Showing papers on "L band published in 1997"

Mobile satellite communication system including a dual-frequency, low-profile, self-steering antenna assembly

Abstract: A mobile satellite communication system includes an antenna assembly mountable on a vehicle and a satellite tracking assembly. The antenna assembly includes an antenna device for receiving first satellite signals from a first satellite in a first frequency band and for transmitting and receiving second satellite signals to and from a second satellite in a second frequency band, and a drive subassembly for rotating the antenna device relative to the vehicle in response to a control signal. The satellite tracking assembly maintains the antenna device pointed at the first and second satellites as the vehicle moves. The system further includes a receiver coupled to the antenna device for receiving the first satellite signals and a transceiver coupled to the antenna device for transmitting and receiving the second satellite signals. The first satellite signals may be video and imagery data signals transmitted in the Ku band by a direct broadcast satellite. The second satellite signals may be two-way digital communication signals transmitted and received in the L band by an AMSC satellite.

Mapping submarine sand waves with multiband imaging radar: 1. Model development and sensitivity analysis

Abstract: In 1989 and 1991, unexpected modulations caused by submarine sand waves were observed with the airborne imaging radar (AIR), a P, L, and C band synthetic aperture radar. The measurements were performed in a sand wave area off the Dutch coast. The sand waves have an asymmetric, sawtooth-shaped profile with the steep slope oriented toward the northeast. During the experiments, wind and current had opposite directions: the wind was directed toward the northeast and the current toward the southwest. Under these conditions, existing models for the imaging mechanism predict that the modulation depth decreases with increasing radar frequency and that the steep slopes show up as dark lines in radar images. The AIR images show a relation between modulation depth and radar frequency as predicted. However, only the P band image of 1989 shows the steep slopes of the sand waves as dark lines. The P band image of 1991 and the L band images of 1989 and 1991 show a sawtooth-shaped modulation which cannot be explained by existing theory. A new model is developed that is one dimensional in position space and fully two dimensional in wavenumber space. The radar cross section is calculated using both first-order Bragg and an integral equation scattering model in which the cross section originates from a spectral band rather than a single value. The new model contains two improvements over previous ones. First, wave blocking or, better, wave reflection is included, though in an approximate manner. It is shown to be of importance at P band only. Second, the contribution to the radar cross section from waves moving both to and from the radar is included, whereas some previous models consider only one of these contributions. This explains the observed modulations, at least qualitatively, under the assumptions that the angular distribution of short waves is almost constant and that waves moving against the wind have small relaxation rates.

50 years of radio-scintillation observations

Abstract: The author attempts a brief summary of the history of ionospheric fading from sources beyond the upper atmosphere. The concentration is on the early studies of scintillation. The first sources used as transmitters were radio stars with varying diameters. With the advent of satellite transmissions at altitudes varying from 300 km to several Earth radii, fading was studied as a function of various regions of the globe. In years of high solar flux, transionospheric propagation through polar and equatorial regions has experience deep fading at frequencies ranging from 54 MHz to 4 GHz. Fading of radio signals from satellites still plays a role in evaluating operational and proposed system effectiveness. The relevance of these studies to Global Positioning System reception and users of proposed systems at L band is discussed.

Dual-band dual-polarized microstrip antennas for SAR applications

Abstract: In SAR applications two important frequency bands are the L-band, around 1.275 GHz, and the C-band at 5.3 GHz. The nominal bandwidth at both bands is desirable to be about 100 MHz. The authors report the design and construction of a dual band antenna for SAR in which the L band elements are perforated. The configuration is discussed and measurements of impedance and radiation patterns are given.

