Engineering topics

Miranda, Felix

Publications and source records attributed to Miranda, Felix.

25 records · Page 2

NASA NTRS2004

Optimizing Satellite Communications With Adaptive and Phased Array Antennas

A new adaptive antenna array architecture for low-earth-orbiting satellite ground stations is being investigated. These ground stations are intended to have no moving parts and could potentially be operated in populated areas, where terrestrial interference is likely. The architecture includes multiple, moderately directive phased arrays. The phased arrays, each steered in the approximate direction of the satellite, are adaptively combined to enhance the Signal-to-Noise and Interference-Ratio (SNIR) of the desired satellite. The size of each phased array is to be traded-off with the number of phased arrays, to optimize cost, while meeting a bit-error-rate threshold. Also, two phased array architectures are being prototyped: a spacefed lens array and a reflect-array. If two co-channel satellites are in the field of view of the phased arrays, then multi-user detection techniques may enable simultaneous demodulation of the satellite signals, also known as Space Division Multiple Access (SDMA). We report on Phase I of the project, in which fixed directional elements are adaptively combined in a prototype to demodulate the S-band downlink of the EO-1 satellite, which is part of the New Millennium Program at NASA.

Ingram, Mary Ann↗

NASA NTRS2004

On the Fringe Field of Wide Angle LC Optical Phased Array

For free space laser communication, light weighted large deployable optics is a critical component for the transmitter. However, such an optical element will introduce large aberrations due to the fact that the surface figure of the large optics is susceptable to deformation in the space environment. We propose to use a high-resolution liquid crystal spatial light modulator to correct for wavefront aberrations introduced by the primary optical element, and to achieve very fine beam steering and shaping at the same time. A 2-D optical phased array (OPA) antenna based on a Liquid Crystal on Silicon (LCOS) spatial light modulator is described. This device offers a combination of low cost, high resolution, high accuracy, high diffraction efficiency at video speed. To quantitatively understand the influence factor of the different design parameters, a computer simulation of the device is given by the 2-D director simulation and the Finite Difference Time domain (FDTD) simulation. For the 1-D OPA, we define the maximum steering angle to have a grating period of 8 pixel/reset scheme; as for larger steering angles than this criterion, the diffraction efficiency drops dramatically. In this case, the diffraction efficiency of 0.86 and the Strehl ratio of 0.9 are obtained in the simulation. The performance of the device in achieving high resolution wavefront correction and beam steering is also characterized experimentally.

Wang, Xighua↗

NASA NTRS2004

Linking Satellites Via Earth "Hot Spots" and the Internet to Form Ad Hoc Constellations

As more assets are placed in orbit, opportunities emerge to combine various sets of satellites in temporary constellations to perform collaborative image collections. Often, new operations concepts for a satellite or set of satellites emerge after launch. To the degree with which new space assets can be inexpensively and rapidly integrated into temporary or "ad hoc" constellations, will determine whether these new ideas will be implemented or not. On the Earth Observing 1 (EO-1) satellite, a New Millennium Program mission, a number of experiments were conducted and are being conducted to demonstrate various aspects of an architecture that, when taken as a whole, will enable progressive mission autonomy. In particular, the target architecture will use adaptive ground antenna arrays to form, as close as possible, the equivalent of wireless access points for low earth orbiting satellites. Coupled with various ground and flight software and the Internet. the architecture enables progressive mission autonomy. Thus, new collaborative sensing techniques can be implemented post-launch. This paper will outline the overall operations concept and highlight details of both the research effort being conducted in <he area of adaptive antenna arrays and some of the related successful autonomy software that has been implemented using EO-1 and other operational satellites. Keywords: collaborative remote sensing smart antennas, adaptive antenna arrays, sensor webs. ad hoc constellations, mission autonomy and

Mandl, Dan↗

NASA NTRS2003

Packaging Considerations for Integrated RF Microphotonic Receiver at Ka-Band

The NASA Computing, Information and Communications Technology (CICT) Program is supporting the development of an RF microphotonic Ka-band receiver. The receiver consists of a lithium niobate micro-disk that enables the incoming RF signal (up to Ka-band) to be coupled to the optical signal (approx. 200 THz). The modulated optical signal is detected by the high-speed photonic signal processing electronics. When compared with an all-electronic approach, the microphotonic receiver technology offers 1 Ox smaller volume, smaller weight, and smaller power consumption, greater sensitivity, and optical isolation for applications in extreme environments. It could potentially be implemented to support planetary surface-to-surface and surface-to-relay communications, as well as high-data-rate inter-satellite links. We are currently studying a number of fabrication and integration issues that could result as this technology is advanced for potential insertion into a NASA mission. The results of our preliminary effort to integrate the RF microphotonic receiver components (e.g., the lithium niobate micro-disk, the optical elements, and the Ka-band patch antenna) on an etched silicon wafer will be presented, In addition, the concomitant integration and packaging issues, and the potential NASA applications will be discussed.

Nguyen, Hung↗

NASA NTRS2003

Diffraction Efficiency of Thin Film Holographic Beam Steering Devices

Dynamic holography has been demonstrated as a method for correcting aberrations in space deployable optics, and can also be used to achieve high-resolution beam steering in the same environment. In this paper, we consider some of the factors affecting the efficiency of these devices. Specifically, the effect on the efficiency of a highly collimated beam from the number of discrete phase steps per period is considered for a blazed thin film beam steering grating. The effect of the number of discrete phase steps per period on steering resolution is also considered. We also present some result of Finite-Difference Time-Domain (FDTD) calculations of light propagating through liquid crystal "blazed" gratings. Liquid crystal gratings are shown to spatially modulate both the phase and amplitude of the propagating light.

Titus, Charles M.↗

NASA NTRS2002

Continuous Beam Steering From A Segmented Liquid Crystal Optical Phased Array

Optical communications to and from deep space probes will require beams possessing divergence on the order of a microradian, and must be steered with sub-microradian precision. Segmented liquid crystal spatial phase modulators, a type of optical phased array, are considered for this ultra-high resolution beam steering. It is shown here that in an ideal device of this type, there are ultimately no restrictions on the angular resolution. Computer simulations are used to obtain that result, and to analyze the influence of beam truncation and substrate flatness on the performance of this type of device.

Pouch, John↗

NASA NTRS2002

Continuous Beam Steering From a Segmented Liquid Crystal Optical Phased Array

Titus, Charles M.↗