Abstract: The present invention relates to a mobile radio base station (14) capable of communicating with a large number of mobile stations by implementing space diversity and time-division retransmission techniques in a digital communication system. The digital base station contains a plurality of antenna elements (16.sub.1 -16.sub.M) and a plurality of retransmission branches (18.sub.1 -18.sub.M) associated in a one-to-one relationship. When the base station receives a digital communication signal from a mobile station, each antenna element receives the signal with a unique random phase (.theta..sub.1 -.theta..sub.m) due to the effects of the environment on signal transmission. The signal is then processed through the plurality of retransmission branches, where each branch adapts to compensate for the random phase of the signal received by its associated antenna element.

Abstract: The present invention relates to transmitters (10) and receivers (30) for use in a spread spectrum radio communication system wherein transmitters generate FH-MFSK signals by adding elements of each user's Q level encoded message sample and that user's unique Q level, L-length frequency-hopping address sequence using the rules of algebra for finite fields. The receivers (a) spectrum analyze received transmissions during each chip or period of the L-length sequence to determine which Q level frequencies are received and (b) generate a set of decoded message signals by subtracting corresponding chip elements of a particular user's FH address sequence from those of the detected frequency levels using the rules of algebra for finite fields.

Abstract: The present invention relates to a point-to-multipoint or broadcast TDMA or FDMA satellite arrangement wherein each up-link message unit is intended for reception at one or more geographically dispersed remote receiving sites within a wide service area. In one arrangement of a TDMA or FDMA satellite, the up-link message units are received and each message unit is directed to a transponder and to one or more down-link antenna ports for concurrent transmission to each of the destinations receiving sites for such message. An alternative TDMA satellite arrangement provides for each up-link message unit to be temporarily stored during the receiving frame period and then transmitted in accordance with a predetermined frame format during the appropriate time segments of the subsequent frame period to all of the destinational receiving sites. A technique for providing such predetermined frame format is also disclosed.

Abstract: The present invention relates to wideband antenna arrangements for suppressing selected sidelobes comprising a main antenna (10) comprising a predetermined aperture (l) and two sidelobe suppression means (12, 14, 40, 42) disposed adjacent and on symmetrically opposite sides of the main antenna in the plane of the sidelobes to be suppressed. The distance between the suppression means preferably approximates the width of the aperture of the main antenna and the aperture size of the suppression means controls the sidelobe suppression region at the aperture of the main antenna. The suppression means can comprise two auxiliary antennas or two sections of the main antenna focusing reflector having apertures (l.sub.1) which are smaller than that of the main antenna.

Abstract: An efficient recombination laser comprises a resonant laser cavity, a gaseous laser material disposed in the cavity, and means for providing a plasma discharge in said laser material, which plasma discharge is confined to a cylindrical region along the axis of the laser cavity. The plasma in the gaseous laser material expands outward radially from the cylindrical region at the axis of the cavity and cools by interacting with the adjacent unexcited gas. The maximum laser gain is provided in an annular region, which annular region is adjacent to and surrounds the initial discharge cylindrical region. In one embodiment of the present invention, the means for providing the plasma discharge comprises two pin-type electrodes which extend into the cavity along the cavity axis.

Abstract: The present invention relates to an antenna arrangement for suppressing selected sidelobes where the arrangement comprises a main focusing reflector (10), a main feed arrangement (14) and at least two auxiliary feed arrangements (20 and 21) disposed on opposite sides of, and a predetermined equal distance from, the main feed arrangement in the plane of the sidelobes to be suppressed. All feed arrangements radiate the same signal and their individual beams are radiated in a direction whereby the central ray thereof impinge the same point on the main reflector. By proper adjustment of the phase, amplitude and transverse off-axis distance of the auxiliary feed arrangements from the main feed arrangement, the combined E-field distribution of the auxiliary feed arrangements at the edge of the reflector in the plane of the sidelobes to be suppressed will be equal and opposite to the E-field distribution of the main feed arrangement.

Abstract: A plurality of semiconductor lasers (431-434) and a photodetector (120) are mounted on a silicon substrate (100) having an integrated circuit (101) fabricated therein. The integrated circuit includes a biasing circuit (405) for establishing a threshold current level that is dependent on the output of the photodetector and a modulator circuit (404) for providing a modulation current that is dependent on the digital values in an input signal. A semiconductor switch (406) selects only one of the plurality of semiconductor lasers for activation by the biasing and modulator circuits. The integrated circuit also includes a circuit (408) that operates the semiconductor switch so as to selectively activate a different one of the plurality of semiconductor lasers in response to either a predetermined output from said photodetector or in response to an external supervisory signal.

