New test and measurement technology addresses wide-bandwidth communications satellite systems

Communications satellites are using wider bandwidths to carry more data for current frequency bands and the newer Iia-band. This technology is challenging the capability of traditional test equipment and test systems to monitor signal quality through satellite transponders before satellites are launched. Wide-bandwidth signal generation and receiver capabilities are needed for measurements such as noise power ratio (NPR) and error-vector magnitude (EVM). This paper presents new test and measurement technologies that have been developed far increased bandwidth capability up to 500 MHz wide. A stimulus-response system is presented as an example of how to test a wide-bandwidth communication system. The equipment includes an arbitrary waveform synthesizer (AWS) and microwave up-converter for the source; the receiver includes a microwave down-converter, highspeed digital oscilloscope, vector signal analyzer, and PC. The equipment generates broadband modulated signals that can stimulate a device-under-test (DUT), and the DUT output can be analyzed for signal quality with measurements such as EVM. For a measurement example, a wideband EVM measurement is described, including communications system troubleshooting techniques and actual test data in the form of a constellation diagram. The appendix section provides I/Q diagram examples for analyzing quadrature-modulated communications systems.