Calibration and experimental results of a two‐dimensional interferometric radiometer laboratory prototype

Abstract: In recent years, Earth observation by means of aperture synthesis radiometry has received special attention by some space agencies as a possible solution to achieve high radiometric accuracy and spatial resolution at low microwave frequencies (L band), where the apparent brightness temperature is much more sensitive to soil moisture and sea surface salinity This paper presents the characterization and calibration procedure, as well as some synthetic images measured with an X band experimental Y-shaped Synthetic Aperture Interferometric Radiometer prototype developed at the Polytechnic University of Catalonia The instrument is composed of a single pair of antennas that can be moved along the arms of an Y structure to synthesize a set of baselines An experimental procedure is proposed to evaluate and then calibrate offset, inphase, quadrature, and amplitude errors generated by receivers and correlators

Wideband characterisation and modelling of the mobile satellite propagation channel at L- and S-bands

Abstract: The effects of the wideband propagation channel are critical in the design of mobile satellite systems (MSS), providing world-wide voice and data communications requiring higher data rates and quality of service. The variational effects of the narrowband propagation channel with respect to the elevation angle have been widely reported and modelled. However, there is very little data on the effects of wideband parameters with respect to the elevation angle. These can be very important in characterising the channel for terminal equipment, since they determine the maximum data rates or equalisation requirements for future mobile satellite systems and satellite personal communication networks. There is an increasing need to be able to accurately model the channel characteristics in order to optimise the design of radio mobile satellite systems. The wideband model is useful for simulation and evaluation of the performance of L-band (1540-1560 MHz) and S-band (2315-2335 MHz) mobile satellite systems.

Low cost phase shifters for L-band phased array antennas

Abstract: This paper discusses the methods of designing good quality PIN diode phase shifters for operation at L-band using low cost PIN diodes. This is demonstrated in the design example of a 4-bit phase shifter for possible use in an L-band vehicle mounted phased array antenna for mobile satellite communications. It is shown that the performance of the phase shifters can be of good quality over a 7% bandwidth (between 1.54 GHz and 1.66 GHz) as is required for the Mobilesat system in Australia. This quality performance is achieved by including extra compensation circuits in the biasing networks of the PIN diodes. By using these extra compensation networks, the parasitic elements are tuned out producing almost ideal on-off switches and therefore good quality phase shifters over the required frequency band.

Terrestrial communication system using satellite transmission techniques

Abstract: A terrestrial communication system, facilitating audio, video, data, and any other type of communication within a local geographical area, and with an extremely large number of communication channels being made available simultaneously at a very low cost. It comprises at least two local terrestrial satellite (LTS), preferably located in a mast or any other supporting structure, each LTS having high frequency communication equipment substantially corresponding to a conventional geostationary satellite for digital transmission of video, audio, or data, arranged to transmit in the L Band (1-2 GHz), the S Band (2-4 GHz), or a high frequency band with a relatively low power output and having a preferably omnidirectional antenna installation for transmission in a substantially horizontal plane. The signals can be digitalized according to MPEG-2 or according to any known signal algorithm.

Characterisation of the satellite-to-indoor channel based on narrow-band scalar measurements

Abstract: A model for the satellite-to-indoor channel is presented taking account of the diffuse character of the electromagnetic field. The results of measurements, giving further data on the satellite to indoor channel, are described. In the measurements the satellite was simulated by a helicopter. The collected data were evaluated by a method where advance separation of slow and fast fading is not a prerequisite of the application.

Four-channel micro-wave satellite television receiver

Abstract: The utility model relates to a four-channel micro-wave satellite television receiver which is composed of a power circuit and four single-channel receiver units, wherein, each single-channel receiver unit is composed of a tuning circuit, a vision and audio frequency processing circuit, a video amplification and crack phase circuit and an automatic frequency tuning circuit, and both the tuning circuit and the vision and audio frequency processing circuit are composed of special integrated components. The utility model which synchronously receives four channels of satellite television signals has the characteristics of great receiving capacity, low cost, convenient operation, high integrated level and good performance. The utility model is widely applied to the closed circuit television systems and television repeater stations, and the utility model is not only applied to the C band earth surface, but is also applied to the L band and S band frequency modulation multi-channel microwave distributing system receiver stations.