Comparison of Integrated Digital Radiometer with Concurrent Water Vapor Radiometer Using the Alphasat Receivers in Milan, Italy

In June 2014, NASA Glenn Research Center (GRC) and the Politecnico di Milano (POLIMI) jointly deployed a pair of coherent 20 GHz and 40 GHz beacon receivers to the POLIMI campus in Milan, Italy to characterize the atmospheric channel at Ka- and Q-band within the framework of the Alphasat experiment. The Milan receivers observe the continuous-wave beacons broadcast over Europe by the Aldo Paraboni Technology Demonstration Payload (TDP #5), and, in September 2017, both channels were upgraded to incorporate a novel digital radiometer (DR) measurement which NASA has recently employed in other propagation measurement campaigns. In November 2016, a co-located water vapor radiometer (WVR) was also installed at POLIMI, and the concurrent data from both the WVR and DR thusly enables validation of this new DR technique against the established WVR. Herein, we preliminarily investigate the calibration of the DR measurements using the WVR data and also assess a calibration method that may be implemented where WVR data is not readily available

Ka-to-W Band EM Wave Propagation: Tropospheric Effects and Countermeasures

Near future satellite and terrestrial telecommunication (TLC) systems are expected to benefit from the use of operational frequencies spanning the Ka, Q, V and W bands, the main advantages being the availability of larger bandwidths and the smaller antenna size for a given gain. Moreover, the possibility of using on‐board antennas with enhanced directivity is attractive for satellite systems whose coverage area is subdivided into spot beams for frequency reallocation or regional services. For example, the W band is attractive for fixed satellite services (FSS), especially for geostationary high‐throughput systems (HTSs), in which the use of such frequencies for the feeder link (i.e. large available bandwidth) could reduce significantly the number of gateways with respect to Ka and Q/V bands. As for deep space missions, the main driver for the interest in using frequencies in the Ka to W bands is the possible increase in the on‐board antenna gain with respect to the values at X band considered for current or planned missions. The drawback of using electromagnetic waves at frequencies in Ka, Q, V and W bands is the definite impact of the impairments caused by the troposphere. As a consequence, the design of TLC systems at such frequencies, and in particular satellite‐based ones, cannot rely on the classical approach of simply assigning an extra power margin to counteract atmospheric fades. The extensive use of fade mitigation techniques (FMTs), such as link power control (LPC), site diversity or on‐board adaptive power allocation, from the propagation side, adaptive coding and modulation (ACM) and data rate adaptation (DRA), from the telecommunication side, is mandatory. A reduction of the quality of service (QoS) should also be considered. This chapter deals with all these aspects characterizing the propagation of electromagnetic waves in the Ka, Q, V and W bands, spanning from the main impairments induced by the troposphere (and how they change as the frequency increases), to how extreme atmospheric conditions can be handled making use of suitable FMTs

Feasibility of Ultra-Wideband Channels at Millimeter Wavelengths Faded by Rain in GeoSurf Satellite Constellations

We have studied the interference caused by amplitude and phase distortions induced by rain in ultra-wideband communication systems designed for using amplitude modulation in GeoSurf future satellite constellations. The results concern radio links simulated with the synthetic storm technique at Spino d'Adda (Italy), Madrid (Spain) and Tampa (Florida), which are sites located in different climatic regions. The conclusions are (a) the three sites, although in different climatic zones, are practically indistinguishable; (b) the channel signal-to-noise ratio can be increased or decreased by interference with equal probability. Channel theoretical capacity loss, even in the worst case, is very limited and rain, therefore, does not cause significant linear distortions in ultra-wideband channels at millimeter waves; therefore, these channels could be used at millimeter waves

Evidence of a Critical Histidine Residue in Soluble Aspartic Aminotransferase

Photooxidation of extramitochondrial α-aspartate aminotransferase in the presence of methylene blue or Rose bengal leads to a loss of enzymatic activity which follows first order kinetics. Amino acid analysis shows that histidine is the only amino acid residue significantly affected by photooxidation. Of the 8 histidine residues present in the enzyme monomer, 2 are oxidized rapidly at a rate identical with that of the activity loss, while the other 6 are destroyed much more slowly. The pH dependence of the rate of the photo-induced inactivation of the enzyme corresponds to that expected for the photooxidation of imidazole groups. The behavior of the enzyme in Sephadex G-200 is identical before and after extensive photooxidation, while the starch gel electrophoretic pattern changes after photooxidation. It is concluded that the loss of enzyme activity caused by photooxidation is related to the destruction of 1 histidine residue

Periodic stability analysis of wind turbines operating in turbulent wind conditions

Abstract. The formulation is model-independent, in the sense that it does not require knowledge of the equations of motion of the periodic system being analyzed, and it is applicable to an arbitrary number of blades and to any configuration of the machine. In addition, as wind turbulence can be viewed as a stochastic disturbance, the method is also applicable to real wind turbines operating in the field. The characteristics of the new method are verified first with a simplified analytical model and then using a high-fidelity multi-body model of a multi-MW wind turbine. Results are compared with those obtained by the well-known operational modal analysis approach

Comparison of Instantaneous Frequency Scaling from Rain Attenuation and Optical Disdrometer Measurements at K/Q bands

