Abstract: A satellite communications system. The inventive system (10) includes an arrangement (11) disposed on a first satellite for transmitting a plurality of unidirectional beams of electromagnetic radiation (32, 34, 36 and 38). Each beam is transmitted by an optical fiber (22, 24, 26 and 28) and has a unique modulation and a known coverage area. At least one of the beams (34) is received by a remote satellite receiver (30) which retransmits a signal with the modulation of the received beam. The retransmitted signal is received at the first satellite and the modulation thereon is extracted to identify which beam was received by the remote satellite. This information is used to change the coverage of the transmitted beams until the remote satellite detects all of the transmitted beams. At this point, data communication in the normal course may be effected.

Abstract: A transmission apparatus for an orbiting satellite which can establish stabilized frame synchronization even if the distance between the round-trip satellite and a communications terminal varies and which can minimize the displacement between a frame signal received on the ground and another frame signal generated in a communications terminal. The transmission apparatus comprises M (M is an integral number equal to or greater than 2) composers for forming frame signals, M transmitters for outputting M spot beams having different radiation directions, and M delay circuits interposed between the composers and the transmitters. The delay times of the delay circuits are set so that they are long where the radiation angles of the corresponding spot beams are small, but they are shorter where the radiation angles are larger.

Abstract: A satellite system facilitates communications between earth stations and both geostationary satellites and non-geostationary satellites in an orbit at a lower altitude than that of said the geostationary satellites by preventing the non-geostationary satellite from transmitting signals that might possibly interfere with signals transmitted by the geostationary satellites. The non-geostationary satellite includes position acquisition subsystem for determining the position, and in particular the latitude, of the non-geostationary satellite relative to the surface of the earth. A data processor determines a forbidden band of locations on the surface of the earth all possible geostationary satellites and the non-geostationary satellite, at its determined position, are separated by less than a specified minimum discrimination angle.

Abstract: An array antenna mounted on a spacecraft in its stowed state. After the spacecraft is launched in a predetermined position or on a predetermined orbit, the array antenna is extended to a flat plate form or a curved surface form. The array antenna has a structure that a plurality of subarrays are connected by plate springs or the like. The array antenna is extended in a kite form by using cables for connecting a spacecraft body and the subarrays or is extended by using an extension pole mounted on the spacecraft body. Each subarray includes a variable phase shifter to switch a shape and a direction of a directivity beam. A feeder line, a power supply line, a control signal line and the like connect the spacecraft body and each subarray.

Abstract: A communications satellite payload provides for efficient communications between user devices, such as hand held cellular telephones, and terrestrial gateways that may be connected to world-wide public telephone and telegraph (PTTs) networks. The satellite payload simultaneously supports a plurality of independent antenna beams, for example 12 or 16 beams, on both the uplink and downlink for user devices employing full duplex communications. The satellite payload furthermore supports an identical number of full duplex channels between a terrestrial gateway and the satellite. The communications satellite payload is carried by one satellite of a plurality of such satellites in a low earth orbit (LEO) constellation to provide worldwide communications. Downlink beam forming occurs prior to final amplification of transmitted signals, thereby reducing losses within the beam forming equipment.

Abstract: A direct television broadcasting satellite facility (S1, S2, S3) having at least two coverage areas (T1, T2). At the beginning of the life of the facility, with present Standards, only two satellites (S1, S2) each having two beams (F1 & F2 and F'1 & F'2) are used, each satellite having 12 channel and redundancy amplifiers for five channels. When high-definition television is subsequently introduced progressively, the amplifiers will be coupled together in parallel and in pairs, and at least one additional satellite (S3), identical to the two initial satellites, will be launched when required.

Abstract: Earth-fixed cell beam management methods which may be employed to allocate beams generated by a constellation of low Earth orbit satellites (12) flying in orbits below geosynchronous altitudes are disclosed. These beams (19) are electronically steered so that they illuminate "Earth-fixed cells" (26) as opposed to "satellite-fixed cells." In a system that employs satellite-fixed cells, the "footprint" of the beams propagated by a spacecraft defines the zone on the ground called a "cell" which is illuminated by the spacecraft. This satellite-fixed cell moves constantly as the spacecraft moves around the globe. In sharp contrast, an "Earth-fixed cell" (26) is a stationary region mapped onto the surface of the Earth (E) that has permanent fixed boundaries, just like a city or a state.

