On the design of active Rx/Tx-diplexers with wide frequency spread

Abstract

This contribution deals with the performance analysis of an active diplexer for Rx/Tx integrated satellite communication antenna systems. To ensure a low noise figure of the receiver a passive diplexer with low insertion loss cascaded with a low noise amplifier (LNA) and a band-pass filter is used to separate Rx from Tx. This approach may lead to a relatively high Tx power level at the LNA input, which could even drive the latter into compression and affect the bit error rate (BER). This work analyzes the influence of phase and amplitude compression on the BER for different modulation schemes. Two-tone measurements are performed to characterize two different commercially available low noise amplifiers. The measured results are used to analyze the performance degradation for modulation schemes that are commonly used in Satcom. Maximum power levels of the parasitic Tx signal which prevent a significant rise in the BER are inferred. This information is useful for the design of diplexers.