This paper reports two techniques for optimizing harmonic termination in power amplifiers. In the first technique, the active antenna approach, the antenna element acts as radiator and as part of the output tuning circuit. The second method, based on photonic band-gap (PBG) structure, incorporates a periodic harmonic tuning structure for microstrip lines. In this structure, a periodic 2-D pattern is etched in the microstrip ground plane. A wide stopband suitable for broadband harmonic tuning, has been demonstrated experimentally. These methods yield high efficiency power amplifiers, and reduce unwanted radiation from the antenna at harmonics. Two power amplifier examples are presented.
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