Measuring the RF, microwave or millimeter wave performance of materials and components often requires a substantial length of transmission line or cables to connect the microwave source/receiver to the test apparatus. Such cables may be subject to environmental variations (e.g. temperature or pressure) that change the overall phase delay and amplitude of signals that travel through said cables. Furthermore, some testing requires physical motion of the cable, which is another source of phase and amplitude error.
This paper describes a new correction method, which determines and corrects for phase and amplitude errors in transmission line cables (patent pending). Unlike previous published methods, the present technique does not require any specialized circuitry at the device under test (DUT). Instead, it utilizes in-situ reflections that already exist in the measurement apparatus to obtain a reference phase and amplitude signal. The described algorithm combines these reflections with frequency and time-domain signal processing to compensate for erroneous phase and amplitude shifts that occur during a measurement. This paper demonstrates the correction methodology with materials measurements examples. Additionally, this phase and amplitude correction may be applicable for scatter and antenna measurements. It can be applied to either reflection or transmission measurement data.
