Second harmonic zone injection for amplifier linearisation

Second harmonic zone (SHZ) injection is a feedback technique for reducing the intermodulation distortion (IMD) at the output of an amplifier, which is based on feeding the SHZ intermodulation products (IMP), back to the amplifier's input. The technique is analyzed theoretically and practical results demonstrate the linearisation performance. Two feedback prototypes were built, one using a frequency doubler and the other using a buffer amplifier as a distorter, where 14 dB and 13 dB improvement was obtained respectively in reducing the third order IMP (IMP/sub 3/). The performance of the technique with changing frequency and input power level was also investigated.