Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 34

One of the first noticeable effects of large signal drive is the generation of harmonics at multiples of the input frequency. Harmonics are described by their order and either by their output power or, more commonly, by the power relative to the output power of the fundamental, and almost always in dBc (dB relative to the carrier). Second harmonic is short for second‐order harmonic and refers to the harmonic found at two times the fundamental, even though it is in fact the first of the harmonic frequency above the fundamental; third harmonic is found at three times the fundamental, and so on. Surprisingly, there are not well‐established symbols for harmonics; for this book, we will use H2, H3 … Hn to represent the dBc values of harmonics or order 2, 3 … respectively. In Chapter 6, the measurements of harmonics are fully developed as part of the description of X‐parameters and utilize the notation b_{2, m} to describe the output normalized wave power at port 2 for the mth harmonic. A similar notation is used for harmonics incident on the amplifier.

One important attribute of harmonics is that for most devices the level of the harmonics increases in dB value as the power of the input increases and to a rate directly proportional to the harmonic order, as shown in Figure 1.6. In this figure, the x‐axis is the drive power, and the y‐axis is the measured output power of the fundamental and the harmonics.

Figure 1.6 Output power of harmonics of an amplifier.