Abstract: The present invention relates to a time compandor (40) including a cascaded pair of chirp transformers (41,42) of chirp rates .beta. and .sigma., respectively, capable of companding a continuous time signal x(t) to form a companded and delayed output signal x(a[t-.tau.]). Each chirp transformer includes a pi-network arrangement of linear dispersive filters (44,45,46,47,48,49), wherein the first chirp transformer (41) performs a Fourier transform on a continuous time input signal x(t) to produce X(.beta.t) and the second chirp transformer (42) performs an inverse Fourier transform on the product of the output of the first chirp transformer and a signal associated with the desired time delay .tau., to form the desired companded output signal x(.sigma./.beta.[t-.tau.]), where .sigma./.beta.=.alpha. is the desired companding rate, and .tau. is the desired time delay.

Abstract: The present invention relates to a wide-field-of-view antenna arrangement which permits the angular range over which multiple beams may be transmitted or received to be increased by taking into consideration the location of the tangential and sagittal focal regions associated with multibeam systems. The subreflector (18,24) is positioned relative to the main reflector (10,20) such that the tangential and sagittal focal regions lie behind the subreflector of a Cassegrainian arrangement, or alternatively in front of the subreflector of a Gregorian arrangement for a predetermined wide-field-of-view.

Abstract: The present invention relates to a transmitter, a receiver and techniques for use in a frequency-hopping, multilevel frequency shift keyed (FH-MFSK) radio system which permits the selective concurrent transmission of one or two encoded frequencies per time slot of the transmitted sequence for improving reception at a receiver experiencing interference from the system transmitters above a predetermined interference threshold level. An alternative arrangement permits all transmitters and receivers to communicate with one another by transmitting a separate one of multiple frequencies in a separate one of an equal number of multiple frequency subbands forming the system frequency band during each time slot for providing flexibility in system design. Combinations of the two arrangements can also be employed.

Abstract: The present invention relates to a technique for efficient spectrum utilization in mobile radio systems divided into a plurality of geometrically-shaped cells (10-21). Mobiles (24) in each cell are served by at least one base station (30-40) comprising a directional antenna having a beamwidth corresponding to the overall area of the associated cell. Each base station communicates with mobiles within the associated cell using separate primary channels (C.sub.p) within a first portion of the system frequency spectrum when a mobile is not experiencing interference above a predetermined interference level, and switches a mobile to a separate secondary channel (C.sub.p) within a selected section (f.sub.1, f.sub.2, f.sub.3) of the remaining second portion (f.sub.i) of the system frequency spectrum when the interference at a mobile exceeds the predetermined interference level. Each selected section used in adjacent portions of adjacent cells being within a different frequency subband of the second portion.

Abstract: The present invention relates to an antenna arrangement capable of correcting for astigmatism over a broadband range, the antenna arrangement comprising a main focusing reflector arrangement (10), such as, for example, a Cassegrainian antenna system, a feed arrangement (12) and an astigmatic correction means (14) disposed between the feed arrangement and the main focusing antenna arrangement. The astigmatic correction means comprises a first and a second doubly curved subreflector (18, 16) which are curved in orthogonal planes to permit the launching or reception of an astigmatic beam of constant size and shape over a broadband range. By proper choice of the angle of incidence at each subreflector, cross-polarization and astigmatism of the beam can be canceled simultaneously.

Abstract: The present invention relates to an antenna arrangement capable of correcting for astigmatism over a broadband range, the antenna arrangement comprising a main focusing reflector arrangement (10), such as, for example, a Cassegrain antenna system, a feed (12) and astigmatic correction means (14) disposed between the feed and the main focusing antenna arrangement. The astimatic correction means comprises a first and a second doubly curved subreflector (16, 18) or lens (30, 32) which are curved in orthogonal planes to permit the launching of an astigmatic beam of constant size and shape over a broadband range.

