Showing papers on "L band published in 2006"

New satellite‐based systems for ionospheric tomography and scintillation region imaging

Abstract: [1] The new constellation of radio beacons called Coherent Electromagnetic Radio Tomography (CERTO) will be available for measurements of ionospheric total electron content and radio scintillations. These beacons transmit unmodulated, phase-coherent waves, VHF, UHF, and L band frequencies. A fixed radio of 3/8 is used between successive frequencies. Total electron content (TEC) can be measured using the differential phase technique. The range between beacon and receiver is removed from the phase measurements, leaving a differential phase that is proportional to TEC. The three CERTO frequencies cover a wide range for determination of the radio scintillation effects caused by diffraction after propagation though ionospheric irregularities. All of the CERTO beacons are in low Earth orbit with inclinations ranging from equatorial to polar. Each satellite that carries CERTO has other plasma instruments that complement the beacon data. In addition, a Scintillation and Tomography Receiver in Space (CITRIS) instrument will be placed in orbit to detect signals from the CERTO beacons and from the array of 56 Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) VHF/S band radio beacons placed around the word by the French Centre National D'Etudes Spatiales. CITRIS will record ionospheric occultations and radio scintillations with a unique occultation and ground-to-space geometry. New algorithms have been developed for the multifrequency CERTO and CITRIS data to provide improved acquisition and analysis of TEC and scintillation data in ionospheric studies. The data from the CERTO constellation of beacons and receivers may be used to update space weather models.

Surface effect of rain on microwave backscatter from the ocean: Measurements and modeling

Abstract: [1] The effect of rain on the ocean surface alters the relationship between the surface wind vector and microwave backscatter, presenting an obstacle to wind retrieval via scatterometry. To address the effect of rain on surface backscatter, we develop a physically based ocean surface wave model modified by rain. Microwave backscatter is then calculated using a multiscale scattering model. Comparisons to observations at Ku band are used to validate and tune our surface model. Simulations give insight into backscattering surface features: ring waves result primarily from the collapse of the splash-created stalk, and the impulse responsible for the generation of ring waves has a radius roughly 5 times the drop's radius. Comparisons also show that backscatter from stationary splash features is necessary to accurately reproduce the effect of rain at Ku band. For Ku band our simulations expand upon prior measurements showing that rain increases backscatter and diminishes azimuthal variations. There is, however, a wind relative azimuthal signature in the backscatter for most rainfall rates. Simulations at Ka band, C band, and L band without the contribution from stationary splash features show that rain-created ring waves often alter backscatter. The effects are greatest at Ka band where they mirror changes to the very high-frequency region of the surface wave spectrum. C band backscatter is increased at moderate and high incidence angles and is sensitive to rain-induced damping. The effect of rain on L band is to decrease backscatter at high rain rate, and it is also dependent on rain-induced damping.

A novel lightweight dual-frequency dual-polarized sixteen-element stacked patch microstrip array antenna for soil-moisture and sea-surface-salinity missions

Abstract: The main motivation for this paper is to discuss the development of a novel compact and light-weight dual-frequency, dual linearly polarized, high-efficiency, stacked-patch microstrip-array antenna for use in standalone aircraft-based remote sensing applications. Results from simulation, fabrication, and testing of a sixteen-element stacked-patch array antenna, optimized for an L-band frequency of operation, are presented. The design center frequencies were 1.26 GHz and 1.413 GHz with 10 MHz and 25 MHz bandwidths in each band, respectively. Due to the large number of design parameters and demanding design requirements of beam-efficiency, sidelobe levels, and polarization characteristics, particle-swarm optimization (PSO) and finite-difference time-domain (FDTD) simulations were used for synthesis and analysis. Cancellation techniques, based on symmetry, were applied to the antenna ports, with a custom-built feed network to reduce cross polarization. Simulations and measurement results from a spherical near-field test facility confirmed excellent performance of the array configuration, with a beam efficiency of greater than 90%, isolation better than -35 dB, and cross polarization in the main beam of the array better than -40 dB. From the sixteen-element array simulations and experimental verifications, one of the objectives of the present study is to suggest the possibility of using customized dual-frequency, dual-polarized arrays as potential feeds for reflectors to replace the traditionally used conical horns for future soil-moisture and sea-salinity missions

A Second Generation L-band Digital Radiometer for Sea Salinity Campaigns

Abstract: An airborne, fully polarimetric L-band radiometer system intended for sea salinity campaigns is described. The radiometer is of the digital kind: the L-band signal is directly fed into a fast A to D converter using sub-harmonic sampling. All Stokes parameters are calculated digitally in a fast FPGA. Special attention is paid to detection and mitigation of interference from external active sources: the digital radiometer principle with fast sampling provides unique possibilities for RFI detection, and for mitigation of pulsed signals before final integration. Keywords; microwave, radiometer, sea salinity, RFI mitigation

Wideband Microtrip Bandpass Filters for Radio Astronomy Applications

Abstract: This paper presents wideband bandpass filters with a novel microstrip configuration. Using quarter-wavelength resonators, internal coupling between resonators was realized by interdigital capacitors (IDC) and capacitive open-ended stubs. Impedance steps, was utilized for external couplings. Two wideband filters at L band and C band with a fractional bandwidth (FBW) of 48% and 76%, respectively, were demonstrated as the concept for use in e-MERLIN receivers of radio astronomy applications. The measurement performance agrees well with the simulation.

