXES), are discussed for comparison of the two light sources. Both RIXS and RXES are sometimes referred to as a “renaissance” in X-ray science and are, therefore, strongly expected to be adopted in the 4GSR beamlines.