Showing papers on "L band published in 2004"

Multiband single-layer frequency selective surface designed by combination of genetic algorithm and geometry-refinement technique

Abstract: This paper proposes an optimization-design method for the frequency selective surface (FSS) based on the genetic algorithm (GA) incorporated with a geometry-refinement technique. The present method takes the connectivity condition of the elements into consideration, thereby resulting in an easy fabrication. As an example, we design the multiband single-layer FSS for transmitting L band (1.5 GHz band) and S band (2.5 GHz band) and also reflecting Ka band (20/30 GHz band). The designed FSS has bandwidths broader than previous FSSs. Finally, the validity of the present method is proved by the agreement between the calculated and the measured transmission responses for the designed FSS.

Characterization of the jitter in a mode-locked Er-fiber laser and its application in photonic sampling for analog-to-digital conversion at 10 gsample/s

Abstract: This paper compares two approaches for evaluating the amplitude and timing jitters of an Er-fiber laser mode-locked at 10 GHz. Using a low-noise oscillator as the clock drive for the mode-locking, relative amplitude jitter was measured as low as 0.0384% and timing jitter as low as 0.0153% (/spl Delta/f=100 Hz-40 MHz). Applying the mode-locked pulse train in a photonic sampling experiment at 10 Gsample/s, a spurious free dynamic range (SFDR) of /spl sim/48.5 dB (over the Nyquist bandwidth of 5 GHz) for multiple analog inputs at L band (1-2.6 GHz). These results correspond to an analog-to-digital conversion resolution of /spl sim/8 SFDR bits at 10 Gsample/s. Finally, the use of "instantaneous companding" is demonstrated to correct for third-order distortions generated by a Mach-Zehnder modulator used in the photonic sampling link.

L-band PS Analysis: JERS-1 results and TerraSAR-L predictions

Abstract: Long term interferometry with L band can be studied using data from the Japanese satellite JERS, that flew from 1992 to 1998. Notwithstanding problems like electromagnetic interference and limited information on the across track baselines, still the quality of the system makes the data very useful. This makes it possible the identification of Permanent Scatterers in urban and semi urban areas, with very high density (up to 150/km ) with coherence up to .9 in an interval of time of several years. In turn, this allows the better determination of the orbits, and allows a comparison with similar data from ERS 1. Namely, a similarity is found with data acquired during the 3 days repeat cycle. The longer wavelength therefore is seen to correspond to a longer decay time of the temporal coherence, thus explaining the high quality results obtained. The higher average coherence allows to combine the phase information of several adjacent points, and therefore to at least partially reduce the effects of the higher geometric dispersion of the differential interferometry outcomes due to the very same longer wavelength. In conclusion, while the technique appears too coarse for direct estimation of building motion, it appears very interesting for vegetated areas and for areas where the velocity of the motion would create alias in C band. Introduction The Japanese satellite JERS-1 has been operational from 1992 to 1998. It used a sensor in L band (λ=23,5cm, f0=1.275GHz, 18x6m ground range x azimuth resolution) with polarization HH; it had a sun-synchronous orbit with altitude 568 km. Images were acquired every 44 days. The acquisition angle is 35°, greater than ERS-1, and the foreshortening effect is weaker. Moreover, the orbit is lower and allows getting a resolution higher than in case of ERS. The longer wavelength makes JERS useful for geologic applications in areas covered by vegetation, due to the higher penetration of the signal. Unfortunately, JERS images are affected by various problems (ambiguity in azimuth values, imprecision of the on board clock, low signal to noise ratio, limited information from ephemeredes, etc.) caused by a power loss of the signal transmitted from the platform to the ground. Images are also more sensible to noise due to the interaction with ground radars. Figure 1: C band and L band (SIR-C/X-SAR images of Flevoland in Holland). color scheme: HH: red, HV:green, VV: blue ERS satellites operate in C band with VV polarization, while JERS uses L band with HH polarization. Both ERS and JERS show a strong layover effect. Due to its acquisition geometry, ERS is twice as sensible to the vertical component of displacement as JERS. Figure 2 allows a comparison of the geometric distortions of the two sensors.

Dynamical gain control in the serial structure C+L wide-band EDFA

Abstract: The dynamic gain properties of a serial structure of C+L wide-band EDFA are investigated. It is found out that changing of C band (L band) signal has almost no effect on the gain spectra of L band (C band), so that dynamical gain control can be realized by mature fast linear pump control via monitoring of C band and L band input signal respectively. The method was demonstrated experimentally for the first time.

A simple algorithm for spatial disaggregation of radiometer derived soil moisture using higher resolution radar observations

Abstract: The SMEX02 experiments held in June-July 2002, at Iowa demonstrated the potential of an L band radiometer (PALS) in estimation of near surface soil moisture under dense vegetation canopy conditions. The L band radar was also shown to be sufficiently sensitive to near surface soil moisture. However, the spatial resolution of a typical satellite mounted L band radiometer is of the order of 10's of kilometers which is not sufficient to serve the science needs of land surface hydrology and weather modeling applications. Disaggregation schemes for deriving sub pixel estimates of soil moisture from radiometer data using higher resolution radar observations hold the promise of making global soil moisture observations at much finer scale available. The HYDROS instrument is proposed to have an L band radiometer and L band radar onboard. The passive instrument has spatial resolution of the order of tens of kilometers and operates along with the active instrument that takes observations at a resolution of tens of meters. This paper presents a simple approach for disaggregation of coarser resolution radiometer estimates of soil moisture using higher resolution radar backscatter measurements. The algorithm has been applied to a coincident PALS radar/radiometer and AIRSAR dataset acquired during the SMEX02 campaign

Coherent multiple-frequency chirp exciter for L band radars

Abstract: This work presents design examples of coherent multiple-frequency chirp exciter for long distance L band surveillance radars. The implemented technique for pulse compression is the use of linear frequency modulation during the pulse. Long-duration linear FM pulses are obtained by the use of cascade two dispersive SAW delay lines and are converted to the desired carrier frequency. The set of all local oscillator frequencies are obtained by direct frequency synthesis method. All of the frequencies in the synthesizer are derived from the same high stability oscillator source.

Satellite L-band front end design

Abstract: The design, simulation and experiments of an L-band front end for the new AMSAT Phase 3E satellite are presented here. The double conversion receiver for the transponder and command unit is based on the double PLL frequency synthesizer synchronized by an ultra stable oscillator positioned on-board the satellite.

Detection and localization of L-band satellites using an antenna array

Abstract: Argus is an experimental L-band radio telescope, consisting of a large number of low-gain antennas networked together to facilitate detection and localization of astronomical transients over the entire sky instantaneously. In this paper, we report an experiment in which we used Argus to observe man-made satellites, namely the 1691 MHz WEFAX signal from the GOES-12 satellite and the combined 1575.42 MHz signal from the US GPS constellation. This is a useful interim step to astronomical observations because WEFAX and GPS are strong relative to astronomical sources, yet weak enough to provide a meaningful test of the ability to operate with high sensitivity in field conditions.

Comparison of measured galactic background radiation at L-band with model

Abstract: Radiation from the celestial sky in the spectral window at 1.413 GHz is strong and an accurate accounting of this background radiation is needed for calibration and retrieval algorithms. Modern radio astronomy measurements in this window have been converted into a brightness temperature map of the celestial sky at L-band suitable for such applications. This work presents a comparison of the background predicted by this map with the measurements of several modern L-band remote sensing radiometers.