Investigate C+L Band EDFA/Raman Amplifiers by Using the Same Pump Lasers

Abstract: A hybrid C+L band erbium-doped fiber amplifier/Raman fiber amplifier (EDFA/RFA) is constructed by sharing common 1480 nm pump source(s). It is based on three-level amplification mechanism in the C band and Raman shift amplification mechanism the in L band, respectively. The gain spectra of C+L band are flattened by optimally dividing the pump power ratio of 1:29 for EDFA/RFA. Gain variation is 14±1 dB for the C band EDFA and 13±1.5 dB for the L band RFA without gain equalization. The low noise, hybrid C+L band EDFA/RFA may find vast applications in WDM system and lightwave transmission.

Mitigation of Interference From Iridium Satellites by Parametric Estimation and Subtraction

Abstract: Radio astronomy is the science of observing the universe at radio frequencies. In recent years, radio astronomy has faced a growing interference problem as radio frequency (RF) bandwidth has become an increasingly scarce commodity. Communication systems such as Earth orbiting communication satellites creates severe interference to the radio telescopes. This thesis proposes an algorithm to mitigate the radio frequency interference (RFI) from the Iridium satellite system. A technique is presented here to detect the downlink signal of Iridium, estimate the parameters of the signal, synthesize the noise-free version of the signal and finally subtract the recreated signal from the radio telescope output. Using both simulated and real data captured by a radio telescope testbed, we demonstrate that for Iridium bursts with 20 dB signal to noise power ratio (SNR), the proposed algorithm achieves more than 15 dB cancellation. The method proposed here can be implemented using present-day digital signal processing hardware and software. A performance analysis of this proposed cancellation scheme in the radio astronomy RFI mitigation regime is presented.

Simulation and measurement of the satellite to indoor propagation channel at L- and S-band

Abstract: The satellite to indoor propagation channel in L- and S-band is becoming of significant importance because future satellite broadcast and navigation systems (as e.g. S-DMB and Galileo) are aiming at optimum performance in all kind of environments, i.e. even in indoor scenarios. In the framework of the EU FP6 project MAESTRO, Fraunhofer IIS has carried out measurements of the satellite to indoor coverage for the geostationary Worldspace-Afristar satellite for different types of buildings in Athens and Erlangen. The satellite to indoor propagation channel depends on several parameters as building layout and materials. Wave propagation models are mandatory for analysing the various influences in detail. For the accurate simulation a ray-optical model which considers 3D building vector data has been implemented by AWE Communications.

Dispersion-compensating system

Abstract: In the dispersion-compensating system of the present invention, a demultiplexer demultiplexes optical signals in a signal wavelength band of 1520 nm to 1620 nm propagating through a first common transmission line into C band (1520 nm to 1565 nm) and L band (1565 nm to 1620 nm). Then, the demultiplexer outputs the optical signals of C band into a first branched transmission line and the optical signals of L band into a second branched transmission line. A first dispersion-compensating device is provided on the first common transmission line and compensates for the dispersion in C and L bands. A second dispersion-compensating device is provided on the second branched transmission line and compensates for the dispersion in L band, which has not fully been compensated for by the first dispersion-compensating device. Hence, the dispersion of optical transmission line can fully be reduced in a wide signal light wavelength band.

Instantaneous Frequency Measuring Receiver for L band

Abstract: This paper presents the design, parameters and results of measurements 6-bits IFM receiver for L band. The device is a complete solution, including limiting amplifier, trigger circuit and a circuit detecting whether a given frequency is out of band (OOB). This receiver is based on one microwave frequency discriminator.

C+L band erbium-doped fiber ASE source enables high-speed FBG sensor interrogation

Abstract: We have developed and prototyped C+L band erbium-doped fiber ASE source by making use of both forward and backward ASEs with double-pass configuration. Simulations and experiments are performed for different pump powers and fiber lengths to optimize the design. The spectrum bandwidth of 80.6nm (1526.7~1607.3nm) with flatness of 5.22dB is realized. Pumping-conversion efficiency of about 18.9% is reached. This C+L band light source will be used to extend illuminating bandwidth of the high-speed interrogator which has been prototyped and been used by different clients. The sampling rate can be up to 5 kHz. The broadband light source allows the interrogator no moving part that enables high-speed FBG sensor interrogation.

A UHF (950 MHz) Band RFID Reader Compliant with Japanese Radio Law

Abstract: Using the measured propagation characteristics of RFID systems standardized in the EU and US, we developed a 950-MHz radio frequency identification (RFID) reader compliant with the Japanese Radio Law of April 2005 We also created a measurement environment in which a tag response can be evaluated using test equipment

Micro-satellite based high resolution geolocation mapping of L-band communication sources from low earth orbit.

