L band

About: L band is a research topic. Over the lifetime, 674 publications have been published within this topic receiving 4570 citations.

A diplexer for gigawatt class high power microwaves

Abstract: With the rapid development of high power microwave (HPM) technologies, HPM devices with several output frequencies are becoming more and more attractive. Diplexer is a microwave device with two output frequencies, here, an L/X band diplexer with novel structure is tried to be employed in the HPM system. In order to obtain the same radiation direction for the L and X band microwaves in the diplexer, the reflection of L band microwaves and transmission of X band microwaves are realized by an array of irises. To obtain the required performance, the width and thickness of the irises and the distance between them should be well chosen. The diplexer is investigated through theoretical analysis and numerical computation, and the final design described in this work, is the result of an overall optimization process. In simulation, both the reflectivities of L-band microwaves and the transmissivities of X band microwaves reach 99.5%, and the power handling capacity of the diplexer is higher than 5.6 gigawatt (GW). Then, the L/X band diplexer is designed and fabricated according to the optimized results. After that, a series of experiments are carried out to test the diplexer. The cold test results show that the reflectivities of L band microwaves are as high as 97.5%, and the transmissivities of X band microwaves are up to 98.8%, and the acquired radiation patterns show that the designed diplexer is suitable for the diplexing of L/X band microwaves, in a word, the cold test results of the diplexer are in good agreement with the simulational results. In the end, the diplexer is tested with GW class HPMs. The radiated HPMs have little change in the pulse duration and magnitude with the diplexer applied, that is to say, there is no microwave breakdown during the HPM reflection and transmission.

Multifocus processing of L band synthetic aperture radar images of ocean waves obtained during the Tower Ocean Wave and Radar Dependence Experiment

Abstract: As part of the Tower Ocean Wave and Radar Dependence Experiment (TOWARD) objectives, the mechanisms of SAR imaging of ocean waves are investigated using L band SAR data over the Naval Ocean Systems Center tower. This paper provides experimental evidence needed to validate the differing hypotheses. Various processing methods are investigated to generate spectra with large degrees of freedom. The results show that waves traveling in the aircraft direction are most detectable at focus settings in the range 10.0–15.0 m/s, which is consistent with the Marine Remote Sensing Experiment (MARSEN) observations reported by Jain and Shemdin (1983). Waves traveling in the direction opposite to the aircraft are most detectable at settings equal to −5.0 to −15.0 m/s. The SAR imaging system acts as a low-pass filter with the peak of the ocean wave height spectrum occurring at higher wave numbers compared with the peak in the SAR image spectrum.

Exploration of possible GNSS signals in S-band

Abstract: Satellite navigation has become such a worldwide priority that many countries are actively deploying or considering their own systems or modernizing those that already exist. As a consequence, the number of signals transmitted in L band will be significantly increased in the next few years so that only scant spectrum will be available for new systems or signals. Since current signals will have to be maintained many years in order to guarantee backward compatibility for legacy receivers, we can foresee that the search for new frequency allocations will be ranked at the highest level with a view to future evolutions of current systems. In this context S-band spectrum between 2483.5 and 2500 MHz, which is already allocated to the radio determination satellite service (RDSS), can be used for satellite navigation - although the allocation in the Radio Regulations is only primary in parts of Asia, Africa and the Americas - is a particularly interesting possibility as synergies with future mobile communication systems in the band immediately above could be exploited to provide both navigation and communication services using one unique S-band terminal with an efficient, common antenna. Only at the next World Radiocommunications Conference in 2012 will the decision be made whether to make the existing patchwork of RDSS allocations global, but the studies completed so far show this to be promising. A global allocation will provide an important opportunity for a worldwide convergence between systems of the mobile satellite service (MSS) and the radio determination/navigation satellite service (RDSS / RNSS). This paper aims to analyze the suitability of this band for navigation purposes as well as the effects that the introduction of these kind of signals would produce on the other radio services present in the same and adjacent bands. We will also present the results obtained from link and error budget calculations and interference assessment that have been performed using various hypothethical of navigation signals in S band. Opportunities for Galileo-2 signals are currently being studied having in mind possible additional frequencies in C and/or S band and/or L band, in complement to the E5a, E5b, E6 and E1 legacy OS, SoL, CS and PRS signals. The paper will give special attention to possible synergies between a hypothetical Galileo-2 S-band signal, IRNSS/GINS and Beidou/COMPASS, which will use L and S bands, other RNSS/RDSS systems and mobile satellite service systems such as GLOBALSTAR-2. These signals will be compared, and synergies between them explored. Several possible waveforms centred on a frequency close to 2491 MHz will be analysed in terms of intersystem interference and in terms of navigation and data transmission performance. The analysed waveforms in Sband will be BPSK(1*1.023 Mcps), BPSK(4*1.023 Mcps), BPSK(8*1.023 Mcps), BOC(1,1) and MBOC.. Power flux density (pfd) and interference computations showing compatibility between a potential Galileo-2 Sband component, S-band GNSS signals, GLOBALSTAR, mobile services (MS) and fixed services (FS) will be presented.

Skylab L band microwave radiometer observations of soil moisture revisited

Abstract: In preparing for future L band soil moisture satellite missions, investigators have employed ground, aircraft and satellite sensors. Of the satellite sensors, there has been only one instrument that provides any heritage at L band, the Skylab S-194 instrument that operated in the 1970s. Data from theses missions have been analyzed and reported in a few applications, however, these studies utilized either the linear regression approach or the Antecedent Precipitation Index (API). We explore the use of products from climate model reanalysis projects as ancillary data to exploit the S-194 data for a broad range of soil moisture conditions by employing a radiative transfer approach. The spatial resolution and the accuracy of reanalysis outputs are major limitations to this approach.