On the effects of memoryless nonlinearities on M-QAM and DQPSK OFDM signals

Published versio

Super-High-Frequency /SHF/ communications system performance on ATS. Volume 1 - System summary

Super high frequency communication systems performance on ATS - Vol.

On-board processing for future satellite communications systems: Satellite-Routed FDMA

A frequency division multiple access (FDMA) 30/20 GHz satellite communications architecture without on-board baseband processing is investigated. Conceptual system designs are suggested for domestic traffic models totaling 4 Gb/s of customer premises service (CPS) traffic and 6 Gb/s of trunking traffic. Emphasis is given to the CPS portion of the system which includes thousands of earth terminals with digital traffic ranging from a single 64 kb/s voice channel to hundreds of channels of voice, data, and video with an aggregate data rate of 33 Mb/s. A unique regional design concept that effectively smooths the non-uniform traffic distribution and greatly simplifies the satellite design is employed. The satellite antenna system forms thirty-two 0.33 deg beam on both the uplinks and the downlinks in one design. In another design matched to a traffic model with more dispersed users, there are twenty-four 0.33 deg beams and twenty-one 0.7 deg beams. Detailed system design techniques show that a single satellite producing approximately 5 kW of dc power is capable of handling at least 75% of the postulated traffic. A detailed cost model of the ground segment and estimated system costs based on current information from manufacturers are presented

Communication satellite systems for Alaska

Technical and cost factors for implementation of Alaskan communication satellite syste

High linearity broad-band helix TWTs

Helix travelling-wave tubes (TWTs) are extensively employed as final power amplifiers in satellites. These applications demand low spectral noise and high efficiency across a broad band. Research has been carried out to achieve these criteria in a helix TWT design. A deeper understanding has been gained on how the basic parameters of a TWT affect its non-linear performance. By selecting and controlling the parameters that are critical to the amplifier’s nonlinear performance the designs corresponding to the important and desired conditions have been identified. The main simulation tool for modelling the interaction processes in a generic helix TWT was a large-signal model (LSM). A helix slow-wave structure is normally tapered to maintain its phase relationship with the electron beam and to maximise its output RF power. By determining the sensitivity of the helix dimensions on the nonlinear performance at different regions along the tube, a non-uniform slow-wave structure design has been developed for a more linear performance. Since the conditions of high linearity and efficiency could not be achieved simultaneously, the best trade-off was attained. The performance across the frequency band of 10.7 to 12.75GHz was computed for the uniform and tapered helix designs. With the use of a simulated multi-stage collector with optimised electrodes, the overall TWT performance was determined. Further understanding has been gained on the fundamental processes in the tube that cause the generation of nonlinear transfer curves and spectral distortion. The modelling of RF beam current and helix voltage waveforms and their characteristics provided a unique insight. In addition, the formation and deceleration of the electron beam bunches have been shown for the various important conditions; revealing the desirable physical conditions within the beam

Design and implementation of a X-band transmitter and frequency distribution unit for a synthetic aperture radar

Synthetic aperture radar (SAR) can provide high-resolution images of extensive areas of the earth's surface from a platform operating at long ranges, despite adverse weather conditions or darkness. A local consortium was established to demonstrate a consolidated South African SAR ability to demonstrate to the local and international communities, by generating high quality images with a South African X-band demonstrator. This dissertation forms part of the project. It aims to describe the design and implementation of the transmitter and associated frequency distribution unit (FDU) for the SASAR II, X-band SAR. Although the transmitter and FDU are two separate units, they are ultimately linked. The transmitter has the task of taking a low-power, baseband, chirp waveform and. through a series of mixers, filters and amplifiers, converting it to a high-power, microwave signal. The FDU is essentially the heart of the transceiver and provides drive to all the mixer local oscillator (LO) inputs. It also clocks the DAC and ADC which allow the essentially analogue transceiver to communicate with the digital circuitry. It is found that the chirp signal produced is of satisfactory fidelity. LO feed through, however, is superimposed at the chirps' centre frequency. As a result of previous stages, spurious signals exist at 16 MHz offset from the chirps' centre frequency and at 9142 MHz. The system transfer function reveals that 2 dB roll-off is present at the outer frequencies of the chirp signal. Group delay in the transmitter filters and amplifiers is held responsible for this

TDRSS telecommunications study. Phase 1: Final report

A parametric analysis of the telecommunications support capability of the Tracking and Data Relay Satellite System (TDRSS) was performed. Emphasis was placed on maximizing support capability provided to the user while minimizing impact on the user spacecraft. This study evaluates the present TDRSS configuration as presented in the TDRSS Definition Phase Study Report, December 1973 to determine potential changes for improving the overall performance. In addition, it provides specifications of the user transponder equipment to be used in the TDRSS

Study of modulation techniques for multiple access satellite communications

Multiple access communication utilizing small ground stations for satellite communication modulation - multiplexing technique

Advanced passive communication satellite systems comparison studies. Volume 3 - Appendices Final report

Saddle reflector use in passive communication satellites - Vol.