Land vehicle antennas for satellite mobile communications

The RF performance, size, pointing system, and cost were investigated concepts are: for a mechanically steered 1 x 4 tilted microstrip array, a mechanically steered fixed-beam conformal array, and an electronically steered conformal phased array. Emphasis is on the RF performance of the tilted 1 x 4 antenna array and methods for pointing the various antennas studied to a geosynchronous satellite. An updated version of satellite isolations in a two-satellite system is presented. Cost estimates for the antennas in quantities of 10,000 and 100,000 unites are summarized

Estimation and control of non-linear and hybrid systems with applications to air-to-air guidance

Issued as Progress report, and Final report, Project no. E-21-67

Concepts and cost trade-offs for land vehicle antennas in satellite mobile communications

Several antenna design concepts, operating at UHF (821 to 825 MHz transmit and 866 to 870 MHz receive bands), with gain ranging between 6 and 12 dBic, that are suitable for land mobile vehicles are presented. The antennas may be used within CONUS and ALASKA to communicate to and from a geosynchronous satellite. Depending on the type of steering mechanism, the antennas are broken down into three categories; (1) electronically scanned arrays with phase shifters, (2) electronically switched arrays with switchable power dividers/combiners, and (3) mechanically steered arrays. The operating characteristics of two of these design concepts, one a conformal antenna with electronic beam steering and the other a nonconformal design with mechanical steering, were evaluated with regard to two and three satellite system. Cost estimates of various antenna concepts were made and plotted against their overall gain performance

Breakdown performance of vacuum circuit breakers using alternative CF3I-CO2 insulation gas mixture

In this paper, sulphur hexafluoride (SF6) insulated vacuum interrupter circuit breakers have been used to explore replacing SF6 gas with a trifluoroiodomethane and carbon dioxide (CF3I-CO2) gas mixture. The search for an alternative insulation gas is driven by the well known extreme global warming potential of SF6. For this purpose, the circuit breaker gas compartment of a piece of gas insulated switchgear (GIS) was filled with a CF3I gas mixture and then tested using lightning impulses up to the rated withstand strength. The tested ring main unit was initially designed to be insulated with SF6 gas. The unit is a three-phase switchgear containing two switches per phase; a selector interlock and a vacuum bottle circuit breaker per phase. The test programme performed in this investigation demonstrated the breakdown performance and insulation strength of the new gas mixture as well as the vacuum circuit breakers behavior when insulated with a new insulation medium. Data on the dielectric properties of the proposed gas mixture is presented, and the performance of the tested vacuum circuit breaker is discussed. Promising results are obtained which indicate the suitability of this more-environmentally friendly gas for high voltage insulation purposes

Detection of vibronic bands of C3_3 in a translucent cloud towards HD 169454

We report the detection of eight vibronic bands of C$_3$, seven of which have been hitherto unobserved in astrophysical objects, in the translucent cloud towards HD~169454. Four of these bands are also found towards two additional objects: HD~73882 and HD~154368. Very high signal-to-noise ratio ($\sim$1000 and higher) and high resolving power ($R=80,000$) UVES-VLT spectra (Paranal, Chile) allow for detecting novel spectral features of C$_3$, even revealing weak perturbed features in the strongest bands. The work presented here provides the most complete spectroscopic survey of the so far largest carbon chain detected in translucent interstellar clouds. High-quality laboratory spectra of C$_3$ are measured using cavity ring-down absorption spectroscopy in a supersonically expanding hydrocarbon plasma, to support the analysis of the identified bands towards HD~169454. A column density of N(C$_3$) = $(6.6 \pm 0.2) \times 10^{12}$ cm$^{-2}$ is inferred and the excitation of the molecule exhibits two temperature components; $T_{exc}= 22 \pm 1$ K for the low-$J$ states and $T_{exc}= 187 \pm 25$ K for the high-$J$ tail. The rotational excitation of C$_3$ is reasonably well explained by models involving a mechanism including inelastic collisions, formation and destruction of the molecule, and radiative pumping in the far-infrared. These models yield gas kinetic temperatures comparable to those found for $T_{exc}$. The assignment of spectral features in the UV-blue range 3793-4054 \AA\ may be of relevance for future studies aiming at unravelling spectra to identify interstellar molecules associated with the diffuse interstellar bands (DIBs).Comment: 15 pages, 13 figures, submitted to MNRA

PERFORMANCE OF PARALLEL SURGE ARRESTERS

The operation of parallel surge arresters can improve energy absorption capability if the arresters are similar and are installed close to each other. However, it has been reported that any small difference in the individual V-I characteristics can lead to unbalance in current sharing. When the arresters are installed some distance away from each other, travelling wave effects can modify the effectiveness of parallel arresters for surge overvoltage protection and, in this case, detailed simulations are required to ascertain the level of protection. Such a situation occurs in practice with large substations or short underground cable connections. Various studies have shown that a requirement for two-arrester protection is closely dependent upon the type and length of cable used. In the case of overhead lines, the distances are much bigger and the main objective of line arresters is to reduce the flashover rates due to surge overvoltages. This is especially relevant to lines located in regions of high lightning activity, lines with compact/uprated design where the phase-to-phase and phase-to-earth air clearances are reduced. In this paper, we present a study of parallel arresters considering the separation distance and their application to overhead lines. Various scenarios of overhead line configurations were considered and the overvoltage levels were calculated for each case. Assessment of flashover performance is also conducted for a number of conditions. A number of calculation techniques were used and compared

On Detecting Some Defective Items in Group Testing

Group testing is an approach aimed at identifying up to $d$ defective items among a total of $n$ elements. This is accomplished by examining subsets to determine if at least one defective item is present. In our study, we focus on the problem of identifying a subset of $\ell\leq d$ defective items. We develop upper and lower bounds on the number of tests required to detect $\ell$ defective items in both the adaptive and non-adaptive settings while considering scenarios where no prior knowledge of $d$ is available, and situations where an estimate of $d$ or at least some non-trivial upper bound on $d$ is available. When no prior knowledge on $d$ is available, we prove a lower bound of $\Omega(\frac{\ell \log^2n}{\log \ell +\log\log n})$ tests in the randomized non-adaptive settings and an upper bound of $O(\ell \log^2 n)$ for the same settings. Furthermore, we demonstrate that any non-adaptive deterministic algorithm must ask $\Theta(n)$ tests, signifying a fundamental limitation in this scenario. For adaptive algorithms, we establish tight bounds in different scenarios. In the deterministic case, we prove a tight bound of $\Theta(\ell\log{(n/\ell)})$. Moreover, in the randomized settings, we derive a tight bound of $\Theta(\ell\log{(n/d)})$. When $d$, or at least some non-trivial estimate of $d$, is known, we prove a tight bound of $\Theta(d\log (n/d))$ for the deterministic non-adaptive settings, and $\Theta(\ell\log(n/d))$ for the randomized non-adaptive settings. In the adaptive case, we present an upper bound of $O(\ell \log (n/\ell))$ for the deterministic settings, and a lower bound of $\Omega(\ell\log(n/d)+\log n)$. Additionally, we establish a tight bound of $\Theta(\ell \log(n/d))$ for the randomized adaptive settings