electrical and electronics
Smooth-Walled Feed Horn
The technology is a monotonically-profiled, smooth-walled scalar feed horn optimized between 33 and 45 GHz. The phase center for this horn is near the aperture and is stable in frequency. The feed horns monotonic profile is compatible with machining by progressive plunge milling in which successively more accurate tools are used to realize the feed profile. This technique has been used for individual feeds and is potentially useful for fabricating large arrays of feed horns, such as multimode Winston concentrators, direct-machined smooth-walled conical feed horns, and for dual-mode feed horns.
Method for Absolute Calibration and Tracking of Large Format Detectors Using Laser Radar
The purpose of this technology is to obtain charge coupled device (CCD) pixel location knowledge in 6 degrees of freedom with detector alignment precision of tens of microns of absolute uncertainty in a mechanical coordinate system. This non-contact approach involves the use of laser radar to obtain the orientation of the CCD pixels on a large format detector. This information can be used to align a detector in an optical system or interpolate image data from the CCD and correlate image features with physical locations in real space. The X, Y pixel value results for image analysis can be transformed into a three dimensional coordinate system. Using the laser radar, the CCD pixels are physically mapped and then related to external metrology targets on the detector housing. To accomplish this mapping, the laser radar is pointed at and focused on three or more locations on the detectors active area where a full frame readout of the detector is captured. This approach addresses a couple of technical challenges. The first challenge was to place a detector accurately and effectively as to have the OTE pupil image in plane with the detector pixels. Lastly, once the detector alignment is accomplished, how can the location of key features be established in the working coordinate system. This solution satisfies both of those challenges.
Low Frequency Wideband Step Frequency Inverse Synthetic Aperture Radar
This technology is a low frequency (25~100 MHz) wide band (75 MHz) subsurface imaging ISAR. Use of low frequencies allows the electromagnetic energy to penetrate to a greater depth, enabling observation of the interior of a solid object to a higher resolution than can be achieved with alternate technologies. Higher bandwidth has been used in earlier ISAR systems; however these require expensive high bandwidth RF components, and also higher speed data processing units. The new ISAR system uses a novel step frequency technique which eliminates both these requirements. The step frequency approach keeps the local bandwidth very small; enabling data processing at much lower speed. And by stepping through the frequencies, this ISAR achieves much higher overall bandwidth and consequently very high range resolution.
Solid-State Microwave Power Module
Typically, microwave power modules (MPMs) are useful only for radar and navigation purposes because they lack the linearity and efficiency required for communications. In standard configurations, conventional MPMs require both a solid-state amplifier at the front end and a microwave vacuum electronics amplifier at the back end. By contrast, Glenn's design features a wideband multi-stage distributed amplifier system. The low-power stage is a high-efficiency gallium arsenide (GaAs) pseudomorphic high-electron-mobility transistor (pHEMT)-based monolithic microwave integrated circuit (MMIC) distributed amplifier. The medium-power stage is configured to pick up and amplify the low-power signal. This stage can be either another high-efficiency GaAs pHEMT or a gallium nitride (GaN) HEMT-based MMIC distributed amplifier, depending on the need. The high-power stage, configured to pick up the signal from the second amplifier, is a high-efficiency GaN HEMT-based MMIC distributed amplifier, which supplants the traveling-wave tube amplifier found in most microwave power modules. In Glenn's novel MPM, the radar functions as a scatterometer, radiometer, and synthetic aperture imager. The high-speed communications system down-links science data acquired by Earth-observing instruments. The navigation system functions like a transponder for autonomous rendezvous and docking, and estimates the range information. Glenn's MPM gives systems the versatility to use a single power module to drive not only radar and navigation but also communications systems.
Frequency Diversity Pulse Pair Algorithm for Mitigation of Radar Range-Doppler Ambiguity
This technology mitigates the Doppler ambiguity by creating an innovative frequency. This frequency diversity technique takes advantage of the recent development in digital waveform generation and digital receiver technologies by transmitting a pair of pulses (or more pulses) with slightly shifted center frequencies in each pulse repetition period. Radar return signals from these pulses can be separated by the digital filters implemented in the digital receiver. In Doppler radar operation, the maximum unambiguous range is determined by the radar transmission pulse repetition time. This unique frequency diversity technique is implemented by alternating the order of the pulse pair with center frequencies as f1, f2, and f2, f1, then integrate the phase estimates of f1/f2 pulse pair and f2/f1 pulse pair in equal numbers. This approach will cancel the phase shift as a function of range between the pulses to enable the retrieval of Doppler phase. Although this method is more advanced, it also has its inherent limits, such as increased phase error and increased complexity in radar hardware to transmit and receive dual polarized signals. Despite its faults, it is a step forward in the evolution of the Doppler radar and its growing applications.
