Showing papers on "L band published in 2003"

Design of an L-band microwave radiometer with active mitigation of interference

Abstract: Radio frequency interference (RFI) impairs L-band radiometry outside the protected 20 MHz frequency band around 1413 MHz. However, bandwidths of 100 MHz or more are desired for certain remote sensing applications as well as certain astronomy applications. Because much of the RFI in this band is from radars with pulse lengths on the order of microseconds, traditional radiometers (i.e., those which directly measure total power or power spectral density integrated over time scales of milliseconds or greater) are poorly-suited to this task. Simply reducing integration time and discarding contaminated outputs may not be a practical answer due to the wide variety of modulations and pulse lengths observed in L-band RFI signals, the dynamic and complex nature of the associated propagation channels, and the logistical effort associated with post-measurement data editing. This motivates the design and development of radiometers capable of coherent sampling and adaptive, real-time mitigation of interference. Such a radiometer will be described in this presentation. This design is capable of coherently-sampling up to 100 MHz bandwidth at L-band. RFI mitigation is implemented in FPGA components so that real-time suppression is achieved. The system currently uses a cascade of basic time- and frequency- domain detection and blanking techniques; more advanced algorithms are un- der consideration. The modular FPGA-based architecture provides other benefits, such as the ability to implement extremely stable digital filters and the ability to reconfigure the system "on the fly". An overview of the basic design along with on-the-air results from an initial implementation will be provided in the presentation. Related L-band RFI surveys will be described to illustrate the relevance of this approach in a variety of operating conditions.

UHF and L band propagation measurements to obtain log-normal shadowing parameters for mobile satellite link design

Abstract: Tree shadowing is significant for mobile satellite radio propagation investigation and must be known for successful link design. Therefore, there are limited data on the relevant problem. For this purpose, propagation measurements at L and UHF band were performed in Trabzon, Turkey, in 1993 and 1996, respectively. These experiments were executed with a transmitter on the top of a high building, and the receiver system was located in a van outfitted with the antenna on its roof and receiver equipment in its interior. Measurements were carried out for 14 different tree types, and the results of both bands are presented in tabular and graphical forms. Experiments were repeated for the same trees during the months April to September. The variations of the tree attenuation were examined during these months with and without foliage. Average values of the tree attenuations were found to be 8.60 and 11.00 dB for UHF and L band, respectively. The scaling factor between L and UHF band attenuations in decibels was determined to be approximately 1.32. Using these measured parameters, fade depth statistics were calculated using a lognormal shadowing model. To establish validity of obtained results for the design of mobile satellite links, the results were compared with previous investigations.

Characterization of L-band RFI and implications for mitigation techniques

Abstract: We describe measurements of radio frequency interference (RFI) in the 1200-1800 MHz band as observed from NASA s P-3 research aircraft during a flight along the Mid-Atlantic coast of the U.S. at altitudes of 2,000 and 20,000 ft. Both power spectra and coherently-sampled waveform data were obtained. Our results indicate that the spectrum below 1400 MHz is typically dominated by pulses from ground based radars, which, while very strong, individually have transmit duty cycles of on the order of 0.1%. We detect but are unable to identify some relatively weak intermittent RFI inside the 20 MHz protected band centered at 1413 MHz. We detect no significant RFI above 1420 MHz, but the limited sensitivity of this particular experiment makes it impossible to rule out the presence of RFI at levels damaging to total power radiometry. Implications for radiometer design, including possible active countermeasures for RFI mitigation, are discussed.

Wide band optical fiber amplifier

Abstract: Disclosed is a wide band optical fiber amplifier for amplifying C and L-band optical signal components having an economical configuration, high amplification efficiency while exhibiting a low noise figure. The amplifier includes first and second isolators; first, second, and third amplification units; a distributor; a gain flattening filter; and first and second reflectors. The amplifier receives C and L band optical signals and process the signals by: amplifying C and L band signals; gain flattening the only C band signal twice; amplifying C and L band signals for the second time; splitting the C band signal from L band signal; subjecting L band signal to be amplified three more times; and combining resulting C and L band signals.

Monitoring forests from L-band microwave observations

Abstract: In the near future, spaceborne low-resolution measurements of the L-band brightness temperature will be available from areas covered by all sorts of vegetation. Several studies have addressed the problem of estimating soil moisture at L-band for bare soil and crops, where a simple radiative approach with little need for ancillary information (τ−ω model) proved to be suitable. The possibility to obtain information about forests needs to be studied. The formulation of the τ−ω model can be maintained to simulate the microwave emission if τ and ω are defined as effective parameters. However, knowing the sensitivity of τ and ω to configuration parameters (angle and polarization) is required in the inversion process. As a first step of the study, we investigate the dependence of the model parameters on angle, polarization and understory layer. Keywordspassive microwaves, SMOS, forest monitoring

Radio wave propagation measurements for land-mobile satellite systems at 2.33 GHz

Abstract: The performance of a mobile satellite communications link is dominated by roadside attenuation due to vegetation or manmade structures. Previous measurement campaigns characterized land-mobile satellite channels at UHF and L bands. In 1997, the FCC allocated S-band spectrum to the Digital Audio Radio Satellite (DARS) service to provide nationwide radio services to the North American continent via satellite. This article describes a propagation measurement campaign at 2.33 GHz for DARS systems. Measurements were taken in various propagation environments and typical values of propagation constants for standard models are presented.

A broadband, ship based, electronically steered L-band SATCOM antenna

Abstract: In this paper an antenna for the L-band satellite communication system INMARSAT is presented. The INMARSAT System (Downlink: 1525-1559 MHz, Uplink: 1626.5-1660.5 MHz) was mainly build for voice and data communication between offshore ships and the mainland. Therefore these antennas have to have a steerable beam, so they can be pointed to the satellite regardless of the ships position on sea, as well as to compensate for the movement of the ship itself. So far the antennas for such systems have been steered mechanically. In this paper a new, cost effective and electronically steerable conformal array antenna for the INMARSAT system is presented.

Low-cost high reliability digital satellite electronic tuner

Abstract: The utility model relates to a digital satellite electronic tuner with low cost and high reliability. A down frequency conversion of I/Q signal in L band is realized by passing a filter, an amplifier, an attenuator, a frequency conversion circuit, corresponding filters, and a local oscillating auxiliary circuits. The utility model comprises a filter, a two-stage high frequency amplifying and attenuating device 1, a lower frequency converter 2 that directly convert L band signals into analog base band I/Q signals, a QPSK demodulator and FEC that processes the output TS flow after receiving the analog base band I/Q signals from the down-frequency converter 2 and passing the double-tuning filter 2. Compared with prior art, the utility model greatly reduces the cost of tuners while improving the performance and reliability of the product.