Design of a low noise amplifier for a satellite receiver at Ka band for tropical region

Abstract

In satellite communication systems, Ku and C bands have become highly congested and future applications need to move towards Ka band. Satellite downlink communication for Ka band at 20GHz in the tropical region is challenging because of high precipitation rate and susceptible to high rain attenuation. That is why there is a need to study rain fade and BER performance of RF receiver at Ka band for tropical region. Low Noise Amplifier is the most crucial part of a RF receiver as it is located immediately after the antenna in the receiver. An LNA with a quite high gain and low noise figure can mitigate the noise contribution role of next stages of RF receiver and thus enhancing the receiver BER performance. In this project, a six staged cascaded Low Noise Amplifier with a high gain of 35.236 dB and a noise figure of 2.242 dB has been designed. Rain fades using ITU-R model are calculated for 99.9%, 99.99% and 99.999% availabilities for vertical, horizontal and circular polarization. The rain fades at 99.99% availability for vertical, horizontal and circular polarizations are found to be 34.741 dB, 40.843 dB and 37.635 dB respectively. Integrating the designed LNA into a RF satellite earth station receiver, the BER performance of the receiver is estimated for different availability rates for different levels of PSK modulation schemes and different polarizations. The bandwidth of 20 MHz for DBS-TV has been used. The result shows that BER performances are unacceptable at 99.9%, 99.99% and 99.999% availabilities for all three types of polarizations and all levels of PSK modulation schemes. However performances are found acceptable at varying availabilities from 99.1% to 99.7% for BPSK and QPSK modulation with different polarizations. From 8-PSK to higher level of PSK modulation schemes, BER is inappropriate for 99.1% or higher availabilities for all three polarizations. The minimum fade margins for BPSK, QPSK, 8-PSK, 16-PSK, 32-PSK are 2.88 dB, 5.89dB, 11.22 dB, 17.07 dB, 23.08 dB respectively by considering 8.5 dB as threshold for DBS-TV.