Abstract: The present invention relates to a hybrid mode waveguide or feedhorn antenna for transforming the TE.sub.11 mode into the HE.sub.11 mode. The waveguide or feedhorn comprises a circular waveguide including a tubular section at the TE.sub.11 mode entrance port changing in the antenna configuration to a conical section that flares outward to the feedhorn mouth, and a spiro-helical projection bonded to the interior surface of the waveguide. In a first arrangement, the spiro-helical projection comprises an initially flattened dielectrically coated wire that gradually returns to a rounded configuration in closely spaced helical turns after which the spacings between turns gradually increase linearly in the tubular section and then continue with uniform spacings in the conical section.

Abstract: The present invention relates to technique for reducing near-in sidelobes of an offset antenna. The method comprises positioning at least one piece of microwave absorbing material on a sector of the edge of the reflecting surface of the offset main reflector closest to the focal point of the antenna. The material is positioned on the portion of the edge of the reflecting surface nearest the focal point of the main reflector in such a manner as to achieve substantial selective reduction of the near-in sidelobes generated by the antenna.

Abstract: The present invention relates to a precision phase modulator wherein a carrier signal of constant amplitude and frequency and a modulating signal are applied to the two inputs of the first one of a cascade of linear suppressed-carrier amplitude modulators. Each subsequent modulator of the cascade arrangement concurrently modulates the output signal of the previous modulator of the cascade with the modulation signal. The input carrier signal and the output signal of each modulator of the cascade is tapped-off and weighted, the weighted carrier input and outputs of the even-numbered modulators and the weighted outputs of the odd-numbered modulators are separately added and are combined in quadrature to provide a phase modulated output signal.

Abstract: The present invention relates to millimeter waveguide shorts and methods for making said shorts wherein an exemplary rectangular cross-sectioned waveguide short comprises a base substrate such as steel shimstock or foil having a width equal to the associated millimeter waveguide, a raised portion disposed laterally on both sides of the substrate at alternate quarter-wavelength sections adjacent one end of the substrate. The raised portions comprise a first layer of good electrically conductive material disposed on the substrate and a second layer of an insulating material formed atop the first layer. Alternatively, the exposed substrate sections can be gold plated. A preferred method comprises the steps of masking alternate quarter-wavelength sections of the exposed major surfaces adjacent one end of the substrate, depositing the first layer material on the unmasked quarter-wavelength sections and depositing the second layer material on the exposed major surfaces of the first layer material.

Abstract: The present invention relates to a method for use in a communcation system of providing efficient access by low traffic stations while keeping the buffering requirements for high traffic stations at a minimum. The method provides a TDMA architecture which includes a plurality of different frame rates which is dependent on the traffic requirements between station pairs. In operation, a sequence of a plurality of s switching frames are used to form a super frame and each communication burst of a switching frame is divided into a plurality of q subbursts representative of q transmission channels so that a maximum of (q.multidot.s) transmission channels are available for assignment in corresponding bursts during a super frame. When traffic demands require n.multidot.

Abstract: The present invention relates to antennas which have reflector arrangements that produce a large image with minimal aberrations at the exit aperture thereof of a small feed array. In the present arrangement, the feed array is placed at the conjugate plane relative to the exit aperture of a geometrically confocal reflector system comprising a parabolic main reflector and a parabolic subreflector so that exact imaging of the array is obtained at the exit aperture. In such arrangements, alignment and surface accuracy errors of the various reflectors can be easily corrected by appropriately changing the phase or the position of the associated elements of the feed array. A three-reflector arrangement having sequential geometric confocality is disclosed which also alters the focal length of the main reflector sufficiently to permit the inclusion of polarization and/or frequency diplexing means in the overall reflector system.

Abstract: The present invention relates to a satellite communication system which uses a separate up-link and down-link fixed spot beam for communication with each of a plurality of, for example, spaced-apart high traffic demand ground areas and an up-link and a down-link scanning spot beam for communication with a plurality of, for example, spaced-apart low traffic demand ground areas on a time division multiple access (TDMA) basis. More particularly, a satellite repeater is disclosed for accomplishing the switching of signals concurrently received via the up-link fixed and scanning spot beams to the appropriate down-link fixed and scanning spot beams. Additionally, a transmission and a switching format is disclosed for the efficient multiple access of the low traffic demand ground station areas while still providing minimal buffering demands for the high traffic demand ground station areas.

Abstract: The present invention relates to method and apparatus for substantially reducing the effects of interference at a receiver between concurrently received first and second digital signals which use the same frequency spectrum. Interference between signals is effectively reduced by transmitting the first digital signal in an uncoded form while concurrently transmitting the second digital signal with both reduced capacity when compared with the first signal and in coded form using a forward error correcting code such as, for example, a block or convolutional code. At the receiver intercepting both digital signals, a suitable detection process is performed to decode the second signal and separate both signals. The present invention is applicable to the simultaneous satellite transmission of an area coverage beam and a plurality of spot coverage beams or to increase capacity on a radio channel.