Abstract: An energy transmission arrangement emits a microwave energy signal to a target location on the basis of a pilot signal received from the target location. The arrangement includes a plurality of pilot antennas for receiving the pilot signal and a plurality of antenna elements for transmission of the energy signal. The pilot signal as received at a first pilot antenna is multiplied at a phase conjugation circuit and divided into a plurality of transmission signals corresponding to the plurality of antenna elements. A target direction is calculated based on a phase difference of the pilot signal as received at each of the other pilot antennas and a phase adjustment circuit is provided for adjusting the phases of each of the transmission signals on the basis of the calculated target direction.

Abstract: A phased array for transmitting to a microwave powered aircraft is focussed and steered by feedback from the aircraft. Each antenna of the array is phase modulated in turn, and the resulting amplitude modulation of the field at the aircraft is used to calculate a correction to the antenna phase, which is telemetered back to the array system and applied to the antenna phase shifter.

Abstract: A earth station calling another station sends a link setting-up a request to a control station. The control station memorizes in a transformed reference system the contour of a global geographical coverage including all the earth stations together with the earth positions of the latter. Subsequent to the request, the control station simulates the optimum evolution of the radioelectric coverages of the satellite so as to include, both on emitting and receiving, the calling and called stations in respective coverages with guaranteed minimum antenna gains. The total power of the satellite and the positions of the stations are notably considered in this simulation. If the result of simulation is positive, an emission authorization is sent by the control station to the calling station, and satellite antennae are reconfigured by phase shift and power control values emitted by the control station.

Abstract: A multichannel communication system carries signals having a different frequency range in each channel. In order to achieve a particular output power level from each channel, an amplifier is associated with each channel to boost the signal level. For reliability, a switching arrangement switches amplifiers among the channels in accordance with a priority, or substitutes a redundant amplifier for a degraded or failed unit in a channel. The amplifier is subject to distortion at the desired output level, and is cascaded with a distortion equalizer or linearizer for reducing the total distortion. In accordance with the invention, each distortion equalizer is fixedly connected in one channel, and is optimized for the relatively narrow frequency range of that channel, rather than being switched together with the amplifier and being optimized over the total or cumulative bandwidth of all the channels.

Abstract: Orbiting satellites project footprints on the earth. Each footprint is divided into cells. Footprints of nearby satellites overlap one another, and the overlap increases as satellites approach a pole from the equator. The positions of all cells generated by all satellites are simulated at numerous points throughout an orbit. Cells are marked as being active or inactive to compensate for the overlap at each simulated point. Channel sets are assigned to cells within a reference footprint, and this assignment is propagated throughout all footprints in the referenced footprint's orbit. The channel set sequences are propagated to other orbits after taking into account inactive cells located near boundaries between the orbits. Each satellite stores channel set assignments for its cells at the various points throughout its orbit. All satellites switch their communication parameters at the same instant in response to the channel set assignments.

Abstract: Spacecraft payload architecture which includes an array (10) of radiating elements preceded by an amplification stage (17) and a focusing optical system (11), characterized in that the architecture is adapted to a telecommunication mission by taking into account the overall requirements of the system, namely the radiation performance required for the mission, efficient rating of the amplification stage and attractive overall balances.

Abstract: There is provided a method and means for controlling the amount of overlap and gaps in coverage of antenna pattern cells of a moving satellite communication system, by determining the relative spatial location of overlapping or gaping cells of converging or diverging satellites as a function of time; determining a point where antenna coverage of one or more cells from a first moving satellite will overlap or gap one or more cells from a second satellite; and turning off or on one or more of the overlapping or gaping cells so as to eliminate interference therebetween without leaving substantial coverage gaps between adjacent antenna patterns.

