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Showing papers on "L band published in 1995"


Journal ArticleDOI
TL;DR: In this paper, the backscatter measurements were performed from the German Forschungsplattform Nordsee (FPN) in the North Sea in order to determine the ocean wave-radar modulation transfer function (MTF), which relates the backseat t ered radar power to the long surface waves.
Abstract: Radar backscatter measurements were performed from the German Forschungsplattform Nordsee (FPN) in the North Sea in order to determine the ocean wave-radar modulation transfer function (MTF), which relates the backseat t ered radar power to the long surface waves. The radar operated quasi-simultaneously at 1.0 GHz (L band), 5.3 GHz (C band), and 10.0 GHz (X band) at HH and VV polarization by using a single antenna. MTFs obtained at these radar frequencies and polarizations are compared. Our measurements of the dependence of the MTF on wind speed and long wave frequency are in agreement with earlier measurements. It is shown that the dependence of the coherence between the backscattered radar power and the long ocean wave height is a strongly decreasing function of radar frequency. This implies that a real aperture radar operating at a low radar frequency, e.g., at L band, is best suited for imaging ocean waves. Residual MTFs, Mres, are calculated by subtracting the theoretical tilt and range MTFs from the measured total MTFs. According to conventional ocean wave radar modulation theory, Mres should be identical to the hydrodynamic MTF and therefore be independent of polarization. However, the experimental data show a strong dependence of the modulus and phase of Mres on polarization. We find larger values of |Mres| for HH than for VV polarization at C and X bands. In principle, a difference between Mres for HH and VV polarization can be explained by a three-scale composite surface model which takes into account also the modulation of the Bragg waves by intermediate-scale waves (i.e., waves with wavelengths between the long waves and the Bragg waves). However, the differences observed in this experiment are found to be much larger than expected from this theory.

32 citations


01 Jan 1995
TL;DR: In this article, the results of an airborne measurement campaign aimed at the characterization of the mobile satellite link are presented in a survey of wide and narrowband results for a wide range of elevation angles and environments.
Abstract: The results of an airborne measurement campaign aimed at the characterization of the mobile satellite link are presented in this paper. The experimental tests were carried out at 1.8 GHz. The objective of the campaign was to obtain results applicable to all proposed satellite constellations: LEO, HEO, and GEO. Therefore, the measurements were performed for elevation angles from 10 deg...80 deg using a light aircraft. A set of different environments and operational scenarios have been investigated, typically for hand-held and car-mounted applications. We present a survey of wide- and narrowband results for a wide range of elevation angles and environments. For the wideband characterization, the power delay profiles of the channel impulse response are presented and discussed. Figures for the delay spread versus elevation and for the carrier-to-multipath ratio versus time are also given. The narrowband behaviour of the channel is described by power series.

26 citations


Proceedings ArticleDOI
01 Jan 1995
TL;DR: In this paper, a multiway switched radial power divider for use in a mobile satellite antenna-array operating in the microwave L-band is described, which features good return loss and small insertion losses over a 7% bandwidth.
Abstract: A multiway switched radial power divider for use in a mobile satellite antenna-array operating in the microwave L-band is described. The divider is designed using low-cost substrate and inexpensive switching diodes. It features good return loss and small insertion losses over a 7% bandwidth.

26 citations


Proceedings ArticleDOI
07 Aug 1995
TL;DR: In this paper, the authors describe the successful demonstration of a 4-bit optoelectronic (OE) switched Silica-waveguide time-delay network designed to steer a 4 x 24 element conformal array at L band (0.8-1.4 GHz).
Abstract: Since the fwst demonstration(1) of an optical steered phased array antenna, many architectures for implementing optical beam-forming networks have been proposed and realized(2). Among the reported schemes, those offering true-time-delay (lTD) still has the best potential for meeting future needs in multifunction and multiband operations, especially over wide scan angles. Thus far, the photonic timeshift modules demonstrated for system insertions were all composed of fiber-based delay-lines, whose lengths were trimmed individually to meet specific time-delay requirements, as dictated by the aperture size and steering angle of the array. An integrated waveguide-based delay-line technology offers several advantages over their fiber-based counterparts. First, the waveguides are typically fabricated by photolithographic processes with dimensional precisions of micronmeters. This enables better differential phase accuracy to be achieved, especially for the fine bits of the time-shifter. Although there is an initial investment for the photomask design, subsequent reproduction of identical sets of delay-lines becomes more efficient and precise with the waveguide-based technology. Secondly, the time-delay module can be packaged more compactly if the waveguide-waferboard can be adopted, in addition, as a monolithic or hybrid integration platfom for the active components. In this paper, we will describe the successful demonstration of a 4-bit optoelectronic (OE) switched Silica-waveguide time-delay network designed to steer a 4 x 24 element conformal array at L band (0.8-1.4 GHz).

5 citations


Journal ArticleDOI
TL;DR: Multiple-symbol Viterbi decoding and dual-space equal-gain diversity reception for trellis-coded differential M-ary phase-shift-keying (DPSK) modulation are investigated as two mitigation techniques for severe channel impairments expected from a land mobile satellite communication channel at K band and, for comparison purposes, at L band.
Abstract: Mobile satellite communication systems at K a /K band (30/20 GHz) are attractive because of their large bandwidth availability and potentiality to support smaller earth-stations and satellite antennas compared with L-band (1.6/1.5 GHz) systems. In this paper, multiple-symbol Viterbi decoding and dual-space equal-gain diversity reception for trellis-coded differential M-ary phase-shift-keying (DPSK) modulation are investigated as two mitigation techniques for severe channel impairments expected from a land mobile satellite communication channel at K band and, for comparison purposes, at L band. The multiple-symbol Viterbi decoder (MSVD) is a modified Viterbi decoder with inputs from multiple differential detectors. The channel is modelled as Rayleigh distributed multipath fading with a lognormally distributed line-of-sight (LOS) component due to shadowing. Four trellis-coded modulation (TCM) schemes are studied. The dependency of the system performance improvement on the decoder structure, the TCM scheme, and the system RF frequency band is presented.

2 citations



Proceedings ArticleDOI
18 Jun 1995
TL;DR: A multibeam digital beamforming (DBF) antenna, developed for a future mobile satellite communications system, is mounted on a vehicle for a receiving experiment in a mobile environment using a satellite signal in the L band.
Abstract: A multibeam digital beamforming (DBF) antenna, developed for a future mobile satellite communications system, is mounted on a vehicle for a receiving experiment in a mobile environment using a satellite signal in the L band. The multibeam is formed by 2-dimensional FFT signal processing. Automatic acquisition and tracking of an arriving signal are achieved by selecting a maximum beam out of the multiple beams in real-time.

01 Jan 1995
TL;DR: In this paper, a digital beamforming (DBF) antenna is mounted on a vehicle for a receiving experi- ment in a mobile environment using a satellite signal in the L band.
Abstract: Digital Beamforming (DBF) antenna, developed for a future mobile satellite communications system, is mounted on a vehicle for a receiving experi- ment in a mobile environment using a satellite signal in the L band. The multibeam is formed by 2-dimensional FFT signal processing. Automatic acquisition and tracking of an arriving signal are achieved by selecting a maximum beam out of the multiple beams in real-time.