Abstract: A system and method for tracking a user. The system is adapted for use in a wireless communication system and creates a plurality of beams within a coverage area. A first beam is directed at a user in a first microcell and a number of additional beams illuminate microcells immediately adjacent the first microcell. The system is equipped with a mechanism for detecting movement of the user from the first microcell to one of the immediately adjacent microcells. On the detection of movement of the user, the system redirects the first beam from the first microcell to a second microcell, the second microcell being one of the adjacent microcells. In the illustrative embodiment, the system is implemented in a stratospheric platform based communication system including a hub adapted to communicate with a stratospheric platform. A transceiver and a phased array antenna are disposed on the platform to communicate with the hub and with the user. A second antenna is provided on the platform to communicate with the hub.

Abstract: A novel mobile satellite communications technique for hand-held terminals includes a satellite system having a plurality of individual satellites all in communication with a ground telecommunications hub. A signal processed by the ground telecommunications hub is radiated through multiple paths to a plurality of the individual satellites in the satellite constellation simultaneously. The radiated signal is then re-radiated by the plurality of individual satellites to a mobile satellite terminal that receives the re-radiated signal from the plurality of individual satellites simultaneously such that the same frequency spectrum may be re-used by another mobile user.

Abstract: A satellite-based communications system operating at high data rates includes a plurality of communications satellites each having an uplink and a downlink antenna for receiving and transmitting a plurality of spot beams which may be fixed or scanned. The fixed beams may be directed to areas of high satellite use. The scanned beams may be rapidly scanned between areas of use insufficient to support a dedicated beam. The scanned beam allows potentially nearly ubiquitous coverage by using high frequency beams. To rapidly scan, beam forming networks have a plurality of phase coefficients that may be changed so that the angle of the beam may change. A controller coupled to the beam forming network may be used to change the phase coefficients in response to beam inputs such as the desired beam and configurations of the other beams on the satellite.

Abstract: A method for uplink power control and time synchronization in a satellite communications system that is achieved using satellite-based measurements of the uplink signal power and signal arrival time. Uplink signals transmitted from an originating terminal are received by a communications satellite which measures the received signal power and arrival time. The satellite transmits a downlink signal to the originating terminal containing information of the measured uplink signal power and arrival time. The originating terminal receives the downlink signal and transmits subsequent uplink signals with an uplink signal power and transmission timing based on the information transmitted by the satellite.

Abstract: Methods for the design and fabrication of micro-electro-mechanical switches are disclosed. Two different switch designs with three different switch fabrication techniques are presented for a total of six switch structures. Each switch has a multiple-layer armature with a suspended biasing electrode and a conducting transmission line affixed to the structural layer of the armature. A conducting dimple is connected to the conducting line to provide a reliable region of contact for the switch. The switch is fabricated using silicon nitride as the armature structural layer and silicon dioxide as the sacrificial layer supporting the armature during fabrication. Hydrofluoric acid is used to remove the silicon dioxide layer with post-processing in a critical point dryer to increase yield.

Abstract: A coordinatable system of geosynchronous (24-hour), inclined, and slightly elliptical satellite orbits enables spectrum re-use by forming “highways” of moving “slots” in the latitudes above and below the geostationary (GSO) belt worldwide. Each of a plurality of repeating ground tracks is shared by multiple satellite orbits (and thus slots). These are phased to achieve minimum specified angular separation from other slots using the same frequencies. Ground track (and thus orbital) parameters are chosen to realize specified shapes and are located at specified longitudes of symmetry to maximize the total number of slots. Consideration is given to specified constraints on service area coverage, elevation angle, and time coverage.

Abstract: A system and method for free space optical communication include at least one reconfigurable terminal (30) using dual-wavelength operation for isolation between transmitted and received signals in combination with polarization switching to separate and steer the transmitted and received signals to and from corresponding transmitters (40) and receivers (48). The polarization based switching provides wavelength independent beam steering to facilitate interchanging of wavelengths for transmitted and received signals. A controllable or passive polarization changer (56) such as a wave plate or polarization rotator allows the communication terminal (30) to be reconfigured without also requiring the repositioning and associated precision alignment of beam steering optics (54, 62, 66).

Abstract: A system of inclined geosynchronous satellite orbits has a service area defined on a surface of the earth. The service area has elevation angles greater than a predetermined minimum elevation angle elevation angle from the horizon. A satellite has an orbit with respect to the earth having a sky track when viewed from within said service area. An operating arc is defined by a subset of points on the sky track within the service area. The satellites operate consecutively on the operating arc.

Abstract: A satellite-based communications system operating at high data rates includes a plurality of communications satellites each having an uplink and a downlink antenna for receiving and transmitting a plurality of spot beams corresponding to a plurality of coverage areas at a plurality of frequencies. The system further includes a plurality of dedicated communications links between a source location in one of the plurality of coverage areas and a destination location in another one of the plurality of coverage areas wherein the plurality of dedicated communications links are each assigned an exclusive time interval for transmitting and receiving communications signals to and from each of the plurality of satellites. The plurality of satellites each have an uplink and downlink antenna beam switch coupled to the uplink and downlink antennas for selecting a reconfigurable subset of the plurality of spot beams based on the time interval.

Abstract: A semiconductor passivation technique uses a plasma enhanced chemical vapor deposition (PECVD) process to produce a silicon-rich nitride film as a passivation layer on a Group III-V semiconductor device. The silicon-rich film has a nitrogen to silicon ratio of about 0.7, has a relatively high index of refraction of, for example, approximately 2.4, is compressively stressed, and is very low in hydrogen and oxygen content.