Rain attenuation is strongly dependent on the rain rate, but also on the rain drop size distribution (DSD). Typically, models utilize an average drop size distribution, such as those developed by Laws and Parsons, or Marshall and Palmer. However, individual rain events may possess drop size distributions which could be significantly different from the average and will impact, for example, fade mitigation techniques which utilize channel performance estimates from a signal at a different frequency. Therefore, a good understanding of the characteristics and variability of the raindrop size distribution is extremely important in predicting rain attenuation and instantaneous frequency scaling parameters on an event-toevent basis. Since June 2014, NASA Glenn Research Center (GRC) and the Politecnico di Milano (POLIMI) have measured the attenuation due to rain in Milan, Italy, on the 20/40 GHz beacon signal broadcast from the Alphasat TDP#5 Aldo Paraboni Q/V-band Payload. Concomitant with these measurements are the measurements of drop size distribution and rain rate utilizing a Thies Clima laser precipitation monitor (disdrometer). In this paper, we discuss the comparison of the predicted rain attenuation at 20 and 40 GHz derived from the drop size distribution data with the measured rain attenuation. The results are compared on statistical and real-time bases. We will investigate the performance of the rain attenuation model, instantaneous frequency scaling, and the distribution of the scaling factor. Further, seasonal rain characteristics will be analysed

Three Years of Atmospheric Characterization at Ka/Q-band with the NASA/POLIMI Alphasat Receiver in Milan, Italy

Since June of 2014, NASA Glenn Research Center (GRC) and the Politecnico di Milano (POLIMI) have jointly conducted a propagation campaign within the framework of the Alphasat propagation experiment through a propagation terminal at the POLIMI campus in Milan, Italy. The terminal utilizes the 20 GHz and 40 GHz beacons broadcast by the Aldo Paraboni Technology Demonstration Payload (TDP #5), and consists of dual coherent Ka- and Q-band beacon receivers. These provide a direct measurement of the signal attenuation and scintillation and are complemented by concurrent weather instrumentation that provides measurements of the atmospheric conditions at the receiver. The primary goal of these measurements is to improve model predictions of communication system performance at 40 GHz. Over three years of concurrent measurements have now been collected from the terminal, and herein we present a statistical analysis of the results thus far, as well as a summary of recent hardware upgrades to the receivers that were made in September 2017

Preliminary Results of the NASA Beacon Receiver for Alphasat Aldo Paraboni TDP5 Propagation Experiment

NASA Glenn Research Center (GRC) and the Politecnico di Milano (POLIMI) have initiated a joint propagation campaign within the framework of the Alphasat propagation experiment to characterize rain attenuation, scintillation, and gaseous absorption effects of the atmosphere in the 40 GHz band. NASA GRC has developed and installed a K/Q-band (20/40 GHz) beacon receiver at the POLIMI campus in Milan, Italy, which receives the 20/40 GHz signals broadcast from the Alphasat Aldo Paraboni TDP#5 beacon payload. The primary goal of these measurements is to develop a physical model to improve predictions of communications systems performance within the Q-band. Herein, we describe the design and preliminary performance of the NASA propagation terminal, which has been installed and operating in Milan since May 2014. The receiver is based upon a validated Fast Fourier Transform (FFT) I/Q digital design approach utilized in other operational NASA propagation terminals, but has been modified to employ power measurement via a frequency estimation technique and to coherently track and measure the amplitude of the 20/40 GHz beacon signals. The system consists of a 1.2-m K-band and a 0.6-m Qband Cassegrain reflector employing synchronous open-loop tracking to track the inclined orbit of the Alphasat satellite. An 8 Hz sampling rate is implemented to characterize scintillation effects, with a 1-Hz measurement bandwidth dynamic range of 45 dB. A weather station with an optical disdrometer is also installed to characterize rain drop size distribution for correlation with physical based models

Comparison of Integrated Digital Radiometer with Concurrent Water Vapor Radiometer using the Alphasat Receivers in Milan, Italy

In June 2014, NASA Glenn Research Center (GRC) and the Politecnico di Milano (POLIMI) jointly deployed a pair of coherent 20 GHz and 40 GHz beacon receivers to the POLIMI campus in Milan, Italy to characterize the atmospheric channel at Ka- and Q-band within the framework of the Alphasat experiment. The Milan receivers observe the continuous-wave beacons broadcast over Europe by the Aldo Paraboni Technology Demonstration Payload (TDP #5), and, in September 2017, both channels were upgraded to incorporate a novel digital radiometer (DR) measurement which NASA has recently employed in other propagation measurement campaigns. In November 2016, a co-located water vapor radiometer (WVR) was also installed at POLIMI, and the concurrent data from both the WVR and DR thusly enables validation of this new DR technique against the established WVR. Herein, we preliminarily investigate the calibration of the DR measurements using the WVR data and also assess a calibration method that may be implemented where WVR data is not readily available

Radio Wave Satellite Propagation in Ka/Q Band

In 2013 the European Space Agency, in cooperation with Inmarsat, launched the Alphasat communication satellite hosting four Technology Demonstration Payloads (TDPs). One of them is the Aldo Paraboni payload, supported by the Italian Space Agency (ASI) and executed by ESA in the framework of the Advanced Research in Telecommunications Systems (ARTES) 8 Telecom program. In addition to the Communication experiment, it includes the Alphasat Scientific Experiment transmitting coherent beacon signals at Ka-band (19.701 GHz) and Q-band (39.402 GHz). The satellite supports a Europe-wide experiment to investigate the atmospheric propagation effects occurring in Ka and Q bands. The demand for increasing bandwidth in the satellite radio communication domain is moving the communication channels to the higher frequency bands. Hence for both research and commercial purposes is especially important to effectively explore the Q band that is affected by attenuation, depolarization and scintillation due to different atmospheric effects. In 2014 the Department of Broadband Infocommunications and Electromagnetic Theory at Budapest University of Technology and Economics joined the ASAPE (AlphaSat Aldo Paraboni Experimenters) group and developed a ground station to be installed in Budapest. This work was supported by the European Space Agency under its Plan for European Cooperating States program. Our paper gives the background of the Alphasat Scientific Experiment and overviews the design phases of the receiver station in Budapest. We present also the processing and validation of data recorded so far and our future experimenting plans