Showing papers on "L band published in 1992"
TL;DR: In this article, the morphological aspects of scintillations were used to estimate average fade rates and ground correlation distances and the theoretical Nakagami m distribution was found to be the best for describing various levels of fade.
Abstract: Satellite radio systems suffer loss of information in a wide band of frequencies during periods of intense ionospheric scintillation activity when the received signal undergoes rapid and deep fading. In order to assess the problem and to determine a proper fade margin for an Earth-space link, system engineers require information on signal statistics as well as on the morphological aspects of scintillations. Our observations near the northern boundary of the equatorial scintillation belt at (18.9° N geomagnetic) within the Indian zone show that the signal at 4/1.5 Ghz has faded often beyond 10 dB pp, and at times beyond 24 dB pp at 4 Ghz during equinoctial months of high solar activity during the years of 1989–1990. In addition to the morphology at 4 Ghz, information on signal statistics, such as cumulative amplitude distribution function, fade rate distribution, and signal reliability for different message lengths for some events of scintillations, both at C and L band, has been presented. The theoretical Nakagami m distribution has been found to be the best for describing various levels of fade. Autocorrelation and power-spectrum analysis have been used to estimate average fade rates and ground correlation distances. Performance evaluation of satellite Earth terminals using small antennas has been carried out to show the vulnerability of the system in the hostile ionospheric environment notwithstanding the advanced modulation systems being employed.
47 citations
01 Jan 1992
TL;DR: In this article, the design, realization and measurement of an ultra low-noise, cryogenically-coolable, L-band amplifier for radio astronomy applications are described.
Abstract: The design, realization and measurement of an ultra low-noise, cryogenically-coolable, L-band amplifier for radio astronomy applications are described. The amplifier exhibits 3 K (0.045 dB N.F.) average noise temperature over 600 MHz. bandwith with 36 dB of gain at ambient temperature of 12.5 K and 2 K average noise at physical temperature of 4.2 K. Excellent agreement between measured and predicted results verifies the validity of a recent published wideband model of a FET for L-band frequencies.
28 citations
01 Jan 1992
26 citations
15 citations
TL;DR: In this paper, a top-mounted high-gain antenna of the phased-array type was used for aerial satellite communication experiments, where the aircraft wing direction coincides with the satellite direction, in contrast with the small fading observed in the cases where aircraft wing is out of the beam pointing to the satellite.
Abstract: Aeronautical satellite communication experiments were conducted using a top-mounted high-gain antenna of the phased-array type. Slow fading of 3 to 4 dB in the L-band channel was observed when the wing direction coincides with the satellite direction, in contrast with the small fading observed in the cases where the aircraft wing is out of the beam pointing to the satellite. >
4 citations
06 Dec 1992
TL;DR: Numerical results show that remarkable capacity can be achieved utilizing high-Earth-orbit satellites complemented by terrestrial gap-filler transmission and it is shown that a geostationary satellite can provide limited service availability and limited capacity to mobile users but can be used for experimental purposes.
Abstract: Trellis-coded quasi-orthogonal code-division multiplexing (TCQO-CDM) is introduced as a transmission technique for digital audio broadcasting. The technique shows good performance over the satellite L-band fading channel and also in the terrestrial gap-filler type of transmission. Preliminary satellite link budgets based on extensive computer simulation results are provided. The capacity achievable by the terrestrial single-frequency gap-filler network utilizing the same satellite frequency and user receiver is also discussed. Numerical results show that remarkable capacity can be achieved utilizing high-Earth-orbit satellites complemented by terrestrial gap-filler transmission. A variety of transmission rates and hence broadcasting services can be realized. It is shown that a geostationary satellite can provide limited service availability and limited capacity to mobile users but can be used for experimental purposes. >
3 citations
TL;DR: In this article, a multiband propagation measurement campaign for the high elevation angle land mobile satellite channel is reported, where simultaneous narrowband sounding of the channel has been carried out in suburban, wooded and open areas of the UK using a helicopter-mounted platform to simulate the satellite signal at various elevation angles.
Abstract: Results of a recent multiband propagation measurement campaign for the high elevation angle land mobile satellite channel are reported. Simultaneous narrowband sounding of the channel has been carried out in suburban, wooded and open areas of the UK using a helicopter-mounted platform to simulate the satellite signal at various elevation angles. Propagation related link degradations in the land mobile-satellite channel have been observed to be less severe when the path elevation angle is increased or radio frequency decreases.
3 citations
Journal Article•
2 citations
25 Jun 1992
TL;DR: In this article, the elevation and azimuthal radiation patterns for an L-band mobile satellite communications antenna were observed and the most appropriate representation for the ground plane for this antenna when modelled using the Livermore Numerical Electromagnetics Code (NEC-2).
Abstract: The measured elevation and azimuthal radiation patterns for an L-band mobile satellite communications antenna are observed. A question arises as to the most appropriate representation for the ground plane for this antenna when modelled using the Livermore Numerical Electromagnetics Code (NEC-2). A series of numerical modelling trials have been performed using this software and the resulting radiation patterns are compared with those measured. >