Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 99

In addition to the source‐match effects produced by the source impedance, power source‐match, and ratio source‐match, reflections from within the test set of the VNA will also exist, as well as from the test port cables and from any fixtures that provide an interface from the VNA to the DUT. These sources of mismatch are common to all of the previously mentioned source‐match effects and will add to them in a similar way. However, since they are common, their effects on port power and gain are also the same.

The reflection and mismatch between the reference channel split and the test port coupler affect the incident signal, a1, but are not monitored by the reference channel receiver. Reflections after the test port coupler also affect the a1 signal but will be apparent in changes measured on the reflected signal, b1. However, their composite effect will add to the overall source‐match, and their effects on measurements can be compensated provided they remain stable. In addition, mismatch and loss after the test port coupler can be characterized in such a way that changes to these values, such as due to drift in a test port cable, also can be compensated in some cases. Mismatch correction in power measurements is discussed in detail in Chapter 3.