Abstract-This paper discusses the improvement in the third-order intermodulation product (IM3) performance obtainable from RF and microwave amplifiers by two alternative injection techniques. The first is the addition to the amplifier input of the second harmonics of the input spectrum and the second is the addition to the amplifier input of the difference frequencies between the spectral components of the input signal. Both techniques are considered in theory, by simulation and in practice. Both techniques give useful improvements in two-tone IM3 performance. The second harmonic technique reduced the IM3 level by 43 dB in an amplifier at 835 MHz. The difference-frequency technique gave a reduction of 48 dB in an amplifier at 880 MHz. The difference-frequency technique also gives a greater improvement for complex spectra signals.

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the levels of the 3rd order IM but also the required circuitry is simple, inexpeinsive and small in size. ABSTRACT 1DESCR.IPTION Thrs paper describes a novel techtuque for reducmg the thud-order intermodulation product levels in a nonlinear amplifier. This technique is based on feeding the second harmonic signal produced at the output of the amplifier back to its input. Mathematical analysis and computer simulation are presentedl. The results of the related experiment whch gave a measurement of 16 dE3 reduction in the level of the ~r d order intermodulation is reported.

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