For a long time, power meters were built using a combination of a base unit and an external power sensor connected via a cable. The RF signal was converted to a voltage signal in the power sensor, amplified and then digitized and displayed in the base unit. Purely analog signal transmission was used between the power sensor and the base unit in this type of power meter. This approach has the benefit that a power sensor appropriate for the task at hand can be selected without requiring a new base unit. The obvious disadvantage is that a power sensor can never be used without a base unit.
Today, the situation has changed due to the advancing miniaturization of components as well as the availability of small, high-performance, energy-efficient processors. A power meter can now be manufactured as a small, integrated unit and connected directly to a PC or base unit via a standard USB interface. In this case, the base unit does not perform any analog signal processing. Instead, it is used primarily for control and measured value display.
This solution has a clear advantage: The integrated power meter does not consist of multiple components and can be characterized in full during the manufacturing process. This eliminates the need to calibrate the combination of the sensor and base unit with a reference signal prior to usage. Moreover, signal processing is less vulnerable to unwanted influences since it is performed inside an integrated device, and zeroing is required only for very small signal amplitudes.
>>Continue reading this article directly on EDN. It covers sensor technologies, multipath diode sensors in particular, measurement accuracy, and mismatch. The examples given use the R&S NRP-Z sensors.