electrical and electronics
Ultra broadband planar via-less mm-wave crossover with high isolation
This technology is accomplished in a few short steps. First, the microstrip is converted to a CPW line on the ground plane layer of the microstrip line. Second, the CPW line is approximately half-wavelength long around the crossing area. And finally, the width of the ground plane cut and the center line of the CPW on the bottom ground plane is maintained at minimum value to reduce radiation and cross coupling to the top microstrip line. This device is designed at 150 GHz on single-crystal silicon substrate and has an operating bandwidth of 130% with a minimum line isolation of 34dB. Similar performance can be maintained while scaling and line isolation can be further improved when operating at a lower frequency than 250 GHz.
Oceanic Surface Air Pressure Sensing
Understanding the characteristics of a weather system is vital to predicting the path and severity of storms such as hurricanes and typhoons. The surface air pressure over the ocean is one of the key characteristics that can be used in making those predictions. Current long-range technologies can perform only loose estimations of the surface air pressure based on wind speed and direction. Direct measurements of the air pressure require costly and risky plane missions through the storm to collect periodic data. The oxygen band radar system developed by NASA at its Langley research facility allows for the continuous remote monitoring of atmospheric pressure over the worlds oceans. The technology incorporates the use of a low-power laser frequency specific to the known oxygen band. By using this narrow band, the researchers are able to measure surface level oxygen density and subsequently, air pressure. The increased knowledge of localized air pressure will significantly enhance the predictive power of weather forecasting models and allow for the development of new models.
Interference Reduction Algorithm for Continuous Wave Lidar Return Data
The NASA algorithm was developed to support the ASCENDS mission Laser Absorption Spectrometer (LAS) for carbon dioxide measurements in the mid-to-lower troposphere. The LAS is a satellite-based continuous wave lidar system capable of monitoring global variability of carbon dioxide concentration in the troposphere from space, with a measurement range of up to ~500 km (low earth orbit). The modulation algorithm (a filtered pseudo-noise code algorithm) is capable of eliminating cross-channel noise and interference by modulating the lidar return signal using a time shifting approach. Figures 1 and 2 below demonstrate these capabilities. The technology builds on a strong remote sensing and lidar technology heritage at NASAs Langley Research Center. The algorithms are complete, have been verified as error-free by independent third parties, and flight tests aboard a Dassault HU-25C Guardian Falcon jet are scheduled for Fall of 2014. Lidar system specifications for the test bed include: -- Three 17.7 cm telescopes -- CW lidar system powered by three 10W erbium-doped fiber amplifiers to provide 30W average laser power -- A low noise, high gain HgCdTe detector and cryocooler The algorithms are mission ready and are available for licensure and implementation in a wide range of continuous wave lidar applications.
Low Frequency Portable Acoustic Measurement System
Langley has developed various technologies to enable the portable detection system, including: - 3-inch electret condenser microphone - unprecedented sensitivity of -45 dB/Hz - compact nonporous windscreen - suitable for replacing spatially demanding soaker hoses in current use - infrasonic calibrator for field use - piston phone with a test signal of 110 dB at 14Hz. - laboratory calibration apparatus - to very low frequencies - vacuum isolation vessel - sufficiently anechoic to permit measurement of background noise in microphones at frequencies down to a few Hz - mobile source for reference - a Helmholtz resonator that provides pure tone at 19 Hz The NASA system uses a three-element array in the field to locate sources of infrasound and their direction. This information has been correlated with PIREPs available in real time via the Internet, with 10 examples of good correlation.
Infrasound Sensor Technology
Large aircraft can generate air vortices in their wake, turbulence that can prove hazardous to aircraft that follow too closely. Because wake vortices are invisible, all takeoffs at busy airports are spaced several minutes apart. This separation gives the vortices time to dissipate, even though they only occur 10% of the time, with resulting loss of operational efficiency. Similarly, clear air turbulence is invisible and can also be hazardous to aircraft. By detecting such disturbances through their infrasound emissions, precautions can be taken to avoid them. Other phenomena can be detected through infrasound, including tornadoes, helicopters on the other side of mountains, underground nuclear explosions and digging tunnels. Through the unique properties of infrasound, many of these can be detected from hundreds of miles away. NASA's infrasound sensor is a highly refined microphone that is capable of detecting acoustic waves from 20 Hz down to dc, the infrasound range. The design is robust and compact, eliminating the bulk and weight found in other technologies. Where most alternative methods are restricted to certain weather conditions and locations, the NASA sensor filters noise from wind and other sources, allowing its use under any weather or geographic conditions.