LXI in satellite system testing

Satellites are used for a wide range of military/aerospace applications including weather prediction, navigational and communications. Since performance of satellite systems is highly dependent upon transmission quality and therefore achieving constant magnitude and linear phase response constant group delay (that is derived from the phase) versus frequency of the transmission coefficient within the used frequency band. Test engineers must find a reliable way to measure group delay where the transmitters and receivers are geographically separated from one another, as well as from their controller, by significant distances. A new two-tone method that makes use of LXI technology has been developed that allows users to measure relative group delay with high precision on converters and mixers without Local Oscillator (LO) access as is typically the case in satellite communication systems. In this case, the phase of the transmission coefficient cannot be measured directly because the input and the output signal have different frequencies. Moreover, the phase of the output signal is influenced, not only by the device under test (DUT), but also by the frequency and phase drift of its local oscillator. Additionally, in the case where input and output of the transmission system are located far apart, the group delay and phase are very difficult to measure. This paper describes how to measure group delay on a transmission system by means of two LXI based network analyzers, one at the transmitting end and the other at the receiving end, that communicate with one another using LXI peer-to-peer LAN messages. Based upon widely used standards such as Ethernet and the Web, the LXI standard enables the connection of intelligent instrumentation which supports distributed processing of measurement data and provides a high bandwidth interconnect system for supporting applications with high data demands.