For many types of multiple-input devices, precise testing requires accurate control over the amplitude and phase of multiple stimulus signals applied to the inputs of the unit under test (UUT). Examples include phased-array radar systems and multiple-input/ multiple-output (MIMO) devices used in commercial communications and wireless networking. In these applications, precise control over amplitude and phase makes it possible to accurately simulate parameters such as the angles of arrival of incident signals.
The testing of a multiple-input receiver presents one key challenge: providing the desired signal at the end of long test cables. Simulating this scenario presents two requirements. One is the ability to measure changes in phase and amplitude at the UUT, not at the test equipment. The other is the need to make real-time corrections to the amplitude and phase of each waveform. This level of control is needed to ensure proper alignment of the simulated incident signal in the presence of reflected signals from the inputs of the UUT. The approach described here was designed to test radar receivers. One of its key contributions is the ability to “know” the actual phase at the UUT and make changes on the fly. This enables precise receiver calibration and highly realistic threat simulations.
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