Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 78

Until recently, RF thermocouples were the most common type of power sensor used. These thermocouples convert heating directly into a DC voltage and, because their small size and thus small thermal mass, are much faster responding and have a larger dynamic range than either thermistors or calorimeters. As with other sensors, these require calibration with a precision source but are typically DC blocked, so the source must be a low‐frequency AC source. These sensors are commonly used throughout the RF industry but have the detriment of being somewhat slow‐responding (with response times in the several to tens of millisecond range), but they are extremely linear and relatively non‐responsive to harmonics. That is, harmonic power will be detected as an RMS error of the power of desired signal. Since harmonics 20 dBc or lower represent less than 1% of the power of the main signal, the error due to harmonics is quite low.