Abstract: Current civil spectrum monitoring systems are largely terrestrial-based and only cover a localised area limited to within the radio horizon of the measurement sites. Such systems typically use fixed frequency tuning receivers and can only acquire one specific frequency at a time. The aim of this research is to develop a system that is capable of performing global radio spectrum surveillance by mapping what frequencies are being transmitted and from which locations on the surface of the earth. The research comprise two areas, namely; 1) the use of orbiting satellites to host specialised radio frequency acquisition receivers; 2) the development of novel signal processing algorithms to extract the geolocation information and analyse the emission spectrum of the individual transmitting sources. The system configuration was designed based on a form of two-dimensional correlation function (otherwise known as the Ambiguity Function) to geolocate and map the source signals. It uses the principle of time correlation to identify the along-track location of a target, and Doppler difference frequency tuning to select the across-track range at which the correlation functions are to be evaluated. In this manner, a geolocation map can then be generated by stepping through and evaluating the individual correlation function at the various across-track ranges. In the proposed system, a constellation of two satellites will be used to form a measurement baseline. Each satellite will carry a specialised 'Microscan' receiver payload to scan through the entire monitoring bandwidth repetitively in fractional time, sampling the radio environment as it orbits Earth. The acquired data will then be down-linked during the next pass over the ground station for further post-processing. Spectrum analysis and transmitter geolocation will be achieved by selectively processing the relevant frequency bins of interest. To enhance the system's ability to detect weak radio sources, the Post-Detection Integration technique will be used to achieve the required processing Signal-to-Noise Ratio (SNR). The principles of Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) will be applied to resolve targets located within the receiving swath. A novel variable slip technique was also conceived which will enable the entire receiving swath to be mapped from just one second worth of complex sampled data obtained by each of the receiving satellite. Simulation results confirmed that the proposed system has an along-track range resolution to the target which is inversely proportional to the signal bandwidth, typically a few hundred meters for CDMA mobiles. Across track resolution is variable and can always achieve this resolution or better. The processed SNR is proportional to the signal integration time so that given enough integration time, any radio sources can be detected however small the received SNR. The proposed system will make comprehensive global surveying of radio spectrum usage possible for the first time and will be useful for civil radio governing agencies. With some adaptation, such a system can also potentially function as a low cost electronic intelligence (ELINT) gathering asset suitable for use by military establishments.

S+C+L band double-pass EDFA

Abstract: A new S+C+L band double-pass EDFA has been experimentally demonstrated. Almost 20 dB gain has been measured in a 120-nm range, with a 30 dB peak in each band for a -30 dBm signal power.

A Wide-Band Thulium-Doped Silica Fibre Amplifier

Abstract: We investigate a silica-based thulium-doped fibre amplifier, which is a promising candidate for an amplifying device in the S band, in detail using a single wavelength upconversion pumping scheme centred at 1064 nm. Our experimental results show that in terms of gain and noise figure, the bi-directional pumping scheme is the best one in the three pumping schemes, named forward, backward and bi-directional pumping schemes. The amplifier has a gain not only in the S band, but also in the C band, even in the L band. The gain is above 3 dB from 1525 nm to 1580 nm with a peak of 7.5 dB.

Spectral and Noise Purity of Coherent Multiple-Frequency Chirp Exciter for L Band Radars

Abstract: This paper presents results of spectral analysis and design performance of the up-converter module of the coherent multiple-frequency chirp exciter for long distance L Band surveillance radars. Some measured results of spectral and noise purity of the exciter with coherent frequency synthesizer driven from high stability oscillator source are included. The experimental results are in good agreement with requested values.

Optical Amplifier Hybrid Devices for S-Band Telecommunications--A Comparison

Abstract: Amplifier hybrids coupling different amplifier types are characterized and evaluated for application in S-band telecommunications. Combinations including a fiber-optic parametric gain module are also studied for S-C/L band wavelength conversion.

Analysis and Design of a Receiver for L-Band Synthetic Aperture Microwave Radiometer

Abstract: The requirement of a receiver used in the synthetic aperture microwave radiometer is presentedBased on the re- quirement,a receiver used in the L-hand synthetic aperture microwave radiometer is designedSystem simulation of the re- ceiver is carried out in the Advanced Design System(ADS)The result is given and the local oscillator influence to the re- ceiver is analyzedThe gain of the system is 129 dBThe noise coefficient is 18 dB

Remote controlled horn/lens feed for a 25 metre radio telescope

Abstract: A remotely controllable L band feed system was required for three 25 metre diameter radio telescope antennas, which form part of the MERLIN array in UK. A combined horn and lens feed system has been designed. In order to avoid compromising other feed systems on the same antenna the lens is stowed away when not in use. Details are given of the optical design approach as well as the mechanical functionality and manufacturing methods. Three complete systems have been manufactured and installed on radio telescopes; test methods and measured results are shown. Aperture efficiencies slightly in excess of 50 % were obtained, which is excellent for an L band feed on this type of 25 metre cassegrain antenna. System noise temperature results were a little disappointing, but there are clear pathways to improving this. All three feed systems have been used successfully for radio astronomical observations.