14.6-GHz LiNbO/sub 3/ microdisk photonic self-homodyne RF receiver

Nonlinear optical modulation combined with simultaneous photonic and RF resonance in an LiNbO/sub 3/ microdisk modulator is used to create a self-homodyne photonic RF receiver. Carrier and sidebands are mixed in the optical domain, and the modulated optical signal is detected using a photodetector. The photodetector has a bandwidth matched to the baseband signal. It filters out the high-frequency components and generates the baseband photocurrent. Receiver operation is demonstrated by demodulating up to 100-Mb/s digital data from a 14.6-GHz carrier frequency without any high-speed electronic components. A bit error rate of 10/sup -9/ is measured for 10-Mb/s downconverted digital data at -15-dBm received RF power. Preliminary results of employing this photonic RF receiver in a short-distance Ku-band wireless link demonstrate the potential of using high-quality optical microresonators in RF receiver applications

Technology Assessment and Experimentation Plan

An assessment is given of the critical and enhancing technologies necessary to build the basic personal terminal (BPT), the supplier, and the Network Management Center (NMC). The experimentation plan for testing the Personal Access Satellite System (PASS) utilizing ACTS is detailed. The experiment plan gives a list of candidate experiments and describes the proposed experimental set-up. ACTS will be used in the Microwave Switch Matrix (MSM) mode. The Microwave Switch Matrix - Link Evaluation Terminal (MSM-LET) at the NASA Lewis Research Center will serve as the microwave front-end for the PASS supplier and the NMC. Link budgets are given for both the forward and return links between the supplier and the basic personal terminal. The equipment required for the experiments is identified

Adaptive multibeam phased array design for a Spacelab experiment

The parametric tradeoff analyses and design for an Adaptive Multibeam Phased Array (AMPA) for a Spacelab experiment are described. This AMPA Experiment System was designed with particular emphasis to maximize channel capacity and minimize implementation and cost impacts for future austere maritime and aeronautical users, operating with a low gain hemispherical coverage antenna element, low effective radiated power, and low antenna gain-to-system noise temperature ratio

Microwave vs optical crosslink study

The intersatellite links (ISL's) at geostationary orbit is currently a missing link in commercial satellite services. Prior studies have found that potential application of ISL's to domestic, regional, and global satellites will provide more cost-effective services than the non-ISL's systems (i.e., multiple-hop systems). In addition, ISL's can improve and expand the existing satellite services in several aspects. For example, ISL's can conserve the scarce spectrum allocated for fixed satellite services (FSS) by avoiding multiple hopping of the relay stations. ISL's can also conserve prime orbit slot by effectively expanding the geostationary arc. As a result of the coverage extension by using ISL's more users will have direct access to the satellite network, thus providing reduced signal propagation delay and improved signal quality. Given the potential benefits of ISL's system, it is of interest to determine the appropriate implementations for some potential ISL architectures. Summary of the selected ISL network architecture as supplied by NASA are listed. The projected high data rate requirements (greater than 400 Mbps) suggest that high frequency RF or optical implementations are natural approaches. Both RF and optical systems have their own merits and weaknesses which make the choice between them dependent on the specific application. Due to its relatively mature technology base, the implementation risk associated with RF (at least 32 GHz) is lower than that of the optical ISL's. However, the relatively large antenna size required by RF ISL's payload may cause real-estate problems on the host spacecraft. In addition, because of the frequency sharing (for duplex multiple channels communications) within the limited bandwidth allocated, RF ISL's are more susceptible to inter-system and inter-channel interferences. On the other hand, optical ISL's can offer interference-free transmission and compact sized payload. However, the extremely narrow beam widths (on the order of 10 micro-rad) associated with optical ISL's impose very stringent pointing, acquisition, and tracking requirements on the system. Even if the RF and optical systems are considered separately, questions still remain as to selection of RF frequency, direct versus coherent optical detection, etc. in implementing an ISL for a particular network architecture. These and other issues are studied

Study to investigate and evaluate means of optimizing the Ku-band communication function for the space shuttle

The forward link of the overall Ku-band communication system consists of the ground- TDRS-orbiter communication path. Because the last segment of the link is directed towards a relatively low orbiting shuttle, a PN code is used to reduce the spectral density. A method is presented for incorporating code acquisition and tracking functions into the orbiter's Ku-band receiver. Optimization of a three channel multiplexing technique is described. The importance of Costas loop parameters to provide false lock immunity for the receiver, and the advantage of using a sinusoidal subcarrier waveform, rather than square wave, are discussed

Airborne UHF Radar for Fine Resolution Mapping of Near Surface Accumulation Layers in Greenland and West Antarctica

The usefulness of accurate, fine resolution accumulation layer measurements over central Greenland and West Antarctica is significant for the improvement of ice sheet models. These models are critical to both global climate models as well as understanding sea level rise. Previously developed accumulation layer radars were used as templates for the current single channel system. Improvements were incorporated including increased output power, increased receiver sensitivity, single antenna operation, and reduced susceptibility to external noise sources. Steps were also taken to reuse previously purchased components to reduce development costs. Externally developed Vivaldi and elliptical dipole antennas were utilized. Collected data shows the system is capable of measuring layering to a depth of nearly 300 m in most dry snow regions of Greenland and West Antarctica with a resolution of ~0.5 m. Future revisions will focus on reducing size and weight, as well as incorporate multiple receive channels to allow for clutter rejection algorithms to be applied; this will allow for viable data collection in percolation and wet snow zone of major ice sheets

A Two-stage approach to harmonic rejection mixing using blind interference cancelling

Current analog harmonic rejection mixers typically provide 30–40 dB of harmonic rejection, which is often not sufficient. We present a mixed analog-digital approach to harmonic rejection mixing that uses a digital interference canceler to reject the strongest interferer. Simulations indicate that, given a practical RF scenario, the digital canceler is able to improve the signal-to-interference ratio by 30–45 dB

Engineering evaluations and studies. Volume 3: Exhibit C

High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed

Experiment definition phase shuttle laboratory, LDRL-10.6 experiment. Shuttle sortie to ground receiver terminal

System development and technology are described for a carbon dioxide laser data transmitter capable of transmitting 400 Mbps over a shuttle to ground station link

Experiment definition phase shuttle laboratory (LDRL-10.6 experiment): Shuttle sortie to elliptical orbit satellite

The following topics were reviewed: (1) design options for shuttle terminal, (2) elliptical orbit satellite design options, (3) shuttle terminal details, (4) technology status and development requirements, (5) transmitter technology, and (6) carbon dioxide laser life studies