Abstract: A method and system for determining a position of an orbiting transceiver in a communications network includes at least a first and second transceiver at a first and second known location, respectively, on Earth. The first and second transceivers are adapted to transmit and receive communications signals to and from the orbiting transceiver. A processor coupled to one of the first and second transceivers determines a first and second range measurement between each of the first and second transceivers and the orbiting transceiver, respectively, as well as corresponding first and second range rates representative of a time rate of change of the first and second range measurements.

Abstract: A method and system for transmitting, and a signal comprising multiple frequency bands from a single slot antenna are disclosed. The system comprises a slot antenna and a micro-electro-mechanical (MEM) switch, coupled to the slot antenna. The MEM switch is opened and closed, thereby changing the resonant frequency of the slot antenna. The slot antenna transmits a first frequency when the MEM switch is open and a second frequency when the MEM switch is closed. The method for transmitting a first frequency and a second frequency from a slot antenna comprises the steps of transmitting the first frequency from the slot antenna, closing a micro-electro-mechanical (MEM) switch coupled across the slot antenna, therein changing the resonant frequency of the slot antenna, and transmitting the second frequency from the slot antenna after the MEM switch is closed.

Abstract: A novel organic light-emitting pixel structure provides improved contrast pixels suitable for use in high-contrast passive- and active-matrix displays. A dark, low-reflectance film is placed on a reflective or transparent substrate, which acts to absorb and/or trap ambient light impinging on the pixel and improving its contrast between on and off states. Optical scattering is reduced by fabricating a vertical wall around each pixel which effectively blocks out light emitted from adjacent pixels, and prevents the scattering of the pixel's own emitted light. Light is emitted through a transparent upper electrode, which allows the substrate to be non-transparent. An active-matrix display is thus built on a single silicon substrate, with the crystalline silicon transistors needed to drive the active-matrix fabricated alongside their respective pixels, and with the walls surrounding the pixels formed from the drive circuitry itself.

Abstract: An improved mobile digital radio system is disclosed. A plurality of satellites and terrestrial repeaters transmit substantially identical information that is contained in an original time division multiplexed data stream. Each satellite transmits on a separate frequency band, and all terrestrial repeaters transmit on one shared frequency band. A mobile receiver simultaneously processes the frequency bands. The receiver selectively parses and concatenates a plurality of time division multiplexed data streams to substantially recompose the original data stream. The output may be a high fidelity audio signal, data for display, or a combination of audio and displayed data.

Abstract: An integrated circuit is protected from reverse engineering by connecting doped circuit elements of like conductivity with a doped implant in the substrate, rather than with a metallized interconnect. The doped circuit elements and their corresponding implant interconnections can be formed in a common fabrication step with common implant masks, such that they have an integral structure with similar dopant concentrations. The metallization above the substrate surface can be designed to provide further masking of the interconnects, and microbridges can be added to span strips of transistor gate material in the interconnect path.

Abstract: A system and method for restricting access to a satellite repeater transponder (100) utilizes a pseudo-random noise generator (102) to automatically modulate a local oscillator (18) about a nominal frequency during frequency translation within the satellite transponder. The carrier signals of authorized user terminals (106) will be modulated with a matching or inverse noise waveform produced by a pseudo-random noise generator (114), so that the noise signal modulated onto the carrier signal will only be cancelled out in authorized transmissions. Thus, an unauthorized user terminal will be unable to recover the baseband signal due to insufficient carrier to noise ratio in the expanded bandwidth created by the pseudo-random frequency modulation in the satellite repeater.

Abstract: A welded wire termination for use in thermally and mechanically stressful environments is provided by forming a wire termination tab on a conductive pad to define a tubule for receiving a wire, either stranded or solid. The tubule is tweezer welded to form a welded termination joint between the wire and the conductive tab. The tubule easily captures all of the stranded wires and increases the surface area of the weld to a solid lead. A tweezer weld exerts pressure laterally on the tubule, and thus does not exert a force on the underlying substrate that could damage the substrate. This approach creates only a single electro-mechanical connection from the wire to the conductive pad, which is inherently more reliable than multiple connections such as those that are crimped first then welded.

Abstract: A method of routing data packets in a communication network having one or more intelligent routing nodes. Each routing node maintains routing and address resolution information for all nodes within the routing node's domain. Upon detecting a data transmission from a source node to a destination node using a sub-optimal path. The routing node communicates updated routing information to the source node. The source node stores this information such that the subsequent data packets containing the same network address can be transmitted from the source node to the destination node in a single hop.

Abstract: An electronically scanned antenna that is manufactured using semiconductor material and device fabrication technology. The antenna has a semiconductor substrate having a plurality of stubs projecting from one surface. The semiconductor substrate may be silicon, gallium arsenide, or indium phosphide, for example. A first conductive layer formed on the surfaces of the semiconductor substrate and along sides of the stubs so that the stubs are open at their terminus. The conductive layers form a parallel plate waveguide region. A diode array having a plurality of diode elements is formed in the semiconductor substrate that are disposed transversely across the semiconductor substrate and longitudinally down the semiconductor substrate between selected ones of the plurality of stubs. The diode array may comprise an array of Schottky or varactor diodes, for example.

Abstract: A power supply circuit for an ion engine suitable for a spacecraft has a voltage bus having input line and a return line. The power supply circuit includes a pulse width modulation circuit. A plurality of bridge inverter circuits is coupled to the bus and the pulse width modulation circuit. The pulse width modulation circuit generates operating signals having a variable duty cycle. Each bridge inverter has a primary winding and a secondary winding. Each secondary winding is coupled to a rectifier bridge. Each secondary winding is coupled in series with another of the plurality of rectifier bridges.