Abstract: An antenna system provides a substantially spherical radiation pattern about a structure located above ground level, by locating the individual radiation pattern of each of a plurality of individual antennae, each positioned to have a radiation pattern covering only a portion of the desired sphere, and then applying all antenna signals, during either transmission or reception time intervals, through space-diversity and/or time-diversity apparatus, to cause the patterns of all of the antennae to combine into the desired substantially-spherical pattern. The antennae may have substantially hemispherical patterns, with each antenna of a pair thereof being directed in a direction generally opposite to the other antenna of that pair.

Abstract: An antenna pointing equipment of the present invention includes an error estimating section and a pointing angle correcting section. The error estimating section records the difference between a pointing mechanism angle detected by an angle detector and a reference angle estimated by a satellite position calculator, a pointing angle calculator and an angle estimating section in the tracking control mode and, for example, averages recorded differences to obtain a quantitative error of the estimated reference angle in the acquisition control mode. The pointing angle correcting section corrects the estimated reference angle for its error. The antenna pointing equipment also includes an area-impossible-to-track controller. The controller obtains an area which cannot be tracked by the antenna on the basis of orbital elements of a space navigation satellite and a target and forcible switches from the tracking control mode to the acquisition control mode when the target enters that area.

Abstract: A system for controlling a radiation pattern of an antenna array carried on a spacecraft, to provide and maintain a desired pattern over a preselected area remote from the spacecraft, without physical movement of the array with respect to the spacecraft even if the spacecraft is physically reoriented with respect to the remote earth area, uses sensors, carried on the spacecraft, for determining spacecraft reorientation relative to the preselected earth area, so as to provide at least one error signal responsive to any spacecraft reorientation; a phased-array antenna system, inertialessly reconfigures the array radiation pattern responsive to a set of directional pointing data; a loop provides the directional pointing data in a manner serving to minimize the error signals from the sensing means and thus cause the antenna radiation pattern to remain substantially fixed on the remote earth area even if the spacecraft is reoriented.

Abstract: In mobile communications, it is required that the beam direction is maintained to track the desired direction as the mobile is moving. For such a purpose, the mobile includes an angular rate sensor mounted therein which detects the state of turn in the mobile and to control the beam direction of the antenna in accordance with the state of turn as well as the strength of radiowave received by a receiver in the mobile. Antenna elements are in the form of microstrip antenna and are arranged in plane on the same dielectric substrate. Feeding and drive circuit layers for controlling the transmission and reception at the antenna elements are stacked into a single layered unit. This enables the antenna system to be formed into a low-profile structure. The dielectric substrate of the microstrip antenna element is formed by stacking a plurality of dielectric substrate different in dielectric constant from one another.

Abstract: A method for steering the gain of a multiple antenna Global Positioning System (GPS) receiver toward a plurality of a GPS satellites simultaneously is provided. The GPS signals of a known wavelength are processed digitally for a particular instant in time. A range difference or propagation delay between each antenna for GPS signals received from each satellite is first resolved. The range difference consists of a fractional wavelength difference and an integer wavelength difference. The fractional wavelength difference is determined by each antenna's tracking loop. The integer wavelength difference is based upon the known wavelength and separation between each antenna with respect to each satellite position. The range difference is then used to digitally delay the GPS signals at each antenna with respect to a reference antenna. The signal at the reference antenna is then summed with the digitally delayed signals to generate a composite antenna gain.

Abstract: A multiple access communications system comprises a node spacecraft GEO and several user spacecraft LEO.sub.1 to LEO.sub.n. Each user spacecraft LEO.sub.1 to LEO.sub.n includes a transmit/receive terminal head 18.sub.1 to 18.sub.n, and the node spacecraft GEO includes n transmit/terminals 22 to 22.sub.n and a single beacon unit 24. The beacon beam may be operated to initiate acquisition phases which allow two-way communication to be established between the transmit/receive terminals 22.sub.1 to 22.sub.n on the node spacecraft and the transmit/receive terminals 18.sub.1 to 18.sub.n on the corresponding user terminals. The acquisition phases include a period during which the beacon scans an uncertainty cone associated with the node spacecraft. This scanning period is reduced for second and subseqeunt acquisitions by using the first and subsequently acquired communication links to provide a more accurate estimate of the angular attitude of the node spacecraft, thus reducing the extent of the uncertainty cone.

