In this paper, a 500 GHz frequency tripler with an idle harmonic control technique is proposed, in which the 3rd-harmonic wave at the input port and the fundamental-wave at the output port are recycled with simple control circuitry. Especially for the output fundamental-wave, it is controlled by a carefully designed function-combined probe. Besides, both of input and output probes adopted an inline waveguide-to-microstrip transition using a wedge-waveguide iris to realize an inline input-output configuration. The designed tripler was fabricated, and measured. The measured maximum efficiency is 3% under 20 mW input power with a peak output power of 0.55 mW at 500 GHz, and the available bandwidth convers a range of 460-540 GHz. With the proposed harmonic-wave control technique, the conversion efficiency of the tripler was improved. The good output performance of the 500 GHz tripler verifies the effectiveness of the proposed idle harmonic control technique and function-combined design concept.
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