Relative Path Loss Research Articles

The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope

We provide an overview of the capabilities and performance of the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope when used in its multi-object spectroscopy (MOS) mode employing a novel Micro Shutter Array (MSA) slit device. The MSA consists of four separate 98″ × 91″ quadrants each containing 365 × 171 individually addressable shutters whose open areas on the sky measure 0.20″ × 0.46″ on a 0.27″ × 0.53″ pitch. This is the first time that a configurable multi-object spectrograph has been available on a space mission. The levels of multiplexing achievable with NIRSpec MOS mode are quantified and we show that NIRSpec will be able to observe typically fifty to two hundred objects simultaneously with the pattern of close to a quarter of a million shutters provided by the MSA. This pattern is fixed and regular, and we identify the specific constraints that it yields for NIRSpec observation planning. In particular, the roll angle at which a given NIRSpec MSA observation will be executed will, in most cases, not be known before the observation is actually scheduled. As a consequence, NIRSpec users planning MOS mode observations cannot at the proposal stage know precisely which subset of their intended targets will be observable, and will therefore need to intentionally oversize their submitted target catalogues accordingly. We also present the data processing and calibration steps planned for the NIRSpec MOS data. The significant variation in size of the mostly diffraction-limited instrument point spread function over the large wavelength range of 0.6–5.3 µm covered by the instrument, combined with the fact that most targets observed with the MSA cannot be expected to be perfectly centred within their respective slits, makes the spectrophotometric and wavelength calibration of the obtained spectra particularly complex. This is reflected by the inclusion of specific steps such as the wavelength zero-point correction nd the relative path loss correction in the NIRSpec data processing and calibration flow. The processing of spectra of morphologically extended targets will require additional attention and development. These challenges notwithstanding, the sensitivity and multiplexing capabilities anticipated of NIRSpec in MOS mode are unprecedented, and should enable significant progress to be made in addressing a wide range of outstanding astrophysical problems.

S-UTD-CH model in multiple diffractions

ABSTRACTThe propagation of electromagnetic waves in empty space is an extremely simplified case. Thus, the significant question is how an electromagnetic wave propagates in an environment with obstacles such as buildings, trees or hills. Electromagnetic waves are partially reflected and partially diffracted from these obstacles. To predict the relative path loss of electromagnetic waves at the receiving position, many electromagnetic-wave propagation models have been proposed. These propagation models can be classified into models based on numerical integration and those based on ray tracing. Uniform theory of diffraction (UTD) and slope-UTD (S-UTD) models are ray-tracing-based propagation models and are briefly explained in this paper. In addition, detailed information is provided about the improved slope UTD model, which is called the S-UTD with Convex Hull (S-UTD-CH) model. The fundamentals of the S-UTD-CH model are the S-UTD, convex hull and Fresnel zone concept. In particular, the S-UTD-CH model can be applied to multiple diffraction scenarios in the transition region. Moreover, the S-UTD-CH model is considered an optimum model in terms of its accuracy and calculation or computation time. Widespread simulation results are provided to compare the models based on theoretical rays in terms of prediction accuracy and computation time. To compare these models, different operation frequencies and transmitting antenna heights are considered by using a high-performance computing technique.

Measurement-Based Performance Comparison of Colocated Tripolarized Loop and Dipole Antennas

In this paper, a colocated tripolarized loop (TPL) antenna is proposed and a colocated tripolarized dipole (TPD) antenna is also designed for multiple-input multiple-output (MIMO) performance comparison. Both antennas have satisfactory performances of impedance bandwidth and isolation. The channel measurements are conducted in a nonlossy reverberation chamber (RC), a lossy RC, a corridor, and an office room. For both antennas, the measured average correlation coefficients (CCs) in the nonlossy RC are the smallest, close to 0.1, in the lossy RC are the largest, 0.3–0.5, and in the two indoor scenarios are slightly larger than that in the nonlossy RC. Except for the signal correlation, the relative path loss (RPL) should also be included to fairly compare the channel capacities. If the RPL is considered, a strong dependence of the channel capacity on the propagation properties can be seen. For both antennas, the channel capacities in the two indoor scenarios are 20%–30% smaller than that in the nonlossy RC. Interestingly, both antennas have similar condition numbers (CNs) in all the four scenarios, whose PDFs are close to that of the independent identically distributed (i.i.d.) complex Gaussian channel, which reveals that both antennas can obtain nearly three independent parallel subchannels and good multiplexing performance.

Application of S-UTD-CH Model into Multiple Diffraction Scenarios

Propagation prediction models based on ray tracing in coverage estimation for digital broadcasting systems are compared. Geometrical Theory of Diffraction (GTD), Slope Uniform Theory of Diffraction (S-UTD), and Slope UTD with Convex Hull (S-UTD-CH) models are compared for computation time and propagation path loss. S-UTD-CH model is optimum model with respect to computation time and relative path loss.

UHF Propagation in the Magnetic Resonance Bore

The magnetic resonance (MR) bore's structure, loading parameters, and material makeup greatly influence the ability of a frequency-specific signal to propagate. The relative path loss behavior of the MR bore has been determined experimentally at ultra-high frequencies (UHFs). An experiment is conducted to determine signal attenuation when the bore is empty (air-filled) or dielectrically loaded (patient-filled). This information is especially important to the wireless network designer who is implementing an in-bore physiological monitoring network. Experimental results show that the MR bore exhibits impressive path loss performance at 434 MHz, with greatest signal strength arriving at the receiver when the bore is dielectrically loaded.

Indoor propagation measurements at infrared frequencies for wireless local area networks applications

In a combination tutorial and research paper, propagation aspects of transmission at infrared (IR) frequencies for wireless in-building communications are explored. The tutorial section of the paper presents basic principles of propagation at IR, a comparison with indoor radio propagation, and the derivation of the channel's baseband model. The research aspect of the paper reports on the results of recent frequency response measurements at eight different sites in a university building. A major result shows that the indoor wireless optical channel is very dynamic, with great variations in the channel's characteristics for data collected in different rooms, in different locations within the same room, and for different orientations of the optical receiver at the same location of the same room. Numerical values of the channel's relative path loss and 3 dB bandwidth, along with frequency response plots covering a wide range of conditions, are presented and discussed. Finally, on the basis of the results of measurements, schemes for improving the performance of future wireless in-building optical transceivers are proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency response and path loss measurements of indoor channel

An improved method of operation of an HP network analyser to perform measurements of the frequency response of the indoor RF propagation channel and the relative path loss envelope and phase of a CW signal is described. An improved postprocessing procedure is also described. Test results obtained for indoor measurements in the 1–2 GHz band (2.3 ns resolution after windowing) and 945 MHz path loss measurements are presented as examples.