Abstract: A precision satellite tracking system incorporating a novel smoothing processor. The satellite tracking system estimates an angle between an antenna boresight and a desired line of sight to a moving satellite. The smoothing processor receives a sequence of pointing error measurements and using a Taylor series mathematical model of the satellite motion, the processor utilizes the sequence of measurements to generate the coefficients of the Taylor series model. The processor then executes a sequential, discounted least mean square algorithm to estimate the satellite's angular position, velocity, and acceleration as a function of time. Based on these estimates, the processor determines incremental adjustments to azimuth and elevation pointing angles of the antenna to maintain the center of an antenna beam on the moving satellite. The information is used in a program track mode to continually update the pointing of the antenna beam during the measurement process.

Abstract: A locating system employs a multiple satellite configuration employing rotating scanning patterns for generating peak signal data which can be used to calculate the position of a signal source within a scanned region. One preferred embodiment utilizes two spaced satellites in high earth geosynchronous orbit and simultaneous narrow antenna beam rotation patterns to scan a substantial portion of the earth's surface. The invention is particularly advantageous for locating stolen vehicles and for tracking inventory. The system may also be used for determining altitude of a signal source that may, for example, be located on an aircraft in flight.An alternative embodiment employs a peak-detecting ground-based receiver and satellite or other scanning devices which generate and transmit a signal to the receiver indicating the precise current position of the antenna of each satellite.

Abstract: A satellite communication system employing a satellite in a geostationary orbit about the earth for communicating with ground stations disposed along a region of the earth positioned along an arc of a great circle of the earth. The satellite carries a frequency-scanning antenna array oriented for scanning a beam of electromagnetic radiation in one plane aligned with the arc of the great circle. Each position of the beam is formed with a different frequency of the radiation. The operating frequency of each ground station is selected to match the frequency of a beam directed from the satellite to the ground station. An antenna assembly formed of two confocal parabolic reflectors provides for a multiplication of the effective aperture of an array of radiating elements of the antenna, and also for a demagnification of a scan angle of radiation emanating from the array of radiating elements.

Abstract: A modular direct radiating antenna system for producing highly contoured beam patterns is disclosed. The system comprises a plurality of array modules, each having a number of radiation elements. An intramodule feed network is provided to communicate RF energy between a module port and the radiation elements in an equal-power, equal-phase relationship. A second feed network, an intermodule feed network, is provided to communicate RF energy between an antenna system port and the respective module ports. The second feed network is adapted to couple the power and adjust the electrical path lengths so that the RF power communicate between the respective module ports and the system port is of predetermined relative amplitudes and phases. The intermodule excitation power and phase distribution across the entire planar array aperture produces the desired contoured beam to encompass a required area.

Abstract: Measurement of flux density at the edges of the footprint of an RF transmission from a spacecraft with a view to determining the spacecraft antenna pointing error is difficult because of atmospheric fading local to the measuring station. Previous proposals to permit determination of pointing error in the face of such effects involve additional hardware on board the craft. Herein, it is proposed to induce a relatively small repetitive scanning motion of the spacecraft hence producing an oscillatory flux density variation at peripheral ground stations and then measuring the oscillatory component relative to the average flux density--frequency analysis equipment operable to discriminate the known frequency of the variation over a plurality of wavelengths can be used giving substantial accuracy improvement. A series of measurements enable the diurnal pointing error pattern to be determined and hence a spacecraft attitude correction command program to be produced.

Abstract: A communications satellite has several radiating elements connected respectively to the output ports of a hybrid matrix power amplifier the input ports of which are connected to respective output ports of a low level beam forming network. The low level beam forming network has input ports to which are applied individual beam signals and these are combined within the network to provide at the network output ports different component sums of the input signals. By selecting appropriate connections between the beam forming network and the hybrid matrix power amplifier on the one hand and between the hybrid matrix power amplifier and the radiating elements on the other hand, desired beam overlap and equal power amplifier loading can be achieved.