Abstract: The present linear amplifier uses nonlinear components where an input signal with amplitude and phase variations is concurrently applied to a limiter (41) and an envelope detector (42) which provide signals that serve as a carrier signal and a modulating signal, respectively, to a phase modulator comprising two or more linear suppressed-carrier amplitude modulators (50) connected in cascade. The weighted carrier signal and weighted outputs of the even-numbered amplitude modulators (50.sub.2, 50.sub.4, . . . ) are added separately from the weighted outputs of the odd-numbered amplitude modulators (50.sub.1, 50.sub.3, . . . ) to generate two signals which are combined in a quadrature coupler (56). The two outputs of the quadrature coupler are separately amplified in a pair of amplifiers (60, 61) and combined in a second quadrature coupler (64) to provide a substantially linearly amplified output signal of the input signal.

Abstract: The present invention provides a polarization coupler which is capable of coupling or separating dual linear polarized microwave signals having frequencies which extend over extremely wide frequency bands. The present polarization coupler (11) comprises a main waveguide (12) and a side-arm waveguide (13) with a plurality of septa (16) arranged at the junction to reflect energy of a first polarization (E.sub.1) between the main and side-arm waveguide while energy of a second polarization (E.sub.2) passes the junction unaffected.

Abstract: The present invention relates to an antenna system for providing substantially perfect axial symmetry in the radiation pattern which combines (a) a curved main reflector, (b) at least two confocal subreflectors disposed to sequentially reflect a ray in either direction between the main reflector and a focal point of the antenna system as provided by the subreflector most distant along the feed axis from the main reflector, and (c) a symmetrical feedhorn disposed at the focal point of the antenna system so that its longitudinal axis coincides with the equivalent axis of the antenna system.

Abstract: The present invention relates to a method of cophasing the feed elements of a transmitting or a receiving phased array antenna. To cophase a transmitting antenna, the method entails transmitting a lower sideband and an upper sideband signal from a first and a second one of the feed elements, respectively, while transmitting a carrier signal used to generate the sideband signals on all other feed elements of the array. At each receiver the reference phase angle between the received sideband signals is measured and stored. The above step is sequentially repeated for the first and a third, the first and a fourth, etc., one of the feed elements, and the phase angle measured, subtracted from the reference phase angle, and stored. With the above method, the phase angle between each feed element and the second one of the feed elements is determined and stored and subsequently transmitted back to the transmitter for use in transmitting signals to each receiver.

Abstract: The present invention relates to method and apparatus for providing a communication arrangement between two or more independently operable microprocessor units (MPUs). Large amounts of data or data in block format are capable of being passed between MPUs via the present intercommunication channel with little handshaking between MPUs. In the present arrangement, a plurality of MPUs sequentially access, under the control of a synchronous clock, a common memory for random access to blocks of memory for writing data therein or for reading data previously written therein without the necessity for contention resolving means.

Abstract: The present invention relates to method and apparatus for communicating with one or more receiver stations disposed within a blackout region located in the vicinity of and surrounding each spot beam coverage area, the blackout region being caused by interference between concurrently transmitted and overlapping global coverage and spot coverage antenna radiated beams using the same frequency band despite the application of global beam interference suppression techniques at the spot beam receiving areas. Access to the receiver stations within each blackout region is provided by selectively turning off the associated interfering spot beam during a predetermined interval of time while ensuring that the power level of the radiated global coverage beam is not suppressed within the accessed blackout region to permit the global coverage beam to communicate with these receiver stations.

Abstract: The present invention relates to an indicator arrangement for indicating the condition of a phase locked loop. The indicator comprises a flip-flop having its two input terminals connected directly to the input terminals of the phase detector of the phase locked loop in a manner such that under a lock condition the signal at the first input terminal of the flip-flop will be advanced in phase from the signal at the second input terminal. Under such condition a first output signal will be generated at a first output terminal of the flip-flop to activate a "lock" indicating device. When out of lock, the signal at the second input terminal of the flip-flop will be advanced in phase to the signal at the first input terminal and (a) a second output signal will be generated at the first output terminal causing deactivation of the indicating device, and (b) a first output signal will be generated at a second output terminal to activate a no-lock indicating device when desired.

Abstract: Circuitry useful in PCM coders for effectively shifting the idle channel noise signal to a level midway between the code state boundaries thereby significantly reducing the likelihood that noise signals will cross a boundary and be encoded.

Abstract: The present invention relates to novel launcher reflectors which are used with reflector antenna systems to compensate for the dominant aberration of astigmatism which was found to be introduced in the signals being radiated and/or received at the off-axis positions. A major portion of such phase error is corrected by using, with each off-axis feedhorn, an astigmatic launcher reflector having a curvature and orientation of its two orthogonal principal planes of curvature which are chosen in accordance with specific relationships, the launcher reflector being fed by a symmetrical feedhorn.

Abstract: The present invention relates to method and apparatus for substantially cancelling interference between signals using the same frequency spectrum which are received via overlapping area coverage and spot coverage antenna beams. At the transmitter where the overlapping area and spot coverage beams are concurrently transmitted, a predetermined portion of the area coverage signal is coupled into each of the spot beam signals which will be overlapped at the associated spot beam receiver area by the area coverage beam. The predetermined portion coupled into each spot beam signal will have a magnitude and phase to substantially cancel the area coverage signal at the associated spot beam receiver area.