Abstract: The present invention relates to a subharmonically pumped hysteretic superconductor-insulator-superconductor (SIS) junction mixer. The hysteretic junction (10), achieved by not suppressing the critical current I.sub.c of the junction, is responsive to a first source of a pump signal (12) at a frequency .omega..sub.p and a second source of an input signal (14) at a frequency .omega..sub.i, to produce a non-zero output signal at a frequency .omega..sub.o =.vertline..omega..sub.i -2.omega..sub.p .vertline., during either an overpumped or underpumped condition. The hysteretic nature of the junction allows the mixer to operate in a switching mode, thereby producing low-noise mixing with gain.

Abstract: The present invention relates to an adaptive interference suppression arrangement. In the present arrangement, a main antenna (10) picks up the desired signal and some interfering signal and a small auxiliary antenna (20) is pointed in the direction of the interfering source and picks up a sample of the interfering signal. The interfering sample is then put through a quadrature modulator (24) for adjustment of its phase and amplitude to provide an estimated cancellation signal at the output. This estimated cancellation signal is then combined with the main antenna output to give a corrected signal. After down-converting, the present system detects the power in the corrected signal and a processor (32), in response to such power detection, generates a small dither signal which is added to the control signals to vary the phase and amplitude in the quadrature modulator of the residual interference in the corrected signal.

Abstract: The present invention relates to a spread spectrum, FH-MFSK radio receiver capable of demodulating and decoding one or more concurrently received L-length frequency-hopping, Q level frequency shift keyed signals to determine the correct signal of a particular user. In operation, the receiver spectrum analyzes the received signal to determine which frequency components are present during each of the L chip intervals and then demodulates a particular user's L-length FH address signal with the derived frequency components to arrive at a Q by L-length detection matrix. A detector and checking processor determines which L-length matrix rows have a maximum number of entries and if only one such row exists, that level is deemed the correct message level. Where multiple maximum-length rows are found the processor uses the address sequences of all other users to check if the row entries could have been caused by interference. The row with the minimum matches is deemed the correct message level.

Abstract: The present invention relates to a satellite communication system comprising a plurality of limited scan spot beams which permits high transponder utilization efficiency by virtue of pooling the resources of each terrestrial footprint. In an embodiment of the invention, a satellite comprises a plurality of transponders, the signals from each transponder being directed via one or more associated scanning beams over a separate limited scanning beam region on the surface of a celestial body. In a preferred arrangement, each of the plurality of scanning spot beams is scanned linearly and parallel to the other scanning spot beams in a manner wherein each of the scanning beams covers a separate one of adjacent bands dividing the overall service region on the celestial body. By proper orientation of each of the scan regions or bands, nearly equal volumes of traffic can be served by each transponder.

Abstract: The present invention relates to an N-way non-hybrid power combiner arrangement for microwave amplifiers. In operation, sensing means (19.sub.1, 19.sub.2, . . . , 19.sub.N) are coupled in a one-to-one relationship with the individual amplifiers (12.sub.1, 12.sub.2, . . . , 12.sub.N) to monitor amplifier performance and sense amplifier failure. In one embodiment of the present invention, shorting devices (20.sub.1, 20.sub.2, . . . , 20.sub.N) are disposed adjacent to the outputs of the individual amplifiers and coupled to the associated sensing means in a one-to-one relationship. In an alternative embodiment, open-circuiting devices (30.sub.1, 30.sub.2, . . . , 30.sub.N) are disposed at a predetermined distance from the amplifier outputs along the transmission lines (24.sub.1, 24.sub.2, . . . , 24.sub.N) and coupled to their respective sensing means.

Abstract: The present invention relates to a technique for increasing the rain margin at ground stations of a satellite communication system. In the present technique, spare TDMA time slots in each frame sequence are shared among all ground stations as required by stations experiencing a fade condition which exceed a predetermined power margin. Additional up-link power margin at a faded transmitter can be achieved by either increasing power transmission of a normal burst or by the use of spare time slots plus encoding and preamble field extension techniques for burst extension. Additional down-link power margin to a faded receiver is accomplished by either increased transmitter power transmission or by the use of burst extension and coding and field extension techniques. Apparatus for implementing framing, carrier and clock recovery and start of message detection using extended fields and coding techniques for other data at a transmitter and receiver and disclosed to overcome fade conditions.

Abstract: The present invention relates to a key and keyway arrangement comprising a first slotted member (14) and a second support member (20) including a "U"-shaped wire guide (10) positioned in a manner whereby the ends thereof are fitted into a pair of spaced-apart apertures in the surface of the second member. The members are placed in relative position to each other so as to allow the curved section of the wire guide to protrude into the slot of the first member, forming a tangential relation therewith.