Abstract: Agile (electronically steerable) beam sensing with associated on-board processing, previously used exclusively for positioning of antennas for beam formation and tracking in communications systems, is now also used for satellite active attitude determination and control. A spinning satellite (100) is nadir oriented and precessed at orbit rate using magnetic torquing determined through use of an on-board stored magnetic field model (520) and attitude and orbit estimates (212). A Kalman filter (211) predicts parameters (202, 203) associated with a received signal (204) impinging on the satellite's wide angle beam antenna (201). The antenna system measures the error between the parameter predictions and observed values and sends appropriate error signals (207) to the Kalman filter for updating its estimation procedures.

Abstract: A steerable beam antenna system for use in satellite communication systems and including a main reflector and an antenna array having a plurality of feed elements is disclosed. The antenna array is positionable at or near at least one focal point of the main reflector, and its feed elements can receive microwaves from or transmit microwaves toward the main reflector. A Butler matrix having multiple input ports and multiple outputs is connected to the array of feed elements and substantially performs a spatial Fourier transformation on a generated set of signals to be transmitted which have a predetermined phase relationship between the signals, which is necessary to create the steerable beam. The Butler matrix also can perform an inverse spatial transformation on a set of incoming signals focused on the array by the reflector and received by the feed elements.

Abstract: In antenna arrays having normally unexcited or little-excited elements, a technique for configuring the array to provide both global and spot beam coverage, wherein the normally unexcited or little-excited elements are excited at a higher level, together with other normally excited elements to provide spot beam coverage, the normally unexcited elements being left unexcited to provide global beam coverage. Ring redundancy configurations for amplifiers in a transponder provided in the configuration are optimized to minimize additional hardware requirements. The specific example of the INMARSAT II satellite system is discussed.

Abstract: A radar system for primary and secondary airspace surveillance, and especially for the detection and tracking of moving targets, consisting of a number of elementary satellites connected to nonrigid structures and of a main satellite, which performs accurate measurement of the position and altitude of elementary satellites and real-time adaptive combination of radar signals coming from them, so as to provide a large-phased array operating in the microwave band. This system overcomes the limitations on dimensioned large space-bound antennae found in the literature, minimizing the incidence and effects of undesired echoes and interference and assuring high detection accuracy. The fact that the elementary satellites are all the same (modular) makes possible gradual assembly of the system with possible expansion in time and assures particularly high operating availability.

Abstract: A satellite communications system employs separate subsystems for providing broadcast and point-to-point two-way communications using the same assigned frequency band. The broadcast and point-to-point subsystems employ an integrated satellite antenna system which uses a common reflector (12). The point-to-point subsystem achieves increased communication capacity through the reuse of the assigned frequency band over multiple, contiguous zones (32, 34, 36, 38) covering the area of the earth to be serviced. Small aperture terminals in the zones are serviced by a plurality of high gain downlink fan beams (29) steered in the east-west direction by frequency address. A special beam-forming network (98) provides in conjunction with an array antenna (20) the multiple zone frequency address function. The satellite (10) employs a filter interconnection matrix (90) for connecting earth terminals in different zones in a manner which permits multiple reuse of the entire band of assigned frequencies.

Abstract: A locating system employs a single-point device employing unique scanning patterns for generating peak signal data which can be used to calculate the position of a signal source within a scanned region. One preferred embodiment utilizes a satellite in high earth geosynchronous orbit and a simultaneous yaw and roll pattern to scan a substantial portion of the earth's surface. The point source being located may be virtually any form of transmitter of radiant energy such as infrared, electromagnetic, light or acoustical energy. The scanning device may also be positioned in a low earth orbit satellite, an aircraft, a missile or a helicopter. The single-point device re-radiates the signal source transmission to a computer command center which correlates single-point device scanning position data with received transmissions to accurately compute the location of the signal source. Beacons placed at precisely known locations may be used to interpret scan data.

Abstract: An unsupported, flexible, quasi-linear phased-array antenna within a space-based radar system which is tethered to a host satellite in free space. The antenna is formed by a plurality of antenna elements which are connected serially along a common axis. The antenna points in an Earth-pointing direction via gravity-gradient forces acting thereon. The phased-array antenna is capable of radiating a narrow electromagnetic beam in the end-fire direction along the array either in a spot or conical beam for detecting, identifying and tracking moving targets on or near the Earth's surface. According to one aspect of the invention, the phased-array antenna forms an elongated conductor which moves through a magnetic field in space for generating electrical power.