Communications Satellite Corporation

Comsat Corporation

Francois T Assal

Arnold L Berman

Amir Ibrahim Zaghloul

Christoph E Mahle

Ramesh K Gupta

John V Evans

Bernard D Geller

Donald Stuart Arnstein

Robert M Sorbello

John I Upshur

Eric Christopher Kohls

Chunming Chen

Moshe Lieberman

Cristoph Erhardt Mahle

Khodadad Betaharon

Janaki R Potukuchi

A method and apparatus to enable high-quality digital transmissions to a satellite terminal operating in proximity to a radar source combines interleaving a sequence of channel symbols at a land station before transmission of an RF signal to a satellite, increasing the satellite's EIRP to compensate for the effects of the radar's duty factor on received signal power and code distance, detecting the radar pulses at a satellite terminal, blanking the received RF signal to prevent reception of the signal by the modem at the satellite terminal during the radar's ON time, having the modem recognize and eliminate the effect of the gap in the channel signals on its metric calculation, and de-interleaving the sequence of channel symbols. As a result, satellite terminals operating in proximity to radar sources can provide the same quality of service as if there were no radars operating.

Low noise front-end blanking and interleaving for satellite reception in

Highly reliable, light-weight, and low power-consuming microwave redundancy and re-routing electronic switches suitable for on-board satellite applications permit rearranging of communication paths for up- and down-link communications and re-routing of microwave signals to redundant devices in the event of on-board hardware failures.

Solid-state electronic switching module

In a flat plate antenna, insertion loss is reduced significantly by providing an extensive waveguide structure at the back of the ground plane of the antenna. Depending on antenna size, the waveguide may feed the antenna at one or a plurality of points. According to a preferred embodiment, the transition from waveguide to stripline is made via a coaxial connection, with a quarter-wave transformation, including mode suppression walls to direct the energy more efficiently. Alternatively, a direct waveguide to stripline transition may be provided. The technique has wide applicability to a number of antenna designs, including single- and dual-polarization structures, and linear and circular polarization operation.

Waveguide transition for flat plate antenna

A 'modified rearrangeable' switch matrix combines both .beta. switching elements and crossbar switch matrices in a single switch configuration, with .beta. switching elements used at the input and output and at least one crossbar switch matrix in the middle to receive its inputs from .beta. switching elements and provide its outputs to .beta. switching elements.

Switch matrix including both B switching elements and crossbar switch

On-board satellite switching is performed in three stages, an outer stage of switching on the up-link side for routing the received signals to either demodulators or frequency translators, a first inner stage of switching, preferably a baseband switch and processor, for routing and processing the outputs of the demodulators, a second inner stage of switching, e.g., a microwave switch matrix, for routing the outputs of the frequency translators, and an outer stage on the down-link side for assembling and routing the down-link spot beams. For a multiple hopping-beam system, the outer stages are microwave switch matrices, and for a hybrid scanning-hopping system the outer stages are beam forming matrices. A general purpose modified rearrangeable switch matrix is also disclosed.

Multiple spot-beam systems for satellite communications

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.

Combined global/spot beam configuration for satellite communications

A method of measuring input-backoff to an amplifier in a time-division multiple access (TDMA) communication system having a carrier recovery segment and a clock recovery segment prior to a data segment in a traffic burst. A monitoring station transmits a CW pilot signal within the amplifier's bandwidth. In the guard time between bursts, the monitoring station measures the unsuppressed pilot level output by the amplifier. While a ground station is transmitting an unmodulated carrier during carrier recovery or a carrier modulated at the clock frequency during clock recovery, the monitoring station measures the suppressed pilot level, suppressed by the non-linear interaction of pilot and carrier. The amount of pilot suppression is related to the input power back-off of the carrier by a previously measured or a theoretically derived relationship. The carrier-to-suppressed noise ratio is determined by measuring the carrier level during the carrier recovery and by measuring the suppressed noise during carrier or clock recovery through a noise filter centered away from any transmitted signals or their intermodulation products.

Monitoring of input backoff in time division multiple access

A microwave PIN diode switch is provided with circuitry to achieve impedance matching at both input and output ports and for both 'on' and 'off' switching states.

Resistively matched microwave PIN diode switch

A four-port waveguide switch is described which allows any two pairs of ports to be connected together. A separate waveguide independently connects each port with each of the remaining ports. In each of the six separate waveguides there is provided at least one resonant cavity having a passband that includes the frequencies of the incident microwave signals to be switched. A disrupting structure is provided for each resonant cavity. Each disrupting structure may be switched between a first state wherein the respective cavity is not detuned and a second state wherein the respective cavity is detuned such that it reflects the incident microwave signals. By switching the appropriate disrupting structures to their second state, any of the three possible connecting states of a four port switch of the present invention can be obtained.

Waveguide switch having four ports and three connecting states

A redundant microwave configuration providing a highly flexible routing of a plurality of inputs to a plurality of outputs is characterized by at least two switching layers wherein each switching layer comprises a plurality of four port switches and the switches in at least one of the switching layers are connected in a ring, corresponding switches in the layers being interconnected. This redundancy configuration is not limited to microwave applications only but could be implemented at all other frequencies. One microwave configuration employs 2N amplifiers between said switching layers as building blocks to provide N inputs to N antenna ports. This configuration allows any combination of (m-N) amplifier failures without loss of service, where N .ltoreq. m .ltoreq. 2N. In other configurations, only one type of switch is used and fewer than 2N amplifiers are used for N inputs and N outputs. Moreover, by properly choosing path lengths, the outputs of two or more amplifiers can be combined where greater power output is required than that provided by a single amplifier. In still other configuratons, the switching layers are directly connected, and one of the switching layers comprises a matrix of fast switching elements.

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Bethesda, MD, United States of America

Francois T Assal